Rainforests are forests characterized by high rainfall, with annual rainfall between 98 and 177 in. The monsoon trough, alternatively known as the intertropical convergence zone, plays a significant role in creating the climatic conditions necessary for the Earth’s tropical rainforests.
- It has been estimated that there may be many millions of species of plants, insects and microorganisms still undiscovered in tropical rainforests.
Rainforests are also responsible for 28% of the world’s oxygen turnover, sometimes misnamed oxygen production, processing it through photosynthesis from carbon dioxide and consuming it through respiration.
- The undergrowth in some areas of a rainforest can be restricted by poor penetration of sunlight to ground level.
- If the leaf canopy is destroyed or thinned, the ground beneath is soon colonized by a dense, tangled growth of vines, shrubs and small trees, called a jungle.
Tropical rainforests are located in the tropics, i.e., in the equatorial zone between the Tropic of Cancer and Tropic of Capricorn.
- Tropical rainforests exist in Southeast Asia (from Myanmar (Burma) to the Philippines, Malaysia, Indonesia, Papua New Guinea and northeastern Australia), Sri Lanka, sub-Saharan Africa from Cameroon to the Congo (Congo Rainforest), South America (e.g. the Amazon Rainforest), Central America, and on many of the Pacific Islands (such as Hawaii).
- Tropical forests cover a large part of the globe, but temperate rainforests only occur in few regions around the world.
- A tropical rainforest typically has a number of layers, each with different plants and animals adapted for life in that particular area.
- The emergent layer contains a small number of very large trees called emergents, which grow above the general canopy, reaching heights of 45–55 m, although on occasion a few species will grow to 70–80 m tall.
- The densest areas of biodiversity are found in the forest canopy, a more or less continuous cover of foliage formed by adjacent treetops.
- True exploration of this habitat only began in the 1980s, when scientists developed methods to reach the canopy, such as firing ropes into the trees using crossbows.
- Exploration of the canopy is still in its infancy, but other methods include the use of balloons and airships to float above the highest branches and the building of cranes and walkways planted on the forest floor.
- The understory or under-storey layer lies between the canopy and the forest floor.
- Away from riverbanks, swamps and clearings, where dense undergrowth is found, the forest floor is relatively clear of vegetation because of the low sunlight penetration.
- If rainforest trees are cleared, rain can accumulate on the exposed soil surfaces, creating run-off and beginning a process of soil erosion.
- Human induced deforestation plays a significant role in causing rainforests to release carbon dioxide, as do other factors, whether human-induced or natural, which result in tree death, such as burning and drought.
- Some climate models operating with interactive vegetation predict a large loss of Amazonian rainforest around 2050 due to drought, forest dieback and the subsequent release more carbon dioxide.
- Five million years from now, the Amazon rainforest may long since have dried and transformed itself into savannah, killing itself in the progress.
- Littoral rainforest growing along coastal areas of eastern Australia is now rare due to ribbon development to accommodate the demand for sea change lifestyles.
- At present rates, tropical rainforests in Indonesia would be logged out in 10 years and Papua New Guinea in 13 to 16 years.