Monitoring Packard’s milkvetch (Astragalus packardiae) in Southwestern Idaho, 2017 results

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Packard’s milkvetch (Astragalus packardiae) is a 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 most rare members of the Idaho flora. Conservation concern for Packard’s milkvetch is based on the species’ limited geographic distribution and small population size. Due to ongoing conservation actions as a result of a rangewide monitoring program that was initiated in 2008 to help assess the conservation status of Packard’s milkvetch, many of the species’ threats such as OHV and livestock disturbances have been alleviated. Monitoring is based on sampling at 21 permanently marked plots that encompass most Packard’s milkvetch subpopulations located on public land. Sampling included the full complement of monitoring protocols in 2008 - 2012, and again in 2015, but was limited to the collection of ground disturbance data for 2013 - 2014. In 2016, abundance and ground disturbance sampling was conducted for all plots, but plant community and plant demography sampling was limited to collection of data at two plots. In 2017, monitoring was limited to abundance sampling and photo points at sixteen plots and demography monitoring at five plots. This report summarizes 2017 monitoring results and makes comparisons to earlier datasets. <br>

Abundance sampling in 2017 tallied a total of 1,520 Packard’s milkvetch plants in sixteen plots, a nearly 119% increase from the 2016 tally of the same plots (696 plants). In 2017, the percentage of plots that had an increase in Packard’s milkvetch compared to 2016 was 88%. The only year that abundance was higher occurred in 2012. <br>

In 2017, demography sampling was conducted on a total of 46 Packard’s milkvetch in five plots. Of the 46 plants sampled, 30 plants were new in 2017, and 64% were reproductive. Longevity and life stage transition data were compared to that of the same plots for the entire 2008-2017 monitoring period. One-year plants in 2017 had the highest longevity at 33%, followed by the same values for 2-year and 5+-year plants. In 2015, the highest percentage of plants were in the one-year longevity category, followed by two-year plants. In plots 1-4 and 4-1, 21 plants present in 2016 were not present in 2017. In 2017, a larger percentage of Packard’s milkvetch were 8+ years old as compared to 2015. <br>

The mean number of flowers/fruits per reproductive Packard’s milkvetch was close to the means in 2008 and 2011, and greater than the means of 2016, 2015, and 2012. <br>

Packard’s milkvetch protection and conservation measures continue to be implemented by the partnership of BLM and Idaho Fish and Wildlife Office. Continued monitoring of Packard’s milkvetch will help to assess these actions and provide rationale and guidance for future adaptive management measures. <br>

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Reference Code: U18BIR01IDUS <br>

Full Citation: Sue Birnbaum. 2018. Monitoring Packard’s milkvetch (Astragalus packardiae) in Southwestern Idaho, 2017 results. Report prepared for the Idaho Bureau of Land Management and Idaho Fish and Wildlife Office, Boise, Idaho. 19 pp, plus appendixes <br>

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

Keywords: Packard’s milkvetch, Astragalus packardiae <br>