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Management plan for Twisted Oak Moss in Canada [Proposed] 2011: Populations and Distribution

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Twisted oak moss has a widespread but scattered global distribution. It has been reported from North America, Chile, southern Europe, eastern Asia, Japan, South Africa, and, possibly, New Zealand and Australia (COSEWIC 2004). Its North American distribution closely follows the distribution of Garry oak ecosystems. It is found along portions of the south coast of British Columbia and inland through Washington and Oregon and into California (Figure 3); this distribution does not follow that proposed by Mischler (2007), as he includes another, more widespread species of uncertain taxonomy, S. pagorum, within his description.

In Canada, twisted oak moss has a narrow distribution in southern coastal B.C. (Figure 4; Table 1). It is most common in the Victoria area, with populations in the municipalities of Oak Bay, Saanich, and Victoria (Miles 2001, COSEWIC 2004). Outside of the Victoria area, twisted oak moss has been found in scattered populations: Pedder Bay, west of Victoria; Duncan, north of Victoria: Galiano Island; Salt Spring Island; and Nanoose Hill (Notch Hill), north of Nanaimo. Total populations for twisted oak moss in B.C. is 27, with two new populations documents since the COSEWIC status report (Table 1). Most occurrences are represented by numerous small (<1 cm2) patches that are restricted to relatively small areas at each site.

Before 2001, this species had been observed only occasionally in B.C. A 2001 study focusing on the distribution of the form of this species that produces gemmae (Miles 2001) showed that twisted oak moss is relatively widespread in the Victoria area, although rather uncommon within this range. It was found on only about 5% of the hundreds of trees examined. During field work for the COSEWIC status report ( COSEWIC 2004), more than 400 Garry oaks in sites near Duncan and Nanaimo and on Salt Spring Island were examined and twisted oak moss was found on only three trees. COSEWIC (2004) lists 31 populations, but some populations have been combined based on the B.C. Conservation Data Centre and NatureServe separation criteria for populations to be at least 1 km from one another (NatureServe 2009). Because of financial constraints put on her study, Miles (2001) mainly looked for and collected the smaller plants without hairpoints on the leaves. Therefore, this species may be more common in the Victoria area than her survey showed. Monitoring of populations has not been initiated.

The B.C. populations of twisted oak moss probably represent less than 1% of its global distribution and abundance (there are no reported estimates of global distribution and abundance for this moss). The population trend for the species is not known.

Figure 3. North American distribution of twisted oak moss (the dot in B.C. represents all extant locations)

Twisted Oak Moss North American distribution map

Figure 4. British Columbia distribution of twisted oak moss (the Victoria area set of dots represents multiple populations in Victoria, Langford, Esquimalt, Colwood, Oak Bay, and Saanich)

Twisted Oak Moss British Columbian distribution map
Table 1. Population[1] data for twisted oak moss in British Columbia (Miles 2001, COSEWIC 2004; populations 22 and 24 are occurrences documented since completion of the COSEWIC status report).
Population number and locality Dates
observed		 Estimated number of patches and extent[2] Land tenure
1. Pedder Bay 1976 ? (no data collected) unknown
2. Langford 2002 >20 patches (1.8) municipal
3. Esquimalt 2002 >20 patches (0.7) municipal
4. Colwood 2002 >20 patches (0.1) municipal
5. Victoria 2001, 2002 >20 patches (0.3) municipal park
6. Victoria 2001, 2002 5–20 patches (0.2) municipal park
7. Victoria 2002 >20 patches (0.6) municipal park
8. Victoria 2002, 2003 >20 patches (1.8) private property
9. Victoria 2003 >20 patches (1.8) municipal park
10. Victoria/Oak Bay 2007, 2008 >20 patches (>2.5) on multiple trees Camosun College
2001, 2002 >20 patches (1.0) municipal
11. Oak Bay, Victoria 2001, 2002 >20 patches (1.0) municipal
12. Oak Bay, Victoria 2002, 2003 <5 patches (<0.01) private property
2001, 2002 >20 patches (0.5) municipal
13. Oak Bay, Victoria 2001, 2002, 2003 5–20 patches (0.2) municipal park
14. Saanich 2001, 2002 5–20 patches (0.03) municipal park
15. Saanich 2002, 2003 5–20 patches (0.03) municipal park
2002 >20 patches (0.6) municipal park
2002 5–20 patches (0.3) likely municipal
2001 >20 patches (0.1) municipal park
2001 5–20 patches (0.06) municipal park
16. Saanich 2002 >20 patches (2.6) municipal
17. Saanich 2002, 2003 5–20 patches (0.8) University of Victoria
18. Saanich 2002 5–20 patches (0.4) municipal
19. Saanich 2002 5–20 patches (0.05) municipal park
20. North Saanich 2002 <5 patches (< 0.01) municipal
21. Galiano Island 2002 <5 patches (0.06) CRD regional park
22. Salt Spring Island 2006 >20 patches (<1.0) B.C. ecological reserve (provincial government)
2002 5–20 patches (<0.01)
23. Salt Spring Island 2001, 2002, 2007 <5 patches (<0.02) B.C. ecological reserve (provincial government)
24. Salt Spring Island 2005 a few patches private property
25. Duncan 2001 unknown Nature Conservancy of Canada
26. Duncan 1978 unknown B.C. ecological reserve (provincial government)
27. Nanoose Hill (Notch Hill) 1975, 1980, 2009 unknown
unknown
3–5 patches (<0.03)		 Department of National Defence (federal government)

