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[RIO DE JANEIRO] A study has shown for the first time that 'selective' logging in the Brazilian Amazon increases the likelihood that an area of rainforest will be cleared at a later time.

Selective logging, which refers to the practice of felling only certain trees in a given area, is promoted as a sustainable alternative to clear-felling.

But the study published this week by Proceedings of the National Academy of Sciences found that from 1999 to 2004, 16 per cent of selectively logged areas were deforested within one year of logging, and one-third were cleared within four years.

Researchers led by Gregory Asner of the Carnegie Institution of Washington, United States, used high-resolution satellite images to measure the extent and intensity of logging across 46,000 square kilometres of the Brazilian Amazon.

Nearly all selective logging in this area took place within 25 kilometres of main roads. The probability of deforestation for a selectively logged area was up to four times greater than for intact forests.

"This is surprising because selective logging has been heralded by the timber and conservation sectors as an alternative to clear-cutting of the forest," Asner told SciDev.Net. "Since logged forests are eventually consumed by deforestation for pastures and ranches, logging is clearly not being managed as a long-term investment in forest resources."

Asner says that the small roads loggers create give farmers access to new areas of forest to clear. "The roads are the link between selectively logging a forest then clearing it."

Co-author José Silva of the Brazilian Agricultural Research Corporation (Embrapa) says that the government has taken some steps to control logging more effectively.

These include granting timber producers access to plots of forest on the condition that they manage them sustainably, and creating the Brazilian Forest Service to manage forests set aside for timber production.

"The recent policies combined with economic and ecological zoning, better control of illegal exploitation and the use of areas already converted for agricultural activities will change the current scenario", says Silva.

Philip Fearnside of Brazil's National Institute of Amazonian Research, told SciDev.Net: "Logging is a major threat to Amazonian forest and has so far been one of the most difficult activities for the government to control."

Link to full paper in Proceedings of the National Academy of Sciences*

*[link will be made live by 4 August]