Cryptic paw (Nephroma occultum) COSEWIC assessment and status report: chapter 4

Distribution

Global range

Nephroma occultumis a western North American endemic known from Alaska, British Columbia, Washington and Oregon. The northernmost known population is Mile 9 of the Richardson Highway, Alaska (64°47' N 147°22' W), the southernmost is near Roseburg, Oregon (43°27’N122°54' W), the westernmost is near Seward on the Kenai Peninsula, Alaska  (60°33' N 151°16' W), and the easternmost is near the Duncan River, British Columbia (50°42’ N 117°06’W).

In 1994, Nephroma occultum was known from five localities in Oregon, two from Washington and 21 from British Columbia (Goward 1995a). In 1994, N. occultum was included on the suggested list of species to be surveyed and managed for in the federal forests of Washington and Oregon (FEMAT 1993, USDA and USDI 1994, USDA and USDI 2003). This resulted in the discovery of many new stations and today there are 182 documented localities in Oregon and eight in Washington. In contrast, in British Columbia where lichen surveys are not required for forest harvesting, there have been 24 new populations recorded since 1994. More populations will likely be found in British Columbia as opportunities for lichen surveys in the appropriate habitat opportunistically arise. In Alaska, six populations have been documented, all within the last 10 years (Geiser et al. 1994,Zavarzin and Timdal 2004, S. Sharnoff pers. comm. 2005, C. Derr pers. comm. 2005, and K. Dillman pers. comm. 2005). As of 2004, there are a total of approximately 241 documented populations of Nephroma occultum, worldwide.

Figure 4 shows the world distribution of Nephroma occultum. While most localities (including the type locality) are in Oregon, more than 50% of the range occurs within Canada. NatureServe (2005) suggests that “it seems to have its center of distribution in Oregon”; however, Figure 4 clearly demonstrates that Oregon represents the southern limit of the range (see also Appendix 1).

Figure 4. Global distribution of Nephroma occultum.

Figure 4.  Global distribution of Nephroma occultum.

Canadian range

Within Canada, Nephroma occultum is restricted to the province of British Columbia where it is known from 45 localities. The distribution of this lichen can be thought of as two zones that run from the northwest to the southeast (this alignment is the dominant geographic pattern of British Columbia and reflects the tectonic development of the western mountain ranges, which influence regional climate; Figure 5). The largest zone is defined by intermontane valleys of the Coast and Cascade Ranges, from the Taku (58°40’N) to the international border near Chilliwack (49°03’N). This zone is discontinuous north of 56°N, and collections are sparse or absent where the lack of roads limits access, which is true for much of this rugged area. Disjunct populations are also known along an inland zone that coincides with the Columbia Mountains. The inland range is entirely within British Columbia and spans from the upper Fraser River (53°43’N) in the north, to the Duncan River (50°42’N) in the south.

Throughout most of its Canadian range, Nephroma occultum is primarily restricted to old growth forests in very humid intermontane regions at lower elevations. N. occultum is able to colonize younger forests where the macro-climate is sufficiently humid and source populations are nearby. Assuming the existence of the appropriate habitats, N. occultum can be expected to occur throughout the range shown as the shaded area in Figure 4.

Figure 5. Distribution of Nephroma occultum in Canada and adjacent Alaska.

Figure 5. Distribution of Nephroma occultum in Canadaand adjacent Alaska

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