Wetlands of the New Jersey Pine Barrens: The Role of Species Composition in Community Function

Abstract

Of the 25% of the New Jersey Pine Barrens that is wetland, about 60% consists of hardwood-dominated or pitch pine-dominated communities. Although these swamps have different dominant trees, the shrub and herb layers share many species, and the types intergrade. Twelve stands representing four variants of these swamps were sampled for species composition, biomass, net primary production and nitrogen dynamics. Pine lowlands, which have large numbers of small trees and a dense layer of small shrubs, have a low total stand biomass (56 mt/ha), but a high NPP (8027 kg/ha per year). Because of physical damage from moving water and flotsam, hardwood swamps affected by stream floodwaters have lower biomass (133 mt/ha) and NPP (5434 kg/ha per year) than do swamps with either short hydroperiods or long hydroperiods of stationary to slowly moving floodwater (biomass 146-150 mt/ha, NPP 5857-6643 kg/ha per year). The absolute and relative abundance of small-stemmed shrubs is correlated with site hydrology; large-stemmed species are found in wet sites, whereas small-stemmed species are found in the drier sites. The shrub species differ in the relative amounts of perennial and leaf tissue. These differences, together with the differences in occurrence of large and small species, account in part for the differences in net production and nitrogen cycling among the wetland types.