PARENT SESSION
Contributed Oral Session 83: Human Impacts on Coastal Areas
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal

Floristic dynamics on the barrier island 'pimples' of the Virginia Coast Reserve LTER site.

McMillan, Brett^{*,1, 2}, Day, Frank^{1, 3}, ¹ Old Dominion University, Norfolk, VA² email:, bmcmilla@odu.edu³ email:, fday@odu.edu

ABSTRACT- 'Pimples' are dune landforms that have been found in the USA's Gulf coastal plane and on the barrier islands that are part of the Virginia Coast Reserve Long Term Ecological Research site (VCR LTER; Virginia, USA). In contrast to more typical crescent-shaped or parabolic dunes, pimples are flat-topped and circular to slightly ovate when viewed from above. Although pimples are typically <1.5 m higher than the elevation of the surrounding marsh and only 10-100 m in diameter, they may support several distinct vegetation zones. This zonation is likely controlled by the vertical positions of the land, sea, and freshwater table surfaces. We are studying plant assemblages on pimples and the environmental factors influencing them, principally aspect, slope, elevation, depth to fresh water, and nutrient availability. Furthermore, pimples appear to be semi-isolated dune 'islands' within the barrier islands, and, through our research, we are determining the extent of their similarity to larger dunes so that they may be used as natural mesocosms for studying upland ecology on the VCR barrier islands. Multivariate analysis of floristic structure on pimples has demonstrated the importance of the interaction of water table and elevation in determining species distribution. Not surprisingly, water level best explained distribution of most hydrophytes, whereas height above marsh explained presence of xerophytes. Nevertheless, some plants heretofore considered belonging to marsh or dune appeared more plastic in their habitat preferences. Other seemingly generalist species were found to prefer specific aspects, i.e., eastern vs. western exposure. This probably reflects the importance of exposure to salt spray or winds from the ocean. Collection of soil nutrient, water quality, and water availability data has further strengthened analysis of possible factors that create microhabitat differences on these dunes and determine small-scale distributions of individual species.

Key words: 'pimple' dunes, barrier islands, LTER, multivariate statistics