Community assembly and longleaf pine savannah restoration

Identifying the underlying mechanisms that determine species membership during community assembly is an integral part of developing successful approaches to ecological restoration.  Two factors that are important in determining species membership in a community are abiotic conditions and the traits of potential colonists from the species pool.  We examined these factors in a longleaf pine savannah restoration experiment conducted at the 80,125 ha U.S. Department of Energy Savannah River Site (SRS) near Aiken, South Carolina, USA.  Specifically, we examined the role of leaf litter depth and species dispersal modes in dictating colonization success.  We transplanted 31 herbaceous understory species native to longleaf pine savannahs in 50 3x3m² plots at each of six separate sites within SRS.  An additional 50 non-planted (control) plots at each site were used to document the accumulation of all planted and non-planted species within the site over a two year period.  In addition, all planted species within a 10m area surrounding each site were surveyed to document the spread of species away from the planted/control matrix into the adjacent landscape.  The rate of total species accumulation in control plots differed significantly among sites and ranged from 1.84 - 4.67 spp/yr.  The rate of planted species accumulation also differed among sites and ranged from 0.65 - 2.89 spp/yr.  Among individual species, Chrysopsis gossypina exhibited the greatest colonization rate (66 plots/yr).  A significant negative relationship exists between colonization and litter depth.  Outside of the planted/control matrix, Desmodium marilandicum exhibited the greatest mean rate of spread to the surrounding landscape (1.91 m/yr).  Overall, species that have wind-dispersed seeds exhibited the greatest colonization success.  Results suggest that species selection and appropriate site management are important factors in promoting species recruitment in local and landscape-level restoration projects.