Canopy dynamics in unlogged and logged forest stands in the eastern Amazon

Selective logging of tropical forests damages residual trees and creates canopy openings throughout the stand. In the Amazon, reduced-impact logging results in significantly less damage than conventional unplanned logging; yet either logging method leads to substantial fragmentation of the forest canopy. Increased mortality rates of trees damaged in logging have been documented. In this paper, we investigate the effect of logging disturbance on treefall rates.Using repeat inventories of canopy trees (≥35 cm dbh) in six large (≥50-ha) forest stands at two sites in the eastern Amazon, we measured mortality rates in three treatment classes: unlogged, conventionally logged (CL) and logged using reduced-impact methods (RIL). At least 3000 trees were mapped and inventoried per stand prior to timber harvests. In the second inventory, 3 years after harvests in the logged stands, all trees were located and scored as living, standing dead, uprooted or broken.We found significantly higher overall mortality rates for trees in logged forest (both CL and RIL stands) than in adjacent unlogged forest. This effect was largely due to higher rates of treefall (i.e., stems uprooted or broken from natural causes). Moreover, significantly higher treefall rates were recorded for trees in logged forest that were not damaged in the logging than for trees in unlogged stands. Treefall rates were nearly twice as high in conventionally logged forest as in forest logged using reduced-impact methods. We found indirect support for the hypothesis that increased treefall rates in logged forest are related to increased canopy opening and fragmentation through analysis of the locations of fallen trees in relation to canopy disturbance.