Spalding's campion (Silene spaldingii) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Silene spaldingiiis primarily restricted to mesic grasslands that make up the Palouse prairie (Hitchcock and Maguire 1947; USDI-FWS 2001), a division of the Pacific Northwest bunchgrass habitat type (Tisdale 1982). The species occurs on the deep, productive silt/loam (loess) typical of the Palouse prairie (NatureServe 2003, Lorain 1991). Silene spaldingii populations are also known to extend into the edge of Pinus ponderosa woodlands (NatureServe 2003). The elevation ranges from 580 to 1220 m (NatureServe 2003).

Across its range, the species occurs in fragmented patches as a result of large-scale anthropogenic changes to the Palouse prairie over the last century (USDI-FWS 2001). In its US range, the plant is often found near scattered Pinus ponderosa trees, and there seems to be a preference for gently sloping, northerly aspects in the Palouse prairie (NatureServe 2003).

Silene spaldingii is typically associated with native perennial grasses such as Festuca idahoensis, F. campestris, and Agropyron (Pseudoroegneria) spicatum. Other associated species may include Antennaria microphylla, Arnica sororia and Hieracium cynoglossoides (H. scouleri var. griseum), as well as Koeleria cristata(K. macrantha), Achillea millefolium, Geum triflorum, Geranium viscosissimum, and Balsamorhiza sagittata. Associated shrubs include Symphoricarpos albus and Rosaspp. (USDI-FWS 2001, Lesica 1999). Silene spaldingii is also known to occur in association with Pinus ponderosa (USDI-FWS 2001, Lichthardt and Gray 2002).

The Canadian population of Silene spaldingii can be considered part of northwest Montana’s metapopulation, also occurring on Tobacco Plains. Silene spaldingii, in Montana, has been more extensively studied than has the Canadian population. The British Columbia population is 1.3 km north of the closest Montana location. The grasslands of western Montana are transitional between the Palouse prairie type of Washington and Oregon and grasslands of the Northern Great Plains (Antos et al. 1983). In these grasslands, S. spaldingii occurs in the bottom of shallow swales and on cool slope exposures with relatively deep soil. Common grasses in these habitats include Festuca campestris, F. idahoensis, and Poa pratensis. Common forbs are Antennaria microphylla, Arnica sororia, and Hieracium cynoglossoides (H. scouleri var. griseum) (Lesica 1999). Silene spaldingii in Canada was observed growing with Lupinus sericeus, Hypericum perforatum, and Castilleja thompsonii (Miller and Allen 1997).

The mean precipitation for Eureka, Montana, six km south of Tobacco Plains, is 37 cm/yr for 1971-2000. The January minimum and July maximum temperatures for this period were –9.4° and 29°C, respectively (Eureka Ranger Station Normals, 2005).

Trends

Less than 2% of the Palouse prairie habitat remains due to agricultural conversion, grazing, invasion of nonnative plant species, altered fire regimes and urbanization (USDI-FWS 2001). The Palouse prairie on Canada’s Tobacco Plains (Figure 5) appears to be affected by all these factors (Miller and Allen 1997).

In addition, the area is suffering from a prolonged drought. The U.S. National Weather Service office in Great Falls, Montana ranked the last water year (Oct 2002-Sept 2003) at Kalispell (approx. 100 km SE of Tobacco Plains), as the fifth driest year out of 103 years on record (NWS – Great Falls 2003). In addition, precipitation at Eureka has also been below average for the years 1999, 2000, and 2001.

Figure 5. Roosville area of Tobacco Plains, British Columbia, in the foreground. The highway in the photo is in the U.S.A. Photo by Shyanne J Smith 2003

Figure 5.  Roosville area of Tobacco Plains, British Columbia, in the foreground. The highway in the photo is in the U.S.A


Historically, fire has played an important role in maintaining grasslands by limiting the establishment of woody vegetation (Barrett and Arno 1982, Koterba and Habeck 1971). The current suppression of natural fire, and absence of anthropogenic burning, may contribute to an ongoing loss of habitat.

The Tobacco Plains habitat in Canada appears to have been heavily grazed, with introduced Bromus tectorum occurring throughout. It has been noted by researchers in the U.S.A. that Silene spaldingii competes very poorly with introduced weedy species (Lorain 1991, WNHP and USDI Bureau of Land Management 1997). In addition, the introduced flowering herb Hypericum perforatum competes with S. spaldingii for pollinators (Lichthardt and Gray 2002), and was observed by the report writers at the Tobacco Plains site in 2003. Bombus species are thought to be the only significant pollinators of S. spaldingii, and may be susceptible to agricultural development and fire, since they live near the ground (Lesica 1993, Lichthardt and Gray 2002).

Protection/ownership

The Tobacco Plains Silene spaldingii population reported from 1995 was found on rangeland of a ranch near Roosville. There is a possibility that the species may also occur on the adjacent Tobacco Plains Indian Reserve but lack of permission to enter the reserve prevented searching for the species in 2003. Since the population occurs on private property, and the species is not listed under the Wildlife Amendment Act as a threatened or endangered species in British Columbia, it has no legal protection.

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