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Mining has become a major economic activity in Amazonia. The environmental impacts of mining operations by corporations are largely localized and of minimal significance, particularly since some earlier water pollution concerns have been addressed. At most, 4,500 km of forest is likely to be cleared to gain access to all known exploitable mineral deposits in Amazonia (Hoppe 1992). Settlement and development activities associated with the poles of growth generated by mining concerns are likely to have more widespread impacts.
Bauxite mining requires the removal of large quantities of overlying soil, and if precautions are not taken sediment can be washed into nearby watercourses. At one point, seven miles of Lake Batata near Minerac,ao Rio Norte on the Trombetas had filled in with reddishbrown soil, thereby killing trees and destroying fish and wildlife habitats (Mee 1988: 279). Corrective measures have been taken by building a siltation pond, and Lake Batata is being restored.
Mineração Rio Norte, which operates the bauxite mine along the Trombetas, eventually replants areas scraped to gain access to the aluminium ore. Topsoil is stockpiled and then spread back once an area has been mined. Several native trees are planted to speed up restoration of the land (Gradwohl and Greenberg 1988:173). Such recuperation efforts are costly, but Mineração Rio Norte is demonstrating leadership in environmental management, and technologies developed by the company are likely to prove useful at many other mining sites in the humid tropics.
The manganese field at Serra do Navio in Amapa has been mined by ICOMI since the early 1960s, and is nearing the end of its economic life. The ore is taken by rail to Porto Santana, a deep-water port on the northern bank of the Amazon. Sizeable oil-palm plantations and smallscale settlement have sprung up along the railroad. The manganese mines still operating in the vicinity of Serra do Navio are well managed and do not provoke any significant ecological damage. Oilpalm plantations along the railroad are well adapted to the climate and soils of the region and provide good ground cover.
At Carajás, forest-clearing around mines is minimized, and road and rail sidings are planted to Brachiaria humidicola, a perennial grass from Africa. Holding ponds to decant mining sediment have also been established by Companhia Vale do Rio Doce (CVRD) at Carajas. Outside the 400,000 ha concession granted to CVRD at Carajás, forest-clearing by farmers and ranchers is rampant, particularly along the 890 km railroad to Itaqui in Maranhão. The lesson learned here is that sound environmental management practices within a concession are no guarantee that natural resources will not be destroyed around the periphery. A broader, more integrated approach to regional development is thus called for that explores the linkages and interactions between land-use systems.
Itinerant gold miners and mercury pollution
In contrast to most corporate mining operations, small-scale gold-mining activities in Amazonia are causing widespread ecological damage. According to official figures, itinerant gold miners unearthed US$13 billion worth of gold in the Brazilian Amazon between 1980 and 1988 (Almeida 1992). The gold rush in Amazonia during the 1980s rivalled the California gold rush of the nineteenth century and is exceeded only by production from the mines of South Africa (Godfrey 1992). Clandestine gold trading probably increased that figure several fold. Little wonder that gold mining has attracted so much attention in the Amazon, even though few miners ever become wealthy.
Itinerant gold mining is causing one of the most serious environmental problems in Amazonia today: mercury pollution. Itinerant miners use the toxic element to precipitate gold when washing gravel. Between 5 and 30 per cent of the mercury is lost during this process, and much of the mercury finds its way back to water (Maim et al. 1990). A further 20 per cent vaporizes when the amalgamate is torched to obtain the gold, both in the field and in goldbuying stores. The high rainfall and humidity in the region facilitate reoxidation of vaporized mercury. Mercury pollution of the air is particularly acute in the districts of certain towns where gold stores tend to concentrate (Biller 1994: 8).
