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Philip M Fearnside
The term ecoregion, as used in this article, refers to "natural" ecological systems, or terrestrial and aquatic areas as they were when Europeans first arrived in the New World. The original extent of natural ecoregions is presented, grouped by bioregion, major habitat type, and major ecosystem type. The definitions of these terms, given in the Glossary, are taken from Dinerstein et al. (1995); the rating codes are given in the footnotes to the table. Indications of the extent of remaining natural ecosystems, the threats to their continued existence, and the status of protected areas are discussed, together with priorities for conservation.
Ecosystems can be classified in many ways, making the number of categories vary widely depending on the use intended. Here, the system adopted by Dinerstein et al. (1995) is used. This divides the continent into 95 terrestrial "ecoregions," exclusive of mangroves. These are grouped into four "major ecosystem types:" tropical broadleaf forests, conifer/temperate broadleaf forests, grasslands/savannas/shrublands, and xeric formations. Within each of these categories are varying numbers of "major habitat types," such as tropical moist broadleaf forests. These are further divided into nine "bioregions." Amazonian tropical moist forests, for example, is a bioregion.
The 95 ecoregions, with their hierarchical groupings, are presented in Table I. Also included are the ratings for conservation status, biological distinctiveness, and biodiversity priority derived by Dinerstein et al. (1995). This study made a systematic survey of the status of natural ecosystems in Latin America and the Caribbean (LAC) and applied a uniform methodology to assigning priorities to these ecosystems for conservation efforts. The work was done for the United States Agency for International Development (USAID) by the WWF–US Biodiversity Support Program (BSP). The document is based on three workshops, plus consultations with relevant organizations and individual experts (the list of contributors contains 178 names).
Table I. Terrestrial Ecoregions of South Americaa
Major ecosystem type Major habitat type Bioregion Ecoregion name Ecoregion number Countries Original area (km2) Conservation statusb Biological distinctivenessc Biodiversity priorityd Tropical broadleaf forests Tropical moist broad-leaf forests Orinoco tropical moist forests Cordillera La Costa montane forests 17 Venezuela 13,481 3 2 I Orinoco Delta swamp forests 18 Venezuela, Guyana 31,698 4 3 III Guianan Highlands moist forests 20 Venezuela, Brazil, Guyana 248,018 5 2 III Tepuis 21 Venezuela, Brazil, Guyana, Suriname, Colombia 49,157 5 1 II Napo moist forests 22 Peru, Ecuador, Colombia 369,847 4 1 I Amazonian tropical moist forests Macarena montane forests 23 Colombia 2,366 3 2 I Japurá/Negro moist forests 24 Colombia, Venezuela, Brazil 718,551 5 1 II Uatumã moist forests 25 Brazil, Venezuela, Guyana 288,128 4 3 III Amapá moist forests 26 Brazil, Suriname 195,120 4 3 III Guianan moist forests 27 Venezuela, Guyana, Suriname, Brazil, French Guiana 457,017 4 3 III Paramaribo swamp forests 28 Suriname 7,760 3 3 III Ucayali moist forests 29 Brazil, Peru 173,527 2 1 I Western Amazonian swamp forests 30 Peru, Colombia 8,315 4 1 I Southwestern Amazonian moist forests 31 Brazil, Peru, Bolivia 534,316 4 1 I Juruá moist forests 32 Brazil 361,055 5 2 III Várzea forests 33 Brazil, Peru, Colombia 193,129 3 1 I Purús/Madeira moist forests 34 Brazil 561,765 4 4 IV Rondônia/Mato Grosso moist forests 35 Brazil, Bolivia 645,089 3 2 II Beni swamp and gallery forests 36 Bolivia 31,329 4 4 IV Tapajós/Xingu moist forests 37 Brazil 630,905 3 4 IV Tocantins moist forests 38 Brazil 279,419 2 4 III Northern Andean tropical moist forests Chocó/Darién moist forests 39 Colombia, Panama, Ecuador 82,079 3 1 I Eastern Panamanian montane forests 40 Panama, Colombia 2,905 2 1 I Northwestern Andean montane forests 41 Colombia, Ecuador 52,937 2 1 I Western Ecuador moist forests 42 Ecuador, Colombia 40,218 1 2 I Cauca Valley montane forests 43 Colombia 32,412 1 1 I Magdalena Valley montane forests 44 Colombia 49,322 1 1 I Magdalena/Urabá moist forests 45 Colombia 73,660 2 3 II Cordillera Oriental montane forests 46 Colombia 66,712 3 1 I Eastern Cordillera Real montane forests 47 