ANTANANARIVO - The pace of deforestation in Africa has probably been underestimated by satellite imagery, lending new urgency to efforts to save the continent's wild treasures, a scientist said on Thursday. "The consensus is that Africa is losing about 0.4 to 0.7 percent of its forests each year but this is likely an underestimate," said Holly Gibbs, a Ph.D. candidate at the University of Wisconsin who has been studying the phenomenon. She said deforestation in Africa has not been properly assessed because satellites have difficulty distinguishing between human-induced changes and seasonal climate changes which can deceptively cloak a stressed forest in a veneer of green.
"If you have rain over an open woodland forest, common to parts of Africa, it will 'green up' or sprout flowers. If the satellite takes its image at that time it can have the impression that there is more forest as a result," she said, speaking at a conservation conference in the Malagasy capital.
She also said that part of the problem is that net estimates are usually used.
These allow young, regenerating forests and commercial plantations to offset rates of clearing, giving a false impression about the pace at which primary forest is being lost.
"We have to move beyond net estimates and look at gross rates of clearing to be able to fully assess the impact of human land use changes on Africa's forests," she said.
Gibbs said more on-the-ground data was needed to get a clearer picture of African deforestation and that it was necessary to track the fate of cleared land.
Land cleared in Africa by slash and burn farmers can lose its nutrients after a few years, forcing peasants to move on in a vicious cycle which depletes the forest and the soil.
According to U.N. estimates, Africa lost about 23 million hectares of forest in the 1980s and another 20 million in the 1990s.
The stakes are high as deforestation on the world's poorest continent exacerbates a host of other problems. In Malawi forest loss has been associated with erosion of valuable soil which contributes to periodic food shortages.
Conference host Madagascar has lost as much as 90 percent of its original forest, depriving its unique wildlife -- a key tourist attraction -- of crucial habitat