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Critical Habitat

Recovery Strategy for the Contorted-pod Evening-primrose (Camissonia contorta) in Canada

7. Critical Habitat

The Species at Risk Act defines critical habitat as “…the habitat that is necessary for the survival or recovery of a listed wildlife species and that is identified as the species’ critical habitat in a recovery strategy or in an action plan for the species.” An identification of critical habitat towards the survival and recovery of existing populations of Contorted-pod Evening-primrose is included in this recovery strategy. This identification is based on the best currently available scientific information, and will be updated as further information arises. This critical habitat identification is only for the immediate survival and limited expansion of seven of the eight extant populations of Contorted-pod Evening-primrose in Canada, and is not sufficient to meet the population and distribution objectives.

No critical habitat can be identified for Population 6 because of uncertainty of the location of plants that might occur at the site. Although the population was lost to the development of a golf course between 2004 and 2006, there was a report of a small number of plants occurring there in 2007 (Table 1). However, it is not known if the plants had recolonized remnant habitat patches in the original location or were in a new nearby location. Some additional habitat occurs south of Population 8 on the Tsawout Indian Reserve; however, permission to use these data has yet to be granted to they cannot be used in the identification of critical habitat. No critical habitat for the re-establishment of the extirpated Population 9 can be identified at this time because the exact location of the original site is unknown due to the age of the record (last observed in 1893). See Table 7 for recommendations to fill these gaps in the critical habitat identification.

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7.1 Identification of the Species’ Critical Habitat

Critical habitat for Contorted-pod Evening-primrose in this recovery strategy includes occupied and unoccupied habitat as follows:

  • Occupied habitat – consisting of all known occupied habitat plus adjacent areas needed to maintain the habitat attributes as described below.

  • Expansion habitat – additional habitat contiguous to the occupied habitat that is capable of sustaining Contorted-pod Evening-primrose with little or no intervention (for expansion of populations and/or seasonal flux in occupied area), but is currently unoccupied. Unoccupied but contiguous habitat is being included as a precautionary measure to ensure where possible that sufficient habitat is available for the populations to reach population and distribution objectives at each site. Predicted minimum viable population size is approximate for this species at this time, but currently all of the Canadian populations of Contorted-pod Evening-primrose are smaller than the predicted size expected for plant populations to be viable over the long term (see Section 3.3), so all suitable or potentially suitable sites adjacent of each population are considered critical habitat. As further scientific information is gained on minimum viable population size, the polygons will be expanded or contracted as necessary. Expansion habitat as currently mapped will not necessarily provide enough area to meet the population and distribution objectives.

7.1.1 Attributes of critical habitat

Figure 3 shows typical habitat for Contorted-pod Evening-primrose in Canada. Both physical and biological features important to the conservation of Contorted-pod Evening-primrose were considered in determining which areas to propose as critical habitat. These habitat attributes include: space for individual and population growth, water, minerals, light and other nutritional or physiological requirements; and sites for germination or seed dispersal.

Figure 3. Typical habitat for Contorted-pod Evening-primrose in Canada.

These habitat attributes include: space for individual and population growth, water, minerals, light and other nutritional or physiological requirements; and sites for germination or seed dispersal.
© Matt Fairbarns

Site and Soil: Sites occur between 1-30 m above sea level although most plants are found <2 m above sea level. The slope angle varies from 0-35% although most plants occur on slopes of <3%. Where the slopes are steeper, the populations generally occur on west or south facing aspects. Soil pits were not excavated due to the potential for damage to Contorted-pod Evening-primrose and other rare plants occurring on the occupied sites and similar nearby habitat. The soils, which are rapidly drained, consist of deep (> 30 cm) sand usually with a negligible component of coarse fragments, fine soil particles or organic matter. In the early growing season (February and March) the soil tends to remain moist for prolonged periods. The soil moisture level diminishes as the growing season progresses so that by the time the fruits are developing and the plants are senescing the soil experiences significant water deficits for prolonged periods. The surface is characterized by a high proportion of exposed mineral soil and very little vegetated cover or litter.

Plant community: Contorted-pod Evening-primrose is restricted to dune and sandy backshore ecosystems with no trees or tall shrubs. Associated species are as follows. Low native shrubs are usually absent although small amounts of Tall Oregon-grape (Mahonia aquifolium) may occur along the periphery of some populations. The herb layer is usually sparse and Contorted-pod Evening-primrose occurs in gaps between other herbaceous species, where competition is reduced. Native herbaceous species are generally uncommon although low-growing sand-loving species such as Black Knotweed (Polygonum paronychia), Indian Consumption Plant (Lomatium nudicaule) and Yellow Sand-verbena (Abronia latifolia) are occasionally abundant. Haircap moss (Polytrichum piliferum) also is often present.

Biological processes: Summer drought causes the herbaceous vegetation to die back in June and July so moisture competition is probably a critical stressor and plant adaptations to moisture stress undoubtedly play a critical role in determining species competition. Contorted-pod Evening-primrose plants possess a moderately deep taproot which accesses soil moisture below the rooting zone of some co-occurring herbaceous species, but generally dies by mid-summer.

Physical processes: Contorted-pod Evening-primrose does not appear to depend upon seepage, salt spray or wind to prevent encroachment by woody species. Summer drought, often exacerbated by rapidly-drained soils, probably plays a major role in limiting competition from less drought-tolerant species. Wildfire may have also played a significant role in maintaining ecosystem properties and functions in the past but current policies have led to the strong suppression of fire.

