Chapter 4 - Major ecosystems of the American humid tropics with emphasis on the Central Selva of Peru

Classification of the American humid tropics
Classification of the Central Selva within the American humid tropics
Protection of major ecosystems in the humid tropics
Conflicts between protected areas and other types of natural resource use
Bibliography

Classification of the American humid tropics

The green mantle which covers the majority of the American humid tropics hides an impressive diversity of habitats. The Central of Peru alone contains 11 different life zones (Table 4-1) with six additional transitional life zones (ONERN, 1976). This variety is, in large part, the result of mountainous topography. Because tropical humid conditions exist from sea level to 3,800 meters or more, this diversity is also found in Bolivia, Ecuador, Colombia, Venezuela, Panama, and Central America. Relatively minor mountain ranges and flooding in low lying areas also contribute to the mix.

The annual mean temperature in the lowland humid tropics exceeds 24° C and the precipitation equals or exceeds the return to the atmosphere of evaporated and transpired water. Annual precipitation is greater than 1500 mm, with no more than two dry months, and no frosts occur (NRC, 1982).

The Holdridge (1967) method of classifying natural life zones provides useful information for regional development planning. Table 4-2 illustrates how the Holdridge system corresponds with the Brack (1976) system regarding the Peruvian Central Selva. The latter system corresponds closely with the biogeographical classification of Udvardy (1975) as well as that of Cabrera and Willink (1973) (Table 4-3).

Provinces lying within the American humid tropics contain some 898 million hectares, of which the most important are the Amazonian (28.5%), the Paranan or Brazilian Rain Forest (20.7%), the Madeiran (18.4%), the Guyanan (9.5%) and the Yungas (7.0%). These five provinces contain more than 84 percent of the American humid tropics. The Peruvian Central Selva lies chiefly within the Yungas province, and to a lesser degree, in the Amazonian.

Yungas Province

In the Peruvian Central Selva the Yungas Province lies between 3,500 and 3,800 meters above sea level, where annual rainfall averages 2,000-4,000 mm but varies from a minimum of 800 to a maximum of approximately 6000 mm. Mean temperature ranges from 7-11 ° C in the coldest and highest zones to 19-26° C in the hottest and lowest areas (Tables 4-1 and 4-2).

Table 4-1
NATURAL LIFE ZONES IN THE PERUVIAN CENTRAL SELVA AND THEIR PRINCIPAL CHARACTERISTICS

Table 4-2
CORRESPONDENCE BETWEEN HOLDRIDGE LIFE ZONES AND THE BRACK CLASSIFICATION OF DISTRICTS AND PROVINCES IN THE PERUVIAN CENTRAL SELVA

Table 4-3
BIOGEOGRAPHIC PROVINCES IN THE AMERICAN HUMID TROPICS

Elfin Forest District (Monte Chico)

The Elfin Forest district is found between 3,500-3,800 meters and 2,500-2,800 meters above sea level. This district corresponds to the Tropical Montane Wet Forest and the Tropical Montane Rain Forest of Holdridge (Table 4-2), Annual mean precipitation varies between 840 and 1,720 mm in the wet forest and between 2,000-4,000 mm in the rain forest. Low mean temperatures (only 7-12° C) and foggy conditions frequently occur.

This district is characterized by irregular relief, with slopes of over 60 percent in its higher regions adjacent to the Puna Province, with steep hillsides of more than 75 percent at lower elevations. Soils are relatively deep at the highest altitudes and very thin in the Tropical Montane Rain Forest life zone. Higher soils are slightly acid, of medium and heavy texture, and are classified as phaeozems or luvisols. Dystric and eutric cambisols also exist. At lower altitudes, lithosols predominate, but transitional forms approaching cambisols also occur.

