Management plan for Twisted Oak Moss in Canada [final] 2011: Needs of Twisted Oak Moss

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.

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.

• Population statistics, including size and number of patches per population, are not known for many populations.
• Age of host trees is not known at the extant sites.
• Research on reproduction and dispersal success is needed.
• The distribution and land tenure of twisted oak moss needs to be clarified.
• The effects on twisted oak moss of competition with other species are not known.
• Habitat conditions (e.g., exposure, level of shading, elevation, role of disturbance) for twisted oak moss are not known.
• The microhabitat attributes (e.g., of the bark) and microclimate conditions (moisture, temperature, light exposure) for twisted oak moss are not known.
• Whether lack of recruitment is a threat to twisted oak moss at the known sites needs to be determined.
• Whether air pollution has negative effects on twisted oak moss needs to be determined.