have not spotted.
Dr Grainger first examined data published every 10 years by the United Nations Food and Agriculture Organization (FAO) since 1980. These cover all forest in the humid and dry tropics and appear to indicate decline. FAO's Global Forest Resources Assessment 2000, for example, showed that all tropical forest area fell from 1,926 million hectares to 1,799 million hectares between 1990 and 2000. Ten years earlier, however, FAOs previous report said that tropical forest area fell from 1,910 million ha to 1,756 million ha for the same 90 countries between 1980 and 1990.
Owing to corrections to the earlier study, the 1990s trend was just like a 're-run' of that in the 1980s, said Dr Grainger. The errors involved in making estimates for forest area could easily be of the same order as the forest area reported cleared in the previous 10 years. Even if you take enormous care, as FAO does, I argue that large errors are inevitable if you produce global estimates by aggregating national statistics from many countries. This has important implications for the many scientists who rely on FAO data.
Since errors in national statistics are higher for forests in the dry tropics than for forests in the humid tropics, in places near the Equator such as Amazonia, Borneo and the Congo Basin, he repeated the process just for tropical moist forest, with a different set of data, in the hope it would give a clearer picture. This time he found no evidence for decline since the early 1970s. Indeed, while his own estimate in 1983 of tropical moist forest area in 1980 was 1,081 million hectares, the latest satellite data led to an estimate of 1,181 million hectares for the same 63 countries in 2000.
He is cautious about the apparent slight rise. We would expect to see some increase in estimates as we use more accurate satellite sensors. This is even apparent in FAOs data. It is sad that only in the last 10 years have we begun to make full use o
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| Contact: Simon Jenkins S.Jenkins@leeds.ac.uk 44-011-334-34031 University of Leeds Source:Eurekalert |
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