Rainforests have high rainfall and are defined as having a mean annual rainfall greater than 1750 mm. There are two types: temperate and tropical rainforests. Tropical rainforests are found in South America, Africa, and Southeast Asia. They contain two-thirds of the planet’s plant and animal biodiversity. The rainforest biome has a layered structure, with the emergent layer at the top, the canopy in the middle, and the forest floor at the bottom. The canopy has the greatest biodiversity on Earth.
Rainforests are forests with high amounts of rainfall, making them have very different characteristics than other forests, such as coniferous forests. Rainforests are variably defined as having a mean annual rainfall greater than 1750 mm and 2000 mm (68 in to 78 in). There are two types of rainforest: temperate rainforests, which are found in small numbers on the coasts of all continents except Africa and Antarctica, and tropical rainforests, such as the Amazon rainforest in South America, which have the numerous unique flora and fauna synonymous with the term “rainforest”.
Tropical rainforests are found in South America (Amazon rainforest), Africa (African rainforest) and Southeast Asia (Southeast Asian rainforest), Madagascar and that’s about it. Just a couple of hundred years ago, tropical rainforests covered 12% of the surface of the continents, but today that number has shrunk to less than 6%, due to both human-induced deforestation and the southward flow of the Sahara desert in Africa Rain forest. Most of the world’s rainforests are within 20 degrees of the equator, where it is warmest and often wettest.
Although the world’s rainforests represent only 6% of the world’s surface, they contain two-thirds of the planet’s plant and animal biodiversity. They’ve also been called “the lungs of the Earth,” although this is false, as rainforests don’t actually produce more oxygen than they absorb. The rainforests are covered with deciduous evergreens, some up to 80 m (260 ft) tall.
The rainforest biome has a layered structure. At the top is the emergent layer, where the tallest trees emerge from the canopy below. The emergent layer is usually between 45 m (150 ft) and 55 m (180 ft) high, although some very tall trees will sometimes project 80 m (260 ft) above the ground. The emerging layer is populated by eagles, butterflies, bats and some monkeys. The plants here must be resistant to strong winds and high temperatures.
Beneath the emergent layer is the famous canopy, the area of greatest biodiversity in the rainforest and on Earth itself. About 40 percent of all plant species and more than half of all insect species on Earth are thought to live in the canopy, which only began to be investigated by scientists in the 1980s. The canopy is 30 m (100 ft) to 40 m (130 ft) above the ground. Here the branch is so large that it forms a more or less continuous sheet of foliage over areas of many hundreds of thousands of square miles.
At the bottom of the rainforest is the forest floor. Little light gets here and the nutrients are often washed away by the rain. Numerous bacteria break down organic material rapidly, precluding the formation of humus. The forest floor has low biodiversity compared to the canopy above it, but even greater biodiversity than any other habitat on the planet.
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