OOS 31-4 - The contributions of lianas to tropical tree mortality

Friday, August 16, 2019: 9:00 AM
M103, Kentucky International Convention Center
Eva Arroyo, Ecology, Evolution and Environmental Biology, Columbia University, New York, NY, Marco D. Visser, Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, S Joseph Wright, Smithsonian Tropical Research Institute, Panama, Panama and Helene Muller-Landau, Smithsonian Tropical Research Institute, Panama
Background/Question/Methods

Lianas are a distinguishing feature of tropical forests. Previous studies have found decreased growth and increased tee mortality in areas with high liana abundance, resulting in changes in forest structure such as lower biomass and tree height. Despite their demonstrated impact on tree growth and mortality, lianas remain largely unincorporated in many forest carbon models. We investigated the proportion of tree mortality that is attributable to lianas – specifically defined as the excess mortality among liana-infested trees, as a proportion of all tree mortality. We used data on species identity, liana infestation status and tree survival from repeat censuses within tropical forest dynamic plots in Pasoh Forest Reserve in Malaysia and Barro Colorado Island in Panama. Calculating the proportion of tree mortality due to lianas is tricky for two reasons. First, liana infestation status and mortality rates are often confounded by other factors; for example, shade-tolerant tree species with low background mortality rates often have high prevalences of liana infestation. Second, liana infestation status of individual trees changes over time as trees gain and lose lianas, and datasets on tree mortality of infested vs. uninfested individuals often have long time lags between the observation of infestation status and the observation of survival or mortality. We addressed these challenges by applying a hierarchical Bayesian model with random effects for species, and incorporating a Markov transition model explicitly fitting the rates at which trees gain and lose lianas.

Results/Conclusions

In both forests, we found that more than 15% of the total mortality of trees greater than 20 (BCI) or 30 (Pasoh) cm in diameter was due to lianas, with a somewhat higher rate for BCI than for Pasoh. Interspecific variation in the proportion of mortality due to lianas was high in both forests. Species with higher baseline mortality rates also had higher liana-induced mortality rates, consistent with previous findings that light-demanding species are less tolerant of liana infestation. Given the high percentage of liana-attributable tree mortality, incorporating lianas in forest models is crucial in order to understand site and species differences in tree mortality and therefore carbon flux.