BC Conservation Data Centre: Conservation Status Report
Calochortus lyallii
Lyall's mariposa lily
| Scientific Name: | Calochortus lyallii |
|---|---|
| English Name: | Lyall's mariposa lily |
| Provincial Status Summary | |
| Status: | S3 |
| Date Status Assigned: | March 31, 2011 |
| Date Last Reviewed: | April 30, 2019 |
| Reasons: | Calochortus lyallii has an extremely restricted extent of occurrence, with only five populations over less than 100 square kilometres. A total of over two million individuals were estimated in in 2009, and most of the occurrences have good or excellent viability. Poor seed dispersal is a an intrinsic limiting factor and stochastic factors such as a long fire interval, unfavourable climatic conditions and high rates of herbivory by small mammals may be combining to limit population size. Since the South Okanagan Grasslands Protected Area (where most occurrences are located) was established in 2001, anthropogenic threats have declined substantially. Threats from invasive alien plant species, livestock trampling and forest ingrowth still exist but do not appear imminent. |
| Range | |
| Range Extent: | A = <100 square km |
| Range Extent Comments: | Calochortus lyallii is restricted to 4.9 square kilometres in extreme south-central BC, west of Osoyoos and south of Richter Pass (Calculated using GIS tools - alpha hull analysis in 2011). There have been no notable contractions or expansions in the Canadian range of Calochortus lyallii since regular monitoring first began in 1996 (M. Miller, pers. comm., 2010). |
| Area of Occupancy (km2): | EF = 26-500 |
| Area of Occupancy Comments: | The index of area of occupany is 28 square kilometres or 7 - 2km x 2km grid cells, as calculated with GIS tools. The actual habitat area occupied is approximately 0.1 square kilometres. |
| Occurrences & Population | |
| Number of Occurrences: | AB = 1 - 20 |
| Comments: | There are five known populations or occurrences of Calochortus lyallii in BC. The five populations include 14 natural subpopulations and one additional subpopulation that was artificially established in 1996. The area of potentially suitable habitat is vast and many habitats still wait to be surveyed at East Chopaka as well as on Mt. Kobau to the north and Chopaka and Snowy Mts. to the west. It is thus possible that the number of known occurrences will increase with increasing survey coverage (M. Miller, pers. comm. 2010). |
| Number of Occurrences with Good Viability / Ecological Integrity: | C = 4 - 12 |
| Comments: | Populations range from a few hundred to hundreds of thousands of individuals. Miller and Douglas (COSEWIC 2001b) observed that the number of juveniles entering the population in one year was generally comparable to the proportion that "exited", which suggested that recruitment was occurring at approximately replacement rates. Miller (2004) stated that there is no evidence to suggest that any populations are not viable. Based on population sizes and threats to persistence, 4 of the 5 populations have been ranked as having either good or excellent viability. |
| Number of Occurrences Appropriately Protected & Managed: | B = 1 - 3 |
| Comments: | One population is located entirely on private land, but four populations occur within a Provincial Park (South Okanagan Grasslands Protected Area) and are therefore regulated by the Provincial Park Act. The Act protects the species from commercial logging, mining exploration and development. Furthermore, a stewardship plan has been developed for Calochortus lyallii in the SOGPA (Dyer et. al 2008), and stipulates the monitoring and control of invasive weeds. Since 2001, direct human disturbance to Lyall's mariposa lilly habitat inside the PA has been minimal. No new anthropogenic threats were observed during surveys in 2007 and 2009, though low densities of invasive alien plant species were found in association with Lyall's mariposa lily and will continue to pose a long-term threat to habitat integrity. According to the Okanagan Region Management Direction Statement for this site (MWLAP 2003), two existing tenures in the protected area are held by ranching operations for pasture land, and the tenure holders are permitted to make improvements to fencing and livestock watering facilities. The population found near the eastern boundary is vulnerable because adjacent lands to the east and west are private rangelands. The Ministry of Transportation manages the one road into the site and can administer weed control/fire abatement at its discretion. Thus, none of the populations are currently effectively protected from all possible threats, particularly invasive species. |
| Population Size: | G = 100,000 - 1,000,000 individuals |
| Comments: | There are five populations of Calochortus lyallii with a total of 15 subpopulations. Occurrences range in size from a few hundred to hundreds of thousands of individuals, with an estimated total of between 730,617 to 893,503 mature (flowering and non-flowering) plants and over two million total individuals in 2009. Populations 3 and 4 are larger than previously thought, due to recent discoveries of additional subpopulations and a 2007 resurvey of subpopulation 3c revealed that it is also more extensive than first reported (M. Miller, pers. comm. 2010). |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | Moderate, non-imminent threat |
