Porsild's bryum (Haplodontium macrocarpum) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

Brassard and Hedderson (1983) remarked that Mielichhoferia macrocarpa sites are constantly moist with seepage or splash. This is true for all sites seen during the growing season; however, Cleavitt (2002a) has noted that their sites become dry seasonally when water at the sites is frozen (i.e., usually November to late June). Flowers (1973) also noted this for sites in Utah, and this period of freezing-desiccation may represent an important aspect of 'suitable habitat' for M. macrocarpa for two reasons. This moss may be physiologically adapted to this environmental regime (see section on Physiology) and the disturbance caused by the ice actually may reduce competition with other species (see section on Interspecific Interactions).

Mielichhoferia macrocarpa has been collected from mainly montane areas on limestone, basalt, sandstone and shale (Brassard & Hedderson 1983). At the Alberta study sites, it occurs on silt in cracks of calcareous conglomerate, limestone, and shale. Despite the observation of Shacklette (1967) on one population growing on basalt in Alaska, from which he concluded that the species was found only on substrates with greater than average concentrations of heavy metals, the bulk of collection information does not support such a substrate restriction. Experimental confirmation of this would require chemical analysis of substrates and heavy metal toxicity experiments. The substrates reported in herbarium collections encompass many rock types, although they tend to be calcareous (Brassard & Hedderson 1983; Cleavitt pers. obs.). In an experiment comparing establishment on native versus non-native substrates (in this case, acidic substrate high in organic matter), M. macrocarpa had significantly lower regeneration on the acid substrate and is therefore demonstrably a calciphile, i.e. requiring basic substrates by physiological intolerance of other substrates (Cleavitt 2001).

Trends

Although the re-collection of the species at the same sites over time suggests long-term habitat stability, there are exceptions. The Straitsview population in Newfoundland was recently reduced from several hundred colonies to nine colonies. This site was noted by Hedderson (pers. com.) as harboring the largest known Newfoundland population. Local people commented that the winter of 2001-2 was particularly bad for ice scouring and rock fall in that area. Populations in Alberta were damaged during 2002 by drought conditions. Several of the populations in the Cadomin area had decreased in size since their last documentation in 2000. It is not known how fast Mielichhoferia macrocarpa populations can recover from these disturbances.

Protection/ownership

This section largely discusses the visited sites and position information for these sites is given in Appendix 1. Several Alberta populations are known to be in designated protected areas. Part of the Cadomin - Mountain Park populations are located in the Whitehorse Creek Wildland Park established in 2000. However, several important populations remain unprotected and vulnerable to damage by recreational use or development of the area. Most notably a population currently located by a fire pit in the Whitehorse Creek campground was recently threatened by road building development relating to the Cheviot Mine Project (development application still active as of 2003). The location fits the description of Pegg's 1966 collection record, and the Mountain Park population first collected by Vitt in 1984. The Trolls Falls population is located in the Kananaskis Country Provincial Park, although the site currently has very high visitor traffic and no special restrictions against disturbing the rock cliff. The recently discovered British Columbia population is located in an area between and outside Muncho Lake and Stone Mountain Provincial Parks. Because the sites are opposite a parking area along the Alaska Highway, they are likely to attract a good number of unmonitored visitors who may inadvertently scrape populations from the rocks. The Newfoundland populations are on Crown land with no protection status (Djan-Chékar, personal communication). The two largest populations are at Cape Onion and White Cape.