Approximately half a million gold miners (garimpeiros) were operating in Amazonia during the early to mid-1980s (Mallas and Benedicto 1986). In the 1990s, the gold fever has cooled somewhat, especially in Rondônia and southern Pará, but several hundred thousand men and women are probably still engaged in gold mining in the Brazilian Amazon. By the late 1980s, about 100 metric tons of gold were being exported annually from the Brazilian Amazon. For every kilogram of gold produced, an estimated 1.32 kg of mercury is lost to the environment - 45 per cent into rivers and streams and 55 per cent into the atmosphere (Pfeiffer and Lacerda 1988). Some 100 tons of mercury were thus finding their way into the region's ecosystems at the close of the 1980s (Nriagu et al. 1992).
Mercury has been employed in gold and silver mining in Latin America since early colonial times, but the current scale of mercury use for mining is unmatched. A Mexican miner, Bartolome de Medina, devised a process for extracting silver from its encasing ore with mercury in the mid-sixteenth century (McAlister 1984: 228). Mercury was used extensively as an amalgam in silver mining in Mexico and Peru during the sixteenth and seventeenth centuries. The Spanish employed quicksilver to refine a little gold in Hispaniola in the sixteenth century.
Brazil depends on imports for its mercury needs, and most of it is consumed by the informal gold-mining sector (Biller 1994: 6). Itinerant miners account for more than 70 per cent of Brazil's gold production, so the use of mercury is highly diffused in Amazonia and would be hard to control. Technologies exist for reducing mercury contamination, such as the use of retorts when torching amalgam, but thus far they have not been widely adopted.
During the colonial period in Colombia, placer miners separated gold from sediment rich in iron oxide by employing the glutinous sap of several plants, including crushed leaves of cordoncillo (Piper sp.), encinillo (Weinmannia sp.), and chica (Jacquinia aurantiaca). When mixed with water, the foamy sap captured the iron oxide flakes, allowing the gold particles to settle to the bottom of the pan (West 1952). Organic precipitates would be much more environmentally benign than mercury, although Jacquinia aurantiaca is a piscicide. Such ancient practices are worth investigating, particularly to compare gold recovery rates with mercury.
Gold mining in rain forests is not confined to Amazonia, although it is most prevalent there. Large numbers of itinerant miners are operating with mercury in other regions, such as southern Guyana, Venezuela, and parts of Central America (Parsons 1955). Gold miners had to be evicted from a park on the Osa Peninsula of Costa Rica where they were clogging rivers with sediment. The Costa Rican government relocated the miners at considerable expense. In southern Guyana, dredgers are sucking up river beds and discharging large quantities of sediment back into the water, thereby altering its turbidity.
Although gold has been panned from alluvial deposits in the Tapajos valley since the 1950s, the Amazon gold rush started in earnest in 1980 when gold prices soared to US$850 per ounce. International investors had apparently grown anxious about the Iran-Iraq war and were buying substantial quantities of gold on the world market.
The most celebrated gold find in Amazon was at Serra Pelada, approximately 100 km south-west of Marabá in January 1980; within a few months, 20,000 garimpeiros had swarmed to the mountain once isolated in a sea of forest (Santos 1981: 161; Schmink 1985). In June 1980, Serra Pelada was producing about 6 kg of gold per day, and by 1986 the mountain had been reduced to a gaping pit, 110 metres deep (Mallas and Benedicto 1986). By 1990, most of the gold miners had moved on, but much of the forest around Serra Pelada had been cleared by settlers.
Every state in the Brazilian Amazon is currently experiencing a rapid influx of fortune-seekers. Regional airports, such as at Monte Dourado in Para and Boa Vista in Roraima, are hives of activity, with small planes constantly ferrying miners and their supplies to and from remote airstrips. During the height of the gold rush in the 1980s, other regional airports, such as Santarém, Itaituba, and Maraba in Para, Alta Floresta in Mato Grosso, and Porto Velho in Rondônia, also witnessed swarms of single- and twin-engined aircraft serving far-flung gold-mining camps.
