Rainforests are forests that are characterized by high levels of rainfall, with definitions based on a minimum usual annual rainfall of about 68 to 78 inches. The monsoon trough, or otherwise known as the intertropical convergence zone, holds an important role in producing the climatic conditions that are essential for the Earth’s tropical rainforests.
About 40 to 75 percent of all biotic species are native to the rainforests. It’s been estimated that there might be many millions of species of plants, insects and microorganisms that have remained undiscovered within the tropical rainforests. Tropical rainforests have been named the “jewels of the Earth” and the “world’s largest pharmacy”, due to the fact that over one quarter of natural medicines have been discovered there. Rainforests are also held responsible for 28 percent of the world’s oxygen turnover, occasionally misnamed oxygen production, processing it through photosynthesis from carbon dioxide and consuming it through respiration.
The undergrowth in certain areas of a rainforest can be restricted by poor penetration of sunlight to ground level. If the leaf canopy is damaged or thinned, the ground beneath is soon colonized by a dense and tangled growth of vines, shrubs, and small trees, called a jungle. There are two types of rainforests; tropical rainforests and temperate rainforests.
The tropical rainforests are distinguished in two words: wet and warm. Average monthly temperatures exceed 64 degrees Fahrenheit during all months of the year. The average rainfall is no less than 66 inches and can surpass 390 inches although it usually lies between 69 and 79 inches.
Many of the world’s rainforests are associated with the located of the monsoon trough, alternatively known as the intertropical convergence zone. Tropical rainforests are rainforests located in the tropics, found in the equatorial zone. Tropical rainforest is existent in Southeast Asia, Sri Lanka, sub-Saharan Africa from Cameroon to the Congo, Central America, South America, and on many of the Pacific Islands. Tropical rainforests have been called the Earth’s Lungs, although it’s now known that rainforests contribute very little net oxygen addition to the atmosphere through photosynthesis.
The temperate rainforests cover a large portion of the globe, but they only occur in few regions around the world. Temperate rainforests are rainforests in regions that are temperate. They are found in North America, Europe, East Asia, South America, and New Zealand and Australia as well.
The tropical rainforests are separated into four main layers, each with different plants and animals that are adapted for life that that certain area: the emergent, canopy, understorey/understory and forest floor layers.
The emergent layer is made of up a small number of very large trees called emergents which grow above the general canopy. These trees reach heights of about 45 to 55 meters, although occasionally a few species will grow to be 70 to 80 meters tall. They need to be able to withstand the hot temperatures and the strong winds that are typical above the canopy in some areas. Butterflies, bats, certain monkeys, and eagles inhabit this layer.
The canopy layer is made up of the majority of the largest trees, usually 98 to 148 feet tall. The most dense areas of biodiversity can be found in the forest canopy, a more or less continuous coverage of foliage created by adjacent treetops. This canopy is, from estimates, home to about 50 percent of all plant species, suggesting that perhaps half of entire life on Earth could be found there.
The understorey/understory layer is located between the canopy and the forest floor. This hosts a number of birds, lizards and snakes, as well as predators such as boa constrictors, leopards and jaguars. The leaves here are much larger. The insect life is also very plentiful. Many seedlings that will grow to the canopy level are present in this level. Only about 5 percent of the sunlight shining on the rainforest canopy reaches this level. This layer can be referred to as a shrub layer, although the shrub layer might also be considered a separate level.
The forest floor, the bottom-most layer, acquires only 2 percent of the sunlight. Only plants that are adapted to low light can grow in this region. Away from riverbanks, clearings and swamps, where dense undergrowth is found, the forest floor is quite clear of vegetation due to the low sunlight penetration. It also contains decaying plant and animal material, which disappears rapidly, because of the warm and humid conditions promoting quick decay. Many types of fungi growing here help decay the plant and animal waste.
Image Caption: Rainforest between Kuranda and Cairns, North East Queensland. Credit: Tim35/Wikipedia