The role of the surrounding landscape matrix in invasion of conservation linkages by non-native plants

Background/Question/Methods

Conservation linkages, such as highway undercrossings, hedgerows, and riparian corridors, are widely promoted to combat the negative effects of fragmentation. An often-discussed though understudied concern is that linkages will also aid non-native plant movement. We still understand little about what and how specific landscape characteristics promote invasion. Edge habitat has often been linked to invasion, and as natural habitats become more fragmented due to development, the amount of edge increases considerably. Because of their relatively long and linear shape, conservation linkages could promote plant invasion, and this may largely depend on a linkage’s landscape context, such as the nature of the surrounding matrix. As part of a broad study to address the potential problem of linkages encouraging invasive plants, I am focusing on large-scale conservation linkages in Southern California that are part of region-wide attempts to increase and enhance landscape connectivity. I am examining the patterns and potential mechanisms of plant invasion associated with these specific landscape features, emphasizing the role of edge effects and the impact of matrix types. I collected data from nine linkages dominated by chaparral and coastal sage scrub in San Diego and Western Riverside Counties.

Results/Conclusions

Surveys confirm that plant invasion has a spatially explicit structure with linkage interiors being more invaded than their edges. These spatially-explicit patterns varied among invasive species with different dispersal syndromes (wind vs. animal vs. bird). In turn, these patterns depend upon the types of matrix that surround the linkage. Therefore what constitutes a landscape for a wind-dispersed invasive species is not the same as that of an animal-dispersed invasive species or a bird-dispersed species. Few if any studies have examined this landscape ecology concept in a comparative, large-scale manner. This observational study complements research I am conducting in northern California in an agricultural hedgerow system. Conclusions from both the small-scale and large-scale aspects of this research will help land managers/owners effectively prioritize invasive plant management within their linkages and will advance our conceptual understanding of invasive plant movement and connectivity at the landscape level.