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ABSTRACT Lightning frequency in tropical forests has been increasing for decades and lightning is a major agent of forest biomass mortality, but the implications of increased lightning frequency are unclear. Here, we provide a species‐ and spatially explicit implementation of lightning in a mechanistic forest dynamics model. We evaluated the model's ability to reproduce current‐day observations in a Panamanian tropical forest, and the sensitivity of model outputs to plausible changes in lightning frequency. The lightning‐enabled model simulated aboveground biomass (AGB), carbon flux, and stem densities that were consistent with observations. As expected, AGB declined with increasing lightning frequency. However, the magnitude of AGB decline was greatly reduced when trees were assigned empirically derived, species‐specific lightning tolerances. Changes in species composition weakened the sensitivity of AGB to increasing lightning: the AGB of a small number of large‐statured, lightning‐tolerant species increased with increasing lightning frequency. In addition, the effect of lightning on AGB tended to saturate at high lightning frequencies because of the combined effect of changes in size structure and composition. Specifically, the number of large, lightning‐susceptible trees was relatively small at high lightning frequencies. Overall, this study shows that an empirically informed representation of lightning captures the contemporary effects of lightning on forests, indicates that changes in lightning frequency will change forest AGB, species composition, and size structure, and shows that forests can partially acclimate to higher lightning frequency through changes in composition. Thus, more widespread inclusion of the lightning into global ecosystem models would be an important step toward improving simulations of forest responses to global change. 

ABSTRACT Lightning is an important agent of tree mortality and gap formation. Here we quantified spatial and temporal patterns of lightning‐caused canopy disturbance in a 50‐ha plot in Panama using monthly drone imagery, and compared these patterns with field measurements of disturbance severity and spatial extent. Of 22 lightning strikes that we tracked, the impacts of 18 were monitored for at least 12 months (range of 17–50 months), and 67% of these 18 strikes led to canopy disturbances. The mean time for the first and last canopy disturbance to appear post‐strike was 8.2 months (range: 0.8–14 months) and 14.6 months (range: 0.8–23.9 months), respectively. Canopy disturbances were generally highly irregular in shape (i.e., not circular), and clustered around the rooting point of the directly struck tree. A mean of 43% (± 19%) of the total lightning‐associated canopy disturbance area was within 10 m of the rooting point, whereas only 3% (± 5%) occurred 30–40 m from this point. Drone‐based measurements of canopy disturbance area and volume were good predictors of variation in ground‐estimated dead biomass (r² = 0.48 and 0.46, respectively), reflecting their strong association with overstory dead biomass (r² = 0.42 and 0.41, respectively). The total drone‐estimated canopy disturbance area was 49% of the ground‐estimated canopy disturbance area. Thus, lightning typically causes canopy disturbances that are detectable with drone imagery despite their irregular shape, and drone‐detected gap formation lags 8–15 months poststrike, potentially disconnecting drone‐detected disturbances from their ultimate cause. 

Abstract Temperature is a key abiotic condition that limits the distributions of organisms, and forest insects are particularly sensitive to thermal extremes. Whereas winged adult insects generally are able to escape unfavorable temperatures, other less-vagile insects (e.g., larvae) must withstand local microclimatic conditions to survive. Here, we measured the thermal tolerance of the larvae of three saproxylic beetle species that are common inhabitants of coarse woody debris (CWD) in temperate forests of eastern North America: Lucanus elaphus Fabricius (Lucanidae), Dendroides canadensis Latreille (Pyrochroidae), and Odontotaenius disjunctus Illiger (Passalidae). We determined how their critical thermal maxima (CTmax) vary with body size (mass), and measured the thermal profiles of CWD representing the range of microhabitats occupied by these species. Average CTmax differed among the three species and increased with mass intraspecifically. However, mass was not a good predictor of thermal tolerance among species. Temperature ramp rate and time in captivity also influenced larval CTmax, but only for D. canadensis and L. elaphus respectively. Heating profiles within relatively dry CWD sometimes exceeded the CTmax of the beetle larvae, and deeper portions of CWD were generally cooler. Interspecific differences in CTmax were not fully explained by microhabitat association, but the results suggest that the distribution of some species within a forest can be affected by local thermal extremes. Understanding the responses of saproxylic beetle larvae to warming habitats will help predict shifts in community structure and ecosystem functioning in light of climate change and increasing habitat fragmentation. 

Abstract Temperature extremes often limit animal distributions. Whereas some poikilotherms (e.g., winged insects) can escape local thermal extremes, many less vagile organisms (e.g., insect larvae and arthropods with limited dispersal ability) are at the mercy of local microenvironmental conditions. Here, we quantified the thermal tolerance of an abundant, endemic, Nearctic millipede (Euryurus leachii), and explored the effects of seasonality, mass, and sex on its critical thermal maxima (CTmax). We also measured the thermal microenvironments of dead wood representing different decay classes. Overall, the mean CTmax for this species was ca. 40.5°C. Mass and sex had no effect on millipede CTmax. However, the mean CTmax for millipedes collected in the fall was 0.6°C higher than for individuals collected in the spring. An exposed dry log representing one common microhabitat for E. leachii readily warmed to temperatures exceeding its CTmax. The results suggest that CTmax is a seasonally plastic trait in E. leachii and that microclimatic conditions potentially limit the local distribution of this species. With habitat fragmentation and climate change contributing to warmer temperatures in forested systems, understanding the responses of detritivores like E. leachii can help predict potential shifts in community composition and ecosystem processes. 

Abstract Lightning is a common agent of disturbance in many forest ecosystems. Lightning-damaged trees are a potentially important resource for beetles, but most evidence for this association is limited to temperate pine forests. Here, we evaluated the relationship between lightning damage and beetle colonization of tropical trees. We recorded the number of beetle holes on the trunks of trees from 10 strike sites (n = 173 lightning-damaged trees) and 10 matching control sites (n = 137 control trees) in Panama. The trunks of lightning-struck trees had 370% more beetle holes than control trees. The abundance of beetle holes increased with increasing total crown dieback among both control and lightning-damaged trees, and with larger tree diameter among lightning-struck trees. Beetle holes also were more abundant in trunk sections of lightning-damaged trees located directly below a damaged section of the crown. The results of this study suggest that lightning damage facilitates beetle colonization in tropical forest trees and provide a basis for investigations of the effects of lightning-caused disturbance on beetle population dynamics and assemblage structure.