BC Conservation Data Centre: Conservation Status Report
Plagiobothrys tenellus
slender popcornflower
| Scientific Name: | Plagiobothrys tenellus |
|---|---|
| English Name: | slender popcornflower |
| Provincial Status Summary | |
| Status: | S1? |
| Date Status Assigned: | April 30, 2019 |
| Date Last Reviewed: | April 30, 2019 |
| Reasons: | A total of thirteen populations have been recorded in British Columbia, six of which have not been seen since 1958 and are presumed extirpated. Only one occurrence, on Saturna Island, has recently (2011-12) been verified as extant and it has been more than 10 years since individuals have been observed at the other six sites. Populations are small, fragmented, appear to undergo significant annual fluctuations, and occupy small habitat areas, making them potentially vulnerable to climate change as well as to small, localised disturbances such as habitat conversion, invasion of alien plants, encroachment of native and alien vegetation and altered grazing and browsing regimes. Three occurrences are known to occur in protected areas. Total population size for Plagiobothrys tenellus in BC is estimated at ca. 1,000 plants, and individual populations are widely separated. The range extent of P. tenellus in BC is 300 square km; the area of occupancy is 28 square km. Short-term (10-year) population trends are not well known because few occurrences have been visited more than once, and no focused monitoring has been undertaken. Long-term trends are negative and there is strong evidence that overall numbers have declined significantly over the past century. |
| Range | |
| Range Extent: | C = 250-1,000 square km |
| Range Extent Comments: | The range extent is 300 sq km (COSEWIC 2008). |
| Area of Occupancy (km2): | EF = 26-500 |
| Area of Occupancy Comments: | The area of occupancy is 28 sq km using a 2km x 2km grid. |
| Occurrences & Population | |
| Number of Occurrences: | B = 6 - 20 |
| Comments: | Of the 13 occurrences on record for British Columbia, only seven are still considered likely extant. One EO is on southeastern Vancouver Island north of Victoria, while the remainder are on nearby Gulf Islands (Galiano, Mayne, Pender and Saturna Islands). However, only one EO (Saturna Island) has been recently surveyed (in 2010/11). All other EOs were last confirmed prior to 2000. Searches conducted in 2010/11 failed to find any plants at six of the known EOs (Parks Canada Agency), although this may have been due to imprecise locality information or because searches were not perfectly timed to coincide with the species' brief flowering period. |
| Number of Occurrences with Good Viability / Ecological Integrity: | AB = 0 - 3 |
| Comments: | An EO is considered to have good viability if it is likely to persist for the foreseeable future (i.e., at least 20-30 years) in its current condition or better, and if it exhibits favorable characteristics with respect to population size and/or quality and quantity of occupied habitat (NatureServe 2009). In the case of Plagiobothrys tenellus, few of the EOs documented to date appear to meet this criteria, although recent population and habitat data are lacking for several EOs. Of those that have been surveyed since 1990, the Saturna Island EOs has the highest recorded abundances (> 1000 plants), and may be the most likely to persist in the short term. However, a small habitat area is occupied and it is unclear whether this EO is self-sustaining in the long term. The Vancouver Island population is exceedingly small and likely of low viability. Little is known about the other populations, as some have not been observed for up to 25 years. Attempts to locate the South Pender Island, North Pender Island, and two Galiano Island populations were unsuccessful in 2010/11, and their present status is unclear. |
| Number of Occurrences Appropriately Protected & Managed: | A = None |
| Comments: | Plagiobothrys tenellus receives a level of protection at three of the seven extant locations. On Saturna Island the species occurs within Gulf Islands National Park Reserve and on Galiano Island within a provincial park. The southeastern Vancouver Island EO is in a regional park. Of the remaining four locations, three may also fall within the boundaries of protected areas; however, because their exact whereabouts are unknown, this has yet to be determined. The South Pender Island EO may occur within the Gulf Islands National Park Reserve, the North Pender EO may be in a local park, and one of the Galiano Island EOs may be on a property held by a land trust (Galiano Conservancy Association). The habitat ownership of the Mayne Island EO is unknown (COSEWIC 2008). |
| Population Size: | CD = 250 - 2,500 individuals |
