As urbanization increases, many of the remaining large green spaces in densely populated areas are abandoned post-industrial brownfield sites. These areas are well-studied in Europe, but remain relatively under-researched in North America. We began by observing differences between brownfield floras and floras of similarly disturbed, but unpolluted old fields in New Jersey. We then sought quantitative answers to the following questions: 1. How are brownfield floras different from old-field floras? 2. What site and soil characteristics differentiate brownfield floras? We conducted vegetation surveys at seven old fields and six brownfields in spring, summer, and fall. We collected and analyzed soil samples for texture, nutrients, organic matter, pH, salts, total nitrogen, total carbon, and heavy metals. We explored the composition and structure of old-field and brownfield vegetation across seasons with a multivariate analysis of variance and non-metric multidimensional scaling. We also ran two greenhouse experiments using perennial species from the Asteraceae family commonly found in either brownfields or old fields. One experiment mimicked different soil conditions found in brownfields. The second was a competition experiment of a non-native dominant brownfield species, Artemisia vulgaris, with a native dominant old-field species, Solidago canadensis, in brownfield and old-field soil.
Results/Conclusions
There was no significant difference between brownfield and old-field floras in species richness, evenness, or non-native cover. We found brownfields to have significantly lower Shannon diversity in spring and lower total and native cover in all seasons. Many native species are present in brownfields, but are not reaching degrees of dominance that they do in old fields. An experiment with different soil conditions showed that low nutrients reduced growth in all species more than heavy metals. A competition experiment failed to demonstrate an expected difference in performance between the dominant native and dominant non-native in either soil type. While results are limited by greenhouse conditions and duration of one growing season, they indicate that heavy metals may not be the determining factor limiting the growth of dominant native species in brownfields. Gravel and sand content of the soil have significant negative correlations with percent cover of natives in the survey data. Nutrient and water stress resulting from soil with high gravel/sand content may be the most important factors differentiating brownfield and old-field floras. We predict a difference in general stress tolerant traits between these floras, rather than a difference in specific adaptations for metal tolerance.