The undergrowth in a rainforest is restricted in many areas by the lack of sunlight at ground level.[5] This makes it possible for people and other animals to walk through the forest. If the leaf canopy is destroyed or thinned for any reason, the ground beneath is soon colonized by a dense tangled growth of vines, shrubs and small trees called a jungle.[6]
Tropical rainforests are currently fragmenting due to human activity. Habitat fragmentation caused by geological processes such as volcanism and climate change have occurred in the past, and have been identified as drivers of speciation.[7] However, fast human driven habits destruction is suspected as being one of the major causes of species extinction.
The rainforests are home to more worldwide species than all other biomes added together. 80% of the world's biodiversity are found in tropical rainforests.[8] The leafy tops of tall trees - extending from 50 to 85 metres above the forest floor - forms an understory. Organic matter that falls to the forest floor quickly decomposes, and the nutrients.
Rainforests are partly characterized by high rainfall. This often results in poor soils due to leaching of soluble nutrients. Generally the soils of rainforests are classified as Oxisols, which are annually replenished with fertile silt.
Tropical rain forests have been subjected to heavy logging and agricultural clearance throughout the 20th century, and the area covered by rainforests around the world is rapidly shrinking.[9][10]
Rainforests are also often called the "Earth's lungs"; however, there is no scientific basis for such a claim as tropical rainforests are known to be essentially oxygen neutral, with little or no net oxygen production.[11][12]
The rainforest is humid. Tall, broad-leaved evergreen trees are the dominant plants, forming a leafy canopy over the forest floor. Taller trees, called emergents, may rise above the canopy. The upper portion of the canopy often supports a rich flora of epiphytes, including orchids, bromeliads, mosses, and lichens, who live attached to the branches of trees. The undergrowth or understory in a rainforest is often restricted by the lack of sunlight at ground level, and generally consists of shade-tolerant shrubs, herbs, ferns, small trees, and large woody vines which climb into the trees to capture sunlight. The relatively sparse under story vegetation makes it possible for people and other animals to walk through the forest. In deciduous and semi-deciduous forests, or forests where the canopy is disturbed for some reason, the ground beneath is soon colonized by a dense tangled growth of vines, shrubs and small trees called jungle.
The temperature ranges from 21°C to 45°C and 125 to 660 cm of rainfall yearly.
Layers
The emergent layer contains a small number of very large trees which grow above the canopy layer, reaching heights of 45-55 m, although on occasion a few species will grow up to 40 m or 50 m tall. They need to be able to withstand the hot temperatures and strong winds. Eagles, butterflies, bats and certain monkeys inhabit this layer.
The canopy is the primary layer of the forest and forms a roof over the two remaining layers. Most canopy trees have smooth, oval leaves that come to a point. It's a maze of leaves and branches. Many animals live in this area since food is abundant. Those animals include: snakes, toucans and tree frogs.
Little sunshine reaches the understory layer, so the plants have to grow larger leaves to obtain sufficient sunlight. The plants in this area seldom grow to 3 m (10 feet). Many animals live here including jaguars, red-eyed tree frogs and leopards. There is a large concentration of insects here.
The shrub layer and forest floor are very dark. Few plants grow in this area, as a result. Since hardly any sun reaches the forest floor things begin to decay quickly. A leaf that might take one year to decompose in a regular climate will disappear in 6 weeks. Giant Anteaters live in this layer.
Natural History
Tropical rainforests have existed on Earth for hundreds of millions of years. About 300 million years ago in the Carboniferous on the continent of Euramerica the tropical rainforest ecology collapsed. The rainforest was fragmented due to a change in climate. There was a great loss of amphibian diversity while at the same time the drier climate spurred the diversification of reptiles.[7]Human uses
Negative Human Impacts
Humans are clearing the Amazon Rainforest rapidly for farming, lumber, and livestock raising, at an approximate rate of 1.5 acres per second or 50 football fields per minute, which causes the rainforest to become endangered.(75 acres per minute)[citation needed]Habitation
Tropical rainforests are unable to support human life.[13] Food resources within the forest are extremely dispersed due to the high biological diversity and what food does exist is largely restricted to the canopy and requires considerable energy to obtain. Some groups of hunter-gatherers have exploited rainforest on a seasonal basis but dwelt primarily in adjacent savanna and open forest environments where food is much more abundant. Other peoples described as rainforest dwellers are hunter-gatherers who subsist in large part by trading high value forest products such as hides, feathers, and honey with agricultural people living outside the forest.[13]Conversion to agricultural land
With the invention of agriculture, humans were able to clear sections of rainforest to produce crops, converting it to open farmland. Such people, however, obtain their food primarily from farm plots cleared from the forest [13][14] and hunt and forage within the forest to supplement this.Agriculture on formerly forested land is not without difficulties. Rainforest soils are often thin and leached of many minerals, and the heavy rainfall can quickly leach nutrients from area cleared for cultivation. People such as the Yanomamo of the Amazon, utilise slash-and-burn agriculture to overcome these limitations and enable them to push deep into what were previously rainforest environments. However, these are not rainforest dwellers, rather they are dwellers in cleared farmland[13][14] that make forays into the rainforest. Up to 90% of the typical Yanamomo diet comes from farmed plants.[14]
Cultivated foods and spices
Coffee, chocolate, banana, mango, papaya, macadamia, avocado, and sugarcane all originally came from tropical rainforest and are still mostly grown on plantations in regions that were formerly primary forest. In the mid-1980s and 90s, 40 million tons of bananas were consumed worldwide each year, along with 13 million tons of mangos. Central American coffee exports were worth US$3 billion in 1970. Much of the genetic variation used in evading the damage caused by new pests is still derived from resistant wild stock. Tropical forests have supplied 250 cultivated kinds of fruit, compared to only 20 for temperate forests. Forests in New Guinea alone contain 251 tree species with edible fruits, of which only 43 had been established as cultivated crops by 1985.[15]Pharmaceutical and biodiversity resource
Tropical rainforests are called "the world's largest pharmacy"[citation needed] because of the large amount of natural medicines discovered in rainforests that are derived from rainforest plants. For example, rainforests contain the "basic ingredients of hormonal contraception methods, cocaine, stimulants, and tranquilizing drugs" (Banks 36)[citation needed]. Curare (a paralyzing drug) and quinine (a malaria cure) are also found there.Positive Impacts
- An increase in tourism has increased economic support, allowing more revenue to go into the protection of the habitat. Tourism can contribute directly to the conservation of sensitive areas and habitat. Revenue from park-entrance fees and similar sources can be utilised specifically to pay for the protection and management of environmentally sensitive areas. Revenue from taxation and tourism provides an additional incentive for governments to contribute revenue to the protection of the forest.
- Tourism also has the potential to increase public appreciation of the environment and to spread awareness of environmental problems when it brings people into closer contact with the environment. Such increased awareness can induce more environmentally conscious behavior. Tourism has had a positive effect on wildlife preservation and protection efforts, notably in Africa but also in South America, Asia, Australia, and the South Pacific.[16]
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