Dense spike-primrose (Epilobium densiflorum) COSEWIC assessment and status report: chapter 7

• Previous page
• Table of contents
• Next page

Population Sizes and Trends

There have been an estimated minimum of 19 and perhaps as many as 31 reported occurrences of Epilobium densiflorum in Canada (Table 2). 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, all of whom are familiar with the species. Over 1,000 ha of suitable habitat in over 80 sites has been investigated and much of it has been surveyed more than once during this period. During the past decade alone, over 500 person-days have been spent searching for rare species in suitable habitats. This survey effort includes two searches specifically for Epilobium densiflorum (approximately 10 person-days in 2001 and 8 person days in 2003). Despite the concentrated effort, only four populations were found in surveys carried out in 2001 and or 2003. Both 2001 and 2003 appear to have been suitable years for surveying Epilobium densiflorum, based on the number and vigour of plants at population No. 1 (2001, 2003), population No. 3 (2003), population No. 4 (2001, 2003) and population No. 2 (2001). The poor condition of population No. 2 in 2003 can be attributed entirely to physical site disturbance (see below).

Confirmed extant occurrences

Population No. 1

This large population has been known at least since 1999, although there are also a few older collections from Wellington with vague location data (e.g., Carter’s 1912 collection = UBC 86850) that may have been made at this site. Over 2,000 plants were counted in 2001. Surveys in 2003 demonstrated that although the majority of the population occurs within the area surveyed in 2001, the occupied area actually extends several hundred metres beyond the 2001 survey area.

Population No. 2

This population has been known at least since it was observed by Adolf and Oldriska Ceska in 1992. It is not clear how many plants occurred on the site in 1992 but there were 40 plants in 1994 and 420 plants in 2001. Considering the absence of additional survey data between 1994 and 2001, this sizable increase in number of this annual species is not viewed as a case of extreme fluctuation in population size (>1 order of magnitude). Further survey data would be needed to justify this assertion. The population occurred in and around a shallow ditch along a dry gravel roadside. The soil remained moist late into the spring as it was fed with water from a short seasonal runlet. Between 2001 and 2003 the area was modified by road grading, the establishment of a new lane running up the slope, and piling of slashed shrubs. Only one plant was observed in 2003. This represents a decline of about 10% of the total population.

Population No. 3

This population has been known at least since it was collected in 1966 (UVIC 009971). Earlier collections from the Sidney area may have also been made in this area (e.g., Macoun’s 1908 collection = CAN 83551). The population size and areal extent was not estimated in 1966, but there were 50 plants on the site in 2003 covering an area of approximately 2.5 m². Although the original 1966 collection locality is labelled somewhat differently, the 2003 observation likely refers to the same patch of plants. It occurs at the junction of two short roads, one of which was identified in the 1966 collection. No habitat similar to that indicated for the 1966 collection is found elsewhere in the area.

The property at the site of population No. 3 is a private lot. The plants grow in a shallow ditch or swale within a mowed residential lawn that is readily seen from the roadside. The main axis of most plants had been chopped off when the lawn was mowed but flowers had developed on axillary branches and fruit were already beginning to swell when the plants were observed in 2003.

Population No. 4

This large population has been known since 1958. The population appears to be relatively stable with numbers varying from 900 in August 1993, 750 in August 2001 and approximately 800 in August 2003.

Other reported occurrences

Historic collections

Qualicum

This population is represented by Carter’s 1910 collection labelled “Qualicum, Vancouver Island” (UBC 86863) and perhaps by his 1916 collection labelled “Wellington and Little Qualicum” (V 003398). The coastal strip from Qualicum Beach north to the mouth of the Qualicum River has been heavily developed for residential and recreational use since the plants were collected but small areas of suitable habitat may remain. Suitable sites throughout the species’ range in BC have been surveyed repeatedly, but with such a large extent of occurrence and the imprecise locality data for the historic Qualicum collection it is impossible to ensure that every patch of suitable habitat has been seen.

Departure Bay

This population is represented by a single collection made by Macoun in 1887 (CAN 83554). The area is now the site of a major ferry terminal and the vegetation has been dramatically altered by industrial development along with the establishment of many non-native grasses and forbs in the few remaining natural areas.

University of Victoria

This population was first reported in 1962 (UVIC 00967) and has not been seen since. It occurred under Garry oaks along a shaded trail. The Garry oak woodlands and meadows in and near the University of Victoria have been heavily impacted over the past 40 years. The disturbances include seeding and haying (which continued into the 1980s), temporary soil caching on the meadows during the Commonwealth Games and site development associated with the continued expansion of the university.