Ecuador, Colombia, Peru 84,442 3 1 I Santa Marta montaneforests 48 Colombia 4,707 3 2 I Venezuelan Andesmontane forests 49 Venezuela, Colombia 16,638 2 1 I Catatumbo moistforests 50 Venezuela, Colombia 21,813 1 4 III Central Andean Tropical moist Forests Peruvian Yungas 51 Peru 188,735 2 1 I Bolivian Yungas 52 Bolivia, Argentina 72,517 2 2 I Andean Yungas 53 Argentina, Bolivia 55,457 3 3 III Eastern South American tropical moist forests Brazilian Coastal Atlantic forests 54 Brazil 233,266 1 1 I Brazilian interior Atlantic forests 55 Brazil 803,908 2 2 I Tropical dry broad leaf forests Orinoco tropical dry forests Llanos dry forests 74 Venezuela 44,177 2 4 III Amazonian tropical dry forests Bolivian Lowland dry forests 76 Bolivia, Brazil 156,814 1 1 I Northern Andean tropical dry forests Cauca Valley dry forests 77 Colombia 5,130 1 4 III Magdalena Valley dry forests 78 Colombia 13,837 1 4 III Patiá Valley dry forests 79 Colombia 1,291 1 4 III Sinú Valley dry forests 80 Colombia 55,473 1 4 III Ecuadorian dry forests 81 Ecuador 22,271 1 1 I Tumbes/Piura dry forests 82 Ecuador, Peru 64,588 2 1 I Marañion dry forests 83 Peru 14,921 2 3 II Maracaibo dry forests 84 Venezuela 31,471 2 4 III Lara/Falcón dry Forests 85 Venezuela 16,178 2 4 III Central Andean tropical dry forests Bolivian montane dry forests 86 Bolivia 39,368 1 3 II Conifer/temperate broadleaf forests Temperate forests Southern South American temperate forests Chilean winter rain Forests 87 Chile 24,937 2 2 I Valdivian temperate forests 88 Chile, Argentina 166,248 3 1 I Subpolar Nothofagus forests 89 Chile, Argentina 141,120 3 3 III Tropical and subtropical coniferous forests Eastern South American tropical and subtropical coniferous forests Brazilian Araucaria forests 105 Brazil, Argentina 206,459 1 3 II Grasslands/savannas/shrublands Grasslands, savanas, and shrublands Orinoco grasslands, savannas and shrublands Llanos 110 Venezuela, Colombia 355,112 4 3 III Amazonian grasslands, savannas, and shrublands Guianan savannas 111 Suriname, Guyana, Brazil, Venezuela 128,375 4 3 III Amazonian savannas 112 Brazil, Colombia, Venezuela 120,124 4 3 III Beni savannas 113 Bolivia 165,445 2 3 II Eastern South American grasslands, savannas, and shrublands Cerrado 114 Brazil, Paraguay, Bolivia 1,982,249 3 1 I Chaco savannas 115 Argentina, Paraguay, Bolivia, Brazil 611,053 3 2 I Humid Chaco 116 Argentina, Paraguay, Uruguay, Brazil 474,340 3 4 IV Córdoba montane savannas 117 Argentina 55,798 3 4 IV Southern South American grasslands, savannas, and shrublands Argentina monte 118 Argentina 197,710 4 3 III Argentina Espinal 119 Argentina 207,054 4 3 III Pampas 120 Argentina 426,577 2 3 III Uruguayan savannas 121 Uruguay, Brazil, Argentina 336,846 3 3 III Flooded grasslands Orinoco flooded grasslands Orinoco wetlands 128 Venezuela 6,403 4 3 III Amazonian flooded grasslands Western Amazonian flooded grasslands 129 Peru, Bolivia 10,111 4 3 III Eastern Amazonian flooded grasslands 130 Brazil 69,533 3 3 III São Luis flooded grasslands 131 Brazil 1,681 2 4 III Northern Andean flooded grasslands Guayaquil flooded grassland 132 Ecuador 3,617 2 3 II Eastern South American flooded grasslands Pantanal 133 Brazil, Bolivia, Paraguay 140,927 3 1 I Paraná flooded savannas 134 Argentina 36,452 2 3 II Montane grasslands Northern Andean montane grasslands Santa Marta paramo 137 Colombia 1,329 3 1 I Cordillera de Mérida paramo 138 Venezuela 3,518 4 1 I Northern Andean paramo 139 Ecuador 58,806 3 1 I Central Andean montane grasslands Cordillera Central paramo 140 Peru, Ecuador 14,128 3 1 I Central Andean wet puna 141 Bolivia, Argentina, Peru, Chile 183,868 3 2 I Central Andean wet puna 142 Chile 188,911 3 2 I Central Andean dry puna 143 Argentina, Bolivia, Chile 232,958 3 2 I Southern South American montane grasslands Southern Andean steppe 144 Argentina, Chile 198,643 4 4 IV Patagonian steppe 145 Argentina, Chile 474,757 3 2 I Patagonion grasslands 146 Argentina, Chile 59,585 3 3 III Xeric formations Mediterranean scrub Central Andean Mediterranean scrub Chilean matorral 148 Chile 141,643 2 1 I Deserts and xeric shrublands Orinoco deserts and xeric shrublands La Costa xeric shrublands 168 Venezuela 64,379 2 4 III Arayua and Paría xeric Scrub 169 Venezuela 5,424 2 3 II Northern Andean deserts and xeric Shrublands Galapagos Islands xeric scrub 170 Ecuador 9,122 3 1 I Guajira/Barranquilla xeric scrub 171 Colombia, Venezuela 32,404 2 3 II Paraguná xeric scrub 172 Venezuela 15,987 2 3 II Central Andean deserts and xeric shrublands Sechura Desert 173 Peru, Chile 189,928 3 3 III Atacama Desert 174 Chile 103,841 3 3 III Eastern South American deserts and xeric shrublands Caatinga 175 Brazil 752,606 3 3 III Restingas Northern Andean restingas Paranaguá restingas 176 Venezuela 15,987 2 2 II Amazonian restingas Northeastern Brazil restingas 177 Brazil 10,248 1 1 I Eastern South American restingas Brazilian Atlantic coast restinga 178 Brazil 8,740 1 1 I
