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EASTERN SLOPES OF PERUVIAN ANDES
The eastern slopes of the Peruvian Andes (picture) form a complex, rather natural geographical and biogeographical region (Map 72). Similar topography and vegetation formations are present on the Andean slopes facing the Amazon Basin from Venezuela to northern Bolivia, from c. 400 m elevation in the lowlands to often more than 3500 m. In Peru at c. 5°S, a natural barrier often called the Huancabamba Depression (see CPD Site SA32) is formed between the Northern Andes and Central Andes by the Marañón River (Vuilleumier 1977; Duellman 1979). This is our northern limit of the Peruvian eastern-slope region. The southern limit is arbitrarily the boundary between Peru and Bolivia.
Although the region can be delimited with these altitudinal, topographical and political boundaries (Map 72), the eastern slopes are not homogeneous. They have great vegetational and floristic diversity which is directly related to the region's geological and climatic diversity.
There are two major geological subdivisions. From 6°-11°S is a largely Precambrian metamorphized sedimentary rock mass with some areas of Tertiary-Quaternary volcanism, some Palaeozoic intrusives, and some sedimentary formations of Late Triassic-Jurassic, Tertiary and Quaternary ages (Peñaherrera 1989). The other subdivision extends from 11°-15°S and consists mostly of Early Palaeozoic sedimentary rocks, often locally metamorphized, with significant Permian-Triassic intrusives, and Tertiary sedimentary and metamorphic rocks.
General edaphic conditions in the two subdivisions might be different, because of the preponderance of different rock types. Surely greater edaphic diversity will be found in the transition zone (around 11°S) between the two geological areas, where large intrusive blocks are present amid a complex mix of sedimentary and metamorphic rocks. This expectation is supported by observations on the relationship between great edaphic variation and the resulting high floristic diversity in Yanachaga-Chemillén National Park (10.5°S, 75.5°W) (R.B. Foster, pers. comm.).
The Peruvian eastern slopes can be subdivided preliminarily into six physiographic provinces (Young 1992):
1. The Chachapoyan province, from 4.5°-7°S, consists of a series of north-west-trending mountain ranges.
2. The Western Huallaga province, from 7°9.5°S, is located in the upper watershed of the Huallaga River and contains two parallel mountain chains - the Eastern Cordillera of the Andes and farther east the Cordillera Azul.
3. The Upper Pachitea River province, from 9°-11°S, includes two mountain ranges originating from the Cerro de Pasco area, and the headwater rivers draining into the Pachitea River.
4. The Tambo River province, from 11°-13.5°S, includes the headwaters of the Perené and Ene rivers.
5. The Urubamba River province, from 11°-14°S, is in the drainage basin of the Cusco highlands.
6. The Madre de Dios province, from 12°-14.5°S, includes the watershed of the Madre de Dios River.
The climate of the eastern slopes has been little studied; long-term records of precipitation and temperature do not exist. Based on extrapolated isolines of median temperatures and rainfall, local climatic regimes appear to vary from 9°-25°C and 500-7000 mm per year. Circulation is out of the Amazon Basin from east to west, and the most rain occurs from November to April, when the Intertropical Convergence Zone is south of the Equator. In the southernmost portion of the region, climatic patterns also are affected by cyclone systems originating in southern South America during its winter (ONERN-AID 1986).
More than 25 life zones in the Holdridge system have been designated for this region, using extrapolations of the limited climatic data, and separated by latitude (tropical to the north of 12°S and subtropical to the south), humidity province (dry, moist, wet, pluvial) and elevation (Tosi 1960; ONERN 1976). Drier life zones are in rain shadows in deep north-south trending valleys. Perhumid zones occur where the cloud belt forms: 1500-2500 m in the south, often 2500-3000 m in the north, except on lower peaks or mountain ranges.
An informal version of this life-zone system can be helpful to name the vegetation formations: Lowland tropical or subtropical forest, found from 200-500 m; a premontane forest zone, occurring roughly from 500-1500 m; lower montane forest formations, located from 1500-2500 m; and upper montane forest (picture), found from approximately 2500 m to local treeline -which is at 3000-4000 m, with the highest elevations in the south and in areas not repeatedly burned by fires originating in adjacent high-elevation grasslands. The physiognomy of a particular forest and its species composition depend greatly on the local precipitation. Trees in cloud-belt forests tend to be somewhat shorter and covered with epiphytes.
Each of the six physiographic provinces is unique in the relative importance of these vegetation formations (Young 1992). The three northern provinces include elevations from 400-4000 m, whereas the southern provinces range from 400-5000 m and can be 30% covered by "puna" grasslands in their highest elevations (see CPD Site SA33).
