Click for next page ( 117


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 116
lo Vanishing Forests and Vanishing Species Human activity has altered nearly every landscape on earth, but none so extensively as the expansive tracts of forest that have been cleared for agriculture, settlements, and logging. Much of today's farmland in North America was covered with forests only a few hundred years ago. Forest clearing for agricultural and industrial purposes had created the pastoral, managed land- scapes of France, England, and Germany by the eighteenth and nineteenth centuries. While forest clearing still continues in some parts, Europe and North America have more forests overall than they did a century ago. As people migrated from rural areas to cities in the transformation from an agrarian to an industrial society, the .. . ~ . `, ~ ~ ~ O farms they abandoned often reverted to woods. Recently, scientists and the public have focused their con- cern on deforestation in the tropics, particularly because tropical forests contain more than half of the world's plant and animal species and because tropical soils are notoriously unproductive once cleared of their forest cover. They are also concerned be- cause as trees are cut and burned, or as they decompose, they release carbon back to the atmosphere, adding to the carbon re- leased as humans burn fossil fuel to satisfy their energy needs. 116

OCR for page 116
VANISHING FORESTS AND VANISHING SPECIES 117 Deforestation in the tropics has accelerated dramatically since World War TI, but estimates of the area covered by the worId's tropical forests anct the rates of deforestation vary wide- ly, mainly because countries use different survey procedures and definitions of "forest" and because satellite images of the entire globe are expensive and difficult to analyze. Simply put, we do not have reliable and up-to-date information on how much of the earth's surface is covered by forests and how fast it is being cut down. The most extensive assessment of the state of tropical forests was a 3-year investigation in the late 1970s by the U.N. Food and Agriculture Organization and the U.N. Environment Pro- gramme. The study revealed that just three countries Brazil, Indonesia, and Zaire contain a major share of the worId's trop- ical forests. The study focused on two basic forests types. The first, closed tropical rain forests, have a relatively tight canopy of mostly broad-leafed evergreen trees sustained by 100 centime- ters (256 inches) or more of annual rainfall. The seconct, open tropical forests, have a canopy that is not continuous but covers more than 10 percent of the ground. When both types are con- sidered, Brazil contains 26.5 percent of the world total, Zaire 9.2 percent, and Indonesia 6.! percent. Peru, Angola, Bolivia, and India each have about 3 percent. The remainder is distributed among some 70 other tropical countries. The study concluded that about I! million hectares (about 27 million acres) of tropical forest is disappearing each year and that rates of deforestation vary greatly from country to country. In Zaire, for instance, deforestation rates were as low as 0.2 percent per year (which amounts to 1.S million hectares defor- ested each year), but in the Cole d'Ivoire rates were as high as 7 percent (which amounts to 2.9 million hectares). Based on these rates, tropical rain forests would disappear altogether within 25 years from four countries in the Americas, three countries in Africa, and two countries in Asia. Within 50 years, tropical rain forests wouIcl vanish from 13 additional countries. Philip Fearnside, of the Brazilian National Institute for Ama- zonian Research, analyzed satellite photographs to decipher de

OCR for page 116
118 THE FACES OF GLOBAL ENVIRONMENTAL CHANGE forestation trends in the Brazilian Amazon. His analysis in- dicates that deforestation in the Brazilian Amazon is highly concentrated in areas where colonization and immigration are intense, such as Rondonia, and that rates of deforestation in- creased exponentially between 1975 and 1980. Eneas Salati, a hydrologist and climatologist at the University of Sao Paulo in Brazil, and his colleagues calculate that if current trends continue, forests will be completely cleared from most of the Amazonian states by the year 2000. WHY ARE THE FORESTS DISAPPEARING? In developed countries, the competing interests of loggers, developers, naturalists, hikers, and hunters pose a challenge for forest management, but these conflicts pale in comparison with the challenges in developing countries. in poor countries, hun- dreds of millions of people depend on the resources from the forest for their very survival land for their crops, fuel wood for cooking, and fodder for their animals. Governments, too, look to forests to provide much-needed foreign exchange as de- mand grows in the richer developed countries for exotic tropical hardwoods. The reasons for deforestation in the tropics are many. Rapid- ly increasing populations need land on which to grow food. Land is concentrated in the hands of a few, leaving millions in search of unclaimed parcels. Roads and highways are built, making the forests accessible. One of the agents of deforestation is shifting cultivation, a practice in which subsistence farmers clear and burn a plot of land in the forest, grow crops for one or a few years, and then al- low the land to remain fallow for several years before repeating the cycle. This age-old method of subsistence agriculture recy- cles nutrients to the soil and maintains productivity of the land without fertilizers, provided the fallow period is long enough to regenerate the forest growth. But with increasing population and pressure on the land, in many places the fallow period is