| Comments: |
[CD] The establishment of the South Okanagan Grasslands Protected Area in 2001 and subsequent management actions have helped to substantially reduce anthropogenic threats. No new logging is planned and most of the conifer seedlings that were erroneously planted into occupied habitat patches in 1995 as part of a post-fire salvage operation have since been removed (Miller and Douglas, 2001). Threats from invasive alien plant species, livestock trampling and forest ingrowth (secondary succession) still exist, but do not appear imminent (M. Miller, pers. comm. 2010; Southern Interior Rare Plants Recovery Implementation Group 2008c). Currently, stochastic factors such as a long fire interval, unfavourable climatic conditions (e.g. overly wet conditions in spring) and high rates of herbivory by small mammals may be combining to limit population size (M. Miller pers. comm. 2010). Invasive plants do not appear to be spreading rapidly into most occupied habitat patches, but they are well-established in adjacent areas of East Chopaka and will therefore continue to pose a long-term threat to habitat integrity. Among recent management initiatives has been the introduction of a biocontrol program aimed at controlling noxious weed pests such as hound's-tongue and this weed is being manually removed at sites where it is found. Provided timely action is taken, it may be possible to prevent the establishment and spread of invasive plants into critical habitat areas (M. Miller, pers. comm. 2010). Several types of negative biotic interactions involving both vertebrates and invertebrates combine to depress fruit set, and hence the amount of seed available for recruitment into the population (Miller and Douglas, 2001). Grazing and predation by insects and rodents present a threat (many plants each year lose a portion of their basal leaf to invertebrate grazers and in addition to directly feeding on bulbs, pocket gophers produce large soil mounds that can kill the bulbs by preventing their emergence), yet the presence of substantial populations of C. lyallii in BC suggests that these natural impacts are not significant (N. Kondla, pers. comm. 2003). The area in which C. lyallii occurs is licensed for grazing, although regulations exist which limit the intensity and timing of grazing on this area of Crown range and fencing improvements have helped limit, but not eliminate, the movements and thus the impacts from cattle trampling. In the past, cattle visitation had a significant negative impact on the average per capita seed production of the C. lyallii population at one site. Also of concern is the impact that soil compaction may have on seed germination rates and seedling survival. However, presumably C. lyallii has survived more than 100 years of livestock grazing in the area, which suggests that grazing alone is not a substantial threat to the species' survival (N. Kondla, pers. comm. 2003) and recent surveys suggest that cattle activities do not pose significant threat to the majority of the population. (M. Miller, pers. comm. 2010). |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | G = Relatively Stable (<=10% change) |
| Comments: |
[G] The number of populations (5) has remained stable since 1997, when regular monitoring began, and there have been no notable contractions or expansions in the range of the species. Mature plant abundance at previously known sites has declined by roughly 27-57% but since the number of subpopulations has increased five-fold as a result of ongoing survey efforts, the total known population size remains approximately what it was in 1997 (M. Miller, pers. comm. 2010). Survey data from 1997, 2007, and 2009 indicate that mature plant numbers have fluctuated over the past 12 years. Between 1997 and 2007 the total population of mature plants declined by an estimated 88%, from roughly 860,000 to roughly 100,000 individuals. Flowering plant numbers declined over this same period by approximately 94%. Despite these declines, by 2009 the total population size had rebounded to previous levels, in part to population extensions resulting from recent surveys (M. Miller, pers. comm. 2010). Because past plant counts have typically emphasized flowering individuals (which are much easier to spot from a distance than the inconspicuous sterile leaves), some of the apparent decline in overall abundance between 1997 and 2007 is probably due to a reduction in flowering rates, rather than a reduction in the number of mature individuals per se. Comparable figures are not available for 2009, but it is also likely that some of the observed rebound in abundance from 2007 to 2009 was due to higher numbers of plants flowering rather than to an outright increase in total numbers (M. Miller, pers. comm. 2010). |
| Long-Term Trend: | U = Unknown |
| Comments: |