1 Populations are separated by a distance of at least 1 km based on the NatureServe criteria, and land tenure park names represent different parks. Municipal parks are managed by municipal governments (Colwood, Esquimalt, Langford, North Saanich, Oak Bay, Saanich, and Victoria), whereas regional parks are part of the Capital Regional District (CRD) parks system.

2 The number in parentheses is the approximate area of the population in m2; this usually includes other bryophytes and exposed bark.

In B.C., twisted oak moss is restricted to the bark of trees, principally living on older Garry oaks, although it has been found once on bigleaf maple (Acer macrophyllum; Miles, pers. comm. 2006). It grows most commonly on lower tree trunks, but is occasionally found on the upper branches. Twisted oak moss usually forms isolated patches and is rarely found growing with other mosses or lichens, which may indicate that it does not compete well with other epiphytic species. As well, it may grow on drier and more protected microhabitats that other mosses do not utilize as habitat on the trees, but more research on microhabitats is needed to determine whether this is true (McIntosh, pers. comm. 2009). Most populations of twisted oak moss are found on trees in open habitats where the climate is characterized by hot to mild, dry summers and cool to cold, wet winters. Due to the limited number of scientific studies on this species, very little is known about its biological needs (e.g., microhabitat requirements, microclimate conditions, reproduction or dispersal mechanisms) and habitat conditions (e.g., exposure, level of shading, elevation, role of disturbance).

Fragmentation of Garry oak ecosystems, which support the host tree for this species, along with the loss of approximately 95% of these ecosystems (Fuchs 2001) is a key limiting factor.

An additional potential limiting factor for twisted oak moss is its small size, which may be a competitive disadvantage. However, it appears that this species readily takes advantage of open microhabitats on tree bark. Due to its small size and small patch size, this species is susceptible to stochastic events.

Table 2. Threat classification for twisted oak moss.
1 Loss of host trees Threat attributes
Threat category Habitat loss or degradation Extent Widespread
Local Range-wide
General threat Host tree removal Occurrence Anticipated in urban areas Probable
Frequency Recurrent Probable
Specific threat Destruction or removal of species and alteration of habitat Causal certainty Medium Probable
Severity High Probable
Stress Killing of species, reduced reproduction Level of concern High
2 Direct removal from host tree Threat attributes
Threat category Disturbance or harm Extent Localized
Local Range-wide
General threat Removal from host tree or damage Occurrence Anticipated in urban areas Probable
Frequency Recurrent Probable
Specific threat Destruction or removal of species Causal certainty Low Probable
Severity Low Probable
Stress Killing of species, reduced reproduction Level of concern Low
3 Lack of recruitment of host trees Threat attributes
Threat category Habitat degradation Extent Widespread
Local Range-wide
General threat Lack of Garry oak recruitment due to invasive grasses, browsing, and conifer encroachment Occurrence Anticipated in urban areas Unknown
Frequency Recurrent Unknown
Specific threat Lack of future suitable habitat Causal certainty Low Unknown
Severity Low Unknown
Stress Decreased recruitment, lower population viability, local extirpation Level of concern Medium

Loss of host trees
Urbanization, road construction, and agricultural development have all been the cause of the removal of mature Garry oak trees. Most or all of the populations and their viability could be reduced or populations extirpated if the host tree is removed. Garry oak tree removal (for safety or residential housing development) has occurred in the past and is ongoing due to urban development and home yard maintenance activities. Three of the known populations of twisted oak moss are within ecological reserves, which do not allow the removal of Garry oaks, but the three identified private properties are potentially under this threat. There is no information on the remaining populations regarding this threat.

