Date of Award

Winter 2007

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Ecological Sciences

Committee Director

Frank P. Day

Committee Member

Joseph Rule

Committee Member

G. Richard Whittecar

Committee Member

Donald R. Young


The habitats at the VCR LTER that were the focus of the current study are the Hog Island and Parramore Island 'pimples', small, rounded dunes forming along main dune ridges of the barrier islands. There are distinct plant assemblage zones found on pimples, although most of these dunes are 10–20 m in diameter. Hypotheses of the study were that fresh water availability was a main determinant of differences between assemblages and that pimple size and location would influence diversity and assemblage structure. Research goals were (1) to describe the plant assemblages on pimples, (2) to relate edaphic and geomorphological factors to pimple assemblage diversity and composition at different spatial scales, and (3) to compare assemblage—environment interactions on pimples and main dune ridges. Accomplishing these goals entailed field vegetation surveys of a representative sample of pimple and dune plant assemblages and environmental monitoring. There were distinct assemblage types that segregated themselves by habitat type: marsh, shrub thicket, and dry summit. Shrub assemblages were less diverse than either marsh or summit habitats. There was no relationship between pimple size and diversity or location. Differences in diversity and composition among pimples were as great as differences among transects within pimples. Pimple diversity and species composition were different from the main dunes. Fresh water availability was important in differentiating differences, both among transects and among species, but it was not the only important factor. Nutrients, such as boron, were also important in describing variation among species. It is likely that interactions between water and other factors (e.g. the accumulation of some mineral nutrients in the marsh after they are leached from the dune summits) are the most important determinants to species abundances. A secondary goal was to evaluate ordination techniques used in pattern detection throughout the study. Canonical correspondence analysis and non-metric multidimensional scaling performed best overall. CCA, which is a direct gradient analysis, described groups of transects and species that largely matched my a priori assumptions. Furthermore, it provided correlation data about species—environment relationships that were equivalent to multiple regression. NMS, a distance-based, indirect-gradient method, described high percentages of variation (> 80%) in the first two or three axes, but relationships between environment and species abundances had to be inferred. Bray-Curtis ordination and especially principal components analysis did not explain as much variation in the data.


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