Plant-scale pattern among herbs and shrubs of a fire-dominated coastal plain forest

Abstract

Herb and shrub layer vegetation was surveyed in the oak-pine upland forest of the Pine Barrens region of New Jersey (USA). To describe spatial distributions of individual species, 15 4 m2 quadrats were censused in each of 34 stands. At the scale of whole stands, stem densities were significantly related to several forms of historical disturbance including canopy defoliation and fire. At the scales of 1 m2 and 4 m2 quadrats, distributions of the 19 most abundant species were all aggregated to some degree, with clonal species more strongly clustered than non-clonal. Shrub stems tended to be strongly clustered, and to be distributed independently of leaf litter. By contrast, tree seedlings were only marginally clustered, and were significantly more common in quadrats with a lower litter cover. Clonal herbs exceeded shrubs in degree of aggregation, but were also sensitive to the local accumulation of leaf litter. Distributions of non-clonal herbs were sensitive to leaf litter, but were only marginally clustered, and appeared to depend upon gaps in the tree canopy. Rather than supporting a single life history, a combination of disturbance types has allowed a variety of species with different ecological requirements and growth forms to coexist in the same site. Overall species diversity can be maintained in this ecosystem without invoking community-level interactions.