Landscape and local factors influence abundance of a human-dispersed invasive plant

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T. Trevor Caughlin, Cody A Hall, Andrii Zaiats, Louis Jochems, Matthew C Clark and Nicholas Kolarik, Department of Biological Sciences, Boise State University, Boise, ID

Background/Question/Methods
Plant distributions in urban environments can provide insight into ecology and evolution, with immediate applicability to human well-being. Puncturevine, Tribulus terrestris, is an invasive plant that exemplifies the need to understand the drivers of plant abundance in cities. Puncturevine is an invasive plant throughout the United States that disperses via spiny seed pods. Among other detrimental impacts, puncturevine can destroy bike tires and damage animal paws, motivating control measures in cities where it is invasive. We investigated the landscape and local factors that explain puncturevine abundance at the city-scale in Boise, ID. We hypothesized that puncturevine abundance would be driven by three factors: (1) suitable microhabitats for establishment, (2) relative degree of human traffic in a road network, (3) and socioeconomic status of neighborhoods. To test these hypotheses, we quantified goathead abundance along transects placed throughout the city using a GPS unit. We then related GPS data to a high-resolution land cover map, property value, and the road network. Using hierarchical Bayesian models to account for spatial autocorrelation, we tested the relative importance of the several covariates previously mentioned to explain abundance.
Results/Conclusions
As a result of our data collection, we counted 448 total flowering plants over a walking distance of 81.3 km. The total area of our study ended up covering 87,127 m². Our results indicate that connectivity in the road network had a strong influence on goathead abundance, with a significant increase in abundance as betweenness (a metric of network centrality) increased. Altogether, our study demonstrates that factors interact across scales to influence the distribution of an invasive plant. Our results provide guidance for land managers to spatially-target puncturevine removal at sites where they are most likely to establish and spread across the city. Understanding the drivers of invasive plants with detrimental impacts on ecology and human livelihood will aid in the sustainability of cities in an era of ever-increasing urban land cover.