Secondary succession in disturbed and abandon urban areas such as brownfields is largely under studied. Yet, brownfields are prevalent in the United States with over 450,000 sites throughout the country, many of which are in urban areas. While there are many different amalgamations of species composition found on urban brownfields, most studies reveal two themes: an alternative stable state of vegetation or the advent of late successional species over time. However, to our knowledge no study to date has shown long-lived climax succession trees of northeastern U.S. forests inhabiting and tolerating conditions found on brownfields. We ask: does heavy metal contamination preclude long-lived species, such as oaks, from establishing on brownfields? Our study was conducted in Liberty State Park (LSP) in Jersey City, NJ. Within LSP is a 102 ha of the park remains closed to the public because it is classified as a brownfield due to metal concentrations that exceed the normal trace amounts of unaltered soil types. Within the brownfield is a pioneer forest that colonized over 50 years ago. We replicated 700 meter (m) long, 10m wide vegetation belt transects originally conducted in 2003 during the fall of 2012. In the fall of 2014 we conducted 30m vegetation radius plots to focus on community composition. The purpose of these transects was to document late succession tree with a primary focus on oaks. During the surveys tree genus and species, diameter breast height (DBH), tree height, GPS coordinates and field site descriptions were recorded. We used vegetation and metal gradient map overlays in QGIS to understand oak habitat preference.
Results/Conclusions
We found two species of oaks, within the brownfield at LSP: Quercus rubra (northern red oak) and Quercus coccinea (scarlet oak). Surprisingly, 74% of all oaks were found in high metal sites: 87% Quercus rubra and 61% Quercus coccinea. 78% of all oaks were found in pioneer forests: 77% Quercus rubra and 80% Quercus coccinea. There were no significant differences for oak DBH or height between metal loads or vegetation type. Likely due to the lack of seed sources, late successional trees such as oaks are still relatively sparse in the studied site, even after more than 50 years of succession. However, we can rule out soil pollution as an important hindering factor for the establishment of late successional trees. Furthermore, oaks may associate with pioneer forest because the pioneer tree species may amend soil, therefore facilitating oak colonization.