Monitoring Packard’s milkvetch (Astragalus cusickii var. packardiae) in Southwestern Idaho, 2015 results

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Packard’s milkvetch (Astragalus cusickii var. 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 rarest members of the Idaho flora. Conservation concern for Packard’s milkvetch is based on the species’ limited geographic distribution, small population size, habitat decline, and vulnerability of its habitat to multiple, ongoing disturbances and threats. A rangewide monitoring program was initiated in 2008 to help assess the conservation status of Packard’s milkvetch and support pro-active and adaptive land management efforts for the species and its habitat. Monitoring is based on sampling at 21 permanently marked plots that encompass most Packard’s milkvetch subpopulations located on public land. An eighth consecutive year of data collection occurred in 2015. 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. This report summarizes 2015 monitoring results and makes comparisons to earlier datasets. <br> Abundance sampling in 2015 tallied a total of 812 Packard’s milkvetch plants, representing a 44% decrease compared to the 2008 - 2012 mean. Counts were lower than any previous monitoring year at 76% of plots, with the declines exceeding 50% in many cases. Monitoring recorded one or more ground disturbance factors at all plots in 2015. However, a large proportion of these disturbances predated the 2015 season. Total ground disturbance cover was lower or intermediate compared to previous years for all plots, with the rangewide average of 5.0% being lower than any previous year. Analysis showed no significant difference in the annual abundance of rangewide total ground disturbance between the eight monitoring years, but did detect a significant downward trend for the 2008 to 2015 dataset. Evidence of recent motorized disturbance was limited to a single track at 1 plot that appeared more likely to be from an ATV than a motorcycle. Most motorcycle tracks recorded prior to 2015 were no longer visible. Monitoring the past few years shows off-road motorcycle use to be nearly eliminated at habitat occupied by Packard’s milkvetch. The 2015 analysis found a significant downward trend in rangewide motorcycle track disturbance since the monitoring program began. Cattle and/or sheep track-related disturbance was recorded at all plots in 2015, although nearly all of it dated from previous years. Livestock track-related ground cover averaged 2.4% across all plots, a value lower than most previous years. Analysis of the 2008 - 2015 dataset detected no significant difference in the annual abundance of rangewide livestock track disturbance, nor did it find a significant upward or downward trend for this attribute. Other disturbances such as animal digging and water rivulet erosion exceeded 1% ground cover at several plots, but were relatively minor overall. Plant community sampling found total introduced species cover exceeded native species cover at most plots in 2015, a pattern similar to previous years. Introduced grass species such as cheatgrass (Bromus tectorum), medusahead rye (Taeniatherum caput-medusae), or bulbous bluegrass (Poa bulbosa) were the most abundant herbaceous species recorded on most transects. Mean rangewide introduced grass species cover across all plots was 9.9% in 2015, intermediate to the lowest and highest values from previous years. Analysis failed to detect a significant difference in 2015 rangewide introduced grass species cover compared to previous years, but did find a significant upward trend in rangewide introduced grass species cover between 2008 and 2015. <br> A pilot project initiated in 2012 to restore a buffer of shrub-steppe habitat at two Packard’s milkvetch subpopulations included the establishment of treatment and control plots to monitor efficacy of the restoration treatments. Herbicide application and follow-up seeding and planting with native shrub and forb species began at one site in October 2013. In 2014, introduced annual grass species abundance showed a significant decrease compared to pre-treatment at this location. Sampling in 2015 showed annual grasses returned to their pre-treatment prominence, but also found significant increases in abundance for a few forb species and gray rabbitbrush (Ericameria nauseosa) compared to baseline values. Monitoring will continue to play an important conservation role for Packard’s milkvetch by helping to assess the effectiveness of conservation actions and providing rationale and guidance for future adaptive management measures. <br> Contents include: Introduction, Methods, Data Analysis, Results, Discussion, Acknowledgements, References, Figures, Tables, and partial Appendices. Includes Appendices 1, 2, 5, and 7. Missing Appendices 3, 4, and 6. Appendices are titled as: Appendix 1. Maps and GPS coordinates for Packard’s milkvetch monitoring plots; Appendix 2. Sampling information for Packard’s milkvetch monitoring plots; Appendix 3. Copies of 2015 field data sheets for Packard’s milkvetch monitoring plots; Appendix 4. Spreadsheets for 2015 Packard’s milkvetch monitoring data (Compact Disc); Appendix 5. Field observation notes for Packard’s milkvetch monitoring plots, 2015; Appendix 6. Photos for Packard’s milkvetch monitoring plots, 2015 (Compact Disc); Appendix 7. Plant community monitoring data for 2015.

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Reference Code: U16MAN02IDUS <br>

Full Citation: Mancuso, M. 2016. Monitoring Packard’s milkvetch (Astragalus cusickii var. packardiae) in Southwestern Idaho, 2014 results. Report prepared by Mancuso Botanical Services for theIdaho Bureau of Land Management, Boise, ID. 47 pp., plus appendices <br>

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

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