Interactive effects of land use history and natural disturbance on seedling dynamics in a subtropical forest

Human-impacted forests are increasing in extent due to widespread regrowth of secondary forests on abandoned lands. The degree and speed of recovery from human disturbance in these forests will determine their value in terms of biodiversity conservation and ecosystem function. In areas subject to periodic, severe natural disturbances, such as hurricanes,it has been hypothesized that human and natural disturbance may interact to either erase or preserve land use legacies. To increase understanding of how interactions between human and natural disturbance influence forest regeneration and recovery, we monitored seedlings in a human- and hurricane-impacted forest in northeastern Puerto Rico over a ~10 yr period and compared seedling composition and dynamics in areas that had experienced high- and low intensity human disturbance during the first half of the 20th century. We found that land use history significantly affected the composition and diversity of the seedling layer, and altered patterns of canopy openness and seedling dynamics following hurricane disturbance. The area that had been subject to high-intensity land use supported a higher density, but lower diversity,of species. In both land use history categories, the seedling layer was dominated by the same two species, Prestoea acuminata var. montana and Guarea guidonia. However, seedlings of secondary successional species tended to be more abundant in the high-intensity land use area, while late successional species were more abundant in the low-intensity area, consistent with patterns of adult tree distributions. Seedlings of secondary forest species showed greater increases in growth and survival following hurricane disturbance compared to late successional species, providing support for the hypothesis that hurricanes help preserve the signature of land use history. However, the increased performance of secondary forest species occurred predominantly in the low-intensity land use area, suggesting that hurricanes act to homogenize differences in species composition between areas with differing land use histories by increasing secondary forest species regeneration in areas that experienced little direct human disturbance. Our results suggest that through effects on seedling dynamics, hurricanes may extend the signature of land use history beyond the average recovery time of forests not subject to intense natural disturbance events