Direct removal from host tree
Some landowners remove mosses and lichens from oaks on their property and may unknowingly remove patches of twisted oak moss. Damage can occur to the moss found at the bases of oaks in parks during routine grass or weed maintenance, and dog urination has killed mosses at the bases of some trees where the twisted oak moss has been seen (McIntosh, pers. comm. 2009). Branch pruning has happened historically and is ongoing due to urban development and home yard and municipal maintenance activities. These activities are anticipated to occur in the future, especially in urban areas.

Lack of recruitment of host trees
On many urban private properties young oaks are often removed, particularly from cultivated lawn areas. However, there is no information on the specific occurrence of these threats to the known populations. Since there may be mature oaks at some locations that can support twisted oak moss, it may take some time before the lack of recruitment of Garry oak affects twisted oak moss in these locations. Whether lack of recruitment will affect twisted oak moss needs to be determined for each of the known populations.

In certain areas of urban Victoria, there are resident deer populations that browse on all types of vegetation, including oak saplings and seedlings. In some areas, such as in the Mount Maxwell Ecological Reserve on Salt Spring Island, there are abundant older oaks; most are 90–140 years old, while some veterans date back to the 1700s (Smith, pers. comm. 2009). However, regeneration of oaks in this ecological reserve is minimal, apparently due to browsing by deer and feral sheep, although the situation is improving following efforts to remove the sheep.

Potential threats
Other potential contributors to the lack of recruitment of host trees in some areas are invasive grasses, which produce a thick thatch and may not allow acorns to reach safe germination sites, and the encroachment of conifer trees, mainly Douglas-fir (Pseudotsuga menziesii), due to fire suppression.

Air pollution may be a potential threat to twisted oak moss populations in the Victoria area. Adams and Preston (1992) note that compared to other moss species in the United Kingdom, twisted oak moss appears to be one of the most sensitive and adversely affected by air pollution. Many of the known sites for twisted oak moss in B.C. are near roadways; automobile exhaust pollution may affect some populations, although this is unknown. Most or all of the urban populations could have their viability reduced and some could be extirpated.

The Garry Oak Ecosystems Recovery Team (GOERT) has a land owner contact program for informing land owners of the potential for Garry oak species to be found on their lands. The team has also produced a field manual (GOERT 2009) to educate land owners and land managers about species at risk found in Garry oak ecosystems, including twisted oak moss, and to suggest management activities.

The management goal is to maintain known populations of twisted oak moss in British Columbia.

No quantitative management goal is possible for this species as basic population demographics and population trends are unknown for all known populations. As this species is restricted to small and specialized habitats, it is highly susceptible to being disturbed or destroyed. Therefore, to prevent twisted oak moss from becoming threatened or endangered, all known populations should be maintained. Once the knowledge gaps have been filled, particularly clarification of the species’ distribution, the goal can be refined.

  1. To initiate habitat protection[3] for existing populations by 2016.
  2. To mitigate the threats of direct destruction to the moss and determine if lack of recruitment of host trees is a direct threat to all known populations by 2015.
  3. To clarify the distribution of twisted oak moss in British Columbia and to update population and distribution objectives as needed by 2014.
  4. To increase public awareness of the existence and conservation value of twisted oak moss by 2016.
  5. To address knowledge gaps relating to demographics, effects of competition with other species, microhabitat attributes, and microclimate and habitat conditions for this species by 2016.

3 Protection can be achieved through various mechanisms including: voluntary stewardship agreements, conservation covenants, sale by willing vendors on private lands, land use designations, and protected areas.