The gravity of the mercury pollution problem has attracted the attention of the national press in Brazil. Few data are available, though, to assess the dimensions of mercury accumulation in fish. Mercury concentration in rivers and streams varies markedly by location, and mercury contamination in fish also varies according to species (Biller 1994: 8). Some Kayapó Indians have acquired dangerously high levels of mercury, presumably from eating fish and drinking water from polluted rivers and streams (Hecht and Cockburn 1989: 143). Of 106 individuals sampled in four communities in the Tapajós watershed, over 60 per cent had mercury levels in their urine high enough to warrant regular testing as recommended by the World Health Organization (Thornton et al. 1991). Around half of the 97 river sediment samples taken from the Tapajós and its effluents exceeded the 1 ppm mercury considered the limit for safety by the Brazilian environmental secretariat (Thornton et al. 1991).
Predatory fish, such as tucunare, pirarucu (Arapaima gigas), aruanã (Osteoglossum bicirrhosum), most species of piranha, and many species of catfish, are likely to accumulate mercury more rapidly than herbivorous species. In the Madeira river system, several species of predatory fish, such as dourado (Brachyplalystoma flavicans), filhote (B. filamentosum), and other catfish (Pseudoplatystoma spp.), have accumulated high levels of mercury, up to 3.81 fig mercury/g (Maim et al. 1990; Pfeiffer et al. 1989). Levels of mercury in excess of 0.5 Gig are generally considered a potential threat to human health. These large catfish are frozen and sent to markets in the United States and central and southern Brazil (Goulding 1981). Omnivorous fish, such as highly prized tambaqui (Colossoma macropomum), and eggs of detritus feeders, such as Scarf catfish (Loricariidae), have also been found with high levels of mercury along the Madeira River (Martinelli et al. 19B8). Preliminary analyses of fish and human hair along the margin of the Tucurui reservoir also reveal that mercury is entering the food chain along the Tocantins River (Braunschweiler 1991).
If mercury levels rise in fish, an important source of protein in the region, then the poor are especially likely to suffer. If the region's fish become unsafe to eat, wealthier inhabitants can more easily turn to beef, chicken, or imported fish. The long residence time of mercury in river sediments can contribute to health hazards long after the goldmining frontier has moved on (Fuge et al. 1992), so damage from gold mining in Amazonia may be felt for decades to come. A trend towards gold mining from barges in rivers, such as the Madeira and the Negro, is particularly worrisome in this regard. In 1985, some 1,400 boats were pumping up sediment from the bottom of the Madeira in search of gold (Pfeiffer and Lacerda 1988).
The spectacular surge in gold mining is having other adverse environmental effects. Gold-mining camps are among the worst areas for malaria transmission in Amazonia. Gold miners may be introducing new strains of malaria (Plasmodium falciparum and P. vivax) to which local populations have no resistance. Thus Indians are likely to suffer more severe malaria symptoms if gold miners are operating nearby. In Roraima, for example, hundreds of Yanomami Indians have succumbed to malaria, owing in part to infections brought in by the nearly 20,000 gold miners who started arriving in 1987 (Robinson 1991). In a two-week period in 1992, 44 Yanomamo died from malaria in the Parafuri village alone.
Gold miners are likely accelerating natural selection among malaria parasites for resistance to drugs used for prophylaxis and treatment. In some areas, miners are apparently employing drugs that are usually reserved for treating chloroquine-resistant strains of falciparum malaria. In the early 1970s, Fansidar was the drug of last resort for treating infections of falciparum malaria that would not respond to chloroquine treatment. Now Fansidar is largely ineffective in most areas of Amazonia, in part because miners have used the drug as a prophylaxis, thus increasing selection pressures for resistance.
The treatment and prophylactic strategies of gold miners warrant further study. A first impression was that gold miners often suffered so much from malaria because they were not taking adequate precautions, ranging from the use of mosquito nets to standard prophylaxis with chloroquine. If, on the other hand, significant numbers of miners are using last resort treatments for chloroquine-resistant falciparum malaria, such as mefloquine and doxycycline, as a prophylaxis then malaria is likely to become an even more widespread public health problem in the Amazon basin.
