Monitoring Mulford’s milkvetch (Astragalus mulfordiae) in the Boise Foothills: 2019 results

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Mulford’s milkvetch (Astragalus mulfordiae) is a perennial, whitish-flowered plant species endemic to southwestern Idaho and adjacent eastern Oregon. It has been a priority conservation concern for many years due to its limited distribution range, the small size of most populations, and problems with habitat loss and degradation. Habitat decline and outright habitat loss are most acute and chronic in the Boise Foothills portion of the species’ range and largely related to urban development pressures. By the mid-1990s it was becoming clear that monitoring information was needed to help Boise City and Ada County land managers be more pro-active in their conservation actions on behalf of Mulford’s milkvetch and other rare plant species in the Boise Foothills. Towards this end, a series of 12 Mulford’s milkvetch monitoring plots were established in the Boise Foothills in 1999 and 2000. The objective of the monitoring program is to provide population, habitat, and disturbance trend information for Mulford’s milkvetch occurrences to support the species’ long-term conservation. Monitoring data at the Boise Foothill plots were collected in 1999, 2000, 2001, 2002, 2005, 2006, 2007, and 2008. In 2019, Boise City and the Idaho Native Plant Society collaborated to resample Mulford’s milkvetch monitoring plots located in the Boise Foothills. A total of 37 Mulford’s milkvetch plants were tallied on transects in 2019, with most having fewer plants compared to previous monitoring years. Eight transects had no Mulford’s milkvetch. The 37-plant tally for 2019 represents a 83% decrease compared to 2008. All plots had one or more ground disturbance factors in 2019, with total ground disturbance in plots ranging from <1% to 15.1 %. Mean total ground disturbance for all plots in 2019 was 6.2%, a value lower than all previous monitoring years except 2006. Primary ground disturbance factors in 2019 included animal digging at 7 plots, deer tracks at 2 plots, animal tracks (likely deer and/or dog) at 1 plot, and a walking trail at 1 plot. Plant community data collected in 2019 showed Mulford’s milkvetch plots in the Boise Foothills to be characterized by a sparse to open shrub layer, high grass cover dominated by non-native weedy species, mainly cheatgrass, and low to moderate cover of a mix of native and introduced forb species. Overall, the 2019 monitoring data indicates the conservation status of Mulford’s milkvetch in the Boise Foothills is in jeopardy. The conservation for Mulford’s milkvetch and other Boise Foothill rare plant species will likely become more challenging as the human population in the Boise metropolitan area continues to grow. Monitoring provides documentation upon which land managers can base conservation priorities and actions that benefit rare plant species in the Boise Foothills.

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Reference Code: U19MAN01IDUS <br>

Full Citation: Mancuso M, Brabec M. 2019. Monitoring Mulford’s milkvetch (Astragalus mulfordiae) in the Boise Foothills: 2019 results. Prepared for: Boise City Department of Parks and Recreation. Boise, Idaho. 18 pp. <br>

Location: ELECTRONIC FILE - BOTANY: PLANT SPECIES: Astragalus mulfordiae <br>

Keywords: Astragalus mulfordiae, Mulford’s milkvetch, monitoring, Boise Foothills <br>