Seaside centipede lichen (Heterodermia sitchensis) COSEWIC assessment and status report: chapter 2

• Previous page
• Table of contents
• Next page

Executive Summary

Species information

Heterodermia sitchensis Goward & Noble is a pale greyish, leafy, basally attached lichen belonging in the Physciaceae. It can be recognized by the presence of marginal cilia and tiny urn-like structures near the lobe tips. It was described from western Vancouver Island.

Distribution

In Canada, H. sitchensis occurs only in coastal British Columbia, where it ranges 210 km from northern Vancouver Island south to Pacific Rim National Park. Outside of Canada, it is known from a single outlying population in coastal Oregon.Within this region, it is known exclusively from the Very Wet Hypermaritime subzone of the Coastal Western Hemlock Zone (Meidinger & Pojar 1991).

Habitat

Throughout its range, H. sitchensis occurs exclusively at seaside on nitrogen-enriched twigs in the lower canopy of oldSitkaspruce trees.

Biology

In keeping with its strong tendency to colonize small twigs, H. sitchensis is a short-lived species with a life cycle in the order of 10 to 15 years. By the end of that period, its substrate is usually overgrown to mosses, hepatics and other lichens, all of which tend to outcompete it. Heterodermia sitchensis reproduces exclusively via soredia, i.e., powdery asexual propagules made up of algal cells and fungal hyphae. Dispersal seems poor, with forest birds probably providing important vectors for this species.

Population sizes and trends

A total of 227 thalli of H. sitchensis have been recorded in Canadato date. These are divided among twelve spatially separate populations, two of which are now extirpated, and the three largest of which contain 148 thalli, or 65% of all thalli. Population size can vary markedly from year to year, depending on the intensity of winter storms. However, no long-term trends in population size have been documented to the present time.

Limiting factors and threats

As a pioneer lichen, H. sitchensis must colonize at frequent intervals. In order to become established, however, it must first successfully disperse its propagules to seaside Sitka spruce twigs subject to high concentrations of nitrogen. The infrequency of such habitats ensures that H. sitchensis is rare throughout its range, and hence especially vulnerable to disturbance.

Where not protected by legislation (as in parks), H. sitchensis is threatened primarily by logging activities, especially where large old Sitka spruce trees are targeted. Other threats include damage by winter storms, housing developments and, on a smaller scale, twig collection for campfires.

Special significance of the species

Heterodermia sitchensisis among the most northerly members of a predominantly tropical to warm temperate genus. It is also essentially endemic to Canada, where it occupies a very narrow latitudinal range along the west coast of Vancouver Island. The soredia-bearing "urns" located near the lobe tips in this species are seemingly unique among lichens.

Existing protection

H. sitchensisis known from ten localities in Canada, five of which are situated in Pacific Rim National Park Reserve. Here they are protected from human disturbance by the National Parks Act.

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. Species designated at meetings of the full committee are added to the list.  On June 5^th 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 for 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 entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species. 

Definitions (2006)

Species

Any indigenous species, subspecies, variety, or geographically defined 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.

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. Species designated at meetings of the full committee are added to the list.