Disturbances influence dynamics of stands of sand pine, a prominent tree in coastal and inland scrub habitat.  Periodic intense fires have been hypothesized to produce even-aged/sized populations via catastrophic mortality of trees that produce seeds that survive fires in closed cones.  In contrast, uneven-aged/sized populations have been suggested to result from frequent regeneration via cones that open annually in habitats not experiencing stand-replacing fires. Hurricane-generated non-catastrophic mortality of trees should open all stands, facilitating regeneration and generating multiple aged/sized cohorts if seeds are dispersed into openings. We conducted a field study in 2007-2008 to assess effects of recent tropical cyclones (2004-2005) on structure and dynamics of stands across the range of sand pine. We examined sand pine in 15 stands across the range of sand pine from Alabama to southern Florida. At each site, we established 30x30m plots in which we measured diameter and assessed effects of hurricanes on damage and survival of all sand pines >1.5m DBH.  Surviving sand pines <1.5m were also located and measured for height and diameter. We grouped trees into 10 cm size classes to examine size-dependent mortality and related mortality to location relative to the coast as well as to recent hurricane paths.

Results/Conclusions

Overall survival of recent tropical cyclones averaged 63.0% ± 6.4 (S.E.), ranging from 29.6 to 92.4% among sand pine stands. Survival was positively related to distance from the eye of the most recent hurricane to pass the stand, but not the location of the stand relative to the coast. Survival in all stands decreased as tree size increased, with most large trees killed in all stands. Nonetheless, slopes of survival-size relationships were increasingly negative for stands located further from the coast because more of the smaller trees survived. Size relationships of trees smaller than 1.5m differed for coastal and inland stands. Slopes of diameter-height relationships were twice as great for inland stands as coastal stands; small pines should reach overstory height more quickly in inland than coastal stands. Such rapid growth suggests that effects of hurricanes on interior stand structure should disappear within a couple decades, resulting in the impression that stands are even-aged, dating from the last stand-replacing fire, even though they are composed of multiple cohorts. In contrast, slow growth in coastal stands should result in stands appearing uneven-sized and uneven-aged. Periodic effects of hurricanes, with or without stand-replacing fires, thus should drive stand dynamics of sand pine.