Assessment of Spalding’s catchfly (Silene spaldingii S.Watson) Element Occurrences in Idaho

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Spalding’s catchfly (Silene spaldingii S.Watson) is a federally-listed Threatened plant species endemic to the mesic bunchgrass grasslands in eastern Washington, west-central Idaho, northeastern Oregon, and intermontane valleys of Montana. In Idaho it occurs in Palouse Grasslands and Canyon Grasslands. Currently 48 element occurrences (EOs) of Spalding’s catchfly have been documented in Idaho on both public and private land. Prior to our assessment, many of these had not been revisited in at least several years. From 2012 through 2017, we assessed ten EOs in priority order (Priority EOs) based on ownership, data of last visit, size, and accessibility; we obtained permission to assess five of these EOs on private land. Over this time period, we also assessed two new EOs (recently documented) and two EOs in conjunction with other projects. We contacted the Bureau of Land Management, U.S. Forest Service, and the Nez Perce Tribe to ensure that any EOs recently found by these agencies were submitted to the Idaho Fish and Wildlife Information System (IFWIS) database. For each assessed EO, we completed a Rare Plant Observation Form (RPOF), a standard form documenting habitat, associated species, landscape attributes, disturbances, and other features. During each field assessment, we counted and mapped plants using a hand-held GPS unit and took several photos. Many of these EOs were originally mapped on topographic maps using compasses and altimeters, thus, our GPS points provided precise point locations of plants. The majority of assessed priority EOs appears to have decreased in population and/or subpopulation size and extent compared to size and extent previously documented. Eight of the ten priority EO assessments documented 20-80% fewer plants than previous counts. Comparisons of plant numbers documented at flowering time are difficult. Both the original surveys and the assessments were conducted at flowering time (late July - August) and are likely underestimates since many aboveground plants can senesce/disappear by flowering time and the number of plants disappearing varies considerably from year to year. Additionally, some plants can remain dormant belowground for one to two years. During our EO assessments, we incidentally revisited several known EOs and documented new EOs of other rare plant species, including woodyroot milkvetch (Astragalus riparius), greenband mariposa lily (Calochortus macrocarpus var. maculosus), Palouse thistle (Cirsium brevifolium), Palouse goldenweed (Pyrrocoma liatriformis), rough goldenweed (Pyrrocoma scaberula), plumed clover (Trifolium plumosum ssp. amplifolium), and broadfruit mariposa lily (Calochortus nitidus). RPOFs were completed and submitted to IFWIS for these EOs. We also examined the IFWIS database and coordinated with database managers to ensure that all known EOs and EO data from past studies were entered in the database.

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Reference Code: U19PEK01IDUS <br>

Full Citation: Pekas, K.M., J. Lichthardt, and J.Hill. 2019. Assessment of Spalding’s catchfly (Silene spaldingii S.Watson) Element Occurrences in Idaho. Idaho Natural Heritage Program, Idaho Department of Fish and Game, Boise. Pp. 45, plus appendices. <br>

Location: ELECTRONIC FILE - BOTANY: PLANT SPECIES: Silene spaldingii <br>

Keywords: Greenband mariposa lily (Calochortus macrocarpus var. maculosus), broadfruit mariposa lily (Calochortus nitidus), Canyon Grasslands, Idaho, Palouse goldenweed (Pyrrocoma liatriformis), Palouse Grasslands, Palouse thistle (Cirsium brevifolium), plant conservation, plumed clover (Trifolium plumosum ssp. amplifolium), rare plants, rough goldenweed (Pyrrocoma scaberula), Spalding’s catchfly (Silene spaldingii), woodyroot milkvetch (Astragalus riparius) <br>