Spatial Distribution of Native Cushion Plants and Invasive Species along Waterworks Trail, Missoula, Montana: Implications for Plant Richness and Competition

Invasive species can significantly impact the distribution and richness of native plants, resulting in competitive exclusion. This study investigates the spatial variation in species richness of native cushion plants in relation to invasive species along Waterworks Trail in Missoula, Montana. This study assessed how elevation, distance from trail, and upslope (above the gate) vs downslope (below the gate) direction (east vs west) influenced the distribution of both the cushion plants and the invasive species. Species richness of cushion plants was higher on the west side of the trail, particularly at lower elevations. In contrast, the east side exhibited lower richness of cushion plants, and was characterized by a higher density of invasives. Invasive species were found in higher concentrations farther from the trail, with a higher presence of cheatgrass on the east side. These findings suggest that invasive species, particularly cheatgrass, may inhibit the growth of cushion plants, especially on the east side of the trail where a steep slope may promote wetter conditions than cushion plants prefer. Our study illustrates that native cushion plants and invasive species are not likely to coexist in the same space, potentially due to use of different niches. Future work should investigate whether removal of invasive species would allow native cushions plants to spread.