Location and General Description
There are large areas of white-sand campinas, or grasslands, on the upper Madeira and Tapajós Rivers. The vegetation in the large southern portion of the region follows the complex topography of the Chapada dos Parecis, a mountainous region with elevations to 1,200 m in the State of Rondônia. There, the landscape comprises steep-sided, flat-topped mountains with rocky meadows and semi-deciduous forests on the upper elevations in a patchwork of mostly open submontane forest and woodland savannas. To the south, the ecoregion is bordered by the transitional forests combining Amazonian and cerrado elements in the State of Mato Grosso. The northern portion, extending to the Amazon River is on the low, flat plain of the Amazon Basin. The terrain rises slowly in the south and east onto portions of the ancient, uplifted Brazilian Shield.
Along the Madeira River seasonally flooded forest (treated in the Monte Alegre Várzea ecoregion) occurs. The floodwaters of this whitewater river (carrying suspended solids) deposit nutrient-rich sediments on the forest floor. The Tapajós River rises on the well-weathered ancient Brazilian Shield and, flowing in a stable course, carries no sediment. Other large rivers that dissect this region are the Maués, Aripuanã, and Canumã. Many dozens of smaller rivers and hundreds of tiny streams drain the interior reaches of the region.
Because this is a large and heterogeneous ecoregion, the rainfall, seasonality, and ambient temperatures also vary. Annual precipitation in the northern and southern portions of the region is below 2,000 mm, whereas a section of the Middle Madeira River receives as much as 4,000 mm of rain. Much of the region receives between 2,000 and 3,000 mm annually. Annual temperature ranges from 23° C in the mountains to an average of 27° C in the humid lowland areas. Soils are naturally diverse because the region lies over several geological substrates, ranging from the soft sedimented lowland basin to the hard crystalline basement of the Brazilian Shield. Elevation in the region ranges from 20 m at the Amazon River to 1,126 m at the highest peak of the Chapada dos Parecis, although the majority of the landscape lies below 200 m.
Along the clearwater Tapajós and Aripuanã Rivers, white-sand igapó forest is predominant, hosting large trees such as Triplaris surinamensis, Piranhea trifoliata, Copaifera martii, and Alchornea castaneaefolia in forest that is slightly more open than that in non-flooded areas. The dense lowland rain forest has a high 30 m canopy with some emergent trees as high as 45 m. The rare local endemic tree Polygonanthus amazonicus was once found near Maués. This is the western limit of the widespread, tall emergent tree Dinizia excelsa, and the eastern limit for naturally occurring cacao (Theobroma cacao). A characteristic showy tree of this region is the purple-flowered Physocalymma scaberrima, a hardwood timber tree with red wood popular in making furniture.
Legumes such as Eperua oleifera, E. campestris, Palovea brasiliensis, Elizabetha paraensis, E. bicolor, E. durissima, and Coumarouna speciosa are common. Trees in other families include Lophanthera lactescens and Polygala scleroxylon, a tree with very hard and heavy wood, as well as Joannesia heveoides, Manilkara excelsa, and Duckeodendron cestroides (Ducke and Black 1953). Theobroma microcarpum reaches its eastern limit in the Tapajós River Basin. A variety of interesting trees occurs in the hill woodlands of the Upper Marmelos and Middle Tapajós Rivers including the ‘dwarf rubber tree’ Hevea camporum, the elegant palm Euterpe longibracteata, the enormous Huberodendron ingens, and rare monotypic Brachynema ramiflorum (Ducke and Black 1953).
Mammals reportedly number 183 species and birds 621. The Tapajós River acts as a barrier to the distribution of animals, plants, and insects. For example, the white-fronted capuchin (Cebus albifrons) and saki (Pithecia hirsutus) occur on the west side of the river and the saki Chiropotes albinasus only occurs on the east. The Madeira-Tapajós interfluve has a high primate diversity. This is the eastern limit of the woolly monkey (Lagothrix lagothricha). The dwarf marmoset (Callithrix humilis) was recently found along the eastern bank of the Madeira and western bank of the Lower Aripuana. The marmoset (Callithrix humeralifer) is a narrow endemic occurring only in the north of this region. The squirrel monkey with naked ears (Saimiri ustus) and dusty titi (Callicebus moloch) are endemic to the south-central Amazon. The white-lipped peccary (Tayassus pecari), collared peccary (T. tajacu), puma (Puma concolor), panther (Panthera onca), tapir (Tapirus terrestris), and brocket deer (Mazama spp.) are some of the larger mammals. As many as 90 species of bats are found.
