BC Conservation Data Centre: Conservation Status Report
Zeltnera exaltata
western centaury
| Scientific Name: | Zeltnera exaltata |
|---|---|
| Scientific Name Synonyms: |
Centaurium exaltatum
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| English Name: | western centaury |
| Provincial Status Summary | |
| Status: | S1S2 |
| Date Status Assigned: | April 30, 2019 |
| Date Last Reviewed: | April 30, 2019 |
| Reasons: | A total of localities have been documented in British Columbia, few of which are likely to have good viablity. Only two EOs have been recently verified as extant. The majority of occurrences are at valley bottom on lake shores where they are highly vulnerable to both human and stochastic disturbances, competition from invasive species, and impacts of climate change. The scope and severity of threats are high. Only one EO is known to occur in a protected area. Total population size for C. exaltatum in BC is estimated at around 10,000 plants, and individual populations are widely separated. The range extent of C. exaltatum in BC is approximately _ km2; the area of occupancy is 24 square kilometres. Short-term and long-term trends are unknown but there is strong reason to suspect that overall numbers have declined over both the short term and over the past century. The BC range currently makes up 100% of the Canadian range but less than one percent of the species' total North American range. The likelihood of a rescue effect is low. |
| Range | |
| Range Extent: | AB = <100-250 square km |
| Range Extent Comments: | Using GIS tools the range extent is calculated to be 109 sq km. |
| Area of Occupancy (km2): | D = 6-25 |
| Area of Occupancy Comments: | Using GIS tools and the index of occupied area this species occupies 6 four square kilometer grid cells (24 sq km). |
| Occurrences & Population | |
| Number of Occurrences: | A = 1 - 5 |
| Comments: | As of December 2011, there were six recorded occurrences of Centaurium exaltatum in British Columbia (BC Conservation Data Centre 2010). However, the species has only recently been verified at Mahoney Lake (2009) and Osoyoos Lake (2001). Other EOs at Turtle Lake (near Oliver) and Kamloops Lake are historical. The occurrences at Richter Pass and Gallagher Lake have not been verified within the past 10 years. |
| Number of Occurrences with Good Viability / Ecological Integrity: | B = 1 - 3 |
| Comments: | Of the EOs surveyed since 1999, only Osoyoos Lake and Mahoney Lake appear likely to persist under current conditions. The very small Richter Pass population (ca. 50 plants in 1999) occurs in an unprotected roadside ditch susceptible to disturbance, and has a poor estimated viability (BC Conservation Data Centre). Viability of all other EOs cannot be estimated at this time due to a lack of recent census data. |
| Number of Occurrences Appropriately Protected & Managed: | B = 1 - 3 |
| Comments: | The Mahoney Lake EO occurs within the boundaries of an Ecological Reserve. None of the other EOs are known to receive any protection. |
| Population Size: | AE = 1 - 10,000 individuals |
| Comments: | As of March 2010, the size of the British Columbia population was unknown. Approx. 10,000 plants were counted at Osoyoos Lake in 2001, although this estimate may now be out of date. Recent population counts are unavailable for other EOs, except Mahoney Lake, where three plants were counted in 2009 (BC Conservation Data Centre). |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | Substantial, imminent threat |
| Comments: | Much of the shoreline habitat around Osoyoos Lake has been lost to urban and residential development, and many rare plant species have become extirpated there as a result. Current and future development plans for the portion of the lake supporting Centaurium exaltatum are unknown. The shoreline of Osoyoos Lake is frequented by boaters and swimmers; since the Osoyoos Lake EO is located adjacent to a public beach, it is especially vunerable to trampling and other human disturbances. The artificial management of the water levels of Lake Osoyoos by the Zosel Dam in Oroville by the United States under the International Joint Commission poses a possible threat to this species, as has been suggested for other rare plants growing in the same vicinity (COSEWIC 2009). Lake levels have been managed for at least the last twenty years and Centaurium exaltatum presumably remains at the site, although we do not have any data on population changes over this period (the distribution of this species before the dam was built is unknown but may have been more widespread). However, it may take more time in order for the influence of the dam on lake levels and on the habitat to affect this species. The shorelines along many portions of the shore of Osoyoos Lake have slowly been eroded away by wave action. Although wave action has always been present, wave action would have affected a much broader elevational range of shore before the dam was built, and the shore would not have had the cut banks that appear today (COSEWIC 2009). This may eventually threaten the population of C. exaltatum. Invasive species pose a continuing or potential threat at all locations, in particular Reed Canary Grass at Osoyoos Lake. Its aggressive spread in moist habitats and wetlands has been well documented in other parts of North America and British Columbia. The slopes above the east side of Osoyoos Lake have been converted almost 100% to vineyards. Sediments and chemicals from storm water discharge, agricultural fertilizers, and pesticides from vineyards can impact riparian ecosystems, posing a potential threat to C. exaltatum (COSEWIC 2009). At Richter Pass, C. exaltatum grows in an unprotected roadside ditch subject to disturbance. This EO is vulnerable to road maintenance activities. Since the species requires moist substrates to germinate and thrive, climate change could have a devastating impact on extant populations and habitat if it results in increased duration and frequency of droughts. |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | AH = Decline of >90% to increase of <25% |
