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.