Invasion by Sweet Clover (Melilotus) in Montane Grasslands, Rocky Mountain National Park
Exotic (nonnative) invasion, often fostered by anthropogenic disturbances, can be detrimental to the biodiversity of indigenous plant communities. We examined the impact of two exotic species, Melilotus officinalis and M. alba (yellow and white sweet clover) in the montane grassland community in Rocky Mountain National Park to determine (1) whether native and exotic plant diversity differs between patches within grasslands that are invaded by Melilotus species and patches that are not invaded (control patches) and (2) whether the presence of Melilotus species are associated with specific exotic species. Variables that were recorded included species richness, species composition, and percent cover in invaded and control patches at multiple spatial scales. The results showed that more exotic, annual/biennial, and forb species occurred within patches invaded by Melilotus species, while more native, perennial, and grass species occurred in nearby control patches. Moreover, the invaded patches had several exotic species that were not found in control patches, whereas certain native species were only found in control patches. In some instances, the presence of Melilotus in the native community appeared unrelated to disturbance; some colonies were in seemingly undisturbed meadows well beyond disturbance edges. The data also showed that Melilotus species spread beyond original mapped boundaries in a span of two seasons.