The Negro–Branco moist forests (NT0143) is an ecoregion of tropical moist broadleaf forest to the east of the Andes in southern Venezuela, eastern Colombia and northern Brazil, in the Amazon biome. It lies on the watershed between the Orinoco and Rio Negro basins. It includes both blackwater and whitewater rivers, creating different types of seasonally flooded forest. The vegetation is more typical of the Guiana region than the Amazon.
The Negro-Branco moist forests ecoregion is on the watershed between the Orinoco in Venezuela and the Rio Negro, which is known as the Guainía River in Colombia and is a major tributary of the Amazon River.[4]
Rivers include nutrient-poor clearwater and blackwater rivers, the latter type stained dark by tannin, and nutrient-rich whitewater rivers.[1]
The blackwater Vichada River forms the northern border in Colombia, and the clearwater Ventuari River forms the northern border in Venezuela, both tributaries of the Orinoco.
In Colombia the whitewater Guaviare and Inírida rivers are in the Orinoco Basin.
The southern border in Colombia is defined by the middle Guaviare and by the upper reaches of the blackwater Guainía / Rio Negro to the Venezuela-Colombia border.
In Venezuela the blackwater Casiquiare canal, a distributary of the Orinoco, feeds the Guainia/Negro River.
The Rio Negro defines the southern border in Brazil to the whitewater Rio Branco.[4]
Environment
The ecoregion is on the ancient Guiana Shield, a craton formed in the Precambrian.
Elevations range from 120 metres (390 ft) in the west to over 400 metres (1,300 ft) in the east in Venezuela.[4]
Terrain includes lowland plains, rolling hills and low sandstone plateaus.[1]
Until recently the lowland plains of the region were covered in lakes and seas, which deposited layers of sediment.
Soil types are generally poor in nutrients, mainly podzols on the old alluvial terraces.[4]
The ecoregion is part of the Río Negro-Juruá Moist Forests, a global ecoregion, the other parts being the Caquetá, Solimões–Japurá and Japurá–Solimoes–Negro moist forests.
The reasonably intact global ecoregion has high annual rainfall, diverse soils and varied terrain, resulting in a high level of biodiversity.
It has not been studied in great depth by scientists.[5]
The flat Casiquiare peneplain in Venezuela holds forests, savannas and other formations.
It contains blackwater and whitewater rivers, which create igapó and várzea forest along their flooded banks.
There are seasonally flooded and terra firme evergreen lowland forests reaching 40 metres (130 ft), and low evergreen flooded palm forests that reach 20 metres (66 ft).
The dominant trees of the low palm forests are Mauritia flexuosa, Mauritiella aculeata, and dense groups of Euterpe catinga, Iriartea setigera, and Socratea exorrhiza.[4]
The ecoregion covers most of the Alto Orinoco-Casiquiare Biosphere Reserve.
A small part of the ecoregion is in the Pico da Neblina National Park.
There are few threats to the ecoregion, which is inaccessible and has no roads.
The forest is largely intact.
People in riverine communities engage in small-scale rotation agriculture.
There is some low-level logging and in some areas the understory is routinely burned by Brazil nut collectors.
Leaves of the Leopoldinia piassaba palm are harvested to make brooms for sale internationally, and this may be unsustainable.[4]
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