FRAME program results: The ecology of forest fragments in managed ecosystems
Within human-dominated temperate zone landscapes, small deciduous forest fragments comprise the majority of habitat available to the plant and animal diversity dependent on the structure and environment created by trees. The 100 km coastal band of the eastern US in particular brings together extremely high human population densities and many small forest fragments. In addition to abiotic stressors such as heat island effects and pollution, many urban forests are further altered into "novel ecosystems" dominated bu nonnative invasive plants. To lay a solid foundation for studies urban forest ecology, we randomly selected 32 sites along a range of urbanization in the US states of Delaware and Pennsylvania and Delaware. These sites were gridded on 25 m. Data on soil, litter, vegetation at all heights, arthropods, birds, and small mammals were collected from 10-25 points within each site, depending on site size, and analyzed using a variety of statistical methods.
Despite their relatively close proximity to each other, the 32 forest fragments included in the FRAME showed a wide range in age (50-150 y), soil characteristics, tree composition, and vegetation. Invasion by nonnative plants ranged from 0-86% of stems at study points. Strong correlations were seen between leaf litter depth and nonnative plant density, black-legged tick density, and soil Ca levels. Best models selected under AIC showed the density of nonnative plants to be the best predictor of territory density for several bird species, and for total bird territory density. Our findings support the value of further exploration into the varied role of nonnative plants in the forest understory.