There are no historical data on long term population trends, but based on the pattern of performance observed during an intensive demographic study conducted for subpopulations 1a, 2a and 3a from 1996 to 2000, the stochastic or long term growth rate calculated by Miller was 0.99, which would predict these subpopulations to decline by 1% annually over the long term. As there is no evidence of external factors causing systematic declines, the overall population at East Chopaka was projected to remain essentially stable over the long term (M. Miller, pers. comm. 2010). Historically, there may have been some loss of suitable habitat at East Chopaka due to forest encroachment and ingrowth stemming from fire suppression practices (and possibly climate warming) during the past century. Aerial photographs from 1938 show more extensive grasslands and less forest cover at similar habitats and elevations throughout the south Okanagan region than occur at present (T. Lea, pers. comm. 2007). Nevertheless, habitat trends at East Chopaka have improved considerably since the mid 1990s, when disturbances from forestry activities such as logging and afforestation, along with unfettered livestock grazing, were judged to pose imminent threats both to the integrity of the habitat and the long-term survival of Lyall's Mariposa Lily (Miller and Douglas 2001). A wildfire that burned over East Chopaka in 1994 temporarily helped reduce the canopy cover and slow the progression of forest ingrowth. More importantly, the largest Canadian occurrences of Lyall's Mariposa Lily are now protected within the South Okanagan Grasslands Protected Area, established in 2001. Since 2001, direct human disturbance to Lyall's Mariposa Lily habitat inside the Protected Area has been minimal. No new anthropogenic threats were observed during 2007 surveys, although low densities of invasive species (e.g., Cynoglossum officinale and Verbascum thapsus), were found in association with Lyall's Mariposa Lily at four sites. Grazing impacts, for the most part, appeared minor (M. Miller, pers. comm. 2010). |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | The northern edge of Calochortus lyallii's global range occurs in BC. The factors constraining a species at the extreme limit of its range are likely quite complex and a combination of climatic, environmental, and physiological factors may prevent C. lyallii from migrating further north or from expanding its local range. Field experiments indicate that C. lyallii is self-compatible, but since anthesis occurs before the stigma is receptive, plants probably don't self-pollinate unless pollen is transferred between flowers. Although bulbifery (the asexual reproduction of new bulb offsets) has been documented in other mariposa lilies, it has not been observed in C. lyallii. Instead, reproduction appears to be exclusively by seed (Miller, 2004). The lack of obvious mechanisms for wind or animal vector seed dispersal in C. lyallii helps to account for its characteristically patchy distribution and its very slow rate of spread into unoccupied habitat patches. This species appears able to tolerate a certain amount of trampling and disturbance by livestock, thanks to its deep-seated bulbs. It also appears to be a good competitor, as it is often found growing in dense monospecific patches (M. Miller, pers. comm., 2010). |
| Environmental Specificity: | B=Narrow. Specialist or community with key requirements common. |
| Comments: | In BC, Calochortus lyallii is limited to grasslands and natural openings in Douglas-fir forests on all aspects at elevations ranging from 900 to 1300 m. It prefers partial to full sun and does not establish under dense canopy. Sites are typically grassy slopes dominated by bluebunch wheatgrass and Idaho fescue and are moderately dry to dry water-shedding with shallow, nitrogen-medium to nitrogen-rich soils. This species is fire tolerant, and because it is shade-intolerant, likely depends on periodic fires to maintain sufficient open habitat. BC populations appear to have responded favourably to a wildlfire that burned over much of the East Chopaka habitat in 1994 and temporarily helped reduce the canopy cover and slowed the progression of forest ingrowth. The survival and growth of seedlings is positively correlated with soil depth and C. lyallii is most apt to establish successfully on deep soil where there is at least some vegetation or litter cover (M. Miller, pers. comm., 2010). |
| Other Rank Considerations: | |
| Information Gaps | |
| Research Needs: | Information is needed on the level of livestock grazing that is compatible with Calochortus lyallii's ability to persist and flourish. It is also not known what effect increased competition from introduced species has on C. lyallii''s ability to persist (COSEWIC 2001b); however, any sudden change in community organization could be disruptive to individual species and ecosystem structure and function. Consequently, the spread of weeds on Black Mountain, and particularly their encroachment into C. lyallii habitat, should be monitored. The effects of fire (or conversely, fire suppression) on C. lyallii population dynamics should also be documented. There was a big fire in Methow Valley in Washington State, which is the global epicenter of C. lyallii abundance. Communication with government agencies in central Washington could provide information on how this affected the species (M. Miller, pers. comm. 2003). |
| Inventory Needs: | Extensive areas of suitable habitat remain to be surveyed at East Chopaka, on Mt. Kobau to the north, and on Chopaka and Snowy Mts. to the west. It is thus possible that additional populations will be discovered (M. Miller, pers. comm. 2010). |
| Stewardship | |
