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COSEWIC assessment and status report on the Dense Spike-primrose (Epilobium densiflorum) in Canada

Habitat

Habitat requirements

Raven and Moore (1965) describe its habitat as wet places that are sometimes seasonally dry, from sea level to 2600 metres. In Canada, Epilobium densiflorum occurs in vernally moist meadows and roadsides (which dry below the permanent wilting point for much of the summer) in the dry coastal lowland zone (Coastal Douglas-fir zone – moist maritime subzone) of British Columbia (Douglas and Meidinger 2002). The permanent wilting point is reached when soil moisture has reached the point where it is not sufficient to meet the needs of a plant and it subsequently dies.

Gilkey and Dennis (1967) describe its habitat in Oregon as low ground and dried pools. In California, it occurs along stream banks and outwashes less than 2600 metres above sea level (Hoch 1993).

In Montana, it occurred on a disturbed site in vernally wet soils around pools about 900 metres above sea level (Booth and Wright 1966, Montana Natural Heritage Program 2003). In Idaho, Epilobium densiflorumoccurs on sites that are more or less moist early in the season, and then become dry later on (Davis 1952). In Utah, it occurs in marshy areas from 1310 to 1435 metres above sea level, in two counties (Welsh et al. 1987).

Trends

The amount of potential habitat has declined greatly over the past century as coastal areas in southeast Vancouver Island have been developed for residential and recreational use. Less than 1% of the Coastal Douglas-fir biogeoclimatic zone remains in a relatively undisturbed state (Pacific Marine Heritage Legacy 1996). Garry oak ecosystems in the Victoria region have declined from 10,510 ha in 1800 to 512 ha in 1997 (Lea 2002); even more has been lost since then, and most of what remains has been heavily altered through invasion by exotic grasses and shrubs. Habitats suitable for Epilobium densiflorum have probably suffered proportional declines in area and quality.

This past trend in habitat destruction and alteration mirrors the loss of populations of Epilobium densiflorum. Most pre-1980 collections of Epilobium densiflorum lack precise location data, which makes it difficult to identify the changes that took place in their specific populations. Nine of the nineteen locales (Qualicum, Departure Bay, University of Victoria, White Rapids Road, Swartz Bay, Rithet’s Bog, Uplands Park, King’s Pond and North Pender Island) have seen widespread property development since the time of collection and it is likely that the occupied habitats were destroyed. Two other locales (Wallace Drive, Swan Lake) have been greatly modified by the invasion of robust species and it is likely the occupied habitats were substantially modified as a result.

Habitat protection/ownership

Population No. 4 lies within a park belonging to the Capital Regional District. This is the only site that currently has any formal protection. The Capital Regional District (CRD) has recently given the conservation and management of rare threatened and endangered plants and wildlife, and their supporting habitats, precedence over all other park uses (Capital Regional District Parks 2000). The City of Victoria planted Abies grandis on this site several years ago, before the area was transferred to the CRD. Apart from the threat posed by Abies grandis, thehabitat has also been invaded by woody vegetation including Crataegus monogyna (introduced) and Alnus rubra (a native species). These woody species have had a serious impact on the habitat and may eventually lead to a decline in the population.

Population No. 1 and population No. 3 occur on private land. Population No. 2 occurs along a road allowance through Cowichan Tribal Lands (Indian Reserve property). The area occupied by population No. 1 is now the subject of a residential development proposal (pre-development environmental studies began in September 2003). Neither it nor the other two populations on private lands has any protection.