The many interesting birds include a number of tinamous (Crypturellus spp., Tinamus spp.), six macaws (Ara spp.), many parakeets (Paratinga spp., Pyrrhura spp., Brotogeris spp.), parrots (Amazona spp., Pionus spp.), and hoatzins (Opisthocomus hoazin). River wildlife includes black caimans (Melanosuchus niger), yellow-spotted sideneck turtles (Podocnemis unifilis), American manatees (Trichechus inunguis), and river dolphins (Ina geoffroyensis and Sotalia fluviatilis). Some of the venomous snakes that occur here are fer-de-lance (Bothrops asper), palm pit-vipers (Bothriechis spp.), coral snakes (Micrurus spp.), bushmasters (Lachesis muta), as well as boa constrictors (Boa constrictor). The neotropical rattlesnake (Crotalus durissus) occurs in the dry uplands.
This region hosts one of the most degraded environments of central Amazonia. It is located in central Rondônia where colonization and subsequent deforestation has left over one-third of the landscape of the state denuded and degraded. Most of this occurs along the Humaitá-Cuiabá road, but significant land degradation has occurred along the Transamazon Highway from the middle Tapajós to Humaitá. The southern edge of Amazonia, in general, suffers from encroaching development from the savanna regions to the south. Mining that is both intensive and illegal has left great scars on the banks of the Tapajós and Madeira Rivers. The protected area system is not well implemented here. The Amazonia National Park straddles the Tapajós River near Itaituba, covering 9,935 km2, but suffers from inadequate administrative capacity. The Pacaas Novos National Park protects 7,648 km2 of montane and submontane area in the Chapada dos Parecis.
Types and Severity of Threats
Rapid expansion of the helter-skelter development patterns along roads and riverways with increasing colonization poses the greatest threat to the environment and its inhabitants. Timber extraction also has degraded many of the forests near the Madeira River and the highways. Gold mining on the Tapajós, especially near the city of Itaituba, continues to threaten aquatic life and to destroy landscape elements along the rivers. This is considered a frontier region where continued development poses a major threat to the wildlife and ecological integrity.
Justification of Ecoregion Delineation
This ecoregion is bound on three sides by large rivers, the Solimões (Amazon) to the north, Madeira to the west, and Tapajós to the east, which act as formidable barrier to the distributions of many species. In the southeastern region the river boundary changes to a habitat boundary, and is delineated by a distinct change in vegetation and species assemblages along the Mato Grosso tropical dry forests. The linework for this transition follows IBGE (1993) map, which classifies this portion of the ecoregion as "submontane open ombrophilous forest" (and to the north as "submontane dense ombrophilous forest" and "lowland dense ombrophilous forest"). The Bolivian portion of this ecoregion is delineated following Ribera et al. (1994), and follows the Rio Madeira boundary south until it abuts with the Beni savanna and later the Chiquitano dry forests, whose distinct vegetation justifies this separation. The rivers which bind this river also have isolated it and many species are restricted here, many of which are endemic. Further justification is offered by de Silva (1998).
Ducke, A., and G. A. Black. 1953. Phytogeographical notes on the Brazilian Amazon. Anais da Academia Brasileira de Ciências 25: 1-46.
Fundação Instituto Brasilero de Geografia Estatástica-IBGE. 1993. Mapa de vegetação do
Brasil. Map 1:5,000,000. Rio de Janeiro, Brazil.
Ribera, M.O., M. Libermann, S. Beck, and M. Moraes. 1994. Mapa de la vegetacion y areas protegidea de Bolivia. 1:1,500,000. Centro de Investigaciones y Manejo de Recursos Naturales (CIMAR) and Universidad Autónoma Gabriel Rene Moreno (UAGRM), La Paz, Bolivia.
Silva, J.M. C. 1998. Um método para o estabelecimento de áreas prioritárias para a conservação na Amazônia Legal. Report prepared for WWF-Brazil. 17 pp.
Prepared by: Robin Sears
Reviewed by: In process