A Paradigm of Human Use of the Earth
It is said hunters and gatherers lived lightly on the land, though some lived more lightly than others. North American Indians eliminated some sea mammals along the California coast and ate the biggest oysters in Chesapeake Bay. Earlier on, Native Americans in the late Pleistocene, only 50 or 60 human generations removed from us (they were then new immigrants from Asia), helped exterminate the so-called Pleistocene megafauna, the large mammals (mammoths, mastodons, camels, horses, sloths) in North and South America. Their hunting probably forced the evolutionary development of the plains bison into a smaller and earlier maturing beast. Burning, to renew the berries and browse of a woodland for game, to drive game animals, to keep grasslands open, changed whole landscapes. It moved the prairies east, opened meadowlands in the eastern forests, and created open forests of fire resistant trees (many large and old) such as the mountain forests of the western United States, the park-like oakwoods of southern New England, and the southern forests of longleaf pine. Burning by Australian aborigines transformed the landscape of Australia, turning shrubland into grass, and was probably one reason so many Australian animals went extinct shortly after the aborigines arrived. Hunting and gathering was an adaptation that worked. Human populations slowly grew.
The development of agriculture was probably related to increasing human population and a drying post-glacial climate, and the related failure of some gathered foods. With agriculture, human influence on the earth increased. An ideal natural world became a cultivated one: a garden. Forests were cut or grasslands cleared to grow grain, rivers were diverted for irrigation, hillsides terraced to grow maize and rice. Forests were also cut for cooking fuel, to burn brick, smelt metal ores, build houses and ships. Grazing animals, whose meat, wool and skins helped feed and cloth the people in the villages, kept the trees from regrowing. Greek shepherds girdled trees to increase the grass. Eroding soil raised river beds, silted harbors, pushed river deltas far out to sea. By 8000 years ago the removal of forests and the cultivation of the ground, by increasing the release of carbon dioxide from forests and soil, was raising the level of carbon dioxide in the atmosphere. The development of paddy rice cultivation 5000 years ago increased the level of methane in the atmosphere (methane is another greenhouse gas that oxidizes to carbon dioxide). Together these gases warmed the atmosphere sufficiently to prevent the start of another continental glaciation, whose glaciers had begun forming 4000-5000 years ago in northeastern Labrador. The ice melted under the benign climatic conditions produced by early agriculture. So our unheard of 10,000 years of favorable climate is partly a human artifact.
Early agriculture was hard on the land (though Romans understood the benefits of crop rotation) and farmland wore out as nutrients were used up and topsoil eroded. Upland fields were being abandoned in Jordan 8000 years ago. About the Mediterranean, during the Bronze Age (and in many cases continuing until modern times), less favorable lands (hilly uplands) were farmed and abandoned in 1000 year cycles. The new settlers would come upon the foundations and walls of their predecessors amidst the dense scrub. Once forested high uplands, warm and moist enough for trees, such as the Andean altiplano or the Tibetan plateau, became grazing lands, with scattered cultivation. Some lands, such as the Negev Desert of Israel (indeed, much of the Middle East and North Africa), were essentially denuded, their hills eroded to gravel, during long periods of occupation. Irrigated lands, such as those in the Tigris and Euphrates Valley of what is now Iraq, salted up over a thousand of years of irrigation, and were also abandoned. Deserts were created, partly by the drying of the climate, partly by the removal of their vegetation. This process has continued until the present. Degraded and abandoned land worldwide now amounts to about 5 billion acres (enough for 0.5-1 trillion trees).
Until the development of fossil fuels, the human habitat was more or less limited to the natural world, though agriculture manipulates the natural world considerably more than hunting and gathering and so supports more people per unit of land. In an agricultural society, increase in the food supply depends on developments in agriculture, or new land. The human population was capable of much faster growth—exponential growth, as Malthus pointed out—and even if populations were limited (by late marriage, taboos on intercourse, or exposure of infants, all only partly successful) poverty and hunger in agricultural societies were common. Long cycles of relative prosperity and depression, along with cycles in the settlement and abandonment of marginal lands, dominated European history for the last few millennia, and probably also the histories of other settled agricultural regions. The material life of a peasant in 16th century Europe was little different from that of one in Roman times. The collapse of agricultural societies from soil erosion, soil saltation, or slight changes in climate (Sumeria, Egypt’s Old Kingdom, the Maya, the Anasazi of the North American Southwest, the pre-Inca Tiahuanaco civilization, Rome) was common.
The invention of the coal-burning steam engine changed all this. The engine was used to pump water from the mines, in order to mine more coal (or iron ore). The coal powered the trains that transported the coal, the trains manufactured of (and running on tracks made from) coal-smelted iron. Coal and iron ore were essentially inexhaustible. Cheap transportation by steam ship meant food could be quickly transported all over the world. Coal became the basis of the modern chemical industry, replacing or supplementing wood (once distilled into several components), oil seeds and fiber plants and animals as a natural resource. The invention of a method of manufacturing nitrogen fertilizer from nitrogen gas in the air, the energy for the reaction supplied by coal, doubled or tripled crop yields and meant the nitrogen-fixing legumes formerly used in rotation to renew soils could be disposed of and food crops grown in their place, increasing the area of cropland by 30-50%. Coal heated houses, baked bread, brewed beer, ran factories, lighted houses. In newly settled lands wood, if abundant, might replace coal for a time. During the twentieth century other fossil fuels (oil, natural gas), along with hydroelectricity and nuclear power, helped supply the increasing energy demands of modern society. Capital, formerly limited to returns on agricultural investment or real estate (both limited by population growth, of people, crops or animals: capital comes from the French word for cattle), where returns might be 3-4% a year, found enormous returns in the developing markets of a rapidly growing world. As Fernand Braudel remarked, the ceiling on human possibilities vanished. For the first time since the development of agriculture, there was plenty of food (if you could afford it); and a limitless supply of energy. Population doubled every 25 years in newly settled North America, rather than every few hundred years in Europe, and the landscape was settled at half a percent (later 1%) a year, leading to enormous returns on investments in land. More capital meant more investment and more manipulation of the landscape.
Between 1850 and 1980 five billion acres of new land were cleared, in North and South America, Australia, and Eurasia. Forests were turned into fields, their timber burned or sawn, and the ashes sold; grasslands were plowed. Rivers filled with silt eroded off the fields and with sawdust from the mills, their fish spawning sites buried; and later with industrial effluent, petroleum and sewage. Steam driven trawlers scraped the bottoms of the oceans bare, breaking off their coldwater corals and sessile plants and animals, habitat for juvenile cod, hake and halibut. Scallop trawls brought up the bottom itself, which had to be shoveled, minus the scallops, off the deck. Sulfur dioxide, various hydrocarbons, soot and heavy metals from burning coal, from coke plants, from metal smelters and foundries filled the air, and men’s lungs, and settled out on the land and washed into waterways, where they ended up in the organs and flesh of fish. Modern suburbs were, like ancient ones, an escape from polluted and dangerous cities. After World War II and the development of the modern chemical industry, based largely on petroleum and chlorine, these materials were joined by tens of thousands of more or less toxic and bioaccumulating chlorinated hydrocarbons. At the same time, human prosperity and population reached unprecedented levels. All this, together with human settlement patterns (dispersed by the car), and—with the growing amount of machinery and capital—the increasing human ability to “pick up” the environment (eliminate, say, the tiny pools where amphibians bred, and which migrating shorebirds visited, and turn everything to pavement, plowed fields, planted forests, lawns), affected animal and plant populations, many of which began to disappear. Some, like songbirds and large game animals, seemed to stabilize at 5-10% of their former abundance in the late twentieth century. In 1958, a scientist named Charles Keeling set up instruments on a mountain in Hawaii to measure the carbon dioxide content of the atmosphere, to answer a simple question: what’s happening with all that carbon dioxide? The curve of carbon dioxide went steadily and increasingly up. In the 1970s, the possibility of global warming, from carbon dioxide and other gases produced by the burning of fossil fuels, from land clearing and agriculture, among other activities, was a crazy idea, by the 1990s not so nuts. Human contribution of carbon dioxide to the atmosphere was reaching 10% of that fixed annually by photosynthesis; while human contributions of usable nitrogen to the biosphere (nitrogen usable by plants: from fertilizer, planted legumes, animal manure, combustion of gas, coal, oil) equaled the natural contribution. Human intervention in the biogeochemical cycle of sulfur was reaching 30%. Paleoclimatological correlations of carbon dioxide and temperature in the past made the modern situation ominous. Temperature changes were obvious in the modern Arctic, where the sea ice was melting and the permafrost collapsing. And in the temperate world the movement of birds, mammals, plants and butterflies north or upslope was well documented: the plants and animals knew something we didn’t.
When a plant or animal, freed of its native parasites and predators, expands into a new habitat, it often overextends itself. Meadow voles, released on a grassy island without predators, will increase until no vegetation is left; then the population crashes, the vegetation (somewhat) regrows, and a much smaller population of voles cycles around a much smaller food supply. Fossil fuels let us construct a new habitat on the whole planet. This process is still going on. The use of fossil fuels freed us from the constraints of organic agriculture and from the limits of energy that came from wind, water and growing trees. At the same time, antibiotics, public health measures and insecticides freed us from most debilitating diseases and parasites; inorganic fertilizers, machine power, irrigation dams, and advances in crop breeding let us expand the agricultural environment virtually indefinitely; trawlers dragging huge nets led to increasing amounts of wild fish, until cultivation of fish (together with fish breeding) began to replace wild catches. The human population rose from 1.6 billion in 1900 to 6-7 billion now, quadrupling (worldwide) in a century. In 2009 the amount of carbon dioxide in the air has already sealed the fate of mountain glaciers that support the flow of rivers that irrigate food for 2 billion people in Asia, as well as the Arctic ice pack with its polar bears, foxes and seals. It will reduce the spring flow of rivers in California, warm continental interiors that are already too warm for good pollination of grain crops in parts of the U.S. South, produce more widely spaced but more intense rains. In 2009 northern forests are collapsing from insect infestation brought on by warmer, shorter winters; the fisheries off industrial coasts are degraded from overfishing and too much anthropogenic nitrogen; chlorinated hydrocarbons, many of which are cancer-causing and/or mimic human hormones continue to accumulate in fish, seabirds and human fat; the sea is rising and becoming more acid.
What to do? Will we reduce our population to 1.5-2 billion people, and reduce our energy use, so those people (2-3 generations of women with one child would do the trick) could run their economy on wind, water, sun, some nuclear and geothermal power, and live within a working biosphere. If we don’t do reduce our population, nature will do it for us.
Some claim the economy a subset of the biosphere. It’s hard to make an effective economic argument for preserving the more charismatic biota of earth (redwoods and grizzly bears; maple trees and chipmunks). On the other hand, the earth’s microbes and invertebrates are essential, being involved (among other things) in decomposition of plant and animal material; the production (through photosynthesis) of oxygen and (through respiration) of carbon dioxide (without some carbon dioxide, the planet would turn into a snowball); the fixing of reactive nitrogen plants can use from inert nitrogen gas in the air; the formation of sulfur compounds (also necessary for plant life). The larger biota (trees, grasses) affect microclimate and (to a lesser extent) the climate over large areas (largely through affecting temperature and rainfall: thus forests extend inland from rainy western coasts). Forests and grasslands control runoff, filter out silt and regulate the chemistry of surface waters and thus influence the lives of fresh water fish (more charismatic biota) and the health (their chemistries, silt loads) of estuaries, the main nurseries for marine fish and invertebrates. In short, they help set favorable conditions for other charismatic biota, in a world formed by invertebrates and microorganisms. Off shore islands, stabilized by grasses and trees, and tidal wetlands (ditto), along with coral reefs, protect sea coasts from storm surges.
Agriculture, together with more minor activities like forestry and fishing, is the human activity that depends directly on a friendly biosphere: that is, on predictable cycles of temperature and precipitation, on predictable river flows, on abundant insect pollinators and abundant insect, avian and mammalian predators of crop pests (beetles and bats help considerably), on the life of the soil. Most of the modern economy depends on stored life: fossil fuels (and their combustion and conversion into chemicals); various probably lifeless minerals; and metal ores (some of which are the products of past life). How much of the biosphere do we need? Food could be produced under plastic greenhouses, cooled by seawater pumped from cool depths, watered by dew condensing from the pipes, on artificial soils; our diets supplemented by the products of various bacterial fermentations. Desert coasts (also energy rich) would become the new agricultural lands. There is no shortage of schemes to bypass the agricultural biosphere.
Of course such ideas are nuts. The fundamental mistake of economics is the assumption that what is made doesn’t matter. This simplifying assumption means the science of economics is quite disconnected from the real world. Such disconnects are what government must compensate for (with, for instance taxes on carbon emissions or bio-accumulating chemicals). Climate change, sea level rise, the increasing pollution of the environment by industrial chemicals, the collapse of the oceans and of populations of land plants and animals, may not be the worst things that will happen to people over the next century: wars over food, religion and water are also likely. But those wars will take place against the inevitable collapse of the environment that sustains us, and in which we have evolved.
Sunday, May 31, 2009
Thursday, May 28, 2009
The Natural History of the Present, Chapter 17: Developed Landscapes
Chapter 17: Developed Landscapes
Developers are the third shaper of the modern landscape. For most of the twentieth century developed landscapes were a small percent of the total landscape, though their location (in flood plains, near ocean estuaries) intensified their ecological effects. The less dense developments of the latter part of the century (such as suburbs, served by cars, or warehouse districts, served by trucks) have spread the effects of human settlement out. By some estimates land is developing 7 times faster than population is increasing. From 1982 to 1997 the population of Pennsylvania grew by 2.5% while developed land increased by 47% (from 1990 to 2000, by a million acres). From 1982 to 1997—15 years—developed land in the United States grew by 25 million acres, an amount equal to 25% of all land developed since 1492. Such numbers explain why deer, coyotes and mountain lions have become animals of the suburbs. Developing landscapes near water (most cities are near water) interferes with the ecological function of these landscapes, since their natural variability (flooding; periodically high water tables; river channel migration; erosion of beaches) must be controlled. Such control turns formerly productive rivers into drains. Building and paving increase a landscape’s absorption of heat by changing its reflectivity or albedo. Cities are generally several degrees warmer than the surrounding countryside (about 10º C. by day, 6º C. at night; the denser the city, the greater the effect). Cities send their thermal effects, in the form of clouds and rain, downwind. It is thought Tokyo’s torrential summer downpours have been intensified by the continuing spread of the city (a mini-warming, probably intensified by the larger, global one). Summer rainfall near Tokyo increased 20% from 1979 to 1995, and the rate at which the rain falls has also increased. The average temperature of Phoenix, Arizona, has risen 5º F. since the 1960s, and as the city grows may rise 15º-20º more over the next 30 years (apart from any rise caused by a changing climate.) Cities, suburbs and superhighways are all sources of small particulates (from burned fuel), sulfur and nitrogen compounds, metal and rubber dusts, benzene, dioxins, furans, PCBs: the products of combustion, electricity generation, drying paints, industrial discharges, automobile use. Their sewage waters are sources of nutrients, hormones, and hormone mimics, as well as of a high and steady water flow into streams. Fish and alligator populations in waters that receive large flows of treated sewage waters decline sharply; in both the sexual development of males is compromised by human estrogen and estrogen-mimicking chemicals in the water. City roofs and pavements shed runoff into streams, flooding them. City (or suburban) water supplies require dams on rivers or wells to pump out groundwater. Groundwaters (out of sight) are usually overpumped. Overpumped aquifers include the sandstones about Milwaukee, Wisconsin, and the limestone acquifers of South Florida. Cities also have environmental advantages: public transportation is much more energy and materials efficient than private automobiles; heating and cooling costs in apartments are several times less than in detached houses; per capita water use is less (less car washing and lawn watering; fewer private swimming pools). In general, per capita energy use is several times less in cities than in suburbs, or in isolated rural houses, for the same standard of comfort.
Modern development usually begins with bare ground, graded to taste: an immediate, radical simplification. Paving or roofing more than 10% of a watershed begins to degrade its streams, but thanks to driveways, roofs, lawns and roads most suburbs are effectively 25-30% paved. (Los Angeles is 70% impervious surfaces and much of northern New Jersey not much less, which explains its problems with flooding.) Movement of soil and nutrients into watercourses is high during a development’s construction (this can be ameliorated), then falls as erosion is reduced. After development, roads, roofs and parking lots increase the amount of water runoff and its rate of flow and contribute a mixture of combusted hydrocarbons, motor oil, benzene, anti-freeze, brake fluid, metals, automobile greases, tire dust, aromatic hydrocarbons from worn asphalt, nitrogen, phosphorus, sodium chloride, sand and silt to the water. Because the land itself absorbs so little water, and because much of the runoff is carried away in pipes, small rainstorms produce a large flow at any time of year. Piped into watercourses, this flow excavates streambeds and changes the habitat for aquatic invertebrates, amphibians and fish. The rate of runoff amounts to 2 to 4 times natural background conditions. The chemicals and nutrients in the brown watery fluid don’t help. The weathering of soils re-arranged by construction into a new, more stable equilibrium (the soil profile) can take a thousand years and is slowed down by a lack of deep-rooted plants. (It can be speeded up by appropriate plantings and vigorous organic gardening.) Suburbs lack the energy advantages of cities: energy costs for heating and cooling are higher (they can be reduced by good construction, efficient equipment and trees; and space is available for solar electric panels); public transportation usually doesn’t work until houses reach a density of 7 per acre, and then only if the suburb is laid out for it. Most American cities resemble suburbs, with perhaps 4 to 8 houses per acre. Most are not laid out for public transportation. Residential areas are separate from commercial and light industrial ones, instead of having businesses and other places of employment clustered along the main streets (where public transportation runs), with housing adjacent, above, or behind. (The separation is a legacy of the Garden City Movement, which arose with the suburbs, and segregated areas dominated by coal-fired heavy industry, the domain of males, from the bucolic domestic environment run by females.)
The ecological effect of developed lands can be reduced. Drainage water can flow in shallow, vegetated ditches, rather than in pipes. The vegetation slows the flow and cleans the water and returns some of it to ground water. As well as nutrients, cattails and common reed accumulate metals, which can be reclaimed from the harvested plants. Water from parking lots can be led to vegetated areas (shallow wetlands with cattails), or to slightly sunken borders with trees, shrubs and herbs that tolerate some flooding (instead of the raised borders now used); the plants will help deal with the pollutants (their stems and roots act as scaffolds for the microorganisms that degrade them) and take up nutrients. The trees in sufficient numbers will cool the parking area. Parking lots can also have permeable pavements that let the rain sink through, in which case one lets the micro-organisms in the soil deal with the pollutants. Roof drainage from individual buildings can be led to aquifer recharge areas near the street or in the yard; on steep slopes, such recharge areas may have to be connected by wide drainage channels to wetlands down the slope. (Rain gardens in front of a 600 foot long row of houses on a Seattle street absorb 99% of the water from storms.) Open drainage structures (small ponds and marshes) that collect sediments from pipes must be periodically cleaned. Most American cities have enough land available for them to moderate their effect on local watercourses, although some land, right along watercourses, or in very built-up neighborhoods, would have to be purchased (for instance, to allow rivers to flood). Such overflow areas become parkland or wild land. City downtowns that are heavily paved can’t recharge their ground waters; their streams have long since been put in pipes underground, and the rising ground water from aquifer recharge would flood basements. At some cost, mostly for storage, such cities could capture the water that falls on their roofs, thus reducing their run-off and adding to their water resources. (Roof gardens are another possibilty, and besides reducing runoff, lower average summer temperatures in cities by several degrees. Collected roof water can provide 10-20% of a city’s needs, rainfall from the whole area 35-50%; such water is usually used for flushing toilets, which are plumbed with a separate system.) If there is sufficient space nearby, street run-off can be led to constructed wetlands, which are a cheap and effective means of cleaning runoff and regulating its flow (and recharging streambed aquifers), especially in more moderate climates. Sewage water can also be given a final treatment in constructed wetlands. (In severe climates, treatment wetlands are housed in greenhouses and used to grow crops like flowers.) The most efficient way to reduce the toxicity of what flows off city streets is to reduce what ends up on them. This means less toxic automobile greases, fuels and fluids. It means less traffic: getting more miles per gallon of fuel reduces pollutants on the street; so does increased use of public transportation.
It is fashionable to regard a city as an ecosystem, though one with a long reach, bringing in grain from the Middle West, heating oil from Venezuela, exporting sewage sludge to Texas cotton fields, waste paper to China or Europe, unseparated trash to Virginia landfills (where it will one day be dug up and used, as today on Nantucket Island). Rearrangement of nutrient flows are a part of this idea. Some wastes can be recycled on site; dying urban trees can be milled into boards, their branches chipped, the mulch used in city parks. Industries can be designed to use each other’s waste products. Cleaned sewage water is a potential source of some industrial water: certainly cooling water. (Drinking water in many cities in the Mississippi basin consists partly of treated sewage water from upstream; and more and more in the dry West urban water supplies are recycled sewage water that has made a sidetrip through a local aquifer.) Shipping pallets can be turned into flooring, into other lumber, or into shavings for biodegradable packing material. New closed-cycle paper mills that use very little water, perhaps very clean sewage water, can recycle a city’s waste paper in the city, saving immense amounts of energy in haulage. Plastics and metals can be recycled on site. Returnable glass bottles can be refilled with fruit juices, sodas, spaghetti sauces. In any urban manufacturing project, the cost of land and the increased volume of truck traffic are problems. (Trucks that ran on natural gas and that were shut off when stopped would make this much less of a problem.) Yard wastes can be collected and composted with other wastes, such as animal manures (from the 100 million dogs and cats in the United States), and food wastes (from households, restaurants, food processing plants). If the compost is clean and if city soils are not contaminated with metals like lead or cadmium, such composts can be used to grow backyard vegetables. Vegetables can also be grown in rooftop greenhouses. (Photo-voltaic solar collectors are a better use of urban roofs; but the two are not mutually exclusive. Photo-voltaic collectors mounted on buildings shade roofs and walls in hot climates, lengthening the lifetime of building materials and reducing cooling costs.) Miniature worm farms in city kitchens turn kitchen scraps into worm-generated composts. Shredded garbage can also be composted, rather than landfilled, the methane generated during composting collected and used to generate electricity. While the compost will probably not be clean enough to use for growing food (that depends on the efficiency with which things like batteries are removed), it could be used for projects like reclaiming strip-mined land; perhaps for growing fiber or nursery crops. The best solution to keeping trash cleaner and making human settlements less toxic to their surroundings is to keep toxic materials out of the stream of our lives. This requires regulation. For instance, items that contain mercury (such as mercury batteries and energy-saving fluorescent lights) might be purchased with a deposit; this makes them returnable and recyclable. All manufactured goods should be easily recyclable. For instance, one ought to be able to separate a burned-out compact fluorescent bulb, with its mercury lining, from its still functioning ballast base. The problems associated with a returnable item, as well as the added expense of a deposit, would encourage manufacturers to use non-toxic materials.
Most of of our current manufacturing technology is replaceable. Most toxic materials are unnecessary, but part of current industrial chemistry and so cheap to make. Technical alternatives to current materials are legion, but mean new plants, new manufacturing processes, new investment, some sort of guarantee of a market. Use of biodegradable soaps and cleaners lets the homeowner use household graywater (the waste water from sinks, shower, the washing machine) to irrigate lawns and gardens. In much of the country, photo-voltaic panels on roofs, and on walls of high buildings; in corners of yards; over driveways and parking lots; as roofs of garden sheds, would provide all our daytime electricity needs. Solar panels are becoming more efficient, and recent figures indicate that rooftop panels could provide all the electricity needed by a place like England (not an ideal climate for solar power). The electricity needed for night-time would have to be stored (as hot liquids heated by the sun); or come from other sources. With solar electric power the rain of carbon, metals and sulfur that falls on much of the Northern Hemisphere, a lot of it from power plants, and much of our interference with natural waterways (electric power plants are the largest industrial users of water) would be reduced. (New electic power plants can reduce cooling water use by up to 90%, but cost slightly more and so are not built as long as water is free. Assessing power plants for their effects on waterways—say, on fisheries—would make their water use quite expensive.) Twenty-four hours after the failure of the power grid in eastern North America in August 2003 the air downwind had 90% less sulfur dioxide, 50% less ozone, and visibility had increased by 25 miles. Automobile traffic continued at normal levels. The decrease in air pollution was a result of power plants (coal-fired power plants in the Middle West) being shut down. Current economic life depends on the sale of huge quantities of unnecessary things; it would be better if they were also harmless things.