Although mercury contamination and invasion of indigenous lands remain serious issues in Amazonia, these threats have abated to some degree in the 1990s. Gold prices plunged to about US$340 an ounce in early 1993, and many garimpeiros have returned from mining camps to seek their fortunes elsewhere. The end of the Cold War has probably calmed investors' fears and the lustre of gold has diminished somewhat. The closing of many gold shops in Santarem and Porto Velho, as well as diminished small plane activity at such airports as Santarém and Itaituba, are symptoms of the decline in goldmining activity. The extent to which gold mining has declined overall is hard to tell, and in some parts it is actually on the increase. If gold prices climb steeply once again, gold miners are likely to return in force to the backlands of Amazonia.
Western Amazonia has witnessed some sizeable oil strikes within the past 30 years, and prospecting is under way in several parts of the basin. Most of Ecuador's oil production, some 300,000 barrels/day, comes from the Amazon region. Amazonia may yet become a major oil-producing area.
With current technologies and safeguards, oil drilling does not usually pose undue hazards to the environment. Some water pollution occurs around soil extraction sites, but overall such damage is usually localized. Major pipeline leaks cause much greater damage. Two significant leaks have occurred along the Trans-Ecuadorian Petroleum Pipeline: an earthquake ruptured a 30 km section of the pipeline in March 1987, while a massive landslide caused by heavy rains and deforestation sheared the pipeline in May 1989 (Hicks et al. 1990: 9). Civil unrest has occasionally led to sabotage of oil pipelines in Colombia and Peru; should more pipelines be built in Amazonia, such dangers could increase. On the whole, though, the oil industry is not causing any large-scale pollution of the air or waters in Amazonia. An even greater risk would ensue if large numbers of oil tankers began plying the Amazon. The dangers of running aground or colliding with other ships would increase and oil spills would be disastrous for fish production and many agricultural activities.
Roads created to facilitate petroleum extraction help settlers penetrate the rain forest. Roads built to oil fields operated by TexacoGulf in the Ecuadorian Amazon, for example, have opened up some 2 million ha of formerly undeveloped forest lands (Hiraoka and Yamamoto 1980). By the late 1970s, over 30,000 people had taken advantage of the oil company roads to eke out homesteads in the forest. Currently proven reserves of sweet crude in the Ecuadorian Amazon are expected to be depleted by the late 1990s, but substantial reserves of heavier grades of petroleum have been found in eastern Ecuador, which may be tapped in the twenty-first century.
All the world's cocaine is produced from coca plantations on the eastern slopes of the Andes. The seemingly endless appetite for recreational drugs in industrial countries, and increasingly in developing nations, has spurred coca plantings in areas formerly in forest or planted to food crops. A crop once grown for local consumption has become so profitable that it is now much more widely grown than in the past. Traditionally, coca has been used in two forms: a mild stimulant by chewing the leaves or making tea; and as a snuff in rituals by certain indigenous groups of western Amazonia. Now large quantities of coca leaves are processed to concentrate cocaine. Coca cultivation is consequently spreading further into the Amazon lowlands, including Brazil.
Three latent environmental problems may surface because of the cocaine business: deforestation, coca eradication, and the dumping of chemicals used to process coca leaves into paste. Given the secrecy and peril involved in investigating the coca industry, information on such negative environmental impacts will be difficult to obtain. Presumably, they will have mainly local or regional impacts.
Reliable data on planting rates and the cultivated area in coca are understandably hard to gather. More than 700,000 ha of montane forest have apparently been cut in Peru to grow and process coca (Goodman 1993). More tropical forest in Amazonia has surely fallen at the hands of small farmers to grow coca than has been cleared by miners, both corporate and itinerant. The Andean portion of the Amazon basin is especially rich in biodiversity; it would be ironic if some individuals who partake of cocaine also buy albums and "rainforest" products that purportedly support "sustainable" use of tropical forests. Discussion about using defoliants, such as Spike, to eradicate coca plantations has elicited some concern, particularly from environmentalists and ecologists concerned about the impact of herbicides on non-target plants. Biocontrol efforts may prove more effective, provided they do not attack other plant species. On the other hand, coca bushes may do a better job of securing soil on steep Andean slopes than most food crops. While the international market for cocaine remains strong, farmers will find a way to continue planting a crop that produces a handsome profit.
