Lemmon’s holly fern (Polystichum lemmonii) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

In western North America, Polystichum lemmonii is restricted to sites where ferromagnesian or ultramafic rocks outcrop (Kruckeberg 1969; Wagner 1993). Although a number of ultramafic rock outcrops occur in western British Columbia, only the two small ridges in the Baldy Mountain area support the latter species. These rock outcrop (dunite) habitats are also characterized by shallow soils and a sparse groundcover, creating xeric microclimates that also exclude many nearby species adapted to more mesic microclimates. Therefore, these ridges have a typically depauperate ultramafic flora and lack a tree cover. This is in contrast to the surrounding montane forests dominated by Douglas-fir (Pseudotsuga menziesii). Conspicuous species on the ridges include: Common juniper (Juniperus communis), Indian’s dream (Aspidotis densa), alpine sandwort (Minuartia obusiloba) and yarrow (Achillea millifolium).

Trends

Habitat trends are mainly dependant on the development activities at the sites. The most direct threat to Polystichum lemmonii is either mining exploration or forest road construction.

Protection/ownership 

There is no specific legislation for the protection of rare and endangered vascular plants in British Columbia. The Conservation Data Centre has ranked this species as S1 and placed it on the British Columbia Ministry of Sustainable Resource Management Red list. This is the most critical category for imperiled rare native vascular plants in the province. A rank of S1 is considered “critically imperiled because of extreme rarity (5 or fewer occurrences or very few remaining individuals) or because of some factors making it especially vulnerable to extirpation or extinction". Globally, P. lemmonii is ranked as G4 and is frequent to common in its range. The species has been reported for Washington and Idaho (SR) and is ranked S4 in Oregon.

The population in the Baldy Mountain area is on public land but is not part of a protected area. It is conceivable that this area could qualify as an ecological reserve but this status has yet to be proposed.

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