In sunny climates rooftop water heaters also provide hot water, as they do today in Israel and Austrialia, and in the 1920s did in southern California. In temperate climates hot water typically constitutes 35% of household energy use. If appliances and houses were more efficient (also not a technical problem: the cost of a house would be higher, but since utility bills would be less, the overall cost of owning a house would remain the same or fall), rooftop solar cells would provide considerable excess power; this could be used to generate hydrogen from the splitting of water molecules in the presence of a catalyst, and the hydrogen used in fuel cells to generate electricty (water is the waste product); the electricity would run cars, trains, factories, light cities at night. So cities in sunny regions could be virtually energy independent, eliminating most of that Venezuelan and Saudi Arabian oil, and the considerable costs of keeping the Middle East safe for oil development (before the Iraq war, estimated at $50 billion a year, another cost not factored into the price of gasoline). With a concerted effort to cover parking lots and urban superhighways with solar panels, sunny American cities could become net exporters of energy as electricity or hydrogen gas; they would do this without interfering with the natural environment any more than they already are (which is not true of wind power). This is not to say a new industrial base of solar power and hydrogen would be pollution free; the manufacture of the collectors is polluting (it can undoubtedly be made less so) and they must be replaced on a 20 to 50 year cycle. The energy advantage of flat-plate solar collectors (the amount of energy they produce compared to what goes into building them) is 4 or more; that is, you get 4 times more energy out of them than went into making them. In comparison, the energy advantage of oil from the Alberta tar sands is also 4; that from the Texas oil wells of the 1950s was about 80, of all U.S. wells at the peak of U.S. production about 50.) Production of hydrogen by electrolysis is energy-demanding and unless storage of solar power improves (flow batteries, which store electrical power as chemical energy, are a possibility), most night-time power would have to be produced by fossil fuels, as would baseline power (power needed to even out fluctuations in the solar supply). But one would need much less of it: perhaps 60% less, perhaps (as energy efficiency improves) 90-95% less. (At that point, capturing carbon dioxide from the smokestacks of power plants is no longer a problem.)
A landscape altered for human convenience does not perform the ecological work of a natural landscape. Many new developments could be avoided by redeveloping old developments; making the human habitation more dense, but with parkland, playing fields, community gardens. Some of the ecological work done by the landscape can be recovered if aquifer recharge areas and vegetated drains are part of this. A drainage pattern shapes a landscape in a way the usual checkerboard of suburban houses and evergreens cannot: a pleasing case of form following function. In dry climates, trees and shrubs along drainage areas may not need irrigation. Old developments can also be made more energy-efficient and thus reduce their impact on the natural environment. If zoning allows commercial and industrial development as part of the mix, people can walk to the store, the library, the cafe, to work. Development friendly to public transportation usually has commercial or light industrial uses along main transportation routes with residential areas behind; so public transportation is a 10 or 15 minute walk from anywhere. Such communities are more friendly to that considerable part of the population (about 20%) that doesn’t drive: the old, the poor, the young, the disabled. Letting drainage water flow in open channels saves the developer money, as do narrower streets that slow traffic and let the tree canopy shade the area more completely. Such shading makes a difference of several degrees in summer temperatures. Vegetation (such as that in parks and playgrounds) also lowers summer temperatures by evapotranspiration. If we follow Mr. Odum, wild, undisturbed lands should occupy 40% of a new development (these can include wetlands, headlands and beach fronts, but not agricultural land or parks and playgrounds). Such lands should contain parts of all the ecosystems represented in the development and be connected to nearby wild lands.
Zoning presently is a matter of protecting property values: thus keeping chickens, hanging laundry out on a line, or renting out the apartment over the garage may be forbidden. Biologically-based zoning is a matter of protecting landscapes as ecological wholes. It would be based on geography, hydrology, topography, climate, soils, winds, as well as on economic and cultural matters. Working ecosystems require the protection of their essential features, which are not always easy to identify. Healthy streams and aquifer recharge areas are among the easier things to preserve. With streams and aquifer recharge areas comes much else. One of the original plans for Los Angeles left several hundred yards on either side of the Los Angeles River undeveloped. This was to become a mix of developed parkland (playing fields, picnic areas) and wild parkland (trails through the shrubby woods). The potential profit from developing the land overcame civic-mindedness however and so Los Angeles has no Central Park. What organizes the Los Angeles basin are the freeways. Building went right up to the edge of the Los Angeles River, which, following a serious flood in the 1940s, was turned into a cement-lined channel leading directly to the ocean. Now in some places the cement is being removed and the edges of the stream replanted. Here and there water birds use the river. The river is seen as an amenity. Perhaps not yet as an ecological amenity: its water is polluted with viruses from septic systems and parasites from pet faeces, as well as chemicals from local industry and road runoff. All this, from the river and from storm drains, ends up in the ocean off the famous Santa Monica beaches, making a swim there something of a risk.
Habitat fragmentation is one effect of development, again one with unforseen consequences. To keep a full compliment of most species, tracts of Amazon rainforest need to be at least 10 square kilometers, 2400 acres, without roads, powerlines, or much human interference. Viable populations of large predatory animals (grizzly bears, jaguars, tigers) require larger areas (250-300,000 acres, or 400-475 square miles). Better habitat is provided by several connected areas of this size.
People get in the way. Railroad lines restrict the migration of Mongollian gazelles in Central Asia, farmers’ fields block the movements of wildebeast in the Serengeti, hydroelectric reservoirs hamper the movement of woodland caribou in Canada, highways in North America impede travel by grizzly bears. On the Norwegian plateau, roads, powerlines, summer cabins and hydroelectric developments have reduced the winter range of the native reindeer, which stay several kilometers away from such human improvements, by 50%. In a study of a fenced Connecticut watershed (2400 acres protected for water supply), with use limited to 20 people with permits, populations of box turtles fell steadily over the 10 years of the study. The reason was unknown. Both dogs (let off the leash to run) or crows (attracted to the remains of picnic lunches) may have been the problem (both harass and kill turtles). Box turtles breed at 5 to 10 years. They lay 6-8 eggs a year, most of which are eaten by raccoons, skunks and opossums. The animals live for 50 years or more, a common strategy of animals that reproduce slowly. They have trouble dealing with many of the artifacts of modern civilization: for instance, they are too slow to avoid cars and cannot climb over road curbs. In a recent study of Northeastern woodlands, researchers found that woodlands of less than 5 acres (not a small area in the suburbs, where an acre is a large and many older suburbs were built at 4 houses to the acre) had 3 times as many of the ticks that cause Lyme disease and 7 times as many infected ticks per square meter as larger woodlands. White-footed mice and white-tailed deer are the alternate hosts of the tick. The researchers speculated that mouse densites were so high in the smaller woodlands because of the absence of predators. So the continual fragmentation of woodlands by suburban development in southeastern New York and Connecticut, by making life too hard for minks, weasels, foxes, hawks and owls, and too easy for white-footed mice and deer, may have helped cause the rise in Lyme disease there since the 1970s. Of less importance to suburbanites, the same fragmentation has helped reduce populations of migrating songbirds by 50% since the 1950s. In fragmented habitats their nesting success is lower, often below replacement levels, so such habitats become sinks for excess populations rather than sources of new birds. In fragmented habitats populations of the nest parasites (the brown-headed cowbird) and predators of songbirds increase. (Predators on songbirds, especially on nestlings, include jays, skunks, opossums, raccoons, red squirrels and domestic cats; none of these except cats eat many mice.)
Habitat fragmentation is a problem without much of a solution. It will inexorably rearrange plant and animal populations over large areas. Fragmented habitats are much more friendly to introduced aliens or opportunistic native species. One can make developments more friendly to surface and ground waters, and much more energy efficient, and such developments will have populations of birds and animals (reptiles, amphibians, spiders, beetles, songbirds, small mammals, microbes) that can deal with a fragmented habitat. How such communities will work as biological wholes is another matter; it is largely the habitat-shaping plants and the invertebrates and microbes of the soil that make landscapes work (especially for waterways). Vegetated corridors along streams provide a degree of connectedness; a sufficient one for some animals (deer, mink, coyotes). Semi-native habitats can be improved. Habitats can have sufficient food (mice, insects, wild fruits) but lack other amenities (roosts, privacy, hollow logs, dens, tall bushy trees). Some lacks can be corrected. Eastern bluebird populations crashed during the first part of the twentieth century, partly because of competition for nest holes with the introduced starling (competition for food may also have been a problem; starlings are aggressive enough to drive the larger northern flicker away from newly excavated nest holes), partly because of the growing lack of dead trees and decaying fence posts that once held nesting sites, as the landscape became more picked up. Bluebirds have partly recovered thanks to the provision of nesting boxes with entrance holes slightly too small for starlings. Similarly, shrike populations in otherwise good habitat can be doubled by adding hunting perches; at the same time, their nesting success rises (since they must travel less far to find prey). Weasels in small Northeastern woodlands may lack places to hide from domestic cats; foxes may lack safe denning sites, as well as sufficient hunting territory (that is, safely connected semi-wild areas). Busy roads are a constant hazard to both species; vegetated overpasses, wide enough and with enough shrubbery so the animals can keep out of sight are one solution; better than culverts under roads. (Such overpasses are used by large animals crossing the Trans-Canada Highway.) Hawks and owls may lack nesting trees. Amphibians are killed crossing roads to breeding sites (losses can be considerable; here culverts work), snakes are killed on their way to winter dens (reducing their effect on slugs and mice and their abundance to their predators, which may also eat mice). Loggerhead shrikes are apparently in decline because their young forage for insects along roadsides and are run over by passing cars. Specially designed culverts for amphibians, owl nesting boxes, vegetated overpasses and seasonally closed roads can correct some of this. A simple way to control the ticks that cause Lyme disease is to put out cotton balls impregnated with pyrethrum for the mice to build their nests with (the balls are usually stuffed into toilet paper tubes and put at the edge of the lawn). The insecticide kills the ticks on the mice. This will work until the ticks become resistant to the insecticide. One can also get rid of the deer, a necessary link in the tick-deer-mouse-man chain. Because of their effect on forest vegetation, deer should be controlled, and this must be done by people, as people have for the most part excluded their other predators (wolves, mountain lions) from the suburbs. Computer simulations indicate that to lower tick densities much, you must get rid of essentially all the deer. This is difficult, but possible: perhaps it is desireable. Coyotes adapt quite well to suburbs and are not a bad partial solution, but eat dogs and cats as well as mice and the fawns of white-tailed deer. People seem to deal with them better than with the resident Canada geese, which take over backyards, golf courses and soccer fields. Geese can be herded into smaller areas by manipulating the landscape (they avoid shrubbery and tall grass, where predators lurk). A machine pulled behind a tractor (or pushed by hand) could sweep up their dung from playing fields and golf courses; then it could be composted and used for fertiliser (grass-goose-grass is a natural connection, which the geese have exploited). If they were edible (most are contaminated by lead, probably from leaded gasoline), they could be hunted, probably with bird darts, as the Native Americans did. Connecting wild areas helps with habitat fragmentation but the corridors must be wide (200-300 feet). Vegetated highway overpasses help considerably in connecting habitats but are expensive. (They can also be used by people.) Unless human disturbance is kept to essentially zero, which isn’t possible in heavily settled areas, some animals won’t survive. Living with animals as hunting and gathering people did and seeing them as equals (the tribe of mice, the tribe of mountain lions, the tribe of insects) means both respecting and dealing with them. Otherwise deer become tame and eat the shrubbery and mountain lions move in to eat the deer and then us. The lion and the lamb will not lie down with us but will take advantage of the situation, just as we have: that is their biological imperative.
Some parts of the landscape are more essential to wildlife: breeding areas for amphibians (these are likely also to be aquifer recharge areas); trees in which hawks or owls nest; roosting and wintering areas for bats (often mines and caves); groves of pines among the fields of southern Mexico where migrating raptors rest; the Atlantic capes (Cape Cod, Cape May), where migrating songbirds gather to feed before setting off on their thousand mile flight over the ocean to the Caribbean islands or South America. Because of the geography of the North American coast, staging areas like Cape Cod and Cape May are essential for the survival of viable populations of migrating birds. Much of Capes Cod and May have already been developed. Such developments can be made more bird friendly by planting shrubs and trees the birds use (for their fruits, seeds, or insect pests), and by driving slowly and keeping the family cat indoors during migration. Also needing protection are the pathways the migrants follow in their slow springtime return through Central America, where the flowering or fruiting of some shrubs coincides with their passage; and the forests along the Gulf coast where those that fly across the Caribbean arrive in spring. A coastal forest several hundred meters wide to greet the birds and to absorb the force of storm surges would be a good thing from many perspectives. Perhaps a mile wide: Hurricane Katrina destroyed 90% of the structures within a half mile of the Mississippi coast in 2005, the same structures that were destroyed by Hurricane Camille 37 years before, making rebuilding more than pointless. The same landscape, left in its natural state, could do much useful work filtering water before it reaches the sea. Offshore islands, coral reefs, tidal wetlands fed by the mud from rivers, coastal mangrove forests all dissipate the energy in storm waves and limit the destructiveness of storm surges. They are less effective in blocking tsunamis, which are very long waves (the tsunami in southeast Asia in December 2007 was 8 miles long and rolled in for an hour). Coasts exposed to storm surges or hurricanes (where forests are useful in breaking the force of the wind) would be better left without permanent human settlements, and with their forests and wetlands intact. This would benefit not only homeowners and insurance companies, but birds, sea turtles, manatees, satwater crocodiles, and major coastal fisheries.
Another reason for the collapse of songbird populations is that the so-called wintering grounds (actually their native grounds) of many neotropical migrants in Central America and the Caribbean have been developed, logged and fragmented. Birds are adaptable; many neotropical migrants winter well in shade-grown coffee or cacao plantations. The trees in shade-grown coffee plantations include banana, guava, citrus, trees used for firewood, and many other native trees and herbs (up to 300 species of plants have been documented.) Their ground is covered with leaf litter and the invertebrates that live in the litter, the prey of birds that forage on the forest floor. Shade-grown coffee plantations have 60-70% of the diversity of wild tropical forest. Sun-grown coffee produces 5 times as much coffee but the cost of fertiliser and pesticide means it costs 6.5 times as much to grow. Their higher production per acre however makes the land in such plantations more valuable, so 40% of the coffee grown in the western hemisphere is now sun-grown. Native plantings, with stretches of mangrove forest between the beaches, could make Caribbean resorts much more warbler friendly and be good for business. Golf courses could be made more friendly to wildlife, with less water use (only the greens irrigated), fertilisation with composts, mowed along a narrow part of the central fairway, most of the course in native vegetation, even if this is sand or bunchgrass. (Where is the golfer’s sense of adventure?) As bird numbers are reduced we lose the value of the work they do in North American fields and forests. This amounts to 10-20% of the yearly growth of the forests, probably something similar for field crops. Such calculations help put a value on the lands needed during their migrations. As time goes on, more and more such lands will be discovered for more and more species. For instance, some effort is now made to preserve wetlands, but wetlands are intimately connected to uplands, not only for their water supply but because animals like pollinating bees breed in nearby uplands. Wetlands with more intimate connections to uplands, rivers or the sea have a more diverse mix of species. (I note that ‘swamp’ is still a perjorative term.)
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Air blows across the fields and picks up nitrous oxide from bacterially manipulated fertilisers, carbon dioxide from respiring soil, methane from manure. Growing plants scavenge some of the carbon dioxide from the soil and from the air. Cornfields, like forests, deplete the air above them of carbon dioxide in July when they are strongly growing and also transpire soil moisture into the air. (The total moisture transpired during the summer would cover the cornfield to a depth of five feet.) The rising air sheds its moisture and forms clouds on mountain ridges. In temperate regions the average height of the bottoms of such clouds marks the level at which deciduous trees give way to evergreens. Cloud ceilings rise as forests on the slopes below are cleared: perhaps 30 feet per decade lately in the Appalachians; until there were no clouds left in some cloud forests in Costa Rica (and then the amphibians of the forest, which depended on the moisture from the clouds, died). Water drains off fields and forests into rivers and spirals downstream through river channels and riverside wetlands, the river water in intimate connection with huge pools of water that lie under the river valleys themselves. Long sections of these rivers have had their banks reconstructed with rip-rap or concrete, their vegetation removed, their beds altered to increase the water’s depth, all of which changes the temperature of the river and its rate of flow and its horizontal connections with its valley landscape. The nutrient relationships among river water, the riverside soils and ground water is changed. River water flows downhill, over dams, with side trips into fields, through power plants and through municipal water systems, until it reaches an inland basin (the Great Salt Lake, the Dead Sea, the Caspian Sea), or the ocean. From such places it evaporates and is carried by the atmosphere until it falls over the mountains as rain. This exposition leads us to our next chapter.
Developers are the third shaper of the modern landscape. For most of the twentieth century developed landscapes were a small percent of the total landscape, though their location (in flood plains, near ocean estuaries) intensified their ecological effects. The less dense developments of the latter part of the century (such as suburbs, served by cars, or warehouse districts, served by trucks) have spread the effects of human settlement out. By some estimates land is developing 7 times faster than population is increasing. From 1982 to 1997 the population of Pennsylvania grew by 2.5% while developed land increased by 47% (from 1990 to 2000, by a million acres). From 1982 to 1997—15 years—developed land in the United States grew by 25 million acres, an amount equal to 25% of all land developed since 1492. Such numbers explain why deer, coyotes and mountain lions have become animals of the suburbs. Developing landscapes near water (most cities are near water) interferes with the ecological function of these landscapes, since their natural variability (flooding; periodically high water tables; river channel migration; erosion of beaches) must be controlled. Such control turns formerly productive rivers into drains. Building and paving increase a landscape’s absorption of heat by changing its reflectivity or albedo. Cities are generally several degrees warmer than the surrounding countryside (about 10º C. by day, 6º C. at night; the denser the city, the greater the effect). Cities send their thermal effects, in the form of clouds and rain, downwind. It is thought Tokyo’s torrential summer downpours have been intensified by the continuing spread of the city (a mini-warming, probably intensified by the larger, global one). Summer rainfall near Tokyo increased 20% from 1979 to 1995, and the rate at which the rain falls has also increased. The average temperature of Phoenix, Arizona, has risen 5º F. since the 1960s, and as the city grows may rise 15º-20º more over the next 30 years (apart from any rise caused by a changing climate.) Cities, suburbs and superhighways are all sources of small particulates (from burned fuel), sulfur and nitrogen compounds, metal and rubber dusts, benzene, dioxins, furans, PCBs: the products of combustion, electricity generation, drying paints, industrial discharges, automobile use. Their sewage waters are sources of nutrients, hormones, and hormone mimics, as well as of a high and steady water flow into streams. Fish and alligator populations in waters that receive large flows of treated sewage waters decline sharply; in both the sexual development of males is compromised by human estrogen and estrogen-mimicking chemicals in the water. City roofs and pavements shed runoff into streams, flooding them. City (or suburban) water supplies require dams on rivers or wells to pump out groundwater. Groundwaters (out of sight) are usually overpumped. Overpumped aquifers include the sandstones about Milwaukee, Wisconsin, and the limestone acquifers of South Florida. Cities also have environmental advantages: public transportation is much more energy and materials efficient than private automobiles; heating and cooling costs in apartments are several times less than in detached houses; per capita water use is less (less car washing and lawn watering; fewer private swimming pools). In general, per capita energy use is several times less in cities than in suburbs, or in isolated rural houses, for the same standard of comfort.
Modern development usually begins with bare ground, graded to taste: an immediate, radical simplification. Paving or roofing more than 10% of a watershed begins to degrade its streams, but thanks to driveways, roofs, lawns and roads most suburbs are effectively 25-30% paved. (Los Angeles is 70% impervious surfaces and much of northern New Jersey not much less, which explains its problems with flooding.) Movement of soil and nutrients into watercourses is high during a development’s construction (this can be ameliorated), then falls as erosion is reduced. After development, roads, roofs and parking lots increase the amount of water runoff and its rate of flow and contribute a mixture of combusted hydrocarbons, motor oil, benzene, anti-freeze, brake fluid, metals, automobile greases, tire dust, aromatic hydrocarbons from worn asphalt, nitrogen, phosphorus, sodium chloride, sand and silt to the water. Because the land itself absorbs so little water, and because much of the runoff is carried away in pipes, small rainstorms produce a large flow at any time of year. Piped into watercourses, this flow excavates streambeds and changes the habitat for aquatic invertebrates, amphibians and fish. The rate of runoff amounts to 2 to 4 times natural background conditions. The chemicals and nutrients in the brown watery fluid don’t help. The weathering of soils re-arranged by construction into a new, more stable equilibrium (the soil profile) can take a thousand years and is slowed down by a lack of deep-rooted plants. (It can be speeded up by appropriate plantings and vigorous organic gardening.) Suburbs lack the energy advantages of cities: energy costs for heating and cooling are higher (they can be reduced by good construction, efficient equipment and trees; and space is available for solar electric panels); public transportation usually doesn’t work until houses reach a density of 7 per acre, and then only if the suburb is laid out for it. Most American cities resemble suburbs, with perhaps 4 to 8 houses per acre. Most are not laid out for public transportation. Residential areas are separate from commercial and light industrial ones, instead of having businesses and other places of employment clustered along the main streets (where public transportation runs), with housing adjacent, above, or behind. (The separation is a legacy of the Garden City Movement, which arose with the suburbs, and segregated areas dominated by coal-fired heavy industry, the domain of males, from the bucolic domestic environment run by females.)
The ecological effect of developed lands can be reduced. Drainage water can flow in shallow, vegetated ditches, rather than in pipes. The vegetation slows the flow and cleans the water and returns some of it to ground water. As well as nutrients, cattails and common reed accumulate metals, which can be reclaimed from the harvested plants. Water from parking lots can be led to vegetated areas (shallow wetlands with cattails), or to slightly sunken borders with trees, shrubs and herbs that tolerate some flooding (instead of the raised borders now used); the plants will help deal with the pollutants (their stems and roots act as scaffolds for the microorganisms that degrade them) and take up nutrients. The trees in sufficient numbers will cool the parking area. Parking lots can also have permeable pavements that let the rain sink through, in which case one lets the micro-organisms in the soil deal with the pollutants. Roof drainage from individual buildings can be led to aquifer recharge areas near the street or in the yard; on steep slopes, such recharge areas may have to be connected by wide drainage channels to wetlands down the slope. (Rain gardens in front of a 600 foot long row of houses on a Seattle street absorb 99% of the water from storms.) Open drainage structures (small ponds and marshes) that collect sediments from pipes must be periodically cleaned. Most American cities have enough land available for them to moderate their effect on local watercourses, although some land, right along watercourses, or in very built-up neighborhoods, would have to be purchased (for instance, to allow rivers to flood). Such overflow areas become parkland or wild land. City downtowns that are heavily paved can’t recharge their ground waters; their streams have long since been put in pipes underground, and the rising ground water from aquifer recharge would flood basements. At some cost, mostly for storage, such cities could capture the water that falls on their roofs, thus reducing their run-off and adding to their water resources. (Roof gardens are another possibilty, and besides reducing runoff, lower average summer temperatures in cities by several degrees. Collected roof water can provide 10-20% of a city’s needs, rainfall from the whole area 35-50%; such water is usually used for flushing toilets, which are plumbed with a separate system.) If there is sufficient space nearby, street run-off can be led to constructed wetlands, which are a cheap and effective means of cleaning runoff and regulating its flow (and recharging streambed aquifers), especially in more moderate climates. Sewage water can also be given a final treatment in constructed wetlands. (In severe climates, treatment wetlands are housed in greenhouses and used to grow crops like flowers.) The most efficient way to reduce the toxicity of what flows off city streets is to reduce what ends up on them. This means less toxic automobile greases, fuels and fluids. It means less traffic: getting more miles per gallon of fuel reduces pollutants on the street; so does increased use of public transportation.
