Human-mediated Dispersal of the Invasive Plant Alliaria petiolata Along the Appalachian Trail: Methods for Assessment and Management in Recreation Areas

Abstract

The rise in popularity of outdoor recreation has exacerbated the ecological consequences of human land use. Disturbance caused by trail infrastructure and consistent use has made recreation areas susceptible to invasive species establishment and spread. Humans play a considerable role in the spread by acting as accidental invasive seed dispersal vectors. Human mediated seed dispersal (HMD), though not extensively studied, has been shown to impact recreation areas, where tourists carry in seeds from the outside or further spread the seeds of invasive plants already in the area. Thus, methods to remove these seeds before they are unwittingly transported, and to understand the patterns of plant invasion facilitated by HMD, would aid in slowing the spread of invasive species. In this multi-part study I map and characterize all trailside patches of Alliaria petiolata, an invasive plant species growing along the Appalachian Trail in Maryland and determine the factors that affect plant growth in the area. I find that distance from the nearest road, trail surface type, and use level influence patch growth, while canopy cover did not have an effect. I also investigate the efficacy of boot cleaning stations installed in high-traffic, high plant density areas. Cleaning stations do not appear to be effective based on the large disparity between the number of trail visitors versus the number of people who recorded using the station. Finally, I model the HMD dispersal behavior of A. petiolata seeds based on experimentally obtained attachment and detachment rates of seeds carried on shoes over a range of distances. Five semi-mechanistic models were fitted, and these suggest that long-distance dispersal on shoes is aided by decreasing probability of seed detachment with distance. The best fitting model suggests that walking humans can disperse seeds very long distances, up to at least 1km, though most seeds disperse within 15m. These results are examined from a land-management perspective, detailing management steps, including education programs and targeted removal, with the goal of protect the Appalachian Trail and recreation areas like it from aggressive invasive plant species. Key Words: invasive species, Alliaria petiolata, garlic mustard, seed dispersal, recreation ecology, human mediated dispersal, Appalachian Trail