a Data source: Dinerstein et al., 1995.
b Conservation status codes: 1, critical; 2, endangered; 3, vulnerable; 4, relatively stable; 5, relatively intact.
c Biological distinctiveness codes: 1, globally outstanding; 2, regionally outstanding; 3, bioregionally outstanding; 4, locally important.
d Biodiversity priority codes: 1, highest priority at regional scale; II, high priority at regional scale; III, moderate priority at regional scale; IV, important at national scale.
The classification system is hierarchical, starting with four "major ecosystem types" (e.g., Tropical Broadleaf Forests), which are divided into 10 "major habitat types" (e.g., Tropical Moist Broadleaf Forests). These are crossed with 6 bioregions (e.g., Amazonia) and divided into 95 ecoregions (e.g., Rondônia/Mato Grosso moist forests). The system allows the priority of some ecoregions to be promoted upward based on uniqueness and regional representation, even if indicators of diversity and vulnerability are not so high.
The effort was unusual in emphasizing protection of areas with high diversity (a measure of the turnover of species along ecological gradients), as well as the more commonly used diversity (species diversity within a habitat). In the case of mangroves, the diversity assessed is ecosystem diversity, including aquatic animal life. This avoids mangroves receiving the unjustly low diversity ratings that tend to result when assessments are restrained to terrestrial organisms, especially trees.
Although the ecoregions identified in Table I refer to "natural" (pre-Columbian) ecosystems, it should be emphasized that these had already been subject to millennia of influence by indigenous peoples prior to the arrival of Europeans. This influence continues today, together with much more rapid alterations from such activities as deforestation and logging done by nonindigenous residents. "South America" is taken to include the three Guianas (different from usage by the Food and Agriculture Organization of the United Nations (FAO)) and to exclude Panama (however, in the case of ecoregions that extend into Panama, the area estimates in Table I include the Panamanian portions). The ecoregions are mapped in Figure 1. The ecoregion numbering corresponds to Table I and also to the report by Dinerstein et al. (1995); the numbering presented here is not continuous, since the report also includes ecoregions in Mexico, Central America, and the Caribbean. Extensive bibliographic material on the delimitation of the ecoregions and on the state of knowledge about them can be found in Dinerstein et al. (1995).
Mangroves occur along the coasts of Brazil, the three Guianas, Venezuela, Colombia, Ecuador, and northern Peru. Dinerstein et al. (1995) divide them into five complexes: Pacific South America, Continental Caribbean, Amazon–Orinoco–Maranhão, Northeast Brazil, and Southeast Brazil. Each complex is further subdivided into 2–5 units, corresponding to distinct segments of coastline. Mangroves are essential to maintaining populations and ecological processes in surrounding marine, freshwater, and terrestrial ecosystems.
Unfortunately, information is not available on the present extent of each of the 95 ecoregions listed in Table I. Information on the extent of tropical forests in approximately 1990 is available from the FAO Tropical Forest Resources Survey ( FAO, 1993). These data are tabulated by country in Table II. Nontropical areas are covered by a variety of national surveys (Harcourt and Sayer, 1996). National data are important because decisions regarding land-use policies and conservation are taken at the national level—not at the levels of bioregions or ecosystem types. Over half of the South American continent is represented by a single country: Brazil ( Fig. 2).