It is fashionable to regard a city as an ecosystem, though one with a long reach, bringing in grain from the Middle West, heating oil from Venezuela, exporting sewage sludge to Texas cotton fields, waste paper to China or Europe, unseparated trash to Virginia landfills (where it will one day be dug up and used, as today on Nantucket Island). Rearrangement of nutrient flows are a part of this idea. Some wastes can be recycled on site; dying urban trees can be milled into boards, their branches chipped, the mulch used in city parks. Industries can be designed to use each other’s waste products. Cleaned sewage water is a potential source of some industrial water: certainly cooling water. (Drinking water in many cities in the Mississippi basin consists partly of treated sewage water from upstream; and more and more in the dry West urban water supplies are recycled sewage water that has made a sidetrip through a local aquifer.) Shipping pallets can be turned into flooring, into other lumber, or into shavings for biodegradable packing material. New closed-cycle paper mills that use very little water, perhaps very clean sewage water, can recycle a city’s waste paper in the city, saving immense amounts of energy in haulage. Plastics and metals can be recycled on site. Returnable glass bottles can be refilled with fruit juices, sodas, spaghetti sauces. In any urban manufacturing project, the cost of land and the increased volume of truck traffic are problems. (Trucks that ran on natural gas and that were shut off when stopped would make this much less of a problem.) Yard wastes can be collected and composted with other wastes, such as animal manures (from the 100 million dogs and cats in the United States), and food wastes (from households, restaurants, food processing plants). If the compost is clean and if city soils are not contaminated with metals like lead or cadmium, such composts can be used to grow backyard vegetables. Vegetables can also be grown in rooftop greenhouses. (Photo-voltaic solar collectors are a better use of urban roofs; but the two are not mutually exclusive. Photo-voltaic collectors mounted on buildings shade roofs and walls in hot climates, lengthening the lifetime of building materials and reducing cooling costs.) Miniature worm farms in city kitchens turn kitchen scraps into worm-generated composts. Shredded garbage can also be composted, rather than landfilled, the methane generated during composting collected and used to generate electricity. While the compost will probably not be clean enough to use for growing food (that depends on the efficiency with which things like batteries are removed), it could be used for projects like reclaiming strip-mined land; perhaps for growing fiber or nursery crops. The best solution to keeping trash cleaner and making human settlements less toxic to their surroundings is to keep toxic materials out of the stream of our lives. This requires regulation. For instance, items that contain mercury (such as mercury batteries and energy-saving fluorescent lights) might be purchased with a deposit; this makes them returnable and recyclable. All manufactured goods should be easily recyclable. For instance, one ought to be able to separate a burned-out compact fluorescent bulb, with its mercury lining, from its still functioning ballast base. The problems associated with a returnable item, as well as the added expense of a deposit, would encourage manufacturers to use non-toxic materials.
Most of of our current manufacturing technology is replaceable. Most toxic materials are unnecessary, but part of current industrial chemistry and so cheap to make. Technical alternatives to current materials are legion, but mean new plants, new manufacturing processes, new investment, some sort of guarantee of a market. Use of biodegradable soaps and cleaners lets the homeowner use household graywater (the waste water from sinks, shower, the washing machine) to irrigate lawns and gardens. In much of the country, photo-voltaic panels on roofs, and on walls of high buildings; in corners of yards; over driveways and parking lots; as roofs of garden sheds, would provide all our daytime electricity needs. Solar panels are becoming more efficient, and recent figures indicate that rooftop panels could provide all the electricity needed by a place like England (not an ideal climate for solar power). The electricity needed for night-time would have to be stored (as hot liquids heated by the sun); or come from other sources. With solar electric power the rain of carbon, metals and sulfur that falls on much of the Northern Hemisphere, a lot of it from power plants, and much of our interference with natural waterways (electric power plants are the largest industrial users of water) would be reduced. (New electic power plants can reduce cooling water use by up to 90%, but cost slightly more and so are not built as long as water is free. Assessing power plants for their effects on waterways—say, on fisheries—would make their water use quite expensive.) Twenty-four hours after the failure of the power grid in eastern North America in August 2003 the air downwind had 90% less sulfur dioxide, 50% less ozone, and visibility had increased by 25 miles. Automobile traffic continued at normal levels. The decrease in air pollution was a result of power plants (coal-fired power plants in the Middle West) being shut down. Current economic life depends on the sale of huge quantities of unnecessary things; it would be better if they were also harmless things.
In sunny climates rooftop water heaters also provide hot water, as they do today in Israel and Austrialia, and in the 1920s did in southern California. In temperate climates hot water typically constitutes 35% of household energy use. If appliances and houses were more efficient (also not a technical problem: the cost of a house would be higher, but since utility bills would be less, the overall cost of owning a house would remain the same or fall), rooftop solar cells would provide considerable excess power; this could be used to generate hydrogen from the splitting of water molecules in the presence of a catalyst, and the hydrogen used in fuel cells to generate electricty (water is the waste product); the electricity would run cars, trains, factories, light cities at night. So cities in sunny regions could be virtually energy independent, eliminating most of that Venezuelan and Saudi Arabian oil, and the considerable costs of keeping the Middle East safe for oil development (before the Iraq war, estimated at $50 billion a year, another cost not factored into the price of gasoline). With a concerted effort to cover parking lots and urban superhighways with solar panels, sunny American cities could become net exporters of energy as electricity or hydrogen gas; they would do this without interfering with the natural environment any more than they already are (which is not true of wind power). This is not to say a new industrial base of solar power and hydrogen would be pollution free; the manufacture of the collectors is polluting (it can undoubtedly be made less so) and they must be replaced on a 20 to 50 year cycle. The energy advantage of flat-plate solar collectors (the amount of energy they produce compared to what goes into building them) is 4 or more; that is, you get 4 times more energy out of them than went into making them. In comparison, the energy advantage of oil from the Alberta tar sands is also 4; that from the Texas oil wells of the 1950s was about 80, of all U.S. wells at the peak of U.S. production about 50.) Production of hydrogen by electrolysis is energy-demanding and unless storage of solar power improves (flow batteries, which store electrical power as chemical energy, are a possibility), most night-time power would have to be produced by fossil fuels, as would baseline power (power needed to even out fluctuations in the solar supply). But one would need much less of it: perhaps 60% less, perhaps (as energy efficiency improves) 90-95% less. (At that point, capturing carbon dioxide from the smokestacks of power plants is no longer a problem.)
A landscape altered for human convenience does not perform the ecological work of a natural landscape. Many new developments could be avoided by redeveloping old developments; making the human habitation more dense, but with parkland, playing fields, community gardens. Some of the ecological work done by the landscape can be recovered if aquifer recharge areas and vegetated drains are part of this. A drainage pattern shapes a landscape in a way the usual checkerboard of suburban houses and evergreens cannot: a pleasing case of form following function. In dry climates, trees and shrubs along drainage areas may not need irrigation. Old developments can also be made more energy-efficient and thus reduce their impact on the natural environment. If zoning allows commercial and industrial development as part of the mix, people can walk to the store, the library, the cafe, to work. Development friendly to public transportation usually has commercial or light industrial uses along main transportation routes with residential areas behind; so public transportation is a 10 or 15 minute walk from anywhere. Such communities are more friendly to that considerable part of the population (about 20%) that doesn’t drive: the old, the poor, the young, the disabled. Letting drainage water flow in open channels saves the developer money, as do narrower streets that slow traffic and let the tree canopy shade the area more completely. Such shading makes a difference of several degrees in summer temperatures. Vegetation (such as that in parks and playgrounds) also lowers summer temperatures by evapotranspiration. If we follow Mr. Odum, wild, undisturbed lands should occupy 40% of a new development (these can include wetlands, headlands and beach fronts, but not agricultural land or parks and playgrounds). Such lands should contain parts of all the ecosystems represented in the development and be connected to nearby wild lands.
Zoning presently is a matter of protecting property values: thus keeping chickens, hanging laundry out on a line, or renting out the apartment over the garage may be forbidden. Biologically-based zoning is a matter of protecting landscapes as ecological wholes. It would be based on geography, hydrology, topography, climate, soils, winds, as well as on economic and cultural matters. Working ecosystems require the protection of their essential features, which are not always easy to identify. Healthy streams and aquifer recharge areas are among the easier things to preserve. With streams and aquifer recharge areas comes much else. One of the original plans for Los Angeles left several hundred yards on either side of the Los Angeles River undeveloped. This was to become a mix of developed parkland (playing fields, picnic areas) and wild parkland (trails through the shrubby woods). The potential profit from developing the land overcame civic-mindedness however and so Los Angeles has no Central Park. What organizes the Los Angeles basin are the freeways. Building went right up to the edge of the Los Angeles River, which, following a serious flood in the 1940s, was turned into a cement-lined channel leading directly to the ocean. Now in some places the cement is being removed and the edges of the stream replanted. Here and there water birds use the river. The river is seen as an amenity. Perhaps not yet as an ecological amenity: its water is polluted with viruses from septic systems and parasites from pet faeces, as well as chemicals from local industry and road runoff. All this, from the river and from storm drains, ends up in the ocean off the famous Santa Monica beaches, making a swim there something of a risk.
Habitat fragmentation is one effect of development, again one with unforseen consequences. To keep a full compliment of most species, tracts of Amazon rainforest need to be at least 10 square kilometers, 2400 acres, without roads, powerlines, or much human interference. Viable populations of large predatory animals (grizzly bears, jaguars, tigers) require larger areas (250-300,000 acres, or 400-475 square miles). Better habitat is provided by several connected areas of this size.
People get in the way. Railroad lines restrict the migration of Mongollian gazelles in Central Asia, farmers’ fields block the movements of wildebeast in the Serengeti, hydroelectric reservoirs hamper the movement of woodland caribou in Canada, highways in North America impede travel by grizzly bears. On the Norwegian plateau, roads, powerlines, summer cabins and hydroelectric developments have reduced the winter range of the native reindeer, which stay several kilometers away from such human improvements, by 50%. In a study of a fenced Connecticut watershed (2400 acres protected for water supply), with use limited to 20 people with permits, populations of box turtles fell steadily over the 10 years of the study. The reason was unknown. Both dogs (let off the leash to run) or crows (attracted to the remains of picnic lunches) may have been the problem (both harass and kill turtles). Box turtles breed at 5 to 10 years. They lay 6-8 eggs a year, most of which are eaten by raccoons, skunks and opossums. The animals live for 50 years or more, a common strategy of animals that reproduce slowly. They have trouble dealing with many of the artifacts of modern civilization: for instance, they are too slow to avoid cars and cannot climb over road curbs. In a recent study of Northeastern woodlands, researchers found that woodlands of less than 5 acres (not a small area in the suburbs, where an acre is a large and many older suburbs were built at 4 houses to the acre) had 3 times as many of the ticks that cause Lyme disease and 7 times as many infected ticks per square meter as larger woodlands. White-footed mice and white-tailed deer are the alternate hosts of the tick. The researchers speculated that mouse densites were so high in the smaller woodlands because of the absence of predators. So the continual fragmentation of woodlands by suburban development in southeastern New York and Connecticut, by making life too hard for minks, weasels, foxes, hawks and owls, and too easy for white-footed mice and deer, may have helped cause the rise in Lyme disease there since the 1970s. Of less importance to suburbanites, the same fragmentation has helped reduce populations of migrating songbirds by 50% since the 1950s. In fragmented habitats their nesting success is lower, often below replacement levels, so such habitats become sinks for excess populations rather than sources of new birds. In fragmented habitats populations of the nest parasites (the brown-headed cowbird) and predators of songbirds increase. (Predators on songbirds, especially on nestlings, include jays, skunks, opossums, raccoons, red squirrels and domestic cats; none of these except cats eat many mice.)
Habitat fragmentation is a problem without much of a solution. It will inexorably rearrange plant and animal populations over large areas. Fragmented habitats are much more friendly to introduced aliens or opportunistic native species. One can make developments more friendly to surface and ground waters, and much more energy efficient, and such developments will have populations of birds and animals (reptiles, amphibians, spiders, beetles, songbirds, small mammals, microbes) that can deal with a fragmented habitat. How such communities will work as biological wholes is another matter; it is largely the habitat-shaping plants and the invertebrates and microbes of the soil that make landscapes work (especially for waterways). Vegetated corridors along streams provide a degree of connectedness; a sufficient one for some animals (deer, mink, coyotes). Semi-native habitats can be improved. Habitats can have sufficient food (mice, insects, wild fruits) but lack other amenities (roosts, privacy, hollow logs, dens, tall bushy trees). Some lacks can be corrected. Eastern bluebird populations crashed during the first part of the twentieth century, partly because of competition for nest holes with the introduced starling (competition for food may also have been a problem; starlings are aggressive enough to drive the larger northern flicker away from newly excavated nest holes), partly because of the growing lack of dead trees and decaying fence posts that once held nesting sites, as the landscape became more picked up. Bluebirds have partly recovered thanks to the provision of nesting boxes with entrance holes slightly too small for starlings. Similarly, shrike populations in otherwise good habitat can be doubled by adding hunting perches; at the same time, their nesting success rises (since they must travel less far to find prey). Weasels in small Northeastern woodlands may lack places to hide from domestic cats; foxes may lack safe denning sites, as well as sufficient hunting territory (that is, safely connected semi-wild areas). Busy roads are a constant hazard to both species; vegetated overpasses, wide enough and with enough shrubbery so the animals can keep out of sight are one solution; better than culverts under roads. (Such overpasses are used by large animals crossing the Trans-Canada Highway.) Hawks and owls may lack nesting trees. Amphibians are killed crossing roads to breeding sites (losses can be considerable; here culverts work), snakes are killed on their way to winter dens (reducing their effect on slugs and mice and their abundance to their predators, which may also eat mice). Loggerhead shrikes are apparently in decline because their young forage for insects along roadsides and are run over by passing cars. Specially designed culverts for amphibians, owl nesting boxes, vegetated overpasses and seasonally closed roads can correct some of this. A simple way to control the ticks that cause Lyme disease is to put out cotton balls impregnated with pyrethrum for the mice to build their nests with (the balls are usually stuffed into toilet paper tubes and put at the edge of the lawn). The insecticide kills the ticks on the mice. This will work until the ticks become resistant to the insecticide. One can also get rid of the deer, a necessary link in the tick-deer-mouse-man chain. Because of their effect on forest vegetation, deer should be controlled, and this must be done by people, as people have for the most part excluded their other predators (wolves, mountain lions) from the suburbs. Computer simulations indicate that to lower tick densities much, you must get rid of essentially all the deer. This is difficult, but possible: perhaps it is desireable. Coyotes adapt quite well to suburbs and are not a bad partial solution, but eat dogs and cats as well as mice and the fawns of white-tailed deer. People seem to deal with them better than with the resident Canada geese, which take over backyards, golf courses and soccer fields. Geese can be herded into smaller areas by manipulating the landscape (they avoid shrubbery and tall grass, where predators lurk). A machine pulled behind a tractor (or pushed by hand) could sweep up their dung from playing fields and golf courses; then it could be composted and used for fertiliser (grass-goose-grass is a natural connection, which the geese have exploited). If they were edible (most are contaminated by lead, probably from leaded gasoline), they could be hunted, probably with bird darts, as the Native Americans did. Connecting wild areas helps with habitat fragmentation but the corridors must be wide (200-300 feet). Vegetated highway overpasses help considerably in connecting habitats but are expensive. (They can also be used by people.) Unless human disturbance is kept to essentially zero, which isn’t possible in heavily settled areas, some animals won’t survive. Living with animals as hunting and gathering people did and seeing them as equals (the tribe of mice, the tribe of mountain lions, the tribe of insects) means both respecting and dealing with them. Otherwise deer become tame and eat the shrubbery and mountain lions move in to eat the deer and then us. The lion and the lamb will not lie down with us but will take advantage of the situation, just as we have: that is their biological imperative.
Some parts of the landscape are more essential to wildlife: breeding areas for amphibians (these are likely also to be aquifer recharge areas); trees in which hawks or owls nest; roosting and wintering areas for bats (often mines and caves); groves of pines among the fields of southern Mexico where migrating raptors rest; the Atlantic capes (Cape Cod, Cape May), where migrating songbirds gather to feed before setting off on their thousand mile flight over the ocean to the Caribbean islands or South America. Because of the geography of the North American coast, staging areas like Cape Cod and Cape May are essential for the survival of viable populations of migrating birds. Much of Capes Cod and May have already been developed. Such developments can be made more bird friendly by planting shrubs and trees the birds use (for their fruits, seeds, or insect pests), and by driving slowly and keeping the family cat indoors during migration. Also needing protection are the pathways the migrants follow in their slow springtime return through Central America, where the flowering or fruiting of some shrubs coincides with their passage; and the forests along the Gulf coast where those that fly across the Caribbean arrive in spring. A coastal forest several hundred meters wide to greet the birds and to absorb the force of storm surges would be a good thing from many perspectives. Perhaps a mile wide: Hurricane Katrina destroyed 90% of the structures within a half mile of the Mississippi coast in 2005, the same structures that were destroyed by Hurricane Camille 37 years before, making rebuilding more than pointless. The same landscape, left in its natural state, could do much useful work filtering water before it reaches the sea. Offshore islands, coral reefs, tidal wetlands fed by the mud from rivers, coastal mangrove forests all dissipate the energy in storm waves and limit the destructiveness of storm surges. They are less effective in blocking tsunamis, which are very long waves (the tsunami in southeast Asia in December 2007 was 8 miles long and rolled in for an hour). Coasts exposed to storm surges or hurricanes (where forests are useful in breaking the force of the wind) would be better left without permanent human settlements, and with their forests and wetlands intact. This would benefit not only homeowners and insurance companies, but birds, sea turtles, manatees, satwater crocodiles, and major coastal fisheries.
Another reason for the collapse of songbird populations is that the so-called wintering grounds (actually their native grounds) of many neotropical migrants in Central America and the Caribbean have been developed, logged and fragmented. Birds are adaptable; many neotropical migrants winter well in shade-grown coffee or cacao plantations. The trees in shade-grown coffee plantations include banana, guava, citrus, trees used for firewood, and many other native trees and herbs (up to 300 species of plants have been documented.) Their ground is covered with leaf litter and the invertebrates that live in the litter, the prey of birds that forage on the forest floor. Shade-grown coffee plantations have 60-70% of the diversity of wild tropical forest. Sun-grown coffee produces 5 times as much coffee but the cost of fertiliser and pesticide means it costs 6.5 times as much to grow. Their higher production per acre however makes the land in such plantations more valuable, so 40% of the coffee grown in the western hemisphere is now sun-grown. Native plantings, with stretches of mangrove forest between the beaches, could make Caribbean resorts much more warbler friendly and be good for business. Golf courses could be made more friendly to wildlife, with less water use (only the greens irrigated), fertilisation with composts, mowed along a narrow part of the central fairway, most of the course in native vegetation, even if this is sand or bunchgrass. (Where is the golfer’s sense of adventure?) As bird numbers are reduced we lose the value of the work they do in North American fields and forests. This amounts to 10-20% of the yearly growth of the forests, probably something similar for field crops. Such calculations help put a value on the lands needed during their migrations. As time goes on, more and more such lands will be discovered for more and more species. For instance, some effort is now made to preserve wetlands, but wetlands are intimately connected to uplands, not only for their water supply but because animals like pollinating bees breed in nearby uplands. Wetlands with more intimate connections to uplands, rivers or the sea have a more diverse mix of species. (I note that ‘swamp’ is still a perjorative term.)
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Air blows across the fields and picks up nitrous oxide from bacterially manipulated fertilisers, carbon dioxide from respiring soil, methane from manure. Growing plants scavenge some of the carbon dioxide from the soil and from the air. Cornfields, like forests, deplete the air above them of carbon dioxide in July when they are strongly growing and also transpire soil moisture into the air. (The total moisture transpired during the summer would cover the cornfield to a depth of five feet.) The rising air sheds its moisture and forms clouds on mountain ridges. In temperate regions the average height of the bottoms of such clouds marks the level at which deciduous trees give way to evergreens. Cloud ceilings rise as forests on the slopes below are cleared: perhaps 30 feet per decade lately in the Appalachians; until there were no clouds left in some cloud forests in Costa Rica (and then the amphibians of the forest, which depended on the moisture from the clouds, died). Water drains off fields and forests into rivers and spirals downstream through river channels and riverside wetlands, the river water in intimate connection with huge pools of water that lie under the river valleys themselves. Long sections of these rivers have had their banks reconstructed with rip-rap or concrete, their vegetation removed, their beds altered to increase the water’s depth, all of which changes the temperature of the river and its rate of flow and its horizontal connections with its valley landscape. The nutrient relationships among river water, the riverside soils and ground water is changed. River water flows downhill, over dams, with side trips into fields, through power plants and through municipal water systems, until it reaches an inland basin (the Great Salt Lake, the Dead Sea, the Caspian Sea), or the ocean. From such places it evaporates and is carried by the atmosphere until it falls over the mountains as rain. This exposition leads us to our next chapter.
Wednesday, May 20, 2009
The Natural History of the Present, Chapter 16
Chapter 16: Forests
Like fields, forests affect atmospheric chemistry, the chemistry and flow of local streams, local and global precipitation, climate. Root growth accounts for 50% of the net primary productivity in forests (the net yearly production), leaves for 25-35%, growth of wood the rest. About 20% of the mass of forest trees is roots, most in the top few inches of soil. The growth and death of roots delivers carbon to the soil, removing it from the atmosphere. Thus old-growth forests continue to store carbon, even after growth of their trunks has slowed. Storage varies with the type of forest. It falls precipitously in southern pine plantations after 25 years, when their growth begins to slow. The dry Ponderosa forests of the Rockies, with their frequent low level fires, may be carbon neutral, while the mature rain forests of the Pacific Northwest continue to store considerable carbon. In general, forests sequester between 0.5 and 1.0 ton of carbon per acre per year. The alluvial forests of the Mississippi Valley are capable of storing 2 tons of carbon per acre per year—and so, at $20-$50 a ton, or $40-$100 an acre, are worth in carbon storage what they are as farmland. Tropical peat swamp forests in Indonesia sequester 200 tons of carbon per acre in their soils and standing biomass, an argument for paying Indonesian landowners to not cut them down. Destruction of tropical peat swamp forests—for instance, for palm oil plantations to produce green diesel fuel for Europe— takes a century or so to create a carbon benefit and currently produces more carbon dioxide than the burning of fossil fuels in China. Because of the clearing of its tropical forests, per capita emisssions of carbon dioxide in Indonesia are close to those in the West.
Evergreen forests release large amounts of hydrocarbons in the summer, as part of their cooling mechanism; these chemicals become part of global chemistry and in the presence of nitrogen oxides (products of combustion that are always present in the modern atmosphere) and sunlight, produce photochemical smogs. (So President Reagan’s comment that forests produce smog.) At least 120 chemical compounds are present in Sierra Nevada mountain air. These are insect deterrents and thermo-regulating chemicals. The monoterpenes, which prevent and cure cancer, are among the most abundant. Monoterpenes enter the bloodstream through the lungs and the limbic system through the olfactory nerves. So the healthy effect of a breath of mountain air has some basis in fact.