At the highest altitudes, the vegetation is mostly scrub, with isolated trees that scarcely reach 3 to 5 meters in height. Several genera, such as Berberis, Ribes, Baccharis, Gynoxys, Vaccinium, and Polylepis, but Buddteia, Escallonia, and Oreopanax which have their origin in the Puna are also found here, along with species peculiar to the zone, such as those belonging to the genera Podocarpus, Eugenia, Clusia, Brunellia, Rapanea, Ocotea, Myrcia, Laplacea, Solanum, Weinmannia, Pipper, Cinchona, Clethra, and Cecropia. These genera increase in proportion, density, and development in the lower sections of the district, where they can grow to 15 meters in height. Grass species that occur at the higher altitudes completely disappear at lower altitudes, where forest openings are invaded by the bamboo Chusquea. Many Melastomaceae also occur, the trees usually appear covered with epiphytes, and tree ferns of the genera Cyathea, Alsophila, and Dicksonia are common (Tosi,1960).

Faunal species from both the Puna and the Yungas occur together here, but many species from other districts in the Yungas which are common in the Amazonian province are not present in the Monte Chico (Elfin Forest).

Cloud Forest District

The Cloud Forest district described by Brack (1976) includes the Tropical Lower Montane Wet Forest, the Tropical Lower Montane Rain Forest, and the Tropical Lower Montane Moist Forest, although fogs are rare in this last life zone. It lies between 2,500-2,800 meters and 1,600-1,800 meters above sea level and has an annual mean precipitation from 790 to 1,970 mm in the Tropical Lower Montane Moist Forest and reaches almost 4,000 mm in the Tropical Lower Montane Rain Forest. Temperature means range from a minimum of 12° C to a maximum of 18°C.

Topography here is predominantly sloping, with few flat areas. Soils are generally moderately acid to slightly basic and of moderate depth, have medium or fine texture, and high cation exchange capacity. They can include kastanozems and, to a lesser degree, lithosols and redzinas on the steepest sites. Other life zones in this district are characterized by considerable relief, with 70 percent or steeper slopes, and shallow soils, primarily lithosols. Cambisols and acrisols are also present (Tosi, 1960; ONERN, 1976).

The vegetation, like the fauna, is characteristic of the Yungas province and is very rich in endemic forms. Trees can reach 40 meters in height, although they average 20-30 meters. Podocarpus is very common in this district, as is Weinmannia, Ocotea, Nectandra and other Lauraceae, Cinchona, Cedrela, Guarea, Roupala, Clethra, Clusia, Befaria, Laplacea, Ilex, Oreopanax, Cecropia, Brunellia, Ladenbergia, and many others. The bamboo Chusquea, the tree ferns Cyathea, and one nonaerial Carludovica, as well as numerous shrubs, vines, epiphytes, ferns, mosses, and lichens also abound (Tosi, 1960).

On the whole, this district is very rich in fauna, especially birds, bats, and batrachians among the vertebrates, and a great variety of insects. Characteristic fauna are the cock-of-the-rock (Rupicola), the torrent duck (Merganetta), toucans (Aularohrynchus, Pteroglossus), the pudu (Pudu mephistopheles), the false paca (Dinomys branickii) and the spectacled bear (Tremarctos ornatus) (also found in the elfin forest).

The High Forest District

The High Forest district is located between 600-800 meters and 1,600-1,800 meters above sea level, and is a transition zone separating the Amazonian and Yungas provinces. In the Holdridge system, it incorporates the Tropical Premontane Rain Forest, Tropical Premontane Wet Forest, and a large part of the Tropical Premontane Moist Forest life zones. Mean annual rainfall of this district varies between 940 and 1,970 mm, with the least amount of rainfall occurring in the Tropical Premontane Moist Forest. Mean temperatures range from 17°C to 26° C.

In the Tropical Premontane Rain Forest portion of the district, the topography varies between rolling and moderately steep. The soils are comparatively deep, relatively acid, and of medium to heavy texture. Among the edaphic groups, the ortic acrisols, urvisols and the eutric and dystric cambisols predominate. Gleysols and fluvisols, which are the most fertile soils of the region, are also present. In the other two zones in the district, the topography is steep, with slopes of 70 percent or more. The soils are acid and shallow or moderately deep (ONERN, 1976).

