Deforestation & Biodiversity

John Pottage and Chris Trucksess

Deforestation, defined by biologist Charles Southwick as "the destruction of forests; may involve clear-cutting or selective logging" (p. 365), is a predominantly human-driven process that is dramatically altering ecosystems worldwide. "Clear-cutting" involves the indiscriminant removal of every single plant and tree species from within a selected area. The other major process of deforestation, "selective logging," focuses removal efforts on only specific, predetermined tree species within a chosen area. The statistics gathered about human deforestation over time are considerable, and they can be somewhat controversial. Depending on the source and the location selected, the magnitude of deforestation varies. Southwick estimates that, approximately 10,000 years ago, 6.2 billion hectares (23.9 million square miles) of forest existed on earth (p. 117). That figure is equivalent to 45.5% of the earth's total land. He further estimates that, by 1990, this amount had declined 30%, with only 4.3 billion hectares of forest remaining (p. 117). Southwick also acknowledges other estimates that place the total amount of deforestation between 50% and 75% (p. 117). NASA has similar deforestation statistics that confirm these trends. According to their website, 16.5% of the Brazilian Amazon forests have been destroyed. They also note similar magnitudes of deforestation in Southeast Asia (Cambodia, Indonesia, Laos, Malaysia, Myanmar, Thailand, and Vietnam), despite the significantly smaller total area of forest within these countries. These grim figures are somewhat tempered by the NASA finding that, over the past ten years, the deforestation rate has declined from 6,200 square miles per year to 4,800 square miles per year. Though this trend is not cause for celebration (4,800 square miles per year represents a significant amount of forest loss), it does give some hope that the deforestation rate can be reduced. Though diverse and plentiful, the body of deforestation statistics all support Charles Southwick's assertion that "deserts are expanding, forests are shrinking" (p. 117).

Before an exploration of deforestation can be undertaken, it is necessary to consider the diversity of the earth's many forests: "Forests come in many forms and occupy many different environments: wet and dry, hot and cold, high and low" (Southwick, p. 117). Biologists classify forests into four broad categories on the basis of the climate in which they are found, as well as the tree species that they contain. Forests of the first category, "boreal," are generally located within cold and dry climates such as Alaska, Northern Canada, and Siberia. These forests typically contain trees such as the spruce, fir, and larch. Temperate forests, containing trees such as the pine, oak, redwood, and hickory, are found in the cold and wet regions of the Pacific Northwest and Northern Europe. Subtropical forests, living within warm, dry climates such as the Southwestern United States and Mexico, contain the hawthorn, scrub oak, and cork oak. Finally, the tropical forests of warm, wet climates such as the Amazon and Costa Rica, contain rain forests and monsoon forests with such species as buttress trees, lianas, and stilt palms (categories taken from Southwick, chart p. 119). In general, Americans tend to think of deforestation as mainly occurring within the tropical forests of South America. In fact, each type of forest worldwide has been dramatically affected by deforestation. The United States itself has a dismal record of deforestation, with the forests of the eastern half of the country all but disappearing over a period of three hundred years (Southwick, diagram p. 122).

The causes of deforestation are numerous. Southwick advances three economic reasons for deforestation. First, he believes that developing countries remove their forests for agricultural purposes: "in the developing world, and most of the tropics, forests are cut down to provide agricultural land, both pasture and cropland." Southwick also views the exploitation of developing nations for their vast resources by their industrial counterparts as a component of deforestation: "A second driving the insatiable appetite of industrial nations such as the United States, Japan, and western Europe for lumber, pulpwood, and various forest products" (p. 123). Thus, industrial nations use the wood that is harvested from third world countries in order to create materials for housing, furniture, newspapers, magazines, and packaging. Finally, Southwick points out the use of harvested wood for fuel in developing nations. He claims that "firewood and brush supplies 52 percent of all energy use in sub-Saharan Africa" (p. 124).

In addition to those listed by Southwick, there are other causes for deforestation. A forest might disappear due to natural causes, such as fire (caused by lightning strikes), landslides, and tree-specific diseases. Subsistence also drives a considerable portion of deforestation, as individual farmers in poor countries will often clear a small plot of land in order to produce the bare amount of food needed to support their families (NASA website). Finally, deforestation occurs to satisfy the goal of land development. The construction of houses, hotels, office buildings, roads, and parking lots all require the removal of large sections of forest.