| Protection: | Appropriate management actions by landowners and managers is needed. The most significant population, southwest of Richter Pass, contains more Calochortus lyallii plants than all other sites combined, and it is relatively undisturbed. Loss of this population could seriously affect the species' ability to maintain itself at the current limit of its range, and it could compromise the species' ability to expand its range northwards if global warming causes habitat changes (COSEWIC 2001b). Other populations on the east and west slopes also occupy areas of critical habitat. They have unique suites of habitat conditions, biotic as well as abiotic, that contribute to the variability needed for healthy population dynamics. Therefore, the most effective way of safeguarding critical habitat for C. lyallii on Black Mountain is to safeguard the entire grass-forb community rather than just individual sites (COSEWIC, 2001b). Depending on the status of the proposed Grasslands Provincial Park and the activities permitted on the lands occupied by C. lyallii, it may be afforded greater protection than it was previously. |
| Management: | Miller and Douglas (2000) recommended (1) fencing off extant Calochortus lyallii populations; (2) reducing grazing levels by restricting the number of cattle allowed on Black Mountain in a given year; and (3) delaying the timing of grazing (previously scheduled to occur in the spring) so that it takes place after C. lyallii has completed its reproductive cycle and ceased activity for the year. These recommendations have now been incorporated into a draft Stewardship Plan prepared by BC Parks and Ministry of Environment. Specific actions outlined in the Plan include monitoring and controlling invasive alien plants, monitoring cattle grazing, forest encroachment and unauthorized activities at known sites, incorporating best management practices and appropriate strategies (i.e. pasture rotation schedules) into range use plans to protect C. lyallii and identifying addiitonal potential threats as they are observed. Beginning in 2005, BC Parks and MoE staff have conducted semi-annual surveys within South Okanagan Grasslands Protected Area to monitor and manage potential threats to the species (M. Miller, pers. comm., 2010). |
| Version | |
| Author: | N. Kondla, S. Hartwell and M. Donovan |
| Date: | September 29, 2010 |
| References | |
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B.C. Ministry of Environment. 2015b. Management Plan for Lyall?s mariposa lily (Calochortus lyallii) in British Columbia. B.C. Ministry of Environment, Victoria, BC. 19 pp.
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B.C. Ministry of Environment. Recovery Planning in BC. B.C. Minist. Environ. Victoria, BC.
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COSEWIC. 2001b. COSEWIC assessment and status report on the the Lyall's mariposa lily Calochortus lyallii in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 24 pp.
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Dyer, O., Gunoff, S. Bunge and C. Klym. 2008. Stewardship plan for the Lyall's Mariposa Lily in the South Okanagan Grasslands Protected Area: 2008 to 2012. Working Report. Minist. of Environ. Penticton. 8 pp.
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Klym, C., S. Bunge and O. Dyer. 2007. Lyall's Mariposa Lily inventory, monitoring and stewardship: 2005-2007. Working Report. BC Ministry of Environment. Penticton. 7 pp.
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Kondla, N.G. 2003. National Recovery Plan, Lyall's Mariposa Lily. Novus Consulting rep. for B.C. Minist. Water, Land and Air Prot. 16pp.
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Miller, M., and G.W. Douglas. 2000. Status Report on Lyall's Mariposa Lily, Calochortus lyallii, in Canada. Unpubl. rep. submitted to the Comm. on the Status of Endangered Wildl. in Can. Ottawa. 32pp.
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Miller, M.T. 2004. Demographic perspectives on the rarity and persistence of two mariposa lilies (Calochortus) from southern British Columbia. PhD. dissertation, Dep. Biol., Univ. of Victoria, Victoria, BC.
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Miller, M.T. 2005. Draft National Recovery Strategy for Lyall's mariposa lily (Calochortus lyallii). Prepared for the Southern Interior Rare Plants Recovery Implementation Group. Recovery of Natl. Endangered Wildl. Comm., Ottawa, ON. 37 pp.
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Miller, M.T., and G.W. Douglas. 1999b. Status of Lyall's Mariposa Lily, Calochortus lyallii (Liliaceae), in Canada. Can. Field-Nat. 113:652-658.
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Miller, M.T., J.A. Antos, and G.A. Allen. 2007. Demographic differences between two sympatric species of Calochortus (mariposa lily) as revealed by matrix analysis. Plant Ecology 191:265-268.
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Ministry of Water Land and Air Protection. Environmental Stewardship Division. 2003. Okanagan Region Management Direction Statement for Chopaka East site of South Okanagan Grasslands protected area. 22pp.
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Southern Interior Rare Plants Recovery Implementation Group. 2008c. Recovery strategy for Lyall's mariposa lily (Calochortus lyallii) in British Columbia. Prepared for the B.C. Minist. of Environ., Victoria, BC. 17 pp. + annex 9 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: Calochortus lyallii. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 8, 2026).