The vegetation is quite varied and boasts trees of great commercial value such as Cedrelinga, Juglans, Tabeluia, Cedrela, Cordia, Aspidosperma, Guarea, Trichilia, Aniba, Ocotea, Persea, Nectandra, Podocarpus, Weinmannia, etc. Palms belonging to the genera Euterpe, Bactris, Wettinia, and Geonoma are abundant. In abandoned clearings one finds communities of Cecropia, Psidium, Visma, and Melastomaceae, as well as the bamboos Chusquea and Guadua and in less developed soils, the fern Pteridium (Tosi, 1960). Much of the district's fauna is also found in the Amazonian province, such as the mammals Tayassu, Tapirus, Felis, Panthera. Lutra, Mazama, Hydrochoerus, Myrmecophaga, and Priodontes, as well as a large number of birds, reptiles, and batrachians. The diversity of fishes is greater than in the districts mentioned above, but is still low compared with the Amazonian province.

Amazonian Province

The Amazonian province includes, in the Holdridge System, the Tropical Dry Forest, the Tropical Moist Forest, and the Tropical Wet Forest life zones, as well as the lower sections of the Tropical Premontane Moist Forest life zone. It extends from 600-800 meters in altitude to near sea level, although in the Central Selva its lowest altitude is approximately 150 meters.

Climatically, an enormous difference exists between the Tropical Dry Forest, which receives an average 900-1,400 mm of annual rainfall, and the Tropical Wet Forest which, while usually boasting an average mean precipitation greater than 4,000 mm, sometimes experiences almost double that amount. In contrast, the average annual rainfall of the Tropical Moist Forest ranges from 1,900 to 3,400 mm. Average temperatures are very stable, varying between 23° C to 26° C.

The topography of this province is predominately rolling or hilly although in the Tropical Wet Forest Zone it is occasionally steep. The soils are usually deep, fine-textured, and either acid or, in the dry areas, neutral. Acrisols predominate in the humid and very humid life zones. Vertisols and cambisols predominate in the dry life zone. In the humid life zones, vegetation is typically lush high forest, rich in bromeliads, orchids, vines, and reeds. Tree trunks are usually covered by epiphytes and vines, including Araceae, ferns, lichens, and mosses. The highest trees rise more than 50 meters. Four plant strata can be distinguished although five may occur in the very humid zone. The most conspicuous species in this province belong to the genera Cedrela, Swietenia, Chorisia, Virola, Calophyllum, Brosimum, Guazuma, Hura, Simarouba, Spondias, Miroxylon, Aspidosperma, Duguetia, Aniba, Nectandra, and Ocotea among others. Palm genera present include Scheelea, Phytelephas, Socratea, Iriartea and Astrocaryum. Stands of Mauritia, Euterpe and Jessenia occur in hydromorphic areas and in poorly-drained sites. Secondary growth is usually dominated by Cecropia, which sometimes forms pure stands.

In the Tropical Dry Forest the vegetation is shorter and forms three forest strata; scattered trees reach 30 meters in height. In this forest are seen various cacti, conspicuous arboreal plants belonging to the genera Cedrela, Amburana, Hymenaea, Manilkara, Tabebuia, and Schinopsis, and palms of the genera Scheelea, Phytelephas, and Astrocarym.

The fauna is typical of the Amazonian plain and includes a great diversity of primates (Ateles, Alouatta, Cebus, Saimiri, Lagothrix, Saquinus), bats, and rodents. Conspicuous mammals include peccary, tapir, capybara, deer, jaguar, ocelot, puma, otter, and nutria. Also occurring are the rare canids Atelocynus and Speothos, the procyonids Nasua and Potos, diverse mustelids, and a large number of edentates. Dolphins live in the rivers but not manatees. Birds are abundant and there are many reptiles and batrachians. The reptiles include Caiman, Crocodylus, Melanosuchus niger, and the turtles Podocnemis unifilis and P. geochelone.

