The last thing a hungry American would normally think about when ordering a fast-food hamburger might be the mysterious depths of the tropical rain forests.
Yet there is a definite connection.
These towering, tropical forests are being mowed down at a tremendous rate -- somewhere between 50 and 100 acres a minute -- to create pasture partly to feed the American fast-food market. Beef production is a major cause of rain forest conversion, particularly in Brazil.
"The price of a US hamburger does not reflect the total costs -- especially the environmental costs -- of its production in tropical Latin America; and the American consumer seeking best-quality hamburger at the least price is not aware of the ramifications in forest zones thousands of kilometers away," observed a recent report, Conversion of Tropical Moist Forests, by the National Academy of Sciences.
Alarm over the future of these unique jungle habitats is widespread among scientists.
Tropical rain forests are estimated to cover about 6 million square miles -- 6 percent of the globe's total land surface. Four-fifths of this majestic forest is in only nine countries: Bolivia, Brazil, Colombia, Peru, Venezuela, Indonesia, Malaysia, Gabon, and Zaire.
Yet these unique forests, with their towering trees and leafy canopy as much as 200 feet overhead, may hold as much as half of the earth's total inventory of plant and animal species. So the possibility of the disappearance of many such species is a matter of concern to ecologists, botanists, and biologists.
"Once mainly the concern of animal lovers and bird watchers, the worldwide loss of species now poses a major ecological and social challenge. If allowed to occur, the massive biological impoverishment projected for the next few decades will change the nature of life on this planet for all time," wrote Erick Eckholm of World Watch institute in a report on disappearing species two years ago.
While loss of species and the decline of the diversity of natural life is a universal problem, it is most acute in the tropical rain forest. This is the most biologically complex and diverse region on earth. The uniform, tropical climate has led to the establishment of an environment where twice as many plants, animals, and insects flourish in a given area than is common in simpler temperate-zone regions.
Yet this environment -- described by W. H. Hudson in the novel "Green Mansions" -- is a place where nature, ". . . unapproachable with her green, eerie canopy, a sunimpregnated -- cloud above cloud . . ." is extremely fragile. According to the National Academy of Sciences report, recent research suggests that communities with a rich array of species and a complex web of interactions like the tropical rain forest are more fragile than the relatively simple and robust temperate ecosystems.
Those who have studied the rain forests believe that, once disturbed, these environments take hundred of years to return to something comparable to their initial state.
Looking back over the broad expanse of evolutionary time, many scientists see the rain forests as, in the words of eminent British botanist Paul W. Richards, "a factory and storehouse of evolutionary diversity."
During the ice ages, for instance, when the temperate zone became inhospitable, the tropical rain forests served as a leafy ark bearing the seed of the species that recolonized the cooler regions as the ice retreated. Mankind's own primate progenitors are thought by many to have evolved in the arbors of such a forest and to have taken an upright stance when they left the forest for the broad savannah of the (present) Cenozoic Era. Thus, the long-term effect of the destruction of this environment would be to lessen the ability to earth's biosphere to adapt to major climatic changes in the future.
There is a moral-philosophical issue as well. Biologist David W. Ehrenfeld of Rutgers University has argued for preservation of species with what he calls the "Noah principle." He reasoned that, faced with an endangered-species problem of unparalleled magnitude, Noah took on board his ark "every creeping thing of the earth, two of every sort."
He did not take just those species which he considered of economic value, Dr. Ehrenfeld notes. Thus, he argues, if the species exists, it has "an unimpeachable right to continued existence."
If this view is accepted, then there are a large number of species that are having their rights violated daily. In his book, "The Sinking Ark," wildlife specialist Norman Myers concludes that at least one species disappears daily in the tropical forest alone -- and that within a few years the toll may rise to one species per hour. Looking toward the end of the century, Mr. Myers finds the prospect of the elimination of 1 million species "not unlikely."
For those who find philosophical arguments unconvincing, a strong economic case can be made for preservation of the tropical rain forest. Some of the millions of unknown species facing destruction may have economic potential equivalent to rubber or palm oil. One example of this is the recent discovery made by Nobel laureate Melvin Calvin. While on a trip to Brazil, Dr. Calvin discovered a tropical tree that, when tapped, yielded a hydrocarbon so close to diesel fuel that it can be burned directly in a diesel engine.
Similarly, the rain forest represents a storehouse of genetic diversity that could prove of vital importance to world agriculture. Strains of grass with a unique relationship to nitrogen-capturing bacteria were discovered recently in South America. This find increased the possibility that plants other than legumes might be genetically tailored so they can get the bulk of nitrogen from bacteria rather than from increasingly expensive chemical fertilizers.
"Who knows what other irreplaceable plant resources have quietly vanished?" Mr. Eckholm asks. These are some of the major reasons why scientists have become increasingly vocal in their warnings. The National Academy of Sciences review, which is the most thorough attempt to date to determine the rate at which the world's tropical rain forest is disappearing, paints a discouraging picture.
It concludes that virtually all the lowland forests in the Phillipines, the peninsula of Malaysia, and West Africa are likely to be logged off by 1990. The scientists give Central America's rain forest a decade longer. Almost all Indonesia's lowland forests have been scheduled for logging by the year 2000, they report. And extensive areas of Amazonia will be cleared for cattle ranching and agriculture by the end of the century.
