Twisted oak moss (Syntrichia laevipila) COSEWIC assessment and status report: chapter 12

Technical Summary

Syntrichia laevipila

Twisted oak moss - tortule à poils lisses

Range of Occurrence in Canada:
British Columbia

Extent and Area Information

Extent of occurrence (EO)(km²)
~1890km²
Specify trend in EO :
stable
Are there extreme fluctuations in EO?
no
Area of occupancy (AO) (km²)?
< 20km²
Specify trend in AO :
stable
Are there extreme fluctuations in AO?
no
Number of known or inferred current locations :
31, 25 confirmed in recent surveys, 4 not found, 2 sites not visited
Specify trend in # :
unknown
Are there extreme fluctuations in number of locations?
no
Specify trend in area, extent or quality of habitat :
stable – many Garry oak sites are in protected areas and cutting prohibited in 6 municipalities

Population Information

Generation time (average age of parents in the population) :
perennial
Number of mature individuals :
minimum # is 305 individuals (clumps)
Total population trend:
unknown, but may decline sharply in future as older trees die; seedling establishment replacing aging population appears very low
% decline over the last/next 10 years or 3 generations.
unknown
Are there extreme fluctuations in number of mature individuals?
no
Is the total population severely fragmented?
yes
Specify trend in number of populations :
unknown, but individual populations appear healthy
Are there extreme fluctuations in number of populations?
no
List populations with number of mature individuals in each:

Threats (actual or imminent threats to populations or habitats)

tree harvesting, the potential of the death of older host oaks and low rate of seedling establishment

Rescue Effect (immigration from an outside source)

Status of outside population(s)?
USA: occurs in Washington, Oregon, California
Is immigration known or possible?
no
Would immigrants be adapted to survive in Canada?
yes
Is there sufficient habitat for immigrants in Canada?
yes
Is rescue from outside populations likely?
Not known

Quantitative Analysis

Not applicable

Other Status

globally secure; possibly rare in Oregon

Additional Sources of Information: Total Garry oak population in SW B.C. is estimated at &gt;100,000 stems of all ages. Given that the species is known from 69 trees, and assuming 1 stem/tree, then given that the species was found on 4.3% of the trees examined (about 1600, page 4), a crude population estimate of the number of trees hosting the species could be 4300. However, since the species does not grow on young trees (included in the 100,000 estimate) and appears to have specific requirements with respect to shade (T. McIntosh pers. comm., Feb 2004), then this number is certainly an overestimate.

The Garry Oak Ecosystems Recovery Team has looked at recruitment, and despite the loss of much Garry oak habitat on southern Vancouver Island and the Gulf Islands, has determined that there are probably as many or more Garry oaks on southern Vancouver Island as there were historically due to extensive recruitment due to lack of fires, but most of these are not mature trees.

According to Ted Lea and Marilyn Fuchs (BC Environment, pers. comm., to McIntosh Feb 2004), urban oaks are declining. They will do so more in the future because of homeowner concerns regarding branches and trees falling on structures or people. Lea says that 99% of all deep soil oaks (high potential for twisted oak moss presence) have been lost in Victoria and Cowichan areas (T. Lea, pers. comm., 2004), and in most city sites outside of protected parks (where most of the trees are open or growing on rock outcrops and, therefore, less likely to have the moss on them), there is little to no opportunity for regeneration in many sites (seedlings are mowed or removed by hand). Since most twisted oak moss sites are in the Victoria area (and where about 1/3 to date of the trees where it has been collected are not protected), then there is a real threat.

Status and Reasons for Designation

Status: Special Concern

Alpha-numeric code: Met criteria for Threatened, D2, but designated as Special Concern because of the high potential numbers of Garry Oak host.

Reasons for Designation: This moss is a small species that occurs from British Columbia and Washington southward to California. The Canadian populations are at the northern limits of their range in western North America, and in Canada the species has a restricted distribution where it occurs in the area of south-eastern Vancouver Island and the Gulf Islands. The species is known from 25 sites where it is restricted to the bark of trees, in particular Garry oaks. This species is never dominant where it grows, nor is it frequent in large oak stands.  Many of the known populations are in protected areas. The major threat to the species is the disappearance of mature Garry oaks, which would result in the extirpation of most populations of this species.

Applicability of Criteria

Criterion A (Declining Total Population): does not meet thresholds for decline (no decline is documented)

Criterion B (Small Distribution, and Decline or Fluctuation): does not meet thresholds for small population (too many known sites), or decline or fluctuation

Criterion C (Small Total Population Size and Decline): would meet criteria for Endangered, 2a(i), based on inferred future decline due to lack of regeneration of Garry oak in parts of its range; however, there is no evidence for future decline of Garry oak.

Criterion D (Very Small Population or Restricted Distribution): meets criteria for Threatened, D2

Criterion E (Quantitative Analysis): not applicable.

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