Ecoscience: Tropical Rainforest Destruction

Rainforest destruction is proceeding at an alarming pace in South America, with potentially dire consequences for the planet’s climate. But there is some hope in one Central American country.
September/October 1978
Anne and Paul Ehrlich warn that rainforest destruction is wiping out a reservoir of biological diversity, cultural diversity, and knowledge.


The accelerating rate of tropical rainforest destruction is one of the saddest ecological events in the history of our planet. There is some dispute as to just how rapidly these areas are being cleared. But there is no question that if current trends continue, there will soon (perhaps sometime between the years 2000 and 2050) be no tropical forests at all except for a few scattered reserves and small patches on hillsides too steep to be put to any other use.

There are several reasons for the disappearance of these forests. One factor, of course, is the rapid population growth of the tropical countries. In many Latin American, African, and Southeast Asian nations the population is still increasing at a rate of two to three percent each year. This figure implies that the human density in these lands will double during the next 20 to 35 years. And it seems only natural to suppose that those ever-increasing numbers of people—very poor people at that—will continue to cut their forests (one of the few readily available resources at their disposal) at an ever increasing rate to supply themselves with firewood, building materials, and subsistence farm plots.

In most places, however, it is not population pressure per se that is directly responsible for the destruction of tropical woodlands. It is the opening up of new areas for economic reasons. University of Michigan political scientist Kathleen Foote Durham, for instance, has shown that much of the deforestation in the Peruvian section of the Amazon Basin has not been caused by invasions of subsistence farmers from the "overcrowded" highlands. Instead, large and small "cash-cropping" organizations are behind most of this destruction. These cash-cropping operations, supported in part by the Peruvian government, are producing profitable exports as well as food and lumber for the country's cities located west of the Andes.

In short, then, the forests of Peru—with the help of cheap migrant labor from the highlands—are rapidly being destroyed for the sake of a quick buck. And this is happening while the population and economic pressures on those highlands could be greatly diminished in a far more environmentally sound manner merely by raising the abysmally low yields of native domestic crops (such as the potato). Peruvian government policies to date, however, have consistently favored the colonization of lowland forests over programs designed to improve highland agriculture.

Perhaps an even more dramatic example of the destruction of tropical forests, though, is occurring now in the Amazon Basin of Peru's neighbor to the east, Brazil. This five-million-kilometer (two-million-square-mile) area is being deliberately cleared by the government—over the protests of ecologists in Brazil and elsewhere—in the interests of mineral exploitation, cattle raising, and large cash-crop operations.

For a short time during the early 1970's this development of Amazonia (and especially the Trans-Amazon Highway) was given much publicity as a program designed to provide farmland for people from the overpopulated and ecologically ravaged northeastern part of Brazil. More recently, however, even that facade has been dropped.

In 1974, to be specific, President Geisel of Brazil announced a new program for the economic development of Amazonia which would concentrate upon the aforementioned mining, lumbering, and cattle-raising operations. Thus, instead of the small farm-oriented peasants from the northeast, the Amazon "pioneers" are now to be modeled after the legendary American billionaire, Daniel Ludwig. (Ludwig's Jari Forestry and Ranching Company covers 12,000 square kilometers and has already cleared about 1,000 square kilometers of Amazonian forest.) The rapid multiplication of such operations throughout much of the Tropics would seem to doom the rain forests—and their native human and nonhuman inhabitants.

And why should we care if the tropical forests of the planet are destroyed? Few North Americans have ever seen such a forest, and fewer still would be likely to enjoy a sojourn in one. Unfortunately, however, the lives of future generations in North America will be influenced by the fate of these South American "jungles."

First of all, tropical forests are vital to the proper functioning of the planet's larger ecological system. They influence both the balance of carbon dioxide in the atmosphere and the reflectivity of the earth's surface (both factors play important roles in the governing of the planet's climate.The forests also have the potential—if current "get it while you can" lumbering practices are changed—of yielding a sustainable harvest of high quality woods (such as teak and mahogany) which may be very difficult to substitute for in the future.

And, above all, the tropical "wildernesses" provide a vast and irreplaceable reservoir of organic diversity because many millions of the species of plants and animals which thrive in them can live nowhere else. In fact, plants derived from such areas have already provided Homo sapiens with a vast array of foods, spices, drugs, and other valuable substances. (Prominent examples which immediately come to mind include rice, rubber, quinine, belladonna, bananas, jute, pineapples, cacao, rotenone, and cassava.) Furthermore, the uses of a great many other tropical "gifts of nature" are just now being explored. It would be criminal to wipe them from the face of the earth before we even understand their value.

