Assessment of habitat threats to shrublands in the Great Basin: a case study.

The sagebrush (Artemisia spp.) ecosystem is one of the most imperiled in the United States. In the Great Basin ecoregion and elsewhere, catastrophic wildland fires are often followed by the invasion of cheatgrass (Bromus tectorum L.), eliminating or altering millions of hectares of sagebrush and other shrublands. Sagebrush in the Great Basin also is threatened by displacement from encroaching pinyon-juniper woodlands. Despite these changes, the ecoregion retains some of the Nation’s largest remaining expanses of sagebrush, most of which are federally managed. Because of these losses and degradation, sagebrush associated species are declining. To address these issues, we conducted a regional assessment of habitat threats for 40 sagebrush-associated vertebrates of concern in the Great Basin. Our goals were to (1) evaluate habitat conditions for species of concern for conservation planning and management, (2) demonstrate the application of new methods of regional threat assessment in shrubland communities, and (3) describe implications of results for management. Our analyses suggested that more than 55 percent (4.8 million ha) of sagebrush in the Great Basin is at moderate or high risk of being displaced by cheatgrass. Cheatgrass invasion also threatens other shrubland communities, particularly salt desert scrub (96 percent; 7.1 million ha at moderate or high risk). Substantial areas of sagebrush (41 percent; 2.0 million ha) were predicted to be at moderate or high risk of displacement by pinyon-juniper in the eastern Great Basin. Although little sagebrush (less than 1 percent) was at high risk to both threats, more than one-third was at high risk to cheatgrass and low or moderate risk from woodlands. Habitat loss, including sagebrush and other native plant communities, to cheatgrass could exceed 65 percent (8 million ha) for some of the 40 vertebrate species evaluated. Maintenance and restoration of native shrublands in the Great Basin will require both active and passive management to mitigate the formidable threats posed by cheatgrass and pinyon-juniper woodland expansion.