Ecology: Managing Amazonian rainforest regrowth
Tropical forest regrowth depends on a delicate balance between nitrogen and phosphorus. The findings should help researchers predict how long it takes for tropical forests to recover after clearance, and should contribute to better management of disturbed Amazonian ecosystems.
Around 16% of the original Amazon Basin rainforest has been cleared for agriculture, but it's thought that up to half of this is now being allowed to regrow. Eric A. Davidson and colleagues now show that nitrogen and phosphorus levels influence this regrowth, with different factors proving limiting at different stages of maturation.
Early on after agricultural abandonment, nitrogen levels in the soil are low, so the plants conserve the little that they have. But as the forests mature and nitrogen levels in the soil rise, phosphorus becomes the limiting factor for plant regrowth. Trees become less conservative with nitrogen, nitrogen cycling recovers, and the ecosystem even leaks some nitrogen back to the atmosphere in the form of the greenhouse gas nitrous oxide.

CONTACTEric A. Davidson (Woods Hole Research Center, Falmouth, MA, USA)
Tel: +1 508 540 9900 x132; E-mail: edavidson@whrc.org