Plant Invasion Patterns in an Urbanizing Landscape: Long-term and Recent Dynamics in the Chicago Area

Invasive species are intimately connected to human activities. Invasion biology is better understood by an explicit incorporation of human activities into patterns and processes of biological invasion. Since human alterations of natural systems are most severe in urban areas, such landscapes are good places to examine myriad patterns and processes of invasive species dynamics in both space and time. Here I present four studies that consider plant invasion patterns in the Chicago area at several spatial and temporal scales.;I found a general lack of connection between land use attributes and invasive plant presence and abundance measures for ten ecologically problematic invasive plant species across a 15 square mile urban to suburban transect. This suggests that stochastic processes are largely responsible for their distributions in the urban landscape. I documented how Pinus nigra (Austrian pine) promotes the growth of woody vegetation in both space and time in a native sand prairie ecosystem at Illinois Beach State Park. I also documented and assessed the presence of nine populations of Conium maculatum (poison hemlock), a non-native species never before detected in Cook County, IL, in a specialized roadside habitat. I measured soil contamination and genetic variables for the known populations but did not find any clear answers that explained its specialized habitat preference. Finally, I assessed the historical rates of spread at multiple spatial and temporal scales for a set of 236 non-native plant species in the Chicago area and Illinois. I found that woody species were significantly enriched among the species that demonstrated the most dramatic gains, at a county scale, for two time intervals in the Chicago area, but not in Illinois as a whole.;This research has conservation implications to the extent that a better understanding of invasive plant dynamics makes it easier to manage conservation areas more efficiently and intelligently. Specifically, Chicago-area land managers should prioritize management against rapidly increasing woody species, and recognize that many invasive plant species may be governed by largely stochastic processes that determine their patterns of abundance and spatial distribution across the urbanized landscape.