As wide and varied as are the causes of deforestation, its effects are equally numerous and diverse. One result of large-scale deforestation is climate and atmospheric change, particularly with respect to the global carbon cycle. The dual processes of respiration and photosynthesis account for a significantly large portion of carbon dioxide flow (see diagram of the carbon cycle, from the NASA website). All living creatures produce carbon dioxide through the energy-creating processes of respiration. Trees and plants, however, absorb carbon dioxide from the atmosphere through photosynthesis. With the significant reduction of trees due to deforestation, the amount of carbon dioxide absorbed by photosynthesis would be dramatically less. Thus, carbon dioxide produced by respiration would increase relative to that absorbed by photosynthesis. Carbon dioxide is a so-called "greenhouse gas": it prevents heat from escaping the earth's atmosphere. An increase in atmospheric carbon dioxide, brought about by the loss of trees (and photosynthesis), would potentially increase the risk of global warming: more heat would be trapped within the earth's atmosphere due to the excess carbon dioxide. It is also important to note that the process of tree burning itself further increases the amount of carbon in the atmosphere, although, as illustrated by the diagram, this quantity is relatively insignificant when compared with the amount of carbon cycled through photosynthesis and respiration.

Deforestation also plays a role in the spread of disease. The National Institute of Health has produced evidence that the loss of forests could promote an increase of diseases (NIH website). As forests are eliminated, local temperatures increase. Simultaneously, the risk of flooding and siltation also increases. Both of these conditions, high temperatures and excessive standing water, are ripe for the creation and spread of disease epidemics. The loss of forests and forest-dependent species also results in the potential for the elimination of current or undiscovered medicinal sources.

In addition to general deforestation, there are negative effects that are specific to selective logging (the process whereby only certain species of trees are selected for removal) (Vandermeer & Perfecto, p. 94-5). In order to obtain the desired trees, it is frequently necessary to inflict secondary damage, usually through the construction of roads. Often, non-targeted trees are removed in order to obtain the desired trees, and this damage is "frequently extensive" (Vandermeer & Perfecto, p. 94). Furthermore, roads increase unfiltered runoff and flooding: conditions that can bring about the destruction of more wildlife, as well as increase disease. Finally, a process known as "deterioration of the stand" occurs, whereby only the most valuable trees are removed: "Removing only the valuable species and genetic types while leaving behind the less valuable ones, results in an ever-decreasing fraction of trees in the recuperating stand that belong to the valuable species and genetic types" (Vandermeer & Perfecto, p. 95). The overall effect of this procedure results in a stand of trees that is "less and less valuable as time goes by" (Vandermeer & Perfecto, p. 95).

Finally, deforestation diminishes the biodiversity of a given area. Specifically, this occurs with the loss of the tree species themselves, as well as the loss of the various life forms that depend on these trees. The relationship between deforestation and biodiversity is more complex and intertwined than simple loss of species, and it warrants further detailed investigation.

Biodiversity simply refers to "the number and variety of species in a given area" (Southwick, p. 364). As an example of the tremendous variation of biodiversity worldwide, 1 hectare in northern Michigan contains only eight species of trees, while 1 hectare in Nicaragua contains two hundred tree species. As this example illustrates, the greatest sources of biodiversity are the tropical regions. It is thought that there are five to eighty million different species of life (NASA website). Though they contain only 7% of the earth's land surface, rainforests are thought to contain over half of all these life species (NASA website). Indeed, despite their small claim to the earth's total land, it is an "amazing fact" that "rain forests contain almost all the biodiversity on the planet" (Vandermeer & Perfecto, p. 127).

Scholars have advanced two main metaphors that attempt to describe the relationship between rainforest function and biodiversity (Vandermeer & Perfecto, p. 20-1). One model suggests that the forest is best described by a complex web of interconnections: each species is linked as are the strands of a spider web. Removal of one strand does not necessarily destroy the whole system. The more strands that exist, however, enable the overall web to be strengthened. The other predominant metaphor views rain forests as a house of cards. Each of the many species is likened to a card delicately balanced together with others. Though the cards may be large in number, removal of just one has the potential to bring the whole system crashing down. Though the evidence is inconclusive with regards to which model is correct, it is unequivocally true that biodiversity plays a vital role in the overall health and functioning of a rainforest (Vandermeer & Perfecto, p. 21-3).

Biodiversity, particularly the tremendous amount that is found in rainforests, is highly threatened by deforestation. It is believed that approximately 137 species die each day through extinction, and the destruction of forests is thought to be the single greatest cause of species loss (NASA website). It is also highly likely for the eliminated species to be unknown: of the vast number of species on earth, scientists have only studied and named 1.5 million in detail (NASA website). The loss of species that have not been studied is particularly discouraging, as their potential for unknown benefits is limitless.

