Comparison of Gaps and Intact Shrub Thickets on an Atlantic Coast Barrier Island

Abstract

Shrub thicket (Myrica cerifera) gaps were sampled on a Virginia barrier island to elucidate successional mechanisms in the development of maritime forests. Microclimate, edaphic characteristics and spatial heterogeneity within gaps, as well as within intact thicket understories, were compared for young and aging thickets. Midday photosynthetic photon flux density in gaps ranged from 5–1000 µmol m−2 s−1, but at the gap center photon flux density was up to 15% higher for the aging thicket. Soil temperatures at the surface were 9 C warmer in aging thicket gaps compared to young gaps, and 6 to 14 C warmer when comparing gaps to the understories for the young and aging thickets, respectively. Edaphic characteristics differed little with thicket age; however, gaps in the aging thicket had greater structural diversity. Species richness was 2.5 to 3.7 times greater within gaps than in intact thicket understories, with highest richness within aging thicket gaps. Relative to intact shrub thickets, gaps enhance environmental variability through greater structural diversity. Gaps may facilitate the establishment of later seral species.