igapó

Igapó is a term used in Brazil to describe seasonally flooded forests that occur along the blackwater rivers of the Amazon Basin. During the rainy season, rivers such as the Negro and Tapajós rise and inundate large areas of forest. The water is typically dark, acidic, and low in nutrients, which influences the structure and functioning of the ecosystem. Flooding can last from several weeks to months, after which the land re-emerges as waters recede.

The igapó supports a distinct assemblage of tree and shrub species adapted to prolonged inundation and nutrient-poor conditions. Many trees are deciduous or shed leaves during periods of inundation to cope with low oxygen in the soil. The vegetation differs from other Amazon floodplain forests due to its reliance on species able to tolerate shallow, anoxic soils and seasonal depth changes.

Fauna in igapó is shaped by the annual flood pulse. The inundation creates feeding opportunities for fish and birds and provides nursery habitats for aquatic and semi-aquatic species. Terrestrial animals use the forest during low-water periods, and local communities often rely on fish and other resources harvested from igapó forests.

Relation to other floodplain forests: Igapó differs from várzea, the floodplain forest along whitewater rivers, which receives nutrient-rich sediments and generally supports a different floral assembly. Igapó soils are nutrient-poor and water conditions more acidic. Both systems face threats from deforestation, illegal logging, mining, and hydropower development, underscoring the need for sustainable management of Amazonian floodplains.