Monge, J.A. and Gornish, E.S., 2015. Positive species interactions as drivers of vegetation change on a barrier island.

Positive species interactions have been shown to occur in a variety of plant systems, and the importance of these interactions is expected to vary with resource availability and abiotic stress. The processes by which these types of relationships operate and influence plant communities in coastal environments, however, are not fully understood. Positive species interactions were observed in areas of St. George Island, Florida, shortly after transplanting dune species for a restoration experiment designed to encourage the growth of foredune, interdune, and backdune vegetation. The dune habitats in St. George are subject to abiotic stresses that vary in type and magnitude, and the environmental factors responsible for ameliorating these conditions and encouraging positive vegetation change operate differently across these areas. We (1) investigated if transplants encouraged positive changes in vegetation across dune habitats, (2) determined whether disturbance (through transplanting) played a role, and (3) tested environmental factors involved in positive interactions to explain the changes in vegetation observed across dune habitats. The presence of transplants positively modified vegetation (e.g., species richness or cover) across all dune habitats. Experimental disturbance had no strong overall positive effect on vegetation change. Shading and soil moisture redistribution had differential effects on vegetation change among habitats, suggesting that these environmental factors interact with the abiotic characteristics unique to each dune habitat in complex ways. Our results suggest that experimentation over a longer time scale might be required to fully understand the extent at which positive interactions affect vegetation patterns along stressful environmental gradients.