A forested landscape has a lower albedo (absorbs more of the sun’s heat) and so is warmer in winter; the sheltering trees also make the temperature of the ground much less variable than that of bare ground or grassland. In summer, a forested landscape tends to be cooler because of transpiration by the trees. (On Vancouver Island, in a relatively cool climate, cutting the forests has produced a permanent temperature increase of 1º-2º C.) Over large areas, the albedo of the ground affects temperature, precipitation, and the speed of jet stream winds. Because of their absorption of sunlight, evergreen forests in snowy regions probably have a net warming effect on the climate, despite their absorption of carbon dioxide from the atmosphere. Snow melts some weeks later in forests (especially evergreen forests) and so spring run-off is later; and slower. A later runoff makes (for instance) more water available over a longer period in California rivers. Fog-catching trees, like redwoods, increase streamflow (2 to 3 times more water reaches the ground under redwoods than not); fog-catching forests on the Canary Islands recharge the islands’ aquifers, which dry up when the forests are cut (and cannot regrow because the ground is too warm for condensation to occur); fog-catching shrubs on the Galapagos Islands drip moisture onto soils where it waters herbaceous plants and collects into pools, providing water for giant tortoises. In general, forests lower runoff by intercepting and evaporating 35-50% of the precipitation that falls on them. They thus reduce peak flows (floods) and, by storing more water in their soils and recharging aquifers, increase the low flows of summer. The water that flows from them is cooler. In humid climates such regulation of streamflow is generally desireable; in drier climates, forests, especially introduced forests (eucalyptus in California, saltcedar or Tamarix in the American Southwest, Mediterranean pines in the fynbos shrublands of South Africa) may reduce surface water flow considerably (to zero in small streams), with serious results.
Forests control stream temperatures. Summer water temperatures are 10 degrees lower in shaded reaches of streams. Streams that flow through old-growth forest accumulate fallen logs at a rate of about 1 every 10 feet. The trees help stabilize the streams, creating pools. Their wood is turned by detritus feeders into nutrients for freshwater organisms, which become food for fish; the nutrients are retained in the swirling pools. Salmon reproduce and survive much better in log choked old growth streams, with their shade, slower currents, more complex habitat of pools, more complete nutrient capture by stream organisms, than in the more or less channelized streams of commercial plantations. Undeveloped lakes in Minnesota have about 500 fallen logs per kilometer, or about 1 every 6 feet; while developed lakes have about half that, and near cabin sites have only 1 log every 50 or 60 feet. (People remove them and cut the forest, the source of new logs, along the shore.) In lakes, logs provide habitat and shelter for fish and detritus for invertebrates. The logs become part of the lake’s food chain. Log-free parts of lakes have fewer fish. (Bass, for instance are 5-60 times more abundant near brush shelters.) In rivers, grounded logs catch other snags, form jams, sometimes accumulate sediment and become islands, force the river about them and form side channels. The slowly flowing side channels become habitat for ducks and juvenile fish. Fallen logs along rivers also protect the shoreline, create pools, slow water flow, enlarge (with partial dams) the floodplain and thus the riverine habitat, and provide detritus-based nutrients. Sailing out to sea, rafts of logs, hung with barnacles and other creatures, increase the size of the ocean edge (several hundred thousand per year may have sailed out from pre-contact North America); and perhaps introduce alien organisms to new environments (a job done much more efficiently now by the ballast water in ships). For unknown reasons, floating logs in the ocean attract schools of fish. Floating man-made constructions with homing beacons are used as lures in some West African fisheries. In West Africa many logs from illegal cutting are lost in river drives and float out to sea, ending up on beaches in numbers that interfere with nesting sea turtles.
In aboriginal forests much of the forest was old growth, or so-called primary forest. How much was old growth varied with the type of forest and the site. The mixed deciduous and conifer forests of Maine are thought to have been about 30% old growth. Records from early surveys in Maine indicate that 2% of stands were recently burned, 14% were birch and aspen (short-lived, early successional trees), 25% were young forest (75 to 150 years old), 32% were mature forest (150 to 300 years old), and 27% were old growth (greater than 300 years old). So about 60% were what we would call old forest. Natural forests are subject to many types of disturbance, which range from the deaths and collapse of individual trees to hurricanes or tornadoes blowing down whole tracts of forest. The type of destruction varies with the location of the forest. Natural fires in the northern hardwood/hemlock forests of Maine occur every 800 to 1400 years, an interval much longer than the maximum ages of the trees (250-500 years). Icestorms in interior New England occur perhaps twice a decade and serious hurricanes once a century. Windthrow, along with ice storms, heavy early snows, pathogens and fire (spreading from the more fire-prone coastal and northern forests) likely kept Maine’s forests young. In the Midwest the interval between disturbances is also much greater than the lifetimes of the trees (800 years for straight line winds from thunderstorms, 1000 years or more for tornadoes). The natural fire interval is shorter than in the east (summers are hotter and drier) but about 85% of the forests of the Upper Midwest were mature and old growth. Catastrophic crown fires occur every 150-500 years years in mesic stands of Douglas fir on the western slopes of the Cascades in Washington. Less destructive ground fires are more common. The trees are somewhat fire-resistant and also have adaptations to fire. Once the lower branches of a Douglas fir become shaded and begin using more resources than they produce, they lose their needles, die, and fall off; in time this removes the fuel ladder that lets ground fires reach up into the crowns of the trees. Huge floods occur perhaps once a century on creek bottoms inhabited by coastal redwoods; some trees are felled by the floods. New shoots sprout from their trunks and broken-off stumps. Trees still standing send out adventitious roots into the deepened muck, and benefit from the new soil. (Fifteen such floods have raised the floodplain along Bull Creek, a tributary of the Eel River of northern California, by 30 feet over 1000 years.) Such adaptive behavior lets the trees live for two millennia and outcompete the Douglas firs and California bays on rich alluvial flats. Stand and soil-removing fires follow insect infestation every 50 to 200 years in boreal spruce-fir forests, resulting in complete stand replacement and temporary soil impoverishment (many nutrients are vaporized).
North America now lacks large tree-breaking animals like the elephants that renew acacia woodlands in Africa, but insects like spruce budworm kill stands of balsam or spruce, which may then be replaced by birch or aspen (which are periodically defoliated by tent caterpillars). Budworm outbreaks, like that from 1950-1954 in Atlantic Canada, kill whole forests, when then burn and regrow. During a budworm outbreak, budworm larvae increase from 1000 per acre to 8 million per acre, and the populations of wood warblers that eat budworms increase by 10 times or more; but not enough to contain the insects. (A virus or the death of the forest does that.) By allowing the (less dominant) aspen and birch to replace the (more) dominant spruce and fir, budworms renew old or stressed conifer forests. Conifer productivity on a site reaches its maximun extent at relatively low levels of nitrogen. Hard to break down, conifer litterfall ties up (the unneeded) nitrogen, while the nitrogen in the leaves and branches of the more demanding hardwoods is quickly recycled. So patches of aspen and birch among the conifers raise the productivity of the forest and the spread of the trees after a budworm outbreak (and fire) help renew the soil. (Nitrogen availablility under an intact stand of hemlocks — another conifer — is low, but equals that of a hardwood forest when small groups of sugar maple share the canopy with the hemlocks.) Some writers claim hardwood trees and shrubs have a keystone function in conifer forests. They provide habitat for butterflies and moths, which attract birds, which also eat caterpillars that eat conifer foliage; they provide habitat for parasitoids that help control conifer-eating insects; and their sprouting ability stabilizes soils after disturbances like treefall of fire. The spruce-fir forests of Atlantic Canada, where budworms and hardwoods have been controlled by spraying, and the proportion of spruce is falling thanks to heavy cutting (the forests are being turned into monocultures of faster-growing balsam fir) are becoming less productive.
Beaver dams in northeastern conifer swamps also kill conifers, which are replaced by damp-tolerant aspen and alder, whose litterfall enriches the forest edges. The trees themselves enrich the habitat, as well as provide food for beaver. The turnover of the plants and animals in the ponds (which also store soil and nutrients moving downstream) increases the nutrients available for the trees. Browsing by mammals also shapes forests; an increase in browsing by deer, elk, moose, snowshoe rabbits, meadow voles, by decreasing the survival of the more palatable species (oak, white pine, eastern hemlock, Canada yew, northern white cedar), will change the future composition of a forest, and reduce a mixed herbaceous understory to ferns and grass. Heavy browsing by elk in Yellowstone tends to eliminate streamside willows and reduce beaver wetlands on small and medium-size streams; the streams straighten out, become more erosive, cut more deeply into their beds, thus lowering water tables. Browsing by elk also prevents reproduction by aspen (another beaver food). The reintroduction of the wolf to Yellowstone let both types of tree come back, partly by reducing the elk herd (wolves seem to keep the herd 20-30% below what weather and vegetation would allow), but mostly by changing elk behavior: elk are frightened of spending too much time in dense cover where they might be ambushed by wolves. With the return of willow and aspen, beaver came back, trout became more abundant in the deeper, slower streams and a greater variety of songbirds bred in the streamside vegetation.
People influence forests. Throughout the temperate zone, people began to shape forests long before they had reached equilibrium with their post-glacial environments (3000 to 6000 years ago in much of North America). Anthropogenic fire, such as the cool ground fires set in early spring or fall by Native Americans in the oak and pine woods of southern New England, produced an open park-like wood of large nut-bearing trees, mixed with areas of younger vegetation, amidst much larger areas (such as white cedar swamps and spruce-fir forests) that were never (or rarely) burnt. Anthropogenic fire probably created the open oak and hickory forests of the Middle West. Without fire, they are now returning to the more shade-tolerant beech and maple. Primary forests have large trees, with a standing biomass 3 to 6 times that of second growth (and several times the board footage, which explains the size of the early cuts). The most productive old-growth forests in the eastern United States carried 125 to 250 tons of wood per acre. In old photographs the tall trunks of Middle Western oaks and sycamores dwarf the nineteenth-century biologists standing beside them. The large old trees in these forests produced enormous amounts of nuts and seeds, the so-called mast.
Once they reach a certain age all the trees in a forest produce mast. Most trees produce some seeds after a few decades, but become large producers as they mature in size and have spreading branches and root systems capable of supporting larger numbers of seeds. (The story is the same as with fish, where large females produce many times the eggs of smaller animals.) Mast production is related to crown development, so burning, by thinning the forest, increases mast production; the more rapid turnover of nutrients in a burned forest may also help produce more seeds. In the cool Northeast, a red oak begins producing acorns at 25-50 years, and then continues production (which would reach a peak at perhaps 150 years) for 100-300 years. White oaks and sugar maples, longer-lived trees, produce large crops of mast for longer periods. The smaller seeds of ash, maple, elm, those of the evergreens, are food for birds and rodents. The several varieties of red crossbills, a finch of the boreal forests, specialize in the seeds of specific species of evergreens, to which the shapes of their beaks and tongues (the seed-extracting devices) are adapted. Seed production by conifers and birches (an alternate food) tends to be synchronous over a large area, but irregular, so the birds move long distances (hundreds to thousands of miles) over the boreal forest in their search for food, and adjust their breeding schedules to the supply of seeds. With sufficient food, they will breed in mid-winter, with temperatures -30° F. or below. Thus the populations of many northern seedeaters (crossbills, redpolls, pine siskins, pine and evening grosbeaks) are not regional but continental. The rodents that eat the tree seeds support populations of predatory birds and animals (weasels, minks, martens, owls), and recycle (like the birds) most of the nutrients in the seeds back to the trees through their droppings. The larger tree seeds (beechnuts, acorns, hickory nuts, pecans, formerly chestnuts) are eaten by both the rodents and the larger animals (deer, elk, turkeys, bear, probably buffalo). Such animals and the nuts themselves were once eaten by people; aboriginal people also ate the small rodents (mice, squirrels), which are extremely abundant in mast-producing forests. (About 222,000 mice and other small rodents live in a typical 10 square miles of eastern forest, which explains the presence of mouse skeletons in human coproliths.) Recently 3-5 billion passenger pigeons supported themselves on the mast of the Eastern forests (squirrels may have exceeded that number), nesting where the acorn crop from the last year remained on the ground in the spring. Their habit of migrating over wide fronts in parallel flocks has been interpreted as an adaptation to locating areas of sufficient food to nest. (As part of their scheme to keep populations of seed-eaters low, so some nuts will survive to sprout, most nut trees bear only every second or third year.) Much of the forestland that supported those birds has been converted to cornfields; corn, cattle and pigs have replaced the passenger pigeons and beechnuts. (Over time, in settled countries, the best forestland always becomes agricultural land. So wildlife abundance inevitably falls.)
Trees reach economic maturity long before they reach biological maturity and so, under modern economic management, are cut down soon after they become large producers of mast. This changes the nutritional relationship of the forest with its inhabitants, reducing the numbers of seed-eating animals and their fur-bearing predators, while increasing the numbers of animals that eat browse. (White-tailed deer, cottontail rabbits and grouse do well; turkeys, squirrels and bear are probably reduced. Many animals, including deer, turkeys and bear, eat both browse and mast). It eliminates the tall, old trees raptors use for nest sites, from whose dead lower limbs flycatchers hunt, and the old rotten trees in which woodpeckers and chickadees excavate nest-holes, and in whose large hollows bears and raccoons den. Economic maturity is determined by a change in the rate of increase in the mass of the tree. As trees approach their final heights, the yearly increase in new wood fiber slows. In long-lived woody plants, maintenance respiration increases with age; so there is a necessary reduction in net annual production of fiber, that is, of growth. Risk of loss of the tree from windthrow or disease also rises with age; so the trees are cut. Douglas firs, trees that reach ages of 500-700 years, that stand a century or two as dead snags, and whose fallen logs take up to 300 years to rot, and so whose individual influence on the forest spans a millennium, are cut down soon after they reach the majority of their height growth at 80 years. Redwoods that once grew for 2 millennia or more are also cut at 80 years. Old Douglas firs support a community based on arboreal lichens, whose mass can be 4 times that of the foliage. The tops of old-growth redwoods support another forest 150 feet up. Protruding redwood tops break off in storms and the upper branches bend up, turning the top into a small forest of two-foot thick vertical branches, dead stubs, soil (which collects in cavities left by broken-off stubs and in hollows in the branches), with banks of fern, blueberries, seedlings of Douglas fir and Sitka spruce, and nesting seabirds. (Part of the temperate rainforests that occupy west-facing coasts worldwide, most redwoods are found within 10 miles of the sea. They grow where their limbs and needles can comb water from coastal fogs—12 inches during the usual summer dry season—and out of the reach of salt spray. Marbled murrelets nest in their crown forests, ancient murrelets among their roots, the former now in steep decline as their nesting habitat has shrunk from 2 million to a few thousand acres.) Southern pines, grown mostly for paper pulp, are cut at much shorter rotations, 25-35 years (younger trees make better pulp). Like browsing, cutting changes the composition of the forest. The cutting rotation in the Northeast is now too short for hemlock, a tree that can live 600-900 years and is probably worth cutting at 150 years. (The crown forests of old hemlocks show some of the characteristics of old redwoods.) Frequent cutting in the Maine woods has favored balsam over red spruce (another slow-growing tree). In 1902 the volume of spruce was 7 times that of fir; today the two are virtually equal in volume. Frequent cutting in the forests of northern Pennsylvania favors trees that sprout (cherry, oak, maple) over softwoods like white pine and hemlock. Early logging probably favored American chestnut, which rose from 4-15% of forest volume in early surveys of New Jersey and Connecticut to 60% (becoming the most abundant tree species) in 1900. While oaks and hickories produced hundreds of pounds of nuts per acre, chestnuts produced thousands.
Cutting can also mimic natural process. In Sweden white spruce usually reproduces itself through small gaps, such as the death of a large tree. Such forests can be reproduced by selective cutting that leaves most of the forest intact and also leaves existing snags and fallen trees (until recently the United States Forest Service required their removal on logging sites) and some old trees. One would also leave most of the deciduous trees, which have important functions in conifer-dominated woodlands. Spruce-fir stands in boreal North America are often fire-adapted communities, reproduced by stand-replacing fires. Such communities can be maintained by a modified clearcutting, leaving wide bands of trees along watercourses, with large, scattered clumps of trees about old trees left in the cut as nesting sites, sources of seed and future snags. Tops and slash are left on the ground. Spruce and fir are usually used for pulp in the Northeast and so are cut as soon as they are large enough to make cutting economic (this size goes down as logging becomes more mechanized). Red spruce makes valuable lumber (it is used for pianos); it is a slow-growing tree and leaving clumps of red spruce among the balsam to mature increases the variety and value of the forest. Letting some aspen and birch mature (birch for sawlogs, aspen for pulp) increases the forest’s productivity and makes it more friendly to game animals. To minimize blowdown and drying of the forest, such clear-cut strips are usually limited to a width 1.5 times the height of the trees (or 100-150 feet). Such cuts attempt to mimic the effects of catastrophic disturbance in primary forests and leave the landscape conducive to the movement of seeds and animals. In the East, such cuts are not burned (similar, lodgepole pine cuts in the West probably benefit from being burned). Leaving merchantable trees in the woods increases the future health and productivity of the forest. It reduces the volume of wood harvested, and thus current profits to the landowner. In the future, losses in volume will be compensated by the more valuable logs from old trees.
As forests mature, they accumulate dying and fallen trees. Fallen trees cover up to 20% of the forest floor in mature Douglas fir woodlands in California. A recent checklist for old-growth forests in the East included 3-4 logs greater than 16 inches in diameter, per acre, on the forest floor: a much smaller number. Hollow trees become den or nesting trees for various animals and birds; large hollow trees are used by bats and chimney swifts as well as hibernating bears: Audubon counted 9000 chimney swifts leaving one hollow sycamore. (Bats now make use of attics and mines, chimney swifts use chimneys, both birds having become in the Northeast—like the nighthawks which nest on the flat roofs of commercial buildings, and whose notes drop from the skies of suburban evenings—animals of settled landscapes.) Downed trees create new habitat on the forest floor for invertebrates, rodents, birds and amphibians. Soil accumulating on the upslope side of a log provides habitat for burrowing insects and small mammals, while the downslope side provides shelter and nesting sites. An acre of Maine woodland has more biomass of salamanders than of moose: a fact only briefly surprising. Rotting logs have a greater mass of living tissue (in their plants and decomposers) than growing ones. Nitrogen-fixing bacteria living in the guts of Pacific dampwood termites fix nitrogen for the termites. The nitrogen ends up in the nutrient-poor ecosystem of the rotting log and fertilizes tree seedlings growing on it. The invertebrates of the logs and the forest floor (earthworms, centipedes, millipedes, spiders, beetles, mites, springtails, psocids, nematodes) are eaten by small mammals, birds and amphibians (shrews, toads, frogs, thrushes, salamanders; also by the less abundant snakes and turtles); the amphibians, reptiles, birds and mammals form one basis of the forest’s food chain. The fallen logs also act as dams to keep forest soil from moving during rains and thaws. The old trees of a primary forest create a moister, shadier environment. Their large limbs are habitat for lichens that synthesize their nutrients (including nitrogen-rich proteins) from the air. These nutrients enter the forest ecosystem through leaching and litterfall, and through the dung of the squirrels and rodents (often different species than the mast-eaters) that eat them. It is said that young Douglas firs first grow on the nitrogen banked in the soil by the nitrogen-fixing shrubs that follow forest fires, then (as adults) on the nitrogen synthesized by their lichens. A major food of the rodents of old growth woods are the fruiting bodies of the mycorrhizal fungi that are allied with the roots of the trees. The fungal spores pass through the rodents’ digestive systems unharmed and are deposited on the forest floor and in their tunnels and burrows, generating more fungi. These rodents are part of a new food chain of the primary forest that ends in predators of the deep woods, such as pine martens and spotted owls. The water that flows out of such woodlands, thanks to the shade and the lack of sediment, is cold and clear (sometimes tinged brown with tannins), nutrient poor, habitat for salmon and trout. Tree roots stabilize the streams; and the trees themselves, falling across the brooks and larger creeks, also stabilize them, creating pools. Salmon, running upstream, like the seabirds that nest among the trees, contribute nutrients from the sea.
That only a third of the mixed Maine woodland was in primary forest implies a fairly high level of natural disturbance. In much of the Appalachians and Midwest the disturbance regime was several times the lifetime of the trees (even that of the white pines, which live 500 years). The result was old forests with complex mixes of trees of different shade tolerances and ages. In natural forests non-catastrophic replacement is usually in patches. One or a group of trees that rise slightly above the canopy are blown down, or a tree collapses from old age and takes some others with it, and the shade tolerant saplings that have been growing in the understory shoot up. If light is sufficient, the seeds of the shade-intolerant species that have been waiting in the soil sprout and grow. (Yellow birch and white ash will grow in the gap left by a single tree, while red oak, black cherry, sweet birch and tulip tree need larger gaps.) Hurricanes, tornadoes and fires clear larger areas. What develops on a site after a catastrophic disturbance depends on what trees are left alive (the so-called seed trees), the presence of trees that sprout from roots (many deciduous trees and shrubs), the seeds in the soil-bank, and what is brought to the site by birds, mammals and the wind. So the forest one sees on a site depends on the site’s history, its surroundings (another history), and chance. In much of the conifer and mixed hardwood forest of the Boundary Waters Canoe Area, the original fire rotation time was thought to be 50-100 years. Such short rotations favor fire-adapted trees: those that sprout from roots, such as quaking aspen; or that have well-dispersed seeds, such as paper birch; those with serotinous cones carried high in the canopy, such as jack pine or black spruce; or trees whose thick bark lets them tolerate fires, such as red pine, which become fire-resistant after 50 years. Short fire rotations must be fairly ancient in the general area since the Kirkland’s warbler is adapted to breeding in fire-succeeded stands of jack pine; it will breed nowhere else and abandons older jack pine stands. If a new stand escapes fire for 40 years or more, jack pine and aspen slowly succeed to more fire resistant, very mixed stands of black spruce, balsam fir, paper birch and white cedar. Red pines, which are capable of masssive recruitment after a fire slowly die out in very old stands (very old: red pines are still present after 300 years). In this case pines will no longer reproduce if disturbance is limited to windthrow and spruce budworm; they need fire. The spread of hemlock into a stand lengthens the fire frequency indefinitely (they draw up groundwater to the surface and moisten the soil), and if a stand escapes fire for a very long time, a forest dominated by hemlock and the shade tolerant sugar maple may develop. By lengthening the fire frequency, the hemlock makes possible the success of the fire-susceptible maple. Both hemlock and sugar maple produce a forest floor unfavorable to the establishment of other species, so this forest is somewhat self-maintaining (but in fact no more of a “climax” than the more mixed forests it replaced: felled by a windstorm, it will be replaced by aspen, spruce, and birch).
Primary forest in the eastern United States is characterized by fairly large trees (16-20 inches or more in diameter according to a recent checklist; but certainly many first-growth trees were larger). Other characteristics include a relatively small percent of intolerant (pioneer) tree species in the canopy; a full compliment of spring ephemerals suitable to the site (flowers that bloom and set seed before the tree leaves come out; these plants are not too much bothered by occasional logging, but frequent logging, clear-cutting or grazing will reduce them; since they are pollinated and their seeds distributed by ants, they spread slowly and can take centuries to recolonize a site); by a full compliment of bryophytes (mosses, liverworts, lichens: plants of damp and shaded woods), including those characteristic of old growth; by large old logs on the forest floor (microhabitat for many birds, mammals, reptiles, invertebrates, decomposers, mosses, fungi, tree seedlings; forests in northern regions probably need 12 tons of coarse woody debris per acre to maintain site quality); and by large, standing snags. Many of the large trees of a primary forest are rotten. (A complaint of woodcutters in early Maine, who would chop a hole 3 feet into an old pine, 50 feet above the ground, to check its condition before felling it. The wood of such large old pines, so-called pumpkin pine, was valuable for being soft and easily worked.) Many species of birds and mammals in the eastern forests require standing dead trees for perching, foraging, nesting, roosting, and denning. The ivory-billed woodpecker is said to have specialized in debarking large, dead trees to eat the insects beneath the bark. The demise of such trees as southern bottomland forests were logged and converted to agriculture was a major factor in its extinction. (Audubon shows a family of ivorybills collecting beetles from under the bark of a small dead stub.) Many writers would claim that old growth or primary forest is not absolutely necessary in a functioning natural landscape, even along streams, but no one can be sure of this. Some of the forest’s inhabitants (those microbes, fungi, invertebrates) will go extinct without it and the landscape in a larger sense will be reduced. Other writers argue that tracts of old growth must be very large to function truly as primary forest. The woodland must contain the large carnivores (grizzly bears, wolves, mountain lions) whose presence indicates an intact food web. Such tracts require 250,000-300,000 acres of contiguous woodland, with connections to other such areas.
