The post-disturbance assembly of vegetation in urban brownfields greatly differs from that in more natural landscapes. One major reason for the difference is the large soil heterogeneity that includes industrial pollution. However, the role of soil heterogeneity on the transition trajectories of vegetation assemblages is largely unknown. In this study, we explored 1) the differences between vegetation transitions in contaminated, heterogeneous and less contaminated more homogenous soils; 2) which plant species have higher fitness on contaminated soils. We selected two areas in Liberty State Park, Jersey City, NJ with contrasting soil contamination levels. Satellite maps of both areas from 2006-2016 were collected from Google Earth. These images were georeferenced in ArcMap and transformed into raster images which were analyzed by Fragstats and compared temporally and spatially. In particular the movements of vegetation boundaries were tracked. Then, following Grime's Plant Strategy Model, we defined each species in the urban brownfield by three traits: the competitive ability (C), dispersal ability (D) and pollution resistance (R). A compound landscape model was constructed to simulate the progression of the ecosystem. After running the model for 10,000 years, we recorded the surviving species in the contaminated site.
Results/Conclusions
Plant diversity increased over time on the heterogeneous and contaminated soil but decreased on less heterogonous and less contaminated soil. Many vegetation assemblages, like the ones dominated by Phragmites australis and by Fallopia japonica, followed different trajectories of transition on the two differing soils. In addition, by observing the boundary movements between assemblages, we found that forest replaced P. australis stands over time on the more homogenous soil, but forest is being replaced by P. australis on more heterogeneous soil. Shrubland were replaced by forest significantly faster on more heterogenous soil. After running a model of 500 hypothetical species with random C, D and R traits on both soils, we classified these species’ states (survived, extinct, killed or saved by contamination) after 10,000 years and plotted their combined strategies in a ternary diagram. Interestingly, species showed a non-overlapping distribution pattern on the plot and the patterns changed with altering landscape and level of contamination. We concluded that the degree of soil heterogeneity and pollution has a large effect on the transition of plant communities. Species with either a combination of pronounced competitive ability (C) and dispersal ability (D) or high pollution tolerance (R) alone, display higher fitness in heterogeneous and contaminated areas.