Campinarana

Areas of campinarana, which may cover several thousand square kilometres, are found in the transitional region from the Guyana Shield to the Amazon basin.[3] Large stretches of Campinarana are contained within the Japurá-Solimões-Negro moist forests, Negro-Branco moist forests, Guianan piedmont and lowland moist forests, Uatuma-Trombetas moist forests and Guianan savanna.[4] The campinarana ecoregion totals about 31,200 square miles (81,000 km²).[2]

Campinarana is mainly found in flat flooded areas in the Rio Negro and Rio Branco basins in the border region between Colombia, Venezuela and Brazil, but patches are found throughout the Amazon region.[5] Areas of white-sand soils and their characteristic campinarana vegetation are found in the Serra do Cachimbo on the Pará–Mato Grosso boundary, the Parecis plateau in Rondônia, the Atlantic coast near the mouth of the Amazon, and in Maranhão.[6] Similar vegetation is found in northern Peru, eastern Colombia and south western Venezuela.[2]

Temperatures in the region average 24 °C (75 °F) and average rainfall is 2,500 to 3,000 millimetres (98 to 118 in).[2]

Tropical soils are generally infertile, and white sand soils are among the most infertile of such soils, primarily composed of quartz sand.[2] The white sands are found on arenaceous sediments on the low terra firme uplands, on natural levees in a flooded Várzea forest, on restinga sand dunes in a coastal lowland, on Cretaceous sandstone plateaus and on hill areas of granitic rocks.[6] The soil type determines the ecosystem more than temperature or rainfall.[3] Factors affecting the vegetation are poor drainage, extremely sandy soil, intense leaching and impermeable layers below the surface.[7] Campinarana is typically found on leached white sands around circular swampy depressions in lowland tropical moist forest. The soil is low in nutrients, with highly acidic humus.[2]

A study at San Carlos de Río Negro, near the confluence of the Guainia and Casiquiare rivers in southern Venezuela, found the soils were similar to temperate podzols. They had a thick humus layer, a highly leached A horizon, and a well developed Bh horizon at 1 metre (3 ft 3 in). Tropical rainfall over millions of years had intensely leached the soils, which had become infertile due to lack of a source of fresh parent material. They may be short of phosphorus and/or calcium. The water that drains the Campinarana is tea colored, often called blackwater. The low exchange capacity of the podzols lets decomposing organic matter dissolve in soil water as humic acids, from where it is carried into the nearby streams.[8]

The World Wildlife Fund classes the ecoregion as "Relatively Stable/Intact". None of the ecoregion is protected, but most of it is relatively intact due to its low productivity. Some areas have suffered from cattle grazing, with burning to maintain pasturage.[2]