Logged forests are not natural forests. Economic considerations will never allow them to move far into the realm of old growth. Their soils may or may not achieve a net accumulation of carbon. Logging disturbs the soil and exposes it to sun and rain; increased microbial action in the warmed soil releases carbon and other nutrients. The decay of logging debris releases carbon. It takes 10 to 20 years for a logged second-growth forest to begin a net accumulation of carbon, 45 years for regrowth to compensate for the carbon released by the decay of debis left from cutting an old-growth forest. And the carbon in the logs removed returns to the atmosphere quite rapidly. A third to a half of the logs end up as waste (sawdust, planer mill shavings, cut ends of boards), which is burned or decays. The rest of the carbon in the logs returns to the atmosphere after a short detour through the man-made world (for much of the material, made into paper or pallets, less than 10 years; that made into furniture or buildings lasts somewhat longer — less than 50 years on average). But it should be possible to mimic somewhat the process of natural forest succession through logging: to provide a natural variety of habitats (if not in the same proportions as in the aboriginal forest); to leave some old trees and downed logs; to conserve forest soils; and to protect forest streams from too much sun and from the constant pulses of silt and nutrients that logging produces. All this of course will cost the landowners and loggers money, at least at first.
Cutting, like fire, always sets the forest on a new trajectory. In the humid forests of the Northeast and Middle West, selective cutting favors the shade-tolerant beech and sugar maple; clear-cutting the warmth-loving pines and oaks, and other pioneer species like aspen, pin cherry and paper birch. Clear-cutting in dry western forests can eliminate the mycorrhizal fungi on which the trees depend and make reforestation of west-facing slopes difficult. (Adapted to living with certain species of trees, the fungi must find a new host in two years or die.) Clear-cuts, and heavy selective cuts, create more or less even-aged stands, with more pioneer and early successional species, while light selective cutting creates forests of more shade-tolerant species. The early successional forests created by heavy cutting (taking all merchantable trees when entering the woods) are supposed to provide a constant, sustainable yield of wood, at the maximum potential of a site. But, an artifact of cutting, these forests are quite unstable. They seek to produce only fiber. Natural stands in the same areas would be a mosaic of old growth, maturing trees, tangles of young growth, species with different tolerances to light, with a full assortment of the birds, mammals, invertebrates and fish characteristic of the area. The forest in a given place, with its vertebrate and invertebrate inhabitants, would depend on the sorts of disturbance to which the stand had been subject; that is, on the site’s particular history.
Logging influences what trees grow in a forest, and in general speeds up (may double) their rate of growth. Logging also has many negative effects on a forest. Soils are compacted and erode. Soil oxygen levels are lowered. The stems and roots of trees are often wounded. Root compaction and oxygen deprivation slow growth for some time after a cut. Heavy cuts move water and nutrients into streams. In areas where the natural water temperature in summer is near the upper limit of their requirements, clear-cutting may raise stream temperatures above what salmon and trout tolerate. So fish disappear. Cuts along streams remove the trees whose roots hold the bank together. With the additional water and soil moving into them, the streams widen, scour, straighten out and take some time (usually more than a decade) to return to a more stable condition; then the logging starts again. Heavy cutting on steep slopes in the Pacific Northwest makes the slopes liable to landslides following insignificant rains; slides begin three years after logging, when the roots that held the slope together have rotted. Cutting along streams removes the logs that would have become coarse woody debris in the water and on the forest floor. Such logs retard water flow, and help stabilize streams. Logging on the banks fills streams with tops and slash. The cumulative effect on streams can be catastrophic for fish, as is the case with many salmon and trout streams in coastal California, Oregon and Washington. Slope tremendously influences the erosive capacity of water, which increases by the fifth power of its velocity. As the speed of flowing water (down a skid trail, through a culvert) doubles, it is able to carry 32 times the sediment and move particles that are 64 times heavier. Much of the sediment in west coast streams comes from logging roads and skid trails. When these are treated properly (which includes closure to vehicles) after logging is over, the sediment loads decrease, the streams clear, and salmon and trout return to them. Hunters and drivers of recreational vehicles object to such closures, which makes the back country only accessible by horse or foot. (Included with the sediment are some of the hydraulic fluids from the logging eqipment, 70-80% of which escapes in leaks, spills and line and filter failure, and some of the chain oil and engine oil from the saws: arguments for using biodegradable oils.)
A forestry that tried to recreate the forest as an ecosystem would place old growth in the commercial forest along streams. Very lightly logged primary forest (a tree per acre every 5-10 years) would cover the banks of deeply incised streams, and cover the streambank out for 50 to 100 feet otherwise. (A tree per acre every 5-10 years is 4-8 trees per acre for entries at 40 year intervals; depending on the market, logs from such trees might be worth $1000 or more at the mill, or $300 in stumpage to the landowner.) Probably less than 20% of eastern forests have soils good enough to make the risk of growing trees greater than 100-150 years old worthwhile (sites in coves, valleys, the toe slopes of hills, in soils derived from nutrient-rich bedrock: most of the best forest soils in the East are now in agriculture); so one puts old growth where, whether a good commercial risk or not, it will do the most biological good. Then fingers of old growth penetrate the logged woods: primary forests are multi-story forests in the Northeast and upper Middle West, where most trees top out at 80-100 feet, and large white pines penetrate the canopy to reach 150 feet or more. These fingers of old growth will not function well if they back entirely upon clearcuts (winds will blow the trees over, too much sun dry the forest floor). So the forest that abuts the old growth is a mix. If we follow the Maine example, one third would be in early old growth (cut at 125-175 years; perhaps let mature further in better sites); poorer sites would be cut at 80-100 years. The value of the water running off the land and the land’s value as a carbon store will affect cutting choices. Two-thirds of the forest would be maturing and young forest. If the water that runs off the forest is worth $30 an acre, when close to the presettlement original amount and condition, forest management that keeps the water in that condition should be worth that. Carbon storage in trees and soils depends on the site, the forest and its age; if it amounts to half a ton per acre per year and stored carbon is worth $50 a ton (probably a high figure), then carbon storage is worth $25 an acre. Over a 150 year rotation, $55 an acre a year ($8250 dollars) is likely comparable to the stumpage value of the timber.
Logging is always somewhat destructive to a forest. By opening the canopy, logging increases light, temperature and wind speed; it lowers relative humidity; disturbs and compacts soils (especially the top few inches where most of the tree roots grow; this is why the worst time to log is spring, the best time in winter on frozen ground). Logging damages nearby trees and causes wounds in roots and stems that leave trees susceptible to decay or disease. After logging, erosion increases in the forest as a whole and especially on the 5-10% of it that is in roads, skid trails and landings. Something like 65% of the lubricants and coolants used in logging machinery end up on the forest floor. But logging also speeds up natural processes, raising the 2% return in growth on unlogged stands to perhaps 4%. Young stands of northern hardwoods will naturally thin themselves from 1000 trees per acre at four inches diameter at breast height to 40-60 trees per acre at 20 inches diameter. (Since a site can support only so much basal area of tree per acre, as the individual trees get thicker, there must be fewer of them.) This process takes 200 years in nature, but half that if the stand is thinned periodically. Another way to put it is that for the trees in a fully stocked stand to gain an inch in diameter, 20% of them must die. So this is the rationale for periodic logging in ecologically managed forests. Thinning of long-rotation hardwoods in the Northeast usually starts at 30-40 years when they have reached (coincidentally) 30-40% of their mature height. Letting them remain crowded up to then forces the trees to grow taller. (Deciduous trees grow upward in response to light and will adopt a rounder, shorter habit if not forced upward by competition; conifers grow from an apical bud that responds to gravity and so continue upward no matter what the competitive situation.) Thinning lets the crowns develop (the crown should occupy 35% of the height of the tree) and the boles increase in diameter faster. Trees 8 inches in diameter are usually thinned to 200 to the acre. Thinning then continues at 10-40 year intervals, depending on how the site is being managed. In general the longer intervals, which involve fewer entries of heavy machinery into the woods, are better for the forest. Most commercial forestland in the East is young, and logging to re-create a mixed, old-growth forest would have to focus on the trees to be left rather than on the trees removed (the usual focus of loggers). The larger trees in a stand may be the same age as the smaller ones but more vigorous. So one leaves those, whatever their place in the succession. Early and mid-successional species that have been overtopped and suppressed are removed. In general, one leaves vigorous, late successional species with good form and no wounds, that are capable of reaching the overstory. The trees that grow earlier in a succession, such as white birch and red maple and the shrubs, put their growth into stems, flowers and fruits rather than roots; their purpose is to reproduce before they are shaded out. A heavy fruiting may kill them. More long-lived species, such as sugar maples and oaks, put their energy into roots, stems, branches and leaves, and fruit later and at longer intervals. Logging aims at an uneven-aged forest. Several old trees are left per acre, no matter what their status or form: they will become snags, hollow trees, and finally coarse woody debris on the forest floor. Creating such forests takes time, in most cases a century before they become capable of producing a steady flow of timber. In an ideal world, returns from the value of the water flowing off the land and from carbon storage would provide additional income over this time. Logging of old growth in a given woodland would not happen all at one time, since one aims to provide roughly the same proportions of each habitat over time: this lets the various inhabitants of the forest (as well as the loggers and lumber mills) survive.
In an ideal eastern forest, one would cut only those trees unlikely to survive until the next cutting cycle (a variation on John Muir’s sawmill for dead trees). This will result in a forest of shade-tolerant trees: a “climax forest.” Cutting mature trees is likely to damage the surrounding ones however. An alternative is cutting the forest in little clear-cuts, 0.25 acre to 2 acres in size (2 acres is large), somewhat linearly, along the slope. This allows for reproduction of more warmth-loving and intolerant species (oaks, birches, pines). It tends to reproduce the existing forest. About 15% of the forest is left standing in the cut: some green trees for shade and seed, some large trees to become overstory trees, some to become snags and logs on the forest floor. Tops less than 6 inches in diameter and branches are left in the woods. The microhabitat the standing trees and downed logs provides reduces erosion and loss of soil nutrients, the partly shaded habitat is also more friendly for soil microbes and invertebrates, mycorrhizal fungi, small vertebrates and amphibians. The slash helps prevent browsing of saplings by deer. A different mix of trees will grow into the architecture of the remaining forest than into a clearcut. (In former Forest Service guidelines for western forests, stumps were removed and the slash piled and burned, in preparation for replanting ranks of fir or spruce. Except where it is very dry, most forests will reseed naturally, but not to the monocultures of plantations.). As the young trees grow, they are thinned. Timely thinning speeds tree growth but also removes carbonaceous material and nutrients that would add to forest soils (leaving tops and branches from the thinned material helps). The point of thinning in the developing forest should be to create a mixed stand of trees (mixed in age and species), not to harvest the largest and most valuable timber (generally the goal in commercial thinning). The first thinning is done when the trees reach 8 to 12 inches in diameter. This thinning produces poles, sawlogs and firewood. Trees too small to use are left in the woods. One selects for trees suitable for the site and opens up the forest around the better formed, better adapted (to the site), more vigorous trees. Usually commercial selective cuts involve the removal of 50% or more of basal area and all large trees, but cuts in the ecological forest would remove considerably less than that, and leave a cross section of tree ages. Since selective cutting will tend to favor the more shade tolerant trees (such as hemlock and sugar maple in the East), one would also in good seed years cut some larger gaps to allow regeneration of less shade-tolerant species (yellow birch, oaks, pines). Cutting over the long term inevitably reduces the nutrient capacity of a site, but the term is long (probably longer than the climate that supports the forest) and restoration forestry can reduce this loss to near zero. Ecological forests are managed for their processes, but after a time also produce a steady flow of forest products (poles, sawtimber, veneer logs, fuelwood, chips, pulp). A point to be made is that in the modern world the healthiness of a forest may constitute its greatest value (its value as real estate).
There are many different types of forest in the United States. In the latter half of the nineteenth century, logging and fire converted much of the pinery of the upper Middle West into an aspen forest (aspens sprout vigorously from their roots); or in places where the topsoil was burned away by the fires, to shrublands of bird-planted pin cherry, blueberry, grasses, raspberry and shadbush. From 1875 to 1900, logging fires averaged 500,000 acres a year in Michigan and Wisconsin. Much of this area had little value for agriculture and ended up as national forest. (The pinery of the northern forest was originally several hundred billion board feet.) The aspen forest has been maintained as a monoculture by cutting on a short-term rotation (30 to 50 years) for paper pulp and for chips for composition board. Clearcutting the sites removes the conifers and other hardwoods in the stand, and regenerates the aspen from root sprouts. To recreate a more mixed forest, probably a more stable forest (and one with more commercial potential), loggers would remove the mature aspen but retain the conifers and the other hardwoods. Released from competition, these trees would shoot up. The aspen would regenerate, but less strongly, as they must compete with the residual trees. The result would be structural and habitat diversity. Future cuts would treat the forest as a developing old growth woodland, clear-cutting the aspen stands as they matured (their greatest value for grouse and deer tends to be when young), and the evergreens and hardwoods as they reached the first stages of old growth. Along watercourses trees would be let mature further. Some of the canopy would be left standing in the future clearcuts as a legacy of the stand architecture: seed trees, snags, hollow trees, some large old trees, some young and middle-aged trees (living trees might be left in clumps). The clear-cuts would be small and patchy. The alternating dominance of aspen and conifers would mimic the lifecycles imposed on the forest by tent caterpillar and spruce budworm, the insect pests of each species. It would also exploit the opposite effects of aspen and conifers on the nitrogen cycle. Much of the nitrogen that accumulates in conifer needle litter does not break down and is vaporized in stand-clearing fires — especially in boreal woodlands (no stand of black spruce hs been found that did not originate in a fire) — while nitrogen in aspen litterfall is exploited in the rich, easily decomposed leaf litter of the aspens.
Some eastern forests burn naturally. Many more were regularly burned by the Native Americans. Burning altered the forest cover along much of the East Coast, its effects extending up the major river valleys. In the Southeast, burning created the savannahs of long-leaf pine characteristic of the pre-contact coastal plain. (Perhaps 3% of this once enormous habitat remains.) In the Middle West late summer burning produced open forests of oaks and hickories and pushed the edge of the continental grasslands hundreds of miles east. The sunny dry forests of the mountain West naturally burned. Some were burned by Indians. At European contact, probably 20 million acres of the trans-Mississippi West burned every year, much of it grassland and scrub, but 6 million acres of it forest. Virtually all western forests arose out of fire: the cool coastal rainforests of Vancouver Island and British Columbia were perhaps an exception. The types of fires varied. Under natural conditions about 40% of western forests experience low-intensity fires every 1-30 years. These are so-called understory fires. Low intensity or understory fires create forests of large, well-spaced, sun-loving, fire-resistant trees, such as Ponderosa and Jeffrey pine and western larch in the Rockies; giant sequoia, redwood, and some types of oak forests further west. Ponderosa pine forms a relatively pure climax at middle elevations in the western United States. Ponderosa is moisture dependent and grows more thickly at higher elevations (more mixed with Douglas fir), more spaced out at lower and drier ones. The trees in historic old-growth middle elevation forests were 200-400 years old, with 30-40 trees to the acre (one tree per 200 square meters). Grasses and fire resistant herbs and shrubs formed an open understory, which was browsed by elk and deer. Frequent ground fires in such forests scorch the lower branches of the trees (which eventually die and fall off), kill saplings and large shrubs, and thin (often drastically) the pine seedlings and those of shade-tolerant trees, such as true fir and Douglas fir. They burn off the litter layer of undecomposed needles, fallen branches and the dead grasses on the forest floor. Thus they keep fuel loads low and, by pruning trees and killing seedlings, remove the fuel ladder that lets fires reach the crowns of the trees. They maintain the open forest. When such forests are logged, most of the old trees are removed. Fires are suppressed. Shade tolerant Douglas fir, true fir and lodgepole pine seed in and grow up into thick stands of young trees, among the remaining older trees. The tree density is 40 times that of historic old growth stands. Competion for moisture and nutrients in the thick forests stresses the older trees. Without fire to keep competion down, the old larch and Pondersosa pine decline in vigor. Diameter growth slows drastically after 30 years and foliage grows sparse after 80 years. The trees loose the ability to manufacture the resins necessary to combat bark beetle infection (the beetles are drowned in their tunnels by the sticky resins secreted by the tree) and are killed by the beetles or fire. In general, crowded stands are more susceptible to bark beetles, spruce budworm, dwarf mistletoe, root rot, and catastophic crown fires. Because of such poor management in western forests, stand replacing fires are twice as common as historically. In overgrown forests with a history of frequent fire, where fire has been suppressed, insects and fire take control. The resulting catastrophic fires will kill both old growth and young trees and endanger human settlements in the forest.
Ponderosa pines are adapted to light fires. They have deep roots, thick bark, open crowns, large fleshy buds, and long needles spread out to avoid rising heat (not the short densely spaced needles of black spruce that make the tree flare up like a torch). Severe fire in Ponderosa forests makes them hard to regenerate. Ponderosas have heavy seeds that fall within 150 feet of the tree, so unless planted by birds or squirrels, the trees take time to spread; the soil after a hot fire forms a water-repellant surface inimical to vegetation; and the rest of the forest vegetation, also not adapted to severe fires, recovers slowly. One way to regenerate a fire-resistant stand of old-growth Ponderosa pines is to log from below. One removes most of the small and medium sized trees and all the shade tolerant trees (such as Douglas fir, some of which may be large: removing these large trees helps pay for the treatment). All the large pines that are vigorous enough to survive are left. After logging, when conditions allow, the forest is burned, to reduce the fuel load and further thin the Ponderosa and fir seedlings. One wants a mix of different age classes of trees amidst an open understory that will allow periodic prescribed burning. This forest over several decades will become an open forest dominated by shade-intolerant Ponderosa pines, with some young growth and some trees of other species. Such forests are logged every 25-30 years to remove excess small, medium and large trees (those that wouldn’t survive to the next cutting cycle). Some dying old trees are left. The small openings created by each entry allow a new age class of pines to develop. The forests are burned every 10-35 years to keep fuel loads low, recycle nutrients, control Douglas fir and stimulate herb and shrub regeneration. In time, such forests will provide a constant flow of commercial timber: large sawlogs, smaller logs and poles for latilla and viga makers (the traditional southwestern ceiling beams and lattices); chip wood for boiler fuel. The constant flow of wood provides predictable amounts of material for sawmills, pulp mills, wafer board and plywood plants, post and pole plants. Restoring overgrown forests in 1% of Montana a year (not just Ponderosa forests, but all types of forests) would increase timber productivity by 50%. (In 2000, thanks to a century of poorly managed timber cutting, wood production in Montana was 15% of that in 1990.) Such restoration forestry costs about $200 an acre initially. With the second or third cut, the forest breaks even, and after 100 years should turn a profit, which continues indefinitely, and rises with good management. (Fighting crown fires is also expensive, up to $1700 an acre, with no profit in sight.) The United States spends over $2 billion a year fighting fires in the West. This is money that in many cases pays for a history of forest mis-management, a tax on short-term capitalist management and scientific ignorance. Without putting money into good management (an amount equal to that used to fight forest fires would restore 10 million acres a year), such costs will only rise. One tries to recreate the historical forest not only to recreate the past but because this forest is more sustainable, with a lower risk to its biota and a lower risk of catastrophic fire. It makes economic sense; as several writers have pointed out, a forest’s maintenance of ecological process constitutes its greatest value (human or otherwise), its ability to maintain a predictable flow of wood and support a rural population constitutes its greatest social value, while control of its fires raises the value of the land about it as real estate.
The cooler, moister, higher elevation forests of the West are subject to more intense fires (so-called intermediate intensity fires), every 30-100 years. In such forests good fire conditions exist for a short time: a few days or weeks each summer. The fires are intense enough to kill most fire-susceptible trees but the mountainous areas burn unevenly, so much of a site (up to half) remains unburned. Such forests become very mixed in species and in tree ages. Here, logging followed by the suppression of fire leads to dense forests of shade tolerant trees which are susceptible to stand replacing fires. A more sustainable forestry in such overgrown stands, which, as they get older, are favored by spotted owls, martin and fisher, would remove the shade-tolerant trees in a patchy pattern, retain the sun-loving trees, and encourage (with a controlled burn) regeneration of fire-dependent herbs, trees, and shrubs. Such treatments would take place every 40-100 years. In the case of spotted owl habitat, a central (fire-unstable) old growth forest (say of firs) would be surrounded by more open forests of large trees (larch and pine), which would serve as firebreaks. Such firebreaks are usually a quarter of a mile wide. When fire destroys the central old growth, or after it is logged, parts of the firebreak are let develop into the thick, shade tolerant, old growth forest favored by owls. Surrounding undisturbed old growth forests with a matrix of semi-natural wooded habitat makes it easier for the animals of those forests move to other old growth areas.
Moist cold forests on the upper slopes of mountains (the last 20% of western forests) burn occasionally, at 100-400 year intervals, in stand replacing fires. In many ways, they resemble the boreal forests of Canada, altitude here compensating for latitude. Stand replacing fires occur when conditions are unusually dry and fuels are available, often during major droughts. Such forests include lodgepole pine; and the white-bark pine, whose plump seeds help support mountain populations of grizzly bears and which is replanted in areas cleared by wind and fire by Clark’s nutcrackers storing pine seeds for the winter. Such forests become mosaics of burned and unburned patches, of hundreds to thousands of acres. The trees are adapted to catastrophic fires. Lodgepole pine cones open in the heat of fire. Green cones in fire killed western larch and coastal Douglas fir drop viable seed. After a burn, elderberries, currants, gooseberries, bitterberries, ceanothus, wild geraniums and hollyhocks are planted in clearings by birds; aspen and fireweed seeds blow in; alders replenish the nitrogen in the soil. The forest is full of standing dead trees. Depending on the intensity of the fire, willow, aspen and mountain maple may sprout from rootstocks; and other plants grow from seeds in the soil seedbank. Clear-cutting such forests is not a replacement for fire. Clear-cutting leaves no standing dead trees to become breeding places for insects that attract birds; that release nutrients; and whose shade helps in regeneration of trees, herbs and shrubs. Fires affect soils differently from bulldozers and skidders. Fires leave irregular patches and strips of surviving trees and an ashy seedbed for the bird and wind planted seeds from outside the burn. Clearcut stands lack the diversity of fire cleared stands. A better way to log such stands is to remove two-thirds of the trees, leaving most of the overstory trees (such as Douglas fir and western larch) and the rest of the stand in irregular clusters. Burning the slash after logging kills most of the remaining trees and leaves snags and a suitable seedbed for regeneration of the conifers, herbs, shrubs and deciduous trees characteristic of recent burns.
