Porsild's bryum (Haplodontium macrocarpum) COSEWIC assessment and status report: chapter 2

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COSEWIC Executive Summary

Species information

Although this species is currently placed in the genus Mielichhoferia, interpretations of recent molecular data suggested a closer relationship with members of the genus Bryum for this species. Pending publication, the correct name for Mielichhoferia macrocarpa will be Bryum porsildii. The most notable macroscopic characteristics for species recognition include the small size, lax shiny leaves, growth in dense cushions and often copious sporophyte production.

Distribution

The species is widely disjunct throughout northern latitudes and this distribution is referred to as holarctic disjunct. There are ten known localities for Mielichhoferia macrocarpa in Canada and twenty-seven locations in North America. The majority of known sites are associated with western mountain ranges.

Habitat

Consistent aspects of Mielichhoferia macrocarpa habitats include the presence of constant seepage through the rock substrate during the growing season coupled with complete desiccation (due to water freezing) during the winter season. The rock is generally calcareous, but this has not been documented at all collection sites. All of the rock cliff habitats visited are also prone to seasonal disturbance from ice scouring and rock fall.

Biology

Mielichhoferia macrocarpa is capable of both sexual and asexual reproduction and production of spores is frequent when plants of both sexes are present at a site. Survival of individual colonies is controlled more strongly by the rock cliff disturbance regime than by competition with other colonies. On the other hand, competition may be more important during the establishment stage. Much of the existing physiological data for M. macrocarpa suggests that this species is adapted to alternating between long periods (months) of photosynthetic activity and long periods of inactivity in a desiccated state.

Population sizes and trends

Populations (defined subjectively by spatial discontinuity between groups of colonies) differ in the rate of colony mortality. During periods of rock cliff stability, mortality can be as low as 14% over three years. However, when sites are unstable one catastrophic event can reduce a population of hundreds of colonies to near extirpation, and this has been documented in a Newfoundland population. The longest (minimum) record for continued existence of colonies at the same location is 75 years for a Greenland population.

Limiting factors and threats

This moss may be limited by suitable habitat availability and dispersal and establishment ability. Threats to populations of this species include any natural or anthropogenic events that could destabilize its rock cliff habitats. For example, recent natural disturbance events have resulted in a net loss of approximately 15% of the known colonies in Canada.

Special significance of the species

Mielichhoferia macrocarpa was hypothesized to belong to an ancient and once widespread flora and has great scientific value for answering questions relative to this flora in terms of the origins of local populations and species.

Existing protection or other status designations

There is no existing legal protection for this species. It has been ranked as S1 (less than 5 occurrences in Province/State) and G2 (globally rare) on both Alberta and Montana natural heritage program tracking lists. None of the known populations occur in National Parks.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species and include the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal organizations (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership, chaired by the Canadian Museum of Nature), three nonjurisdictional members and the co-chairs of the species specialist and the Aboriginal Traditional Knowledge subcommittees. The committee meets to consider status reports on candidate species.

Definitions (After May 2003)

Species

Any indigenous species, subspecies, variety, or geographically or genetically distinct population of wild fauna and flora.

Extinct (X)

A species that no longer exists.

Extirpated (XT)

A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A species facing imminent extirpation or extinction.

Threatened (T)

A species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^Footnotea

A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)^Footnoteb

A species that has been evaluated and found to be not at risk.

Data Deficient (DD)^Footnotec

A species for which there is insufficient scientific information to support status designation.