SPATIAL AND TEMPORAL GROWTH DYNAMICS OF BARRIER-ISLAND SHRUB THICKETS

Spatial and temporal dynamics of barrier island shrub thickets were in vestigated on Hog Island, a barrier island along the Eastern Shore pen insula of Virginia. The island thickets are dominated by the actinorhi zal shrub, Myrica cerifera. On the accreting, northern half of the isl and, thickets expanded as swale area increased. Analysis of aerial pho tographs revealed that total thicket area increased by nearly 400% fro m 1949 to 1989, paralleling a substantial increase in area for the nor thern portion of the island. Thicket characteristics varied with the a ge and position of the three field sites on Hog Island. At the younges t 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 (approximate to 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 ac cretion. After the stabilization of new land, seedlings establish and grow rapidly to form a thicket. Once established, a thicket rapidly ex pands in the relatively protected, mesic swale environment. Thicket de cline follows, characterized by an increase in vine growth on and arou nd the shrubs and the formation of gaps as the thicket breaks up. Spat ial variation in M. cerifera thickets on Hog Island is related to leng th of time soils have been stabilized and, especially, to time since t hicket establishment.