Field Assessment of Lepidium papilliferum (Slickspot Peppergrass) Element Occurrences: Snake River Plain and Adjacent Foothills

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Lepidium papilliferum (slickspot peppergrass, Brassicaceae) is a small annual or biennial forb that flowers in May and June across southwestern Idaho. It is endemic to the western Snake River Plain, adjacent foothills, and the eastern Owyhee Plateau, where it inhabits slickspots—slight depressions among shrubs where clay and salts have accumulated. Lepidium papilliferum is federally listed as a threatened species and has been the subject of conservation concern for many years. In 2016, we published the status ranks of all known occurrences of L. papilliferum across its range (Kinter and Miller 2016). This report includes the details of our field research used to develop the ranks within the Snake River Plain and Foothills Geographic Areas (GAs). A forthcoming report will cover our field results for the Jarbidge Geographic Area, which is located on the eastern part of the Owyhee Plateau between the Jarbidge River and the East Fork of the Bruneau. We began our research by examining location data from the Idaho Natural Heritage Program database, which is part of the Idaho Fish and Wildlife Information System (IFWIS). From Summer 2012 through Spring 2016, we conducted field assessments at 70 of the 86 occurrences known in the Foothills and Snake River Plain GAs. We did not assess sites that were extensively developed, such as irrigated fields or residential areas, or that were on private land where we were unable to get permission for access. In the field, we walked across the occurrences in a systematic manner and used a handheld Garmin GPS unit to record a waypoint for each slickspot observed. When L. papilliferum was present, we counted individual plants by life stage—rosettes or flowering/fruiting. We also collected data on plant community composition, landscape characteristics, and disturbances. An estimated total of 37,310 L. papilliferum plants were observed—10,543 (28%) rosettes and 26,767 (72%) flower/fruit. Estimated totals by geographic area were: Foothills—4932 (3600 rosettes and 1332 flower/fruit), and Snake River Plain—32,378 (6943 rosettes and 25,435 flower/fruit). Development and invasion by noxious weeds and other non-native species constitute the most widespread disturbances to L. papilliferum throughout the study area. Incidental to our inventories in mapped areas, we found L. papilliferum outside of 24 previously mapped occurrences. These data expand the known occurrences, and will be added to the IFWIS database. These incidental discoveries indicate the need for future surveys. At 31 occurrences, we did not find L. papilliferum during our field assessments. We recommend re-evaluating these 31 occurrences at least once in the near future. If assessments at a given occurrence are possible in 5 of the next 12 years, and no plants are found, the rank can be changed to ‘Extirpated’ (NatureServe 2002, Kinter and Miller 2016).

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Reference Code: U18MIL01IDUS <br>

Full Citation: Miller, J.J., and C.L. Kinter. 2018. Field Assessment of Lepidium papilliferum (Slickspot Peppergrass) Element Occurrences: Snake River Plain and Adjacent Foothills. Idaho Natural Heritage Program, Idaho Department of Fish and Game, Boise. 91 pp. plus appendices. <br>

Location: ELECTRONIC FILE - BOTANY: PLANT SPECIES: Lepidium papilliferum <br>

Keywords: Lepidium papilliferum, slickspot peppergrass, Element Occurrence, monitoring, habitat, rare plant conservation, sagebrush steppe, Idaho, Snake River Plain, foothills <br>