Spalding's campion (Silene spaldingii) COSEWIC assessment and status report: chapter 4

Distribution

Global range

Silene spaldingii is known from the Roosville area of southeastern British Columbia south into adjacent northwestern Montana and from north-central Idaho south through eastern Washington to northeastern Oregon (Figure 3). Montana has the largest population of Silene spaldingii, with an estimated 10,000 plants on the Dancing Prairie Preserve, approximately 7 km south of the Canadian population; this consists of a metapopulation that extends to within 1.3 km of the BC population. The earliest observation at the Dancing Prairie Preserve was in 1985. Based on the large size of this population it is, therefore, not a recent arrival in the area (Scott Mincemoyer, pers. comm. 2005 to E. Haber). Since the nearby British Columbia population is likely a satellite population of the larger Dancing Prairie Preserve population, it is also reasonable to assume that the Canadian plants have been present for some time.

Figure 3. Global distribution of Silene spaldingii (USDI-FWS 2001, Lorain 1991, Lichthardt and Gray 2002).

Figure 3.  Global distribution of Silene spaldingii

Canadian range

The Canadian range of Silene spaldingii is limited to the northern section of Tobacco Plains that extends into southeastern British Columbia from Montana (Figure 4). Tobacco Plains is located in a narrow glacial valley at 835-850 m elevation, running approximately from Eureka, Montana through Roosville, British Columbia (Lesica 1999).

Figure 4. Distribution of Silene spaldingii in Canada (Douglas and MacKinnon 1998).

Figure 4.  Distribution of Silene spaldingii in Canada

Silene spaldingii was first observed at Tobacco Plains in Canada in 1988 and later reported by Lorain (1991). The first collection of S. spaldingii in British Columbia was made by M. Miller in 1995 at Tobacco Plains (Miller and Allen 1997).

The known extent of S. spaldingii occurrence in Canada is estimated to be approximately 300 (Mike Miller, pers. comm.), with the same size area of occupancy. The reported population occurs in one known location, although intensive searches of an adjacent Indian Reserve have yet to be made. Approximately 50% of the Canadian Tobacco Plains area has been searched. Total potential habitat in the area around the original reported population is not likely more than .03 km² (ca 3 ha).

Silene spaldingii is just one of a number of species recently discovered (since the 1980s) along the British Columbia border from the Princeton area to the Roosville area. Some of these species include: Antennaria flagellaris, Carex vallicola, Collomia tenellus, Floerkea proserpinacoides, Hedeoma hispida, Lipocarpha micrantha, Orobanche ludoviciana, Orthocarpus barbatus, Phacelia ramosissima, Psilocarphus brevissimus and Trichostema oblongum (Douglas et al. 1998a). Most of these species have at least one thing in common; the areas in which they were found were never subjected to botanical collecting. Examination of collection localities in all major herbaria in Canada reveal that none of the many active field botanists working along the border ever collected in the immediate vicinity of the recently collected plants.

One of the earliest collections of this species made in Montana about 90 km south of the Roosville, BC, locality was in 1894 from the vicinity of Columbia Falls (Logan Creek 2005). This clearly indicates that the species has been in the immediate area south of the BC site for quite some time and likely has also been in Canada for at least as long.

Due to the relatively recent discovery of Silene spaldingii at Tobacco Plains, it is difficult to assess changes to the species’ historical range. It may be assumed that range loss has occurred as a result of agricultural and residential development, as has occurred with S. spaldingii range in the U.S.A. (USDI-FWS 2001).

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