II. ASPECTS OF THE GEOGRAPHY OF PERU

A. Geomorphology
Orographically, the Peruvian territory can be divided into two main regions: the Andes and Amazonia (PULGAR-VIDAL, 1981). The Andes comprise the Pacific coast in the west and the elevations of the cordillera in the east. The cordillera traverses Peru from the north to the south, forming chains of mountains with elevations of more that 6000 m a.s.l., and includes plateaus, junctions, valleys, and lakes.

The Andes form the watershed between those rivers that drain into the Pacific Ocean in the west and those that finally drain into the Atlantic Ocean in the east.

According to PEÑAHERRERA (1986), nearly 10% of the Peruvian territory is formed by the beaches and deserts of the Pacific coast, which is intersected by the valleys and deltas of the rivers that drain into the Pacific ocean. The Andean region comprises about 25% and Amazonia about 65% of the Peruvian territory.

The forested Amazonian region commences on the eastern slopes of the Andes at about 3800 m a.s.l. and extends into an immense plain that is interspersed with all those rivers which form the hydrographic network of the Amazon. It comprises three geomorphologically different units: the ceja de selva between 800 and 3800 m a.s.l., the selva alta between 400 and 800 m a.s.l., and the selva baja between 80 and 400 m a.s.l.. We will make special reference to the latter region because it embraces the habitats of most Peruvian primates.

The ceja de selva (between 800 and 3800 m a.s.l.) is a very hilly terrain with deep and narrow river canyons and slopes with an inclination of more than 40º. The numerous rivers are characterized by narrow beds filled with large boulders. Although they are covered by luxuriant cloud forests (bosques de nubes), the slopes of the river canyons are generally inappropriate for human settlements and agricultural activities. Selective timber logging in this area accelerates soil erosion and landslips, leading to so-called huaycos after heavy rains.

Since the times of the Inca empire, man has progressively invaded the ceja de selva, a process which has accelerated in our century. Agricultural activities have increased notably, especially with the cultivation of tea and coffee, stock-farming and the illegal cultivation of the coca plant.

In the ceja de selva primates of the genera Lagothrix, Ateles, Callicebus, Aotus and Saguinus are found.

The topography of theselva alta is characterized by long narrow valleys which are the extensions of the large canyons of the ceja de selva. In modem times, these valleys and the lowest and most recently formed terraces have been almost completely occupied by human settlements, due to the higher suitability of their soils for agricultural activities. Higher terraces are easily eroded in a manner that leads to hills with rounded tops, looking plain from a distance but which constitute watersheds for the principal rivers and their tributaries. As long as the natural vegetation is maintained, the numerous creeks carry water constantly. However, after tree felling, these creeks transform into seasonal streams with high morphological dynamics during the rainyseason. Terraces of this type can be found in San Ignacio (Department of Cajamarca), in the upper parts of the valleys of the rivers Huallaga, Juanjui and Tingo de Saposoa, north of Bellavista (Department of San Martín), and in the lower parts of the Rio Urubamba (Department of Cusco).

Soil erosion by slow or creeping landslips is common in the selva alta. It increases when the forest is cut down and also affects human settlements and plantations located in the bottom of the valleys.

The rivers are bounded by precipices formed by sandy and calcareous rocks which are covered with abundant arboreal vegetation. Examples for such precipices can be found in the Cajón de Sión and Pericote of the Huallaga river between Tocache y Juanjui and the canyons of El Vaquero between Shapaja and Chazuta, but the most impressive are the so-called Pongos de Manseriche, Rentema and Huaracayo of the Marañón, the canyon of Tingo María formed by the Huallaga, and the canyons of the rivers Apurímac and Urubamba. Before entering the selva baja, the major rivers have eroded the counterforts of the eastern Andes in the Pongo de Manseriche of the Marañón, Pongo de Aguirre of the Huallaga, Pongo de Tambo, of the Rio Tambo, and Pongo de Mainique of the Rio Urubamba.

Primate populations have disappeared from large areas of the selva alta as a consequence of intensive agricultural activities, lumbering, and hunting.

The selva baja or Amazonian plain (between 80 and 400 m a.s.l.) comprises the largest portion of the Peruvian territory. It is characterized by the presence of extended high ground terrain with a hilly topography which is steep and clearly dissected in the west adjacent to the selva alta, and with smoother undulations in the east. The westernmost hills may reach altitudes of 100 m. In some areas, high ground zones represent old river terraces and lake bottoms or eruptions of sand. This high ground terrain is interspersed with ample swampy and seasonally inundated areas which often represent former river courses.

The low-lying swampy and seasonally inundated areas are covered with dense forests, so-called tahuampas, aguajales, renacales, ceticales, etc. which are products of the eutrophization of the river meanders (ENCARNACIÓN, 1985). The inundated areas have the most productive soils for short-term agriculture and agrosylviculture of native fruit species (Sioli, 1974), but the swampy areas are of only marginal value for forestry and agriculture. Therefore, they represent alternative areas for wildlife management, e.g. of primates.

B. Climate
Due to its location between the tropics, Peru should have a warm, humid and rainy climate. However, the chain of the Andes one of the highest mountain ranges in the world the anticyclonic circulation of the southern Pacific Ocean, the Peruvian Current with its temperate waters, and the El Niño Current with its warm water have given rise to a variety of climatic conditions, from tropical, warm and humid in Amazonia and on the northern coast around Tumbes, to the cold and dry climate of the punas and high cordilleras, the and climate of the central coast and the western slopes of the Andes, and the temperate climate of the medium attitudes and interandean valleys. A gradient is apparent along the Pacific Coast with regard to temperature and rainfall. An area of high temperature and heavy precipitation exists on the northerncoast which allows for the existence of tropical forests and the presence of Alouatta palliata and Cebus albifrons. While the central coast shows temperate climate with sparse winter rain, the southern coast is much colder with sparse rain in the summer.

