COMPARISON OF GAPS AND INTACT SHRUB THICKETS ON AN ATLANTIC COAST BARRIER-ISLAND

Shrub thicket (Myrica cerifera) gaps were sampled on a Virginia barrie r island to elucidate successional mechaisms in the development of mar itime forests. Microclimate, edaphic characteristics and spatial heter ogeneity within gaps, as well as within intact thicket understories, w ere compared for young and aging thickets. Midday photosynthetic photo n flux density in gaps ranged from 5-1000 mu mol m(-2) s(-1), but at t he gap center photon flux density was up to 15% higher for the aging t hicket. Soil temperatures at the surface were 9 C warmer in aging thic ket gaps compared to young gaps, and 6 to 14 C warmer when comparing g aps to the understories for the young and aging thickets, respectively . Edaphic characteristics differed little with thicket age; however, g aps in the aging thicket had greater structural diversity. Species ric hness was 2.5 to 3.7 times greater within gaps than in intact thicket understories, with highest richness within aging thicket gaps. Relativ e to intact shrub thickets, gaps enhance environmental variability; th rough greater structural diversity. Gaps may facilitate the establishm ent of later seral species.