The effect of gap dynamics on the size and spatial structure of Solidago sempervirens on primary coastal dunes

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Abstract. The role of gap dynamics in shaping the spatial and size distributions of the gap specialist Solidago sempervirens (seaside goldenrod) were examined on the primary dune grassland (Ammophila breviligulata, American beachgrass) of an Atlantic barrier island. Results suggest that coastal dune blowouts are patchy disturbances that allow S. sempervirens to temporarily establish and disperse seed. Natural measurements and clipping experiments demonstrated that A. breviligulata competitively dominated S. sempervirens in undisturbed grasslands. Coastal dune blow‐outs reversed this dominance by temporarily burying A. breviligulata and increasing densities and above‐ground biomass of S. sempervirens. Examination of size/density distributions of S. sempervirens suggested that blow‐outs were seed sources but not regeneration sites. Regeneration was found primarily in neighboring transition and undisturbed grassland areas. Comparison of lateral growth by A. breviligulata on blow‐out margins suggested that disturbances were closed by lateral encroachment from gap edges. After blow‐out recovery, greater densities and skewed size distributions of S. sempervirens could still be detected for a number of years after blow‐out recovery.