THE RELATIONSHIP BETWEEN THE SOIL SEED BANK AND ABOVEGROUND VEGETATION OF A COASTAL BARRIER-ISLAND

The germinable soil seed bank is described from a coastal barrier isla nd off the northwest coast of Florida, USA. Soil samples collected fro m seven vegetation types, recently deposited dredge spoil and unvegeta ted areas in autumn 1990 and spring 1991 were placed out in greenhouse trays. 110 taxa germinated from the samples with the largest number ( 41) being C-3 perennial dicots. The largest number of taxa germinated from dry (57) and wet (54) swales, the fewest (one species: Heterothec a subaxillaris) from strand. Similarity of seed bank densities to abov e-ground species cover was low (Jaccard's Index = 0.36), not different between vegetation types, but higher in the autumn than in the follow ing spring. Compositional gradients in the seed bank and above-ground vegetation determined using DCA ordination were highly correlated and related to distance from mean high water, and plot elevation. At the l andscape scale, the seed bank provided an equally clear delineation of vegetation types to that based upon the above-ground vegetation. The seed bank of low disturbance, late-succession vegetation types (wooded dunes, swales, marshes) was well developed (high species richness, em ergent density, and percentage annual species) with the exception that the large-seeded woody species (i.e. Quercus spp.) were absent from t he wooded dune seed bank. By contrast, a poorly developed and transien t seed bank occurred in more frequently disturbed (extensive sand move ment, salt spray), early successional dredge spoil, unvegetated areas and strand. These contrasts support a general pattern of increasing se ed bank development and a persistent rather than transient seed bank w ith decreasing disturbance frequency, increasing time since disturbanc e and successional maturity.