TROPICAL RAIN FORESTS AND THE MAIN CAUSES OF THEIR DECREASE
Palacký University, Faculty of Science, Department of Botany
Main causes of tropical rain forests decrease are a gathering of fuelwood, comercial exploitation of timber, agriculture and cattle breeding. The problem of deforestation is close-knit combined with the fragmentation phenomenon. Natives harness tropical rain forests as a source of fuelwood and wood for construction needs and after deforestation, they use the area for growing crops. Developed countries used tropical rain forest as a source of timber for building industries, production of furniture and other industries.
There’s lot of reasons for conservation, the main ones are scientific research, wildlife conservation and tourism.
Deforestation, fragmentation, edge effect, fuelwood, exploitation, forest plantations, shifting cultivation, slash-and-burn, cattle breeding, conservation.
In these days there’s a significant modification of landscapes in many parts of the world. One of the most endangered bioms is the biom of tropical rain forest. Every year 110 000 km2 is destroyed (Myers, 1983). The deforestation of these areas has got four main reasons – 1. A need of fuel and construction wood, 2. A comercial exploitation of timber, 3. Agriculture and 4. Cattle breeding.
The fragmentation phenomenon is conected with successive deforestation. Due to a selective exploitation forest patches become isolated a they work like small islands. Organisms have smaller habitats and are exposed to different enviromental conditions, especially at the forest edges. There are some positive influences for example increase of light intensity, but most of the influences are negative. Trees are less resisting to wind gusts, fire or colonisation by lianas and creepers.
There are three types of edge effect (Osborne, 2000):
- Abiotic effect including changes in the enviromental conditions,
- Direct biological effect including changes in the abundance and distribution of species,
- Indirect biological effect including changes in species interaction such as brood parasitism, competition, herbivory, pollination, predation and seed dispersal.
The fuelwood gathering
It is startling that one whole half of all exploited wood in the world is used as fuelwood. The main reason probably is an increase in oil prices. According to Myers (1983) one person uses fuelwood from the equivalent of half a hectare of tropical rain forest each year. About fifteen persons may be taking wood from one hectare of forest. Fortunately, they use wood mostly from secondary forests, scrub patches and village woodlots.
Fuelwood gathering hits about 25 000 km2 of primary rain forest every year. According to Myers (1983) the indirect responsibility is taken by oil-exporting countries.
The comercial exploitation of timber
The main reason of huge exploitation of timber in tropical rain forest is that people want more and more wood, pressure for exploitation is growing. Its utilization is versatile – building industries, production of furniture, number of beverages and food, photographic film, explosives, clothing, paper etc.
According to Myers (1983) about 45 % of exploited wood is used for construction needs, from witch 60% in developed world. Regrettably, only a smal part of exploitation production is profitable wood. A trunk makes only 13,4 % of a stam biomass, brunches make 25,8 %, leaves 56 % and roots 4,8 % (Wadsworth, 1983).
A disadvantage of exploitation in tropical rain forests is its selectivity. In Amazonia there are about 2500 tree species, from which only about 50 are exploited. About 400 tree species have comercial value. That’s why wood-cutters také only 20 to 400 trees from each hectare. But the trees, which remain, are damaged, because their crowns are linked together by lianas. Only 50 % of remaining trees is undamaged (Fig. 1).
The solution of these problems may be forest plantations. They are founded in deforested areas, where the soil is too poor for cultivating crops. The main advantage of these plantations is that they produce more usable wood than native forests. Unluckily, the wood thickness is lower than in the native forest, because trees in the plantations grow faster. Direct comparsion of productivity isn’t possible, because native forests are much older than planted trees.
Fig. 1: The effect of extracting 8% of trees by selective logging
Agriculture leads to the replacement of natural comunities with crop plants (mostly rice, maize and manioc). Myers (1983) estimated that in 1970s 140 milion persons lived as forest farmers. It corresponds to 20 milion families. Each family clears a hectar of forest every year. Together it makes 200 000 km2/year. Most farmers exploit secondary forest, but 50 milion cultivators destroy primary forests.
Some ethnic groups practise shifting cultivation. It means that they grow crops on a piece of cleared land and after a few years, they move to another, so the nature vegetation can reclaim the land. In this way the people get enough food for their own needs and even some crops for sale, especially coffe and cocoa.
In Latin America the major type of agricultural procedure is called slash-and-burn. Farmers select an area of the forest, then the vegetation is cut and allowed to dry. After a week to few months the remaining dry vegetation is burned. There’s no chance for natural vegetation to regenerate. Crops are cultivated from one to five years, then the soil looses fertility.
The cattle breeding
The cattle breeding is the main cause of forest conversation in Latin America. First of all vegetation is usualy destroyed by herbicide. After deforestation the pastures are productive six to ten years, then they overgrow by weed and shrubs. According to Myers (1983) Brazil had 95 milion head of cattle in 1973. This large number had got two reasons:
- Brazil wanted to control its part of Amazonia.
- There was a big increase of demand for beef.
Tropical rain forest soils are very poor, so after a few years pastures became exhausted of nutrients and needed to fertilize. It led to an increase of expenses. There was a problem of toxic weed too. Some farmers lost about one fifth of their cattle.
For example in Central America there was a boom of cattle breeding in the 2nd half of 20th century. Costa Rica and some other states became a source of cheap beef for USA. A little matter of interest: a cow from Montana is four times as expensive as a cow from Costa Rica. Between 1940 and 1983 50% of native forest disapeard in Costa Rica due to founding of new pastures (see Fig. 2). According to Myers (1983) in 1976 Costa Rica had almost 2 milion head of cattle, from which 80% were exported, mainly to USA.
Fig. 2: Deforestation rates and trends in Costa Rica 1940 - 1983
Reasons for conservation
Tropical rain forests are the most richest and fascinating biom in the earth and at the same time they are less protected than any other biom. Mere 2 % are conservated like parks or reserves (Meyers, 1983).
Myers (1983) states that there are ten main reasons for conservation of tropical rain forests.
- Tropical rain forests have a great diversity. This biom is a unique net of sample ecosystems.
- In this biom evolutionary process continue undisturbed.
- Tropical rain forests have a part in climatic stability.
- There are a lot of possibilities for science research.
- There are a lot of possibilities for benchmark and monitoring studies.
- They make possible conservation of wildlife in all its variety.
- This biom is a gene pool for a lot of species.
- There’s need to conservate watershed processes to avoid flooding and soil erosion.
- It is important to conservate wildlands.
- Recreation and tourism can bring money into these regions.
People harness tropical rain forests in many ways, but most of these ways are destructive for this biom. Developed countries should stop exploitation of timber and help with founding new parks and reservations to protect the great nature wealth before it would be too late.
Myers, N. (1983): Conservation of rain forests for scientific research, for wildlife conservation, and for recreation and tourism.-in: Golley, F. B. [ed.] (1983): Tropical Rain Forest Ecosystems: 325-334, Elsevier Scientific Publishing Company, Amsterdam-Oxford-New York.
Myers, N. (1983): Conversion rates in tropical moist forests.-in: Golley, F. B. [ed.] (1983): Tropical Rain Forest Ecosystems: 289-299, Elsevier Scientific Publishing Company, Amsterdam-Oxford-New York.
Osborne, P. L. (2000): Tropical Ecosystems and Ecological Concepts.- Cambridge University Press, Cambridge.
Wadsworth, F. H. (1983): Production of usable wood from tropical forests.-in: Golley, F. B. [ed.] (1983): Tropical Rain Forest Ecosystems: 279-288, Elsevier Scientific Publishing Company, Amsterdam-Oxford-New York.