BC Conservation Data Centre: Conservation Status Report
Tonella tenella
small-flowered tonella
| Scientific Name: | Tonella tenella |
|---|---|
| English Name: | small-flowered tonella |
| Provincial Status Summary | |
| Status: | S3 |
| Date Status Assigned: | April 30, 2019 |
| Date Last Reviewed: | April 30, 2019 |
| Reasons: | In BC, Tonella tenella is only known from three locations. All of the occurrences appear to have good viability, as long as the habitat remains undisturbed by development. There is a single protected occurrences of T. Tenella. The BC population contains more than 371 individuals. Area of occupancy is estimated at 6 square kilometres using a 2 km x 2 km grid analysis. The short-term trend over the last 10 years is probably stable, but no demographic data are available to document trends. Long-term trends over the last 200 years are also unknown. The scope and immediacy of the most devastating threat (development) is moderate and severity is high. Continuing habitat degradation by competition from introduced species is also a concern. This species also has narrow environmental specificity. |
| Range | |
| Range Extent: | A = <100 square km |
| Range Extent Comments: | Known range in BC is estimated at 3400 square metres (Douglas and Penny 2003), but the species could occur in other suitable sites in the dry coastal Douglas-fir zone in the Gulf Islands or on southeastern Vancouver Island. The occurrence of Tonella tenella in BC is at the northern extent of the species' range, and the closest other known population is in the Columbia River Gorge. |
| Area of Occupancy (km2): | D = 6-25 |
| Area of Occupancy Comments: |
Using a 2 km x 2 km grid analysis, this species occupies 3 grid squares in BC (6 sq km). Field observations of this plant show that it occupies ca. 81 square metres (Douglas and Penny 2003; J. Penny, pers. comm. 2009). At the private land site, plants occur in a narrow band of outcrop and talus extending up the mountainside for approximately 425 m. The four subpopulations there cover about 1-40 square metres each. The plant is inconspicuous and extremely difficult to detect, and it is quite likely that other subpopulations occur on the slope (Douglas and Penny 2003). |
| Occurrences & Population | |
| Number of Occurrences: | A = 1 - 5 |
| Comments: | In BC, Tonella tenella is known from three locations on Saltspring Island and Vancouver Island (Douglas and Penny 2003; COSEWIC 2003; J. Penny, pers.comm. 2009). |
| Number of Occurrences with Good Viability / Ecological Integrity: | B = 1 - 3 |
| Comments: | The three occurrence appears to have good viability, as long as the habitat remains undisturbed. |
| Number of Occurrences Appropriately Protected & Managed: | A = None |
| Comments: | There is one protected occurrence of Tonella Tenella on Mount Erskine on Saltspring Island(Douglas and Penny 2003; COSEWIC 2003; J. Penny, pers.comm. 2009). Another of the occurrences is on privately-owned waterfront property with no active stewardship or management plan. |
| Population Size: | C = 250 - 1,000 individuals |
| Comments: | The BC population contains more than 371 individuals with most occurring on the private land site (230-315 individuals, with the four subpopulations containing 30 to 150 plants each) (Douglas and Penny 2003; COSEWIC 2003; J. Penny, pers. comm. 2009). The plant is inconspicuous and extremely difficult to detect, and it is quite likely that other subpopulations occur. |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | Moderate and imminent threat |
| Comments: | The scope and immediacy of threats are moderate. The most immediate threat to Tonella tenella in BC is probably a housing development on the waterfront property, affecting 1/3 of the BC population (Douglas and Penny 2003). Previous owners planned to build a residence on the site but no work was ever done. In recent years, Salt Spring Island has shown a marked increase in population and associated development, with waterfront property at a premium. Habitat degradation affects all three populations but to a lesser severity. Although a large number of native forbs occur in these areas, much of the vegetation is dominated by introduced species, particularly grasses, including a number of species of Bromus. These species pose a threat to the long-term survival of T. tenella because of intense competition. Fire suppression over the last century has increased fuel loads and a very hot fire could destroy the seed bank in shallow soils over bedrock, extirpating T. tenella. Weed cover can also increase after a fire, putting any surviving Tonella at a competitive disadvantage. |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | U = Unknown |
| Comments: | The short-term trend over the last 10 years is probably stable, but no demographic data are available to document trends. |
| Long-Term Trend: | U = Unknown |
| Comments: | Long-term trends over the last 200 years are unknown. Demographic data only exist from 2002 (COSEWIC 2003) and more research is needed to determine trends. |
| Other Factors | |
| Intrinsic Vulnerability: | C=Not intrinsically vulnerable |
| Comments: | Tonella tenella is probably not intrinsically vulnerable. Self-pollination ensures adequate seed set, but no studies have been done to document genetic variabiltiy in the population. |
| Environmental Specificity: | B=Narrow. Specialist or community with key requirements common. |
| Comments: | Environmental specificity is narrow. Shaded, shallow soils over bedrock outcrops and talus support a specific flora unique to this kind of habitat. |
| Other Rank Considerations: | |
| Information Gaps | |
| Research Needs: | Demographic data only exist from 2002 (COSEWIC 2003) and more research is needed to determine trends. No studies have been done to document genetic variabiltiy in the population. Peripheral populations are sometimes genetically and morphologically divergent from central populations and may have an evolutionary and ecological significance out of proportion to the percentage of the species they represent. |
| Inventory Needs: | More sites on both the Gulf Islands and southeastern Vancouver Island need to be searched for this species. The last inventory was done in 2002 (COSEWIC 2003). Searches have been made in other potential habitats on Salt Spring Island as well as on Vancouver Island, but because T. tenella is so small and difficult to detect, it is quite likely that other subpopulations remain undetected. Searches need to be made in spring and early summer before plants dry up and die in summer drought. |
| Stewardship | |
| Protection: | The private site should be protected by purchase, or by a conservation covenant or easement with the owner. Protection of genetically distinct peripheral populations may be important for the long-term survival of the species as a whole. |
| Management: | In the absence of fire, the site might need to be managed to control the spread of woody species that could crowd out small annuals. |
| Version | |
| Author: | Christy, J.A. and J.L. Penny |
| Date: | February 22, 2005 |
| References | |
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Douglas, G.W. and J.L. Penny. 2003c. COSEWIC status report on the small-flowered tonella Tonella tenella in Canada in COSEWIC assessment and status report on the small-flowered tonella Tonella tenella in Canada. Comm. on the Status of Endangered Wildl. in Canada. Ottawa. 1- 14 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. 2005. Conservation Status Report: Tonella tenella. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 15, 2026).