2 JULY 1988, Page 12

. . . and statistics 'ONE species becomes extinct every

half hour. Half of the world's plant and animal species is being scraped from the face of the earth. The last of the rainforest hardwoods are being sold off.'

(Friends of the Earth advertisement, Observer, 19 June) WE do not know how many species there are, nor how widely distributed they are, nor can we measure how many have become extinct, so we cannot say a species becomes extinct every half hour. Estimates of the number of species vary between five million and 30 million, so that to assert that half the world's plant and animal species is being 'scraped from the face of the earth' is unwarrant- able.

The most recent and authoritative survey of tropical rainforests (broadly equivalent to those containing 'rain- forest hardwoods') is J. P. Lanly's Tropical Forest Resources (1982, FAO). This put the deforestation rate for closed tropical broadleaf forests at 7.1 million hectares a year, or 0.6 per cent of the total. Even six years later, assuming the deforestation rate remains roughly stable, there should be 91.5 per cent of the 1982 total of over 1,180 million hectares left. It would take well over a century at the present rate before the last tropical rainforest hardwoods could be said to have been 'sold off, in the presumed sense that they have been felled and processed by timber com- panies. (£20 goes to Robert Whelan, of Richmond, Surrey) Send examples to '. . . and statistics': £20 for the best published; £10 for every other one published — the first opened if two or more cover the same example.