Twisted oak moss (Syntrichia laevipila) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

In British Columbia,Syntrichia laevipila is restricted to the bark of trees, in particular Garry oak. It appears most common on tree boles, but is also found on tree bases and on upper branches. Recent investigations have revealed that it is also on big-leaf maple in the Victoria area, although this may be an unusual habitat for this species in Canada. Also, big-leaf maple is characteristic of more mesic habitats and is not common in the open habitats characterized by Garry oak. Most populations of the twisted oak moss are found on exposed bark of trees in open habitats where the climate is characterized by hot to mild, dry summers and cool to cold wet winters. In the United States, it is also found on Garry oak as well as, occasionally, on other tree species, in particular big-leaf maple (Harpel 1997). Merrifield (2000) provides detailed habitat information for this species in Oregon, noting that it is common only on drier aspects of Garry oaks, and that S.laevipila var. meridionalis was found at lower elevations than S. laevipila var. laevipila (under 100m vs. up to ~200m).

Syntrichia laevipila rarely is found growing admixed with other mosses or lichens, which may indicate that it may not compete well with other epiphytic taxa.

Trends

Most of the habitats in which this species was collected appear stable (Table 2, Column C) and, with respect to the trees on which they grow, undisturbed (however, the associated habitats of these trees are often heavily disturbed as the trees are on lawns or near roads). There is some concern for those populations within city limits or in areas where only older oaks are found. There is little to no replacement of these older trees and, at some point, these trees will die, probably eliminating these populations of Syntrichia laevipila. Widespread loss of elms (Ulmus spp.) through disease in the Netherlands has greatly reduced the number of populations of Syntrichia laevipila there (van Zanten 1992). This type of destruction of Garry oaks is possible in British Columbia considering that sudden oak death (SOD) has been responsible for wide scale destruction of oaks in California and southern Oregon, although Quercus garryana there is not affected by this disease to date.

Protection/ownership

Approximately one half of the sites are in parks or Ecological Reserves and protected from tree cutting or further development. The other sites are street trees or are located on private lots. Legislation in six municipalities prevents or restricts the cutting of Garry oaks.