Tree and Forest Traits Influencing Lightning Strike Probability

Lightning is a significant disturbance agent in tropical forests, with ecological impacts including tree mortality and influencing forest structure and carbon dynamics. Our research explores the environmental and tree-specific factors affecting the probability of a tree being struck by lightning in Afromontane forests. We surveyed 89 kilometers of transects across ridges, slopes, and valleys in Bwindi Impenetrable National Park, Uganda, and recorded 94 lightning strikes.

Our findings reveal that topography significantly influences strike probability, with ridges experiencing the highest strike density (2.0 strikes/km) compared to slopes (1.4 strikes/km) and valleys (0.25 strikes/km). Elevation alone was not a significant predictor when topography was included, suggesting that a tree's relative position in the landscape plays a crucial role.

At the individual tree level, struck trees were not always the tallest within a 20-meter radius plot. Only 30% of struck trees had the largest diameter at breast height (DBH), and 19.5% were the tallest, highlighting the influence of factors beyond size. However, struck trees exhibited a higher median DBH and a greater proportion of emergent canopy trees compared to controls. Generalized Linear Mixed Models (GLMM) identified DBH (Estimate = 0.025, p < 2.39e-06) and canopy exposure (Estimate = 1.20, p = 2.04e-08) as significant predictors of strike probability.

These results suggest that lightning strikes are influenced by a combination of environmental and tree-specific traits, including topographical context, DBH, and canopy exposure. Our findings contribute to understanding lightning as a selective agent in tropical forests, with implications for forest dynamics and carbon storage.