Inferring drivers of liana mortality from associated patterns of tree death

Evan Gora, Cary Institute of Ecosystem Studies, Millbrook, NY; Smithsonian Tropical Research Institute, Panama City, Panama, David Defilippis, Biological Sciences, Marquette University, Milwaukee, WI and Stefan A. Schnitzer, Smithsonian Tropical Research Institute, Balboa, Panama

Background/Question/Methods
We lack a cohesive understanding of plant death, limiting our ability to understand the causes and consequences of ongoing shifts in plant community dynamics. Trees are well-studied relative to other types of plants and their mortality is largely regulated by disturbances, forest thinning during forest recovery, and habitat conditions. These same factors potentially influence the mortality of plants with alternative life history strategies, but the generalizability of mortality patterns among tropical plant groups remains untested. For example, liana mortality has broad ecosystem-level consequences and is mostly likely to resemble that of trees because of their physiological, anatomical, and phylogenetic similarities. Here we contrasted patterns of liana mortality with relatively well understood patterns of tree mortality to infer the major drivers of tropical woody plant death. Specifically, we evaluated five hypotheses by contrasting 10 years of liana mortality with 5 overlapping years of tree turnover in a 50-ha stand of lowland moist tropical forest in Panama.
Results/Conclusions
Liana mortality rates were 172% higher than tree mortality rates and spatially autocorrelated over larger spatial extents (135m vs 75m). However, spatial patterns of liana and tree mortality were only weakly correlated. Large lianas exhibited tree-like responses to contemporaneous and historic disturbances; specifically, higher mortality rates with increasing disturbance severity and decreasing mortality rates over time post-disturbance. By contrast, the mortality rates of small lianas decreased with increasing disturbance severity and remained consistently low during post-disturbance stand thinning (despite strong evidence of density-dependent liana mortality). Within undisturbed forest patches, lianas and trees exhibited similar increases in mortality rates with increasing soil fertility. These results show that there are commonalities in the major drivers of mortality for these two growth forms. However, the higher intrinsic rates of liana mortality and their limited responses to disturbance caused fundamental differences between the demographics of trees and lianas.