Igapó
Igapó (, from Old Tupi: "root forest") is a word used in Brazil for blackwater-flooded forests in the Amazon biome. These forests and similar swamp forests are seasonally inundated with freshwater. They typically occur along the lower reaches of rivers and around freshwater lakes. Freshwater swamp forests are found in a range of climate zones, from boreal through temperate and subtropical to tropical. In the Amazon Basin of Brazil, a seasonally whitewater-flooded forest is known as a várzea, which is similar to igapó in many regards; the key difference between the two habitats is in the type of water that floods the forest. Characteristics Igapó is primarily characterized by seasonal inundation caused by abundant rainfall; in some areas, trees can be submerged for up to 6 months of the year. These ecosystems are relatively open and feature over 30% canopy cover with an average canopy height ranging from 20–25 m; sparse measurements of trees can reach 33–36 m. Tree composition includes a varied mixture of leaf types and seasonality. Development of tree communities within the freshwater swamp forests rely heavily on microtopography and flooding intensity. Swamp forests can have harsh environments, in which only a few adapted species are able to sustain life or dominate over other tree species. One of the tree species mostly found in freshwater swamp forests are legume trees, in which most swamp forests have high single legume species populations. Legume trees in these forests are thought to be abundant in nitrogen fixation, which is most common in waterlogged locations and is thought to be a favorable trait when experiencing seasonal and/or constant waterlogging. Freshwater swamp forests can be classified into two categories of forested wetlands, which are permanently and periodically flooded forests. It is possible to find these two types because of the high microtopographic variation. Due to these topographic differences, tree communities are delimited and have a distribution over small continuous areas. These forests may be able to sustain a large number of bird, mammal, reptile, amphibian, fish and invertebrate species, however, biodiversity varies between wetland ecosystems and the species richness of the freshwater swamp forests is not entirely known. As for plant species, these forests have a lower diversity compared to other types of forests, such as the terra firme, in South America. Soil chemistry Igapó forests are characterized by sandy acidic soils that have a low nutrient content. The color and acidity of the water is due to soil organic molecules called humic substances (e.g. humic acid, fulvic acid) that are dissolved in the water. The acidity from the water translates into acidic soils. They are the more nutrient poor than a comparable várzea forest. They also “carry less suspended inorganic elements and contain elevated concentrations of dissolved organic material such as humic and fulvic acids”. Therefore, igapó forests support comparatively less life and the environment found within these areas tend to lack species diversity and animal biomass. Várzea forest soils have high nutrient contents because they receive a transport of high