Links between soil and plant community composition patterns in an urban wildland

Background/Question/Methods

Vegetation successional pattern was studied on an extensive, urban brownfield located in Liberty State Park in Jersey City, New Jersey. This former rail-yard site –partly polluted by heavy metal contaminants - revegetated during 40 years of land abandonment largely unaided and developed into a rich mosaic of plant communities that form today one of the largest urban wildlands in the region. The current plant assemblies are a unique mix of native and non-native plant species, thus forming novel communities. We asked (1) whether the current mosaic of vegetation pattern can be explained by current soil factors and (2) what soil factors promote the formation and sustainability of species diversity. During the summer of 2008, plant species composition, community richness and soil variables at different community types of the study area were measured and analyzed with multivariate methods in order to find a correlation that help to explain the current mosaic of vegetation.

Results/Conclusions

Six main vegetation groups were identified: pioneer forest, tall herbs (with dominant, non-native Artemisia vulgaris and Solidago spp.), shrubland (Rhus spp.), grassland (Festuca rubra, Calamagrostis epigeos, and Panicum virgatum savannah), species rich open herb/grassland assembly. Multivariate data analysis was applied regarding soil characteristics as environmental variables. The CCA ordination diagram revealed that soil characteristics such as soil depth, NPK, Al content as well as heavy metal loads (Pb, Cr, Cd) were the strongest factors affecting the spatial distribution of species. Highest marginal effects were showed by Ni (lambda-1=0.62), P (lambda-1=0.53), and K (lambda-1=0.49) content, soil elements which explained a high share of the variance as single variables, but the conditional effects indicated that only P (p=0.002), K (p=0.032) content and soil depth (p=0.05) qualified for the final model to explain species composition.  Non-native species contributed markedly to local species diversity and hot spot of species richness were retained largely in areas with low NPK loads and shallow soils.  This suggests the importance of environmental stress in maintaining biological diversity during succession.