Brook spike-primrose (Epilobium torreyi) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

Search effort

Suitable sites have been surveyed repeatedly since the early 1980s in a series of projects designed to document the distribution of rare plants in open meadows in southeast Vancouver Island and the Gulf Islands. The principal investigators included Adolf and Oldriska Ceska, Chris Brayshaw, Hans Roemer, Harvey Janszen, Frank Lomer, George Douglas and Matt Fairbarns. During the past decade alone, over 500 person-days have been spent searching for rare species in suitable habitats.

This most recent survey effort (2004) includes two searches specifically for Epilobium torreyi, involving approximately 60 hours, not including travel time. These directed searches examined historic locations of Epilobium torreyiand extant/historic locations of other rare species (E. densiflorum, Navarretia intertexta) which occur at the historic Craigflower Meadow location of E. torreyi. The following areas were searched by M. Fairbarns in July 2004: Craigflower Meadow, View Royal; McTavish Road, North Saanich; Khenipson Road, near Duncan; Somenos Creek, near Duncan; Vantreight Farms, Central Saanich; Whitehead Park, Saanich; Willow Way, Central Saanich; Layritz Park, Saanich; University of Victoria; White Rapids Road, Nanaimo; Rithets Bog, Saanich; Viaduct Flats, Saanich; Uplands Park, Oak Bay (sites mapped in Figure 4).

Abundance

Both reported populations of Epilobium torreyi in Canada are presumed extirpated based on surveys in 2001-04 (Table 2). The Craigflower Meadows population was last observed in 1993 and has not been observed in subsequent surveys including detailed examinations in 2001, 2003 and 2004. The McTavish Road population was observed once in 1966, but subsequent searches (including careful surveys in 2001 and 2003) have failed to rediscover the population. The habitats favoured by this species have been the subject of extensive botanical investigation for many years.

Fluctuations and trends

Both historic populations have been extirpated.

Rescue effect

The nearest reported population is from Orcas Island, Washington. The site is approximately 16 km from the nearest point in Canada and 37 km from the nearest historic location in Canada. The Orcas Island collection was documented to be in an atypical habitat (Atkinson and Sharpe 1993). Epilobium torreyi is not known from elsewhere in the San Juan Islands and the next nearest location appears to be in Thurston County, approximately 150 km to the south.

There is little chance of seed dispersal, even from plants on Orcas Island, since the seeds lack a coma or any other structure to aid in long-distance dispersal.