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Lightning is an important agent of mortality for large tropical trees with implications for tree demography and forest carbon budgets. We evaluated interspecific differences in susceptibility to lightning damage using a unique dataset of systematically located lightning strikes in central Panama. We measured differences in mortality among trees damaged by lightning and related those to damage frequency and tree functional traits. Eighteen of 30 focal species had lightning mortality rates that deviated from null expectations. Several species showed little damage and three species had no mortality from lightning, whereas palms were especially likely to die from strikes. Species that were most likely to be struck also showed the highest survival. Interspecific differences in tree tolerance to lightning suggest that lightning-caused mortality shapes compositional dynamics over time and space. Shifts in lightning frequency due to climatic change are likely to alter species composition and carbon cycling in tropical forests., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

The mortality rates of large trees are critical to determining carbon stocks in tropical forests, but the mechanisms of tropical tree mortality remain poorly understood. Lightning strikes thousands of tropical trees every day, but is commonly assumed to be a minor agent of tree mortality in most tropical forests. We use the first systematic quantification of lightning-caused mortality to show that lightning is a major cause of death for the largest trees in an old-growth lowland forest in Panama. A novel lightning strike location system together with field surveys of strike sites revealed that, on average, each strike directly kills 3.5 trees (> 10 cm diameter) and damages 11.4 more. Given lightning frequency data from the Earth Networks Total Lightning Network and historical total tree mortality rates for this site, we conclude that lightning accounts for 40.5% of the mortality of large trees (> 60 cm diameter) in the short term and probably contributes to an additional 9.0% of large tree deaths over the long term. Any changes in cloud-to-ground lightning frequency due to climatic change will alter tree mortality rates; projected 25-50% increases in lightning frequency would increase large tree mortality rates in this forest by 9-18%. The results of this study indicate that lightning plays a critical and previously underestimated role in tropical forest dynamics and carbon cycling., (© 2019 The Authors. New Phytologist © 2019 New Phytologist Trust.)

Small cursorial ectotherms risk overheating when foraging in the tropical forest canopy, where the surfaces of unshaded tree branches commonly exceed 50 °C. We quantified the heating and subsequent cooling rates of 11 common canopy ant species from Panama and tested the hypothesis that ant workers stop foraging at temperatures consistent with the prevention of overheating. We created hot experimental "sunflecks" on existing foraging trails of four ant species from different clades and spanning a broad range of body size, heating rate, and critical thermal maxima (CT max ). Different ant species exhibited very different heating rates in the lab, and these differences did not follow trends predicted by body size alone. Experiments with ant models showed that heating rates are strongly affected by color in addition to body size. Foraging workers of all species showed strong responses to heating and consistently abandoned focal sites between 36 and 44 °C. Atta colombica and Azteca trigona workers resumed foraging shortly after heat was removed, but Cephalotes atratus and Dolichoderus bispinosus workers continued to avoid the heated patch even after >5 min of cooling. Large foraging ants (C. atratus) responded slowly to developing thermal extremes, whereas small ants (A. trigona) evacuated sunflecks relatively quickly, and at lower estimated body temperatures than when revisiting previously heated patches. The results of this study provide the first field-based insight into how foraging ants respond behaviorally to the heterogeneous thermal landscape of the tropical forest canopy.

Sodium (Na) is uncommon in plants but essential to the metabolism of plant consumers, both decomposers and herbivores. One consequence, previously unexplored, is that as Na supplies decrease (e.g., from coastal to inland forests), ecosystem carbon should accumulate as detritus. Here, we show that adding NaCl solution to the leaf litter of an inland Amazon forest enhanced mass loss by 41%, decreased lignin concentrations by 7%, and enhanced decomposition of pure cellulose by up to 50%, compared with stream water alone. These effects emerged after 13-18 days. Termites, a common decomposer, increased 7-fold on +NaCl plots, suggesting an agent for the litter loss. Ants, a common predator, increased 2-fold, suggesting that NaCl effects cascade upward through the food web. Sodium, not chloride, was likely the driver of these patterns for two reasons: two compounds of Na (NaCl and NaPO(4)) resulted in equivalent cellulose loss, and ants in choice experiments underused Cl (as KCl, MgCl(2), and CaCl(2)) relative to NaCl and three other Na compounds (NaNO(3), Na(3)PO(4), and Na(2)SO(4)). We provide experimental evidence that Na shortage slows the carbon cycle. Because 80% of global landmass lies >100 km inland, carbon stocks and consumer activity may frequently be regulated via Na limitation.

We quantified the effects of deforestation, and subsequent cultivation and forest regeneration, on the abundance and composition of mosquito larval habitats, specifically phytotelmata (plant-held waters), in the western Amazon basin. Recently deforested sites were characterized by increased phytotelm density (1.6 phytotelmata/m2) and greater relative abundance of fallen-plant-part phytotelmata (76%) compared to intact forests (0.9 phytotelmata/m2 and 25% fallen plant parts). As a result, the total volume of colonizable phytotelm water was significantly larger in new clearings. Subsequent cultivation of cleared land with mixed crops including pineapple and plantain had similar consequences: phytotelm density (2.2 units/m2) was significantly larger in plantations than in forests due to greater relative abundance of water-filled plant axils (71% vs. 39% in forest). Such axils are the preferred larval habitats for Wyeomyia spp. mosquitoes, which showed a similarly significant increase in production in plantations (0.25 larvae/m2) vs. forests (0.04 larvae/m2). Likewise, Limatus spp. mosquitoes were an order of magnitude more abundant in altered landscapes (especially in recently deforested and cultivated areas) than in mature forest, due to increased abundance of fallen-plant-part phytotelmata, in which they are typically the most common colonists. Because they are potential vectors of pathogens in a region of high endemic and emergent virus activity, increases in local abundance of Limatus spp. and Wyeomyia spp. due to large-scale deforestation and agriculture may influence rates of disease transmission.

