Using GIS and floristic quality to assess forests in suburban New Jersey

Forests in suburban landscapes are subject to numerous stresses, from both external land uses and internal ecological processes. In the absence of historical data and quality reference sites, management of these forests requires quantitative metrics to assess the relative importance of external and internal factors in determining their integrity. We sampled forests in 6 county parks in a suburban landscape (Monmouth County, NJ), in order to test the utility of a proposed floristic quality assessment index (FQAI) in integrating determinants of plant biodiversity in these stands. Circular plots (100 m², n= 174) were placed at 100 m intervals along multiple transects across each forest stand. Vegetation, surface soil properties, extent of deer browse, and presence of earthworms were assessed in each plot. We observed 256 vascular plant species, of which 42 were non-native (16%). Species richness (mean=18.9, SE=0.51) was positively correlated with FQAI (r²=0.24, p<0.001); however, non-native species richness and the number of species experiencing deer browse were also positively correlated with FQAI. Spatial patterns of FQAI, invasion, and browse were highly heterogeneous and did not reveal consistent regions of forest health within each park. This result suggests that FQAI alone may not provide an adequate synthesis of the effects of stressors on suburban forests.