BC Conservation Data Centre: Conservation Status Report
Purshia tridentata / Hesperostipa comata
antelope-brush / needle-and-thread grass
| Scientific Name: | Purshia tridentata / Hesperostipa comata |
|---|---|
| English Name: | antelope-brush / needle-and-thread grass |
| Provincial Status Summary | |
| Status: | S1S2 |
| Date Status Assigned: | March 31, 2021 |
| Date Last Reviewed: | March 31, 2021 |
| Reasons: | This highly fragmented ecological community occupies a small portion of its range. Fewer than 80 element occurrences are mapped for this ecological community. None of the element occurrences are assessed as having Excellent Ecological Integrity and only seven are assessed with Good Ecological Integrity. Short term trends (1995 - 2008) indicate a loss of greater than 30% of the area (Iverson, 2012, Lea 2008). Overlapping threats are very high to high; persistent threats include conversion to agricultural land, invasive alien plants, and livestock grazing pressures. |
| Range | |
| Range Extent: | D = 1,000-5,000 square km |
| Range Extent Estimate (km2): | 3789 |
| Biogeoclimatic Unit: |
BGxh1/02
IDFxh1 PPxh1 |
| Range Extent Comments: | The range extent estimate of this ecological community is based on Version 9 of the Biogeclimatic Ecosystem Classification (BEC) map (B.C. Ministry of Forests, Lands, and Natural Resource Operations. 2014). |
| Area of Occupancy (km2): | E = 20-100 km² |
| Area of Occupancy Comments: | This ecological community is identified in 32 km2, or 0.84% of its range (Iverson, 2012). |
| Spatial Pattern: | Large patch |
| Occurrences | |
| Number of Occurrences: | C = 21 - 80 |
| Comments: | There are 72 element occurrences mapped throughout the range of this ecological community (Iverson, 2012). |
| Number of Occurrences with Good Viability / Ecological Integrity: | C = 4 - 12 |
| Percent Area with Good Viability / Ecological Integrity: | F = Excellent (>40%) |
| Comments: | There are seven of the 72 occurrences with good ecological integrity (Iverson, 2012). None have excellent ecological integrity. These seven occurrences occupy 54% of the total area of occupancy (17.32 of 32.10 km2). |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | AB = Very high - high |
| Comments: | Cumulative impacts from overlapping threats warrant a Very High - High threats rating. High threats include conversion to agricultural land and vinyards. Alien invasive plants are also a high threat to this ecological community, and and are exacerbated by overgrazing and high fragmentation by linear corridors. Fire suppression, recreation impacts, and impacts from livestock farming and ranching are moderate threats to this community. |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | E = Decline of 30-50% |
| Comments: | From 1995 to 2008, there was a loss of 26% of the area occupied by this ecosystem (Iverson, 2012). In addition to these more recent losses, it is estimated that a portion of the changes observed by Lea (2008) occurred within the previous 40 years. Within the range of this ecological community, road density is high (3.3 km/km2) (B.C. Ministry of Forests, Lands, and Natural Resources Operations and Rural Development, Digital Road Atlas, accessed 18/01/2018). Roads and other linear corridors contribute to ongoing fragmentation and degradation of this ecological community and facilitate the spread of invasive alien plants. |
| Long-Term Trend: | D = Decline of 50-70% |
| Comments: | Once widespread in the south Okanagan, this community now occurs in small, fragmented patches (Lea, 2008; TEM 2009). The calculated loss of this ecosystem since 1800 (Lea 2008, Iverson 2012) is 67%. |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | This community is considered to be moderately vulnerable to disturbance with recovery potential within 10-100 years. Soil characteristics and the integrity of the microbiotic soil crust are key factors in the recovery of the community. |
| Environmental Specificity: | B=Narrow. Specialist or community with key requirements common. |
| Comments: | This community is found on very hot, dry sites on sandy, gravelly, glaciofluvial terraces, usually with an aeolian capping of sands. |
| Other Rank Considerations: | This community is ranked G2 by NatureServe. |
| Information Gaps | |
| Research Needs: | Research the relationship of soil texture to the predominance of Hesperostipa comata versus Pseudoroegneria spicata in the range of Purshia tridentata. Undertake a climate impact vulnerability assessment and model bioclimate, refugia, and areas of potential loss and/or expansion. |
| Inventory Needs: | Use the existing plot data to compare soil characteristics with predominance of Hesperostipa comata versus Pseudoroegneria spicata. |
| Stewardship | |
| Protection: | |
| Management: | |
| Version | |
| Author: | Iverson, K. and E. A. Cameron |
| Date: | February 06, 2018 |
| References | |
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B.C. Ministry of Environment. 1993. South Okanagan Conservation Strategy: Habitat Mapping. Draft maps prepared by Habitat inventory Sect., Wildl. Branch.
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B.C. Ministry of Forests, Lands, and Natural Resource Operations. Biogeoclimatic Ecosystem Classification (BEC) Map, WHSE_FOREST_VEGETATION.BEC_BIOGEOCLIMATIC_POLY [ESRI ArcSDE format]. Version 9. Ministry of Forests, Lands, and Natural Resource Operations, Forest Analysis and Inventory Branch, Victoria, B.C. Updated Regularly.
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B.C. Ministry of Forests, Lands, and Natural Resources Operations and Rural Development. Digital Road Atlas (DRA) - Master Partially-Attributed Roads, WHSE_BASEMAPPING.DRA_DGTL_ROAD_ATLAS_MPAR_SP [ESRI ArcSDE format]. Ministry of Forests, Lands, and Natural Resource Operations, GeoBC. Victoria, B.C. Updated Regularly.
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Faber-Langendoen, D., L. Master, J. Nichols, K. Snow, A. Tomaino, R. Bittman, G. Hammerson, B. Heidel, L. Ramsay, and B. Young. 2009. NatureServe Conservation Status Assessments: Methodology for Assigning Ranks. NatureServe, Arlington, VA.
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Iverson, Kristi. 2012. Ecosystem status report for Purshia tridentata / Hesperostipa comata (antelope-brush / needle-and-thread grass) in British Columbia. Prepared for B.C. Ministry of Environment, Conservation Data Centre, Victoria, B.C. 34 pp.
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Lea, T. 2008. Historical (pre-settlement) ecosystems of the Okanagan Valley and Lower Similkameen Valley of British Columbia - pre-European contact to the present. Davidsonia 19(1): 3-36.
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Lloyd, D., K. Angove, G. Hope, and C. Thompson. 1990. A guide to site identification and interpretation for the Kamloops Forest Region. B.C. Minist. For., Res. Branch, Victoria, B.C. Land Manage. Handb. No. 23. 399pp.
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Master, L., D. Faber-Langendoen, R. Bittman, G.A. Hammerson, B. Heidel, J. Nichols, L. Ramsay, and A. Tomaino. 2009. NatureServe conservation status assessments: factors for assessing extinction risk. NatureServe, Arlington, VA.
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Salafsky, N., D. Salzer, A. J. Stattersfield, C. Hilton-Taylor, R. Neugarten, S. H. M. Butchart, B. Collen, N. Cox, L. L. Master, S. O'Connor, and D. Wilkie. 2008. A standard lexicon for biodiversity conservation: unified classifications. Cons. Biol. 22:897-911.
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Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.
Suggested Citation:
B.C. Conservation Data Centre. 2018. Conservation Status Report: Purshia tridentata / Hesperostipa comata. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 8, 2026).