Coastal Vines: Untangling a web of ecosystem interactions

Background/Question/Methods

Coastal regions are considered to be sentinels of global change, due to an inherent vulnerability to storms and sea level rise.  Barrier islands are particularly susceptible, as the interactions between aquatic and terrestrial free surfaces are further exaggerated.  An understanding of the complex interactions and ecological processes in these environments will aid in predicting responses to future global changes, many of which will be initially detectable in coastal zones, and may have economic as well as ecological impacts.  Woody and herbaceous climbing plants – generically vines – play a special role in these coastal communities.  As successional processes occur, dense-canopied shrub thickets begin to deteriorate and allow for establishment of vine species in the understory.  Vines infiltrate thicket canopies, accelerating their decline and advancing succession by enlarging gaps and attracting seed-dispersing birds.

I quantified relationships between vines and the woody community within the context of environmental constraints on two barrier islands.  Community diversity along cross-site transects was evaluated, and LiDAR data were exploited to obtain elevation profiles for construction of habitat polygons for vine species and specific communities.

Results/Conclusions

Woody plant and vine communities were found to vary with distance to shoreline and with time since disturbance.  At Duck, NC, where the substrate and dune ridge is stable and elevation is largely uniform, saline sea spray is the primary factor affecting species diversity across the site, and has little influence beyond the first dune ridge-swale complex.  Apart from these areas immediately behind dunes, the plant communities are highly similar with respect to both woody and vine species.  At Hog Island, VA, communities differed with distance to shoreline, time since disturbance, and elevation gradients.  In terms of landscape position, the highest species diversity was noted in low elevation areas at greatest distance to the ocean.  Comparison of species diversity and community composition in the dynamic environments of Hog Island with the stable environment of Duck suggests that species composition varies primarily in response to physical factors such as sea spray and freshwater availability, which are integrated in a landscape position analysis.  Community diversity is more predictable by age of an area, or time since disturbance.  Ongoing research will explore physiochemical site differences and physiological impacts of vines on woody supporting vegetation.  This current and continued exploration will contribute to the broader understanding of plant interactions in a sensitive and responsive ecosystem.