OCR for page 116
VANISHING FORESTS AND VANISHING SPECIES 119 cut short. Eventually, the soil becomes unproductive, crops no longer flourish, and the trees do not grow back. The assessment by the U.N. Food and Agriculture Organization and the U.N. Environment Programme in the late 1970s estimated that shift- ing cultivation causes 70 percent of deforestation in Africa, 50 percent in Asia, and 35 percent in the Americas. in densely populated countries, such as Ethiopia and India, with little or only seasonal rainfall and open woodlands, defor- estation occurs as people gather firewood for fuel and fodder for animals. The U.N. Food and Agriculture Organization es- timated in a 1983 report that, worldwide, three quarters of the 2 billion people who rely mostly on wood for fuel are cutting wood faster than it is growing back. With less wood available, women, the traditional fuel wood gatherers, have no option but to collect cow dung, which once would have fertilized the soil, for cooking fuel. Deprived of nutrients, the ability of the land to regenerate forests is compromised further. In the Amazon, the opening of highways over the last 20 years promoted new and easy access to forested areas. The expancled access, combined with government incentives for de- velopment of the region, made it possible for the activities asso- ciated with rapid deforestation to take place land speculation, cattle ranching, timber extraction, clearing for cash crops like rubber, cocoa, and sugar cane, and exploration for of! and min- erals. Government policies, too, have a large influence on how forests are used. Robert Repetto, an economist at the World Resources Institute, concluded in a 1988 report that tax and tracle regimes, land tenure laws, agricultural resettlement programs, and administration of timber concessions with loggers are but a few of the policies that aggravate deforestation. He finds that these policies can contribute significantly to the wasting of forest resources. In the Brazilian Amazon, for instance, generous tax credits created over 12 million hectares of large cattle ranches, even though most of the ranches would have been unprofitable without these subsidies.

OCR for page 116
20 THE FACES OF GLOBAL ENVIRONMENTAL CHANGE SOIL EROSION, RAIN MACHINES, AND CARBON Why are forests such an important part of the earth system? On a local scale, trees protect the soil from rain and wind that would otherwise wash or blow it away. Despite the image of luxuriant growth in tropical forests, most of the soils that support them are remarkably unproductive. High temperatures and rainfall throughout the year encourage leaching of nutrients from the soil, so that few nutrients remain except for those held by the plants themselves. Once forests are cleared for agriculture, grazing, or log- ging, there is no guarantee that the trees can grow back on the impoverished soil. Haiti, for example, deforested over the centuries, sports a landscape dominated by sparse grasses and bare mineral soil and bedrock. In Haiti and other areas where deforestation has been extensive, such as in the AtIantic coast of Brazil and the mountains of southern China, not only may the soil be damaged but there are few adult trees to provide seeds for new forests. Soil erosion is a natural process. Without it, deltas would not form as soil erodes from the land and travels as sediment through streams and rivers. But the soil exposed in a defor- ested site greatly accelerates this natural process, so much so that some dams have filled with sediment far more rapidly than expected. Salati explains that, although there are very few stud- ies of soil erosion and river sediment loads in tropical areas, the few existing data do show that erosion losses can be 100 times greater in soils changed to agricultural use when compared to similar soil covered with forest. On a regional scale, forest ecosystems recycle the rainwa- ter back to the atmosphere through evaporation from the soil and leaf surfaces and through transpiration from plants, a pro- cess so efficient that ecologists refer to tropical forests as "rain machines." The rainfall patterns in the Amazon basin, and prob- ably other regions such as the Brazilian central plateau, depend on the existence of the forests. Salati and colleagues, study- ing the effects of deforestation on the recycling of rainfall in the