Table 3. Recommended management actions for twisted oak moss.
Priority Obj. No. Threat or concern addressed Conservation Framework action group Management action Timeline
(start date)
High 1,4 Habitat loss and degradation, Direct harm Habitat Protection
  • Determine land ownership of populations
 2011
Habitat Protection; Private Land Stewardship
  • Utilize the Garry Oak Ecosystems Recovery Team’s land owner contact program and outreach program to contact landowners (3) and land managers (BC Parks and Protected Areas, University of Victoria, Camosun College, Department of National Defence, Capital Regional Parks, Nature Conservancy of Canada) to gain their cooperation to steward and manage lands for persistence of the species, as well as to deliver public educations and outreach concerning twisted oak moss and its management to naturalist and outdoor recreation clubs, and local governments (7).
 2012
Habitat Protection; Private Land Stewardship
  • Develop site-specific management plans to reduce threats and maintain or increase populations where required
 2013
Habitat Protection
  • Review tree cutting bylaws and determine if minimal diameter of Garry oak trees is small enough to prevent removal, and recommend changes to various municipalities if not
 2012
Habitat Protection
  • Establish monitoring protocols to assess populations and their responses to management techniques
 2012
High 2 ALL Monitor Trends
  • Establish monitoring protocols to assess threats
 2012
Monitor Trends
  • Monitor sites to assess the effects of mitigation actions and protection measures
 2012
Monitor Trends
  • Collect ongoing data on site parameters that will allow interpretation of population trends
 2013
Monitor Trends
  • Adapt management of sites based on the above and on type of land tenure
 2014
High 3 Knowledge gap: population statistics; clarification of distribution Compile Status Report
  • Survey all known sites to determine population size
 2012
Compile Status Report
  • Conduct inventory surveys in areas of potential habitat that have not been previously searched and document any new populations
 2013
Medium 5 Knowledge gaps Compile Status Report
  • Conduct demographic studies
 2014
Compile Status Report
  • Determine the effects of competition from other species
 2014
Compile Status Report
  • Determine microhabitat attributes
 2014
Compile Status Report
  • Determine microclimate and habitat conditions
 2014
Compile Status Report
  • Determine if lack of recruitment of Garry oak trees is a threat to this species
 2012
Compile Status Report
  • Determine air pollution effects
 2014
Compile Status Report
  • Determine age class of host trees
 2014

Recommended actions have been categorized by the action groups of the Conservation Framework.

Habitat protection
Once the knowledge gaps have been investigated for the compilation of an updated COSEWIC status report, habitat protection measures should be implemented on the unprotected populations. Currently, of the 27 known populations, there are three private locations and one unknown tenure (population #1 at Pedder Bay). To protect these unprotected populations, municipal tree protection bylaws could be amended to include the protection of young, smaller diameter Garry oaks as well as the retention of mature Garry oak trees. The remainder of the 27 populations are on municipal property, two are on institutional lands (University of Victoria and Camosun College) one on federal lands (Department of National Defence), three are in ecological reserves, one is on Nature Conservancy lands, and one is in a regional park. Protection at these 27 sites could be improved by adopting some existing best management practices for urban and rural development within British Columbia developed by the Ministry of Environment (Ministry of Environment 2006); the BMPs include a general section on Garry oak ecosystems. However, more specific best management practices could be developed for this ecosystem and the associated species.

Private land stewardship
Through the Garry Oak Ecosystems Recovery Team’s land owner contact program, land owners and land managers can be made aware of the species and possibly engaged in future survey and stewardship activities for this species. The GOERT outreach program also works with other partners, such as the Habitat Acquisition Trust Foundation and the Garry Oak Meadow Preservation Society, to increase awareness of the values of Garry oak ecosystems.

Monitor trends
The extant populations should be revisited to confirm population sizes. Once population statistics have been gathered, an effective monitoring strategy must be implemented so that success of all aspects of the management plan can be measured. This must be completed concurrent with or closely following the documentation of population attributes.

Threats, although described in a general nature in COSEWIC (2004) need to be more fully described and understood for each known population, and possible mitigation measures need to be defined. Further, threats that can be measured must be monitored and assessed, and, if mitigative measures are introduced, these must also be monitored.

Compile status report
As baseline information is needed to complete an updated COSEWIC status report for this species, areas of potential habitat should be thoroughly investigated for twisted oak moss. In order to undertake effective management of twisted oak moss, this information should include: population statistics, including the size and numbers of patches per population, and the extent of occurrence at each known population.

Research is needed to determine the demographics, effects of competition with other species, reproduction, and dispersal methods, as well as the habitat and microhabitat attributes for this species.

Objective 1: Land owners at the three private locations and land managers for all of the seven municipalities and the remaining institutional, provincial, and federal properties have been contacted and have applied the appropriate tools (e.g., stewardship, best management practices) for habitat protection by 2016.