Classification of the Central Selva within the American humid tropics

Now that we have seen something of the diversity of the major ecosystems in the Peruvian Central Selva we must remember that this region comprises scarcely 0.5 percent of the humid tropics in North, Central, and South America and includes only two of the six provinces recognized by Cabrera and Willink (1973) and two of the 13 recognized by Udvardy (1975). Numerous mountain ranges, although less significant than the Andes, also contribute to the region's complexity.

As the climatic, topographic, geologic, and edaphic characteristics all vary, so also do biota, although they may share similar characteristics. Many plant genera and species of both flora and fauna may occur throughout the large majority of biogeographic provinces, but a great many are also endemic to each province and occasionally to each life zone. For example, some conspicuous mammals, like the peccary (Tayassu tajacu), the jaguar (Panthera onca), the ocelot (Felis pardalis), the puma (Felis concolor), and the deer (Mazama americana) have a wide distribution. Others, like Tapirus terrestris, have extensive ranges, but only in certain provinces. Tapirus bairdi, meanwhile, appears in Central America, while Tapirus pinchaque is only found in certain districts in Peru, Colombia, and Ecuador. Other species are endemic to one or a few Holdridge life zones. For example the yellow-tailed monkey (Lagothrix flavicauda) is found only in the Atlantic province, and the monkeys of the genera Leontopithecus occur only in the Sierra del Mar province of Brazil.

Soils

Only 7 percent of the American humid tropics contain moderately fertile soils. The remainder is covered with soils that are acid and infertile (oxisols and ultisols), poorly-drained, sandy and infertile, or shallow.

The most abundant are the oxisols (50%), followed by the ultisols (32%). Both are acid and poor in nutrients, although oxisols have good physical properties and are deep and well-drained. The ultisols are similar morphologically since they are also well drained and deep. However, they exhibit a marked increase in the percentage of clay in their deeper portions and their physical properties are less favorable, since they usually occur on hillsides and are thus susceptible to erosion (NRC, 1982, Sanchez and Cochrane, 1980). Oxisols and ultisols also contain serious chemical deficiencies: high acidity, toxic levels of aluminum, deficiencies in phosphorus, calcium, magnesium, sulfur, zinc, and other micro-nutrients; low cation exchange capacity, and high phosphorus-fixing capacity. Some oxisols have low water retention capacity. On the other hand, evidence now indicates that these soils are not as susceptible to laterization as previously believed (NRC, 1982).

The young soils called inceptisols, entisols, gleysols, andosols, cambisols and fluvisols, and regosols and litosols in the Central Selva description may be either fertile or infertile and cover 14 percent of the American humid tropics. The remaining 4 percent are covered with alfisols (luvisols, eutric nitosols, planosols), spodosols (podzols) and vertisols.

Unfortunately, different nomenclature systems have been used in the edaphology of the humid tropics. Each method has its positive points, but it can become confusing for professionals who are not soil specialists. The U.S. National Research Council (NRC, 1982) has provided information (Table 4-4) that can prove useful in correlating different classification systems.

Table 4-4 - SOIL CLASSIFICATION TERMINOLOGY IN THE HUMID TROPICS

Ecosystems

Each biographic province, or district, and each life zone contains a number of units that are sufficiently differentiated, organized, and stable to be considered ecosystems themselves. Such areas include rivers, lagoons, ravines, swamps, floodplains, hills, and mountainsides. And ecosystem diversity is even greater if one considers the semi-natural (some would say artificial) ecosystems created through human intervention. Table 4-5 illustrates some of the most common ecosystems.

All ecosystems, as well as the species within them, are influenced significantly by other ecosystems, especially adjacent ones. Aquatic ecosystems, for example, are closely influenced by the terrestrial ecosystems that surround them. In effect, rivers are only functional parts of larger units. Their water runs off from land surfaces or arises from ground water that drains into rivers. Chemical and physical action of this runoff carries all it can move, including particulate and soluble material derived from the decomposition and remineralization of organic material.