OCR for page 116
VANISHING FORESTS AND VANISHING SPECIES 121 central Amazon, point out that in a healthy stand of rain forest, about half of the rainfall is evaporated from the surface of soils and leaves or transpired by plants and the other half runs into streams and rivers, eventually returning to the ocean. With deforestation, this vigorous recycling of water will weaken and couict react to lower rainfall in the region. The rapid runoff of rainfall from deforested areas has led some scientists to link the 1988 flood in Bangladesh to defor- estation in the Himalayas. in the worst flood in Bangladesh's history, two thirds of the country was under water for several days, and 25 million of the country's Il0 million people were left homeless. The researchers hypothesize that deforestation has made the upland watersheds of the Himalayas less able to store water and moderate the flow of water into the streams, in turn accelerating the flow of water into the Brahmaputra River and exacerbating flooding as the river flows into the Bay of Bengal. Forests assume an essential role on the global scale. The forest cover absorbs energy that would reflect back to the at- mosphere if the soil were bare. Plants take up carbon from the atmosphere as they grow, and release carbon back to the atmosphere when they are burned or die and decompose. On balance, if the amount of forest cover were to remain constant, the uptake would equal the release of carbon over the long term. But as more trees are cut than are planted worldwide, more car- bon is released to the atmosphere than is stored, adding to the carbon dioxide being released from the burning of fossil fuels for energy. Salati, with colleagues Reynaldo Luiz Victoria, also of the University of Sao Paulo, Luiz Antonio Martinelli, of the Centro de Energia Nuclear na Agricultura of Brazil, and Jeffrey Richey, of the University of Washington, find, based on a large range of estimates about rates of deforestation and how much biomass the forests contain, that annual emissions of carbon dioxide from deforestation in the Amazon alone account for 4 to 25 percent of carbon dioxide emissions to the atmosphere worldwide. Other estimates indicate that deforestation could

OCR for page 116
122 THE FACES OF GLOBAL ENVIRONMENTAL CHANGE account for about 20 percent of the buildup of carbon dioxide in the atmosphere. The difficult task of estimating how much carbon is entering the atmosphere because of deforestation is complicated further because plants themselves respond positively to increased con- centrations of atmospheric carbon dioxide. Like sunlight, wa- ter, and nutrients, carbon dioxide is required for plant growth. With an increase in atmospheric carbon dioxide, growth can proceed more rapidly, which in turn would theoretically in- crease the amount of carbon dioxide that trees could remove from the atmosphere. Researchers have observed that in green- houses growth rates do increase over the short term when plants are fumigated with carbon dioxide. But there have been very few long-term experiments on mature trees in their natural set- tings. Quite simply, the question of whether increased con- centrations of atmospheric carbon dioxide will stimulate plant growth enough to offset some of the carbon being released to the atmosphere from deforestation is an open one. Another open question is how global warming itself could alter the distribution of forests and consequently change the amount of carbon taken up from the atmosphere. Climate mod- elers generally agree that temperature increases from human- induced global warming would be greatest in the high lati- tudes. The tropics would experience only modest temperature increases. So those forests in the high latitudes of Canada, Alaska, the Soviet Union, and Scandinavia might expand north- ward into areas previously covered by tundra vegetation. Areas now covered with grasses would store more carbon in their biomass if they became forests. But these possibilities are spec- ulative and require a great deal of scientific investigation. Because of the\ important role of forests in determining the amount of carbon in the atmosphere, some researchers argue that reforestation could help counteract the buildup of atmo- spheric carbon dioxide from human activities. Roger A. Sedjo, a senior fellow at Resources for the Future, and colleagues cal culate that new forest plantations covering an area of approx- imately 465 million hectares would be required to remove 2.9