Table II. Area of Tropical Forest Present in 1990 (km2)a
Tropical rain Moist deciduous Dry deciduous Very dry Desert Hill and Country forests forest forestb forest Desert montane forest All forestsb Bolivia 0 355,820 73,460 0 40 63,850 493,170 Brazil 2,915,970 1,970,820 288,630 0 0 435,650 5,611,070 Colombia 474,550 41,010 180 0 0 24,900 540,640 Ecuador 71,500 16,690 440 0 0 31,000 119,620 French Guiana 79,930 30 0 0 0 0 79,970 Guyana 133,370 31,670 0 0 0 19,120 184,160 Paraguay 0 60,370 67,940 0 0 270 128,590 Peru 403,580 122,990 190 2,690 1,840 147,770 679,060 Suriname 114,400 33,280 0 0 0 0 147,680 Venezuela 196,020 154,650 2,220 1 0 103,900 456,910 Total 4,389,320 2,787,330 433,060 2,691 1,880 826,460 8,440,870
a Data source: FAO, 1993.
b Includes cerrado, caatinga, and chaco.
An idea of the extent of existing ecosystems can be gained from measurements of land cover in 1988 made using 1 × 1 km resolution data from the AVHRR sensor on the NOAA satellite series (Stone et al., 1994). These are tabulated in Table III.
Table III. Land Cover in South America in 1988
Country Closed tropical moist forest Recently degraded IMF Closed forest Degraded closed forest Woodlands Degraded woodlands Savanna, grasslands Degraded savanna, grasslands Scrublands, Shrublands Desert, bare soil Water Snow, rock, ice Other Total Argentina 1.2 0.0 96.8 0.6 645.4 15.7 755.4 232.8 894.8 37.9 34.0 31.4 35.7 2779.8 Bolivia 323.5 12.7 409.2 24.6 345.1 102.2 87.7 86.2 4.8 16.5 11.9 0.1 1.1 1089.4 Brazil 3522.3 519.7 3686.0 1692.2 1555.9 330.0 740.0 179.4 0.0 0.0 80.9 0.0 124.0 8388.5 Chile 0.0 0.0 134.1 29.1 75.2 29.8 101.1 14.0 86.9 186.8 7.0 16.6 3.8 684.5 Colombia 581.6 5.4 622.5 11.4 116.3 14.5 255.5 64.0 0.0 0.0 3.1 0.0 22.8 1110.1 Ecuador 115.5 1.7 121.0 1.7 33.7 4.3 41.9 13.3 3.2 2.5 0.6 0.0 0.8 223.1 French Guiana 78.8 0.0 79.8 2.4 0.6 0.0 0.2 0.0 0.0 0.0 0.1 0.0 1.0 84.1 Guyana 159.4 2.0 171.6 2.4 5.4 0.3 18.4 1.5 0.0 0.0 1.2 0.0 3.7 204.3 Paraguay 0.3 0.0 8.9 0.2 209.1 50.7 104.0 26.5 0.0 0.0 0.6 0.0 1.1 401.1 Peru 620.8 19.1 654.7 19.1 88.0 78.8 139.0 97.4 64.3 88.0 8.3 0.7 5.6 1244.1 Suriname 126.0 2.5 128.5 10.0 0.5 0.3 1.2 0.4 0.0 0.0 1.1 0.0 3.3 145.2 Uruguay 1.4 0.0 2.1 0.0 0.9 0.0 154.1 11.0 0.0 0.0 3.0 0.0 5.9 177.0 Venezuela 379.1 0.2 415.5 9.9 33.9 40.2 243.3 82.0 27.2 0.0 11.4 0.0 8.4 871.8 Unclassified 313.0 Total 5909.9 563.4 6530.7 1803.7 3109.8 666.9 2642.0 808.5 1080.6 331.7 163.2 48.9 217.2 17,716.1 Continent (%) 33.4 3.2 36.9 10.2 17.6 3.8 14.9 4.6 6.1 1.9 0.9 0.3 1.2 Category (%) 8.7 21.6 17.7 23.4 100.0
Note. All values in thousands of km2 or percent. "TMF" includes tropical moist, semideciduous, and gallery forests, "Grasslands" includes those seasonally flooded, "Closed Forest" includes TMF, montane forests, cool and temperate deciduous forests, and tropical seasonal forests, "Degraded Grasslands" includes agriculture, "Desert, Bare Soil" includes inland salt marsh communities, and "Other" includes wet vegetation and mangroves. Source: Stone et al., 1994. Reproduced with permission, the American Society for Photogrammetry and Remote Sensing. Stone, T. A., Schlesinger, P., Houghton, R. A., and Woodwell, G. M. (1994). A map of the vegetation of South America based on satellite imagery. Photogramm. Eng. Remote Sens. 60(5), 541–551.