The Chachapoyan province originally was covered mostly by moist premontane and lower montane forests, and includes some dry forest on its western and northern boundaries with the Marañón River. The Western Huallaga River province is about half covered by moist to wet montane forests, with the lower elevations originally dominated by dry to moist premontane and lowland forests. The Upper Pachitea River province is extremely humid, with moist, wet and pluvial forests occurring at all elevations. The Tambo River province once had extensive areas of dry to moist premontane and montane forests, but the remaining forests are located mostly at lower elevations and in more humid areas; one sizeable lowland area, the Gran Pajonal, is a savanna maintained by human-induced burning (Scott 1978). The Urubamba River province was originally more than 50% lowland forest, and the rest is rugged terrain with dry to pluvial premontane and montane forests. The Madre de Dios province is about equally lowland forest and premontane to montane forests.
Certain broad generalizations can be made, but there is little information with which to propose floristic provinces for the region. There are no endemic plant families and few endemic genera: e.g. Guraniopsis (Cucurbitaceae); Pterocladon (Melastomataceae); Anodiscus (Gesneriaceae); Cylindrosolenium (Acanthaceae); and Neokoehleria and Sauroglossum (Orchidaceae). However there are numerous endemic species, undoubtedly due to topographical and ecological barriers. A sizeable number of the species are restricted to one of the six physiographic provinces.
A very conservative evaluation of vascular plant species richness in the moist to pluvial life zones of Peru's eastern slopes estimated 1700-2000 species at 1500-2500 m and 1000-1200 species at 2500-3500 m (Young 1991; León, Young and Brako 1992). The combined elevational zone (1500-3500 m) is c. 5% of Peru's surface area and may have 2400-2800 species, or c. 14% of the 18,000-20,000 species estimated for all of Peru (Gentry 1980). By assuming similar species richness for the altitudinal belt of premontane forest at 500-1500 m, adding another 1000 species present only in the Amazon bottomlands, plus perhaps 300 species restricted to the dry-forest life zones, 7000-10,000 vascular plant species probably comprise the eastern-slope flora of Peru. Thus the eastern slopes, which represent c. 20% of Peru's area, support half of its plant species.
From 400-1500 m, diverse families include pteridophytes such as Dryopteridaceae and Pteridaceae; monocotyledons such as Araceae, Arecaceae and Orchidaceae; and dicotyledons such as Acanthaceae, Annonaceae, Asteraceae, Bignoniaceae, Euphorbiaceae, Fabaceae, Lauraceae, Menispermaceae, Moraceae, Rubiaceae and Solanaceae. Speciose genera include Adiantum, Polypodium, Calathea, Philodendron, Ficus, Inga, Miconia, Mikania, Paullinia, Piper, Psychotria, Solanum and Trichilia.
From 1500-2500 m, diverse families include pteridophytes such as Cyatheaceae, Dryopteridaceae, Hymenophyllaceae, Polypodiaceae and Pteridaceae; monocotyledons such as Araceae, Bromeliaceae, Orchidaceae and Poaceae; and dicotyledons such as Asteraceae, Campanulaceae, Fabaceae, Lauraceae, Melastomataceae, Moraceae, Piperaceae, Rubiaceae, Solanaceae and Urticaceae. The most speciose genera are Hymenophyllum, Tillandsia, Epidendrum, Maxillaria, Pleurothallis, Calceolaria, Miconia, Peperomia, Piper and Solanum.
Above 2500 m, diverse plant families include pteridophytes such as Dryopteridaceae, Hymenophyllaceae and Pteridaceae; monocotyledons such as Bromeliaceae, Orchidaceae and Poaceae; and dicotyledons such as Asteraceae, Ericaceae, Melastomataceae and Scrophulariaceae. The most speciose genera are Huperzia, Hymenophyllum, Bomarea, Tillandsia, Epidendrum, Pleurothallis, Calceolaria and Weinmannia.
There is little sustainable use of the native plant resources in the region, except among traditional tribal peoples. Several groups of tribal peoples are present, mostly using land below 800 m. From north to south, important linguistic groups are the Aguaruna, Nantipa, Chayahuita, Lowland Quechua, Cashibo, Amuesha, Machinguenga, Huachipairi, Maschos and Arasaire. Numerous useful species and wild relatives of economic plants are present, probably including many actual and potential medicinals.
In general, timber trees (Lauraceae, Meliaceae, Podocarpaceae) and ornamental plants (Acanthaceae, Bromeliaceae, Gesneriaceae, Orchidaceae) are removed wherever accessible. The upper elevations in particular harbour many ornamental plants, e.g. ferns, bromeliads and orchids, which are transported to Lima and exported.
