Abstract
Coastal geomorphology and vegetation are expected to be particularly sensitive to climate change, because of disturbances caused by sea-level rise and increased storm frequency. Dunes have critical reciprocal interactions with vegetation; dunes create habitats for plants, while plants help to build dunes and promote geomorphological stability. These interactions are also greatly affected by disturbances associated with sand movement, either in accretion (dune building) or in erosion. The magnitude and intensity of disturbances are expected to vary with habitat, from the more exposed and less stable foredunes, to low-lying and flood-prone interdunes, to the protected and older backdunes. Permanent plots were established at three different spatial scales on St George Island, FL, USA, where the vegetation and dune elevation were quantified annually from 2011 to 2013. Change in elevation, either through accretion or erosion, was used as a measure of year-to-year disturbance over the 2 years of the study. At the scale of different dune habitats, foredunes were found to have the greatest disturbance, while interdunes had the least. Elevation and habitat (i.e. foredune, interdune, backdune) were significantly correlated with plant community composition. Generalized linear models conducted within each habitat show that the change in elevation (disturbance) is also significantly correlated with the plant community, but only within foredunes and interdunes. The importance of disturbance in exposed foredunes was expected and was found to be related to an increasing abundance of a dominant species (Uniola paniculata) in eroding areas. The significant effect of disturbance in the relatively stable interdunes was surprising, and may be due to the importance of flooding associated with small changes in elevation in these low-lying areas. Overall, this study documents changes in the plant community associated with elevation, and demonstrates that the foredune and interdune communities are also associated with the responses of specific species to local changes in elevation due to accretion or erosion.
Highlights
Coastal sand dunes provide the first line of defense against storms and high water levels in many parts of the world (Sallenger 2000; Ruggiero et al 2001; Feagin et al 2005)
Vegetation on the dunes varied among habitats, as shown by the nonmetric multidimensional scaling (NMDS) (Fig. 4), with a significant effect of habitat (F 1⁄4 56.1, P, 0.001) and replicate grid nested within habitat (F 1⁄4 10.1, P, 0.001)
Few studies have correlated disturbance in dunes with plant community composition and no prior studies have investigated how the effect of disturbance varies at different spatial scales
Summary
Coastal sand dunes provide the first line of defense against storms and high water levels in many parts of the world (Sallenger 2000; Ruggiero et al 2001; Feagin et al 2005). Coastal ecosystems are sensitive to sea-level rise and any changing frequencies of tropical storms and hurricanes, all of which are predicted to occur with global climate change Duran and Moore 2013; Prisco et al 2013) These climate effects may be especially important because dunes have a high ecosystem value as habitat for endemic plants and animals, while sheltering bay (e.g. seagrass, oyster beds and saltmarsh) habitats, as well as inland wetlands and marshes (Martinez and Psuty 2004; Gutierrez et al 2011). The vegetation on dunes has served as a model system for influential studies of plant succession and ecology (Cowles 1899; Oosting and Billings 1942); because dunes form near shore, dunes that are progressively inland create chronosequences for vegetation studies
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