It also should be noted that many animals of the tropical forest, ranging from morpho butterflies to jaguars, have direct commercial value and—as pollinators, herbivores, etc.—are intimately involved in the maintenance of a diversity of plants. As the Tropics are mowed down, any future benefits that might be derived from this vast storehouse of organic variety will be sacrificed for all time.

Another great loss will be the reservoir of cultural diversity represented by the rain forest peoples around the world such as the Malayan aborigines, the Philippine Tasaday, and the Yanomamo of Brazil. There were 230 separate tribes of Brazilian Amerindians in 1900. By 1957, the number had been reduced to 143. That's 87 distinct human cultures lost in just one tropical country in a little over half a century! The same attrition—often deliberately accelerated by genocidal acts of governments and individuals from the invading western culture—continues today in Brazil and elsewhere.

All these losses are irreversible and something must be done to save the tropical forests and their indigenous cultures. Obviously, once all these unique populations and species of organisms become extinct, the restoration of the equatorial jungles will become impossible. It will never be possible to rebuild them, at least not with their original biotic composition. Furthermore, the structure of most tropical forests—especially the very wet rain forests—makes them extremely vulnerable to irreversible destruction even if reservoirs of the necessary species are somehow available to recreate the land's original flora and fauna. And, of course, once a culture is destroyed, there is absolutely no way it can be brought back again.

Aside from the grounds of compassion and interest (which should be enough), there are also practical reasons for trying to preserve the cultural diversity that "progress" is increasingly trampling underfoot. The knowledge—for instance—which enables primitive cultures to get along with nature, may prove invaluable to a western society that has largely forgotten how. Who knows, some "primitive" peoples may even be able to tell us modern "civilized" folks how to get along with each other!

In order to understand the fragility of tropical forests we should consider how they were once used for slash-and-burn agriculture. When the population densities of such "farmers" were low, they could work a given area indefinitely. First, a worker would clear a small plot of ground before the rainy season began. Then, after the debris had dried, he burned the plot. This fire created a rich layer of ash and killed off many potential insect pests. The nomadic farmer could then plant his crops and—when the rains came—he would wield his machete or hoe to fight back the weeds which sprang up to compete with his garden.

It is worth noting that many slash-and-burn agriculturists traditionally planted a variety of crops in each clearing. In other words, their small plots resembled miniature ecosystems and thereby were less susceptible to pests and diseases than modern mono-crops, did not deplete the soil's nutrients a great deal, and provided their growers with a varied diet.

After the harvest the farmer might move on, or he might once again burn the dried debris in his clearing. If he stayed, of course, there would be less material to fuel the second burning ... and thus less ash and a cooler fire. The little plot of land would be left less fertile that it had been the first time, and fewer of the pests on the bit of earth would be killed. Each cycle, then, would produce a less satisfactory crop, which would soon cause the man to abandon the plot we've just described for another. In atypical slash-and-burn society, the community (yes, some still exist) is so small that fallow plots remain uncultivated until the forest has completely reclaimed them and the land is finally ready for another cycle of farming.

You will note that this sequence is very different from that followed in farming a small piece of land in, say, Iowa. The original grassland ecosystem of the North American plains has created a very deep nutrient-rich soil that can be exploited for many seasons. Iowa also has an automatic pest-control mechanism called "winter."

But the tropical rain forest has little in common with the American prairie. In a rain forest most of the nutrients are not in the soil, but in the plants themselves. The trees have very shallow, spreading root systems which rapidly take up any nutrient released by the decay of organic matter. When these trees are cut down and burned to ashes, the nutrients in that ash are rapidly leached away (as they would not be from a more complex prairie soil exposed to the rain).

Furthermore, a small clearing in a tropical rain forest is easily recaptured by native vegetation. The surrounding forest wall helps protect the thin soil from torrential rains and baking tropical sun, and many of the leached nutrients are taken up by nearby trees whose roots extend into the clearing. The larger the clearing, though, the more difficult this natural process of reforestation becomes.

It follows, then, that when populations of slash-and-burn farmers grow too large, and have to extend the sizes of their clearings to compensate for the poorly "rested" soil in each patch of land, they begin a trend which is nearly impossible to reverse. The larger clearings expose more and more soil to the deleterious effects of the sun and rain. Which, of course, depletes the soil further and makes it even more difficult for the native vegetation to move back in and reclaim the damaged earth. The entire system runs ever more rapidly downhill, to the disadvantage of both the forest and the people living there. Some people believe that the collapse of the Mayan civilization was caused, in part, by overpopulation and over intensive use of slash-and-burn agriculture.

