Skip booklet index and go to page content

COSEWIC assessment and status report on the contorted-pod evening-primrose (Camissonia contorta) in Canada

Limiting Factors and Threats

Habitat loss

Golf course development has resulted in a major loss of suitable habitat at the Saanich C population.

Recreational activities

Recreational use has had the most significant impact on sand flats within the Canadian range of Camissonia contorta. Recreational use is concentrated on suitable Camissonia sites due to the relative scarcity of sandy shores in the area. Seven of the eight extant/extirpated populations have been moderately to heavily and extensively altered by recreational activities, including:

  • Heavy trampling associated with hiking, dog-walking, sunbathing and picnicking at populations 1,2,4,7 and 819 of 28 locations, including populations 1, 2 and 4 as well as areas adjacent to population 7.
  • Heavy 4-wheel drive traffic in populations 5, and 6 and 8. Over the past decade there has been a significant increase in the area destabilized by vehicle ruts at the site where population 8 formerly occurred. Such activities almost certainly led to the extirpation of the population, which was last seen in 2002 (Adolf Ceska pers. comm. 2004)

Invasive plants

Camissonia contorta is a stress-tolerator, thriving in xeric, sandy habitats where other native species are stunted or absent. A number of alien, invasive species have entered these ecosystems in the past century and a half, and many of them now dominate habitats otherwise suited to C. contorta. The major threats came from Cytisus scoparius, Bromus rigidus, B. tectorum, B. sterilis, Aira praecox, A. caryophyllea and Rumex acetosella. Cytisus scoparius was present immediately adjacent to or within all seven extant populations and has presumably invaded areas formerly suited to Camissonia contorta. Given one or two decades, Cytisus scoparius has the ability to completely stabilize semi-active sand areas by forming dense thickets. This will eventually allow further succession and eliminate open habitats. Page (2003) calculated that the combined area of grass/bryophyte and open dune and grass/bryophyte cover near population 2 declined by over 15%, from 6.3 ha in 1932 to 5.3 ha in 1995(unfortunately the decline was not partitioned among the two cover types and the loss of grass/bryophyte cover does not reflect a direct loss of habitat for C. contorta).

Other invasive species that posed a serious threat at one or more sites included Allium vineale, an aggressive onion which is spreading rapidly in areas where it has become established (especially at population 5), and Ammophila arenaria which tends to stabilize dunes and thereby alter substrate dynamics in the vicinity of Camissonia contorta (especially at population 7).

Table 2. Threat matrix for surveyed sites. Sites numbered as in Table 1.
LocationHabitat LossRecreationInvasive PlantsHerbivoresDemographic Collapse
pop. 1 Metchosinmediumheavyheavymediummoderate
pop. 2 Saanich Amediummediumheavymediumminor to moderate
pop. 3: Northern Gulf Island Alightlightlightlightmoderate
pop. 4: Northern Gulf Island Blightmediummediumlightmoderate
pop. 5 and 6 Saanich B and Cheavyheavyheavymediumminor
pop. 7 Saanich Dmediumheavyheavymediummajor
pop. 8 Saanich Elightheavyheavymediumextirpated

Introduced herbivores

Plants in populations1, 2, 5, 6 and 7 experience lightto moderate  levels of herbivory and eastern cottontail droppings are abundant at most of these sites as well as in the location where population 8 formerly occurred. The impact of rabbit grazing on competing vegetation appears to outweigh the minor impacts of grazing on Camissonia contorta itself.  

Demographic collapse

Some populations of Camissonia contorta are threatened simply by their small size. Pavlik (1996) suggests that the minimum population size for plants varies from as few as 50 plants for some life forms to as many as 2,500 plants for others. C. contorta, as an annual herb which does not produce ramets and occurs as a stress-tolerant species in highly variable environments, fits the profile of a species which that would have a high minimum viable population size according to Pavlik’s criteria. Accordingly, six of the seven extant populations of C. contorta with fewer than 1,000 individuals are apparently threatened by the possibility of demographic collapse and the threat is moderate (750 or fewer individuals) or major (100 or fewer individuals) in four or five sites.