Rainforests are the oldest and most biologically diverse ecosystems in the planet. Rainforests cover approximately 7% of the Earth´s surface, and contain more than half the world´s plant and animal species. Rainforests get from 170-200 cm (67- 79 inches) of rainfall per year, and their climate is very hot and wet. Rainforests are divided into different layers of vegetation, with each layer containing plants and animals adapted for that particular biotic ecosystem. The tropical rainforest biome is thought to be home to over half the plant and animal species in the world. It is thought that millions of plants, insects, and microorganisms may remain undiscovered in rainforests.
Tropical rainforests are located around or near the equatorial zone, with some of the largest forests in the Amazon basin in South America, the Congo Basins in Indonesia, Central Africa, and New Guinea. The climate in these biomes is characterized by high annual rainfall and constant warm temperatures. The average temperature may exceed 18° C (64° F) throughout the year and the average yearly rainfall is above 165 cm (65 inches). Despite the abundant vegetation in tropical forests, soil quality is very poor. Most trees obtain their nutrients from the decaying of animals and leaves coming from the top layer.
The forest floor, which is the bottom layer close to the ground in a tropical forest, receives only two percent of sunlight. The low amounts of sunlight determine the poor vegetation found here. Decaying plant and animal matter are also found here; however, it quickly disappears due to the great variety of fungi organisms which decompose plant and animal waste. Soil quality is poor due to rapid bacterial decay which prevents the accumulation of humus, which is an organic component of soil. Animals, including the tapir, okapi, rhinoceros, apes, reptile species, amphibians, and insects inhabit this layer.
The understorey, which is the layer above the floor layer, receives five percent of daily sunlight. This causes plants to grow to no more than a few meters, which originates development of considerably larger leaves. The vegetation in the undersorey layer includes small trees, shrubs that can thrive with little or no sunlight, herbs, and large climbing woody plants, which can climb into the trees to capture sunlight. Animals in this layer include the boa constrictor, leopards, poison dart frogs, ring-tailed coati, reptiles, and many species of insects.
The canopy layer begins at approximately 18 meters (60 feet) from the ground. The majority of trees grow to about 30-45 meters (98- 148 feet) tall. The branches of the trees give support to other plants. It is estimated that 75-90% of biodiversity is found within the canopy. The canopy supports a rich flora of epiphytes, including mosses, lichens, bromeliads and orchids. These plants obtain their nutrients from the water and matter that collects on the supporting plants. Arthropods, the largest animal group, are thought to be as much as 20 million in the canopy. The canopy is inhabited by many avian species, and other animals, including the spider monkey, kinkajou, scarlet macaw, among others.
The emergent layer, the top layer, contains a small quantity of very tall trees ones of which occasionally may reach the height of more than 60 meters (200 feet) above the forest floor with trunks of up to 5 meters (16 feet) wide. Small animals, such as birds, insects, snakes, and bats, which are small enough to be supported by the tree tops, are very common in the emergent layer. Other animals, such as the sloth inhabit the emergent layer, feeding on flowers, leaves and plants. The spider monkey spends most of its time swinging from branch to branch, and feeding on fruits and plant seeds. It is estimated that approximately one third of the planet´s bird species are found in the emergent layer.
Temperate rainforest occur in latitudes between the tropics and the Polar Regions. The temperatures in this regions ranges from 4-12° C (39-54° F) a year, and the annual average precipitation is over 140 cm (55 inches). Life diversity is immense in temperate forest, but not as in the tropical forest. Soil is richer in nutrients, and the roots of trees grow deeper into the ground to obtain water and minerals. The decomposition rate is slow in temperate forests. Plants and animals get more sunlight energy and are more able to adapt to changes. Although temperate forest covers a large part of the globe, they occur in a few regions, including North America, South America, Northwestern Europe, Asia and New Zealand.
