Ecological restoration drives differences in functional composition of native and non-native plant communities in urban forest patches

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Sara M. Do and Lea R. Johnson, Department of Plant Science and Landscape Architecture, University of Maryland, College Park, MD, Lea R. Johnson, Division of Research and Conservation, Longwood Gardens, Kennett Square, PA

Background/Question/Methods
Urbanization transforms landscapes, affecting biodiversity and ecological functions as species are filtered out by altered conditions. To restore ecological processes, functions, and native biodiversity, municipalities have turned to ecological restoration of urban forest patches. While changes in functional composition and diversity have been indicated as a measure of restoration success, little is known about the effect of ecological restoration on the functional composition of native and non-native plant communities in urban forest patches. To test whether ecological restoration drives changes in the functional composition of native plant communities differentially from non-native plant communities, we sampled 30 sites dominated by invasive plants in New York City Park forest patches where ecological restoration was begun 15-20 years prior, and 30 sites in NYC Park forest patches that were similarly dominated by the same set of invasive plants but did not undergo any ecological restoration during the same period. Using data describing 12 functional traits, we calculated community weighted means for functional composition of each trait for native and non-native plant communities.
Results/Conclusions
Ecological restoration drove changes in the functional composition of native and non-native plant communities. Functional traits of native and non-native plants significantly differed between restored and unrestored sites. In restored sites, there were more native plants with seeds dispersed by hoarding (p = 0.006) and fewer non-native lianas (p = 0.0001). These trends reflect the success of restoration techniques that removed invasive vine species and planted native, later-successional native species with large seeds. Restored sites also had more native and non-native tree stems (p = 0.005 and p = 0.0037, respectively) and fewer native and non-native plants dispersed by endozoochory (p = 0.0009 and p = 0.0004, respectively). There were more wind pollinated native plants in restored plots (p < 0.0001), while wind pollinated non-native plants had similar abundances between restored and unrestored plots. This difference was driven by the planting and regeneration of native tree species and further reflects the success of planting later-successional native trees with wind pollination. This study provides insight into how ecological restoration affects the functional composition of native and non-native plant communities that can help inform the management of native plant communities in urban areas.