Southwest Amazon Moist Forests

The endangered Peruvian spider monkey is found throughout the moist forest canopies of this ecoregion in both Brazil and Bolivia. They reach almost a meter in body length and are known for their acrobatic agility as they swing effortlessly from branch to branch using their arms, feet, and sometimes their prehensile tail. Spider monkeys are one of the largest primates in the South America forest and play a very important ecological role as a disperser for some of the larger tree and vine seeds which smaller species cannot open. Since they are constantly on the move, they help carry the seeds far away from the mother trees as they consume the fruits.

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 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 vertically bisected by the Serra do Divisor mountain range. Elevations range from 300 m in the west to 100 m on the eastern edge of the region. Rainfall in the northern forests reaches 3,000 mm annually while the south receives 1,500–2,100 mm. The ecoregion is a mix of upland terra firme forests (non-flooded) on nutrient poor soils, ancient alluvial plains (mostly non-flooded) on nutrient rich soils, and várzea forests (seasonally flooded) with their soils being enriched by the influx of new sediments. 

The majority of the forests is dense with a 30–40m canopy and some emergent trees reaching 50 m. 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 south includes kapok, kumaru, possumwood, Brazil nut, and Calycophyllum spruceanum trees. Areas of lower diversity are dominated by highly competitive bamboos, such as the fleshy fruit guadua. 

The Southwest Amazon Moist Forests ecoregion has a vast extent with both regional and local variations in flora and habitat. Endemism and overall richness is high in vascular plants and invertebrates and vertebrate animals. This is the Amazon Basin’s center of diversity for palms. The rare palm Itaya amicorum is found on the Upper Javari River. There are 257 recorded mammal species with 11 endemics. This includes tapir, jaguar, capybara, kinkajou, peccary, marmoset, tamarin, capuchin, squirrel monkey, saki, both two-toed and three-toed sloths, giant anteater, and ocelot. 

There are 782 bird species with 17 endemic. Within one 50 km² area in the southern portion of the region, an astounding 554 bird species were found. There is a strong presence of reptile and amphibian species throughout as well. 

Much of the natural habitat of the region remains intact, protected by sheer inaccessibility. Very few roads exist in the region, limiting development. Intense deforestation is constrained to the few roads that do exist or around urban centres such as Iquitos, Puerto Maldonado, and Rio Branco. People have dwelled along the major rivers for millennia and have subtly altered the forests on a small scale. Protected areas of note within or covering parts of the ecoregion include the National Parks of Manú, Serra do Divisor, Madidi, Isoboro Secure, and Bahuaja-Sonen and reserves such as Tambopata, Manuripi Heath National, Chico Mende, and Alto Juruá. Nonetheless, most protected areas suffer from insufficient administration and patrol.

In some areas, the habitats are threatened by expansion of the agricultural and pastoral frontier, gold mining, and selective logging. Poaching is an issue for a few key species in the region, especially peccary, deer, and monkeys. The spread of invasive bamboo species in both Brazil and Peru outcompetes other native flora and reduces the biodiversity and habitat of the ecoregion. 

The priority conservation actions for the next decade will be to: 1) incentives locals to reduce logging; 2) increase staffing of protected areas; and 3) organize efforts to remove invasive bamboo stands and restore native vegetation.

Citations 

1. Sears, R. 2019. Upper Amazon basin of Peru, Brazil and Bolivia https://www.worldwildlife.org/ecoregions/nt0166 Accessed June 19, 2019.
2. Henderson, A. 1995. The Palms of the Amazon. New York: Oxford University Press.
3. Wallace, R.B., Mittermeier, R.A., Cornejo, F. & Boubli, J.-P. 2008. Ateles chamek. The IUCN Red List of Threatened Species 2008: e.T41547A10497375 . http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T41547A10497375.en Accessed June 19, 2019.