Throughout the tropics, rain forests are being cut down. By different methods and for different reasons, people in tropical regions of the world are cutting down, burning, or otherwise damaging the forests. The process in which a forest is cut down, burned or damaged is called "deforestation."

Global alarm has risen because of the destruction of tropical rain forests. Not only are we losing beautiful areas, but the losses strike deeper. Deforestation causes the extinction of many species and changes in our global climate. If the world continues at the current rate of deforestation, the world's rain forests will be gone within 100 years--causing unknown effects to the global climate and the elimination of the majority of plant and animal species on the planet. 

How Deforestation Happens

Deforestation occurs in many ways. The majority of rain forest cut down is cleared for agricultural use such as the grazing of cattle, and the planting of crops. Poor farmers chop down a small area (typically a few acres) and burn the tree trunks, a process called "slash and burn" agriculture. Intensive, or modern, agriculture occurs on a much larger scale, sometimes deforesting several square miles at a time. Large cattle pastures often replace rain forest to raise beef for the world market.

Commercial logging, the cutting of trees for sale as timber or pulp is another common form of deforestation. Logging can occur selectively, where only the economically valuable species are cut, or by clear-cutting, where all trees are cut. Commercial logging uses heavy machinery, such as bulldozers, road graders, and log skidders, to remove cut trees and build roads. The heavy machinery is as damaging to a forest as the chainsaws are to the trees. 

There are other ways in which deforestation happens, such as the building of towns and flooding caused by construction of dams. These causes represent only a very small fraction of total deforestation.

The Rate of Deforestation

The actual rate of deforestation is difficult to determine and has been the focus of NASA-funded scientists for many years. NASA projects to study the deforestation of tropical forests are conducted by analyzing satellite imagery (pictures taken by satellites in space) to view areas of forest that have been cleared. Figure 1 shows part of a satellite scene, showing how scientists classify the landscape. There are both patches of deforestation and a "fishbone" of deforestation along roads. Forest fragments are isolated forest pieces left by deforestation, where the plants and animals are cut off from the larger forest area. Regrowth--also called secondary forest--is abandoned farmland or timber cuts that are growing back to again become part of the forest. The majority of the picture is undisturbed, or "primary," forest, drained by network of rivers.

Figure 1. Satellite image of deforestation in the Amazon region, taken from the Brazilian state of Para on July 15, 1986. The dark areas are forest, the white is deforested areas, and the gray is regrowth. The pattern of deforestation spreading along roads is obvious in the lower half of the image. Scattered larger clearings can be seen near the center of the image.

The most recent figures by the Food and Agriculture Organization (FAO) estimate tropical deforestation (of the rain forest and other tropical forests) at 53,000 square miles per year (15.4 x 10⁶ ha/yr) during the 1980s (FAO 1993). Of this, they estimate that 21,000 square miles (6.2 x 10⁶ ha/yr) were deforested annually in South America, most of this in the Amazon Basin. Based on these estimates, each year an area of tropical forest large enough to cover North Carolina is deforested. Each year!

The rate of deforestation varies from region to region. BSRSI's research showed that in the Brazilian Amazon, the rate if deforestation was around 6200 square miles per year (1.8 x 10⁶ ha/yr) from 1978-1986, but fell to 4800 sq. miles per year (1.4 x 10⁶ ha/yr) from 1986-1993 (Skole and Tucker 1993). By 1988, 6% of the Brazilian Amazon had been cut down (90,000 square miles, about the area of New England). However, due to the isolation of fragments and the increase in the boundaries of the forest and clearings, a total of 16.5% of the forest (230,000 square miles, nearly the size of Texas) was affected by deforestation. NASA-funded scientists are currently analyzing rates of deforestation for the current decade, as well as studying how deforestation changes from year to year.

Figure 2. Deforestation in the Brazilian Amazon in 1986. The darker the area, the more forest remaining. 

The much smaller region of Southeast Asia (Cambodia, Indonesia, Laos, Malaysia, Myanmar, Thailand, and Vietnam) lost nearly as much forest per year from the mid- 1970s to the mid-1980s, with 4800 square miles per year (1.4 x 10⁶ ha/yr) converted for agricultural use or cut for timber. 
 
