In tropical ecosystems, successional forests are rapidly replacing old growth forests as the dominant forest type. This shift in succesional status combined with projected changes in climate could result in a significant change in the species composition of tropical forests. How changes in species composition will affect stand-level nutrient economy is not well understood. Using species-specific leaf litter nutrient and productivity data combined with randomly generated dominance scenarios, we investigated species effects on leaf litter nutrient inputs. We conducted this research in a 1-ha secondary forest stand (30-yr in 2003) in northeastern Costa Rica. We measured senesced leaf N and P contents of the nine dominant canopy tree species within the study plot and scaled the results to the stand level using % basal area (BA) as a proxy for relative litter contribution (∑[total leaf litterfall x % BA_sp x nutrient concentration_sp]). We created different dominance scenarios using Monte Carlo generated BA distributions of the nine species. We then selected all scenarios in which one of the nine species accounted for greater than 30% of the BA. This allowed us to create communities with each of the nine species as dominant while varying the composition of the remaining tree community.
Results/Conclusions

Both N and P leaf litter inputs differed significantly when the dominant species changed from the current forest community. The change in N inputs was relatively small in relation to the potential change in leaf litter P inputs. P inputs decreased by 23% when Vochysia ferruginea, a shade-intolerant late pioneer species, was dominant. When Casearia arborea, a shade-tolerant species, was the dominant species there was 6% increase in leaf litter P inputs. Our results demonstrate that changes in leaf litter N and P cycling will likely occur as land use and climate change alters forest community composition.