Abstract

Lightning-initiated canopy gaps are an important but relatively understudied disturbance in mangrove forests around the world. To test the hypothesis that root death caused by lightning strikes leads to a decline in mangrove peat surface elevation, I investigated soil surface properties subsequent to lightning-initiated canopy gap formation in a Neotropical mangrove forest, Florida, USA. Specifically, I sampled the amount of live and dead roots, soil bulk density, compaction, and maximal torsional shear strength along with soil surface elevation in new gaps, recovering gaps, and the intact forest. Newly formed lightning gaps had greater dead root biomass, but in general had similar surface soil physical metrics compared to the intact forest. Soil surface elevation declined between 8.5 mm to 60.9 mm in newly formed lightning gaps; this loss was due to superficial erosion (8.5 mm) and subsidence (60.9 mm). Recovering gaps had a smaller live root biomass, no difference in soil physical metrics, and a similar soil surface elevation pattern as the intact forest. Lightning apparently kills many of the shallow surface roots and leads to a decline in the soil surface elevation in new gaps. Subsidence occurring below the shallow soil zone generated the greatest overall soil elevation loss. Soil surface elevation loss in newly initiated lightning gaps can lead to a increased hydroperiod, and because many mangrove seedlings have species-specific responses to surface flooding, soil surface elevation loss can affect long-term recruitment patterns.