Background/Question/Methods
Urban forest ecosystems provide numerous services to improve the well-being of humans. Urban forest composition and diversity are key to the provision of these services. However, these urban forest characteristics often differ from their peri-urban and rural counterparts, arising from inherently different natural and anthropogenic processes and drivers. This research tests the hypothesis of ecological homogeneity of urban ecosystems by focusing on urban tree diversity. Specifically, is the variation between urban and peri-urban forests greater than that of variation along geo-climatic lines in the southeastern US? This study investigated this variation using data from the USDA Forest Service’s Forest Inventory and Analysis program, as well as a newly created, standardized regional urban forestry database with urban forest data from eight urban ecosystems in the southeastern US collected using the USDA Forest Service’s i-tree/Eco protocol. These data include basic forestry measurements and a host of other tree and plot-level environmental variables such as ground covers, land use, and distances to adjacent structures. We compare across urban/peri-urban and eco-zone classifications, utilizing species-accumulation analyses, similarity indices, and PERMANOVA to answer questions about the drivers of differences in species composition and size structure and test hypotheses about ecological homogenization.
Results/Conclusions
In general, species richness was greater in urban versus peri-urban forest ecosystems. Species richness was greater in urban ecosystems, likely due to non-native plantings (of which there is a greater proportion in urban areas versus peri-urban areas). However, in Abingdon, Virginia, estimated species richness was approximately equal in urban versus non-urban ecosystems. We hypothesize that this may be an artifact of sampling in a less populous, more highly forested locality. Similarity indices indicated that urban and peri-urban forest ecosystems were more similar to each other within an eco-zone than were different urban forests across the study region. This result refutes the hypothesis of ecological homogeneity within urban areas, as measured using tree diversity; the urban forests resembled their peri-urban counterparts. However, PERMANOVA results were contrary; tree species composition of urban forests was significantly different than peri-urban ones, but significant differences also were found among urban ecological provinces.