INVASIVE WEEDS IN GLACIER NATIONAL PARK: HABITAT, VECTORS OF SPREAD, AND AREAS AT GREATEST RISK OF INVASION

Abstract

Non-native invasive species have significantly changed the composition and ecosystem function of many North American landscapes. Currently, invasive species are recognized as the second greatest destroyer of biological diversity, superseded only by direct habitat destruction and consequent fragmentation from human development. Glacier National Park, an international Biosphere Reserve and World Heritage Site, is threatened by the encroachment of numerous noxious non-native invasive plant species. Prevention, early detection, and immediate action against invasive weed species in their initial establishment phases are paramount in reducing this threat. To facilitate strategic management actions, this study developed two maximum entropy invasive species distribution models for Glacier National Park. The first model was based entirely on environment variables associated with habitat, while the second model added environmental variables associated with vectors of spread to the environmental variables associated with habitat. The rationale behind the nested model approach was to determine invasion potential based on high quality invasive species habitat followed by invasion potential based on vectors of spread (keeping the relative influence of habitat constant). The two model results were then overlain to evaluate which areas were most susceptible to establishment of invasive species, the spatial distribution of these areas, and the locations with maximum potential for tactical management to prevent further invasive species spread. The analysis produced 10 nested species distribution model sets: a set for each of the 9 virulent priority invasive species individually and a set for all invasive species combined. For all invasive plant species combined, it was found that 30,928 acres (7.6%) of Glacier National Park had high quality invasive species habitat but lower invasion potential, 6,071 acres (1.5%) had high invasion potential but lower quality habitat, and 20,648 hectares (5.1%) had both high potential for invasion and high quality habitat. The latter was considered the area at greatest risk of invasion. The most influential vectors of spread were roads and trails, and the most important environmental factors were elevation, alluvial soils, slope, and forest land cover. Together, these findings and their spatial distributions allow Glacier National Park to prioritize invasive species monitoring, prevention and treatment.