Southwest Amazon Moist Forests Ecoregion (South America)
The Southwest Amazon moist forests are in the upper Amazon Basin, encompassing parts of Brazil, Peru, and Bolivia. The vast ecoregion contains some of the richest and largest tracts of intact tropical rainforest in the Amazon. Its inaccessibility has kept most of the habitat intact.
Southwest Amazon Moist Forests
The Southwest Amazon moist forests are in the upper Amazon Basin, encompassing parts of Brazil, Peru, and Bolivia. The vast ecoregion contains some of the richest and largest tracts of intact tropical rainforest in the Amazon.
The ecoregion is characterized by a relatively flat landscape with alluvial plains dissected by undulating hills or high terraces.
The inaccessibility of this region, along with few roads, has kept most of the habitat intact. Also, several protected areas preserve this extremely biologically rich ecoregion.
The Southwest Amazon moist forests ecoregion covers an extensive area of the upper Amazon Basin comprising four sub-basins:
Pastaza-Marañon and Ucayali sub-basins drain into the upper Amazon River in Peru.
Acre and Madre de Dios-Beni sub-basins drain to the east into the Juruá, Purus and Madeira rivers which, in turn, feed into the Amazon River lower down in Brazil.
The region is bisected north to south between Peru and Brazil by the small mountain range Serra do Divisor. Elevations range from 300 m (980 ft) in the west to 100 m (330 ft) on the region's eastern edge.
Because the Southwest Amazon moist forests ecoregion covers such a vast area, there are climatic, edaphic and floristic differences.
Generally, the northern region is wetter and less seasonal than the slightly drier and more seasonal southern region. The northern forests receive approximately 3,000 mm (120 in) of rain annually, while the southern forests receive 1,500 - 2,100 mm (59 - 83 in) of rain annually.
Therefore, the northern region shares less than half of the tree species with forests in the slightly drier, more seasonal southern region. Temperatures range from 22 - 27 °C (72 - 81 °F) throughout the year.
Flora and Fauna
Most forests are dense with a 30 - 40 m (100 - 130 ft) canopy and some emergent trees reaching 50 m (160 ft). As a result, there can be up to 300 species of trees within a single hectare.
Characteristic trees of the northern region include rubber, mahogany, balsam wood, tagua nut, and strychnine. The southern region consists of kapok, kumaru, possumwood, Brazil nut, and Calycophyllum spruceanum trees. Areas of lower diversity are dominated by highly competitive bamboo, such as the fleshy fruit guadua.
The Southwest Amazon moist forests ecoregion has the highest number of mammals and birds recorded for the Amazonian biogeographic realm: 257, with 11 endemics for mammals and 782 and 17 endemics for birds. There is a strong presence of reptile and amphibian species throughout as well.
Mammals include tapir, jaguar, capybara, kinkajou, peccary, marmoset, tamarin, capuchin, squirrel monkey, saki, both two-toed and three-toed sloths, giant anteater, and ocelot.
Much of the ecoregion's natural habitat remains intact, protected by sheer inaccessibility. For example, Manú National Park, a World Heritage Site, protects pristine lowland forests in southern Peru, a large part of which falls into this ecoregion.
The nearby Tambopata National Reserve protects seven major forest types. This reserve offers refuge to game species over-hunted in other areas, such as tapirs, spider monkeys, jaguars, capybaras, white-lipped peccaries, monkeys, caimans and river turtles.
The Manuripi Heath National Reserve is located in Bolivia's southernmost area of this region, covering 18,900 sq km (7,300 sq mi) of dense tropical forest.
Map depicting the location of the Southwest Amazon moist forests (in purple)