Plant species diversity in the sagebrush steppe of Montana

Abstract

Sagebrush (Artemisia tridentata) is abundant in Montana and is an obvious part of an assemblage of plant species.This community of plants; the sagebrush steppe contains a mixture of grasses, early and late season forbs and shrubs. It is found in semi-arid valleys and plains of Montana and the intermountain western United States, and has received much research attention regarding increasing livestock forage, or of wildlife's dependence on the sagebrush steppe plant communities.Yet, little information on plant species diversity exists. This thesis was undertaken to describe the plant species diversity in three intact sagebrush steppe sites in Montana. The sites were located in Gallitan and Phillips counties. An average of 130 species was found at each site documenting the high levels of diversity that exist in local communities. Diversity measures were similar yet the dissimilarity among sites was high, this could reflect the high diversity of plant species in sagebrush steppe. Of the species recorded none had a restricted range, and this may represent a high rate of migration among local communities. Contrary to a designation as mixed grass prairie at the Phillips county site we found most species representative of the sagebrush steppe and areas of the Great Basin, and the site may be better classified as sagebrush steppe. Introduced plant species were found at all sites. The Burke Park site located in the city of Bozeman has the greatest diversity and abundance of introduced species. The most abundant species were introduced forage grasses. Our results also found that introduced species were negatively associated with the distance to road or trail.This is consistent with other findings that implicate human population density and disturbance as determinants of introduced plant diversity. The implication that human related disturbance and transport of popagules are causes of introduced plant establishment highlights the need for prevention of widespread destruction of sagebrush steppe.