The classic slash-and-burn system—while still alive in some regions—is, of course, rapidly disappearing ... in favor of something much worse. For when forests are cleared wholesale to make way for conventional agriculture—as is common in the Tropics today—the earth is destroyed all the more rapidly. Some tropical soils even turn into a hard, bricklike substance that can never be farmed again (this process is called "laterization").

The removal of forests can drastically alter a local climate too, turning an area where rich growth once flourished into a semi-desert that is subject to alternating floods and droughts (Brazil's northeast is a case in point).

As if all that weren't bad enough, the destruction of vast areas of rain forest (as is occurring in the Amazon Basin) has the potential of altering the climate on a global scale by, among other things, changing the carbon dioxide balance in the atmosphere. Such changes can have dramatic and direct effects, even on those of us who live far from the equator.

In this dark and dismal picture of the Tropics that we've just outlined we can see only one ray of light (there are, no doubt, others), and that is the country of Costa Rica. A decade or two ago this small nation, like other Central American countries, had—thanks to public health measures begun in the 1930's—an extremely high birth rate and a low death rate. By 1965, in fact, Costa Rica's population was growing fast enough to double in just 18 years! But Costa Rica, unlike its neighbors, then instituted a program that has reduced its birth rate from 49 per thousand (in the early 60's) to 28 per thousand (in 1977), and that birth rate is still declining.

The key elements in this population control success seem to have been the political stability engendered by Costa Rica's democratic government, some fortunate historical accidents, and welfare and reform policies which have helped soften the impact of poverty.

For instance: Although Costa Rica has the economic inequities which plague most less-developed countries, one looks in vain in that nation for the makeshift shantytowns that characteristically surround the cities in poorer lands. Why? Partly because for the past 30 years the country has used its resources for development instead of squandering them on a military establishment. (A poor country with an expensive military establishment makes as much sense as a poor family with a pet elephant.)

Besides having taken steps to improve the lives of its people, Costa Rica has worked toward the preservation of its physical and biological endowment. Some 25% of the small nation's land has been set aside in forest preserves or national parks. (Contrast that with Brazil, where the official goal is the setting aside of only 5% of its forests—and in poorly planned preserves at that.)

Costa Rica also has an established institute which studies tropical forest management and agricultural development. This organization is experimenting with indigenous strains of crops and seeks to discover new mixed-crop systems that will be productive in the country's soils and climate. In addition, the Costa Rican-based Organization of Tropical Studies—which specializes in tropical ecology—attracts students and scholars from the United States and other countries. As a matter of fact, we have studied under its auspices, and hope to do so again.

All this is not to say that Costa Rica has solved every one of its problems. Even with reduced fertility, population momentum guarantees that the country's present two million citizens will at least double to four million shortly after the turn of the century. Naturally, this population increase may make the preservation of land and forest resources difficult, even if the current policy of clearing forests for cattle ranching can be contained and the forest reserves protected.

Costa Rica, then, has made a good start at forest conservation (a start that could be emulated profitably by many countries, including the U.S.). Still, it will take vigilance and dedication to avoid losing the gains that this Central American nation has made in the past ten or fifteen years. Furthermore, Costa Rica is only a minor portion of the Tropics, a tiny country. Whether larger nations like Brazil can be encouraged to reconsider their "rape-the-forests-for-profit-today-and-the-hell-with-tomorrow" policies remains to be seen.

Paul Ehrlich (Bing Professor of Population Studies and Professor of Biological Sciences, Stanford University) and Anne Ehrlich (Senior Research Associate, Department of Biological Sciences, Stanford) are familiar names to ecologists and environmentalists everywhere. As well they should be. Because it was Paul and Anne who—through their writing and research—gave special meaning to the words "population," "resources," and "environment" in the late 1960's. (They also coined the term coevolution, and did a lot to make ecology the household word it is today.) But while most folks are aware of the Ehrlichs' popular writing in the areas of ecology and overpopulation (most of us—for instance—have read Paul's book The Population Bomb), far too few people have any idea of how deeply the Ehrlichs are involved in ecological research (research of the type that tends to be published only in technical journals and college textbooks). That's why it pleases us to be able to present these semi-technical columns by authors/ecologists/educators Anne and Paul Ehrlich.