Social and environmental values
Because of the steep slopes and need to protect upper watersheds, essentially all of the region above c. 2000 m should be classified as Protection Forest. Tribal lands and hunting grounds are only protected in a natural state in Manu National Park (see CPD Site SA11 and Gentry 1990) and to a lesser extent near Yanachaga-Chemillén National Park. Tourism could be much more developed for this region, but most benefits from such activity usually have not remained with local peoples.
No less than 13 bird species of restricted range in two Endemic Bird Areas (EBAs) of this region are considered threatened; they are primarily in the fragile high-altitude habitats near treeline. From treeline to 2200 m in the High Peruvian Andes EBA (B27), 30 restricted-range bird species occupy the treeline forest patches or montane forests. In humid forest from 2200-600m on the eastern slopes of the Peruvian Andes, in the Eastern Andean foothills of Peru EBA (B29), 11 restricted-range birds occur.
Approximately 6% of Peru's population lives in the region - 1.5 million people. Below c. 2000 m, and especially in the dry and moist life zones, are important agricultural areas for raising cattle and growing maize, rice and tree crops such as coffee and oranges. The most important agricultural area is in the Department of San Martín. The region's major agricultural products are cassava, cattle, coca leaves, coffee, maize, plantains (Musa × paradisiaca) and rice (Young 1992).
Human activities in the region are extractive or destructive, and few have left lasting gains. At lower elevations in parts of the region there is great demand for land to use for agricultural purposes both illegal (extensive coca plantations) and legal (coffee, fruits, maize, rice). The areas most transformed are the lower elevations of the Western Huallaga River and Urubamba River physiographic provinces; the middle elevations of the Chachapoyan province; and the higher elevations of the Tambo River province (much of which has long been deforested and used in highland agronomic and animal-husbandry systems).
The right of Peruvians, especially local people, to develop this region does not negate the need for careful planning and mitigation of environmental impacts. Highway construction has been a major cause or accomplice of destruction of the natural vegetation and fauna on the eastern slopes (Young 1992). The region's only safe areas are those that are inaccessible. However, if not accessible from the existing highways, much of the eastern slopes is within reach of potential highways, which are already in proposals prepared particularly for the international donor agencies.
There is considerable spontaneous migration into the region (INADE-APODESA 1991; CNP and CIPA 1984; Aramburu, Bedoya Garland and Recharte-B. 1982). Most of the colonists are from highland communities where the possibilities for land acquisition and social services are even more limited than they face on the frontier. Amazonas and San Martín departments receive many people each year from the highlands of Cajamarca. The Selva Central sector, especially in Pasco Department, and the lowlands of Ayacucho have received hundreds from the highlands of Junín and Ayacucho who are fleeing the violence associated with guerilla groups. Madre de Dios Department has numerous colonists from the highlands of Cusco, plus c. 25,000 placer-gold miners. Very few colonists bring agricultural techniques appropriate to the ecological conditions of their new homes. Instead, they often try to recreate the deforested environments they were familiar with in the highlands (ONERN 1985). Natural vegetation remaining in the drier areas (dry and moist life zones) is particularly at risk and unlikely to be spared during the next several decades.
Large development projects in the 1960s and 1970s in the Huallaga Valley and Tingo María-Pucallpa area left a poorly designed and maintained highway system, deforestation and social conditions conducive to turning the area into what is now the world's leading supplier of the illegal coca leaves, which are processed into cocaine (Morales 1989). Development projects in the 1980s in the Selva Central (departments of Pasco and Huánuco) have since been virtually abandoned and almost certainly will have the same fate.
The kind of coca most used for the narcotics trade is grown chiefly from 500-1500 m, and occupies 2500-3000 km² of Peru's eastern slopes (Dourojeanni 1989). Control efforts tend to disperse the coca-deforestation front into more isolated valleys and onto steeper slopes. The Perené River area (departments of Ayacucho and Huánuco) also is being affected, and there is little doubt (unless the demand for cocaine should drop) that the Quillabamba (Cusco) and Madre de Dios areas in the south will be dramatically changed over the next several years.
Three National Parks, Río Abiseo NP (8°S), Yanachaga-Chemillén NP (10.5°S) and Manu NP (11.5°-13°S), include about 18,300 km² or 7% of the eastern slopes, including land in three of the six physiographic provinces (Western Huallaga, Upper Pachitea, Madre de Dios). However, protection is mostly passive, achieved by the parks' inaccessibility; only c. 20 park guards cover this vast area (1000 km² per guard!). Also, many important habitats and endemic species are not within these parks.
