Field Surveys for Spiranthes diluvialis (Ute ladies’-tresses): South Fork of the Snake River

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Spiranthes diluvialis (Ute ladies’-tresses) is an orchid that was listed in 1992 as Threatened under the Endangered Species Act because of its geographic rarity, small occurrence sizes, low reproductive rate, and loss and modification of its riparian habitats (USFWS 1992). 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, primarily along the South Fork of the Snake River. With funding from the Bureau of Land Management (BLM), we surveyed for S. diluvialis along the South Fork of the Snake River from its confluence with the Henrys Fork upstream to Irwin, located on the east end of Swan Valley. Prior to fieldwork, we received recommendations for areas to survey from BLM and US Forest Service personnel, and we examined satellite imagery from the 2015 National Agriculture Imagery Program (NAIP). We identified 141 segments of land as potential habitat for S. diluvialis. To strengthen our search image, we revisited known populations at Kelly Island on 14 Aug 2018 and 20 Aug 2019—no plants were found, and Warm Springs Bottom on 20 Aug 2019—a minimum of 37 plants were observed. In the field, we walked in a systematic manner searching for S. diluvialis and if it was present, we recorded a waypoint for each plant or group of plants observed using a hand-held Garmin GPS unit. We also collected data on plant community composition, landscape characteristics, and disturbance. Our survey routes were mapped as a Tracklog. At areas where S. diluvialis was not present, we documented the dominant species. From 12 to 22 Aug 2018, we conducted surveys and found two new populations northwest and north of Annis Island, and one new population immediately upstream of Table Rock Canyon. A total of 135 plants were observed—133 plants near Annis Island and two plants near Table Rock Canyon. We also identified four areas as good to excellent potential S. diluvialis habitat: two near Lorenzo, one near Bear Gulch, and one between River Mile 883 and Pine Creek. In addition, we conducted a very thorough resurvey at Fisher Bottom in 2018, where we found a total of 333 plants, extending the boundary of the known population. From 21 to 22 Aug 2019, we returned to sites where we found new populations of S. diluvialis, and to the four areas that we considered good to excellent potential habitat in 2018. We observed a total of 168 plants at the populations north and northwest of Annis Island, but no plants were observed upstream from Table Rock Canyon. In the four potential habitat areas, we observed one S. diluvialis plant at a site we called ‘East of Lorenzo and east of River Mile 840’. No plants were observed at the other three areas. We recommend resurveying the populations located near Table Rock Canyon and East of Lorenzo and River Mile 840, because of the low number of plants observed. We also recommend resurveying the remaining three areas that we considered to be good to excellent potential habitat but did not find plants. Although no S. diluvialis plants were observed, surveys should continue for several years to account for prolonged dormancy or mistimed surveys.

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Reference Code: U20MIL03IDUS <br>

Full Citation: Miller, J.J., and C.L. Kinter. 2020. Field Surveys for Spiranthes diluvialis (Ute ladies’-tresses): South Fork of the Snake River. Idaho Natural Heritage Program, Idaho Department of Fish and Game, Boise, ID. 35 pp. plus appendices. <br>

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

Keywords: Spiranthes diluvialis, Ute ladies’-tresses, threatened, habitat, survey, inventory, rare plant conservation, orchid, South Fork of the Snake River, eastern Idaho <br>