OCR for page 116
VANISHING FORESTS AND VANISHING SPECIES 123 ., ~ -''1'-''-'-''-' ~7 I .. : \ ~ if-' / / at r ~ ~ at' ~V//I/~///I///' ~1 -- K//~ ~ A? _ : ~: ~\ ',, ~ ma. An area approximately equal to the 465 million hectares of newly planted forest that would remove the 2.9 billion tons of carbon added annually to the atmosphere. (Reprinted, by permission, from Norman J. Rosenberg et al., eds. 1988. Greenhouse Warming: Abatement and Adaptation, Fig. 8-1, p. 114. Copyright A) 1988, Resources for the Future.) billion tons of carbon, the amount of carbon accumulating each year in the atmosphere. it is unlikely that trees will be planted on this scale, but reforestation projects could make modest dents in the accumulation of carbon dioxide and, at the same time, provide other benefits for water quality and for species that live in the forests. VANISHING SPECIES it is nearly impossible for a biologist to be present at the precise moment when the last individual of a species languishes in a tropical forest. Nevertheless, with the clearing of tropical rain forests for agriculture, grazing, and other uses necessary to support the worIcl's population at a satisfactory standard of living, we know that habitats are destroyed and many species of plants and animals are irreversibly lost before scientists can even identify them.

OCR for page 116
124 THE FACES OF GLOBAL ENVIRONMENTAL CHANGE Human civilization has always been dependent on the natu- ral diversity of living organisms. In the course of history, people have exploited about 7000 species for food. But the species that we have used to support the human population are only a small fraction of the total number of species on earth. Some 1.4 million species have been identified and given scientific names, but sci- entists estimate that millions more have not yet been identified, particularly in the species-rich tropics. Until the 1980s, estimates of the total number of species on earth ranged between about 3 million and 10 million species. Terry L. Erwin, of the Smith- sonian's National Museum of Natural History, later discovered huge numbers of insect, particularly beetle, and other arthropod species in the forest canopies of moist tropical forests in Brazil and Peru, causing him to revise his estimate of the worldwide number of insect species alone to 30 million. Scientists and the public worry that, with deforestation and the loss of natural habitat, many of these species will be gone before they are even known to exist. Trends in the moist forests of the tropics, which cover only 7 percent of the earth's land sur- face but contain over half of the worIcl's species, are especially of concern. These rain forests are incredibly diverse and rich in species, particularly species of insects and flowering plants, though ironically the species that live in rain forests are the least well identified. Thomas Lovejoy, of the Smithsonian Institution, estimates that between 15 and 20 percent of all species will become extinct by the year 2000 because of the destruction of tropical forests. Ecologists have identified "hot spots" around the world where habitats rich in species are in imminent danger. Several areas stand out, according to Norman Myers, an environmental consultant with extensive experience in the tropics, including the Choco forest of Colombia, the Napo center of diversity in Peruvian Amazonia and other centers around the fringe of the Amazon basin, the Tai Forest of Cole d'Ivoire, the montane forests of East Africa, the relict wet forest of Sri Lanka, the mon- soon forests of the Himalayan foothills, northwestern Borneo,