It should be emphasized that many ecosystems can be heavily disturbed by logging and other activities without the change being evident on satellite imagery. This is true for Landsat TM imagery (30 × 30 m resolution) used for deforestation estimates in Brazil, and the limitations are much greater for 1 × 1 km AVHRR data.
Brazil is the country with the most extensive satellite information on forest cover and its loss. Unfortunately, information on nonforest vegetation types such as cerrado is much less complete. Considerable confusion arises between the FAO (1993) classification and others such as the one adopted here because FAO classifies cerrado, caatinga, and chaco as "forests."
Brazil's Legal Amazon region originally had 4 million km2 of forests, the rest being cerrado and other types of savannas. Agricultural advance was slow until recent decades because of human diseases (especially yellow fever and malaria), infertile soil, and vast distances to markets. These barriers have progressively crumbled, although a range of limiting factors restricts the extent and the duration over which many uses of deforested areas can be maintained (Fearnside, 1997a). Deforestation in the region has been predominantly for cattle pasture, with critical contributions to the motivations for the transformation coming from the role of clearing as a means of establishing land tenure and in allowing land to be held and sold for speculative purposes ( Fearnside, 1993).
The Atlantic forests of Brazil (ecoregions 54 and 55) have been almost completely (>95%) destroyed, mainly for agriculture, silviculture, and real estate development. Most of what remains of this extraordinarily rich ecosystem is in protected areas, but unprotected areas continue in rapid retreat. These forests are recognized as major "hot spots" of biodiversity (Heywood and Watson, 1995; Stotz et al., 1996).
In Andean countries, clearing by small farmers has predominated in driving deforestation, in contrast to the predominant role of medium and large cattle ranchers in Brazil. Migration from densely populated areas in the Andean highlands (altiplano) has led to settlement in lowland forests areas, with consequent upsurges in clearing (e.g., Rudel and Horowitz, 1993).
Savanna ecosystems have suffered heavy human pressure. The pampas of Argentina and the Uruguayan savannas of Uruguay and southern Brazil (ecoregions 120 and 121) have largely been converted to agriculture. The Brazilian cerrado, originally covering 2 million km2, is the largest ecoregion in South America, as well as holding the largest number of species of any of the world's savannas. The cerrado was largely intact until the mid-1970s. Clearing, especially for soybeans and planted pasture, reduced the cerrado to 65% of its original area by 1993 according to Landsat imagery interpreted by Brazil's National Institute for Space Research (INPE). The advance of clearing has proceeded at an accelerating pace, speeded by infrastructure projects and an array of government subsidies.
The temperate and coniferous forests of the Southern Cone have been under severe pressure from logging. These forests are usually logged by clear-cutting in a manner similar to their counterparts in the North American temperate zone. This contrasts with the "selective" logging (highgrading for a few species) that characterizes timber extraction from the diverse forests of the tropical region.
Conversion of natural ecosystems to agroecosystems and secondary forests creates landscapes that maintain biodiversity to varying degrees. "Shifting cultivation" as practiced by indigenous peoples and by traditional nonindigenous residents (caboclos) in Amazonian forests maintains a substantial part of the original biodiversity. This contrasts with the effect of the vast expanses of cattle pasture that have replaced this, either directly or following a phase of use in pioneer agriculture by small farmers who have recently arrived from other places.
In densely settled areas along the coast of Brazil and in the southern portions of the country, agricultural use has gone through a series of "cycles," such as sugarcane and coffee. The productivity of many areas has been damaged by soil erosion and other forms of degradation. Cattle pasture is often the land use replacing these crops. Since the 1970s, plantation silviculture (which now covers over 70,000 km2) and soybeans (130,000 km2) have made large advances.
In Argentina and Uruguay, cattle ranching and wheat and rice farming are major land uses. Natural vegetation is better represented in areas with little agricultural potential, such as mountain and polar areas and arid and semiarid zones.
