A canopy trimming experiment in Puerto Rico: The response of litter decomposition and nutrient release to canopy opening and debris deposition in a subtropical wet forest

Abstract

In this study, we used a replicated factorial design to separate the individual and interacting effects of two main components of a severe hurricane – canopy opening and green debris deposition on leaf litter decay in the tabonuco forest in the Luquillo Mountains of Puerto Rico. We quantify changes in percent mass remaining (PMR), the concentration and absolute amounts of various chemical elements using fresh (green) and senesced leaf litter contained in litterbags of two different mesh sizes. Mass loss was significantly slowed by canopy trimming. There was no significant effect of debris treatment on the PMR of the litter. Canopy trimming increased the percent of initial N, Al, Ca, Fe, and Mg remaining and decreased the percent of initial Mn remaining compared with not trimmed plots. Debris addition increased the percent of initial N and P remaining and decreased the percent of initial Al, and Fe remaining in the decomposing litter compared to no debris added plots. Of the elements studied, only Al and Fe accumulated above 100% of initial. Accumulation of Al and Fe in the canopy trimmed and no debris plotsis most likely dominated by the adsorption of these ions onto the surfaces of the decaying litter. Overall, P showed a rapid initial loss during the first 0.2yr followed by steady loss. Nitrogen was lost steadily from leaf litter. The PMR of fresh and senesced litter was significantly affected by mesh size, with a higher mass remaining in small mesh bags. Fresh litter decayed faster than senesced litter; following patterns of initial N and P concentrations (higher in the former litter type). We found a significantly negative correlation between the Margalef index of diversity for the litter arthropods contained in the litterbags and the PMR, suggesting functional complexity is an important determinant of decay in this forest. Our results imply hurricanes can differentially impact litter decomposition and associated nutrient release via canopy opening and litter inputs.