Extirpated populations

Cedar

This population, which occurred along the Cable Bay Trail, was near the boundary between private timber land and public land managed by the city of Nanaimo. There is limited data associated with the original observation. The original observers returned to the site in 2001 and did not find any plants. The population occurred in small, slightly depressional, shallow-soil pockets on a rocky slope dominated by meadow vegetation. The timber operator began a two-year timber harvesting operation in the vicinity. Their operations may have cut some of the Douglas-fir forests surrounding the meadow, and may have involved vehicle traffic on the meadow itself.

White Rapids Road

This population has been known at least since it was first collected in 1987 (V 171516). Earlier collections from the Wellington area may have also been made in this area (see above). Twenty-seven plants were observed in 2001 although it appears one of the subpopulations observed in 1987 had already disappeared by this point. Since then, the private property where the other two subpopulations occurred has been dramatically altered by clearing, fencing, draining and grazing. No plants could be found during a 2003 survey, although areas within the new fence were not comprehensively surveyed.

The known extent of the White Rapids Road population was separated from population No. 1 by a distance of no more than 3.5 km, and they may have once formed a single continuous population. The intervening area has now been altered by residential development and logging and appears to be unsuited to the species.

Maple Bay

This population, which occurred on private property, was first detected in 1986. The original collectors returned to the site in 2001 and did not find any plants. The shallow roadside ditch where they occurred had been deepened and the surrounding vegetation had changed from an open, grazed meadow to a tall dense sward dominated by Phalaris arundinacea.

Somenos Garry Oak Protected Area

The population occurred on unoccupied crown land that is owned by the province of British Columbia. The site was purchased by the crown in order to establish a protected area but it has not yet been designated as such.

This population has been known at least since it was first collected in 1992 (V 173045). It occurred in a narrow band of flat, seasonally wet area between wetlands along Somenos Creek and dry Douglas-fir forests sloping upwards to the east. The original observers returned to the site in 2001 and did not find any plants. The area was surveyed in great detail in 2003 for a number of rare species that had been previously reported. The former location of Epilobium densiflorum was visited on several different dates in 2003 but no plants were observed.

Portions of the flat area were irreversibly altered when contractors stockpiled fill for a proposed bridge across the creek. The bridge project appears to have been shelved but the fill remains on site. It is not clear whether the plants occurred in this precise area or elsewhere along the flat.

Spencer Pond

This population occurred on a seasonal pond that retains standing water through much of the summer and consequently has a central area dominated by emergent wetland vegetation. There is limited data associated with the original observation. The original observers returned to the site in 2001 and did not find any plants. The site was surveyed carefully in 2003 and no plants were found at that time although there was still suitable habitat in the vicinity of the original observation.

A 1922 collection by Newcombe (labelled “Langford”) may have come from the same population as the Spencer Pond plants (V 007046).

Swan Lake

This population is represented by a single collection made by Macoun in 1908 (CAN 83552). The area is now the site of a nature centre and trail system and has been visited by botanists regularly for many years. The vegetation around Swan Lake has been dramatically altered by hydrological changes and the establishment of many non-native grasses and forbs.

King’s Pond

This population occurred on the Cedar Hill golf course, which is owned by the municipality of Saanich. There is limited data associated with the original observation. The original observers returned to the original collection site (on the west side of King’s Pond) in 2001 and did not find any plants.

Detailed surveys were conducted in August 2003 around King’s Pond as well as in an elongate wetland approximately 100 m to the south, dried-up vernal pools between the two, and upland grassy patches in their vicinity. The drawdown area surrounding King’s Pond is dominated by a diverse assemblage of vigorous introduced species, including Lythrum salicaria. The upland grassy patches are gradually shrinking as patches of introduced shrubs (notably Cytisus scoparius) expand. The drawdown area around the elongate wetland is sparsely vegetated but the timing of drawdown may not favour Epilobium densiflorum. The vernal pools may have offered the most suitable habitat as standing water disappears relatively early in the growing season and they do not bear a dense cover of competing vegetation. Epilobium densiflorum was not observed in the 2003 survey and the population appears to have been extirpated, although the site should be resurveyed in years with different rainfall patterns to confirm this.

