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Is tropical deforestation really occurring? Rhett A. Butler, mongabay.com January 8, 2008 New assessment suggests global deforestation data from the U.N. is deeply flawed and without better monitoring it is impossible to know whether net forest cover in the tropics is expanding or declining.
Examining "all available" forestry data published by the Food and Agriculture Organization of the United Nations (FAO), Dr Alan Grainger, a researcher at the University of Leeds in the U.K., found serious flaws resulting from the aggregation of self-reported of forest figures from individual states. "The errors and inconsistencies I have discovered in the area data raise too many questions to provide convincing support for the accepted picture of tropical forest decline over the last 40 years," Grainger said. "Scientists all over the world who have used these data to make predictions of species extinctions and the role of forests in global climate change will find it helpful to revisit their findings in the light of my study."
"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."
"We would expect to see some increase in estimates as we use more accurate satellite sensors," he explained. "This is even apparent in FAO's data. It is sad that only in the last 10 years have we begun to make full use of the satellite technology at our disposal." Still Grainger says that natural regeneration of forest is occurring in some countries, like Gambia and Vietnam. Previous studies have projected forest recovery where rural populations are abandoning the countryside for cities. Nevertheless some biologists have argued that regenerating forests cannot make up for biodiversity losses associated with the conversion of primary forests to degraded forests. A number of studies have shown that logged forest and recovering forest is biologically impoverished relative to old growth forest. To address inconsistencies in U.N. data, Grainger urges the establishment of a World Forest Observatory to monitor changes in forest cover.
"A World Forest Observatory would bring together existing research teams in Europe, the USA and elsewhere and ensure they are properly funded to continue mapping tropical forest at least every five years. It could also undertake a massive project to analyze all available satellite and other data from the past and reconstruct the trend in tropical forest area since 1970. Only then will we really know what has happened to tropical forests over the last 40 years." CITATION: Alan Grainger (2007). Difficulties in tracking the long-term global trend in tropical forest area. Proceedings of the National Academy of Sciences January 7-11, 2008.
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