The variable climate of the Andean region is determined by the geomorphology of the terrain. It is warm and humid in the deep and narrow eastern interandean valleys, and dry and temperate on the western slopes. Between 1000 and 2000 m a.s.l. on the western slopes, the climate is subtropical and with strong insolation in winter, rainfall below 50 nun, and annual mean temperatures between 17ºC and 19ºC, maxima up to 44ºC and minima as low as 4ºC. On the eastern slopes, mean annual rainfall varies between 400 and 1000 rum, minimum temperatures between 6ºC and 18ºC and maximum temperature reaches 30ººC, generally in the summer. Between 2000 and 3500 m a. s.l. the climate is temperate, with annual mean temperature between 11ºC and 16ºC, maxima between 22ºC and 29ºC, and minima between 4ºC and 7ºC in the winter. Temperature oscillates during the day between 10ºC and 20ºC, with means between 12ºC and 16ºC. Rainfall reaches between 760 and 1200 mm on the western slope and 300 and 1200 rum on the eastern slope. In these altitudes the climate is most favourable to man and its activities. Between 3500 and 4000 m a.s.l., one finds the climate of high tropical mountains, with annual mean temperatures between 7ºC and 10ºC. During the day temperature may reach 20ºC, during the night it may fall below 0ºC. Annual rainfall is above 4000 mm. Finally, above 4000 m a.s.l., very low temperatures make the climate similar to polar and subpolar zones.

In the selva, including the ceja de selva, selva alta and selva baja, annual rainfall generally varies between 800 and 3800 mm. In the selva alta the climate is tropical, with annual mean temperatures between 22ºC and 25ºC, maxima between 33ºC and 36ºC, and minima between 8ºC and 15ºC (nights are frequently cold). Rainfall varies between 500 mm in the north (Jaén in the Department of Cajamarca) and 8500 mm in the south (Quincemil in the Department of Cusco). Rain is abundant during the summer (December to March), but may be less than 100 mm. between June and October.

In the lowland rain forest (selva baja) the climate is tropical with mean annual temperatures above 25ºC and maxima of more than 36ºC (occasionally up to 42ºC in Pucallpa). The lowest temperatures are recorded between the rivers Acre and Tahuamanú in the Department of Madre de Dios. Annual rainfall is higher than 1000 mm, but rarely exceeds 5000 mm. However, exceptionally 10000 mm of rain may fall (Tarapoto in the Department of San Martin). Humidity is always high, due to the network of watercourses and to evapotranspiration.

C. Hydrography
The littoral region of Peru is 3080 km long and 53 rivers drain into the Pacific ocean. The catchment area of the littoral region covers 280000 kM2, corresponding to 22.6% of the Peruvian territory, from the narrow valleys of the western slopes of the Andes to the river deltas of the coast. The Lake Titicaca, at 3809 m a.s.l., has a small inner-Andean catchment area. The largest hydrographic region of Peru, which drains its waters into the Atlantic ocean, covers an area of 960000 kM2 (77.4% of the Peruvian territory), and extends from the punas, peaks and canyons of the Andes through the vast forests of the ceja de selva and the large Amazon floodplain.

Along the courses of the rivers in the ceja de selva and selva alta, a tight geobiotic relationship exists between the forest, the relief of the terrain and the drained water volume.

The rivers Zarumilla and Tumbes on the Pacific coast spring from the western slopes of the Andes in Ecuador; they run through and are closely related to the bosque tropical del Pacífico with its alluvial soils and hilly relief. This forest is the only habitat of Alouatta palliata in Peru.

Numerous rivers are found in the selva region. One of the principal rivers is the Rio Marañón, which runs through Amazonia from the Department of Huánuco, first northward, then eastward. Amongst its principal affluents are the rivers Cenepa, Santiago, Morona, Pastaza and Tigre on the left bank and Utcubamba, Nieva, Samiria and Huallaga on the right bank. The Huallaga runs northward through the central part of the Amazon floodplain until its junction with the Marañón. The major affluents of the Huallaga are the rivers Chinchao, Monzón, Chontayacu, Tocache, Huayabamba, Saposoa, Sisa, Mayo, Paranapura and Aipena on the left bank, and Tulumayo, Biabo, Ponaza and Chipurana on the right bank. The largest hydrographic network is formed by the basin of the river Ucayali -Apurímac; the upper course of this river forms the boundary of the selva baja. Its major affluents are the rivers Urubamba (formed by the rivers Paucartambo, Camisea, Shepagua, Inuya), Sheshea, Tamaya, Maquia and Tapiche on the right bank, and Mantaro, Perené, Pachitea, Aguaytía, Pisqui, Cushabatay and Pacaya on the left bank.

The basins of the river Marañón, Huallaga and Ucayali form the basin of the Amazon in Peru, whose course up to Manaus in Brazil is called Rio Marañón or Solimoes in the hydrographic terminology. Among the major affluents of the Amazon are the rivers Itaya, Nanay, Napo, Yavarí-Yaquerana, Putumayo, Yurúa and Purus (the latter three flow into the Amazon in Brazil).

The basin of the river Madre de Dios covers an area of nearly 95000 kM2 in the southernmost part of the selva in Peru. Its major affluents are the rivers Inambari, Tambopata, Manú, Cashpajali, de las Piedras, Manuripe, Muymanu, Tahuamanú and Acre; several of these rivers flow into the Madre de Dios in Bolivia and Brazil.

The colour of the river waters in Amazonian Peru is an indicator for the drainage area of the rivers and their physical and chemical properties which are important for the close ecological relationship with the vegetation and the fauna.