Negro-Branco moist forests


The Negro-Branco moist forests 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.

Location

The ecoregion has an area of
It overlays the Casiquiare Rift.
The center of the ecoregion is in the extreme south of Venezuela, and covers part of the Parima Tapirapecó National Park.
It extends west into Colombia, where it includes the south of El Tuparro National Natural Park, and extends to the southeast into the Brazilian states of Amazonas and Roraima, including part of the Pico da Neblina National Park.
It adjoins the Caqueta and Japurá-Solimões-Negro moist forests to the south, the Llanos grasslands to the north, the Guianan piedmont and lowland moist forests to the east and the Uatuma-Trombetas moist forests to the southeast.
It also adjoins or contains areas of Rio Negro campinarana.

Hydrology

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.
Rivers include nutrient-poor clearwater and blackwater rivers, the latter type stained dark by tannin, and nutrient-rich whitewater rivers.
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.

Environment

The ecoregion is on the ancient Guiana Shield, a craton formed in the Precambrian.
Elevations range from in the west to over in the east in Venezuela.
Terrain includes lowland plains, rolling hills and low sandstone plateaus.
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.
The ecoregion is part of the Río Negro-Juruá Moist Forests, a global ecoregion, the other parts being the Caqueta, 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.

Flora

The Negro-Branco moist forests are in the tropical and subtropical moist broadleaf forests biome of the neotropical realm.
Vegetation includes flooded and terrra firme lowland moist forest, tall or medium-tall campinarana lowland forest, patches of shrubs and herbaceous savanna-like meadows.
Forests are typical of the Guiana region, with a different mix of plants from the classical Amazon rainforest.
Humiriaceae, Rapateaceae, Tepuianthaceae, Theaceae and Xyridaceae are common families that do not belong to the Amazon flora.
The forests hold relatively few epiphytes or lianas compared to other parts of the western Amazon region.
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, and low evergreen flooded palm forests that reach.
The dominant trees of the low palm forests are Mauritia flexuosa, Mauritiella aculeata and dense groups of Euterpe catinga, Iriartea setigera and Socratea exorrhiza.
The terra firme forest holds Lecointea amazonica, Clathrotropis glaucophylla, Peltogyne venosa, and species in the Ocotea, Nectandra, Licania, Trichilia, Guarea, Toulicia, Erisma and Ruizterania genera.
The tall canopy forests also hold trees of the Oenocarpus, Socratea, Leopoldinia and Bactris genera.
There are patches of campinarana on white sands near the border of Venezuela and Colombia.
There is a high level of endemism of flora including the genera Duckeanthus, Heteropetalum, Pseudephedranthus, Urospathella, Aquiaria, Angostylis, Astrococcus and Chonocentrum.
The economically valuable palm Leopoldinia piassaba is endemic to the ecoregion.
In the Rio Negro basin the many blackwater streams and small rivers flood a large area of igapó forest for 5–6 months each year.
The canopy is up to high.
Common species are Virola elongata, Eschweilera longipes, Eschweilera pachysepala, Aldina latifolia and Pithecellobium amplissimum.

Fauna

There are 194 species of mammals, including a few endemic species such as golden-backed uakari, black bearded saki, Tschudi's slender opossum, least big-eared bat, Guianan spear-nosed bat, Eldorado broad-nosed bat, Venezuelan fish-eating rat, MacConnell's climbing mouse, the guinea pig Cavia guianae and Simon's spiny rat.
Common species include South American tapir, collared peccary, pale-throated sloth, long-tailed weasel, short-eared dog, bush dog and three species of small cats of the Leopardus genus.
There are many reptiles and amphibians.
Snakes include fer-de-lance, palm pit-vipers, coral snakes, boa constrictors and bushmasters.
There are many green iguanas and tegus lizards.
486 species of birds have been recorded, a relatively low number for the Amazon region.
They include the endemic grey-legged tinamou, crestless curassow, double-striped thick-knee, oilbird, tawny-tufted toucanet, Orinoco piculet, Yapacana antbird, gray-bellied antbird, spot-tailed nightjar, azure-naped jay, and white-naped seedeater.

Threats

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.