Differences between Acer saccharum leaves from open and wind-protected sites

Size-correlated variations of sugar maple (Acer saccharum L.) leaf anatomy and mechanical properties were determined for two saplings (from open and wind protected sites) to examine the effects of chronic wind-induced mechanical disturbance on leaf size, rigidity and flexibility. Based on a total sample of 78 leaves, comparisons indicated that the mean size of the open site leaves (n = 37) was smaller in every measured respect compared with that of the closed site leaves (n = 41). Open site leaves had, on average, smaller lamina surface area, shorter and narrower petioles with a smaller volume fraction of lignified tissues than those from the closed site. Biomechanical comparisons also indicated that the petioles of open site leaves were significantly less rigid and more flexible than the petioles of closed site leaves. Despite differences in mean leaf size and petiolar rigidity and flexibility, allometric comparisons indicated the size-dependent variations in leaf properties were continuous across the two sites. Also, the allocation of leaf biomass with respect to stem biomass along the lengths of the two saplings was statistically identical and indistinguishable from an isometric relationship. However, the smaller diametered branches of the open site sapling bore smaller and fewer leaves with less stiff and rigid petioles than those of the closed site sapling. The differences between open and closed site leaves are interpreted to be functionary adaptive and to indicate that chronic mechanical disturbance of developing Acer saccharum leaves prefigures mature leaf size and petiole properties that have the capacity to reduce wind drag. Results from petioles are contrasted with those of mechanically disturbed stems. (C) 1996 Annals of Botany Company