Summary: Lightning is an important agent of plant mortality and disturbance in forests. Lightning‐caused disturbance is highly variable in terms of its area of effect and disturbance severity (i.e. tree damage and death), but we do not know how this variation is influenced by forest structure and plant composition.We used a novel lightning detection system to quantify how lianas influenced the severity and spatial extent (i.e. area) of lightning disturbance using 78 lightning strikes in central Panama.The local density of lianas (measured as liana basal area) was positively associated with the number of trees killed and damaged by lightning, and patterns of plant damage indicated that this occurred because lianas facilitated more electrical connections from large to small trees. Liana presence, however, did not increase the area of the disturbance. Thus, lianas increased the severity of lightning disturbance by facilitating damage to additional trees without influencing the footprint of the disturbance.These findings indicate that lianas spread electricity to damage and kill understory trees that otherwise would survive a strike. As liana abundance increases in tropical forests, their negative effects on tree survival with respect to the severity of lightning‐related tree damage and death are likely to increase. [ABSTRACT FROM AUTHOR]

Lightning is a common source of disturbance, but its ecological effects in tropical forests are largely undescribed. Here we quantify the contributions of lightning strikes to forest turnover and plant mortality in a lowland Panamanian forest using a real‐time lightning monitoring system. We examined 2,195 lightning‐damaged trees distributed among 93 different strikes. None exhibited scars or fires. On average, each strike disturbed 451 m2 (95% CI: 365–545 m2), created a canopy gap of 304 m2 (95% CI 198–454 m2), and caused 7.36 Mg of woody biomass turnover (CI: 5.36–9.65 Mg). Cumulatively, we estimate that lightning strikes in this forest create canopy gaps equaling 0.39% of forest canopy area, representing 20.1% of annual gap area formation, and are responsible for 16.1% of total woody biomass turnover. Trees, lianas, herbaceous climbers and epiphytes were killed by lightning at rates 8–29 times greater than their baseline mortality rates in undamaged control sites. The likelihood of lightning‐caused death was higher for trees, lianas, and herbaceous climbers than for epiphytes, and high liana mortality suggests that lightning is an important driver of liana turnover. These results indicate that lightning influences gap dynamics, plant community composition and carbon storage capacity in some tropical forests. [ABSTRACT FROM AUTHOR]

Tree death due to lightning influences tropical forest carbon cycling and tree community dynamics. However, the distribution of lightning damage among trees in forests remains poorly understood.We developed models to predict direct and secondary lightning damage to trees based on tree size, crown exposure and local forest structure. We parameterized these models using data on the locations of lightning strikes and censuses of tree damage in strike zones, combined with drone‐based maps of tree crowns and censuses of all trees within a 50‐ha forest dynamics plot on Barro Colorado Island, Panama.The likelihood of a direct strike to a tree increased with larger exposed crown area and higher relative canopy position (emergent > canopy >>> subcanopy), whereas the likelihood of secondary lightning damage increased with tree diameter and proximity to neighbouring trees. The predicted frequency of lightning damage in this mature forest was greater for tree species with larger average diameters.These patterns suggest that lightning influences forest structure and the global carbon budget by non‐randomly damaging large trees. Moreover, these models provide a framework for investigating the ecological and evolutionary consequences of lightning disturbance in tropical forests.Synthesis. Our findings indicate that the distribution of lightning damage is stochastic at large spatial grain and relatively deterministic at smaller spatial grain (<15 m). Lightning is more likely to directly strike taller trees with large crowns and secondarily damage large neighbouring trees that are closest to the directly struck tree. The results provide a framework for understanding how lightning can affect forest structure, forest dynamics and carbon cycling. The resulting lightning risk model will facilitate informed investigations into the effects of lightning in tropical forests. [ABSTRACT FROM AUTHOR]

The physical characteristics of habitats shape local community structure; a classic example is the positive relationship between the size of insular habitats and species richness. Despite the high density and proximity of tree crowns in forests, trees are insular habitats for some taxa. Specifically, crown isolation (i.e. crown shyness) prevents the movement of small cursorial animals among trees. Here, we tested the hypothesis that the species richness of ants (Sa) in individual, isolated trees embedded within tropical forest canopies increases with tree size. We predicted that this pattern disappears when trees are connected by lianas (woody vines) or when strong interactions among ant species determine tree occupancy. We surveyed the resident ants of 213 tree crowns in lowland tropical forest of Panama. On average, 9.2 (range = 2-20) ant species occupied a single tree crown. Average (± SE) Sa was ca 25% higher in trees with lianas (10.2 ± 0.26) than trees lacking lianas (8.0 ± 0.51). Sa increased with tree size in liana-free trees (Sa = 10.99A0.256), but not in trees with lianas. Ant species composition also differed between trees with and without lianas. Specifically, ant species with solitary foragers occurred more frequently in trees with lianas. The mosaic-like pattern of species co-occurrence observed in other arboreal ant communities was not found in this forest. Collectively, the results of this study indicate that lianas play an important role in shaping the local community structure of arboreal ants by overcoming the insular nature of tree crowns. [ABSTRACT FROM AUTHOR]