Areas that remain under natural vegetation cover, rather than being converted to other land uses through clearing, are also subject to human use and alteration. Selective logging in tropical forests, for example, leaves much of the basic structure of the ecosystem intact, but also can lead to significant changes that can set in motion a sequence of events leading to complete destruction of the ecosystem. Logging leaves a substantial amount of dead biomass in the forest, including the crowns and stumps of harvested trees and all of the biomass of the many additional trees that are killed by damage sustained during the logging process. Openings created in the canopy allow sunlight and heat to penetrate to the forest floor, drying out the fuel bed more quickly than in unlogged forests. Climatic variations such as those provoked by the El Niño phenomenon make logged forests especially susceptible to entry of fires. Ample opportunities for fires are provided as fields are burned to prepare land for planting and as cattle pastures are burned to control invading weeds. The fires burn slowly through the understory, charring the bases of trees as they go. Many of these trees then die, leading to a positive-feedback process whereby more dead bio-mass and canopy openings are provided and subsequent fires begin with greater ease, killing still more trees. This can degrade the entire forest within a few years (Nepstad et al., 1999).
Tropical forests are also used for "extractivism," or the collection of nontimber forest products (NTFPs) such as rubber and Brazil nuts. This does relatively little damage to the forest, although extractivists do have an impact through hunting and through clearing for subsistence crops. The extractivist population can also play a protective role in defending the forest against encroachment by more aggressive actors such as ranchers and loggers. This is the basis of the extractive reserve system in Brazil (see Anderson, 1990).
Savannas are often grazed by cattle without cutting trees. Cerrado (ecoregion 114), "lavrado," or Guianan savannas (ecoregion 111), the Pantanal wetlands (ecoregion 133), and the llanos of Venezuela (ecoregion 110) are among the savannas often used in this way. Increasing fire frequency, virtually all a result of human-initiated burning, can lead to shifts in species composition and to a drain of nutrients.
Aquatic ecosystems are traditionally exploited by fisheries. This alters the relative abundance of the species present. Use of watercourses as recipients for sewage and other pollutants also affects aquatic life in many ways.
Deforestation is the dominant transformation of forested ecosystems that threatens biodiversity. In Brazil, which holds most of the continent's remaining forests, ranching is the dominant use for land once deforested. In the 1990s, soybeans began to enter forested regions, representing a new force in this process (they had already been a major factor in transformation of the cerrado since the 1970s). The most important effect of soybeans is not loss of forest directly planted to the crop, but the extensive infrastructure of waterways, railways, and highways that are built to transport soybeans and the inputs needed to grow them. The cycle of deforestation that has repeatedly occurred along Amazonian highways can be expected to accompany these new access routes.
Population growth is a fundamental contributor to deforestation and other forms of natural habitat loss. In recent years, however, the redistribution of population through migration has overshadowed the impact of absolute growth in population size. These include migrations from the semiarid Northeast of Brazil to Amazonia, from Paraná to Rondônia, from the highlands of Bolivia, Peru, and Ecuador to the Amazonian lowlands and, in the case of Ecuador, to the Pacific lowlands as well.
Logging is an increasingly important factor in Amazonia, and the catalytic role of this activity in increasing the flammability of the logged forest gives it potential impact far beyond its direct damage. So far, logging in Brazil has been dominated by domestic demand for sawn wood, plywood, and particleboard, which is almost entirely supplied from tropical forests rather than from silvicultural plantations (which produce wood for pulp and, to a lesser extent, charcoal). However, global markets for tropical timber are presently dependent on supplies from Asian forests that will soon come to an end if current rates of exploitation continue. In the 1990s, Asian logging companies began buying land and/ or obtaining concessions in such countries as Brazil, Guyana, and Suriname, and pressure from global timber markets can be expected to increase in the future. Asian loggers are also the principal forces in clear-cutting the Valdivian and Nothofagus forests of Chile (ecoregions 88 and 89).
In eastern Amazonia, demand for charcoal for pigiron smelting in the Carajás area is a potential threat to forests. Carajás, with the world's largest deposit of high-grade iron ore, is expected to be mined for 400 years at the present rate of exploitation. Wood from native forests is inherently cheaper as a source of biomass for charcoal production as compared to plantation-grown sources. Charcoal manufacture has an impact on the forest both through direct removal (including officially sanctioned forestry management systems) and by increasing the profitability of logging and deforestation (see Anderson, 1990).
Deforestation impacts are magnified by fragmentation and edge effects (Laurance and Bierregaard, 1997). This division of the remaining natural habitat into many small islands surrounded by cattle pastures or other highly modified land uses, together with forming edges with increased entry of light, wind, and foreign organisms, results in many changes in the remaining natural ecosystems. Most of these changes are forms of degradation, such as greatly increased mortality in the trees that provide the dominant component of forest structure. Vine loads on trees near edges also increase, leading to further increase in mortality and susceptibility to windthrow.
Climate change represents a major long-term threat to many South American ecosystems. The Intergovernmental Panel on Climate Change (IPCC) has prepared detailed reviews of potential climatic impacts on South America in its 1998 Special Report on Regional Impacts (Chapter 6) and its 2000 Third Assessment Report (Working Group II, Chapter 14).
