The causes of deforestation are complex, and differ from region to region. One of the main causes in many areas is hydropower development. In the Malaysian province of Sarawak on Borneo, where there are still large undisturbed areas of rainforest, a quarter of the forest is threatened by planned hydropower projects (The Sarawak Group, 1987).
Along with mining, settlements and other kinds of development, damming of tropical rivers has traditionally caused about ten percent of the total annual deforestation in the tropics, according to the United Nations Food and Agriculture Organisation (Persson, 1986). But in many areas this figure is a lot higher, and with the many and big development programmes being planned, hydropower projects will probably play an increasing part in the destruction of tropical forests. In addition, hydropower development results in other activity, such as roads, power line paths, construction sites and migration. Each of these factors can be a bigger threat to the forest than the actual submergence.
The giant dams being built in the Third World often involves the forced resettlement of several hundred thousand people. Most of these people are moved to potential agricultural areas. In practice this often means forested areas.
Brazil is the country in the world with the largest area of remaining rainforest, but has also the highest rate of deforestation. The construction of roads is the main cause of this deforestation, as it opens up areas which used to be inaccessible to poor, landless peasants and settlers. In many areas big land owners come into the area, clearing huge areas for pastures. Forest is also cut down on each side of the road to create long strips of agricultural landscape.
In a 1988 report on the cause and effect of deforestation, the Canadian Embassy in Brazil considers development of hydropower to be the fourth most important cause of deforestation, after road building, migration and cultivation of pastures.
Several large dams have until now flooded more than 2 000 square kilometres of rainforest. The Tucurui dam in the state of Para in the eastern Amazon flooded more than 2 400 square kilometres of forest. The area was not cleared of trees before the flooding, and the rotting organic material soon caused major environmental problems. The decomposition releases hydrogen sulphide, which makes the water acidic. The fish, which has been an important source of food for the local population, has disappeared. An increase in the occurrence of diseases like malaria and bilharzia has been observed in the area around the artificial lake.
Everywhere where dams have been built in tropical rainforests, similar problems have occurred, in addition to the loss of the forest and its many life forms. Still hydropower dams are being built in tropical forested areas, and many more are being planned.
In short, the development of hydropower in tropical areas is a strong and growing threat to the tropical forests. In this chapter we will sum up the most important local and global problems connected with deforestation.
2. 2 HOW FAST IS THE FORESTS DISAPPEARING?
Since the middle of the eighties the world has turned its attention to the deforestation in the tropical areas. The situation has been described as one of the most serious environmental problems of our time by climatologists, ecologists and international organisations such as the United Nations Food And Agriculture Organisation (FAO), The United Nations Development Programme (UNDP), the World Bank and the World Resources Institute (WRI).
Several studies have been made to calculate the amount of forest destroyed annually in the tropics. These studies use different definitions of the concepts "forest" and "deforestation", and because of this the results apparently varies significantly. However, Melillo (1985) and Myers (1989, 1993) have made comparisons of these studies, correcting the results by using the same definitions. These comparisons show that the results are not as different as they appear at first sight.
Myers (1993) presents the following numbers:
- Originally the tropical rainforests covered about 14.5 million square kilometres (in many other publications this number is somewhat higher- about 16 million square kilometres).
- Today about 7.5 million square kilometres remains. In other words, almost half of the rainforests have disappeared.
-The total deforestation in 1989 was 142 200 square kilometres. This equals an annual deforestation rate of 1.8 percent. By extrapolating these data we can estimate the deforestation of tropical forest to 148 000 square kilometers in 1991, or 1.97 percent of the remaining forest.
As a comparison FAO (1992) has calculated the annual deforestation in the decade 1981-90 to 169 000 square kilometres. This figure includes both "tropical dry forests" and "tropical moist forests" (tropical rainforests), while Myerís calculations only includes the latter.
In any case the conclusion is that the rate of deforestation is increasing in the tropical forests. If this tendency holds, all the remaining tropical rainforests will be gone in the next fifty years.
However, there is a large regional variation. In Southeast Asia the remaining forests will probably be gone in 20 years, except for the forest in Kalimantan and Irian Jaya in Indonesia and on Papua New Guinea. In West Africa there will be very little forest left by the end of the nineties, apart from Cameroon. In Latin America it is difficult to estimate how much forest will survive the next two decades, except a large area in western Brazil and an area in the highlands of Guyana.
