Forests play a key role in global ecological balance. Nowadays, the world's deforested land increases fastest in Asia ; the decreasing rate of forest is about 20 million ha a year, mainly because of population growth and poverty. In order to monitor these changes, new techniques are being launched, mostly using satellites, which enable to patrol wide and various areas worldwide.

What is a tropical rainforest?

Tropical rainforest is a forest occurring in tropical areas of heavy rainfall. It is abundant with wildlife and vegetation.
Rainforests cover less than 2% of the Earth's surface. They are home to some 50 to 70% of all life forms on our planet. Rainforests are the most productive and the most complex ecosystems on Earth.

What is an ecosystem?

An ecosystem is a living community of plants and animals sharing an environment with non-living elements such as climate and soil. Ecosystems exist on a variety of scales; An example of a small-scale ecosystem (Micro) is a pond. A medium-scale ecosystem (Messo) could be a forest. The tropical rainforest is an example of a very large ecosystem (Biome). Sunlight is the main source of energy. The world has many different ecosystems; each one has its own climate, soil, plants & animals.
Very few ecosystems are natural today because of human activities. More ecosystems are under threat than ever before and need protecting.  

What is the structure of vegetation in the rainforest?  

Emergent trees are the tallest trees and usually over 50 m in height. The sea of leaves blocking out the sun from the lower layers is called the canopy, which contains over 50% of the rainforest wildlife (birds, snakes & monkeys). Lianas are frequent, climbing to the canopy to reach sunlight.
The under canopy mainly consists in tree trunks with epiphytes & lianas.
The shrub layer has the densest plant growth with shrubs & ferns and other plants needing less light.
The forest floor is usually dark and damp with a layer of rotting leaves and dead animals called litter. This decomposes rapidly, within 6 weeks, to form thin humus, rich in nutrients.

What is the impact of humans on the tropical rainforest?  

Deforestation, or cutting down trees, is a major problem caused by humans in the rainforest. The following examples illustrate the present global deforestation rate:  

• 1 ha/second = equivalent to two US football fields. (2,47 acres)
• 60 ha/minute = 150 acres/min.
• 86 000 ha/day = an area larger than New-York City (214 000 acres)
• 31 million ha/year = an area larger than Poland (78 million acres)

Deforestation is due to various impacts, some positive, but the majority negative:

- Slash and Burn:

Most clearances are still made by local people and tribes needing land on which to grow crops. They clear the forest by 'slash and burn'; the vegetation is cut down and then burned. The ash acts like a fertilizer adding nutrients to the soil. When the soil begins to turn infertile, usually after 3 to 5 years, the people move on. This is called 'shifting cultivation', regardless to the negative image of slash and burn, if these periods are maintained to ensure that the forest recovers, 'slash and burn' is a sustainable method of farming in the rainforest.

- Logging:
Commercial logging is the major cause of rainforest destruction in Southeast Asia & Africa. Worldwide, it is responsible for the destruction of 6 million ha/year.  

- Road construction:
Logging roads are being built in order to access the forest better. Clearances are thus expanding more rapidly.  

- Hydroelectric power:
The construction of dams is able to kill entire ecosystems all at once.

- Intensive farming:

When villagers stay on the same land for a long time (because no other land is available), then nutrients in the soil are quickly exhausted. The soil lacks the important humus layer to provide nutrients, because there is no more forest. In the long run, the soil becomes infertile.
The different problems caused by deforestation locally, nationally and globally:
On a local level:

- Ecosystem:

1. About 80% of the nutrients come from trees and plants that provide for 20% of the nutrients in the soil. Nutrients from leaves that fall are instantly recycled back up into plants & trees. When a rainforest is clear-cut, conditions change very quickly. The soil dries up in the sun and when it rains, the soil is washed away. The rainforest never fully recovers; wildlife and plant life are reduced.  

2. Elimination of ethnic groups and their way of life.  

- Soil erosion:

When vegetation is removed, soil is left exposed to heavy rainfall. It is then rapidly eroded. The removal of top soil means little vegetation will grow. In worst case, it can also lead to massive landslides.

On a national level:
Deforestation can consume a country's only natural resource. If deforestation is not managed in a sustainable manner, a country's only natural resource could be lost forever.

On a global level:
Rainforests' canopies absorb carbon dioxide (CO2) which is one of the gases in the atmosphere. When rainforests are burned and cleared, carbon dioxide is released. The more trees are cut down, the less CO2 can be absorbed. This means more CO2 gets into the atmosphere. CO2 allows heat (sun rays) into the atmosphere. However, it will not allow the energy reflected by the earth to escape from the atmosphere. This is called the Green House Effect and this is precisely what causes global warming.

In Indonesia , illegal logging has led to a 'biological catastrophe' affecting thousands of plant and animals species and upsetting the natural biologic equilibrium that keeps rainforests healthy and stable. The mutualism that sustains numerous species has been destabilized which can lead to massive extinctions. For the plants and animals and the myriad species that inhabit the rainforest of Southeast Asia , it may be too late and there is no "forest refuge" left from which to replenish their species. Fragmentation of habitats will cause more interaction of animals with humans, and many animals will be killed or captured for the pet trade. Huge numbers of species will become extinct before their roles in the rainforest have become known, and the rainforest ecosystem of Southeast Asia will collapse in an irreversible way.

If development in the rainforest is to be sustainable (that is to say, despite the resources being used to aid development, they will still exist for future generations to use), a number of measures must be taken:

• Plantation : trees should be replanted in areas of deforestation.
• Shifting cultivation: farmers should move on after 2 to 3 years to allow the rainforest to recover.
• Measuring trees: trees should only be cut down when they reach a certain size. This will ensure younger trees to survive longer and it will encourage careful management of the rainforest.

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