Removal of fauna through hunting is a virtually universal consequence of proximity of human settlements to natural habitats. The removal of fauna can affect seed dispersal, pollination, and other processes needed for maintaining plant and animal communities. Introduction of exotic species also represents a threat to natural ecosystems. Exotic species are a particularly severe problem in the Valdivian and Nothofagus forests of Chile (ecoregions 88 and 89).
Mangrove ecosystems are subject to some unique threats. Shrimp culture in mangrove areas has had severe impacts on the coast of Ecuador. Mangroves in Maranhão have been subject to pressure for charcoal manufacture. In São Paulo state mangroves have often suffered from oil spills and are also losing ground to real estate development. This has also affected restingas (ecoregions 176–178).
Hydroelectric dams have major impacts on river ecosystems by blocking fish migration, by eliminating rapids and replacing well-oxygenated running water with reservoirs that usually have anoxic water in their lower layers. The composition of fish present changes radically and undergoes a succession of changes as reservoirs age. Anoxic water released through the turbines severely reduces fish and freshwater shrimp productivity in the rivers downstream of the dams.
In Brazil, the 2010 Plan, released in 1987, listed over 300 dams for eventual construction in Brazil, independent of the expected date of completion. Of these, 65 dams were in the Amazon region. Economic difficulties have caused projected construction dates to be successively postponed, but the ultimate number of dams has not changed. Most contentious is the Babaquara Dam on the Xingu River, which would flood over 6000 km2 of forest, much of it in indigenous areas. This has been renamed the "Altamira Dam" and appears in the current decennial plan for construction by 2013.
In Chile, the dams planned and under construction on the Bio-Bio River are expected to have major environmental impacts. The Ralco Dam is particularly contentious. In Uruguay, at least five major dams are planned for construction in the next few years.
Industrial waterways, known as hidrovias in Brazil, greatly alter aquatic habitats. No less than seven waterways are under construction or planned for soybean transport on barges: the Paraguay–Paraná (Hidrovia do Pantanal), the Madeira River waterway, the Tocantins-Araguaia waterway, the Teles Pires–Tapajós waterway, the Capim River waterway, the Mamoré–Guaporé waterway, and the Rio Branco and Rio Negro–Orinoco waterways. Waterway construction involves blasting rock obstructions, cutting sharp curves, and dredging sediment from the river beds. The Corumbá–Cáceres stretch of the Hidrovia do Pantanal, if built, would lower the water level in the Pantanal wetlands (ecoregion 133), threatening one of the world's most renowned concentrations of wildlife.
Other threats to aquatic habitats include sedimentation from soil erosion and landslides. This is severe, for example, in rivers draining steep areas of former Atlantic forest in the coastal mountains of Brazil. Mining for gold, tin, and diamonds in Amazonia can also inject large amounts of sediment into streams and rivers.
Destruction of varzea forest (ecoregion 33) in Amazonia can affect aquatic life through loss of important fish breeding areas and food sources for fruit- and seed-eating fish. Destruction of varzea lakes and overfishing represent additional threats.
The choice and design of reserves depend on the financial costs and biodiversity benefits of different strategies. In Brazil, rapid creation of lightly protected "paper parks" has been a means of keeping ahead of the advance of barriers to establishment of new conservation units, but emphasis must eventually shift to better protection of existing reserves (Fearnside, 1999).
Creating reserves that include human occupants has a variety of pros and cons (Kramer et al., 1997). Although the effect of humans is not always benign, much larger areas can be brought under protection regimes if human occupants are included. Additional considerations apply to buffer zones around protected areas. A "fortress approach," whereby uninhabited reserves are guarded against encroachment by a hostile population in the surrounding area, is believed to be unworkable as a means of protecting biodiversity, in addition to causing injustices for many of the human populations involved.
Indigenous peoples have the best record of maintaining forest, but negotiation with these peoples is essential in order to ensure maintenance of the large areas of forest they inhabit (Fearnside and Ferraz, 1995). The benefits of environmental services provided by the forest must accrue to those who maintain these forests. Development of mechanisms to capture the value of these services will be a key factor affecting the long-term prospects of natural ecosystems.
In the case of deforestation in Amazonia, a variety of measures could be taken immediately through government action, including changing land tenure establishment procedures so as not to reward deforestation, revoking remaining incentives, restricting road building and improvement, strengthening requirements for environmental impact statements for proposed development projects, creating employment alternatives, and, in the case of Brazil, levying and collecting taxes that discourage land speculation. A key need is for a better informed process of making decisions on building roads and other infrastructure such that the full array of impacts is taken into account.