A 1920 collection by Anderson (labelled Cedar Hill) may have come from the same population as the King’s Pond plants (V 041702).

Uplands Park

This population has been known at least since it was collected by Melburn in 1953 (V 101214). It was subsequently collected in 1956 (UVIC 009968) and 1961 (DAO collection number unknown). Earlier collections from the area may have come from the same population (e.g., Davidson’s 1913 collection from “between Uplands and Tolmie” = CAN 83551 and Malte’s 1911 collection from “Oak Bay” = CAN 197576). Brayshaw (1991), in summarizing several years of observations, mapped several occurrences in Uplands Park. The park was surveyed unsuccessfully for occurrences of Epilobium densiflorum in 2001, and again in 2003 as part of a very detailed mapping exercise for numerous rare plants.

Rithet’s Bog

This population, which occurred on public lands owned by the municipality of Saanich, was first found in 1951. The authors of this report surveyed the site extensively in 2001 and 2003 and were not able to find Epilobium densiflorum. Most of the wetland is now overgrown by willows and introduced grasses (notably Phalaris arundinacea).

Wallace Drive

This population was collected in 1966 (UVIC 009969) and has not been reported since then. The collector no longer recalls any details regarding the collection site or population (B. Turner, pers. com. August 2003). The label data describes a 3-km segment of Wallace Drive. This area was searched unsuccessfully in August 2003. About 50% of the survey area had been converted to agricultural, residential or light-industry use. The remainder of the search area was either never capable of supporting the species, or had been severely altered by ditching in the 1980s (Dave Fraser pers. com. October 8, 2003) and invasive exotic weeds.

Swartz Bay

This population was first collected by Ashlee in 1954 (UBC 87934). Ashlee collected plants from the same area in 1958 (V 034640). The collection site (“Swartz Bay, weedy fill at the end of landing ramp”) has changed dramatically over the past 49 years and is now the main ferry terminal for Victoria. Most of this area is no longer capable of supporting vegetation. Remnant patches of weedy vegetation were surveyed without success in August 2003.

North Pender Island

The population occurred in a shallow, grassy roadside ditch by the old school on Pender Island, near Otter Bay. It was first collected by Janszen in 1981 (V 113544) but the site has been heavily impacted by construction activities over the past few years and Epilobium densiflorum is unlikely to persist (Harvey Janszen pers. com. 2003).

Misidentified collection

Courtney

Reports of E. densiflorum on mud flats at Courtney were based on a photograph that was later determined to be a different species (R. Walker, pers. com. August 2003).

Imprecise locations

A number of herbarium specimens of Epilobium densiflorum with imprecise location information on their labels may have come from one of the above locations. These include:

1. Sea’s Farm, near Victoria: This 1893 Macoun collection (CAN 83548) may have come from one of several Victoria locations. There is no record of where “Sea’s Farm” was located.
2. Vicinity of Sidney, Vancouver Island: This 1908 Macoun collection (CAN 83551) may have come from population No. 3 or the historical occurrence at Swartz Bay.
3. Sidney: This 1913 Macoun collection (V 003397) may have come from population No. 3 or the historical occurrence at Swartz Bay.
4. Sidney: This 1927 Goddard collection (V 008256) may have come from population No. 3 or the historical occurrence at Swartz Bay.
5. Saanichton: This 1931 Newcombe collection (009071) may have come from the same population as the historical occurrence on Wallace Drive.
6. Victoria, between Uplands and Tolmie: This 1913 Davidson collection (UBC 26117) may have come from the same population as the historical occurrences at King’s Pond, Uplands Park or the University of Victoria.
7. Cedar Hill: This 1920 Anderson collection (V 007046) may have come from the same population as the historical occurrence at King’s Pond.
8. Oak Bay, British Columbia: This 1911 Malte collection (CAN 197576) may have come from the same population as the historical occurrence at Uplands.
9. Goldstream: This 1896 Anderson collection (V 03399) may have come from the same population as the historical occurrence at Spencer Pond.
10. Langford: This 1922 Newcombe collection (V 007046) may have come from the same population as the historical occurrence at Spencer Pond, or alternatively from wet depressions that used to exist along the shores of Langford Lake.
11. Wellington, Vancouver Island: This 1912 Carter collection (UBC 86850) may have come from population No. 1 or the historical occurrence at Departure Bay.
12. Wellington and Little Qualicum: This 1916 Carter collection (V 003398) may have come from population No. 1 or the historical occurrence at Qualicum.