Southwest Amazon moist forests

Southwest Amazon moist forests are an ecoregion located in the Upper Amazon Basin. The region is characterized by a relatively flat landscape with alluvial plains dissected by undulating hills or high terraces. The biota of the southwest Amazon moist forest is very rich because of these dramatic edaphic and topographical variations at both the local and regional levels. This ecoregion has the highest number of both mammals and birds recorded for the Amazonian biogeographic realm: 257 with 11 endemic species for mammals and 782 and 17 endemics for birds. The inaccessibility of this region, along with few roads, has kept most of the habitat intact. Also, there are a number of protected areas, which preserve this extremely biologically rich ecoregion.

The southwest Amazon moist forest region covers an extensive area of the Upper Amazon Basin comprising four sub-basins: (1) both the Pastaza-Marañon and (2) Ucayali River sub-basins drain into the Upper Amazon River in Peru; (3) the Acre and (4) 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. It extends east to the edge of the Purus Arch, or ancient zone of uplift, in the southwestern area of the Brazilian State of Amazonas. It then extends southeast into northern Bolivia and in a narrow band south along the base of the Andes Mountains. Elevations range from 300 metres (980 ft) in the west to 100 metres (330 ft) on the eastern edge of the region. Because the ecoregion covers such a vast area, there are climatic, edaphic and floristic differences within it. Generally, the wetter and less seasonal northern forests (3,000 millimetres (120 in) of rain annually) share only 44 percent of the tree species with forests in the slightly drier, more seasonal southern region. This region receives from 1,500 to 2,100 millimetres (59 to 83 in) of rain annually, in different parts. Temperatures over the year range from 22 to 27 °C (72 to 81 °F).

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