Windthrow in south Florida Pine Rocklands: pit and mound features and plant microhabitat associations following Hurricane Andrew

Ross, M.; Meeder, J.; Sah, J.; Herndon, A.; Ruiz, P.; telesnicki, G.

We examined the effect of environments created by the uprooting of adult trees during Hurricane Andrew (August 1992) on spatial patterning in the pine forest understory. Our two study areas --- a wet site in Big Cypress National Preserve and a more xeric one in Everglades National Park --- differed markedly in morphology and substrate dynamics in pit and mound environments during the posthurricane period. At BCNP, where pine roots occupied continuous marl soils, tipup pits were shallow, wide, and filled in rapidly after the hurricane. At ENP, trees were rooted in limestone bedrock, pits were deeper, and infilling with limestone fragments was irregular.The two sites also differed in the relative favorability of the two major tipup habitats for plant establishment. Following the high water conditions of 1995-96, species richness on BCNP mounds was about 60% higher than in pits. In contrast, pits in ENP were about twice as speciose as mounds. Pit and mound species composition (especially the former) were distinct from background vegetation during the immediate post-hurricane period. However, these relationships did not appear to persist; old tipup features which were still recognizable in the rockland landscape did not differ from undisturbed terrain with respect to plant species composition. Spatial analyses indicated that pine forest understory vegetation was strongly structured at distances between 0.3 and 15 meters. Within that range, units of relatively homogeneous vegetation of all sizes were present at both sites. Our results suggest that the uprooting of pine trees during periodic hurricanes creates ecologically significant substrate variation in the rockland surface, thereby contributing to fine scale structuring in understory species assemblages.