Little is known about the relationship between frequency of occurrence and the expected maximum distance a nonnative species might spread along a trail once introduced to an ecological system with high native species integrity. Understanding how colonization and invasive plant habitat degradation occur in largely intact ecosystems is challenging. Determining which nonnative species are most likely to spread might be possible, given a suite of environmental or trail conditions. Spread may be linked to a particular set of environmental conditions, or to type and level of trail use. A field study conducted on trails in Forest Service and State Park lands on the Kenai Peninsula, Alaska, was designed to determine frequency and spread distance of all nonnative vascular plant species per 100-m segments keyed to vegetation type, canopy cover class, aspect, trail use level, and trail use type. Although the maximum total number of nonnative species decreased with increased distances from trailheads, the average number of species remained nearly constant. Common dandelion, broadleaf plantain, and annual bluegrass exhibited consistent presence per canopy cover class or vegetation type. A nested subset analysis revealed a significant reduction in nonnative species presence beyond a 500-m distance from a trailhead and a moderately strong nestedness pattern. High-use trails exhibited the greatest numbers of nonnative species at the farthest distances from the trailhead and contained a greater number of less common nonnative species. Alaska and other northern biomes have relatively few widespread invasive problems, offering an opportunity to limit ecosystem degradation by invasion. Results suggest that control strategies might focus on high-use trails with open-canopy habitats to prevent spread.
Nomenclature: Common dandelion; Taraxacum officinale F.H. Wigg. ssp. officinale; broadleaf plantain; Plantago major L.; annual bluegrass; Poa annua L.
Interpretive Summary: Land managers are increasingly aware of potential negative effects of invasive species that currently exist at low concentrations with slow spread rates in most areas in Alaska. Fast-spreading exceptions have alerted managers to focusing management strategies on prevention and eradication to avoid wide-scale infestations. Identifying what species to focus control efforts on is important to managers with limited budgets or limited control options. This study measured invasive plant spread along trail systems on and near the Kenai Peninsula in south-central Alaska. Distribution of all nonnative plants along trail systems was assessed by quantifying frequency of occurrence by environmental predictors, including vegetation type, canopy cover class, trail use type, and trail use level. Results indicated that common trailhead species (dandelion, Taraxacum officinale; plantain, Plantago major; annual bluegrass, Poa annua) grow under the widest variety of trail conditions and have the greatest penetration along trails. All nonnative species grow best under open, low-density vegetation conditions (except open–wet conditions, such as wetlands); higher trail use level increases penetration distance. Managers aiming for prevention should focus efforts on removal of uncommon nonnative species found at any distance along trail systems. For eradication efforts, control should start at trailheads and concentrate on open-canopy, high-use areas.