Even though there has been increased attention and knowledge of the importance of the tropical forests, and several attempts to slow down the destruction, the rate of deforestation has increased by 60-90 percent during the eighties (59 percent according to FAO (1992), 89 percent according to Myers (1993)). If stronger means are not taken, there is reason to believe that the deforestation rate will increase even more in the near future.
2. 3 DEFORESTATION AND INDIGENOUS PEOPLE
Several efforts have been made to estimate the number of people living in the tropical forests, and how many of these are indigenous people. In the middle of the seventies a minimum estimate of the number of people living in and of the tropical forests was 140 million, with a growth rate of 3.5 percent (Myers, 1984). The high growth rate is mainly caused by settlers, while the number of indigenous people is decreasing. Myers calculated the population of the tropical forests to 200 million in 1980. In other words, there is a growing population living of agriculture in or in the outskirts of tropical forests.
The inhabitants of tropical forests can be divided into three groups:
- People living as nomadic hunters and gatherers constitute only 1-2 percent of the 140-200 million people living in the tropical forests (ICIHI, 1986), and their numbers are decreasing. These people are descendants of larger societies that have lived in harmony with the forest for a long time.
- Many of the others are native peasants with a long tradition of crop rotation. Most of these have been capable of cultivating the forest without harming it, but the increase in population and economic pressure are forcing them to change their methods and use shorter rotation periods.
- The fastest growing group is the settlers: landless farmers, big landowners and timber and construction workers. None of these are adapted to the environment like the first two groups (ICIHI; loc.cit.).
There is no sharp line between the first two groups, and in the following they are both included in the term indigenous people.
Tropical rainforests are the most strongly threatened habitat where there are still indigenous people. Deforestation and other factors like the search for minerals and oil are forcing them into a steadily decreasing area. Many of the groups have to give up their original way of life, their culture and their religion because of the destruction of the forest.
More than a thousand different groups of indigenous people live in the rainforests and it is still possible that there are tribes yet unknown to the rest of the world (Caufield, 1984). These groups have developed knowledge and cultures in accordance with their environment through thousands of years, and even physically they are adapted to the life in the forest. For many of the people living in these areas the forest is the only resource they have. It gives them food, shelter and cultural ties.
The indigenous people are the only people with thorough knowledge of how the resources of the rainforests can be sustainably harvested. In order to utilise the rainforest in an economically and ecologically sound way it is important to build on this knowledge. Through thousands of years they have tried out herbs, fruits, spices and vegetables that modern science doesnít even know the names of. Just on Papua New Guinea, where the forest is rapidly disappearing, 600 traditional medicine plants have been registered. Only a few of these have been chemically analysed. The wing bean plant, a fast growing plant rich in protein and vitamins which today is grown everywhere in the tropics, wasnít "discovered" by the American Academy of Science until 1974, even though it had been grown for generations by people on Papua New Guinea.
This enormous knowledge of the resources of the rainforests and how they can be used is disappearing forever as the indigenous people become extinct or their culture is destroyed.
The activity which constitutes the biggest threat to indigenous people is the development of hydropower (Burger, 1987). The construction of dams and the flooding of large areas creates enormous problems and destruction for many of the indigenous peoples of the world. A Canadian environmental group sums up the effects of hydropower in the Third World in this way: "New diseases are spreading, peasants are forced to move to land of less quality, food production is decreasing, forests are either submerged or cut down by those who have had to move in search of new land." (Probe 1985, quoted in Burger, 1987).
The hydropower business is big business. The World Bank predicts spending about 100 billion US dollar on hydropower before the year 2000. Usually the affected indigenous people have neither been consulted nor compensated for the loss of their land. Often these projects have caused forced resettlement (see for example Caufield, 1984; Hong, 1987; Alvares and Billorey, 1988; Burger, 1987). In addition, the electricity produced will normally not benefit this part of the population.
2. 4 BIOLOGICAL DIVERSITY
Since the World Commission On Environment And Development (The Brundtland Commission) published its report Our Common Future in 1987 there has been a strong development in the global communityís view on protection and use of the biological diversity. Today the threat against the biological diversity is considered one of the biggest environmental challenges, because the extinction of genes, species and ecosystems is irreversible. The internationally binding convention on biological diversity was negotiated before the 1992 UNCED conference in Rio. As of April 1995, it had been ratified by 117 countries and the European Union.
