Twisted oak moss (Syntrichia laevipila) COSEWIC assessment and status report: chapter 8

Limiting Factors and Threats

Table 2 (Column B) lists the limiting factors and threats for each known population of the twisted oak moss. Tree harvesting or branch cutting may be a threat to the populations of Syntrichia laevipila that are on private property. However, with an increase in awareness of the ecological importance of Garry oaks, supported by legislation in some municipalities, removal of Garry oaks has become highly restricted. Also, many of the known sites for this moss are within protected areas that do not allow for the removal of Garry oaks. A more serious threat is the general lack of regeneration of Garry oaks across their range, even within some protected areas. Although mature oaks are common in Victoria at present, there appears to be little evidence that this population will be maintained over the long term, as young oaks are often removed, at least on many private properties. In other areas, such as in the Mt. Maxwell Ecological Reserve on Salt Spring Island, there are abundant older oaks, but regeneration of oaks there is minimal, mostly due to grazing by feral sheep and goats, and deer, although the situation there is improving following efforts to remove sheep and goats. Since S. laevipila is only found on older oaks, lack of oak regeneration is a major concern.

Table 2. Habitat and General Characteristics of Known Populations of Syntrichia laevipila in British Columbia (see Table 1 for additional population information).
A
Population
B
Limiting Factors and Threats
C
Habitat Condition and Trend
D
Population Size and Trend
E
Protection and Ownership
1 B, C, D, E A, B A (1.0), B street; municipal
2 C, D, E A, B A (1.0), B library; municipal
3 B, C, D A, B C (<0.01), B private lot
4 D A, B B (0.03), B municipal park
5 B, C, D, E A, B A (0.5), B street; municipal
6 C, D, E A, B B (0.2), B municipal park
7 C, D, E A, B A (0.3), B municipal park
8 C, D, E A, B A (0.1), B municipal park
9 C, D, E A, B B (0.2), B municipal park
10 C, D, E A, B B (0.06), B municipal park
11 C, D, E A, B B (0.3), B ?municipal
12 C, D, E A, B A (2.6), B street; municipal
13 C, D, E A, B B (0.8), B University of Victoria
14 C, D, E A, B A (0.6), B municipal park
15 C, D, E A, B A (1.8), B street; municipal
16 C, D, E A, B A (0.1), B recreation center; municipal
17 C, D, E A, B A (0.6), B municipal park
18 C, D, E A, B A (0.7), B school; municipal
19 C, D, E A, B A (1.8), B private lot
20 C, D, E A, B B (0.4), B street; municipal
21 C, D, E A, B C (< 0.01), B street; municipal
22 A A, B C (0.06), B regional park
23 C, D, E A, B B ( <0.02), B Ecological Reserve
24 C, D, E A, B B (0.05), B municipal park
25 C, D, E A, B B (0.03), B municipal park
26 C A, B ? Preserve
27 A A, B ? Ecological Reserve
28 ? ? ? ?
29 ? ? ? ?
30 C A, A C(<0.02), A regional park
31 C, D, E A, B A (1.8), B municipal park

Notes (in all cases, ‘?’ refers to ‘unknown’ or ‘uncertain’):

  1. With respect to Column B: A refers to no noticeable limiting factors or threats, B refers to tree or branch harvesting, C refers to lack of oak regeneration, D refers to potential air pollution, including by automobiles, E refers to human-related disturbances, including dogs.
  2. With respect to Column C: Habitat Condition (‘Habitat’ here refers only to the bark of the tree): A refers to no noticeable disturbance, B refers to moderately disturbed, C refers to heavily disturbed; Habitat Trend: A refers to improving, B refers to stable, C refers to degrading.
  3. With respect to Column D: Population Size: ‘A’ means more than twenty clumps, ‘B’ means five to twenty clumps, and ‘C’ means fewer than five scattered clumps. The number in parentheses is the approximate span of the population in ; this usually includes other bryophytes and exposed bark.; Population Trend: A refers to possibly improving, B refers to apparently stable, C refers to possibly degrading.

Air pollution may also be a threat to Syntrichia laevipila populations within or nearby urban centers, although this is unlikely, as these areas receive sea breezes which keep the air fresh. However, Adams and Preston (1992) note that S. laevipila appears to be one of the most sensitive and adversely affected moss species by air pollution in the United Kingdom. It has been shown to be sensitive to air pollution in other parts of Europe as well (e.g., Sim-Sim et al. 2000). Many of the known sites for the twisted oak moss are near roadways, and automobile exhaust pollution may affect some populations although this is unknown.

Some landowners remove mosses and lichens from oaks on their property, and this is probably of minor concern. Damage can occur to the bases of oaks in parks during routine grass or weed maintenance.

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