Table 4-5
COMMON ECOSYSTEMS IN THE AMERICAN HUMID TROPICS

Interdependence Between Species and Succession

Any disturbance, natural or human, that creates a new habitat or significantly alters an existing one, results in a fixed series of species composition called succession. For example, the first plants in an area benefit from low competition for light and nutrients. This may be the only opportunity for some 75 percent of the forest tree species to reach maturity (Hartshorn, 1978). At the same time, many invertebrates and vertebrates rely on succession for their life cycles: invertebrate species, when young, may require a home in successional vegetation, while as an adult, it may live in climax forest. In other words, successional areas are indispensable to healthy forest regeneration, as well as to the survival of numerous animal species.

Available data suggest that population interaction is more significant in regulating the structure and function of communites in the humid tropics than it is in temperate regions. The roles of bats, birds, insects, and other animals that feed on seeds in open forest clearings are examples of this. The Brazil nut tree, Bertholletia excelsa, depends on certain bees in the family Meliponidae for pollination, and its seeds have to pass through the digestive tracts of certain rodents to be able to germinate. When this tree is not in flower, the bees depend on the flowers of other small trees. Eliminating these trees, then, indirectly impedes Brazil nut fertilization.

Leaf cutter ants of the genus Atta are another example of interdependence. These ants are affected by plant succession, with their nests being more numerous in early successional stages and less so in climax forests. But the ants, in turn, influence plant succession through their selective use of plant species and their contribution of deposited nutrients.

Species Diversity

Species diversity in the humid tropics is extraordinary. Hundreds of species can occur on one hectare, including perhaps one hundred species of trees. The number of animals is still greater: 42,000 species of insects have recently been estimated as occurring on only one hectare (NRC, 1982), and Janzen (1982) found 50 species of ants on hardly one square meter. Over 100 species of mammals, 400 species of birds, 100 species of reptiles, and somewhat fewer batrachians can be found on only one tenth of a square kilometer. This diversity, which so successfully exploits humid tropical conditions and the low fertility of most tropical soils, makes it considerably challenging for man to exploit these ecosystems without losing some of their genetic resources, a substantial portion of which is endemic.

In large measure, evidence suggests that the diversity of tropical species may be the result of the climatic changes that occurred in tropical America during the Quaternary epoch, especially during the last 100,000 years. Particulary significant was the glacier-caused climatic conditions alternately favorable and unfavorable to life. During glaciation, biota became isolated in a few areas where they were able to survive because of the humidity. Between glacial periods, species spread out from these refugia and intermingled. The dispersion that followed repeated glacier-caused isolation created an astonishing diversity of species. The Pleistocene refugia that have been clearly identified in various countries, including Brazil and Peru, are centers of growth for endemic species; preserving them can effectively protect genetic patrimony.

Protection of major ecosystems in the humid tropics

Protected areas are areas that enjoy special legal status, that are under absolute protection or restricted use, and that guarantee the conservation of the ecosystems and species they contain. In Latin America and in other parts of the world, the diversity of terms designating protected areas and the objectives under these terms are so great that the International Union for the Conservation of Nature (IUCN) adopted a nomenclature classifying alternative management categories according to the primary conservation objectives followed in each case. Roman numerals in the list below indicate the IUCN equivalents of Peruvian categories. Seven categories are recognized by the Peruvian legislature: national parks (I-II), national reserves (III), national sanctuaries (III-IV), historic sanctuaries (V), forest reserves (VIII), hunting reserves (VIII), protected zones (VI), and communal reserves (VII). Of these, the first four are part of the National System of Conservation Units. The forest reserves are managed directly by the forest administration proper, not by that of the national parks, while the hunting reserves and communal reserves are managed by the wildlife administration. Protected zones (VI), as a rule, are transitional, usually becoming converted to one of the other categories.

The Peruvian National System of Conservation Units consists of 18 national parks, national reserves, and national and historic sanctuaries that, together, comprise 4,285,499 hectares or 3.33 percent of Peru's territory. The system also includes 2,560,739 hectares accorded the status of Biosphere Reserves, of which three are presently established. Studies of an additional 11 conservation units are at a fairly advanced stage. If established, these areas would protect more than 5 million additional hectares. It is therefore realistic to expect that by the end of the century Peru will be protecting, under special management, more than 7 percent of her territory.

