Relationships between plant invasion and residential expansion across the eastern United States

Kevin M. Potter, Department of Forestry and Environmental Resources, North Carolina State University, Research Triangle Park, NC, Kurt H. Riitters, Eastern Forest Environmental Threat Assessment Center, USDA Forest Service, Research Triangle Park, NC, Songlin Fei, Forestry and Natural Resources, Purdue University, West Lafayette, IN and Basil V. Iannone III, School of Forest Resources and Conservation, University of Florida, Gainesville, FL

Background/Question/Methods
Global urban land cover is projected to increase threefold between 2000 and 2030. Urban areas can support native biodiversity, however they also can negatively impact nearby natural ecosystems in ways such as contributing to biological invasions. Despite our current understanding of urban expansion and mechanisms of plant invasion, studies exploring effects of urban expansion on plant invasion within the wildland-urban interface using data collected at finer scales across large geographical areas and time periods are limited. Here we present findings of regional-scale analyses conducted to fill this research gap. Using the eastern United States as our study region, we utilize two national datasets spanning longer time periods (USFS Forest Inventory and Analysis [FIA] and wildland-urban interface [WUI]) to determine (1) the degree to which rates of urban expansion (changes in ratios of housing density to percent vegetation) relate to current patterns of forest invasive plant species richness and cover, (2) the degree to which interface vs. intermix WUI relate to invasion patterns, and (3) to identify temporal lags in these relationships. Mixed-effects models are used in order to account for potential variability in relationships among ecological sections.

Results/Conclusions
Preliminary analyses reveal that changes in housing density are weakly positively related to regional invasion patterns, with the stronger of these relationships occurring between invasion patterns and earlier rather than more recent time periods of residential expansion, indicating invasion lag. Additionally, the strengths of these relationships vary within our study region among ecological sections. Understanding relationships between plant invasion patterns and urban expansion can provide insight on how localized mechanisms of invasion, such as propagule pressure or disturbance, contribute to regional invasion patterns. Next steps for this research include determining the effects of plant traits and overreliance on a limited plant species pallet for landscaping on longer-term invasion patterns.