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7.1.2 Location of critical habitat

This section describes the physical location of the critical habitat areas. See Table 5 for a list of each site and the geographic area of the polygons in relation to land tenure. Critical habitat polygons are based on recent field data (2004-2010) conducted at all eight currently extant sites and general habitat attributes from all Canadian sites as well as a large population on San Juan Island (Washington State), about 20 km east of the nearest Canadian population. Polygons also incorporate spatial uncertainties associated with sampling techniques (e.g., spatial errors associated with GPS equipment). All values are UTMs in zone 10 using the NAD83 datum. Boundaries were established using a hand-held GPS unit (Garmin E-TREX). During the growing season, habitat attributes of known populations were documented using Ground Inspection forms according to methods outlined in Describing Ecosystems in the Field (Luttmerding et. al. 1990). Winter field work was not necessary because Contorted-pod Evening-primrose is not dependant on winter seepage.

Population 1 (Metchosin)

Population 1 occurs in Witty’s Lagoon Regional Park (Capital Regional District). Critical habitat includes occupied and expansion habitat (Figure 4, Table 5). The existing population consists of fewer than 300 plants (Table 1; Fairbarns pers. obs. 2004).

Population 2 (Saanich A)

Population 2 occurs in Island View Beach Regional Park (Capital Regional District). Critical habitat includes occupied and expansion habitat (Figure 5, Table 5). The existing population consists of fewer than 600 plants (Table 1; Fairbarns pers. obs. 2008).

Population 3 (Savary Island A)

Population 3 occurs on a B.C. Ministry of Transportation and Infrastructure right-of-way on Savary Island at Sutherland Beach. Critical habitat includes occupied and expansion habitat (Figure 6, Table 5). The existing population consists of approximately 200 plants (Table 1; Fairbarns pers. obs. 2004).

Population 4 (Savary Island B)

Population 4 occurs on private land on Savary Island. Critical habitat includes occupied and expansion habitat in three areas of the property (Beacon Point, Death Camas Meadow and Duck Bay; Figure 7, Table 5). The existing population consists of approximately 700 plants (Table 1; Fairbarns pers. obs. 2004; C. Cadrin pers. comm.).

Populations 5 (Saanich B)

Population 5 occurs on James Island, an area of private land. Critical habitat includes only occupied habitat because no expansion habitat has been identified at this location (Figure 8, Table 5). The existing population has not been recently surveyed, but in 2007 consisted of 500-600 plants. (Table 1).

Population 7 (Saanich D)

Population 7 occurs on Gulf Islands National Park Reserve lands and Canadian Coast Guard Agency lands on the northern spit of Sidney Island. The Coast Guard land is in the process of being formally transferred to Parks Canada Agency (R. Walker, pers. comm.). Critical habitat includes occupied and expansion habitat (Figure 9, Table 5). The existing population consists of less than 100 plants (Table 1; Fairbarns, pers. obs.).

Population 8 (Saanich E)

Population 8 occurs in Cordova Spit Municipal Park (District of Central Saanich). Critical habitat includes occupied and expansion habitat (Figure 10, Table 5). The existing population consists of fewer than 300 plants (Table 1; Fairbarns 2007).

Table 5. Approximate area of Contorted-pod Evening-primrose critical habitat for relevant land tenures (in hectares).
PopulationProvincialFederalRegionalMunicipalPrivateTotal
*MOTI*CCGA
*PCA
*CRDCentral Saanich 
Population 1 - Metchosin (occupied)  0.17  0.17
Population 1 – Metchosin (expansion)  0.41  0.41
Population 2 – Saanich A (occupied)  0.41  0.41
Population 2 – Saanich A  (expansion)  0.54  0.54
Population 3 – Savary Island A (occupied)0.28    0.28
Population 3 – Savary Island A (expansion)1.08    1.08
Population 4 – Savary Island B (occupied)    0.380.38
Population 4 – Savary Island B (expansion)    2.182.18
Population 5 – Saanich B (occupied)    4.074.07
Population 7 – Saanich D (occupied) 0.20   0.20
Population 7 – Saanich D (expansion) 0.03   0.03
Population 8 – Saanich E (occupied)   0.20 0.20
Population 8 – Saanich E (expansion)   5.07 5.07
Land tenure total1.360.231.535.276.6315.02

*MOTI = B.C. Ministry of Transportation and Infrastructure, CCG = Canadian Coast Guard Agency, PCA = Parks Canada Agency, CRD = Capital Regional District.

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Figure 4. Location of critical habitat for Population 1 (Metchosin) at Witty’s Lagoon Regional Park.

Location of critical habitat for Population 1 (Metchosin) at Witty's Lagoon Regional Park
© Parks Canada Agency

Figure 5. Location of critical habitat for Population 2 (Saanich A) at Island View Regional Park.

Location of critical habitat for Population 2 (Saanich A) at Island View Regional Park
© Parks Canada Agency

Figure 6. Location of critical habitat for Population 3 (Savary Island A) at Sutherland Beach on Savary Island.

Location of critical habitat for Population 3 (Savary Island A) at Sutherland Beach on Savary Island
© Parks Canada Agency

Figure 7. Location of critical habitat for Population 4 (Savary Island B) at Beacon Point, Death Camas Meadow and Duck Bay on Savary Island.

Location of critical habitat for Population 4 (Savary Island B) at Beacon Point, Death Camas Meadow and Duck Bay on Savary Island
© Parks Canada Agency