There are a few areas the academy researchers foresee remaining into the next millennium. These include forests in sparsely settled central Africa and the western portion of Brazil's Amazonia. This outlook is based on an analysis of the social and economic factors that are contributing to tropical rain forest destruction.
The most dominant factor in the destruction of the tropical rain forest is the subsistence farmer. The populations of countries with rain forests within their boundaries are expected to increase by 64 percent by the year 2000. Many of these countries will not have stable populations for a number of years thereafter. Because economic conditions in most of these countries will thwart efforts to put most of these people to work, they likely will turn to clearing the forests for farming to support themselves.
In these parts of the world the people practice "slash" and burn" agriculture. They clear an area for farming, burn it over, and then grow crops for several seasons until the land loses its fertility or the weeds encroach. Then they move on.
Basic slash and burn agriculture, which allows areas to lie fallow for 10 years or more, is an ecologically appropriate strategy. But when the population becomes too large, or outsiders who do not understand the environmental imperatives move in, the result is destructive.
One scientist has described settlement practices in Peru: "The populations overflowing from the [Andes] mountains down to the Amazon plain do not settle there, but advance like a slow-burning fire, concentrating along a narrow margin between the lands they are destroying and are about to leave behind, and the forest lying ahead of them."
According to the most recent estimate, there are at least 140 million of these forest farmers, occupying some 770,000 square miles of the tropics and destroying at least 39,000 square miles of new forest annually.
A potential answer to this problem is "agroforestry," an approach in which forest farmers are encouraged to plant new trees along with their other crops. Not only is this less expensive than establishing tree plantations, but with the income from the timber grown, the forest farmer can buy the fertilizer and pesticides necessary to increase the yield of his crops by severalfold.
Agroforestry, in itself, could keep the farmers in areas already cleared. And by increasing agricultural yield, this method of farming could take substantial pressure off the tropical forest.
Unfortunately, the spread of agroforestry and other advanced agricultural practices is proceeding much slower than rain forest destruction.
Despite their limited extent, tropical rain forests contain about half of the world's total lumber supply. Right now, these forests provide only a small percentage of the total lumber being used. But worldwide wood use is expected to increase by 135 percent by the end of the decade, and innovations in the wood-product industry have made the tree species in tropical forests more desirable than in the past.
The United States is the second-largest consumer of tropical hardwood, and demand here has been growing at a rate far above that of gross national product or population. Most of this is in the form of hardwood veneer on plywood. Between 1950 and 1973, US imports increased by nine times and are expected to double again by the year 2000.
Until recently the tropical rain forests were not affected by growing demand for paper. But new methods of pulping wood have made it possible to utilize wood chips from 100 tropical species. As world demand for paper products is expected to more than double by the end of the century and to double again by 2040, this represents a significant new pressure on the rain forest.
Unfortunately, commercial logging has an extremely damaging effect on tropical forests, even when only a small percentage of the logs are taken. The trees are woven together with jungle vines, so when one tree is felled it often takes a number of its companions with it. Also, relatively small gouges in the bark of these giant trees can damage them severely by opening the way for insect infestation or disease. As a result, even in cases where only 5 percent of the trees are removed, as much as one-third to two-thirds of the remaining trees are irreparably damaged.
An alternative to logging virgin areas is the establishment of tree plantations. A number of vast plantations are in operation. However, these are extremely expensive to set up, and efforts have fallen far short of increasing demand. also, as monocultures -- that is, growing a single species in a particular area -- these plantations tend to be vulnerable to insect attack and require expensive fertilization.
The World Bank and the United Nations Food and Agriculture Organization estimate that it would require an investment of about $3 billion a year over the next two decades before plantations could make a sizable contribution to tropical timber supplies. Because investment capital of this magnitude is beyond the reach of most countries in which tropical rain forests lie, these countries increasingly are looking for foreign investors. But lack of assurance of the price of wood products and fear of possible nationalization of holdings have kept this investment money back.
Conversion of rain forests into pasture for cattle is already an important factor in tropical Latin America. It is expected to become even more dominant in years to come because of the growing world demand for inexpensive beef.
Between 1950 and 1970 the area of pasture cleared by ranchers in Central America more than doubled, almost entirely at the expense of primary forests. Between 1966 and 1978 some 31,000 square miles of Amazonian forest in Brazil were converted into cattle ranches.
Beef from these ranches is grass-fed and considered suitable only for the fast-food market in the US. Yet this is the fastest-growing part of the food industry in America.
Hamburger prices last year increased by 20 percent in the US. Because of government estimates that increasing beef imports would trim a nickel off the price of a hamburger, import quotas were increased by 13 percent in 1978 and 1979.
Yet, as indicated earlier, the price paid for this beef in the United States does not represent the environmental price of its raising.
Typically, these tropical ranches become unprofitable in less than 10 years because the productivity of the artificial grasslands declines. But the ranchers can generally get another tract of forest to clear. Thus, the National Academy of Sciences report says, they are "practicing a new and broad-scale variation of shifting agriculture" that cuts even deeper into the irreplaceable rain forest.