Other protected areas total c. 6000 km² of the region. They include two designated sanctuaries (Machu Picchu, Ampay), two reserved zones (Apurímac, Tambopata-Candamo), one protection forest (San Matías San Carlos) and one national forest (Biabo). However, the areas are too small (Ampay, 36 km²; Machu Picchu, 326 km²) or receive no actual protection (Apurímac, Tambopata-Candamo, San Matías - San Carlos). Tingo María National Park (180 km²) probably has been destroyed; it was situated at 10°S, which is in the midst of the coca-field area of the Upper Huallaga Valley.
There is little hope for conservation programmes in sectors where the government does not exert control, such as areas with coca-cocaine production and those occupied by guerrilla groups. In other areas, regional development interests, e.g. in building highways, mining, exploiting the timber and then speculating on land values, are currently much stronger than local and international conservation groups. This assessment is based on the recent history of poorly planned development and ineffective conservation efforts in the region. There are, however, large tracts of wilderness on the eastern slopes that potentially could still be protected.
Map 72. Eastern Slopes of the Peruvian Andes, Peru (CPD Site SA37)
Aramburu, C.E.E., Bedoya Garland, E. and Recharte-B., J. (1982). Colonización en la Amazonía. Ediciones CIPA, Lima. 161 pp.
CNP and CIPA (1984). Población y colonización en la alta Amazonía peruana. Consejo Nacional de Población (CNP) y el Centro de Investigación y Promoción Amazónica (CIPA), Lima. 281 pp.
Dourojeanni, M.J. (1989). Impactos ambientales del cultivo de la coca y la producción de cocaína en la Amazonía peruana. In León, F.R. and Castro de la Mata, R. (eds), Pasta básica de cocaína: un estudio multidisciplinario. CEDRO, Lima. Pp. 281-289.
Duellman, W.E. (1979). The herpetofauna of the Andes: patterns of distribution, origin, differentiation, and present communities. In Duellman, W.E. (ed.), The South American herpetofauna: its origin, evolution, and dispersal. Monogr. Mus. Nat. Hist. Univ. Kansas No. 7. Pp. 371-459.
Gentry, A.H. (1980). The Flora of Peru. Conspectus and index to families. Fieldiana Bot., New Series 5: 1-11.
Gentry, A.H. (ed.) (1990). Four neotropical rainforests. Yale University Press, New Haven. 627 pp.
INADE-APODESA (1991). Sistema de información geográfica de la selva alta del Perú: resultados primera etapa. Instituto Nacional de Desarrollo (INADE), Proyecto: Apoyo a la Política de Desarrollo Selva Alta (APODESA), Lima.
León, B., Young, K.R. and Brako, L. (1992). Análisis de la composición florística del bosque montano oriental. In Young, K.R. and Valencia, N. (eds), Biogeografía, ecología y conservación del bosque montano en el Perú. Memorias del Museo de Historia Natural Vol. 21. Universidad Nacional Mayor de San Marcos (UNMSM), Lima. Pp. 141-154.
Morales, E. (1989). Cocaine: white gold rush in Peru. University Arizona Press, Tucson.
ONERN (1976). Mapa ecológico del Perú. Guía explicativa. Oficina Nacional de Evaluación de Recursos Naturales (ONERN), Lima. 117 pp.
ONERN (1985). Los recursos naturales del Perú. ONERN, Lima.
ONERN-AID (1986). Perfil ambiental del Perú. Lima, Peru.
Peñaherrera, C. (1989). Atlas del Perú. Instituto Geográfico Nacional, Lima. 399 pp.
Scott, G. (1978). Grassland development in the Gran Pajonal of eastern Peru. Hawaii Monographs Geography 1: 1- 187.
Tosi Jr., J. (1960). Zonas de vida natural en el Perú. Organización de Estados Americanos, Boletín Técnico No. 5. Lima, Peru. 271 pp.
Vuilleumier, F. (1977). Barrières écogéographiques permettant la spéciation des oiseaux des hautes Andes. In Descimon, H. (ed.), Biogéographie et evolution en Amérique tropicale. Ecole Normale Supérieure, Publ. Lab. Zool. No. 9, Paris. Pp. 29-51.
Young, K.R. (1991). Floristic diversity on the eastern slopes of the Peruvian Andes. Candollea 46: 125-143.
Young, K.R. (1992). Biogeography of the montane forest zone of the eastern slopes of Peru. In Young, K.R. and Valencia, N. (eds), Biogeografía, ecología y conservación del bosque montano en el Perú. Mem. Museo Hist. Nat. Vol. 21. UNMSM, Lima. Pp. 119-140.
This Data Sheet was written by Dr Kenneth R. Young (University of Maryland of Baltimore
County, Department of Geography, Baltimore, MD 21228, U.S.A.) and Dra. Blanca León (Museo
de Historia Natural, Apartado 14-0434, Lima- 14, Peru).
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