Monitoring Packard’s milkvetch (Astragalus cusickii var. packardiae) in Southwestern Idaho, 2014 results

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Packard’s milkvetch (Astragalus cusickii var. packardiae) is a perennial plant species endemic to sparsely vegetated sedimentary outcrops in northeastern Payette County, Idaho. It is a Bureau of Land Management special status plant species and one of the rarest members of the Idaho flora. Documented threats at multiple Packard’s milkvetch subpopulations include wildfire, invasive grass species, off-road motorcycle hill climbing, and livestock tracking. A rangewide monitoring program for Packard’s milkvetch was initiated in 2008 to help assess its conservation status and support proactive and adaptive land management efforts on behalf of the species and its habitat. Quantitative sampling at 21 permanently marked plots included the full complement of monitoring protocols each year from 2008 to 2012, but was limited to the collection of ground disturbance data and re-taking photo point photographs in 2013 and 2014. <br> One or more ground disturbance factors were recorded at all monitoring transects in 2014. Total ground disturbance cover at individual transects ranged from 1.8% to 19.4%, with the rangewide mean of 6.8% lower than most previous monitoring years. Analysis detected no significant difference in the annual rangewide mean for total ground disturbance between the seven monitoring years; nor did it detect a significant upward or downward trend for this attribute. New motorcycle tracks occurred within 1 plot and immediately adjacent to 1 other plot. By 2014, nearly all motorcycle tracks recorded in prior years had disappeared. Mean rangewide motorcycle track ground cover disturbance was 0.2% in 2014, a value lower than any previous monitoring year except 2013. Analysis detected a significant decrease in motorcycle track disturbance for 2014 compared to 2010, but not other monitoring years. In addition, a significant downward trend in rangewide motorcycle track disturbance was found for the seven year dataset. Livestock track-related disturbance was recorded at all transects, although some of this disturbance pre-dated 2014. Abundance at individual plots ranged from <1% to 19.4% ground cover, with the rangewide mean of 4.7% being intermediate compared to values from previous monitoring years. Analysis detected no significant difference in the annual rangewide mean for livestock track abundance between the seven monitoring years; nor did it find a significant upward or downward trend for this attribute. Cattle disturbance was particularly severe at Plot 4-1, with at least 90% of Packard’s milkvetch plants at this location grazed by cattle, including some individuals eaten nearly to ground level. Other disturbances such as animal digging and water rivulet erosion exceeded 1% ground cover at a few transects, but were relatively minor overall. <br> A pilot project to restore a buffer of shrub-steppe habitat at two Packard’s milkvetch subpopulations was initiated in 2012. The project includes 4 plots to monitor efficacy of the restoration treatments, with monitoring based on frequency sampling along transects in permanently marked macroplots. In fall 2013, the BLM began restoration treatment near 1 plot with herbicide applications targeting annual grass species. Analysis found a significant decrease in frequency for Japanese brome (Bromus japonicus), cheatgrass (Bromus tectorum), and medusa-head rye (Taeniatherum caput-medusae) in 2014 compared to 2013 pre-treatment values at this plot. Significant decrease in frequency for these annual grass species was not found at the other 2 habitat restoration plots sampled in 2014. Monitoring will remain a vital management tool to help assess the effectiveness of conservation actions and also help provide rationale and guidance to future adaptive management measures. <br>

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Reference Code: U15MAN01IDUS <br>

Full Citation: Mancuso, M. 2015. Monitoring Packard’s milkvetch (Astragalus cusickii var. packardiae) in Southwestern Idaho, 2014 results. Report prepared by Mancuso Botanical Services for the U.S. Fish and Wildlife Service, Idaho Fish and Wildlife Office, Boise, ID. 68 pp. <br>

Location: BOTANY: PLANT SPECIES: { Astragalus cusickii var. packardiae } <br>

Keywords: Packard’s milkvetch, Astragalus cusickii var. packardiae, endemic, Payette County, Idaho <br>