| Comments: | Short-term (10-year) population trends are not well known because few EOs have been visited more than once during the past decade, and no focused monitoring has been undertaken. However, based on habitat modifications that have taken place along the shores of Osoyoos Lake and throughout the Okanagan Valley during the past decade, there is good reason to suspect that overall numbers have declined in recent years. |
| Long-Term Trend: | Rank Factor not assessed |
| Comments: | The earliest known British Columbia records for Centaurium exaltatum date back to at least 1953, when collection notes indicate the species was "abundant" along the shore of Osoyoos Lake. However, the long-term population trend is unknown. Given the low number of historical collections, this species has likely always been relatively rare in BC. However, based on habitat modifications that have taken place along the shores of Osoyoos Lake and throughout the Okanagan Valley during the past century, there is strong reason to suspect that overall numbers have declined during the past century. |
| Other Factors | |
| Intrinsic Vulnerability: | AB=Highly to moderately vulnerable. |
| Comments: | The species is considered moderately to highly vulnerable on the grounds that it has moderate frequency of reproduction, fecundity, and dispersal capability such that populations can probably recover from decreases in abundance over a period of several years (on the order of 5-20 years or 2-5 generations), but are unlikely to become reestablished through natural colonization following extirpation. Furthermore, the supporting wetland ecosystems may be highly susceptible to changes in composition and structure that cannot be reversed through natural processes even over substantial time periods. |
| Environmental Specificity: | A=Very narrow. Specialist or community with key requirements scarce. |
| Comments: | The main natural limiting factor across the Canadian range of Centaurium exaltatum is its restriction to a rather specific and geographically limited habitat; that is, moist alkaline substrates in the hot dry Bunchgrass zone of the BC southern interior. These areas are highly vulnerable to degradation by invasive plants, residential development, agricultural activities, and climate change. |
| Other Rank Considerations: | The BC range currently makes up 100% of the Canadian range but less than one percent of the species' total North American range. The likelihood of a rescue effect is low. |
| Information Gaps | |
| Research Needs: | Research is needed to determine the current population status of Centaurium exaltatum in British Columbia and to confirm the most recent threat assessments. Current knowledge of C. exaltatum biology is limited to general autecological characteristics and habitat preferences. There is no information on demographic rates and population dynamics have not been monitored, thus population trends are unknown. It is also not known how large the population must be to be self-sustaining under current conditions. Likewise, responses to management activities such as invasive species removal are unknown. |
| Inventory Needs: | Inventories are needed to determine the current abundance and distribution of Centaurium exaltatum in British Columbia, since most survey information is now outdated. The species has only been verified recently at Mahoney Lake (2009) and Osoyoos Lake (2001). Other EOs at Oliver, Kamloops Lake, and Richter Pass are either historical or have not been verified within the past 10 years (as of March 2010). Updated inventories are needed to determine if these EOs are still extant and whether they represent the full extent of the distribution in Canada. |
| Stewardship | |
| Protection: | One of the recently recorded EOs is located in an Ecological Reserve, but other EOs on crown and private land receive no protection. Land tenure of the Kamloops Lake, Turtle Lake, and Osoyoos Lake sites are unknown. Measures should be taken to protect these EOs from land conversion and any other imminent, external threats resulting from human activities. Protection for sites on private property could be achieved through a variety of mechanisms including voluntary stewardship agreements, conservation covenants, and purchase from willing sellers. |
| Management: | No management activities are suggested at this time. Further inventories are required before management needs can be assessed. |
| Version | |
| Author: | Miller, M. |
| Date: | March 15, 2010 |
| References | |
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COSEWIC. 2009d. COSEWIC assessment and status report on the bent spike-rush Eleocharis geniculata, Great Lakes Plains population and Southern Mountain population, in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. ON. vii + 30 pp.
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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. 2010. Conservation Status Report: Zeltnera exaltata. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 6, 2026).