The sagebrush steppe ecosystem (SSE) of North America, which once extended over a vast area of more than 60 million hectares, has become severely fragmented and degraded during the past 100 years. Ongoing anthropogenic impacts such as livestock grazing, natural resource exploration and extraction, and exurban development continue to diminish the ecological integrity of SSE. One consequence has been the invasion of millions of hectares of sagebrush by exotic annual grasses, most notably Bromus tectorum (cheatgrass). Cheatgrass invasion initiates positive feedback loops wherein changes in fire regime, soil biota, and nutrient cycling favor the spread and dominance of exotic annuals, resulting in exponential decline in native plant abundance. Conversion of SSE to exotic annual grassland places SSE-associated species at risk of extirpation in affected areas, and threatens the viability of livestock operations that utilize SSE rangeland. Conservation and restoration efforts in SSE have thus become a high priority for many Western land managers. Directed research that can assist in developing management recommendations is a necessary component of this effort.
Restoration of disturbed lands in the semi-arid West presents particular challenges. High variability in precipitation regime, porous soils, and competition with non-native plants are some of the obstacles to successful establishment of native plant seedlings. In addition, it is likely that insect herbivores, which are ubiquitous in SSE, exert an influence on plant community composition through selective feeding on preferred plant species. These impacts have particular importance during the seedling stage, when plants are most vulnerable. The objective of this study is to determine whether a common, generalist grasshopper species (Melanoplus bivittatus) preferentially consumes native plant seedlings in situations where cheatgrass is present. If so, grasshoppers may represent an additional driver of cheatgrass spread and a constraint on successful native plant establishment in restoration projects. A corresponding question is whether the availability of cheatgrass, during the reproductive phase of the grasshoppers’ life cycle, promotes the fedundity of M. bivitattus, which is classified as a pest species by the USDA and can have severe impacts on crops at outbreak levels.
The study will examine the three-way interactions of grasshoppers, cheatgrass, and a selection of native plants commonly used in SSE restoration projects. Experiments conducted in the greenhouse and laboratory, combined with field surveys of grasshoppers in cheatgrass-infested areas, will attempt to isolate the relative contributions of insect and exotic plant on native plant community composition. Research is led by post-doc Jayne Jonas-Bratten and GDPE student Catherine Cumberland in fulfillment of her Master’s degree in Ecology.
