CROWN ASYMMETRY, TREEFALLS, AND REPEAT DISTURBANCE OF BROAD-LEAVED FOREST GAPS

Gap-edge trees were significantly more likely to fall into pre-existing gaps than in other directions in a moist tropical forest on Barro Colorado Island (BCI), Panama. Trees not at pp edges were more likely to fall away from near neighbors than toward them. We show that gross asymmetries of tree crowns were the rule rather than the exception for all trees. The crowns of most gap-edge trees were strongly asymmetrical into their adjoining gaps, and trees not at gap edges were strongly asymmetrical away from near neighbors. Trees had a strong and significant tendency to fall on these heavy sides. Such treefalls, and related limbfalls, can result in redisturbance of gaps and a retardation of gap regeneration. An analysis of 5 yr of canopy height data from a mapped 50-ha plot on BCI revealed that sites within larger gaps were significantly more likely to be redisturbed by secondary treefalls than were sites in the smallest gaps or nongap quadrats. These results suggest that treefall gaps in tropical forests may be more persistent disturbances than previously thought.