Biodiversity is especially affected by selective logging, and these methods are particularly damaging to the carbon cycle. Selective logging creates large gaps in the forest where the removed species formerly lived. These gaps create new pockets of light in areas that were previously dark. Thus, species that thrive in lighter conditions will be selectively favored by these gaps, and they will overrun areas that had previously been dominated by species that preferred darkness. This process of light change conditions ultimately results in a biodiversity reduction. Initially, the conditions favored the existence of both types of plants: the "dark-loving" plants lived in the shade underneath the tall rain forest trees, and the "light-loving" plants existed in the gaps between trees. After selective logging, the conditions have been altered so that only light remains: thus, the "dark-loving" plants will disappear.
Selective logging also impacts the carbon cycle. Often, slow-growth forests are the first selected for removal because of their high value. Once they are gone, they are usually replaced with fast-growth forests. These fast-growth forests are generally lower in biodiversity, and they absorb less carbon dioxide from the atmosphere than do the previously slow-growth forests. Less carbon dioxide absorption results in increases to "greenhouse gas" levels, as well as increased global warming.

There have been a number of proposed solutions that attempt to slow rates of deforestation and preserve biodiversity. Many believe that governments can and should play a major role in limiting the course of deforestation through the creation of national parks and protective land legislation. Governments can also tax companies that depend heavily on deforestation, and provide grants and subsidies to those that find sustainable alternatives. Individuals can do their part through the leaders they choose to elect, as well as by deciding to support companies that practice environmentally safe methods of resource extraction.

Biologist Charles Southwick has been a major proponent of biodiversity preservation. He argues that there is a need for "greater awareness of these problems [i.e., deforestation] and their consequences on the part of the general public and especially our political and business leaders" (p. 124). He envisions a major process of broad-scale conservation programs, reforestation projects, and more intelligent efforts at finding sustainable uses of forests. As part of these changes, Southwick stresses the need for "substantial social and economic restructuring," as "new jobs must be found in small communities totally dependent on logging" (p. 125). Thus, the previous methods of defining forest property rights, forest value, and attainment of economic well-being through deforestation will need to be redeveloped in order to discover and practice more sustainable uses of forest, with the ultimate goal of biodiversity preservation.

Though these proposals all offer methods by which humans can take action to prevent deforestation and preserve biodiversity, there are a few possible roadblocks. First, humans have a strong need and desire for the forest products. The only way to produce the paper, antique furniture, housing materials (those made of wood), and packages is to cut down trees. Thousands of companies and individuals depend on the fruits of deforestation for their economic well-being. Furthermore, the greater the amount of land that is protected, the more scarce will become the wood that is necessary to make these products. With greater scarcity comes an increase in price. Most people would oppose an increase in the price of paper, furniture, and housing products in the name of biodiversity preservation. Another problem is the principle of diminishing returns. In order to preserve an additional species, the additional amount of land that needs to be protected increases (see diagram in Vandermeer & Perfecto, p. 142). For instance, protection of 5% of the land saves 30 species, 20% saves 60 species, and 40% saves only 80 species (Vandermeer & Perfecto, p. 142). More land protection saves a smaller number of species. Finally, there are proponents of an "evolutionary" approach to biodiversity. They claim that it is not the responsibility of humans to protect other species in the rainforest. It can be argued that species that die because of deforestation simply cannot adapt well to a changing environment (as humans can), and that it is simply their "evolutionary flaws" that brought about their extinction. It can also be argued that biodiversity is not obviously something humans need to survive. After all, millions of humans living in America are not dramatically affected in their daily activities by the extinction of a rare spider species in an Amazonian rain forest.

Though these arguments, particularly those grounded in economics, do present important concerns regarding forest preservation, it is equally important to not under-emphasize the significance to the world's environment of forests and their biodiversity. While the negative consequences of losing a tree species may not be immediately apparent or obvious, it is vital to understand that these types of actions will have consequences at a later time. Though it is simply impossible to know what the ultimate effects will be on our long term survival as a species, it is important to bear in mind that, once a species has been eliminated through extinction, it cannot be brought back. So, for the overall health of our rainforests, their biodiversity, and the limitless potential contained therein, it is crucial for us, as humans, to make as honest an effort as possible at their preservation.


Southwick, Charles H. Global Ecology in Human Perspective. Oxford University Press: New York, 1996.

Vandermeer, J. & Perfecto, I. Breakfast of Biodiversity. The Institute for Food and Development Policy: Oakland, CA, 1995.




Return to ENVS2 homepage

Send message to Swarthmore College Environmental Studies

last updated 5/15/03