Intra- and interannual patterns of reproduction in three Neotropical forests

Background/Question/Methods Tropical forests support perhaps 60% of all flowering plant species and 50% of all terrestrial NPP and carbon stored in terrestrial biomass.  Thus, understanding tropical forest structure and dynamics is of fundamental and applied importance in ecology.  Despite this, there are few long-term studies of tropical forests, particularly of factors affecting flowering and seed production.  We report on studies of long-term quantitative studies of plant reproduction in three Neotropical forests varying in disturbance regime, seasonality, and diversity located in eastern Puerto Rico, central Panama, and Amazonian Ecuador.  These three sites vary in the influence of the Intertropical Convergence Zone, intraannual changes in zenithal sun angles, El Niño Southern Oscillation, the North Atlantic Oscillation, hurricane disturbance, and the potential effects of anthropogenic global change.  Thus they offer three largely independent opportunities to investigate how these factors affect intra- and interannual patterns of plant reproduction in tropical forests.  At each site, flower fall, seed rain, and fruit fall of all plant species are recorded every 1-2.5 weeks using a network of 120-200 traps.  Censuses have taken place for 15 years (Puerto Rico), 21 years (Panama), and seven years (Ecuador). 

Results/Conclusions Data on intraannual patterns of flowering strongly suggest that seasonal patterns of irradiance control the timing of reproduction in Neotropical forests.  Even the one site with seasonal rainfall patterns (a 4 month dry season) shows no impact of seasonal precipitation on community-wide flowering and fruit production.  Phylogenetic analyses of flowering and fruiting times suggest only a weak phylogenetic signal in flowering patterns.  These results allow us to speculate on potential impacts of climate change on seasonal reproduction in Neotropical forests.  The study in Panama shows elevated fruit production in El Niño years and a long-term increase in flower production by trees and lianas of 1.1% and 4.5% per year, respectively.  This steady 19-yr (at the time of analysis) increase, which affects flower production but not fruit and seed production, is suggestive of global change.  Data from Puerto Rico show a strong impact of two hurricanes, which struck the site in 1989 and 1998, on interannual patterns of reproduction and which obscure any long-term trends in reproduction.