Environmental services represent a major value of natural ecosystems, and mechanisms that convert the value of these services into monetary flows that benefit the people who maintain natural habitats could significantly influence future events in the region (Fearnside, 1997b). Environmental services of tropical forests include maintenance of biodiversity, carbon stocks, and water cycling. The water cycling function, although very important for countries in the region, does not affect other continents as the first two services do. At present, avoiding global warming by keeping carbon out of the atmosphere represents a service for which monetary flows are much more likely to result from international negotiations. Activities under the United Nations Framework Convention on Climate Change (UN-FCCC) are at a much more advanced stage of negotiation than is the case either for the Biodiversity Convention or for the "Non-Binding Statement of Principles" and possible future convention on forests.
In the case of carbon, major decisions regarding credits for tropical forest maintenance are likely to be taken at the sixth Conference of the Parties (COP-6) to the Kyoto Protocol, at the end of 2000, considering the IPCC Special Report on Land Use, Land-Use Change and Forestry (SR-LUCF), released in May 2000. Regardless of what is decided at COP-6, global warming is a permanent consideration that can be expected to receive increasing weight in decision making. The threats to natural ecosystems in South America are many, and recognition of the multiple environmental services provided by them is a key factor in ensuring that substantial areas of each of these ecosystems continue to exist, thereby maintaining their biodiversity.
I thank Eric Dinerstein and the World Bank for permission to publish Fig. 1 and Table I, and Tom Stone and the American Society for Photogrammetry and Remote Sensing for permission to publish Table III. Brazil's National Council of Scientific and Technological Development (CNPq AI 523980/96-5) and National Institute for Research in the Amazon (INPA PPI 1-3160) provided financial support. S. V. Wilson and two anonymous reviewers made helpful comments on the manuscript.
Anderson, A.B., Editor, 1990. Alternatives to Deforestation: Towards Sustainable Use of the Amazon Rain Forest, Columbia Univ. Press, New York.
Dinerstein, E., Olson, D.M., Graham, D.J., Webster, A.L., Primm, S.A., Bookbinder, M.P. and Ledec, G., 1995. A Conservation Assessment of the Terrestrial Ecoregions of Latin America and the Caribbean, The World Bank, Washington, D.C.
FAO (Food and Agriculture Organization of the United Nations), 1993. Forest Resources Assessment 1990: Tropical Countries (FAO Forestry Paper 112), FAO, Rome, Italy.
Fearnside, P.M., 1997. Limiting factors for development of agriculture and ranching in Brazilian Amazonia. Rev. Brasil. Biol. 57 4, pp. 531–549.
Fearnside, P.M., 1999. Biodiversity as an environmental service in Brazil's Amazonian forests: Risks, value and conservation. Environ. Conserv. 26 4, pp. 305–321. Abstract-EMBASE | Abstract-GEOBASE | Abstract-Elsevier BIOBASE | $Order Document | Full Text via CrossRef
Harcourt, C.S. and Sayer, J.A., Editors, 1996. The Conservation Atlas of Tropical Forests: The Americas, Simon & Schuster, New York.
Heywood, V.H. and Watson, R.T., Editors, 1995. Global Biodiversity Assessment, Cambridge Univ. Press, Cambridge, UK.
Kramer, R., van Schaik, C. and Johnson, J., 1997. Last Stand: Protected Areas and the Defense of Tropical Biodiversity, Oxford Univ. Press, Oxford.
Laurance, W.F. and Bierregaard, R.O., Editors, 1997. Tropical Forest Remnants: Ecology, Management, and Conservation of Fragmented Communities, Univ. of Chicago Press, Chicago, IL.
Nepstad, D.C., Moreira, A.G. and Alencar, A.A., 1999. Flames in the Rain Forest: Origins, Impacts and Alternatives to Amazonian Fire, Pilot Program to Conserve the Brazilian Rain Forest, Brasilia, Brazil.
Rudel, T.K. and Horowitz, B., 1993. Tropical Deforestation: Small Farmers and Land Clearing in the Ecuadorian Amazon, Columbia Univ. Press, New York.
Stone, T.A., Schlesinger, P., Houghton, R.A. and Woodwell, G.M., 1994. A map of the vegetation of South America based on satellite imagery. Photogramm. Eng. Remote Sens. 60 5, pp. 541–551. Abstract-Compendex | Abstract-GEOBASE | Abstract-Elsevier BIOBASE | $Order Document
Stotz, D.F., Fitzpatrick, J.W., Parker III, T.A. and Moskovitz, D.K., 1996. Neotropical Birds: Ecology and Conservation, Univ. of Chicago Press, Chicago, IL.
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