Poppy fields are sprouting now in the Andes, in response to a resurgent demand for opium and a desire by drug cartels to diversify their product lines. Poppy fields cover at least 20,000 ha in the Colombian Andes (Goodman 1993), and cultivation may spread south into the Amazon basin. This introduced annual does not secure soils well on steep slopes. In discussions about the need for people in developed countries to reconcile their lifestyles with the planet and biodiversity, little attention has been paid to the hedonistic use of drugs. Efforts should be redoubled to educate people about the folly of taking recreational drugs in industrial countries, rather than try and blame coca growers in western Amazonia.
One of the most serious environmental issues associated with coca in Amazonia is the nature and quantity of chemicals used to process coca leaves. In 1986, Peru exported an estimated 6,400 tons of coca paste. Such big quantities would have involved the use of 32 million litres of sulphuric acid, 16,000 tons of quicklime, and 6.5 million tons of acetone.6 In the Upper Huallaga valley alone, coca processors annually dump an estimated 56 million litres of kerosene, 8 million tons of sulphuric acid, and large quantities of acetone, toluene, and carbide (FAO 1990: 12). Coca is also processed in Colombia, Ecuador, and Bolivia. Most of these chemicals and compounds probably found their way into streams and the groundwater in various parts of western Amazonia. If these chemicals are not eliminating fish populations, they may render them unsafe to eat. Such compounds may also trigger mutations in at least some of the fish species important for subsistence and commerce.
The threat of coca-processing chemicals may be diminishing, at least in some areas. In Colombia, for example, coca refiners have recently begun recycling chemicals, rather than ditching them in streams. Such measures do not reflect a concern for the environment; rather they are an effort to circumvent restrictions on the importation or production of precursor chemicals used in processing coca paste.
Of all the issues surrounding environmental change in Amazonia, threats to biodiversity are arguably the most serious in the long run. Species loss as a result of drastic habitat modification, such as logging, is an issue in many parts of the humid tropics, such as in Malaysia (Brookfield, Potter, and Byron 1995). Particularly worrisome is that such biodiversity losses are often not accompanied by any long-term economic benefits to the local people.
The effects of species loss may not be immediately obvious, and are thus not usually considered in economic development plans. Species loss can be hard to quantify in economic terms, and is considered an externality. The impoverishment of habitats is sure to reduce options for future development. Air and water pollution may be more tangible assaults on our living space, but the haemorrhaging of species will drain resources for future generations, quite apart from the ethical and moral questions posed by human-induced extinctions.
Some have argued that we do not really need nature's storehouse of genes because ingenious scientists can concoct novel genes in laboratories at will (Huber 1992). This notion is fallacious. The idea that we can safely dispense with tropical forests or other ecosystems because modern biotechnology has made them redundant is dangerous thinking. Genes need to be synthesized from models. Laboratories and computer memories cannot replicate dynamic evolutionary processes under way around the world.
Impressive advances in biotechnology only underscore the importance of conserving biodiversity since desirable genes can increasingly be switched from one organism to another. The glamour of genetic engineering should not blind the public and policy makers to the need to safeguard the integrity of natural ecosystems.
Loss of biodiversity as a result of development and environmental degradation has emerged as a global concern (Raven 1990; Wilson and Peter 1988). Concern over erosion of biodiversity was initially confined mostly to the scientific community, but is now spreading to the general public and politicians. Tropical deforestation is often at the forefront in debates on biodiversity loss; at least 27,000 species are thought to be lost from such widespread destruction every year (Myers 1993). Actual species loss may be much higher considering that many plant and animal groups are still imperfectly known (Wilson 1992). Amazonia has attracted particular attention in this regard because of its high degree of endemism and vast numbers of animal and plant species, many of them undocumented or poorly studied (Adds 1990). The region's diverse array of plant and animal communities contains many unique species and genes.
