Purshia tridentata / Hesperostipa comata (antelope-brush / needle-and-thread grass), when in excellent ecological condition, is a shrub steppe community characterized by an open shrub layer dominated by Purshia tridentata and a herb layer dominated by native bunchgrasses including Hesperostipa comata (needle-and-thread grass), Aristida purpurea var. longiseta (red three-awn), Pseudoroegneria spicata (bluebunch wheatgrass), and Sporobolus cryptandrus (sand dropseed). It occurs on coarse, sandy soils that were deposited by melting glacial waters or on sandy aeolian veneers over these materials. Within British Columbia, it occurs on low-elevations of the southern Okanagan Valley. The ecological community occurs in an area where there were frequent, low-intensity fires historically.
The B.C. Conservation Framework (2012) ranks this ecosystem as priority one in both goal one (contribute to global efforts for species and ecosystem conservation) and goal three (maintain the diversity of native species and ecosystems). It has a G2 Global status and S1 (critically imperilled, red-listed) Provincial status. Additionally, it supports one of the highest densities of species-at-risk for any ecosystem in British Columbia.
In 1800, there were approximately 9863 ha of antelope-brush / needle-and-thread grass ecosystem. By 2008, only 3217 ha remained, representing a loss of 67.4% of the original extent of this ecosystem. The ecological integrity and condition of antelope-brush / needle-and-thread grass have been severely reduced by the following primary factors: fragmentation by various types of developments (particularly urban/suburban and agricultural developments), alterations to fire regimes, disturbance by domestic livestock, and the spread and continued introduction of invasive alien plants. These factors continue to threaten the remaining occurrences of this ecological community.
Kristi Iverson, Iverson & Mackenzie Biological Consulting Ltd.. 2012. Ecosystem Status Report for Purshia tridentata / Hesperostipa comata (antelope-brush / needle-and-thread grass) in British Columbia, 2012. B.C. Ministry of Environment, Conservation Data Centre
Topic: Species and Ecosystems at Risk
Keywords: B.C. Conservation Data Centre, B.C. Conservation Framework, Ecosystems at Risk, Species at Risk, Status Report, Red List, Okanagan Valley, Terrestrial Ecosystem Mapping, Callophrys affinis, Satyrium behrii, Satyrium californica, hairstreak, Ambystoma mavortium, Blotched Tiger Salamander, Antrozous pallidus, Pallid Bat, Athene cunicularia, Burrowing Owl, Crotalus oreganus, Western Rattlesnake, Hypsiglena chlorophaea, Desert Night Snake