Tropical rainforest

Tropical and subtropical moist broad leaf forests of the world

Tropical rainforests are usually found near the equator. They are common in Asia, Australia, Africa, South America, Central America and on many of the Pacific Islands. Within the World Wildlife Fund's biome classification, tropical rainforests are considered a type of tropical wet forest (or tropical moist broadleaf forest) and may also be referred to as lowland equatorial evergreen rainforests. Minimum normal annual rainfall between 1,750 millimetres (69 in) and 2,000 millimetres (79 in) occurs in this climate region. Mean monthly temperatures exceed 18 °C (64 °F) during all months of the year.^[1] Rainforests are home to half of all the living animal and plant species on the planet.^[2] Tropical rain forests are called the "world's largest pharmacy" because over one-quarter of modern medicines originate from its plants.^[3] The undergrowth in a rainforest is restricted in many areas by the lack of sunlight at ground level.^[4] 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.^[5]

Characteristics

The rainforests are a perfect home to more species or populations than all other biomes combined. 82% of the world's known biodiversity could be found in tropical rainforests.^[6] The leafy tops of tall trees - extending from 50 to 85 meters above the forest floor - forms an understory. Organic matter that falls to the forest floor quickly decomposes, and the nutrients are recycled.

Rainforests are characterized by high rainfall. This often results in poor soils due to leaching of soluble nutrients. Oxisols, infertile, and deeply weathered, have developed on the ancient Gondwanan shields. Rapid bacterial decay prevents the accumulation of humus. The concentration of iron and aluminium oxides by the laterization process gives the oxisols a bright red color and sometimes produces mineral deposits (e.g. bauxite). On younger substrates, especially of volcanic origin, tropical soils may be quite fertile, as are the soils of many seasonally flooded forests, 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.^[7][8]

It has been estimated that many of new species of plants, insects, and microorganisms are still undiscovered and, as yet, unnamed by science. 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.^[9][10]

Amazon river rain forest in Peru

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 rain forest 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 15 to 50 °C and 125 to 660 cm of rainfall yearly.

Layers

Amazon river

The rainforest is divided into five different parts, each with different plants and animals, adapted for life in the particular area. These are: the floor layer, the shrub layer, the understory layer, the canopy layer and the emergent layer. Only the emergent layer is unique to tropical rainforests, while the others are also found in temperate rainforests.

The emergent layer contains a small number of very large trees which grow above the general canopy, reaching heights of 45-55 m, although on occasion a few species will grow to 70 m or 80 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 host to the largest percentage of animals, such as treefrogs, monkeys, birds, gorillas, orangutangs and insects. The canopy is the layer containing many trees just underneath the emergent.

Human uses

Habitation

Tropical rainforests are able to support human populations^[11]. 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.^[12]

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^[15][16] that make forays into the rainforest and up to 90% of the typical Yanamomo diet comes from farmed plants^[17]

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 mangoes. 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.^[18]

Pharmaceutical and biodiversity resource

Tropical rain forests are called "the world's largest pharmacy" because of the large amount of natural medicines discovered in rainforests that are derived from rainforest plants. For example, rain forests contain the "basic ingredients of hormonal contraception methods, cocaine, stimulants, and tranquilizing drugs" (Banks 36). Curare (a paralyzing drug) and quinine (a malaria cure) are also found there.

Tourism

Tourism in the Tropical rainforest has increased over the years having both positive and negative effects. People travel both nationally and internationally to experience rain forests firsthand.

Negative Impacts

As tourism becomes more popular in the tropical rainforests there are many different negative impacts that come from it, these being depletion of natural resources, pollution, and more. Taking walks/hikes in the forest, off-roading or biking and camping all can trample vegetation, introduce weeds and change plant composition. Bringing in any outside influences that come in contact to the plants and nature of the forest can destroy or leave a major impression on the plants. There are also many other environmental impacts on the forest caused by tourism such as: changes in soil condition, increased soil erosion, alterations of faunal composition, increase and introduction of weeds, development of social trails or paths through the forest, changes in water quality, habituation of native fauna, alterations of plant life and composition, and spread of soil pathogens.

Positive Impacts

Onset dates and prevailing wind currents of the southwest summer monsoon.

Despite the negative effects of tourism in the tropical rainforests, there are also several important positive effects.

• 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.^[19]

Animal products

Rainforests provide numerous animal products including honey, game meat, and associated trophies such as hides and ivory.

Ecosystem services

In addition to extractive human uses rainforests also have non-extractive uses that are frequently summarized as ecosystem services. Rain forests play an important role in maintaining biological diversity, modulating precipitation, infiltration and flooding, increasing scientific knowledge and in the spiritual well-being of humans. Such ecosystem services are of use to humans without the need for any modification or management of the forest yourself.

References

• Mann, Charles C., 1491 New Revelations of the Americas Before Columbus New York: Knopf, 2005 ISBN 0739464418

See also

• Deforestation
• Amazon Rainforest
• Rainforest
• Tropical and subtropical moist broadleaf forests
• Temperate rain forest
• List of tropical and subtropical moist broadleaf forests ecoregions

External links

• Rainforest Action Network
• Info on Amazon Rainforest, the largest rainforest in the world
• Rain Forest Info from Blue Planet Biomes
• Passport to Knowledge Rainforests
• Rainforest protection

Conservation efforts

There have been many conservation efforts:

• World Wildlife Fund
  • Amazon - What you can do
• Greenpeace
  • Protect Ancient Forests