SPECIES-DIVERSITY AND SMALL-SCALE DISTURBANCE IN AN OLD-GROWTH TEMPERATE FOREST - A CONSIDERATION OF GAP PARTITIONING CONCEPTS

The importance of spatial partitioning of gap resources in the mainten ance of tree species diversity was studied in an Appalachian old-growt h forest. We established three I-ha plots, subdivided into contiguous 10 x 10 m subplots, in a mesic cove forest with a disturbance regime c haracterized by small canopy gaps (<0.1 ha). For tests of partitioning along the gradient from gap interior to the shaded understory, canopy cover of each subplot was classified as gap, gap border, or non-gap. For tests of gap-size partitioning, gap and gap border subplots were c lassed by gap size. Species-accumulation curves for the regeneration s tratum (stems >1.37 m tall and less than or equal to 10 cm DBH) based on: (1) species per unit area, and (2) species per individual were plo tted for each of the canopy cover classes and for all subplots combine d. The species-area curve for gaps was steeper than the all-subplots c urve that represented the entire gradient from gap centers to the shad ed understory. By contrast, all of the species-individuals curves were similar. Sorrenson's indices showed that only gap subplots, particula rly those associated with large gaps, had highly self-similar species composition. Furthermore, the relative abundance of most species was s imilar between gaps and the shaded understory. However, intolerant spe cies often had higher relative abundance in gaps, especially in gaps g reater than or equal to 0.04 ha in size. We concluded that gap partiti oning hypotheses applied to some intolerants, but not to tolerants. Th e density hypothesis, a null model attributing species richness levels to stem density levels, largely explained the richness patterns in ou r study forest.