The whitebark pine of the high slopes is suffering tremendous mortality from blister rust, an Asian fungus that took almost a century to reach whitebark stands from its initial foothold on the east coast (where it remains a problem in white pine), and may require intensive human intervention to reproduce the rust-resistant trees. The whitebark’s large, oil-rich seeds let grizzly bears gain enough weight to go into winter in good condition and keep the bears in autumn at high elevations out of the way of humans. The bears rob caches of cones hidden by squirrels, then crush the cones between their paws to get out the seeds. (Another late fall bear food is cutworms, whose moths are blown into the mountains from Kansas wheat fields, and whose larvae are found under mountain rocks.) A poor competitor with other trees, whitebark pines grow on the thin, stony soils and in the difficult climates of alpine elevations. They shade the snowpack and stabilize the rocky soils, protecting the quality of the snowmelt and rain that flows in brooks and streams down to the lowlands. Clark’s nutcrackers collect whitebark seeds and cache them several miles away in open areas for the winter. Those that are not retrieved (this number may fall as the pines grow more scarce, and feeding by nutcrackers become a problem for the pines) grow into new stands of trees.
Sustainability is a human concept that may or may not work in nature. Attempting permanance, it implies a constant flow of animals, crop plants or timber from a place. Sustainability in agriculture means maintaining agricultural soils and reducing erosion to the levels at which the soil is rebuilt (essentially zero); and making agriculture one part of the larger ecosystem. Sustainable forestry in the long run probably means maintaining all components of the ecosystem. Such components include disturbances, such as fires, large herbivores and their predators (moose and wolf), the small mammals, amphibians, arthropods and fungi of the forest floor, the soil microflora, the arboreal lichens and mosses of old forests. The purpose in retaining large canopy trees during initial logging operations, and lengthening the rotations, is to produce a forest with more large, old trees, a multi-storied canopy, a greater variation in tree size (these all lead to a more complex forest architecture), with large woody debris on the forest floor, tighter nutrient cycles, shaded refugia for mycorrhizal fungi and nitrogen-fixing bacteria. (One could argue that the fungi, with which many trees have obligate relations, by connecting trees of different ages and species, are a major factor in controlling what happens in the forest.) Such a forest provides for beneficial predator-prey relationships among forest vertebrates and habitat for plants and animals that require structural complexity and late seral conditions, as well as for the needs of those that inhabit young forest. Some birds in Pacific Northwest forests jump in density as the forest enters a state of old-growth, indicating a (non-linear) change in the quality of the habitat. (But bird variety in mature forests is often low.) In woodlands with a history of fire, maintaining open forests of old sun-loving trees, mixed with some shade-tolerant trees and with younger stands, minimizes the destructive potential of fires. (One can’t eliminate fire, only plan around it; the success of Smokey the Bear has caused our present dilemma.) Such forests also maintain the place of the forest globally, which a young forest, maintained on a short rotation, doesn’t: the forest as a store of carbon, as an inoculae for mycorrhizal fungi, lichens and forest bacteria, as a positive influence on the water that flows through them, and on the coastal estuaries that lie below.
Forests managed for their process as well as for timber will produce less total wood fiber. Parts of them should be left undisturbed and separate forestlands should be connected by corridors and buffer zones, that allow plants and animals to migrate. Leaving large trees standing and lengthening rotations to let the forest become old both reduce the amount of wood harvested per acre. The net return per acre however remains the same or rises, since larger logs from old trees have a much higher value. (About half the wood cut in the U.S. goes to paper, though sawtimber is worth 2-5 times as much, good sawtimber more than that.) So the contribution of the forest to the economy remains the same, or rises; but only after a period of forest recovery that would last for about a century. Such forests will require a new infrastructure to use their logs of different species and sizes (saplings, poles, sawlogs). Some thinning operations would be better done by hand, or with horses or light tractors, than by heavy machinery. Modern industrial forestry, faced with forests of declining value, uses harvesting machinery of immense power and mobility in order to make a profit harvesting wood of low quality and low quantity (per acre). The post-harvest machinery tends to homogenize the harvested logs into composite products (like oriented strand board, which has replaced plywood, which requires better logs, for many uses: in this case, resin replaces fiber). Such plants are now being constructed around the perimeter of the Cumberland Plateau in the southern Applalachians, in order to use the second growth hardwood forests of the plateau. The forests will be clearcut to feed the plants, at terrible cost to the biota and watercourses of the region. An alternative, regeneratively harvested forest would produce a mix of graded materials for plywood, oriented strand board, flooring, cabinetry, moldings, wall panelling, furniture, construction lumber, tool handles, fencing and so on. Such a forest would require a more far-sighted and curious forestry, some public funding, and patience.
One faces essentially the same question as in agriculture: whether to focus on the yield per acre per year, or on the forest as habitat and process, a landscape that also produces wood. As with food, one can ask how much wood do we need? Wooden pallets use 1.5 billion board feet of lumber a year in the United States (about 40% of the hardwood cut) and most of them are thrown away after a single use. Re-manufactured pallets could provide the lumber for 300,000 to 600,000 houses a year; or a considerable amount of hardwood flooring, material for composition board, and wood shavings for packing material. A tax on logs (making pallets more expensive) would encourage reuse. A rise in landfill fees would make reuse of lumber in demolished buildings profitable. (Construction debris constitutes 15-40% of landfill contents in developed countries; an increase in Danish landfill fees pushed reuse of construction materials from 12% to 82% over 10 years.) A better recycling effort would reduce the wood needed for paper and cardboard by up to 90%. (Paper can be recycled 9-10 times; 90% recovery probably isn’t possible but 75% probably is. Reducing wood use by recycling would also reduce our carbon footprint.) Alternative fiber crops such as kenaf (an African plant), hemp, hybrid poplar, native trees that sprout from stumps, grown and harvested as saplings by machinery, produce much more fiber per acre than natural forests (2-5 times more in mechanically coppiced forests), and are easier on the land than cotton or corn. Hemp, which can be made into paper or cloth, produces more fiber per acre at a much lower environmental cost than cotton. So does bamboo. In short, we don’t need much of the wood that modern forests produce; but under a capitalist regime land must produce value. Wood fiber (not whole ecosystems) is what forests produce, and it is presently economically advantageous to use the fiber and throw it away. Returning some of the value of regeneratively managed forests to the landowner (their value in slowing soil erosion, protecting streams, controlling water and nutrient runoff, filtering the air, storing carbon, their role in providing habitat for useful wildlife, in regulating local microclimate and rainfall) would help make managing forests for their processes profitable. Such value, in dollars per acre per year, may be worth more than the wood, but that value only becomes apparent when the forests are degraded or gone. (The monies could be raised through a tax on logs.) The appearance of regenerative forests also increases property values. Costa Rica pays its farmers to maintain and replant their forests for all these reasons. In a capitalist world my notions are likely forest dreams; enforceable on public land if the government and the people desire.
The usual fate of forestland in the modern world is to become building lots. Inland from the sea along the Gulf of Mexico in the southern United States were so-called wet pine savannahs. These were grassy meadows with scattered pines growing on waterlogged clay soils, amidst tupelo-cypress swamps. The wet savannahs formed a narrow band between the drier piney uplands and the brackish marshes of the Gulf. The savannahs and the uplands were partly maintained by fire. The savannah soils were naturally acid and nutrient-poor and filtered the water flowing into the coastal marshes. They were the preferred habitat of the Mississippi sandhill crane, now much reduced in numbers. These wetlands, like many southern coastal wetlands, were ditched and drained by timber companies after the Second World War to grow slash pine on short rotations for paper pulp. Fire on the plantations was supressed. Drainage removed the filtering effect of the savannahs, increasing the nutrient flow to coastal waters. After a few rotations, the timberland was sold off for building lots, as air conditioning made life in the Deep South more comfortable, and a rising standard of living made life there more available.
There are other stories. The Menominee Indian Reservation in northeastern Wisconsin includes 220,000 acres of forestland. The forest has been commercially harvested for 140 years, with approximately 2 billion feet of lumber removed from the forest over that time. The volume of standing timber now is greater than when the reservation was established in 1854. The Menominee management program predates current concepts of ecosystem management. The Menominee must log (to support the tribe) and try to manage the forest so as to maintain a more or less even flow of sawtimber and pulpwood. They try to maximize the quality as well as the quantity of sawtimber, with a sustained yield of material, and a diverse mix of native tree species. Harvests are based on excess stocking of overstocked stands. When the stocking rate becomes too great for the site, trees are cut. Trees are let grow as long as they remain healthy and vigorous. Thus the forest contains many large old trees of great value (habitat for the insects and lichens of old-growth forest, great producers of mast). The Menominee cut trees no faster than the forest can regrow, rather than in response to market conditions (say, a rise in the price of red oak logs). Loggers must attend a class in how to cut and skid timber and contracts are terminated if the cutting methods are not satisfactory. About 65% of the forest is managed as a mixed-age forest, with a 15 year cutting cycle. The remainder is managed as even-aged forest. To a casual observer the forest looks pristine. Partly because of the old trees, it contains a much more diverse mix of plants and animals than the surrounding commercial timberland. The Menominee forest has healthy streams. Whether such forests are net accumulators of carbon isn’t certain: the above-ground part of the forest has grown in mass and the soils have probably continued to increase their stored carbon, but 2 billion board feet of wood (about 170 million cubic feet or, counting waste, branches and tops, about double that in woody material) have been removed, and much of its carbon returned to the atmosphere.
In the Acadian Forest Region of the Canadian Maritimes (a division of the Northern Hardwood Region), some writers claim a well stocked 100 acre woodlot will provide full time employment for 4 people, if the logs are sawn into lumber and dried and sold from the lot. The sawdust and slabs, if not burned for heat, are used on the wood roads. (Using these materials on roads slows their conversion to carbon dioxide. Converting them to biochar in a small furnace at 180º C. with a citric acid catalyst makes a soil amendment—biochar charcoal—that greatly increases the productivity of agricultural soils and keeps the carbon out of the atmosphere for several thousand years.) Four employees may be an overestimate but is comparable to those employed in Swiss woodlands. Much depends on the productivity of the site and on the price of lumber. I would think one person per 100-200 acres is a more reasonable estimate for much of the Northern Hardwood Region. This however is much less than the acreage required to keep a modern woodcutter busy (800 acres per job in Canadian industrial forestry). Such woodlands, like the Menominee forest, are managed for their long-term productivity. Sawing the lumber on site lets work in the woods be done when conditions (weather, the state of the ground) are appropriate. Logging might only occupy three months a year. The rest of the year would be spent sawing lumber, working up firewood, thinning, working on roads, perhaps making maple syrup, or renting simple summer cabins. The investment per person in such enterprises is much lower than in modern wood production. Jobs per log or board foot are higher. (Not usually a good thing in the modern world, but it is costs per board foot that matter.) One theory of civilisations’ collapse proposes that as the complexity of a society rises, its costs per unit of investment also rise, and the marginal returns on investment decrease. That is, investment produces declining (or negative) returns. Finally, this decrease in returns (from private investment in manufacturing and agriculture, from public investment in education, a military establishment, public safety and public works) bankrupts the society, which can no longer meet its obligations. Improving the yield of woodland, or of the agricultural landscape, so as to provide a constant flow of high value material provides one way out this impasse.
Like fields, forests affect atmospheric chemistry, the chemistry and flow of local streams, local and global precipitation, climate. Root growth accounts for 50% of the net primary productivity in forests (the net yearly production), leaves for 25-35%, growth of wood the rest. About 20% of the mass of forest trees is roots, most in the top few inches of soil. The growth and death of roots delivers carbon to the soil, removing it from the atmosphere. Thus old-growth forests continue to store carbon, even after growth of their trunks has slowed. Storage varies with the type of forest. It falls precipitously in southern pine plantations after 25 years, when their growth begins to slow. The dry Ponderosa forests of the Rockies, with their frequent low level fires, may be carbon neutral, while the mature rain forests of the Pacific Northwest continue to store considerable carbon. In general, forests sequester between 0.5 and 1.0 ton of carbon per acre per year. The alluvial forests of the Mississippi Valley are capable of storing 2 tons of carbon per acre per year—and so, at $20-$50 a ton, or $40-$100 an acre, are worth in carbon storage what they are as farmland. Tropical peat swamp forests in Indonesia sequester 200 tons of carbon per acre in their soils and standing biomass, an argument for paying Indonesian landowners to not cut them down. Destruction of tropical peat swamp forests—for instance, for palm oil plantations to produce green diesel fuel for Europe— takes a century or so to create a carbon benefit and currently produces more carbon dioxide than the burning of fossil fuels in China. Because of the clearing of its tropical forests, per capita emisssions of carbon dioxide in Indonesia are close to those in the West.
Evergreen forests release large amounts of hydrocarbons in the summer, as part of their cooling mechanism; these chemicals become part of global chemistry and in the presence of nitrogen oxides (products of combustion that are always present in the modern atmosphere) and sunlight, produce photochemical smogs. (So President Reagan’s comment that forests produce smog.) At least 120 chemical compounds are present in Sierra Nevada mountain air. These are insect deterrents and thermo-regulating chemicals. The monoterpenes, which prevent and cure cancer, are among the most abundant. Monoterpenes enter the bloodstream through the lungs and the limbic system through the olfactory nerves. So the healthy effect of a breath of mountain air has some basis in fact.
A forested landscape has a lower albedo (absorbs more of the sun’s heat) and so is warmer in winter; the sheltering trees also make the temperature of the ground much less variable than that of bare ground or grassland. In summer, a forested landscape tends to be cooler because of transpiration by the trees. (On Vancouver Island, in a relatively cool climate, cutting the forests has produced a permanent temperature increase of 1º-2º C.) Over large areas, the albedo of the ground affects temperature, precipitation, and the speed of jet stream winds. Because of their absorption of sunlight, evergreen forests in snowy regions probably have a net warming effect on the climate, despite their absorption of carbon dioxide from the atmosphere. Snow melts some weeks later in forests (especially evergreen forests) and so spring run-off is later; and slower. A later runoff makes (for instance) more water available over a longer period in California rivers. Fog-catching trees, like redwoods, increase streamflow (2 to 3 times more water reaches the ground under redwoods than not); fog-catching forests on the Canary Islands recharge the islands’ aquifers, which dry up when the forests are cut (and cannot regrow because the ground is too warm for condensation to occur); fog-catching shrubs on the Galapagos Islands drip moisture onto soils where it waters herbaceous plants and collects into pools, providing water for giant tortoises. In general, forests lower runoff by intercepting and evaporating 35-50% of the precipitation that falls on them. They thus reduce peak flows (floods) and, by storing more water in their soils and recharging aquifers, increase the low flows of summer. The water that flows from them is cooler. In humid climates such regulation of streamflow is generally desireable; in drier climates, forests, especially introduced forests (eucalyptus in California, saltcedar or Tamarix in the American Southwest, Mediterranean pines in the fynbos shrublands of South Africa) may reduce surface water flow considerably (to zero in small streams), with serious results.
Forests control stream temperatures. Summer water temperatures are 10 degrees lower in shaded reaches of streams. Streams that flow through old-growth forest accumulate fallen logs at a rate of about 1 every 10 feet. The trees help stabilize the streams, creating pools. Their wood is turned by detritus feeders into nutrients for freshwater organisms, which become food for fish; the nutrients are retained in the swirling pools. Salmon reproduce and survive much better in log choked old growth streams, with their shade, slower currents, more complex habitat of pools, more complete nutrient capture by stream organisms, than in the more or less channelized streams of commercial plantations. Undeveloped lakes in Minnesota have about 500 fallen logs per kilometer, or about 1 every 6 feet; while developed lakes have about half that, and near cabin sites have only 1 log every 50 or 60 feet. (People remove them and cut the forest, the source of new logs, along the shore.) In lakes, logs provide habitat and shelter for fish and detritus for invertebrates. The logs become part of the lake’s food chain. Log-free parts of lakes have fewer fish. (Bass, for instance are 5-60 times more abundant near brush shelters.) In rivers, grounded logs catch other snags, form jams, sometimes accumulate sediment and become islands, force the river about them and form side channels. The slowly flowing side channels become habitat for ducks and juvenile fish. Fallen logs along rivers also protect the shoreline, create pools, slow water flow, enlarge (with partial dams) the floodplain and thus the riverine habitat, and provide detritus-based nutrients. Sailing out to sea, rafts of logs, hung with barnacles and other creatures, increase the size of the ocean edge (several hundred thousand per year may have sailed out from pre-contact North America); and perhaps introduce alien organisms to new environments (a job done much more efficiently now by the ballast water in ships). For unknown reasons, floating logs in the ocean attract schools of fish. Floating man-made constructions with homing beacons are used as lures in some West African fisheries. In West Africa many logs from illegal cutting are lost in river drives and float out to sea, ending up on beaches in numbers that interfere with nesting sea turtles.
In aboriginal forests much of the forest was old growth, or so-called primary forest. How much was old growth varied with the type of forest and the site. The mixed deciduous and conifer forests of Maine are thought to have been about 30% old growth. Records from early surveys in Maine indicate that 2% of stands were recently burned, 14% were birch and aspen (short-lived, early successional trees), 25% were young forest (75 to 150 years old), 32% were mature forest (150 to 300 years old), and 27% were old growth (greater than 300 years old). So about 60% were what we would call old forest. Natural forests are subject to many types of disturbance, which range from the deaths and collapse of individual trees to hurricanes or tornadoes blowing down whole tracts of forest. The type of destruction varies with the location of the forest. Natural fires in the northern hardwood/hemlock forests of Maine occur every 800 to 1400 years, an interval much longer than the maximum ages of the trees (250-500 years). Icestorms in interior New England occur perhaps twice a decade and serious hurricanes once a century. Windthrow, along with ice storms, heavy early snows, pathogens and fire (spreading from the more fire-prone coastal and northern forests) likely kept Maine’s forests young. In the Midwest the interval between disturbances is also much greater than the lifetimes of the trees (800 years for straight line winds from thunderstorms, 1000 years or more for tornadoes). The natural fire interval is shorter than in the east (summers are hotter and drier) but about 85% of the forests of the Upper Midwest were mature and old growth. Catastrophic crown fires occur every 150-500 years years in mesic stands of Douglas fir on the western slopes of the Cascades in Washington. Less destructive ground fires are more common. The trees are somewhat fire-resistant and also have adaptations to fire. Once the lower branches of a Douglas fir become shaded and begin using more resources than they produce, they lose their needles, die, and fall off; in time this removes the fuel ladder that lets ground fires reach up into the crowns of the trees. Huge floods occur perhaps once a century on creek bottoms inhabited by coastal redwoods; some trees are felled by the floods. New shoots sprout from their trunks and broken-off stumps. Trees still standing send out adventitious roots into the deepened muck, and benefit from the new soil. (Fifteen such floods have raised the floodplain along Bull Creek, a tributary of the Eel River of northern California, by 30 feet over 1000 years.) Such adaptive behavior lets the trees live for two millennia and outcompete the Douglas firs and California bays on rich alluvial flats. Stand and soil-removing fires follow insect infestation every 50 to 200 years in boreal spruce-fir forests, resulting in complete stand replacement and temporary soil impoverishment (many nutrients are vaporized).
North America now lacks large tree-breaking animals like the elephants that renew acacia woodlands in Africa, but insects like spruce budworm kill stands of balsam or spruce, which may then be replaced by birch or aspen (which are periodically defoliated by tent caterpillars). Budworm outbreaks, like that from 1950-1954 in Atlantic Canada, kill whole forests, when then burn and regrow. During a budworm outbreak, budworm larvae increase from 1000 per acre to 8 million per acre, and the populations of wood warblers that eat budworms increase by 10 times or more; but not enough to contain the insects. (A virus or the death of the forest does that.) By allowing the (less dominant) aspen and birch to replace the (more) dominant spruce and fir, budworms renew old or stressed conifer forests. Conifer productivity on a site reaches its maximun extent at relatively low levels of nitrogen. Hard to break down, conifer litterfall ties up (the unneeded) nitrogen, while the nitrogen in the leaves and branches of the more demanding hardwoods is quickly recycled. So patches of aspen and birch among the conifers raise the productivity of the forest and the spread of the trees after a budworm outbreak (and fire) help renew the soil. (Nitrogen availablility under an intact stand of hemlocks — another conifer — is low, but equals that of a hardwood forest when small groups of sugar maple share the canopy with the hemlocks.) Some writers claim hardwood trees and shrubs have a keystone function in conifer forests. They provide habitat for butterflies and moths, which attract birds, which also eat caterpillars that eat conifer foliage; they provide habitat for parasitoids that help control conifer-eating insects; and their sprouting ability stabilizes soils after disturbances like treefall of fire. The spruce-fir forests of Atlantic Canada, where budworms and hardwoods have been controlled by spraying, and the proportion of spruce is falling thanks to heavy cutting (the forests are being turned into monocultures of faster-growing balsam fir) are becoming less productive.
Beaver dams in northeastern conifer swamps also kill conifers, which are replaced by damp-tolerant aspen and alder, whose litterfall enriches the forest edges. The trees themselves enrich the habitat, as well as provide food for beaver. The turnover of the plants and animals in the ponds (which also store soil and nutrients moving downstream) increases the nutrients available for the trees. Browsing by mammals also shapes forests; an increase in browsing by deer, elk, moose, snowshoe rabbits, meadow voles, by decreasing the survival of the more palatable species (oak, white pine, eastern hemlock, Canada yew, northern white cedar), will change the future composition of a forest, and reduce a mixed herbaceous understory to ferns and grass. Heavy browsing by elk in Yellowstone tends to eliminate streamside willows and reduce beaver wetlands on small and medium-size streams; the streams straighten out, become more erosive, cut more deeply into their beds, thus lowering water tables. Browsing by elk also prevents reproduction by aspen (another beaver food). The reintroduction of the wolf to Yellowstone let both types of tree come back, partly by reducing the elk herd (wolves seem to keep the herd 20-30% below what weather and vegetation would allow), but mostly by changing elk behavior: elk are frightened of spending too much time in dense cover where they might be ambushed by wolves. With the return of willow and aspen, beaver came back, trout became more abundant in the deeper, slower streams and a greater variety of songbirds bred in the streamside vegetation.
People influence forests. Throughout the temperate zone, people began to shape forests long before they had reached equilibrium with their post-glacial environments (3000 to 6000 years ago in much of North America). Anthropogenic fire, such as the cool ground fires set in early spring or fall by Native Americans in the oak and pine woods of southern New England, produced an open park-like wood of large nut-bearing trees, mixed with areas of younger vegetation, amidst much larger areas (such as white cedar swamps and spruce-fir forests) that were never (or rarely) burnt. Anthropogenic fire probably created the open oak and hickory forests of the Middle West. Without fire, they are now returning to the more shade-tolerant beech and maple. Primary forests have large trees, with a standing biomass 3 to 6 times that of second growth (and several times the board footage, which explains the size of the early cuts). The most productive old-growth forests in the eastern United States carried 125 to 250 tons of wood per acre. In old photographs the tall trunks of Middle Western oaks and sycamores dwarf the nineteenth-century biologists standing beside them. The large old trees in these forests produced enormous amounts of nuts and seeds, the so-called mast.
