Lightning Gaps in the Mangrove Forest of Everglades National Park

Whelan, Kevin; Smith, Thomas

With an average of 9,900 cloud-to-ground lightning strikes occurring annually in Florida (Figure 1), lightning-created canopy gaps are a common and important component of the mangrove ecosystem (Figure 2). Figure 1. A picture of a typical lightning strike (photo by Michael Fewings). These gaps produce a mosaic of different successional stages that may be vital as a living seed bank in the mangrove ecosystem. Species dynamics in the mangrove ecosystem of Everglades National Park are affected by the Everglades’ hydrological restoration, sea-level rise, hurricanes, and lightning gaps. Clearly, to understand the dynamics of future mangrove ecosystems, determining how these ecosystems respond to small- and large-scale disturbances will be crucial. Here we characterize the role of lightning gaps within south Florida mangrove ecosystems. By using a serial sampling of recent and closing gaps, we will be able to determine the way these small-scale disturbances affect current and future forest structure in the larger context. Our study area is the mangrove forest of the Shark River region of Everglades National Park (Figure 3). This forest is approximately 15 km wide. From the coast upstream toward the freshwater marshes, canopy height declines from an average of 10.1 m to 5.4 m. The forest consists of stands of mixed mangroves with Rhizophora mangle L. (red mangrove), Laguncularia racemosa (L.) Gaertn (white mangrove) and Avicennia germinans (L.) Stearn (black mangrove). Historically, catastrophic hurricanes occur approximately every 30 years in south Florida. Our study sites have not been substantially disturbed by a hurricane since Hurricane Donna in 1960.