Lightning damages and often kills trees, yet we know very little about its broader ecological effects in tropical forests. Our ongoing research on this topic addresses the following three questions:
1) What are the community- and ecosystem-level consequences of lightning? Most data regarding the effects of lightning at the landscape scale are based on post hoc surveys (reviewed here). However, answering this question requires recording the location of individual lightning strikes in near real-time. In collaboration with Dr. Phillip Bitzer, we are locating lightning strikes on Barro Colorado Island, Panama, via triangulation from video images (like those shown below) and electronic sensors. This lightning monitoring network is described in more detail here.
Results so far indicate that lightning is a major agent of large tree mortality in tropical forests. Currently, Evan Gora is spearheading our efforts to determine the relevance of lightning to carbon cycling via production of dead wood. Over the long term, this project will reveal how factors like topography, soil type, tree size, and climate-driven changes in lightning frequency affect the probability that any given tree will be killed by lightning.
2) Are some trees or tree species more susceptible or resistant to lightning? Published anecdotes spanning more than a century suggest that some tree species are more likely to be struck by lightning than others, but hard evidence is lacking. Data generated by the lightning monitoring network described above eventually will resolve this problem. In the meantime, we are modeling how interspecific differences in the electrical properties of trees affect the outcome of a lightning strike.
For example, the graphic above illustrates how tree size, species identity, and the presence of lianas affect the amount of heating that occurs during a hypothetical lightning strike. More details about this model are provided here.
3) Do lianas (tropical woody vines) provide lightning protection for tropical trees? Given their abundance in tropical forests, their growth form, and their electrical properties, it is likely that lianas provide passive lightning protection for their host trees (more details here). Indeed, both temperate and tropical vines have higher electrical conductivity than trees. Lightning strike surveys in Panama show that liana stems distribute some of the charge away from the focal tree during a lightning strike, but more data are needed to determine if lianas affect the probability of tree death.
The image above shows liana tendrils projecting well above the foliage of the host tree crown (Anacardium excelsum), suggesting that liana stems commonly serve as attachment points for incipient lightning strikes.