| Comments: | The most recent observations for Plagiobothrys tenellus populations (2010/11) suggest that there were fewer than 1000 individuals in Canada (Smith 2012). However, not all EOs have been censused in recent years and there is considerable uncertainty around this estimate. At last report, some populations had only a few individuals, while other populations contained hundreds, but it has been more than ten years since individuals have been observed anywhere but Saturna Island (Smith 2012). In 2010/11 surveys covering seven of the presumed extant locations, surveyors counted 1000-1500 individuals at one location (Saturna Island) but encountered no plants at any other location. This result suggests that populations have declined since the 1990s, although, in some instances, surveyors may have been hampered by a lack of precise locality information, causing them to miss plants. It is also possible that drought conditions may have reduced germination rates and/or detectability of plants during recent surveys. The remaining populations are still considered extant because the habitat has not been destroyed and a dormant seed bank may still persist in the soil. |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | Substantial, non-imminent threat |
| Comments: | [A] Extant EOs are small, fragmented, appear to undergo significant annual fluctuations, and occupy small habitat areas, making them potentially vulnerable to climate change as well as to localised disturbances. Six of thirteen known populations in Canada have likely become extirpated due to land development. Options for new population establishment and transfer between populations are reduced as potentially suitable habitat on private lands continues to be converted to housing and this threat is considered to be a high level of concern (Smith 2012). Three of the remaining seven presumed extant EOs are located within federal, provincial, or regional parks and receive some level of protection from development. Extant populations not within a park or protected area are at risk of being extirpated or reduced in size as habitat for Plagiobothrys tenellus can be highly desirable for ocean views. Recent development of houses on Heck Hill, Mayne Island and a viewing platform on Mt. Norman, South Pender Island may have affected the populations at those locations (Smith 2012). Encroachment of vegetation is limited by heavy grazing and browsing by feral goats at the Saturna Island population. The reduction or elimination of conditions suitable for germination resulting from encroachment of native and non-native plants may be the leading cause of population decline at six locations without grazing (Smith 2012). However, the effects of grazing and browsing on Plagiobothrys tenellus are not well known. |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | EF = Decline of 10-50% |
| Comments: | [BE] Short-term (10-year) population trends are not well known because few EOs have been visited more than once, and no focused monitoring has been undertaken. The Saturna Island EO has the highest recorded abundance (> 1000 plants), but occupies a small area and is prone to significant fluctuations in population size from year to year (COSEWIC 2008). Both the short- and long-term viability are unknown. The Vancouver Island population, the only one that has been visited repeatedly, either fluctuates at low numbers or is declining. There were nine plants noted when the population was first observed in 1977, 13 plants in 1996, 6 in 1997, and only 3 in 1999 (COSEWIC 2008) |
| Long-Term Trend: | EH = Decline of <50% to increase of <25% |
| Comments: | [EG] Population size has declined to less than 1000 individuals within the last century. A historic decline is known since six of a total of 13 known populations are no longer extant. Although the historical population size in Canada is not known, the existence of several historical records from the Victoria area indicates that the species, while likely never common, was once more abundant than at present. During the past century, the Garry oak and associated ecosystems that encompass the historical range of Plagiobothrys tenellus have been substantially altered by urbanization, land development, and fire suppression, to the point where only an estimated 1-5 % remains in a near-natural (i.e., pre-contact) condition (Fuchs 2001, Lea 2006). |
| Other Factors | |
| Intrinsic Vulnerability: | AB=Highly to moderately vulnerable. |
| Comments: | The biology and demography of Plagiobothrys tenellus in Canada have not been investigated. Nevertheless, intrinsic vulnerability is considered "moderate to high" on the grounds (NatureServe 2009) that, while it likely reproduces in most years and fecundity is likely such that populations can recover from decreases in abundance over a period of several years, the species possesses limited dispersal capability such that extirpated populations are unlikely to become reestablished through natural recolonization (unaided by humans). In addition, ecosystem occurrences are highly susceptible to changes in composition and structure that rarely if ever are reversed through natural processes even over substantial time periods. Other factors that may increase vulnerability include: (1) potentially poor competitive ability, especially with respect to invasive alien species; (2) an annual life cycle that is dependent on winter/spring rains, and hence a possible predisposition to demographic failure if the spring/summer drought arrives early; (3) its very small area of physical occupancy which leaves it susceptible to chance events and small-scale disturbance; and (4) its small population size and highly fragmentated distribution which may reduce its genetic diversity and limit the potential for local rescue effects (COSEWIC 2008). |
