The influence of contrasting ground cover vegetation on soil properties in the NJ pine barrens

Abstract

Upland forests of the New Jersey pine barrens are characterized by a pine and oak forest canopy. The herbaceous layer consists primarily of ericaceous shrub species. Scattered throughout the region grass-sedge and lichen–moss dominated patches under a pine canopy can also be found. It is generally believed these patches come about after severe disturbance. These patches can persist even in the absence of further disturbance. In this study, examples of three herb layer community types: ericaceous (predominantly Gaylussacia baccata Wang.), graminoid (almost exclusively Carex pensylvanica Lam.) and lichen–moss dominated communities (Cladonia spp. and Polytrichum juniperinum Hedw.), in close proximity to one another, from three different forest locations were examined. We determined whether graminoid and lichen dominated communities differ significantly in edaphic factors from the surrounding forest herbaceous layer vegetation matrix (ericaceous dominated community). In order to characterize the sites canopy and herbaceous layer vegetation and surface cover were assed. Soil particle size, soil carbon, respiration, microbial biomass and extractable nitrogen were also determined. Our analysis found only minor differences in forest canopy vegetation and no difference in soil particle size among forests or among communities. The results further suggest that differences in soil chemical parameters are the result of differences in the vegetation rooting architecture and decomposability. The lichen–moss dominated communities are distinguished by more bare ground, low bulk density, low nitrogen availability and a preponderance of microbial biomass in the upper 5cm of the soil profile. The high soil bulk density in lichen communities is presumably a function of its smaller root biomass content, greater percent bare ground cover and lower litter inputs. The ericaceous dominated communities are distinguished by greater presence of tree seedlings, low bulk density, lower nitrogen availability a large above ground biomass (AGB) and below ground biomass (BGB). Despite a significantly greater overall AGB the ericaceous community leaf mass is no larger than the graminoid community leaf mass or lichen–moss dominated community AGB. The graminoid dominated communities were distinguished by higher levels of extractable ammonium, soil organic matter (SOM) as represented by loss on ignition (LOI). Although the communities did not vary significantly in soil particle size the Pearson correlation analysis indicates that the significantly greater levels of soil carbon, ammonium and nitrate characteristic of the graminoid community are positively correlated with % silt–clay and negatively correlated with sand. Our results suggest that the subtle physical and chemical property differences between each of the communities may be due to a biogenic origin. This may explain, at least in part, the persistence of differing herb layer community type dominance.