Geomorphological controls on coastal vegetation at the Virginia Coast Reserve

Automatic land cover classification maps were developed from Airborne Hyperspectral Scanner (HyMAP) imagery acquired May 8, 2000 over Smith Island, VA, a barrier island in the Virginia Coast Reserve. Both unsupervised and supervised classification approaches were used to create these products to evaluate relative merits and to develop models that would be useful to natural resource managers at higher spatial resolution than has been available previously. Ground surveys made by us in late October and early December 2000 and again in May, August, and October 2001 and May 2002 provided ground truth data for 20 land cover types. Locations of pure land cover types recorded with global positioning system (GPS) data from these surveys were used to extract spectral end-members for training and testing supervised land cover classification models. Unsupervised exploratory models were also developed using spatial-spectral windows and projection pursuit (PP), a class of algorithms suitable for extracting multimodal views of the data. PP projections were clustered by ISODATA to produce an unsupervised classification. Supervised models, which relied on the GPS data, used only spectral inputs because for some categories in particular areas, labeled data consisted of isolated single-pixel waypoints. Both approaches to the classification problem produced consistent results for some categories such as Spartina alterniflora, although there were differences for other categories. Initial models for supervised classification based on 112 HyMAP spectra, labeled in ground surveys, obtained reasonably consistent results for many of the dominant categories, with a few exceptions.

Automatic classification of land cover on Smith Island, VA, using HyMAP imagery

Spatial and temporal dynamics of barrier island shrub thickets were investigated on Hog Island, a barrier island along the Eastern Shore peninsula of Virginia. The island thickets are dominated by the actinorhizal shrub, Myrica cerifera. On the accreting, northern half of the island, thickets expanded as swale area increased. Analysis of aerial photographs revealed that total thicket area increased by nearly 400% from 1949 to 1989, paralleling a substantial increase in area for the northern portion of the island. Thicket characteristics varied with the age and position of the three field sites on Hog Island. At the youngest site examined (20 yr), recruitment and shrub growth were high. Shrub growth remained high and recruitment continued in the stable central portions of the island (50 yr). However, at the oldest site near a bay side salt marsh (z 130 yr), recruitment was not evident, shrub growth was reduced, and mortality was most apparent. Several "life stages" for shrub thickets were identified relative to island accretion. After the stabilization of new land, seedlings establish and grow rapidly to form a thicket. Once established, a thicket rapidly expands in the relatively protected, mesic swale environment. Thicket decline follows, characterized by an increase in vine growth on and around the shrubs, and the formation of gaps as the thicket breaks up. Spatial variation in M. cerifera thickets on Hog Island is related to length of time soils have been stabilized and, especially, to time since thicket establishment.

Spatial and temporal growth dynamics of Barrier Island shrub thickets

The importance of salinity to small-scale distribution patterns was examined for three shrubs common on barrier islands of the southeastern United States. Field measurements focused on the salt mar...

Salinity and the small-scale distribution of three barrier island shrubs

Flood sensitivity of five woody species common to barrier island swale habitats was quantified in a glasshouse study to examine potential mechanisms affecting observed small-scale distribution patterns. Differential response to short-term (30 d duration) freshwater and saltwater flooding occurred among the five species. OnlyBaccharis halimifolia was sensitive to freshwater flooding. At both low (2 and 5 g L−1) and mid-range (10 g L−1) salinity,Myrica cerifera, Pinus taeda, andB. halimifolia were more sensitive thanJuniperus virginiana orIva frutescens. At low salinity, stomatal conductance was significantly reduced forM. cerifera, P. taeda, andB. halimifolia, although recovery occurred and there was no mortality. At midrange salinity, all five species showed reduced stomatal conductance, but recovery differed. Mortality was highest forM. cerifera andB. halimifolia (60%), followed byP. taeda (40%),I. frutescens (25%), andJ. virginiana (20%). In contrast, 100% mortality occurred for all species in high salinity treatments of 20 and 30 g L−1. Interspecific differences in response to flooding may be a mechanism affecting small-scale distribution patterns of woody species in barrier island swales.

C. A. McCaffrey

Papers

Plant associations on the Virginia barrier islands.