Amazonia contains the largest stretch of tropical forest, spanning 5,000 km from the Andes to the Atlantic, and some 4,000 km from the Guianas and the Upper Orinoco to the scrub cerrado of the Brazilian shield and the seasonally flooded grasslands of the Pantanal. This vast mosaic of forest communities, second growth, natural and man-induced grasslands and swamps contains the richest assortment of plant and animal species in the world, as well as a rich storehouse of genes for crop improvement.
Deforestation can adversely affect biodiversity on two accounts: outright habitat destruction, and ecological changes along the contact zone of remaining forest stands. Whereas deforestation rates in Amazonia appear to have been less dramatic over the past decade than has previously been thought, perhaps in the order of 15,000 km per year during the 1978-1988 period, some 38,000 km of forest may have been degraded (Skole and Tucker 1993). The edge effect of disturbance, ranging from microclimatic changes to the encroachment of swidden and pasture fires, can allegedly alter plant and animal communities as much as 1 km into the forest. Although some may dispute how deeply human influences penetrate the forest in terms of significant ecological disturbance, it is clear that outright deforestation alone is an insufficient measure of biodiversity change. In drier areas of the Amazon, such as around Maraba in southern Pará and in southern fringes of the rain forest in Mato Grosso, the border of isolated patches of forest can easily catch fire when fields or grazing areas are torched in preparation for planting or to destroy weeds and promote new growth of pasture grasses.
Endangered gene pools
Rampant deforestation fuelled by development schemes and pioneer farmers now threatens to destroy the genetic resources of many economic plants and potential crops before they can be tapped for the benefit of people throughout the world (NRC 1991; Smith et al. 1991b, 1992). Also, loss of tribal cultures is resulting in the disappearance of unique varieties of many annual and perennial crops.
Wild populations of crops, and in some cases their near relatives, are increasingly sought by plant breeders for desirable traits, such as pest and disease resistance and tolerance to problem soils. To help make farming more sustainable, researchers, development organizations, and farmers are increasingly seeking genetic solutions to agricultural constraints rather than costly, and sometimes environmentally damaging, chemical applications.
Ironically, forest-clearing to establish farms and plantations can eliminate the very genes that could be used to improve the crops being planted. The shrinking of wild populations of over 47 perennial crop species is currently under way in Amazonia (Smith and Schultes 1990). Perennial crops are important to the livelihoods of most small farmers in the tropics as well as operators of large plantations. Perennial crops that originated in Amazonia provide food, beverages, shelter, medicines, oils, resins, cosmetics, food colourants, and latex for citizens on every continent.
The Amazon contains wild gene pools of such commercially important crops as rubber (Hevea brasiliensis) and cacao (Theobroma cacao), as well as regionally important food and beverage crops such as peach palm (Bactris gasipaes) and guarana (Paullinia cupana), a popular soda in Brazil and now exported to developed countries such as Canada. As the heart-of-palm trade destroys many wild stands, particularly species of Euterpe, entrepreneurs in several Latin American countries are planting peach palm for palmito. Plantations of peach palm for the heart-of-palm trade are especially well developed in Costa Rica and Mexico. The ability of developing countries in the Amazon region as well as in other parts of Latin America, Africa, and South-East Asia to raise and sustain yields of several important cash and food crops will hinge to a large extent on their ability to marshal genetic resources to overcome constraints to production.
The Amazon forest also contains wild populations of hitherto minor crops such as annatto (Bixaorellana) and cupuaçu (Theabroma grandiflorum). Annatto is used by some Indians for body paint and is commonly used as a food colourant in Latin America. Known as achiote in Spanish and urucú in Brazil, annatto occurs spontaneously in various parts of Amazonia and probably originated in Acre. Traditionally, annatto has been grown as a backyard plant but it is now being cultivated on a commercial scale in several Latin American countries, particularly Brazil. After artificial Red Dye No. 3 was banned in the United States because it is a carcinogen, interest in annatto rebounded. Natural red bixin from annatto is increasingly used to colour foodstuffs and cosmetics in both industrial nations and developing countries. Annatto is used to enhance the colour of some peach-flavoured yogurts in the eastern United States, although few consumers probably make any connection with Amazonia when they relish that healthy treat.
