Date of Completion
Robert K. Colwell; Michael R. Willig
Field of Study
Ecology and Evolutionary Biology
Master of Science
Woody species diversity of secondary forest has the potential to converge with that found in old growth forest. This study is the first to examine multiple aspects of species and reproductive trait diversity, and their relationship to each other, across a successional chronosequence. Species richness and species diversity increases with increasing age of forest. Diaspore size and diversity as well as fruit size generally increased with increasing age of forest, but fruit size diversity did not. Abundance of animal-dispersed species increased whereas wind-dispersed species decreased in abundance over succession. Insect-pollinated individuals were most abundant overall. Diaspore diversity, pollination diversity, and reproductive trait richness were significantly correlated with species richness. Our results suggest that different community assembly processes involve different reproductive traits, and that secondary forest plots are on a trajectory to recover levels of diversity found in old growth forest.
Remnant trees, left when tropical forests are cleared for agriculture or grazing, act as nuclei of forest regeneration following field abandonment. This study is among the first to investigate the effects of remnant trees on nearby forest structure and biodiversity, 20-30 years post-abandonment. Regeneration of woody species beneath remnant trees does not significantly differ from reference trees in density or basal area, but species richness is significantly higher around remnant trees. The species composition around remnant trees is significantly different from that around reference trees, more closely resembles that of nearby old growth forest, and has a significantly greater proportion of old growth specialists and generalists. Although remnant trees may initially accelerate secondary forest growth, no evidence suggests that they locally affect stem density and basal area at later stages of regrowth. Remnant trees do, however, have a clear effect on the species composition of the surrounding forest, even after 20-30 years of forest growth.
Sandor, Manette E., "Forest Regeneration on the Osa Peninsula, Costa Rica" (2012). Master's Theses. 369.
Robin L. Chazdon