PARENT SESSION
Poster Session #33: Light Relations.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
155
Measuring tree growth as a function of light using low-level aerial photography.
Wyckoff, Peter1, Clark, James2, 1 2
ABSTRACT- Interspecific differences in the relationship between tree growth and light availability influence forest community composition and may help explain species coexistence. For logistical reasons, studies of light effects on tree growth have been confined to seedlings and saplings. The lack of data for a wider range of tree sizes limits the potential realism of the forest simulation models that will ultimately provide guidance on how light competition contributes to forest diversity. In this study, we assessed the relationship between light availability and growth for a large range of tree sizes using low-level aerial photography. Exposed canopy area, a surrogate for , was determined for individual trees and used with diameter growth data to generate light response functions for nine co-occurring species. These functions explain much of the variability in growth rates of trees that have limited access to light (e.g., r2 = 0.90 for Fraxinus americana, r2 = 0.72 for Carya glabra). However, exposed canopy area is a poor predictor of growth when exposure is high. We estimated exposed canopy areas up to 190 m2, but growth rates of most species asymptote by 40 m2 of exposed canopy area. Results indicate that light strongly limits (and, thus, is a predictor of) growth rates of individuals at low levels, and other factors control growth when light exposure is high. Our results can be directly incorporated into forest stand simulators to allow analysis of how light competition influences diversity.
KEY WORDS: light