OCR for page 116
VANISHING FORESTS AND VANISHING SPECIES 125 certain lowlands of the Philippines, and several islands of the South Pacific. Why does it matter if a lone, unidentified species should go extinct? After all, extinctions have occurred in the past. The history of life is punctuated by five massive extinction episodes, the last of which is most noted because it markec! the end of the age of the dinosaurs and the beginning of the age of mammals. Such extinctions changed the course of evolutionary history, and the extinctions caused by humans will be no exception. Edward O. Wilson, a biologist at Harvard University, estimates that the rate of species loss from deforestation is about 10,000 times greater than the naturally occurring background extinction rate that existed prior to the appearance of human beings. From a human point of view, the loss of a species is the loss of a potentially valuable contribution to humanity. At least 75,000 plant species have edible parts, for instance. Some of these species are superior to those widely used today. The trop- ics have provided the world with most of its ectible species by far. Few people realize, as Mark Plotkin, of Conservation International, points out, that a typical American breakfast of cornflakes, bananas, sugar, coffee, orange juice, hot chocolate, and hash brown potatoes is based entirely on plant species that originated in the tropics. Many currently underexploited tropical species could become familiar sights in U.S. supermar- kets. Other tropical species provide important ingredients for pharmaceuticals, fibers, and petroleum substitutes, like the rosy periwinkle of Madagascar, which provides the basis for an ex- tremely effective medication for Hodgkin's disease and acute lymphocytic leukemia, and the babassu palm of the Amazon basin, which produces oil. No one knows how many other species have the potential to provide similar benefits to society. The diversity of species and populations also constitutes the world's available gene pool, which in the words of Wilson "is one of our planet's most important and irreplaceable resources." Every microorganism, animal, and plant contains from ~ mil- lion to 10 billion bits of information In its genetic code, the product of thousands or millions of years of evolution. Scientists

OCR for page 116
126 THE FACES OF GLOBAL ENVIRONMENTAL CHANGE _ . _ \.4 _ <` 'I ~ 'A - <174: ~ 1~ / if ~ ~ c A////// / Oc dig o ~ 0 400k m , . . . . a Present and future range for a common forest tree, eastern hemlock (Tsuga canadensis), under climate scenarios predicted by two climate models (a and b). Horizontal shading is the present range and vertical shading the potential range, with effective carbon dioxide doubling. Cross-hatched area of overlap is where the trees are likely to be found 100 years from now. Relict colonies might persist to the south in pockets

OCR for page 116
VANISHING FORESTS AND VANISHING SPECIES / \ A.] 127 - --~ \ ^~/////: ~ O4, i, ; ~0 KEY 0 400km b of favorable environment. Significant advance to the north is unlikely, as rates in the past were about 25 kilometers per 100 years, and the most rapid rate known from the fossil record (for spruce) is only 200 kilometers per 100 years. As a consequence, much of the potential range will remain unoccupied. (Reprinted from Toward an Understanding of Global Change. National Academy Press, Washington, D.C., 1988.)

OCR for page 116
28 THE FACES OF GLOBAL ENVIRONMENTAL CHANGE take advantage of this genetic richness to improve those species that are used by humans. Commercial species are continuously crossbred with their wild relatives to improve yield, nutritional quality, responsiveness to different soils and climate, and re- sistance to pests and diseases. Because many of the world's important crop species originated in the tropics, their relatives that provide the means to maintain and improve our crops can only be found there. A wild relative of the domestic tomato- discovered in 1962 quite by accident while Hugh Iltis, director of the University of Wisconsin Herbarium, was waiting to pass a landslide on an excursion in the Peruvian Andes after al- most two decades of research increased the sugar content of the tomato and raised its commercial value by millions of dol- lars. Other species provide singular genetic material for use in medicines. The birth control pill, for example, has its origin In the Mexican yam. Apart from the reasons for maintaining tropical species solely for the purposes of human exploitation, many take the more philosophical view that humans are stewards of the planet and have responsibility for maintaining its diversity. Instead we are eradicating in the blink of an evolutionary eye species that have evolved over the course of millions of years. Even as deforestation threatens biodiversity, the predicted changes in climate portend more stress on the world's plant and animal species. When temperature and precipitation patterns change, so does the geographic range over which a particular species can survive. Robert Peters, an ecologist with the World Wildlife Fund, explains that even very small changes of less than 1C have caused substantial changes in range during this century. The white admiral butterfly and the comma butterfly, for example, greatly expanded their ranges in the British Isles during the past century as the climate warmed about 0.5C, and the birch responded rapidly to warming during the first half of this century by expanding its range north into the Swedish tundra. Unlike animals, plants must rely on mechanisms that dis- perse their seeds mainly animals and winds to adapt to changing conditions. Margaret Davis and Catherine Zabin

