Assessing the impact of lightning on regional disturbance regimes across a tropical forest gradient

The first comprehensive investigation into the ecological effects of lightning revealed that it is a major driver of tropical plant mortality, gap formation, and biomass carbon turnover in a mature tropical forest. These findings demonstrated the capacity of lightning to influence forest dynamics, but those data are restricted to a single mature forest at a spatial scale (~15 km2) that is much smaller than the scale at which the atmospheric processes controlling lightning operate (10s to 100s of km). Given evidence that lightning and severe storm frequency is increasing with climate change, we need large-scale studies of lightning effects across multiple forest types to understand the future forest dynamics and carbon budgets. Here we present the results from the first regional study of lightning ecology, wherein we use an array of electric field change meters (FCMs) to track lightning strikes in real-time over 20,000 km2 in central Panama. This network provides direct measurements of each strike’s intensity with high detection efficiency and a precision accuracy of < 30 m. The ecological effects of these lightning strikes were quantified using subsequent field surveys, validated at medium-scales (15 km2) using drone imagery, and upscaled to quantify regional disturbance regimes by integrating the FCM, drone, and field data.

 

This is the first spatially-explicit record of a regional disturbance regime for any given driver of tree mortality in a tropical forest. We show that lightning exhibits strong patterns of spatiotemporal aggregation. Based on these patterns, we estimate the study area and duration needed to accurately capture the contributions of lightning to plant mortality and biomass carbon dynamics, which is much larger than a typical forest plot (1 ha) and longer than a typical study time-frame for this size plot (10 years). Using field data describing the ecological effects of lightning, we then estimate the absolute contributions of lightning to biomass carbon turnover across the study regions, including 8,000 km2 of tropical forest. We then test if regional patterns of lightning-caused disturbance predict regional variation in forest structure and carbon storage. We expect our findings will be key to more accurate carbon accounting and the development of mechanistic demographic vegetation models.