The biological diversity of plant and animal species is diminishing as fast today as at any time since the dinosaurs died out about 65 million years ago, scientists say.
An estimated 10 million species live on the earth. Tropical forests support 50 percent to 90 percent of this total, although they cover only 7 percent of the earth's surface.
Some scientists say that about 60,000 of the world's 240,000 plant species - and perhaps even higher proportions of vertebrate and insect species - could become extinct in the next three decades unless tropical deforestation is slowed immediately. Some environmentalists estimate that 100 species of plants and animals die out each day.
The World Resources Institute in Washington estimates that tropical deforestation increased 50 percent in the 1980s to an average of about 42 million acres annually.
Biodiversity is threatened in other areas as well: 60 percent of plant species native to the Galapagos Islands are endangered, for example, and marine and freshwater ecosystems face serious degradation.
Temperate climate zones also face threats. London's Observer newspaper recently cited figures showing that 45 percent of Britain's prime forests have been destroyed or damaged in the last 50 years.
The rapid destruction of plant species has wide implications. Scientists continue to find new substances in plants that lead to advances in agriculture and medicine. And environmentalists argue that the disappearance of any one species has implications for the ecosystem in which it lives.
On a broader scale, ecosystem diversity is more difficult to measure than diversity of species. The boundaries of ecosystems, or associations of species, are elusive. But ecosystems provide valuable services such as water purification, soil regeneration, watershed protection, temperature regulation, and nutrient and waste recycling.
In this respect, forested lands are particularly important as a source of livelihood and habitat for millions of people, especially traditional and indigenous groups.
The debate about preservation of species has underscored the gap between industrial and developing nations. Saving large tracts of tropical forests to prevent plant and animal extinctions and help stabilize global climates, which is what northern countries advocate, would directly affect economic self-sufficiency in southern countries.
The world's first biodiversity treaty was adopted on May 22 in Nairobi, Kenya, and is to be signed by world leaders at the Earth Summit. Under the treaty, industrial nations will help fund conservation of species in developing nations and will pay for the samples of those species used in developing new products. Delegates will also consider a nonbinding statement of principles on the management, conservation, and sustainable development of the world's forests.