Throughout the world, the Anthropocene has ushered in an era of intensive urban growth in the temperate deciduous forest biome. This has inevitably meant fragmentation of remaining forests: for example, the 100 km coastal band of the eastern US brings together extremely high human population densities and many small urban forest fragments. While the ecosystem services provided by these green spaces are now being measured and appreciated, they are also threatened by unintended changes from the ground up: soil contamination and nonnative plant invasion. We focussed on soil and plants to establish a basis for subsequent studies of higher trophic levels, selecting plots in a network of forest fragments along an urban-rural gradient in Delaware and Pennsylvania. These plots form the basis of a long-term research program we named FRAME (Forest Fragments in Managed Ecosystems). Plots were successfully established. We measured soil chemistry, volume of leaf litter and coarse woody debris, percent ground cover, stem density of woody plants, tree basal area, and landscape metrics, as well as earthworm, tick, and bird population characteristics.
Results/Conclusions
While our plots cross major physiographic provinces, the Atlantic Coastal Plain and the Piedmont, certain characteristics were observed to hold across urban forest plots. They were characterized by a predominantly native tree overstory and nonnative plant understory, with considerable heterogeneity from one plot point to the next. The most abundant invader was the shrub Rosa multiflora; other important invasive genera included Celastrus spp. and Lonicera spp. Levels of exchangeable Ca, and metals such as Zn and Cu, were elevated in comparison to similarly situated sites in less urban settings. This elevated Ca was also closely correlated with increases in invasion by nonnative plants and earthworm abundance, while nonnative plant invasion was in turn associated with increases in the density of bird territories and ticks. Our findings set the stage for manipulative studies to explore the cascading effects of invasive plant invasion and subsequent removal.