2014 Census of Spiranthes diluvialis (Ute ladies’-tresses) Element Occurrences: South Fork of the Snake River

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Spiranthes diluvialis (Ute ladies’-tresses) is a white-flowered terrestrial orchid that was first described as a new species by C.J. Sheviak in 1984. It occurs in eight western states, from Nebraska to Washington, and in British Columbia. In Idaho, it is known from the eastern part of the state, where it occupies riparian and wet meadow habitats on alluvial substrates and cobble deposits mostly along the South Fork of the Snake River and the Henrys Fork. In 1992, S. diluvialis was listed as Threatened under the Endangered Species Act because of its geographic rarity, small occurrence sizes, habitat loss and modification of riparian habitats, and low reproductive rate (USFWS 1992). In this study, we focused on six occurrences on public lands located along the South Fork of the Snake River that had been inventoried on past censuses by the Bureau of Land Management (BLM) and US Forest Service (USFS). Individuals who had been involved in past counts showed us the occurrences. Though the general location of most occurrences had been previously documented by the Idaho Natural Heritage Program, the boundaries of the occurrences and previous census areas had not been mapped. We mapped each occurrence using a handheld GPS unit, and counted all S. diluvialis plants observed. We conducted field inventories from 11 to 21 August 2014. In the field, we collected data on S. diluvialis occurrence size, distribution of plants, plant community composition, landscape characteristics, and disturbances. At the occurrences we visited (sites that had been censused intermittently since 1996 by the BLM and USFS), we observed a total of 3099 S. diluvialis plants. Most of the plants occurred at Black Canyon, Lufkin Bottom, Warm Springs Bottom, Annis Island, and Pine Creek #3 & #4. These sites accounted for 97% (3015) of the total number of plants observed. No S. diluvialis plants were observed at three sites (Kelly’s Island, Railroad Island, and Twin Bridges Islands). We censused a new location, Fisher Bottom, and found what we believe to be new areas where plants had not been previously censused at Black Canyon, Warm Springs Bottom, and Lower Swan Valley. In our 2014 census along the South Fork of the Snake River, including the new areas found at Black Canyon, Warm Springs Bottom, and Lower Swan Valley, and Fisher Bottom, we found a total of 3505 S. diluvialis plants. We did not assess all existing mapped polygons because some areas no longer contained suitable habitat, could not be accessed due to river dynamics (e.g., water flow, shifting of channel, debris, etc.), or were unknown to agency personnel. We recommend future assessments of existing mapped polygons that we did not assess and reassessment of Fisher Bottom.

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Reference Code: U17MIL01IDUS <br>

Full Citation: Miller, J.J., and C.L. Kinter. 2017. Census of Spiranthes diluvialis (Ute ladies’-tresses) Element Occurrences: South Fork of the Snake River. Idaho Natural Heritage Program, Idaho Department of Fish and Game, Boise. ID. 52 pp. plus appendices. <br>

Location: ELECTRONIC FILE - BOTANY: PLANT SPECIES: {Spiranthes diluvialis} <br>

Keywords: Spiranthes diluvialis, Ute ladies’-tresses, Element Occurrence, sub-Element Occurrence, census, habitat, rare plant conservation, South Fork of the Snake River, Idaho <br>