Neighborhood analysis of tree growth and survival in a hurricane-driven tropical forest
We present a likelihood-based regression method that was developed to analyze the effects of neighborhood competitive interactions and hurricane damage on tree growth and survival. The purpose of the method is to provide robust parameter estimates for a spatially explicit forest simulator and to gain insight into the processes that drive the patterns of species abundance in tropical forests. We test the method using census data from the 16-ha Luquillo Forest Dynamics Plot in Puerto Rico and describe effects of the spatial configuration, sizes, and species of neighboring trees on the growth and survival of 12 dominant tree species representing a variety of life history strategies. Variation in size-dependent growth and mortality suggests a complex relationship between size, growth, and survival under different regimes of light availability. Crowding effects on growth and survival appear to be idiosyncratic to each individual species, and with the exception of pioneers, there is little commonality among species that share similar life histories.
We also explain the implications of differential susceptibility to hurricane damage on species' growth and survival and on their ability to respond to damage to neighboring trees. Tree species in the Luquillo Forest Dynamics Plot differ strikingly in both their susceptibility to hurricane disturbance and the nature of their recovery from wind disturbance, through response of both adult plants and juveniles to enhanced resource availability. At the stand level, intense competitive thinning of densely packed saplings that grew after hurricane damage accounted for the majority of post-hurricane mortality, particularly for shade-intolerant species. At the individual species level, effects of previous hurricane damage on growth and survival depended primarily on variation in the quantity and quality of hurricane damage sustained by target species and their interaction with life history characteristics of these individual species.
Finally, we compare models that make different assumptions about the effects of competing species on tree growth and survival (e.g., equivalence of competitors vs. distinct species-specific effects). Size effects alone could not account for growth and survival for the majority of target species. Our results also demonstrate that competing species have distinct per capita effects on growth of dominant target species. In contrast, we found moderate support for a model that assumed functional equivalence of competitors on survival.