OCR for page 116
VANISHING FORESTS AND VANISHING SPECIES 129 ski, both of the University of Minnesota, forecast the future response of some hardwood species eastern hemlock, yellow birch, beech, and sugar maple to the expected changes in cli- mate. On the basis of climatic conditions projected by two of the general circulation models for an effective doubling of car- bon dioxide, the researchers predict that the species would need to migrate northward by 500 to 1000 kilometers (310 to 620 miles) to remain in their suitable climate. Beech, for instance, which now grows east of the Mississippi River from southern Canada to Florida, would have to shift into New England and southeastern Canada as far north as Hudson Bay. The key question is: How quickly can a species migrate as its suitable habitat changes? Some 10,000 to 12,000 years ago as the last glaciers retreated and temperatures rose 3 to 5C (5.4 to 9F), species of forest trees migrated at rates of 25 to 40 kilometers per century, with the fastest migration by spruce into northwestern Canada at 200 kilometers per century. Analyses of fossil pollen grains indicate that beech forests moved about 20 kilometers per century, far less than Davis and Zabinski indicate would be necessary to keep pace with climate changes projected for the coming century. The rates of climate change predicted for the next century are possibly 40 times faster than at the end of the last ice age. No one knows whether plant species would be able to keep up. For certain, each individual species would respond in its own way. Some may go extinct, and others may survive in reduced numbers or with changes in their geographic distributions. As various species respond, they would be likely to form commu- nities of plant species that are different from those that we have today. Even species that could keep pace with climate change would encounter barriers as they migrated. Cities, oceans, or mountain ranges could get in the way, especially in the case of species isolated in reserves clesigned for the very purpose of conserving them. As Peters explains, conservationists have heretofore managed an unchanging world. "Now we know this is not so," he notes. "The world changes and our conservation plans must change with it."

OCR for page 116
]30 THE FACES OF GLOBAL ENVIRONMENTAL CHANGE PROTECTING THE FOREST RESOURCES While policymakers and the worId's leaders struggle to ad- dress the root causes of deforestation, successful projects around the world demonstrate that it is possible to reconcile economic development with preservation of tropical forests. The project started in 1984 to protect the Khao Yai National Park in northeastern Thailand and simultaneously to provide benefits to villagers living nearby is one such example. Wild elephants were a central theme in the conservation plans. Not only have the elephants been protected, they also have attracted tourism, which benefits the villagers. In 1985 a project on "rural development for conservation" was begun in the nearby village of Ban Sap Tai to offer agricultural assistance, credit, health care, and education. The improvements in economic conditions have reduced the villagers' dependence on the park and their incur- sions to cut trees, plant maize, and poach plants and animals. Similar projects have been implemented that preserve for- ests while allowing the land to be used for agriculture, forestry, or watershed management. Such projects illustrate that the technology and knowledge exist to preserve the worId's trop- ical forests. Judith Grac~woh! and Russell Greenberg, both of the Smithsonian Institution, analyzed case studies of such suc- cessfu! projects. They find that the projects are most likely to succeed when local people participate in the planning and im- plementation and when the plan itself is both environmentally and economically sound. For example, forest reserves can offer an economic return through sustainable agriculture anct forestry and through gathering of nonwood forest products such as latex, fibers, fruits, nuts, and a host of other miscellaneous products. Gradwoh! and Greenberg explain that most environmentally ori- ented projects will not produce as much immediate economic gain as ecologically disastrous exploitation such as cattle ranch- ing and uncontrolled timbering. But "if the goal changes to include both profits and well-being of forests, then ecologically based schemes compare very favorably."