Football-sized cupuaçu, a relative of cacao, grows in the forests of eastern Amazonia and is cultivated in backyards and fields for its refreshing pulp, which is used to make drinks, ice-cream, cakes, and puddings . Cupuaçu sells briskly in Amazonia and is penetrating markets in southern Brazil, and more recently in the United States and Japan. Cupuaçu has made the transition from an extractive product, to an occasional plant in home gardens, to a full-fledged crop, often grown in agro-forestry systems. How many other "cupuaçus" linger in the forest that could one day delight the palate of people in the region and abroad?
Amazonia's lush and diverse forests also contain many plants that could be incorporated into our menu of cultivated species, or are currently on the threshold of domestication. The nuts of patauá (Jessenia bataua) palm, for example, contain an oil similar to the quality of olive oil. The fruits are collected in the wild to make refreshing drinks. Brazil nut is now being grown on a small scale on several private landholdings in the Brazilian Amazon as well as in Malaysia. Domestication of Brazil nut is an important step considering that wild stands of the giant forest tree are falling for ranches, farms, and reservoirs.
Forests also contain pollinators and dispersal agents of wild populations of many crop plants as well as their near relatives . Intricate and often fine-tuned relationships between plants and animals need to be maintained if the integrity of many wild populations of our crop plants is to be ensured. For example, Brazil nut is dispersed by agoutis (Dasyprocta spp.), which bury many of the nuts after gnawing open the hard capsules that encase the protein- and oil-rich nuts (Huber 1910). Some bats pollinate forest trees while others disperse their seeds, and many birds, such as toucans, guans, and curassows (Cracidae), also disseminate many forest fruits. Conservation of forest environments, as well as field gene banks, is thus essential for the long-term viability of many crops important for subsistence and commerce.
Conservation of genetic resources and regional development in Amazonia are intertwined. More studies are needed, however, to document genetic variation in wild populations and domesticated gene pools of Amazonian crops. Also, hard economic data are needed to convince policy makers of the value of preserving forest habitats as resources for development.
Another dimension to the loss of botanical resources in Amazonia is that an invaluable medicine chest is literally being depleted before we can assess even a fraction of the potentially useful drugs. The rapid decline of many indigenous societies represents a loss not only of crop plants and unique varieties, but of ethno-botanical knowledge about which trees, shrubs, and herbs in the forest might offer cures for a wide variety of health complaints (Plotkin 1993). Many drugs are eventually synthesized in laboratories but, as in the case of genes for crop improvement, they have to be discovered first.
The indigenous knowledge base
A salient lesson from global efforts to conserve crop genetic resources is the need to maintain the cultural integrity of indigenous groups. People with a long history of interaction with the forest have much to teach us about sustainable agricultural practices and plant resources. Rural folk are particularly knowledgeable about the location and natural history of wild populations of crops and their near relatives. Tribal peoples are also knowledgeable about the medicinal value of plants in the forest and in their home gardens, a priceless heritage that is increasingly threatened by encroaching civilization (Schultes 1988; Schultes and Raffauf 1990, 1992). Biodiversity and cultural heterogeneity are vital to sustainable development.
Although rural peoples often have affinity with the surrounding plant and animal world, their practices do not always result in conservation of resources. Peasants and ranchers alike frequently clear fields and home gardens up to the margins of streams or rivers. If water courses were left in forest, natural corridors would remain for animal and plant dispersal in cleared areas.
