Tropical rainforest biomes

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From Khan Academy

Biome is another name for a distinct type of ecosystem. Biomes are characterized by their climate, which determines the particular plants found there. The climate and the plants in a biome determine what animals live there. This article addresses the climate and biodiversity of one of Earth’s most diverse and iconic biomes: the tropical rainforest.

The tropical rainforest biome has four main characteristics: very high annual rainfall, high average temperatures, nutrient-poor soil, and high levels of biodiversity (species richness).
 
Rainfall:  The word “rainforest” implies that these are the some of the world’s wettest ecosystems. Rainforests generally receive very high rainfall each year, although the exact amount varies among different years and different rainforests.  For example, South America’s tropical rainforests receive between 200 and 300 centimeters (80 and 120 inches, or 6.5 to 10 feet!) of rain in a typical year. Despite relatively consistent rain in these ecosystems, there are distinct dry seasons in some rainforests. Wet and dry seasons of tropical rainforests vary in their timing, duration and severity around the globe. Tropical rainforests also have high humidity; about 88% during the wet season and approximately 77% in the dry season.
 
Temperature: Tropical rainforests are found near the equator, between the Tropic of Cancer (23°27’N) and the Tropic of Capricorn (23°27’S).  The equator receives direct sunlight. This steady flow of radiation produces consistently high temperatures throughout the year. A typical daytime temperature any time of year in tropical rainforests is 29°C (85°F), although temperatures can be much higher. In the majority of tropical rainforests, there is only a 5°C (9°F) difference in temperature between the seasons.
 
Soil Composition: Since there is a tremendous amount and diversity of foliage in tropical rainforests, you might assume that rainforest soils are rich in nutrients. In fact, rainforest soils are nutrient-poor because nutrients are not stored in them for very long. The heavy rains that occur in rainforests wash organic material from the soil. Although decomposition occurs rapidly in the hot, moist conditions, many of the dead, fallen leaves and other organic detritus are swept away before releasing all of their nutrients. In addition, rainwater seeps into the ground and leaches away nutrients. Nevertheless, the high diversity of decomposers, such as bacteria and fungi accelerates the decomposition process enough that the nutrients released by decomposition are taken up quickly by the plants, instead of being stored in the soil.

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