Wind Stress and Elfin Stature in a Montane Rain Forest Tree: An Adaptive Explanation

Physiognomic trends in a population of Didymopanux pittieri Marchal (Araliaceae), a dominant shade-intolerant tree of the elfin forests of Costa Rica, are related to a gradient of wind stress. Wind stress in this forest increases with proximity to ridgecrests. For a given tree height, trunk girth increases with proximity to the ridgecrest. At the same time twig slenderness decreases. These responses are produced in part by slower elongation of twigs which are exposed to stronger winds. These trends suggest that elfin stature is an adaptive response to greater wind stress along exposed ridges.