Secondary Succession, Gap Dynamics, and Community Structure in a Southern Appalachian Cove Forest

Clebsch, Edward; Busing, Richard

Forest succesion was studied in a species-rich cove forest of the Great Smoky Mountains, Tennessee. Long-term compositional and structural changes in secondary stands, 15-63 yr after agricultural abandonment circa 1920, were compared to an adjacent old-growth stand. Later successional trends were projected by computer simulation. The colonizing stand (15 yr) was dominated by Liriodendron tulipifera and Robinia pseudoacacia. Common old-growth species absent at this early stage included Aesculus octandra, Fagus grandifolia, and Tsuga Canadensis. By year 40, Liriodendron dominated the overstory and all old-growth dominants were represented in the understory. After 60 yr, Acer saccharum was clearly the most abundant understory species; gap model projections indicated that after 200 yr it will dominate the forest. The actual old-growth stand was dominated by Acer saccharum. Species richness peaked at mid-succession (@?50 yr), while diversity (H') and evenness (J') of species biomass were highest at the old-growth stage. Richness peaked with the coexistence of shade-intolerant colonizers in the overstory and shade-tolerants in the understory. Canopy-gap processes of the secondary and old-growth stands differed sharply. The old-growth canopy was composed of large, spreading, and overlapping crowns, while the second-growth stand was composed of narrow, nonoverlapping crowns. Gaps in the secondary stand tended to be small (<100 m^2) but numerous. The regeneration of intolerants was low and individual gap microsites were not markedly different from the understory as a whole. Old-growth gaps were often larger, higher light microsites which contrasted sharply with the shaded forest floor. The wider range of gap sizes in old forests accommodates a variety of species, including intolerants, contributing to the high canopy species diversity of old-growth cove forests.

Secondary Succession, Gap Dynamics, and Community Structure in a Southern Appalachian Cove Forest

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