PARENT SESSION
Oral Session 81: Forest Ecology IV: Seeds, Growth, and Recruitment.
Presiding: J Kush
Wednesday, August 4, 1:30 PM to 5:00 PM, Meeting Room C 120.
Characterizing species regeneration strategies with respect to light availability in a wet tropical forest.
Muller-Landau, Helene*,1, 2, Pacala, Stephen2, Hubbell, Stephen3, 4, Condit, Richard4, Foster, Robin4, 5, 1 University of Minnesota, St. Paul, MN2 Princeton University, Princeton, NJ3 University of Georgia, Athens, GA4 Smithsonian Tropical Research Institute, Panama City, Panama5 Field Museum, Chicago, IL
ABSTRACT- The tremendous diversity of tropical tree species makes it infeasible to build an understanding of tropical forest structure and dynamics on the basis of detailed studies of all component species' characteristics and ecologies. Nonetheless, we need to know how functional traits vary among all species in order to be able to understand and model tropical forest ecosystems. Our objective was to characterize the distribution of tree species in a light-dependence trait space for a tropical forest on Barro Colorado Island (BCI), Panama. We first used three years of detailed growth and light availability measurements on 1500 saplings to precisely characterize the dependence of diameter and biomass growth on light for 23 tree species. This focal species study showed that light availability alone explained 51% of the growth variation among all saplings combined and 16-78% of the variation within individual species. We then combined the direct measurements of light availability with information on the neighborhoods of each sapling – canopy heights in the area and the sizes and distances of neighboring trees – to estimate the probability distribution of different light levels as a function of neighborhood characteristics. Light availability was weakly but significantly associated with neighborhood indices, with nearby canopy heights proving better predictors than local tree or basal area densities. This allowed us to use data on growth and neighborhoods for 73,000 additional saplings in the BCI 50 ha forest dynamics plot to estimate the distribution of sapling light-dependence parameters among all species in the forest. Both the focal species study explicitly linking light with growth and the all-species study implicitly linking light with growth via neighborhoods found that species were continuously distributed in their light-dependence. Wood density explained over 50% of the variation in high light growth but was not significantly associated with low light growth among species.
Key words: functional diversity, wood density , life history strategy, shade tolerance