Assessment of the Severity of Lightning Strike Disturbances in Tropical Forests

Lightning strikes are a major cause of tree mortality in tropical forests. Lightning does not strike the landscape randomly; certain trees are more likely to be struck than others. Here we test the hypothesis that trees with high lightning strike likelihoods are also more likely to tolerate lightning damage and act as biological lightning rods, attracting lightning and absorbing the disturbance while limiting the amount of biomass lost by the forest. We assessed whether trees at higher risk of lightning strikes are more likely to survive, how much their survival reduces the severity of this disturbance, and whether this effect varies across forests of different ages. We combined a lightning strike risk model, which our field surveys confirmed identifies the crowns most frequently damaged by lightning, with 110 events recorded in two different field campaigns on Barro Colorado Island, Panama. The severity of the disturbance increased at low- and medium-risk levels but decreased at the highest risk levels, where struck trees showed a tendency towards higher survival rates. Trees in the highest-risk positions, which have more biomass to lose, retained an average of 12.9 Mg of biomass per event when they survived the strike. At the landscape scale, lightning-tolerant trees in old-growth forest conserve 15% more biomass per hectare per year than those in secondary forest (0.500 vs. 0.434 Mg ha⁻¹ year⁻¹), even though both are impacted at a similar rate. The results suggest that high-risk trees may be able to tolerate lightning-caused disturbance and reduce its consequences on forest biomass loss, and that this lightning-rod tree effect may be accumulated as the forest matures.