Farmers in the Brazilian Amazon report three main reasons why they fell riparian forests, even if they contain economically important species such as açai palm (Euterpe oleracea). First, several crops important for domestic consumption and commerce grow well in the moist, organic-rich soils flanking streams and small rivers in contrast to the generally highly acidic, nutrient-poor upland soils. The common bean (Phaseolus vulgaris), maize (Zea mays), and vegetables reportedly yield better when grown in humid, valley bottoms. It is also easier to irrigate vegetables when they are close to a perennial water source. Second, farmers want to eliminate habitat for predators on their small livestock, particularly ocelot (Felis pardalis), margay (Felis wiedii), and various hawks. Third, newcomers to the region do not yet appreciate the value of some riparian trees and wish to create open, more "productive" landscapes.
The forests and rivers of Amazonia also contain an abundant array of wildlife important for hunting (Ayres and Ayres 1979; Ayres et al. 1991; Bodmer, Fang, and Ibanez 1988, 1991; Dourojeanni 1974; Rios, Dourojeanni, and Trovar 1973; Smith 1976). Some game animals, such as various species of turtle (Podocnemis spp.), could be domesticated or reared in captivity and the young released to the wild. Of the many species of mammals, birds, and reptiles of lowland South America, only one species has been domesticated, the muscovy duck (Cairina moschata). Muscovy ducks still grace the extensive lakes and lagoons of the Amazon flood plain, and some of these wild populations could be helpful to further breeding efforts.
Several wild animals are kept around homes for eventual consumption and some of them are in the process of being domesticated. Most are captured while still young, particularly when their mothers are killed during hunts. Capybara (Hydrochaeris hydrochaeris) and black-bellied tree ducks (Dendrocygna autumnalis) are kept around homes by some farmers along the Amazon flood plain, and they sometimes breed in captivity. Options for animal domestication will be foreclosed if wild populations of such species are drastically reduced.
Habitat destruction is the principal threat to wildlife in the region. The issue of dams and fisheries has already been highlighted, but the clearing of floodplain forests by farmers and ranchers also eliminates breeding and feeding grounds for fish. At least three-quarters of the fish species important in commerce and subsistence derive their nutrition directly or indirectly from flooded forests (Goulding 1980, 1993). A better understanding of land-use systems is thus essential for improved development and conservation efforts.
Although Amazonia is rich in plant and animal species, particularly in forests cloaking the eastern slopes of the Andes, policies that might deflect settlement and development to relatively empty areas, such as cerrados and thorn scrub, need to be considered carefully. Some of the drier areas of South America have higher levels of mammal endemism than the rain forests (Mares 1992). The campos, cerrados, and thorn scrub woodlands (caatinga, Chaco) of South America are much richer in animal and plant species than is generally appreciated (Pimm and Gittleman 1992). Wholesale destruction of low rainfall environments would also greatly reduce biodiversity - and future options for sustainable development in those areas.
The expansive flood plain of the sinuous Amazon River is another perceived venue for increased development efforts. The Amazon flood plain has always been regarded as an underutilized environment in Amazonia with enormous potential for raising food crops, livestock, and fish. Yet the idea that the flood plains can help absorb development pressures from the "fragile" upland forests warrants careful scrutiny. Flood-plain forests along the Amazon have already been largely logged out and extensively cleared. Endemism is especially high in the seasonally flooded forests of the Amazon River. Efforts to boost the productivity of flood-plain areas should focus on already cleared areas, rather than promote the wholesale destruction of the remaining forest and aquatic habitats with the* rich assortment of wildlife.
To help preserve the remaining biodiversity in Amazonia and to reduce pressures to develop contiguous regions, the productivity of agriculture, managed forests, plantations, and ranches must be raised within the well-watered basin. Whenever feasible, such land-use systems should be ecologically diverse. Agro-forestry systems, highlighted later as one of the more viable options for agricultural development in the region, could help maintain some level of biodiversity. Compared with simple monocultures, agro-forestry permits the survival of more animals and plants (Holloway 1991). Also, monocultures of perennial crops, such as oil-palm, create microenvironments for such plants as lichens and mosses that cannot survive in fields of rice or maize.
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