The sagebrush steppe of Montana and southeastern Idaho shows evidence of high native plant diversity, stability, and resistance to the detrimental effects of nonnative plant species

Abstract

The premise of this study is that plant diversity is a neglected aspect of the North American sagebrush steppe, a once expansive biome that is now highly degraded. What kind of plant diversity is expected in the sagebrush steppe when it is not regularly physically disturbed? What ecological gradients most affect how plant diversity changes over large spatial scales? The answers to these questions could have implications for invasive plant management and the reclamation and restoration of the sagebrush steppe. Methods included sampling four regions of the sagebrush steppe in the northeastern portion of this biome. The Pryor Mountains, the Charles M. Russell National Wildlife Refuge, and the region of the Yellowstone Plateau were sampled in mostly Montana. These high-native-cover sagebrush sites were compared with those sampled in the Upper Snake River Plains region of southeastern Idaho. One hectare transects were established in high-native cover sagebrush steppe. These were paired with transects established in immediately adjacent disturbance-prone settings (e.g., roadsides) where sagebrush steppe vegetation remained intact. Geographically adjacent transects were sampled where they differed in at least one important ecological attribute. Key findings included that mountain big sagebrush steppe is evolutionarily distinct from Wyoming big sagebrush steppe and that the maximum temperature during the warmest month of the year was an important gradient for shaping species and phylogenetic beta diversity. Geographical proximity also had a large influence on the local species composition. The degree of disturbance also had less of an effect perhaps because of the influence of geography. The effects of physical disturbance were still detectable using descriptive approaches that compared infrequent with frequently disturbed transects. Regardless, native species diversity was distinctly diminished by physical disturbance, which is argued to be evidence that the sagebrush steppe is inherently ecologically stable. The implications of this research include the identification of specific taxonomic groups at and above the species level that may serve as benchmarks for sagebrush steppe reclamation or restoration. Long term stable conditions (infrequent disturbance regimes) are very much required for the successful restoration of the sagebrush steppe.