Non-native invasive plants are a global threat to natural and agricultural ecosystems, but the landscape characteristics promoting invasion are still poorly understood. Edge habitat often has been linked to invasion, and as natural habitats become more fragmented due to development and agriculture, the amount of edge increases exponentially. Conservation linkages (e.g. highway undercrossings, hedgerows, and riparian corridors) are widely promoted to combat the negative effects of fragmentation, but an often-discussed though understudied fear is that linkages will also aid non-native plant movement. As part of a broader study to address this potential problem, I examined a class of archetypal habitat linkages: hedgerows, linear strips of non-agricultural land that parallel field edges. In California’s agricultural lands, hedgerows are being promoted and planted at a steadily increasing rate. These features capture quintessential linkage characteristics: relatively narrow, linear shape and potential to aid movement. I am examining the patterns and mechanisms of invasive plant movement into, out of, and through these linear landscape features, emphasizing the role of edge effects and linkage structure. In the summer of 2009, I surveyed native and non-native plant richness and abundance in hedgerows within Yolo County.
Results/Conclusions
These surveys confirm that hedgerows do harbor a rich flora of invasive plants and that invasion is spatially structured between different axes of the hedgerows. Edges are more invaded than interiors in both richness and percent cover but hedgerow ends do not differ significantly from the middle. I discuss how these patterns are dependent on key landscape variables, including hedgerow orientation, age, and type of adjacent matrix, and on the dispersal mode of the invasive species. Findings from this observational study will inform my larger-scale research on landscape connectivity and permeability in southern California. Findings from both the small-scale and large-scale parts of this research will inform the planning and management of landscape linkages and further conservation goals by not enhancing invasive plant movement and connectivity.