Lightning is a common source of disturbance in lowland tropical forests. However, the effects of lightning on trees and other forest components rarely are quantified. Resolving this problem is important given that cloud-to-ground (CG) lightning frequency is expected to change in a warmer climate. We quantified lightning-caused death and damage to trees, epiphytes, and lianas (woody vines) in the forest of Barro Colorado Island (BCI), Panama. We tested the hypothesis that the fate of a lightning-struck tree is predictable based on its characteristics (size, identity, and liana occupancy), and characteristics of the lightning flash (intensity and duration).
We used a network of cameras and electronic sensors to locate and characterize lightning strikes on BCI. We surveyed 60 lightning strike sites from 2014-2018 to quantify the average numbers of trees killed and damaged per strike, along with their size and identity. We combined these averages with satellite-based lightning frequency data to calculate the expected numbers of trees killed by lightning per area per year, and estimated the relative contribution of lightning to total tree mortality. Survey data also included the presence and condition of epiphytes and lianas, the presence of termites, beetle activity, herbivore damage, and Azteca trigona ant nests.
Results/Conclusions
BCI receives 10.3 CG strikes km-2 yr-1 and each strike kills an average of 4 trees (range = 0-16) and damaged 11 others (1-32). Lightning is the single most important agent of large tree mortality on BCI; it directly causes 33% of deaths of trees >60 cm in diameter over the short term (up to 13 months post-strike). Although lianas clearly conduct lightning current, the likelihood of tree mortality was not associated with the presence of lianas. Beetle, termite, and herbivore activity conspicuously increased in strike sites 6-12 months post-strike. The number of dead trees and lianas in a site generally increased with lightning flash intensity (peak current) and duration. Finally, epiphytes and Azteca trigona ants consistently survived lightning strikes that killed their host trees.
The results of this study show that changes in lightning frequency with climatic change will affect tree mortality rates, with potentially important consequences for tree population dynamics, forest community structure, and carbon turnover rates. This project also is providing the first data regarding the relevance of lightning to liana, epiphyte, and insect population dynamics. Collectively, these results provide the most comprehensive assessment of the local effects of lightning in any forest.