Urban forests are poorly defined as ecological communities. Substantive links between anthropogenic landscape features and forest ecology are lacking. ‘Urbaness’ is commonly defined by human population density or land use classifications, but their use is inconsistent throughout the literature, and rarely is linked with ecological processes. Furthermore, it is unknown whether urban forests are functioning parts of a patchy urban woodland system or isolated islands amidst an ocean of unsuitable habitat. I first used digital satellite imagery and publicly available U.S. National Park data to link urban land use with forest processes. I then linked those land use classifications with the potential for urban forests to regenerate by investigating tree recruitment in the greater Buffalo, NY (U.S.) metropolitan area. If urban forests link with the greater regional forest ecosystem, then tree species richness should resemble the regional forests. However, if the urban forest patches are isolated, they should contain a subset of the regional forest richness with recruitment limited by forest patch size. Heavy urban cover predicted reduced tree and seedling richness and abundance. Moreover, tree seedling richness decreased with increasing urban land use. Tree seedling richness and abundance both declined when invasive species were present, suggesting invasive species may act as a barrier to tree recruitment. Tree recruitment was more strongly linked with forest patch size than the regional species pool, and active dispersal was limited to wind-dispersed species between urban forests. These results suggest that urban forests are isolated forest islands surrounded by an ocean of urban habitat
