Purus-Madeira Moist Forests

Sitting in the heart of the Brazilian Amazon, the Purus-Madeira Moist Forests is a hot and humid region characterized by high biodiversity and endemism in flora and fauna species. The bare-eared squirrel monkey is one of the many charismatic residents of the ecoregion, where they occur primarily in seasonally inundated forest, river edges, and secondary forest. These small primates spend most of the day foraging among the treetops for insects and other small prey, but also for fruits and other opportunistic snacks along the way. 

Unlike many other native terrestrial mammals whose ecology and movements are conditioned by the seasonally changing river levels—up to 5–10 meters in some areas—these primates are largely unaffected on the treetops. Instead, their movements follow the fruiting cycles of the trees, which in turn follow the inundation cycle—some of the trees even rely on fish to disperse their seeds.

The Purus-Madeira Moist Forest ecoregion lies in the center of the Brazilian Amazon, between the Purus and Madeira Rivers. It extends to the southwest, reaching the lowest foothills of the Carauari Arch, an ancient zone of tectonic uplift. The terrain is mostly a uniform, flat plain dissected by large rivers, flooded forests, and lowland moist forest. This hot and humid tropical ecoregion receives on average 2,500 mm/year of precipitation; most months receive 200 to 300 mm, while July is the driest month with 100 mm. Temperatures over the year average 26° to 27°C with little monthly variation. Elevation of this terrain is between 20 and 60 m.

The Purus-Madeira Moist Forests ecoregion is characterized by high biodiversity and endemism in the flora and fauna. The ecoregion is almost entirely forested with evergreen tropical rain forests. The northern portion hosts forest with a dense, high canopy, 30 m in height, with some emergent trees as tall as 45 m. The lower strata are well developed with a dense understory. The southern portion hosts similar forests but with a more open canopy and less dense understory. 

The most important trees in the dense forests are legume, evergreen, woody plants, mulberry, laurel, and nutmeg. The most important trees in terms of density and frequency are evergreen, Abui, and Patawa palm tree. A characteristic emergent tree of this ecoregion is the purple-flowered Physocalymma scaberrim, a hardwood timber tree popular for furniture. The palm-like Sohnreyia excelsa occurs here along with milk tree.

The fauna is also diverse with a high occurrence of endemic species. Mammals number over 165 species, of which more than 80 are bats. Primates such as bare-eared squirrel monkeys, brown pale-fronted capuchins, woolly monkeys, and five species of titi monkeys occur here; doubtful titi monkey, ashy black titi monkey, and collared titi monkey are endemic to this lowland Amazon region. The avifauna boasts 572 species including seasonal migrant birds such as toucans, large parrots, and macaws. 

Some of the venomous snakes that occur here are fer-de-lance, palm pit-vipers, coral snakes, bushmasters, as well as boa constrictors. Iguanas are ubiquitous and tegus lizards common. Many other reptiles, and amphibians, insects and fungus occur here as well. 

Except for the southern area, the Purus-Madeira Moist Forest ecoregion is remarkably intact. A paved road was built several decades ago along the entire length of the ecoregion from Manaus to Humaitá, but it has been closed for a decade because it was impossible to maintain in such a dynamic environment. The Trans-Amazon Highway does bisect the southwestern end between Humaitá and Lábrea, bringing with it forest conversion to cattle ranching, agricultural fields, and colonization by small farmers. The Cuniã Ecological Station is located in the very southern reach of this ecoregion near the Madeira River, but no other protected areas exist. 

Facing these pressures, the priority conservation action for the next decade are to: 1) restrict controlled and uncontrolled burning in the southern part of this ecoregion; 2) limit cattle ranching, industrial-scale agricultural projects, and road-building; and 3) cease mining activities in the upper reaches of both the Purus and Madeira Rivers that destroy habitat and pollute waterways. 

Citations 

1. Sears, R. 2018. Northern South America: Northwestern Brazil. https://www.worldwildlife.org/ecoregions/nt0157. 7 September 2018.
2. Ducke, A., and G. A. Black. 1953. Phytogeographical notes on the Brazilian Amazon. Anais da Academia Brasileira de Ciências 25: 1-46.
3. Silva, A. L. L. de, P. L. B. Lisboa, and U. N. Maciel. 1992. Diversidade florística e estructura em floresta densa da bacia do Rio Juruá-AM. Boletim do Museu Paraense Emílio Goeldi, Botânica 8: 203-258.