BC Conservation Data Centre: Conservation Status Report
Syntrichia laevipila
twisted oak moss
| Scientific Name: | Syntrichia laevipila |
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| Scientific Name Synonyms: |
Tortula laevipila var. meridionalis
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| English Name: | twisted oak moss |
| Provincial Status Summary | |
| Status: | SU |
| Date Status Assigned: | April 30, 2023 |
| Date Last Reviewed: | April 30, 2023 |
| Reasons: | Syntrichia laevipila is found only on southeastern Vancouver Island where it is restricted primarily to the bark of old Garry oak trees. It occupies an area of less than 20 square km, over a range of ca. 900 square km. Twenty-two occurrences are known, consisting of a minimum of 305 mature individuals. Though many known sites occur within protected areas, many of these are small city parks and most populations face a substantial threat from the potential lack of regeneration of oak trees over the long term. British Columbia populations may also be sensitive to air pollution, as has been observed in populations in the United Kingdom. |
| Range | |
| Range Extent: | CD = 250-5,000 square km |
| Range Extent Comments: | Range in BC is about 1890 square km (COSEWIC 2004). In 2007, the areal extent of all known sites calculated using GIS tools is ca. 900 square km. |
| Area of Occupancy (km2): | D = 6-25 |
| Area of Occupancy Comments: | Occupied area in BC is probably less than 20 square km (COSEWIC 2004). |
| Occurrences & Population | |
| Number of Occurrences: | C = 21 - 80 |
| Comments: | There are 22 element occurrence records mapped in British Columbia. Of the thirty-one populations listed in the COSEWIC status report, several were grouped into a single occurrence based on the 1 km separation distance. Three populations that were unconfirmed in 2002 and were based on herbarium specimens, lacked coordinates and therefore, could not be mapped. A second population on Salt Spring Island was apparently confirmed in 2001/2002 but no coordinates were provided (COSEWIC 2004). Therefore, there may be four additional populations, but whether or not these are extant is unknown. |
| Number of Occurrences with Good Viability / Ecological Integrity: | D = 13 - 40 |
| Comments: | Eighteen of twenty-two occurrences are in good condition. |
| Number of Occurrences Appropriately Protected & Managed: | C = 4 - 12 |
| Comments: | Eleven occurrences, representing one half of all known populations, occur within parks, ecological reserves or other protected areas in BC (COSEWIC, 2004). Although removal of Garry oaks trees is not permitted within protected areas, many of the sites occur within small city parks that are subject to heavy recreational use. Municipal bylaws restrict the removal of trees on private land. However, since the species often grows near the base of the tree, damage to populations may take place by dogs, or during routine lawn maintenance. |
| Population Size: | C = 250 - 1,000 individuals |
| Comments: | There are at least 305 mature individuals (clumps) in the BC population (COSEWIC, 2004). |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | Substantial, non-imminent threat |
| Comments: |
The habitat condition at almost all known sites was stable and subject to moderate to no noticeable disturbance (COSEWIC 2004). The major threat to this species is the lack of regeneration of Garry oaks across their range, which would result in the extirpation of most populations of this species (COSEWIC 2004). Mature oaks are presently common in the Victoria area, but young oaks are often removed by hand or mowed on many private properties and the number of urban oaks are declining due to homeowner concerns about falling trees or branches (T. Lea, pers. comm.). In some areas of mature oaks, (e.g. Mount Maxwell ER) regeneration is minimal due to grazing by feral sheep and goats, but efforts to remove grazing animals from these areas may reverse this trend. Tree harvesting and branch cutting are potential threats to three populations of the Twisted oak moss, but municipal legislation prohibiting the removal of trees and an increased awareness of the ecological importance of Garry oaks has reduced their removal in many areas. Since the species often grows near the base of the tree, damage to populations may take place by dogs. Moss removal by landowners and routine grass or weed maintenance is considered to be a minor concern (COSEWIC 2004). The extent of the damage from crows is unknown, but at one location, birds were observed removing clumps of Syntrichia laevipila and other mosses, in search of insects (W. Miles, pers. comm. 2007). In the United Kingdom, populations of twisted oak moss were adversely affected by air pollution (Adams and Preston 1992). Though many BC populations are located near roadways and urban areas where they are exposed to automobile exhaust, the impacts of air quality on this species in British Columbia are unknown (COSEWIC 2004). In the Netherlands, widespread loss of elms through disease has greatly reduced the number of populations of Twisted oak moss. Oaks in BC may be vulnerable to the type of wide-scale destruction by sudden oak death (SOD) that has occurred in California and southern Oregon, but Quercus garryana has not yet been affected by this disease in BC (COSEWIC 2004). |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | G = Relatively Stable (<=10% change) |
| Comments: | Most of the habitats in which Syntrichia laevipila were collected appear stable, and the trees on which they grow are undisturbed. However, the associated habitats of these trees are often heavily disturbed as the trees are often on lawns or near roads. Populations within city limits or in areas where only older oaks are found are at greater risk of extirpation, because once these old oaks die, there is little to no replacement taking place (COSEWIC 2004). |
| Long-Term Trend: | BE = Decline of 30-90% |
| Comments: | Largely unknown, but population may decline sharply in the future as older trees die. Garry oak seedling establishment to replace aging populations appears to be very low (COSEWIC 2004). |
| Other Factors | |
| Intrinsic Vulnerability: | U=Unknown |
| Comments: | Unknown. It may be somewhat vulnerable in that it is rarely observed growing admixed with other mosses or lichens which may indicate that it is a poor competitor (COSEWIC 2004) |
| Environmental Specificity: | B=Narrow. Specialist or community with key requirements common. |
| Comments: | This species is restricted to the bark of older trees, particularly Garry oak (COSEWIC 2004), a species that grows within a narrow ecological zone in British Columbia. The total Garry oak population is estimated at less than 100,000 stems of all ages. Of the twenty or so other tree species examined by Miles, only one other species (big-leaf maple) supported a population of Syntrichia laevipila (COSEWIC 2004). |
| Other Rank Considerations: | |
| Information Gaps | |
| Research Needs: | In the U. K., populations of twisted oak moss were adversely affected by air pollution (Adams and Preston 1992). Many of the BC populations are located near roadways where they are exposed to automobile exhausts, yet the impacts of this exposure is unknown. |
| Inventory Needs: | The 2001 field study by Miles was thorough (COSEWIC 2004). Miles surveyed about 1200 Garry oak trees across the range of Syntrichia laevipila on Vancouver Island and the Gulf Islands. However, it is also possible that other locations exist and that this species is more plentiful at known sites, since Miles (pers. comm. 2001) reported that not all trees were checked and that only the bottom 2 or 3 m of the tree was checked at many locations. |
| Stewardship | |
| Protection: | |
| Management: | |
| Version | |
| Author: | Donovan, M. |
| Date: | September 04, 2007 |
| References | |
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Adams, K.J. and C.D. Preston. 1992. Evidence for the effects of atmospheric pollution on bryophytes from national and local recording in Biological recording of changes in British wildlife. Harding, P.T. (ed.). ITE Symposium 26.
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COSEWIC. 2004q. COSEWIC assessment and status report on the twisted oak moss Syntrichia laevipila in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 21 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. 2007. Conservation Status Report: Syntrichia laevipila. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Sep 11, 2025).