Among the five national parks (1,984,606 ha), eight national reserves (2,218,006 ha), two national sanctuaries (11,315 ha), and three historic sanctuaries (35,392 ha), only four units belong to the designated Yungas province as classified by Udvardy (1973). These units are Manu (1,532,806 ha), Tingo Maria (18,000 ha), and Cutervo (2,500 ha) National Parks, and Machu Picchu Historic Sanctuary (32,592 ha).

Following Dourojeanni and Rios (1981), only 884,585 hectares of the.Yungas province are protected (4.1%), of which 95 percent belongs to the highlands of Manu. On the other hand, Tingo María and Cutervo are far too small to assure the conservation of their biotas and, in addition, are significantly altered by forest exploitation and shifting cultivation. Nevertheless, Yungas province has special significance because it contains the greatest biological diversity and the highest proportion of biological endemism in Peru. It is also the most threatened by agriculture and grazing expansion. Various studies demonstrate that, in the next two decades, 7 million hectares in this region will be affected, for a total of some 12 million hectares in all (Dourojeanni, 1980). When this happens the loss of floral and faunal species will be great.

Three areas in the Central Selva have been proposed as conservation units. The first is Cutibireni, in the Vilcabamba Cordillera, the second is Yanachaga, and the third is Sira-San Carlos. Yanachaga is an example of the Chanchamayo-Apunnnac Pleistocene refugium, while Sira-San Carlos would preserve a portion of the Pachitea-Ucayali refugium, and Cutibireni a portion of the Urubamba refugium. The projected national park in the Sira cordillera would enclose 1,022 hectares, the Yanachaga conservation unit would contain 226,000 hectares, and the Cutibireni would most likely contain close to one million hectares (Dourojeanni, 1980).

Conservation Units in the American Humid Tropics

Table 4-7 presents a list of the conservation units (national parks and equivalent reserves) recognized by IUCN (1980) that existed in the American humid tropics in 1980. It can be seen that there were 87 established units containing almost 143,000 square kilometers or 16 percent of the region. The Udvardy (1975) provinces best represented are the Panamanian (4.2%), the Amazonian (36%), the Colombian Coast (3,6%) and the Colombian Montane (3.3%). Those least represented were the Guerreran province, the Brazilian Rain Forest, the Sierra del Mar, the Campeche, the Madeiran, the Guyanan, and the Central American, all with less than 1 percent of their territory protected. Only the Yucatan province contained no recognized conservation unit.

The effectiveness of the conservation and management of these 87 units is highly variable. Some areas have been virtually abandoned, although that does not necessarily mean the resources that justified the establishment of these places have been lost.

Table 4-7
CONSERVATION UNITS IN THE AMERICAN HUMID TROPICS BY BIOGEOGRAPHIC PROVINCE (UDVARDY)

There exist no precise guidelines that specify the minimum percentage of a region's or ecosystem's territory which should be protected to assure the survival of its genetic patrimony or to realize other objectives. It is estimated, however, that this figure should at least be between 3 percent and 7 percent. The percentage of protected land in the American humid tropics is well below this figure; nevertheless, the last four years have witnessed the establishment of several new conservation units in Brazil and Central America. With those proposed for Peru and other countries, at least 2 percent of the land should ultimately be protected.

Other protected areas exist that belong to categories not included on the IUCN list: forest reserves, national forests, protected forests, watershed reserves, and others. However, these areas in Latin America generally exist only on paper and have not generated the management they require.

Products and Services Produced by Protected Areas

Among the products that come from protected areas are those that are made from non-woody plants, one of the few species whose exploitation can be acceptable in certain types of protected areas, such as forest and watershed reserves. Non-woody plants are very important to local economies. They provide a wide variety of products, including gums, latex, resins, barks and bark fibers, leaf fibers (especially palms), fruits, seeds, flowers, leaves used in construction, vines for ropes, ornamental plants, medicinal plants, plants used in magic, drugs, fodder, and edible fungi.