Objective 2: Specific details about the known threats of loss of host trees, direct removal of the species from host trees, and recruitment of host trees have been investigated, and potential new threats at all known locations have been documented by 2014. Mitigation measures, best management practices, or specific site management plans are developed and monitored to decrease the impact of these threats by 2016.

Objective 3: Re-surveys of the 27 known locations on Vancouver Island have been conducted and documented by 2014. 60% of suitable habitat not previously searched in Garry oak ecosystems on lower Vancouver Island has been surveyed to document occurrence of twisted oak moss by 2016.

Objective 4: At least six land owners or land managers (in addition to those at currently known sites) within the species’ potential range have been contacted and provided with education and outreach material for twisted oak moss by 2016.

Objective 5: Research on knowledge gaps (e.g., reproduction and dispersal, effects of competition from other species, microhabitat attributes, microclimate and habitat conditions) have been initiated by 2014.

Habitat protection for this species will also protect other flora and fauna of Garry oak ecosystems. In particular, understanding the relationship between twisted oak moss and mature Garry oaks will lead to greater awareness of the importance of maintaining the remaining oaks and associated oak ecosystems. Understanding ways to increase recruitment of host trees and retention of these to maturity will also protect other species that rely on Garry oak ecosystems and will contribute to habitat protection over the long-term.

Land managers and the public should be made aware of the species and engaged in its conservation. This can partially be accomplished by directed land owner contact programs such as through the Garry Oak Ecosystems Recovery Team. GOERT could also work with the Ministry of Environment, BC Parks and Protected Areas Branch, as well as with the municipalities, to clarify distribution and land tenure and to assess and mitigate threats (Table 3).

Adams, K.J. and C.D. Preston. 1992. Evidence for the effects of atmospheric pollution on bryophytes from national and local recording. Pages 31–43 in P.T. Harding, ed. Biological recording of changes in British wildlife. ITE Symposium 26. www.ceh.ac.uk/products/publications/documents/Biological_recordingofchanges.pdf [Accessed Mar. 2, 2010]

B.C. Conservation Data Centre. 2010. BC Species and Ecosystems Explorer. B.C. Min. Environ., Victoria, BC.http://a100.gov.bc.ca/pub/eswp/ [Accessed Feb. 12, 2010]

Committee on the Status of Endangered Wildlife in Canada (COSEWIC). 2004. COSEWIC assessment and status report on the twisted oak moss Syntrichia laevipila in Canada. Ottawa, ON.

Fuchs, M.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., Pacific and Yukon Region.

Garry Oak Ecosystems Recovery Team (GOERT). 2009. Field Manual: Species at Risk in Garry oak and Associated Ecosystems. http://www.goert.ca/documents/Syntrichia_laevipila_insert_sheet.pdf [Accessed Feb. 19, 2010].

Lawton, E. 1971. Moss flora of the Pacific Northwest. Hattori Botanical Lab., Nichinan, Japan.

Miles, W. 2001. Untitled and unpublished report for the B.C. Conservation Data Center.

Ministry of Environment. 2006. Develop with care: environmental guidelines for urban and rural land development in British Columbia. Pages 5.1.-11 – 5.1-12. http://www.env.gov.bc.ca/wld/documents/bmp/devwithcare2006/DWC%202006%20Sec%205-1%20VI%20Region.pdf

Ministry of Environment. 2010. Conservation framework. B.C. Min. Environ., Victoria, BC. http://www.env.gov.bc.ca/conservationframework/index.html [Accessed Feb. 12, 2010]

Mischler, B.D. 2007. Syntrichia. Pages 618–627 in Flora of North America Editorial Committee, eds. Flora of North America north of Mexico. Vol. 27, Bryophytes: Mosses, part 1. Oxford Univ. Press, New York, NY.

NatureServe. 2009. NatureServe explorer: an online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, VA. http://www.natureserve.org/explorer [Accessed Feb. 12, 2010]

Smith, S. 2007. Garry oak savannah stand history and change in coastal southern British Columbia. M.Sc. Thesis, Univ. Guelph, Guelph, ON. 157 pp.

Washington Natural Heritage Program. 2009. List of rare mosses. Washington State Dep. Nat. Resour. www1.dnr.wa.gov/nhp/refdesk/lists/mosses.html

Personal communications

Wynne Miles. Consultant. Victoria, BC.
Terry McIntosh. Consultant. Vancouver, BC.
Shyanne Smith. Botanist. Victoria, BC.

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2022-02-24