 

Figure 3. Deforestation in continental Southeast Asia (excluding Malaysia and Indonesia) from 1973 to 1985. The black represents forest, the lighter areas deforestation. The dark gray represents cloud cover, and white areas are places for which no satellite information was available. During this time period, about 50,000 square miles was deforested. China and India are included on the map but no assessment of their forest cover was made.

Why Deforestation Happens

The cause of deforestation is a very complex subject. A competitive global economy forces the poorer tropical countries the need to raise money. At the national level, the governments of these countries sell logging concessions to raise money for projects, to pay international debt, or to develop industry. Brazil had an international debt of $159 billion in 1995, on which it must make payments each year. Logging companies seek to harvest the forest and make a profit from the sales of valuable hardwoods (such as mahogany) and pulp. 

Because of their basic human need for food, peasant farmers often cause deforestation to raise crops for self-subsistence. Most tropical countries are very poor by U.S. standards, and farming is a basic way of life for a large part of their population. In Brazil, for example, the average annual earnings of a single person in is US $5400, compared to $26,980 per person in the United States (World Bank, 1998). In Bolivia, which holds part of the Amazon rain forest, the average earnings per person is $800. Farmers in these countries do not have the money to buy necessities and must raise crops for food and for sale. 

Deforestation and the Global Carbon Cycle

Carbon dioxide (CO2) is the major gas involved in the greenhouse effect, which causes global warming. All the things that produce CO2 (like a car burning gas) and the things that consume CO2 (growing plants) are involved in the "global carbon cycle."

Tropical forests hold an immense amount of carbon, which joins with oxygen to form CO2. The plants and soil of tropical forests hold 460-575 billion metric tons of carbon worldwide (McKane et al. 1995). Each acre of tropical forest stores about 180 metric tons of carbon.

Deforestation increases the amount of CO2 and other trace gases in the atmosphere. When a forest is cut and replaced by cropland and pastures, the carbon that was stored in the tree trunks (wood is about 50% carbon) joins with oxygen and is released into the atmosphere as CO2.

The loss of forests has a great effect on the global carbon cycle. From 1850 to 1990, deforestation worldwide (including that in the United States) released 122 billion metric tons of carbon into the atmosphere, with the current rate being between 1.6 billion metric tons per year (Skole et al. 1998). In comparison, all of the fossil fuels (coal, oil, and gas) burned during a year release about 6 billion tons per year. 

Releasing CO2 into the atmosphere increases the greenhouse effect, and may raise global temperatures (see Climate Change fact sheet). The role of fossil fuel burned by cars and by industry is well known, but tropical deforestation releases about 25% of the amount released by fossil fuel burning. Tropical deforestation, therefore, contributes a significant part of the increasing CO2 in the atmosphere. 

Deforestation and Biodiversity

Worldwide, there are between 5 to 80 million species of plants and animals, which make up the "biodiversity" of planet Earth (Lawton and May 1995). Most scientists believe the number of species to be between 10 and 30 million. Tropical rain forests--covering only 7% of the total dry surface of the Earth--hold over half of all of these species (Lovejoy 1997). Of the tens of millions of species believed to be on Earth, scientists have only given names to about 1.5 million of them (Stork 1997). Even fewer of these species have been studied in depth. 

Many of these plants and animals of the rain forest can only be found in small areas of them, because they require a special habitat to live. This makes them very vulnerable to deforestation. If their habitat is cut down, they may become extinct. Every day species are disappearing from the tropical rain forests as they are cut. We do not know the exact rate of extinction, but estimates range from one to 137 species disappearing worldwide per day (Stork 1996, Rainforest Action Network 1998). 

The loss of species will have a great impact on the planet. For humans, we are losing organisms that might have shown us how to, for example, prevent cancer or cure AIDS. Other organisms are losing species that they depend upon, and thus face extinction themselves. 
 

After Deforestation

What happens after a forest is cut is very important in the regeneration--growing back--of that forest. Different types of cutting and different uses of the land have very different effects on the ground and surviving organisms that make up a rain forest. 

In a tropical rain forest, nearly all of the life-sustaining chemicals, called nutrients, are found in the plants and trees, not in the ground as in a northern, or temperate, forest. When the plants and trees are cut down to plant crops, small farmers usually burn the tree trunks to release into the ground (or "soil") the nutrients necessary for growing plants. This process is referred to as "slash and burn" agriculture. When rain falls, it washes away most of the nutrients and leaves the soil much poorer in nutrients. After a few years, the ground can no longer support crops, and the farmer has much poorer crops. The time for the soil to "go bad" can be from 3 to 20 years. 

