A comparison of brownfield and old-field plant communities: how site history shapes current patterns of diversity

This dissertation examines the early-successional plant communities that spontaneously establish on brownfields, former industrial sites that remain vacant due to the presence of contaminants, with a comparison to old-field plant communities on former agricultural sites. Brownfields are common in urban areas including most of the Mid-Atlantic region of the United States. Though these sites are a major component of the landscape in areas with history of industry, their ecology has not been extensively studied in North America. Some brownfields remain in early stages of succession for decades, structurally resembling the vegetation of formerly agricultural old fields less than 20 years since abandonment. As more is known about the ecology of old fields, comparing early-successional brownfield and old-field plant communities in New Jersey will provide information on how brownfields are different from the more common early-successional habitat of the region. Through soil analysis and field surveys of six brownfields and seven old fields over two years, a greenhouse experiment testing effects of individual brownfield soil characteristics, and competition experiments in the field and the greenhouse, this dissertation investigates three hypotheses: 1) Brownfield and old-field early-successional communities are different; 2) Non-native species are more abundant in brownfields than old fields; 3) Plant community differences between brownfields and old fields are driven by the difference in environmental stress between the site types, primarily due to metal contamination in brownfields. Soil analysis found that brownfield soils were not all contaminated at the surface with heavy metals, but they had higher gravel and sand content and lower total nitrogen than old-field soils. Brownfield and old-field communities were found to be different by site type in all seasons surveyed. Old fields had higher cover of native forbs, resulting in higher vegetation cover overall than in brownfields. Brownfields and old fields had similar species richness, phylogenetic diversity, and trait diversity. Native species were not more negatively affected by brownfield soil conditions in the greenhouse experiment than were non-native species, and all species were more limited by low-nutrient treatments than a metal contamination treatment. The competition experiments found that a dominant non-native, Artemisia vulgaris L., and a dominant native forb, Solidago canadensis L., were equally matched in brownfield and old-field soils, but that transplants of the native species sourced from old fields reached greater heights and final biomass values. Together the approaches show that differences between the two community types are more due to traits rather than native status of species. The dissertation concludes, brownfield early-successional plant communities are different from old-field communities because the higher environmental stress in brownfields, from a variety of soil characteristics, limits the species composition of the brownfield community to species with stress-tolerant traits while higher competition in old fields limits the species composition of the old-field community to species with competitive traits.Ph.D.Includes bibliographical referencesby Julia Perzle