PARENT SESSION
Monday, August 7, 8:00-11:30 am
COS 2 - Population dynamics I: plants
Chickasaw, Mezzanine Level, Cook Convention Center
Presiders: K Klemow

Relative demographic performance of a dominant tropical rain forest tree: no smoking gun?

Clark, David^{*,1, 2}, Clark, Deborah ^{1, 2}, ¹ La Selva Biological Station, Puerto Viejo de Sarapiqui, Heredia, COSTA RICA² Department of Biology, St. Louis, MO, USA

ABSTRACT- Tropical rain forests are often thought of as containing the greatest diversity of tree species. At local scales, however, forests dominated by a single species are not uncommon. Several hypotheses have been advanced to account for these dominant species. Possibilities include chance dispersal into a vacant niche, release from herbivory, and massive regeneration after past disturbance. Here we examine an alternative hypothesis, superior demographic performance, for the Mimosoid legume Pentaclethra macroloba, the dominant species in old-growth forest at the La Selva Biological Station, Costa Rica. In this forest Pentaclethra ranked first in frequency (12-18% of individuals >10 cm diameter) and basal area (29-44% of total BA) in all edaphic conditions from swamps to oxisol uplands (N=1170 0.01-ha plots). We compared Pentaclethra's ecological and demographic characteristics to those of nine co-existing tree species chosen to represent a broad range of life history patterns. From 1983-2005 we annually assessed mortality, growth (diameter and height), and crown light environments for individuals from 50 cm height to the largest size classes in each species. Analyses to date of mortality and growth do not suggest any relative demographic superiority of Pentaclethra at any post-establishment life stage. There is however some evidence that the abundance of Pentaclethra at the landscape scale may be decreasing. This would be consistent with decline following massive recruitment that occurred under ecological conditions different from today's. However such a decline would also be consistent with a negative response of this moisture-demanding and temperature-sensitive species to global climate change.

Key words: tropical tree demography, dominance, long-term studies