Our common future devoted an entire chapter to the importance of protecting the biological diversity. "Conservation of living natural resources - plants, animals, and micro-organisms, and the non-living elements of the environment on which they depend - is crucial for development. (...) Species and their genetic materials promise to play an expanding role in development, and a powerful economic rationale is emerging to bolster the ethical, aesthetic, and scientific cases for preserving them." (World Commission On Environment And Development, 1987). In the years that have passed since the report was published, thousands of species have become extinct and the biological diversity has been strongly reduced. There are several reasons for this. One of the main reasons is the destruction of ecosystems especially rich in species, such as coral reefs, wetlands and tropical rainforests.
No certain scientific data exist regarding the number of species on Earth. Estimates lie between five and 100 million (Wilson, 1993). Between 1.4 and 1.8 million species have been described (Stork, 1988; Wilson, 1993), which means that most species are still unknown.
There is scientific agreement that between 50 and 90 percent of all the Earthís species live in the tropical rainforests, even though these cover less than two percent of the total surface or six percent of the land. The main reason for this enormous biodiversity is that this ecosystem has been able to develop mostly undisturbed by climate changes and human activity for about sixty million years.
The lifetime of a hydropower plant in a tropical forest is normally 30-40 years. This is the time it takes for the reservoir to fill up with silt and stones. In other words, in these cases short term economical interests are destroying the Earthís oldest and most complex ecosystem.
When the diversity of species is so great in a limited area, there are only a small number of individuals in each species, leaving it very vulnerable to changes in the ecosystem. Every time a group of individuals die because of logging, flooding or other activities, some of the foundation for the survival of this species disappears. The discussion on the destruction of rainforest has often been focused on the extinction of species, but the genetical variation within each species is especially important in this ecosystem, if the species is to survive the ecological changes taking place. In the following we will therefore use the term life forms, which also covers variation within each species.
The annual number of life forms becoming extinct has been discussed extensively (see for example Kaufman and Mallory, 1986) and it is impossible to make an exact calculation as long as the scientific registration is so insufficient. Norman Myers, one of the biologists strongly involved in this discussion, writes: "Only ten years ago a renowned scientist showed not one life form per year was becoming extinct, as was the commonly accepted knowledge. He presented material showing that we are losing one life form per day. Today he believes that the rate is several life forms per day - and that it will rise to several life forms per hour in the next ten years." (Myers, 1987).
The American group of scientists Club of Earth, consisting of nine of USAís leading biologists, characterise this threat against life on Earth as so serious that it can only be compared to a nuclear war.
Even though the rate of extinction is under discussion, there is agreement that a mass extinction unparalleled in recent geological time is going on. Nobody can predict the consequences this will have on life on Earth, but there is no doubt that it will prove a great threat to our biosphere.
Paul and Anne Erlich, who were among the first biologists to study this subject in depth, compares the situation to a plane where the bolts on the wings are removed one by one. For a while nothing happens, until the wing suddenly drops off and the plane crashes. The species that have been "removed" have not caused a disaster so far, but saying that it doesnít matter if some unknown species disappear can be compared to saying that the removal of a few bolts is harmless (Erlich and Erlich, 1981).
The World Bank document Development Projects also considers this issue. The authors write that "some 15-20 percent of the world's estimated 3.5 to 10 million plant and animal species may become extinct by the year 2000 (...) Though they have tremendous future potential as renewable sources of energy, industrial products, medications, genetic inputs to agriculture and applied biological research, if they are not eliminated first" (Baum and Tolbert, quoted in George, 1988).
Besides the flooding of large areas, hydropower development means construction of roads and power lines, which leads to fragmentation and destruction of forest. The regulation of rivers will in many cases block migration paths of fish and other organisms. These interventions in the ecosystems contribute to the reduction of biological diversity.
2. 5 CLIMATE CHANGES
Tropical forests are of great importance to the regulation of the Earthís climate. Both the global hydrological cycle, the distribution of heat and rainfall and the chemical composition of the atmosphere will change because of the deforestation.
Recent research in the Amazon has lead to surprising discoveries on the rainforestís ability to return water to the atmosphere in an ongoing cycle. According to the researchers roughly half the rain that falls on the enormous forests of the Amazon evaporates at once and is returned to the atmosphere, where it condenses again. This is caused partly by the evaporation from leaves, partly by the transpiration of trees due to photosynthesis and other biochemichal processes. In some areas as much as 75 percent is returned to the atmosphere (Salati, 1987).
Since the amount of precipitation around the equator is large, a considerable amount of water vapour is returned to the atmosphere in this way. When the forest disappears the cycle is broken and the local climate becomes dryer. In central Panama, where almost all rainforest has been cut to provide grazing land for the big ranches, the annual precipitation has decreased by 43 centimetres in the last fifty years (Caufield, 1984). Similar observations have been made in other areas.