Once they reach a certain age all the trees in a forest produce mast. Most trees produce some seeds after a few decades, but become large producers as they mature in size and have spreading branches and root systems capable of supporting larger numbers of seeds. (The story is the same as with fish, where large females produce many times the eggs of smaller animals.) Mast production is related to crown development, so burning, by thinning the forest, increases mast production; the more rapid turnover of nutrients in a burned forest may also help produce more seeds. In the cool Northeast, a red oak begins producing acorns at 25-50 years, and then continues production (which would reach a peak at perhaps 150 years) for 100-300 years. White oaks and sugar maples, longer-lived trees, produce large crops of mast for longer periods. The smaller seeds of ash, maple, elm, those of the evergreens, are food for birds and rodents. The several varieties of red crossbills, a finch of the boreal forests, specialize in the seeds of specific species of evergreens, to which the shapes of their beaks and tongues (the seed-extracting devices) are adapted. Seed production by conifers and birches (an alternate food) tends to be synchronous over a large area, but irregular, so the birds move long distances (hundreds to thousands of miles) over the boreal forest in their search for food, and adjust their breeding schedules to the supply of seeds. With sufficient food, they will breed in mid-winter, with temperatures -30° F. or below. Thus the populations of many northern seedeaters (crossbills, redpolls, pine siskins, pine and evening grosbeaks) are not regional but continental. The rodents that eat the tree seeds support populations of predatory birds and animals (weasels, minks, martens, owls), and recycle (like the birds) most of the nutrients in the seeds back to the trees through their droppings. The larger tree seeds (beechnuts, acorns, hickory nuts, pecans, formerly chestnuts) are eaten by both the rodents and the larger animals (deer, elk, turkeys, bear, probably buffalo). Such animals and the nuts themselves were once eaten by people; aboriginal people also ate the small rodents (mice, squirrels), which are extremely abundant in mast-producing forests. (About 222,000 mice and other small rodents live in a typical 10 square miles of eastern forest, which explains the presence of mouse skeletons in human coproliths.) Recently 3-5 billion passenger pigeons supported themselves on the mast of the Eastern forests (squirrels may have exceeded that number), nesting where the acorn crop from the last year remained on the ground in the spring. Their habit of migrating over wide fronts in parallel flocks has been interpreted as an adaptation to locating areas of sufficient food to nest. (As part of their scheme to keep populations of seed-eaters low, so some nuts will survive to sprout, most nut trees bear only every second or third year.) Much of the forestland that supported those birds has been converted to cornfields; corn, cattle and pigs have replaced the passenger pigeons and beechnuts. (Over time, in settled countries, the best forestland always becomes agricultural land. So wildlife abundance inevitably falls.)
Trees reach economic maturity long before they reach biological maturity and so, under modern economic management, are cut down soon after they become large producers of mast. This changes the nutritional relationship of the forest with its inhabitants, reducing the numbers of seed-eating animals and their fur-bearing predators, while increasing the numbers of animals that eat browse. (White-tailed deer, cottontail rabbits and grouse do well; turkeys, squirrels and bear are probably reduced. Many animals, including deer, turkeys and bear, eat both browse and mast). It eliminates the tall, old trees raptors use for nest sites, from whose dead lower limbs flycatchers hunt, and the old rotten trees in which woodpeckers and chickadees excavate nest-holes, and in whose large hollows bears and raccoons den. Economic maturity is determined by a change in the rate of increase in the mass of the tree. As trees approach their final heights, the yearly increase in new wood fiber slows. In long-lived woody plants, maintenance respiration increases with age; so there is a necessary reduction in net annual production of fiber, that is, of growth. Risk of loss of the tree from windthrow or disease also rises with age; so the trees are cut. Douglas firs, trees that reach ages of 500-700 years, that stand a century or two as dead snags, and whose fallen logs take up to 300 years to rot, and so whose individual influence on the forest spans a millennium, are cut down soon after they reach the majority of their height growth at 80 years. Redwoods that once grew for 2 millennia or more are also cut at 80 years. Old Douglas firs support a community based on arboreal lichens, whose mass can be 4 times that of the foliage. The tops of old-growth redwoods support another forest 150 feet up. Protruding redwood tops break off in storms and the upper branches bend up, turning the top into a small forest of two-foot thick vertical branches, dead stubs, soil (which collects in cavities left by broken-off stubs and in hollows in the branches), with banks of fern, blueberries, seedlings of Douglas fir and Sitka spruce, and nesting seabirds. (Part of the temperate rainforests that occupy west-facing coasts worldwide, most redwoods are found within 10 miles of the sea. They grow where their limbs and needles can comb water from coastal fogs—12 inches during the usual summer dry season—and out of the reach of salt spray. Marbled murrelets nest in their crown forests, ancient murrelets among their roots, the former now in steep decline as their nesting habitat has shrunk from 2 million to a few thousand acres.) Southern pines, grown mostly for paper pulp, are cut at much shorter rotations, 25-35 years (younger trees make better pulp). Like browsing, cutting changes the composition of the forest. The cutting rotation in the Northeast is now too short for hemlock, a tree that can live 600-900 years and is probably worth cutting at 150 years. (The crown forests of old hemlocks show some of the characteristics of old redwoods.) Frequent cutting in the Maine woods has favored balsam over red spruce (another slow-growing tree). In 1902 the volume of spruce was 7 times that of fir; today the two are virtually equal in volume. Frequent cutting in the forests of northern Pennsylvania favors trees that sprout (cherry, oak, maple) over softwoods like white pine and hemlock. Early logging probably favored American chestnut, which rose from 4-15% of forest volume in early surveys of New Jersey and Connecticut to 60% (becoming the most abundant tree species) in 1900. While oaks and hickories produced hundreds of pounds of nuts per acre, chestnuts produced thousands.
Cutting can also mimic natural process. In Sweden white spruce usually reproduces itself through small gaps, such as the death of a large tree. Such forests can be reproduced by selective cutting that leaves most of the forest intact and also leaves existing snags and fallen trees (until recently the United States Forest Service required their removal on logging sites) and some old trees. One would also leave most of the deciduous trees, which have important functions in conifer-dominated woodlands. Spruce-fir stands in boreal North America are often fire-adapted communities, reproduced by stand-replacing fires. Such communities can be maintained by a modified clearcutting, leaving wide bands of trees along watercourses, with large, scattered clumps of trees about old trees left in the cut as nesting sites, sources of seed and future snags. Tops and slash are left on the ground. Spruce and fir are usually used for pulp in the Northeast and so are cut as soon as they are large enough to make cutting economic (this size goes down as logging becomes more mechanized). Red spruce makes valuable lumber (it is used for pianos); it is a slow-growing tree and leaving clumps of red spruce among the balsam to mature increases the variety and value of the forest. Letting some aspen and birch mature (birch for sawlogs, aspen for pulp) increases the forest’s productivity and makes it more friendly to game animals. To minimize blowdown and drying of the forest, such clear-cut strips are usually limited to a width 1.5 times the height of the trees (or 100-150 feet). Such cuts attempt to mimic the effects of catastrophic disturbance in primary forests and leave the landscape conducive to the movement of seeds and animals. In the East, such cuts are not burned (similar, lodgepole pine cuts in the West probably benefit from being burned). Leaving merchantable trees in the woods increases the future health and productivity of the forest. It reduces the volume of wood harvested, and thus current profits to the landowner. In the future, losses in volume will be compensated by the more valuable logs from old trees.
As forests mature, they accumulate dying and fallen trees. Fallen trees cover up to 20% of the forest floor in mature Douglas fir woodlands in California. A recent checklist for old-growth forests in the East included 3-4 logs greater than 16 inches in diameter, per acre, on the forest floor: a much smaller number. Hollow trees become den or nesting trees for various animals and birds; large hollow trees are used by bats and chimney swifts as well as hibernating bears: Audubon counted 9000 chimney swifts leaving one hollow sycamore. (Bats now make use of attics and mines, chimney swifts use chimneys, both birds having become in the Northeast—like the nighthawks which nest on the flat roofs of commercial buildings, and whose notes drop from the skies of suburban evenings—animals of settled landscapes.) Downed trees create new habitat on the forest floor for invertebrates, rodents, birds and amphibians. Soil accumulating on the upslope side of a log provides habitat for burrowing insects and small mammals, while the downslope side provides shelter and nesting sites. An acre of Maine woodland has more biomass of salamanders than of moose: a fact only briefly surprising. Rotting logs have a greater mass of living tissue (in their plants and decomposers) than growing ones. Nitrogen-fixing bacteria living in the guts of Pacific dampwood termites fix nitrogen for the termites. The nitrogen ends up in the nutrient-poor ecosystem of the rotting log and fertilizes tree seedlings growing on it. The invertebrates of the logs and the forest floor (earthworms, centipedes, millipedes, spiders, beetles, mites, springtails, psocids, nematodes) are eaten by small mammals, birds and amphibians (shrews, toads, frogs, thrushes, salamanders; also by the less abundant snakes and turtles); the amphibians, reptiles, birds and mammals form one basis of the forest’s food chain. The fallen logs also act as dams to keep forest soil from moving during rains and thaws. The old trees of a primary forest create a moister, shadier environment. Their large limbs are habitat for lichens that synthesize their nutrients (including nitrogen-rich proteins) from the air. These nutrients enter the forest ecosystem through leaching and litterfall, and through the dung of the squirrels and rodents (often different species than the mast-eaters) that eat them. It is said that young Douglas firs first grow on the nitrogen banked in the soil by the nitrogen-fixing shrubs that follow forest fires, then (as adults) on the nitrogen synthesized by their lichens. A major food of the rodents of old growth woods are the fruiting bodies of the mycorrhizal fungi that are allied with the roots of the trees. The fungal spores pass through the rodents’ digestive systems unharmed and are deposited on the forest floor and in their tunnels and burrows, generating more fungi. These rodents are part of a new food chain of the primary forest that ends in predators of the deep woods, such as pine martens and spotted owls. The water that flows out of such woodlands, thanks to the shade and the lack of sediment, is cold and clear (sometimes tinged brown with tannins), nutrient poor, habitat for salmon and trout. Tree roots stabilize the streams; and the trees themselves, falling across the brooks and larger creeks, also stabilize them, creating pools. Salmon, running upstream, like the seabirds that nest among the trees, contribute nutrients from the sea.
That only a third of the mixed Maine woodland was in primary forest implies a fairly high level of natural disturbance. In much of the Appalachians and Midwest the disturbance regime was several times the lifetime of the trees (even that of the white pines, which live 500 years). The result was old forests with complex mixes of trees of different shade tolerances and ages. In natural forests non-catastrophic replacement is usually in patches. One or a group of trees that rise slightly above the canopy are blown down, or a tree collapses from old age and takes some others with it, and the shade tolerant saplings that have been growing in the understory shoot up. If light is sufficient, the seeds of the shade-intolerant species that have been waiting in the soil sprout and grow. (Yellow birch and white ash will grow in the gap left by a single tree, while red oak, black cherry, sweet birch and tulip tree need larger gaps.) Hurricanes, tornadoes and fires clear larger areas. What develops on a site after a catastrophic disturbance depends on what trees are left alive (the so-called seed trees), the presence of trees that sprout from roots (many deciduous trees and shrubs), the seeds in the soil-bank, and what is brought to the site by birds, mammals and the wind. So the forest one sees on a site depends on the site’s history, its surroundings (another history), and chance. In much of the conifer and mixed hardwood forest of the Boundary Waters Canoe Area, the original fire rotation time was thought to be 50-100 years. Such short rotations favor fire-adapted trees: those that sprout from roots, such as quaking aspen; or that have well-dispersed seeds, such as paper birch; those with serotinous cones carried high in the canopy, such as jack pine or black spruce; or trees whose thick bark lets them tolerate fires, such as red pine, which become fire-resistant after 50 years. Short fire rotations must be fairly ancient in the general area since the Kirkland’s warbler is adapted to breeding in fire-succeeded stands of jack pine; it will breed nowhere else and abandons older jack pine stands. If a new stand escapes fire for 40 years or more, jack pine and aspen slowly succeed to more fire resistant, very mixed stands of black spruce, balsam fir, paper birch and white cedar. Red pines, which are capable of masssive recruitment after a fire slowly die out in very old stands (very old: red pines are still present after 300 years). In this case pines will no longer reproduce if disturbance is limited to windthrow and spruce budworm; they need fire. The spread of hemlock into a stand lengthens the fire frequency indefinitely (they draw up groundwater to the surface and moisten the soil), and if a stand escapes fire for a very long time, a forest dominated by hemlock and the shade tolerant sugar maple may develop. By lengthening the fire frequency, the hemlock makes possible the success of the fire-susceptible maple. Both hemlock and sugar maple produce a forest floor unfavorable to the establishment of other species, so this forest is somewhat self-maintaining (but in fact no more of a “climax” than the more mixed forests it replaced: felled by a windstorm, it will be replaced by aspen, spruce, and birch).
Primary forest in the eastern United States is characterized by fairly large trees (16-20 inches or more in diameter according to a recent checklist; but certainly many first-growth trees were larger). Other characteristics include a relatively small percent of intolerant (pioneer) tree species in the canopy; a full compliment of spring ephemerals suitable to the site (flowers that bloom and set seed before the tree leaves come out; these plants are not too much bothered by occasional logging, but frequent logging, clear-cutting or grazing will reduce them; since they are pollinated and their seeds distributed by ants, they spread slowly and can take centuries to recolonize a site); by a full compliment of bryophytes (mosses, liverworts, lichens: plants of damp and shaded woods), including those characteristic of old growth; by large old logs on the forest floor (microhabitat for many birds, mammals, reptiles, invertebrates, decomposers, mosses, fungi, tree seedlings; forests in northern regions probably need 12 tons of coarse woody debris per acre to maintain site quality); and by large, standing snags. Many of the large trees of a primary forest are rotten. (A complaint of woodcutters in early Maine, who would chop a hole 3 feet into an old pine, 50 feet above the ground, to check its condition before felling it. The wood of such large old pines, so-called pumpkin pine, was valuable for being soft and easily worked.) Many species of birds and mammals in the eastern forests require standing dead trees for perching, foraging, nesting, roosting, and denning. The ivory-billed woodpecker is said to have specialized in debarking large, dead trees to eat the insects beneath the bark. The demise of such trees as southern bottomland forests were logged and converted to agriculture was a major factor in its extinction. (Audubon shows a family of ivorybills collecting beetles from under the bark of a small dead stub.) Many writers would claim that old growth or primary forest is not absolutely necessary in a functioning natural landscape, even along streams, but no one can be sure of this. Some of the forest’s inhabitants (those microbes, fungi, invertebrates) will go extinct without it and the landscape in a larger sense will be reduced. Other writers argue that tracts of old growth must be very large to function truly as primary forest. The woodland must contain the large carnivores (grizzly bears, wolves, mountain lions) whose presence indicates an intact food web. Such tracts require 250,000-300,000 acres of contiguous woodland, with connections to other such areas.
Logged forests are not natural forests. Economic considerations will never allow them to move far into the realm of old growth. Their soils may or may not achieve a net accumulation of carbon. Logging disturbs the soil and exposes it to sun and rain; increased microbial action in the warmed soil releases carbon and other nutrients. The decay of logging debris releases carbon. It takes 10 to 20 years for a logged second-growth forest to begin a net accumulation of carbon, 45 years for regrowth to compensate for the carbon released by the decay of debis left from cutting an old-growth forest. And the carbon in the logs removed returns to the atmosphere quite rapidly. A third to a half of the logs end up as waste (sawdust, planer mill shavings, cut ends of boards), which is burned or decays. The rest of the carbon in the logs returns to the atmosphere after a short detour through the man-made world (for much of the material, made into paper or pallets, less than 10 years; that made into furniture or buildings lasts somewhat longer — less than 50 years on average). But it should be possible to mimic somewhat the process of natural forest succession through logging: to provide a natural variety of habitats (if not in the same proportions as in the aboriginal forest); to leave some old trees and downed logs; to conserve forest soils; and to protect forest streams from too much sun and from the constant pulses of silt and nutrients that logging produces. All this of course will cost the landowners and loggers money, at least at first.
Cutting, like fire, always sets the forest on a new trajectory. In the humid forests of the Northeast and Middle West, selective cutting favors the shade-tolerant beech and sugar maple; clear-cutting the warmth-loving pines and oaks, and other pioneer species like aspen, pin cherry and paper birch. Clear-cutting in dry western forests can eliminate the mycorrhizal fungi on which the trees depend and make reforestation of west-facing slopes difficult. (Adapted to living with certain species of trees, the fungi must find a new host in two years or die.) Clear-cuts, and heavy selective cuts, create more or less even-aged stands, with more pioneer and early successional species, while light selective cutting creates forests of more shade-tolerant species. The early successional forests created by heavy cutting (taking all merchantable trees when entering the woods) are supposed to provide a constant, sustainable yield of wood, at the maximum potential of a site. But, an artifact of cutting, these forests are quite unstable. They seek to produce only fiber. Natural stands in the same areas would be a mosaic of old growth, maturing trees, tangles of young growth, species with different tolerances to light, with a full assortment of the birds, mammals, invertebrates and fish characteristic of the area. The forest in a given place, with its vertebrate and invertebrate inhabitants, would depend on the sorts of disturbance to which the stand had been subject; that is, on the site’s particular history.
Logging influences what trees grow in a forest, and in general speeds up (may double) their rate of growth. Logging also has many negative effects on a forest. Soils are compacted and erode. Soil oxygen levels are lowered. The stems and roots of trees are often wounded. Root compaction and oxygen deprivation slow growth for some time after a cut. Heavy cuts move water and nutrients into streams. In areas where the natural water temperature in summer is near the upper limit of their requirements, clear-cutting may raise stream temperatures above what salmon and trout tolerate. So fish disappear. Cuts along streams remove the trees whose roots hold the bank together. With the additional water and soil moving into them, the streams widen, scour, straighten out and take some time (usually more than a decade) to return to a more stable condition; then the logging starts again. Heavy cutting on steep slopes in the Pacific Northwest makes the slopes liable to landslides following insignificant rains; slides begin three years after logging, when the roots that held the slope together have rotted. Cutting along streams removes the logs that would have become coarse woody debris in the water and on the forest floor. Such logs retard water flow, and help stabilize streams. Logging on the banks fills streams with tops and slash. The cumulative effect on streams can be catastrophic for fish, as is the case with many salmon and trout streams in coastal California, Oregon and Washington. Slope tremendously influences the erosive capacity of water, which increases by the fifth power of its velocity. As the speed of flowing water (down a skid trail, through a culvert) doubles, it is able to carry 32 times the sediment and move particles that are 64 times heavier. Much of the sediment in west coast streams comes from logging roads and skid trails. When these are treated properly (which includes closure to vehicles) after logging is over, the sediment loads decrease, the streams clear, and salmon and trout return to them. Hunters and drivers of recreational vehicles object to such closures, which makes the back country only accessible by horse or foot. (Included with the sediment are some of the hydraulic fluids from the logging eqipment, 70-80% of which escapes in leaks, spills and line and filter failure, and some of the chain oil and engine oil from the saws: arguments for using biodegradable oils.)
A forestry that tried to recreate the forest as an ecosystem would place old growth in the commercial forest along streams. Very lightly logged primary forest (a tree per acre every 5-10 years) would cover the banks of deeply incised streams, and cover the streambank out for 50 to 100 feet otherwise. (A tree per acre every 5-10 years is 4-8 trees per acre for entries at 40 year intervals; depending on the market, logs from such trees might be worth $1000 or more at the mill, or $300 in stumpage to the landowner.) Probably less than 20% of eastern forests have soils good enough to make the risk of growing trees greater than 100-150 years old worthwhile (sites in coves, valleys, the toe slopes of hills, in soils derived from nutrient-rich bedrock: most of the best forest soils in the East are now in agriculture); so one puts old growth where, whether a good commercial risk or not, it will do the most biological good. Then fingers of old growth penetrate the logged woods: primary forests are multi-story forests in the Northeast and upper Middle West, where most trees top out at 80-100 feet, and large white pines penetrate the canopy to reach 150 feet or more. These fingers of old growth will not function well if they back entirely upon clearcuts (winds will blow the trees over, too much sun dry the forest floor). So the forest that abuts the old growth is a mix. If we follow the Maine example, one third would be in early old growth (cut at 125-175 years; perhaps let mature further in better sites); poorer sites would be cut at 80-100 years. The value of the water running off the land and the land’s value as a carbon store will affect cutting choices. Two-thirds of the forest would be maturing and young forest. If the water that runs off the forest is worth $30 an acre, when close to the presettlement original amount and condition, forest management that keeps the water in that condition should be worth that. Carbon storage in trees and soils depends on the site, the forest and its age; if it amounts to half a ton per acre per year and stored carbon is worth $50 a ton (probably a high figure), then carbon storage is worth $25 an acre. Over a 150 year rotation, $55 an acre a year ($8250 dollars) is likely comparable to the stumpage value of the timber.
Logging is always somewhat destructive to a forest. By opening the canopy, logging increases light, temperature and wind speed; it lowers relative humidity; disturbs and compacts soils (especially the top few inches where most of the tree roots grow; this is why the worst time to log is spring, the best time in winter on frozen ground). Logging damages nearby trees and causes wounds in roots and stems that leave trees susceptible to decay or disease. After logging, erosion increases in the forest as a whole and especially on the 5-10% of it that is in roads, skid trails and landings. Something like 65% of the lubricants and coolants used in logging machinery end up on the forest floor. But logging also speeds up natural processes, raising the 2% return in growth on unlogged stands to perhaps 4%. Young stands of northern hardwoods will naturally thin themselves from 1000 trees per acre at four inches diameter at breast height to 40-60 trees per acre at 20 inches diameter. (Since a site can support only so much basal area of tree per acre, as the individual trees get thicker, there must be fewer of them.) This process takes 200 years in nature, but half that if the stand is thinned periodically. Another way to put it is that for the trees in a fully stocked stand to gain an inch in diameter, 20% of them must die. So this is the rationale for periodic logging in ecologically managed forests. Thinning of long-rotation hardwoods in the Northeast usually starts at 30-40 years when they have reached (coincidentally) 30-40% of their mature height. Letting them remain crowded up to then forces the trees to grow taller. (Deciduous trees grow upward in response to light and will adopt a rounder, shorter habit if not forced upward by competition; conifers grow from an apical bud that responds to gravity and so continue upward no matter what the competitive situation.) Thinning lets the crowns develop (the crown should occupy 35% of the height of the tree) and the boles increase in diameter faster. Trees 8 inches in diameter are usually thinned to 200 to the acre. Thinning then continues at 10-40 year intervals, depending on how the site is being managed. In general the longer intervals, which involve fewer entries of heavy machinery into the woods, are better for the forest. Most commercial forestland in the East is young, and logging to re-create a mixed, old-growth forest would have to focus on the trees to be left rather than on the trees removed (the usual focus of loggers). The larger trees in a stand may be the same age as the smaller ones but more vigorous. So one leaves those, whatever their place in the succession. Early and mid-successional species that have been overtopped and suppressed are removed. In general, one leaves vigorous, late successional species with good form and no wounds, that are capable of reaching the overstory. The trees that grow earlier in a succession, such as white birch and red maple and the shrubs, put their growth into stems, flowers and fruits rather than roots; their purpose is to reproduce before they are shaded out. A heavy fruiting may kill them. More long-lived species, such as sugar maples and oaks, put their energy into roots, stems, branches and leaves, and fruit later and at longer intervals. Logging aims at an uneven-aged forest. Several old trees are left per acre, no matter what their status or form: they will become snags, hollow trees, and finally coarse woody debris on the forest floor. Creating such forests takes time, in most cases a century before they become capable of producing a steady flow of timber. In an ideal world, returns from the value of the water flowing off the land and from carbon storage would provide additional income over this time. Logging of old growth in a given woodland would not happen all at one time, since one aims to provide roughly the same proportions of each habitat over time: this lets the various inhabitants of the forest (as well as the loggers and lumber mills) survive.
