CROWN ASYMMETRIES OF TREES ON THE EDGES OF LOGGING GAPS IN A FOREST IN GUYANA

Abstract

Active foraging of tree branches for light and space can result in crown asymmetry. By opening canopy gaps, selective logging may increase the prevalence of trees with asymmetrical crowns and the extents of their asymmetries. Crown asymmetry is relevant to forestry insofar as it may stimulate bole curvature, decrease the range of angles over which trees can be directionally felled, increase rates of natural tree fall, and create dangerous conditions for forest workers. In a forest in Guyana that was selectively logged 23 years prior to our study, we evaluated the asymmetries of crowns of trees on the boundaries of mapped felling gaps. For 192 trees ≥ 20 cm diameter, we measured crown radii into and away from 56 canopy gaps. Assuming that tree crowns were symmetrical at the time of gap creation, we estimate the rate of lateral crown expansion into gaps as the difference between crown radii into and away from the canopy opening. We then compared apparent rates of lateral crown expansion into gaps by tree species, gap size, and stem diameter growth rates. We found that 83% of tree crowns were wider on the gap side than into the closed canopy forest, with crowns on average 2.1 m wider towards canopy gaps. Rates of gap-ward crown extension were faster among long-lived light-demanding pioneer species than in more shade tolerant climax species. Among trees ≥ 20 cm diameter at the time of gap creation, stem growth rates are positively but only weakly correlated with crown asymmetry.