Copyright Economist Newspaper Group, Incorporated Mar 21, 1998As long as that belief persists, the pleas of the rich world's environmentalists will be seen as somewhat other-worldly. They want to preserve the forests for two main reasons: because burning them could eventually contribute to world climate change, and because they know that forest loss will reduce biodiversity. Both are worries for the longer term, although recent research suggests that burning trees is now beginning to affect the local climate of the Brazilian rainforest too, making it drier and more liable to accidental fires.
A loss of biodiversity will not start to show up until well into the next century, but it is an issue that gets environmentalists really excited. According to one estimate, tropical rainforests contain around half of all the world's species-far more than the temperate forests of Europe and America. (The Amazon forests also contain about 400 human tribes, which are gradually being squeezed out.) The depletion of rainforests is being blamed for the increasingly rapid rate at which the world is losing species. But scientific understanding of species loss, and its potential dangers, is riddled with uncertainties.
Life's rich pattern
Scientists have little idea how many species exist in the first place. Recent estimates range from 7m to 20m. According to the Global Biodiversity Assessment, a UN-sponsored report in which about 1,000 scientists have had a hand, a good working estimate is between 13m and 14m species. But of that number, says the report, only about 1.75m have been scientifically described.
If scientists have no clear idea how many species exist in the first place, rates of loss are necessarily even harder to divine. Since 1600, over 480 animal species and 650 plant species are recorded as having become extinct. But since the vast majority of all species are unknown, rates of loss of known species are not much of a guide to anything. Besides, species thought to be extinct occasionally pop up from nowhere. So scientists rely on a crude calculation. They have a very rough idea, from a number of detailed studies, how many species are likely to be lost if the size of a particular habitat-a tropical forest, say-is reduced by a certain amount. They then apply this number to the total area of tropical forest lost each year (another very approximate figure, often derived from incomplete satellite data) Using this method, scientists working on the Global Biodiversity Assessment have estimated that, if current rates of forest loss continue over the next 30 years, the number of species in tropical forests will fall by 5-10%.
Losing species, even bugs and spiders, might matter for a number of reasons. Ecosystems containing a broad diversity of species and genes are generally better able to adapt to changing conditions than those with just a handful of species, however abundant. Genetic variation is nature's insurance against all sort of eventualities. It might help cushion, for example, the impact of a sudden change in the world's climate. It also can help reduce the effect of disease. The Irish potato famine was so devastating because in the 19th century only a few varieties of potato were planted in Ireland, and these all happened to be vulnerable to the same disease. At present almost all the world's food crops are based on a mere nine species of plants, but in the future any of thousands of other species might prove invaluable. Today's apparently useless species may contain tomorrow's medicine.
To rich-world inhabitants, the best arguments for preserving the rainforests are spiritual: that the diversity of life is a wonder of nature, whether it has a practical application or not; and that it is good to hold on to some wildernesses in the world. But for developing countries trying to lift themselves out of poverty, such arguments seem utterly irrelevant.
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