In an ideal eastern forest, one would cut only those trees unlikely to survive until the next cutting cycle (a variation on John Muir’s sawmill for dead trees). This will result in a forest of shade-tolerant trees: a “climax forest.” Cutting mature trees is likely to damage the surrounding ones however. An alternative is cutting the forest in little clear-cuts, 0.25 acre to 2 acres in size (2 acres is large), somewhat linearly, along the slope. This allows for reproduction of more warmth-loving and intolerant species (oaks, birches, pines). It tends to reproduce the existing forest. About 15% of the forest is left standing in the cut: some green trees for shade and seed, some large trees to become overstory trees, some to become snags and logs on the forest floor. Tops less than 6 inches in diameter and branches are left in the woods. The microhabitat the standing trees and downed logs provides reduces erosion and loss of soil nutrients, the partly shaded habitat is also more friendly for soil microbes and invertebrates, mycorrhizal fungi, small vertebrates and amphibians. The slash helps prevent browsing of saplings by deer. A different mix of trees will grow into the architecture of the remaining forest than into a clearcut. (In former Forest Service guidelines for western forests, stumps were removed and the slash piled and burned, in preparation for replanting ranks of fir or spruce. Except where it is very dry, most forests will reseed naturally, but not to the monocultures of plantations.). As the young trees grow, they are thinned. Timely thinning speeds tree growth but also removes carbonaceous material and nutrients that would add to forest soils (leaving tops and branches from the thinned material helps). The point of thinning in the developing forest should be to create a mixed stand of trees (mixed in age and species), not to harvest the largest and most valuable timber (generally the goal in commercial thinning). The first thinning is done when the trees reach 8 to 12 inches in diameter. This thinning produces poles, sawlogs and firewood. Trees too small to use are left in the woods. One selects for trees suitable for the site and opens up the forest around the better formed, better adapted (to the site), more vigorous trees. Usually commercial selective cuts involve the removal of 50% or more of basal area and all large trees, but cuts in the ecological forest would remove considerably less than that, and leave a cross section of tree ages. Since selective cutting will tend to favor the more shade tolerant trees (such as hemlock and sugar maple in the East), one would also in good seed years cut some larger gaps to allow regeneration of less shade-tolerant species (yellow birch, oaks, pines). Cutting over the long term inevitably reduces the nutrient capacity of a site, but the term is long (probably longer than the climate that supports the forest) and restoration forestry can reduce this loss to near zero. Ecological forests are managed for their processes, but after a time also produce a steady flow of forest products (poles, sawtimber, veneer logs, fuelwood, chips, pulp). A point to be made is that in the modern world the healthiness of a forest may constitute its greatest value (its value as real estate).
There are many different types of forest in the United States. In the latter half of the nineteenth century, logging and fire converted much of the pinery of the upper Middle West into an aspen forest (aspens sprout vigorously from their roots); or in places where the topsoil was burned away by the fires, to shrublands of bird-planted pin cherry, blueberry, grasses, raspberry and shadbush. From 1875 to 1900, logging fires averaged 500,000 acres a year in Michigan and Wisconsin. Much of this area had little value for agriculture and ended up as national forest. (The pinery of the northern forest was originally several hundred billion board feet.) The aspen forest has been maintained as a monoculture by cutting on a short-term rotation (30 to 50 years) for paper pulp and for chips for composition board. Clearcutting the sites removes the conifers and other hardwoods in the stand, and regenerates the aspen from root sprouts. To recreate a more mixed forest, probably a more stable forest (and one with more commercial potential), loggers would remove the mature aspen but retain the conifers and the other hardwoods. Released from competition, these trees would shoot up. The aspen would regenerate, but less strongly, as they must compete with the residual trees. The result would be structural and habitat diversity. Future cuts would treat the forest as a developing old growth woodland, clear-cutting the aspen stands as they matured (their greatest value for grouse and deer tends to be when young), and the evergreens and hardwoods as they reached the first stages of old growth. Along watercourses trees would be let mature further. Some of the canopy would be left standing in the future clearcuts as a legacy of the stand architecture: seed trees, snags, hollow trees, some large old trees, some young and middle-aged trees (living trees might be left in clumps). The clear-cuts would be small and patchy. The alternating dominance of aspen and conifers would mimic the lifecycles imposed on the forest by tent caterpillar and spruce budworm, the insect pests of each species. It would also exploit the opposite effects of aspen and conifers on the nitrogen cycle. Much of the nitrogen that accumulates in conifer needle litter does not break down and is vaporized in stand-clearing fires — especially in boreal woodlands (no stand of black spruce hs been found that did not originate in a fire) — while nitrogen in aspen litterfall is exploited in the rich, easily decomposed leaf litter of the aspens.
Some eastern forests burn naturally. Many more were regularly burned by the Native Americans. Burning altered the forest cover along much of the East Coast, its effects extending up the major river valleys. In the Southeast, burning created the savannahs of long-leaf pine characteristic of the pre-contact coastal plain. (Perhaps 3% of this once enormous habitat remains.) In the Middle West late summer burning produced open forests of oaks and hickories and pushed the edge of the continental grasslands hundreds of miles east. The sunny dry forests of the mountain West naturally burned. Some were burned by Indians. At European contact, probably 20 million acres of the trans-Mississippi West burned every year, much of it grassland and scrub, but 6 million acres of it forest. Virtually all western forests arose out of fire: the cool coastal rainforests of Vancouver Island and British Columbia were perhaps an exception. The types of fires varied. Under natural conditions about 40% of western forests experience low-intensity fires every 1-30 years. These are so-called understory fires. Low intensity or understory fires create forests of large, well-spaced, sun-loving, fire-resistant trees, such as Ponderosa and Jeffrey pine and western larch in the Rockies; giant sequoia, redwood, and some types of oak forests further west. Ponderosa pine forms a relatively pure climax at middle elevations in the western United States. Ponderosa is moisture dependent and grows more thickly at higher elevations (more mixed with Douglas fir), more spaced out at lower and drier ones. The trees in historic old-growth middle elevation forests were 200-400 years old, with 30-40 trees to the acre (one tree per 200 square meters). Grasses and fire resistant herbs and shrubs formed an open understory, which was browsed by elk and deer. Frequent ground fires in such forests scorch the lower branches of the trees (which eventually die and fall off), kill saplings and large shrubs, and thin (often drastically) the pine seedlings and those of shade-tolerant trees, such as true fir and Douglas fir. They burn off the litter layer of undecomposed needles, fallen branches and the dead grasses on the forest floor. Thus they keep fuel loads low and, by pruning trees and killing seedlings, remove the fuel ladder that lets fires reach the crowns of the trees. They maintain the open forest. When such forests are logged, most of the old trees are removed. Fires are suppressed. Shade tolerant Douglas fir, true fir and lodgepole pine seed in and grow up into thick stands of young trees, among the remaining older trees. The tree density is 40 times that of historic old growth stands. Competion for moisture and nutrients in the thick forests stresses the older trees. Without fire to keep competion down, the old larch and Pondersosa pine decline in vigor. Diameter growth slows drastically after 30 years and foliage grows sparse after 80 years. The trees loose the ability to manufacture the resins necessary to combat bark beetle infection (the beetles are drowned in their tunnels by the sticky resins secreted by the tree) and are killed by the beetles or fire. In general, crowded stands are more susceptible to bark beetles, spruce budworm, dwarf mistletoe, root rot, and catastophic crown fires. Because of such poor management in western forests, stand replacing fires are twice as common as historically. In overgrown forests with a history of frequent fire, where fire has been suppressed, insects and fire take control. The resulting catastrophic fires will kill both old growth and young trees and endanger human settlements in the forest.
Ponderosa pines are adapted to light fires. They have deep roots, thick bark, open crowns, large fleshy buds, and long needles spread out to avoid rising heat (not the short densely spaced needles of black spruce that make the tree flare up like a torch). Severe fire in Ponderosa forests makes them hard to regenerate. Ponderosas have heavy seeds that fall within 150 feet of the tree, so unless planted by birds or squirrels, the trees take time to spread; the soil after a hot fire forms a water-repellant surface inimical to vegetation; and the rest of the forest vegetation, also not adapted to severe fires, recovers slowly. One way to regenerate a fire-resistant stand of old-growth Ponderosa pines is to log from below. One removes most of the small and medium sized trees and all the shade tolerant trees (such as Douglas fir, some of which may be large: removing these large trees helps pay for the treatment). All the large pines that are vigorous enough to survive are left. After logging, when conditions allow, the forest is burned, to reduce the fuel load and further thin the Ponderosa and fir seedlings. One wants a mix of different age classes of trees amidst an open understory that will allow periodic prescribed burning. This forest over several decades will become an open forest dominated by shade-intolerant Ponderosa pines, with some young growth and some trees of other species. Such forests are logged every 25-30 years to remove excess small, medium and large trees (those that wouldn’t survive to the next cutting cycle). Some dying old trees are left. The small openings created by each entry allow a new age class of pines to develop. The forests are burned every 10-35 years to keep fuel loads low, recycle nutrients, control Douglas fir and stimulate herb and shrub regeneration. In time, such forests will provide a constant flow of commercial timber: large sawlogs, smaller logs and poles for latilla and viga makers (the traditional southwestern ceiling beams and lattices); chip wood for boiler fuel. The constant flow of wood provides predictable amounts of material for sawmills, pulp mills, wafer board and plywood plants, post and pole plants. Restoring overgrown forests in 1% of Montana a year (not just Ponderosa forests, but all types of forests) would increase timber productivity by 50%. (In 2000, thanks to a century of poorly managed timber cutting, wood production in Montana was 15% of that in 1990.) Such restoration forestry costs about $200 an acre initially. With the second or third cut, the forest breaks even, and after 100 years should turn a profit, which continues indefinitely, and rises with good management. (Fighting crown fires is also expensive, up to $1700 an acre, with no profit in sight.) The United States spends over $2 billion a year fighting fires in the West. This is money that in many cases pays for a history of forest mis-management, a tax on short-term capitalist management and scientific ignorance. Without putting money into good management (an amount equal to that used to fight forest fires would restore 10 million acres a year), such costs will only rise. One tries to recreate the historical forest not only to recreate the past but because this forest is more sustainable, with a lower risk to its biota and a lower risk of catastrophic fire. It makes economic sense; as several writers have pointed out, a forest’s maintenance of ecological process constitutes its greatest value (human or otherwise), its ability to maintain a predictable flow of wood and support a rural population constitutes its greatest social value, while control of its fires raises the value of the land about it as real estate.
The cooler, moister, higher elevation forests of the West are subject to more intense fires (so-called intermediate intensity fires), every 30-100 years. In such forests good fire conditions exist for a short time: a few days or weeks each summer. The fires are intense enough to kill most fire-susceptible trees but the mountainous areas burn unevenly, so much of a site (up to half) remains unburned. Such forests become very mixed in species and in tree ages. Here, logging followed by the suppression of fire leads to dense forests of shade tolerant trees which are susceptible to stand replacing fires. A more sustainable forestry in such overgrown stands, which, as they get older, are favored by spotted owls, martin and fisher, would remove the shade-tolerant trees in a patchy pattern, retain the sun-loving trees, and encourage (with a controlled burn) regeneration of fire-dependent herbs, trees, and shrubs. Such treatments would take place every 40-100 years. In the case of spotted owl habitat, a central (fire-unstable) old growth forest (say of firs) would be surrounded by more open forests of large trees (larch and pine), which would serve as firebreaks. Such firebreaks are usually a quarter of a mile wide. When fire destroys the central old growth, or after it is logged, parts of the firebreak are let develop into the thick, shade tolerant, old growth forest favored by owls. Surrounding undisturbed old growth forests with a matrix of semi-natural wooded habitat makes it easier for the animals of those forests move to other old growth areas.
Moist cold forests on the upper slopes of mountains (the last 20% of western forests) burn occasionally, at 100-400 year intervals, in stand replacing fires. In many ways, they resemble the boreal forests of Canada, altitude here compensating for latitude. Stand replacing fires occur when conditions are unusually dry and fuels are available, often during major droughts. Such forests include lodgepole pine; and the white-bark pine, whose plump seeds help support mountain populations of grizzly bears and which is replanted in areas cleared by wind and fire by Clark’s nutcrackers storing pine seeds for the winter. Such forests become mosaics of burned and unburned patches, of hundreds to thousands of acres. The trees are adapted to catastrophic fires. Lodgepole pine cones open in the heat of fire. Green cones in fire killed western larch and coastal Douglas fir drop viable seed. After a burn, elderberries, currants, gooseberries, bitterberries, ceanothus, wild geraniums and hollyhocks are planted in clearings by birds; aspen and fireweed seeds blow in; alders replenish the nitrogen in the soil. The forest is full of standing dead trees. Depending on the intensity of the fire, willow, aspen and mountain maple may sprout from rootstocks; and other plants grow from seeds in the soil seedbank. Clear-cutting such forests is not a replacement for fire. Clear-cutting leaves no standing dead trees to become breeding places for insects that attract birds; that release nutrients; and whose shade helps in regeneration of trees, herbs and shrubs. Fires affect soils differently from bulldozers and skidders. Fires leave irregular patches and strips of surviving trees and an ashy seedbed for the bird and wind planted seeds from outside the burn. Clearcut stands lack the diversity of fire cleared stands. A better way to log such stands is to remove two-thirds of the trees, leaving most of the overstory trees (such as Douglas fir and western larch) and the rest of the stand in irregular clusters. Burning the slash after logging kills most of the remaining trees and leaves snags and a suitable seedbed for regeneration of the conifers, herbs, shrubs and deciduous trees characteristic of recent burns.
The whitebark pine of the high slopes is suffering tremendous mortality from blister rust, an Asian fungus that took almost a century to reach whitebark stands from its initial foothold on the east coast (where it remains a problem in white pine), and may require intensive human intervention to reproduce the rust-resistant trees. The whitebark’s large, oil-rich seeds let grizzly bears gain enough weight to go into winter in good condition and keep the bears in autumn at high elevations out of the way of humans. The bears rob caches of cones hidden by squirrels, then crush the cones between their paws to get out the seeds. (Another late fall bear food is cutworms, whose moths are blown into the mountains from Kansas wheat fields, and whose larvae are found under mountain rocks.) A poor competitor with other trees, whitebark pines grow on the thin, stony soils and in the difficult climates of alpine elevations. They shade the snowpack and stabilize the rocky soils, protecting the quality of the snowmelt and rain that flows in brooks and streams down to the lowlands. Clark’s nutcrackers collect whitebark seeds and cache them several miles away in open areas for the winter. Those that are not retrieved (this number may fall as the pines grow more scarce, and feeding by nutcrackers become a problem for the pines) grow into new stands of trees.
Sustainability is a human concept that may or may not work in nature. Attempting permanance, it implies a constant flow of animals, crop plants or timber from a place. Sustainability in agriculture means maintaining agricultural soils and reducing erosion to the levels at which the soil is rebuilt (essentially zero); and making agriculture one part of the larger ecosystem. Sustainable forestry in the long run probably means maintaining all components of the ecosystem. Such components include disturbances, such as fires, large herbivores and their predators (moose and wolf), the small mammals, amphibians, arthropods and fungi of the forest floor, the soil microflora, the arboreal lichens and mosses of old forests. The purpose in retaining large canopy trees during initial logging operations, and lengthening the rotations, is to produce a forest with more large, old trees, a multi-storied canopy, a greater variation in tree size (these all lead to a more complex forest architecture), with large woody debris on the forest floor, tighter nutrient cycles, shaded refugia for mycorrhizal fungi and nitrogen-fixing bacteria. (One could argue that the fungi, with which many trees have obligate relations, by connecting trees of different ages and species, are a major factor in controlling what happens in the forest.) Such a forest provides for beneficial predator-prey relationships among forest vertebrates and habitat for plants and animals that require structural complexity and late seral conditions, as well as for the needs of those that inhabit young forest. Some birds in Pacific Northwest forests jump in density as the forest enters a state of old-growth, indicating a (non-linear) change in the quality of the habitat. (But bird variety in mature forests is often low.) In woodlands with a history of fire, maintaining open forests of old sun-loving trees, mixed with some shade-tolerant trees and with younger stands, minimizes the destructive potential of fires. (One can’t eliminate fire, only plan around it; the success of Smokey the Bear has caused our present dilemma.) Such forests also maintain the place of the forest globally, which a young forest, maintained on a short rotation, doesn’t: the forest as a store of carbon, as an inoculae for mycorrhizal fungi, lichens and forest bacteria, as a positive influence on the water that flows through them, and on the coastal estuaries that lie below.
Forests managed for their process as well as for timber will produce less total wood fiber. Parts of them should be left undisturbed and separate forestlands should be connected by corridors and buffer zones, that allow plants and animals to migrate. Leaving large trees standing and lengthening rotations to let the forest become old both reduce the amount of wood harvested per acre. The net return per acre however remains the same or rises, since larger logs from old trees have a much higher value. (About half the wood cut in the U.S. goes to paper, though sawtimber is worth 2-5 times as much, good sawtimber more than that.) So the contribution of the forest to the economy remains the same, or rises; but only after a period of forest recovery that would last for about a century. Such forests will require a new infrastructure to use their logs of different species and sizes (saplings, poles, sawlogs). Some thinning operations would be better done by hand, or with horses or light tractors, than by heavy machinery. Modern industrial forestry, faced with forests of declining value, uses harvesting machinery of immense power and mobility in order to make a profit harvesting wood of low quality and low quantity (per acre). The post-harvest machinery tends to homogenize the harvested logs into composite products (like oriented strand board, which has replaced plywood, which requires better logs, for many uses: in this case, resin replaces fiber). Such plants are now being constructed around the perimeter of the Cumberland Plateau in the southern Applalachians, in order to use the second growth hardwood forests of the plateau. The forests will be clearcut to feed the plants, at terrible cost to the biota and watercourses of the region. An alternative, regeneratively harvested forest would produce a mix of graded materials for plywood, oriented strand board, flooring, cabinetry, moldings, wall panelling, furniture, construction lumber, tool handles, fencing and so on. Such a forest would require a more far-sighted and curious forestry, some public funding, and patience.
One faces essentially the same question as in agriculture: whether to focus on the yield per acre per year, or on the forest as habitat and process, a landscape that also produces wood. As with food, one can ask how much wood do we need? Wooden pallets use 1.5 billion board feet of lumber a year in the United States (about 40% of the hardwood cut) and most of them are thrown away after a single use. Re-manufactured pallets could provide the lumber for 300,000 to 600,000 houses a year; or a considerable amount of hardwood flooring, material for composition board, and wood shavings for packing material. A tax on logs (making pallets more expensive) would encourage reuse. A rise in landfill fees would make reuse of lumber in demolished buildings profitable. (Construction debris constitutes 15-40% of landfill contents in developed countries; an increase in Danish landfill fees pushed reuse of construction materials from 12% to 82% over 10 years.) A better recycling effort would reduce the wood needed for paper and cardboard by up to 90%. (Paper can be recycled 9-10 times; 90% recovery probably isn’t possible but 75% probably is. Reducing wood use by recycling would also reduce our carbon footprint.) Alternative fiber crops such as kenaf (an African plant), hemp, hybrid poplar, native trees that sprout from stumps, grown and harvested as saplings by machinery, produce much more fiber per acre than natural forests (2-5 times more in mechanically coppiced forests), and are easier on the land than cotton or corn. Hemp, which can be made into paper or cloth, produces more fiber per acre at a much lower environmental cost than cotton. So does bamboo. In short, we don’t need much of the wood that modern forests produce; but under a capitalist regime land must produce value. Wood fiber (not whole ecosystems) is what forests produce, and it is presently economically advantageous to use the fiber and throw it away. Returning some of the value of regeneratively managed forests to the landowner (their value in slowing soil erosion, protecting streams, controlling water and nutrient runoff, filtering the air, storing carbon, their role in providing habitat for useful wildlife, in regulating local microclimate and rainfall) would help make managing forests for their processes profitable. Such value, in dollars per acre per year, may be worth more than the wood, but that value only becomes apparent when the forests are degraded or gone. (The monies could be raised through a tax on logs.) The appearance of regenerative forests also increases property values. Costa Rica pays its farmers to maintain and replant their forests for all these reasons. In a capitalist world my notions are likely forest dreams; enforceable on public land if the government and the people desire.
The usual fate of forestland in the modern world is to become building lots. Inland from the sea along the Gulf of Mexico in the southern United States were so-called wet pine savannahs. These were grassy meadows with scattered pines growing on waterlogged clay soils, amidst tupelo-cypress swamps. The wet savannahs formed a narrow band between the drier piney uplands and the brackish marshes of the Gulf. The savannahs and the uplands were partly maintained by fire. The savannah soils were naturally acid and nutrient-poor and filtered the water flowing into the coastal marshes. They were the preferred habitat of the Mississippi sandhill crane, now much reduced in numbers. These wetlands, like many southern coastal wetlands, were ditched and drained by timber companies after the Second World War to grow slash pine on short rotations for paper pulp. Fire on the plantations was supressed. Drainage removed the filtering effect of the savannahs, increasing the nutrient flow to coastal waters. After a few rotations, the timberland was sold off for building lots, as air conditioning made life in the Deep South more comfortable, and a rising standard of living made life there more available.
There are other stories. The Menominee Indian Reservation in northeastern Wisconsin includes 220,000 acres of forestland. The forest has been commercially harvested for 140 years, with approximately 2 billion feet of lumber removed from the forest over that time. The volume of standing timber now is greater than when the reservation was established in 1854. The Menominee management program predates current concepts of ecosystem management. The Menominee must log (to support the tribe) and try to manage the forest so as to maintain a more or less even flow of sawtimber and pulpwood. They try to maximize the quality as well as the quantity of sawtimber, with a sustained yield of material, and a diverse mix of native tree species. Harvests are based on excess stocking of overstocked stands. When the stocking rate becomes too great for the site, trees are cut. Trees are let grow as long as they remain healthy and vigorous. Thus the forest contains many large old trees of great value (habitat for the insects and lichens of old-growth forest, great producers of mast). The Menominee cut trees no faster than the forest can regrow, rather than in response to market conditions (say, a rise in the price of red oak logs). Loggers must attend a class in how to cut and skid timber and contracts are terminated if the cutting methods are not satisfactory. About 65% of the forest is managed as a mixed-age forest, with a 15 year cutting cycle. The remainder is managed as even-aged forest. To a casual observer the forest looks pristine. Partly because of the old trees, it contains a much more diverse mix of plants and animals than the surrounding commercial timberland. The Menominee forest has healthy streams. Whether such forests are net accumulators of carbon isn’t certain: the above-ground part of the forest has grown in mass and the soils have probably continued to increase their stored carbon, but 2 billion board feet of wood (about 170 million cubic feet or, counting waste, branches and tops, about double that in woody material) have been removed, and much of its carbon returned to the atmosphere.
In the Acadian Forest Region of the Canadian Maritimes (a division of the Northern Hardwood Region), some writers claim a well stocked 100 acre woodlot will provide full time employment for 4 people, if the logs are sawn into lumber and dried and sold from the lot. The sawdust and slabs, if not burned for heat, are used on the wood roads. (Using these materials on roads slows their conversion to carbon dioxide. Converting them to biochar in a small furnace at 180º C. with a citric acid catalyst makes a soil amendment—biochar charcoal—that greatly increases the productivity of agricultural soils and keeps the carbon out of the atmosphere for several thousand years.) Four employees may be an overestimate but is comparable to those employed in Swiss woodlands. Much depends on the productivity of the site and on the price of lumber. I would think one person per 100-200 acres is a more reasonable estimate for much of the Northern Hardwood Region. This however is much less than the acreage required to keep a modern woodcutter busy (800 acres per job in Canadian industrial forestry). Such woodlands, like the Menominee forest, are managed for their long-term productivity. Sawing the lumber on site lets work in the woods be done when conditions (weather, the state of the ground) are appropriate. Logging might only occupy three months a year. The rest of the year would be spent sawing lumber, working up firewood, thinning, working on roads, perhaps making maple syrup, or renting simple summer cabins. The investment per person in such enterprises is much lower than in modern wood production. Jobs per log or board foot are higher. (Not usually a good thing in the modern world, but it is costs per board foot that matter.) One theory of civilisations’ collapse proposes that as the complexity of a society rises, its costs per unit of investment also rise, and the marginal returns on investment decrease. That is, investment produces declining (or negative) returns. Finally, this decrease in returns (from private investment in manufacturing and agriculture, from public investment in education, a military establishment, public safety and public works) bankrupts the society, which can no longer meet its obligations. Improving the yield of woodland, or of the agricultural landscape, so as to provide a constant flow of high value material provides one way out this impasse.
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