Large-scale impoverishment of Amazonian forests by logging and fire

Amazonian deforestation rates are used to determine human effects on the gl obal carbon cycle(1-3) and to measure Brazil's progress in curbing forest i mpoverishment(1,4,5). But this widely used measure of tropical land use tel ls only part of the story. Here we present field surveys of wood mills and forest burning across Brazilian Amazonia which show that logging crews seve rely damage 10,000 to 15,000 km(2) yr(-1) of forest that are not included i n deforestation mapping programmes. Moreover, we find that surface fires bu rn additional large areas of standing forest, the destruction of which is n ormally not documented. Forest impoverishment due to such fires may increas e dramatically when severe droughts provoke forest leaf-shedding and greate r flammability; our regional water-balance model indicates that an estimate d 270,000 km(2) of forest became vulnerable to fire in the 1998 dry season. Overall, we find that present estimates of annual deforestation for Brazil ian Amazonia capture less than half of the forest area that is impoverished each year, and even less during; years of severe drought. Both logging and fire increase forest vulnerability to future burning(6,7) and release fore st carbon stocks to the atmosphere, potentially doubling net carbon emissio ns from regional land-use during severe El Nino episodes. If this forest im poverishment is to be controlled, then logging activities need to be restri cted or replaced with low-impact timber harvest techniques, and more effect ive strategies to prevent accidental forest fires need to be implemented.