| Environmental Specificity: | B=Narrow. Specialist or community with key requirements common. |
| Comments: | In British Columbia Plagiobothrys tenellus shows a specific preference for habitats associated with the Garry Oak ecosystem of southeastern Vancouver Island and adjacent Gulf Islands, where it is generally restricted to dry, steep, grassy, south or southwest-facing slopes and coastal bluffs, often on exposed gravelly soils or rocks (COSEWIC 2008). These habitat conditions are relatively common within the known range of the species. |
| 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. |
| Information Gaps | |
| Research Needs: | Current knowledge of Plagiobothrys tenellus 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. There is no information on the pollination mechanism or whether the population is limited by pollination. The actual threat posed by invasive alien species has not been assessed. Likewise, responses to management activities such as invasive species removal are unknown. One important knowledge gap concerns the viability of the soil seed bank; searchers failed to locate any individuals at several sites surveyed in 2004 and 2010, and the survival of some populations may depend on the existence of a viable seed bank. Whether or not there is a seed bank, it would be beneficial to know what conditions are necessary for successful germination and establishment. What biotic and abiotic factors are currently inhibiting germination, flowering, and seed set? Are there management techniques available to aid recruitment? Are there specific habitat requirements beyond those already indentified? |
| Inventory Needs: | Parks Canada Agency is currently in the process of drafting a recovery strategy for Plagiobothrys tenellus that will incorporate updated information on population sizes and threats collected from surveys conducted in 2010-2011. |
| Stewardship | |
| Protection: | At least three of the seven extant EOs are afforded some protection within regional, provincial or federal parks. The Provincial Park Act protects the population located within a provincial park (on Galiano Island). The Saturna Island population is located within the Gulf Islands National Park Reserve and is protected under the Canada National Park Act. Plagiobothrys tenellus could also be a candidate for listing under the provincial Wildlife Amendment Act (2004) due to its British Columbia Ministry of Environment Red List status (COSEWIC 2008). Land tenure for four other EOs is presently unknown and should be determined. 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: | A SARA-compliant recovery strategy, which identifies management needs of Plagiobothrys tenellus, is currently being drafted by Parks Canada Agency (A. Pelletier, pers. comm. 2009). The Garry Oak Ecosystems Recovery Team should be consulted prior to undertaking any management activities for this species. Future management emphasis will likely be on securing protection for critical habitat, and ensuring proper environmental conditions for population persistence and growth. Site-specific and regional plans will focus on achieving a significant level of control over invasive alien species (and encroaching woody species), ensuring that critical ecological processes are intact, and improving landscape connectivity between potential recovery sites. |
| Version | |
| Author: | Miller, M. and M. Donovan |
| Date: | August 20, 2013 |
| References | |
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COSEWIC. 2008b. COSEWIC assessment and status report on the fragrant popcornflower Plagiobothrys figuratus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 23 pp.(www.sararegistry.gc.ca/status/status_e.cfm).
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Fuchs, Marilyn A. 2001. Towards a Recovery Strategy for Garry Oak and Associated Ecosystems in Canada: Ecological Assessment and Literature Review. Tech. Rep. GBEI/EC-00-030. Environ. Can., Can. Wildl. Serv., Pac. and Yukon Region.
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Lea, T. 2006. Historical Garry Oak Ecosystems of Vancouver Island, British Columbia, pre-European Contact to the Present. Davidsonia 17(2):34-50. http://www.davidsonia.org/bc_garryoak
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Parks Canada Agency. 2014. Recovery Strategy for the Slender Popcornflower (Plagiobothrys tenellus) in Canada . Species at Risk Act Recovery Strategy Series. Parks Canada Agency, Ottawa. vi+ 20pp.
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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. 2013. Conservation Status Report: Plagiobothrys tenellus. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 7, 2026).