Less rainfall in Brazil would probably cause big problems for the planned hydropower plants in the Amazon. This point is seldom made when the effects of deforestation are discussed.
A more widely discussed problem is the effect of deforestation on the heat distribution close to the equator. The vaporisation from the rainforests absorbs a lot of energy, and represents a strong cooling effect in the tropics. Energy is released when the water vapour condenses to rain further north and south. Without the tropical forests, especially the forests of the Amazon, the tropics would become warmer and drier while the temperate zones on both sides of the equator would become cooler, according to some scientists. The tropical forests can thus be seen as the first part of the continual process of "pumping" heat from warm regions to colder regions (Bunyard, 1987).
The Amazon region contains two thirds of all surface fresh water (disregarding glaciers, ground water etc.). Most of this water stays in the region in a perpetual cycle of clouds, rainfall, absorption by vegetation and transpiration. When the forests disappear the climate slowly turns drier. Sooner or later the remaining forest will be affected and maybe die, and the process is reinforced.
It is not possible today to predict accurately the changes in precipitation, temperature etc. caused by deforestation. The only thing certain is that the global climate will change (see Myers, 1984).
There is no longer any doubt that deforestation in the tropics contributes to the increase of carbondioxide in the atmosphere, as most of the forest is burned or decomposes. Carbondioxide contributes to the increased greenhouse effect, trapping heat that would otherwise radiate into space in the atmosphere. The greenhouse effect is caused by the atmosphereís ability to absorb long-wave radiation of heat from the surface of the earth, while short-wave radiation from the sun is let through. An increased amount of greenhouse gases like carbondioxide, methane and CFCs leads to an increased absorption of heat in the atmosphere, slowly heating up the planet.
Even though the biggest source of carbondioxide is the combustion of fossil fuels (oil, gas and coal), deforestation in the tropics plays an important part. Some scientists have suggested that deforestation represent half of the antrophogenic emissions of carbondioxide (Woodwell, 1983). More recent calculations indicate that the percentage is lower. According to Myers (1993), 30 percent of the total antrophogenic emissions of carbondioxide are caused by deforestation.
The emission of substantial amounts of carbondioxide caused by the burning and decomposition of trees is yet another result of the submergence of tropical forests.
TROPICAL FORESTS AND TROPICAL RAINFORESTS
Today the tropical forests cover roughly eight million square kilometres (Terborgh, 1992), an area the size of USA. About 75 percent of the tropical forests are tropical rainforests.
Tropical rainforest is the natural vegetation in the humid parts of the tropics. In a broad belt around the equator, in all places where precipitation is abundant and evenly distributed trough the year, there has until recently existed forests with similar characteristics. As the transition between different kinds of forests happen gradually,
many different definitions of "tropical rainforest" has been proposed (see for example Whitmore, 1975). Depending on the definition, it is possible to make different estimates of the areas covered by rainforest and how fast it is disappearing. The rainforests can be divided into at least 30 subgroups.
The most important common characteristics of tropical rainforests can be summarised as follows (Fridstrom, 1986):
The forest grows in areas with high humidity, caused by frequent rainfall (at least 2 000 mm per year), and with an even temperature (around 27 degrees C).
The forest is evergreen and has no seasonal variations.
The forest has several layers of tree crowns, with the tallest trees being 50-70 metres tall.
The forest is rich in lianas (climbing plants) and epiphytes (plants growing in the trees).
The forest has a lot of different species and life forms, strongly specialised species and is extremely vulnerable to interference.
There are three large separate areas of rainforests. The largest lies in Latin America, where roughly 57 percent of the existing rainforests are located. The second, consisting of about 25 percent of the rainforests, is the Indo-Malaysian region in Southeast Asia. The third and smallest area (about 18 percent) is in Africa, mainly in the Zaire basin, the lower parts of Niger and in some parts of western Africa. In addition there are small areas of rainforests on Madagascar, Mauritius, Reunion, Rodriguez and the Seychelles.
Tropical forests includes, in addition to rainforests, the endangered mangrove forests, dry defoliating forests, humid defoliating forests, and evergreen forests in the tropics. Definitions and limitations vary (see for example UNESCO, 1978; Myers, 1984).
Return to Main Discussion Topic Article
It is 7:27:42 AM on Tuesday, August 21, 2018. Last Update: Monday, July 30, 2001