Document: CHR-3-29-14

Tree canopy asymmetry at forest gap edges.

MUTH, C.C.* and F.A.BAZZAZ

Harvard University, Cambridge, MA 02138, USA ¹

Abstract:
Although plants are sessile organisms, they can forage for resources by growing towards areas with high resource availability and reduced competition. Presumably due to this morphological flexibility, tree canopies are rarely positioned directly above their stem bases and are often asymmetrical. To see if contrasts in light availability lead to the development of canopy asymmetry, we investigated the responses of tree canopies to the heterogeneous light environments at the edges of six experimental gaps. The gaps were created in 1986 and are located in a mixed hardwood forest in central New England. For all gap edge trees greater than 5 cm dbh, canopy extent was determined in eight cardinal directions around each trunk using a densitometer. Canopies and trunks were then mapped and their spatial distributions analyzed. A clinometer was used to determine canopy depth on both the gap side and the closed forest side of each tree. We found that, for canopy trees, the direction of canopy asymmetry was positively correlated with the direction of the gap center. These parameters were not correlated for suppressed trees. In addition, canopy depth was significantly greater on the gap-facing side than on the forest-facing side. Thus, trees along gap edges forage for light by occupying both horizontal and vertical gap space. This morphological flexibility likely increases rates of gap closure and, in turn, may alter patterns of forest succession.

Keywords: canopy asymmetry, forest gaps, light heterogeneity, resource foraging

This abstract is being presented at: 10:30 AM in session:
Poster Session #1: Light Relations.