Protected areas in the humid tropics provide numerous and varied services such as flood and erosion control; a genetic bank, fresh water; ecosystem buffering; and recreation (Miller, 1980). The significance of these services depends closely on the objectives and size of each protected area. Thus, national parks, national reserves, and forest reserves, which are the largest protected areas, provide the most important services from a global perspective. All of these areas, excepting reserved zones, include the provision of some of these services as concrete objectives.

Protected areas may seem to be obstacles standing in the way of development. But if we consider that in two or three decades they will be the only large areas of the American humid tropics left that have not been severely altered by human activity, protecting them will be seen as the only way to insure the survival of the truly irreplaceable services they provide.

Conflicts between protected areas and other types of natural resource use

A number of conflicts exist between protection of an area and other types of natural resource use. These conflicts may be grouped into three categories: conflicts originating over the proposed use of planned or existing natural areas in ways incompatible with these areas' stated objectives; conflicts originating over the proposed use of such areas in ways which are moderately compatible with their objectives; and conflicts occurring in other areas and with other activities as a result of the existence of protected areas.

The first type of conflict is fundamentally irresolvable: one cannot cut and burn vegetation to make fields or pastures in a national park. This incompatibility is so absolute that compromise is not a viable solution. These conflicts must be avoided or prevented because resolving them always creates new problems.

The second type of conflict, unlike the first, may have some solution. This type of conflict arises when exploitation of a protected area's resources is not entirely compatible with the area's objectives. For example, a road might have to be built through a park or national reserve. If its construction adheres to certain restrictions, it may, in fact, be not only feasible but actually beneficial to the protected areas it traverses.

The third type of conflict appears when protected areas have adverse effects on human health and activities. The typical example is the national park or other natural area harboring animals that are agricultural pests, human and livestock parasites, and reservoirs of disease. The closer such areas are to susceptible human activity, the greater is their impact and the conflicts that result. For instance, vampire bats and large cats can attack livestock and then find shelter in adjoining protected areas. This type of conflict generally has an appropriate technical solution.

Important conflicts arise because of the amount of territory that protected areas occupy and the necessity to maintain these areas inviolate. Such is the case with national parks which need to contain large expanses of land. Because they protect examples of different ecosystems and their genetic diversity, they must, out of necessity, occupy lands potentially valuable for agriculture, livestock, or timber harvest. This, too, can aggravate conflicts.

Forest reserves are often created especially to protect highland watersheds. That is, they prevent erosion and maintain the quantity and quality of water supplies. While hunting, fishing or even mining (provided it does not pollute air and water) may not cause problems, conflict rages if forests boast valuable tree species (Podocarpus or Juglans) attractive to lumber interests. The harvest of large tracts of trees is incompatible with soil and water conservation, unless such harvest is conducted with utmost care.

In many cases, the significance of a conflict depends not upon the size of the protected area, or its attractiveness to industry, but on other factors altogether. Such is the case with national and historic sanctuaries. These areas are generally small, ranging in size from hundreds to several tens of thousands of hectares. They either protect designated ecosystems, species, or geologic phenomena, or else are designated as archaeological or historic treasures. However, these areas must remain absolutely inviolate. The importance of conflicts generated by them may become globally significant, as in the case of the hydroelectric plant built in the heart of Peru's Machu Picchu Historic Sanctuary.

It is necessary to keep in mind that conflicts arise not only in relation to the effect protected areas have on neighboring territory or on their own land. They also include activities conducted on neighboring areas that affect protected areas. This is the case with industrial contaminants, such as those produced by metal refineries, cement factories, or pulp and paper mills above or upwind of protected areas. Protected areas can also be damaged by fertilizers, pesticides, and other agricultural contaminants and urban contaminants that are transported by wind and water. The smaller the protected area is, the worse is the resulting damage. Such negative influence on conservation units and other protected areas have led to the creation of the concept of "buffer zones" or "strips" such as when national forests surround a park, reserve, or national sanctuary, or partially isolate them from agricultural and grazing areas and from industrial and urban development.

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