When the fertility of the ground becomes low, farmers seek other areas to clear and plant, abandoning the poor soil. The area previously farmed is left to grow back to a rain forest. However, just as the crops did not grow well because of the soil's poor nutrients, the forest will grow back slowly, also because of the soil's poor nutrients. After the land is abandoned, the forest typically can take 50 years to grow back. 

Another type of farming practiced in rain forests is called "shade agriculture." In this type of farming, many of the original rain forest trees are left to provide shade for shade-loving crops like coffee or chocolate. When the farm is abandoned, the forest grows back very quickly, because much of it was left unharmed in the first place. After this type of farming, forests can grow back as quickly as 20 years.

Other types of farming can be much worse for forest regrowth. Intensive agricultural systems use lots of chemicals like pesticides and fertilizers. The pesticides kill a lot of the living organisms in the area, and pesticides and fertilizers wash into the surrounding areas. In banana plantations, pesticides are used on the plants and in the soil to kill pest animals. However, these pesticides also kill other animals as well, and weaken the health of the ecosystem. Banana plantations also use irrigation ditches and underground pipes for transporting water, changing the water balance of the land. After a banana plantation, or other intensive agricultural system, is abandoned, it can take a great deal of time for a forest to regrow-- possibly even centuries.

When a rain forest is commercially logged, the results are different. Under selective logging, only a few trees are cut down for timber. However, the use of heavy machinery--like bulldozers--in the cutting and hauling of logs tears up the ground and knocks down or damages many other trees. In a study in Indonesia, Andrew Johns found that when cutting down only 3% of the trees, a logging operation damaged 49% of all the trees in the forest (Johns 1989). Yet even with all that damage, the rain forest will grow back relatively quickly if left alone after selective logging, because there are still many trees to provide seeds and protect young trees from too much sun. 

Clearcutting is much more damaging to a tropical rain forest. When the land is commercially clearcut and all of the trees removed, the bare ground is left behind with very little that can grow on it. Unlike when the farmer cleared the land, there are almost no nutrients left behind because all the tree trunks were removed. A clearcut forest can require many years to regenerate--in fact, scientists do not know how long it takes for a clearcut forest to grow back.
 

The Future

The deforestation of tropical rain forests is a threat to life worldwide. Deforestation may have profound effects on global climate and cause the extinction of thousands of species annually. Stopping deforestation in the tropics has become an international movement.

Because the loss of rain forests is driven by a complex group of factors, the solutions are equally complex. Simple solutions that do not address the complex nature of world economics and rain forest ecology have little chance of succeeding. The future requires solutions based in solving the economic crises of countries which have extensive rain forests, as well as improving of the living conditions of the poor people often responsible for deforestation. 
 
 

References

FAO. 1993. Forest Resources Assessment 1990--Tropical Countries. Rome: United Nations Food and Agriculture Organization.

Lawton, J. and R. M. May. 1995. Extinction Rates. Oxford University Press.

Lovejoy, T. E. 1997. Biodiversity: What Is It? Pp. 7-14 in M. L. Reaka-Kudla et al., eds. Biodiversity II: Understanding and Protecting our Natural Resources. Washington, D.C.: Joseph Henry Press.

McKane, R. B., E. B. Rastetter, J. M. Melillo, G. R. Shaver, C. S. Hopkinson, D. N. Fernandes, D. L. Skole, and W. H. Chomentowski. 1995. Effects of Global Change on Carbon Storage in Tropical Forests of South America. Global Biogeochemical Cycle 9: 329-350.

Skole, D. L., W. A. Salas, and C. Silapathong. 1998. Interannual Variation in the Terrestrial Carbon Cycle: Significance of Asian Tropical Forest Conversion to Imbalances in the Global Carbon Budget. Pp. 162-186 in J. N. Galloway and J. M. Melillo, eds. Asian Change in the Context of Global Change. Cambridge: Cambridge University Press. 

Stork, N. E. 1997. Measuring Global Biodiversity and Its Decline. Pp. 41-68 in M. L. Reaka-Kudla et al., eds Biodiversity II: Understanding and Protecting our Natural Resources. Washington, DC: Joseph Henry Press. 

World Bank. 1997. World Development Report. World Bank: Washington, DC