Ecologically, upland, remnant-forest patches in urban landscapes represent regional species pools that have been affected a number of climatic, biogeographical, and human filters. By comparison, emergent forest patches in urban landscapes represented urban species pools being influenced by similar filters. Historical data and the comparison to regional species pools indicated that structure and composition of remnant-forest patches were shifting towards shade intolerant, shorter-lived and wind-disseminated species. Emergent-forest patches formed novel communities, which were also dominated by native and non-native species, which were shade intolerant, shorter-lived and wind-disseminated.
Tree species data from New York and Syracuse, New York, were used to illustrate how species patterns varied across urban-rural gradients and the influence of site legacy. Site legacy was defined by two classes: sites with forest cover pre-1940 (remnant) or sites that developed forest cover post-1940 (emergent). Structurally, diameters at breast height (DBH) were group into four diameter classes: 2.5-15.2 cm; 15.3-30.5 cm; 30.6-45.6 cm; and ≥45.7 cm). Species traits were taken from the literature. Patch properties, such as size, perimeter, and nearest neighbor of similar size were measured on aerial photographs.
Results/Conclusions
When compared to regional species pools, remnant-forest patches had similar composition and structure across diameter classes except for the smallest diameter class. In this diameter class, Rhamnus cartartica, an invasive woody species, dominated. Historical data, however, showed that upland-remnant sites in urban landscapes were shifting from long-lived species, such as Quercus and Carya spp., to short-lived species such as Prunus spp. and Betula spp. Overall, these shifts in upland remnant forest patches, do not imply a species debt, but rather shifts in their importance or contribution to the overall forest structure and resulting functions. Structurally, emergent forests had a similar diameter distribution as the remnant patches forests. Compositionally, emergent-forest patches differed from remnant-forest patches. They were dominated by native (Acer negundro) and non-native (A. platanoides) species, both of which were short-lived and wind-disseminated species. The seed source for A. platanoides was street-side trees, planted for shade. The long-term trajectory of these communities is unknown.