Forests are among the world's most valuable resources, both in a narrowly economic sense and in a broader, ecological sense. Besides yielding over 5,000 commercial products that contribute some 2 percent to the world's total economic production, forests provide recreation, reduce flooding, and prevent soil erosion that clogs rivers with silt. However, if well-grounded policy decisions are to be made concerning which forests must be preserved and how much forest must be preserved, policy makers should have a comprehensive understanding of the arguments for and against the use of forests for economic gain. Two claims often made—one about the oxygen-renewing capacity of forests, the other about the role of forests in preserving biodiversity—merit special scrutiny.

Some consider the tropical rain forests of the Brazilian Amazon region "the lungs of the earth," claiming that the foliage absorbs so much carbon dioxide and produces so much oxygen that the atmosphere would be depleted of the latter if these forests ceased to exist. But this belief is largely a myth. Trees do produce oxygen by photosynthesis, but when trees die, the decomposition process consumes as much oxygen as the trees produced. In net terms, therefore, forests neither produce nor consume oxygen.

Another claim made is that the preservation of biodiversity, the globe's profusion of plant and animal species, requires a stricter policy to conserve forest, especially tropical rain forest. For one thing, many scientists believe that some tropical rain-forest plant species yet to be discovered may contain agents with unique disease-fighting properties. These plants can offer crucial clues, as well as basic materials, for research on new medications. But even if one does not think this indicates that biodiversity is a significant resource, one could agree with the view, widely held by some, that there is a moral imperative to preserve species diversity—or, at least, that to do so would be a noninstrumental, that is, an intrinsic, good.

Actually, careful review of official statistics suggests that tropical deforestation is not occurring as fast as has often been claimed. Some existing forests, however, do consist of commercial plantations, of which some people are highly critical. Such plantations tend to contain significantly fewer plant and animal species than natural forest. However, since plantations are designed to produce large quantities of wood and wood pulp, they reduce the economic pressure on true forests, increasing the latter's capacity to support biodiversity. In addition, the size of such plantations is often overstated by environmental activists. While the World Wildlife Fund claims that plantations make up "large tracts of current forest area," review of official data shows that plantations make up just 3 percent of the world's forest area.