Dwarf sandwort (Minuartia pusilla) COSEWIC assessment and status report: chapter 5
Habitat
Habitat requirements
Minuartia pusilla in British Columbia is found in a climatic and floristic anomaly in coastal British Columbia, the Coastal Douglas-fir Zone. This zone includes a small portion of southeastern Vancouver Island, several islands in the Gulf of Georgia, and a narrow strip of the adjacent mainland (Nuszdorfer et al. 1991). As it is situated at a relatively southern latitude for Canada, on its west coast, and in a rainshadow belt created by the Olympic and Vancouver Island Mountains, the result is a Mediterranean climate with warm, dry summers and mild, wet winters.
Within this region, Minuartia pusilla occurs on the flat top of a coastal headland in a shallow soil depression with about four inches of moraine (Ceska and Ceska 1980). The southeast sloping (0-24%) depression is wet in the spring and mesic to dry later in the season. The soils are a rapidly draining sandy moder with poor nutrient content and no soil moisture late in the season. The root-restricting layer is 1-20 cm and the coarse fragment content about 35-70% (M. Fairbarns, pers. comm.).
The vegetation of the coastal headlands where M. pusilla occurs is controlled by exposure to winds and salt spray. Shrub and tree species such as salal (Gaultheria shallon) and shore pine (Pinus contorta) are unable to grow close to shore. Low-growing herbs are able to grow under such conditions, although they are also limited by those factors. Within the vernal seep habitat, erosion plays a key role in maintaining a constant, fresh supply of mineral soil that is needed for germination by M. pusilla.
Associated species in the vernal seep include the following (A. Ceska and M. Fairbarns, pers. comm.): barren fescue (Vulpia bromioides), beach bluegrass (Poa confinis), blinks (Montia fontana), cudweed (Gnaphalium species), dwarf owl-clover (Triphysaria pusilla), early hairgrass (Aira praecox), erect pygmyweed (Crassula connata var. connata), few-flowered shootingstar (Dodecatheon pulchellum), hairy cat's-ear (Hypochaeris radicata), rattail fescue (Vulpia myuros), red thread-moss (Bryum miniatum), ribwort plantain (Plantago lanceolata), Scouler’s popcorn flower (Plagiobothrys scouleri), slender plantain (Plantago elongata), small-leaved bentgrass (Agrostis microphylla), sticky chickweed (Cerastium glomeratum), and thrift (Armeria maritima ).
In Washington, California, Oregon, and Idaho, the habitat is open, dry soil of big sagebrush (Artemisia tridentata) and ponderosa pine (Pinus ponderosa) forest (Hitchcock et al. 1964). Minuartia pusilla occurs in a variety of primarily xeric habitats, often in waste areas or otherwise sterile sites (Meinke and Zika 1992).
Trends
The Coastal Douglas-fir zone has a very limited range in the province and suitable habitats for Minuartia pusilla within it are also restricted and fragmented. Urbanization, agriculture and the spread of invasive species within the range of M. pusilla may limit its ability to expand to other potentially suitable habitats. These factors have reduced the Garry Oak woodland to less than 5% of its original extent in the Victoria area (Lea 2002). Specifically, within the known site, the habitat has remained virtually unchanged since the discovery of it in 1977 (A. Ceska pers. comm.). Drying of the seep would be disastrous for M. pusilla. Likewise, if conditions become too wet, the species could disappear.Changes in the conditions of the habitat could also allow introduced annual or other native species such as mosses to increase and pre-empt M. pusilla.
Protection/ownership
The single occurrence of Minuartia pusilla is found on Canadian Department of National Defense (DND), C.F.B. Esquimalt, property where public access is restricted. The area in which M. pusilla occurs is currently used as a buffer and training area (for small patrols carrying out map and compass work) with no foreseeable alternate use into thefuture (A. Robinson, pers. comm.). A natural resource management program for these DND properties is going to be implemented. The plan includes recommendations from the science advisory committee, a group that oversees research on the lands. Rare plant demographic studies and mapping are currently part of the research program. Locations of all rare plant species are going to be identified on a sensitive sites map for the properties so that they can be better protected (A. Robinson, pers. comm.).
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