December 2012 Number 1 - Utah Native Plant Society

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Utah Native Plant Society Sentry Milkvetch (Astragalus cremnophylax var. cremnophylax) Update Janice Busco Grand Canyon National Park, Grand Canyon, AZ Abstract. The Grand Canyon endemic Astragalus cremnophylax var. cremnophylax (Sentry milkvetch) was listed as an endangered species in 1990. There are 725 plants within three populations on the South Rim, all found in shallow soils upon large flat Kaibab limestone platforms. Habitat specificity and reduced number of plants make Sentry milkvetch vulnerable to extinction. Recovery plan actions completed in 2008 include seed collection and parking lot removal to allow habitat restoration and population expansion. Planned recovery plan actions include establishment of an ex situ population, seed production, and development of techniques for population augmentation and creation of artificial populations. The Grand Canyon National Park endemic Astragalus cremnophylax Barneby var. cremnophylax (Sentry milkvetch) was listed as an endangered species by the US Fish and Wildlife Service and protected from trampling by South Rim sightseers in 1990. There are approximately 725 individuals known in three locations, all on the South Rim of Grand Canyon. Sentry milkvetch occurs in shallow, well-drained soils or porous limestone pavement in crevices and depressions in large flat Kaibab limestone platforms in unshaded openings in the pinyon-juniper woodland along the canyon edge. The underlying bedrock limestone stores water and is critical to its growth and development (USFWS 2006). Sentry milkvetch is a small, mat-forming perennial plant (Figure 1) and has a thick taproot and woody caudex. Pale purple flowers appear from late April to early May, with seed set in late May to June. Its tiny seeds tend to fall in the mat of the plant; therefore the plant does not spread and remains isolated. Threats to Sentry milkvetch include small population size, vulnerability to drought and stochastic events, digging by ground squirrels and bighorn sheep (Figure 2), low reproductive capacity, limited seed dispersal, limited habitat, and reduced genetic diversity and vigor (Allphin et al. 2005). Figure 1. A mature Sentry milkvetch with a quarter for scale. RECOVERY CRITERIA AND OBJECTIVES In order to downlist the species, the Sentry Milkvetch Recovery Plan (USFWS 2006) requires achievement, maintenance and long-term protection of at least four viable Sentry milkvetch populations of at least 1,000 individuals each, for a total of at least 4,000 individuals in the wild. Recovery will be attained when there are eight viable Sentry milkvetch populations of 1,000 individuals each, with long-term protection. Figure 2. Bighorn sheep damage to Sentry milkvetch. 106
Calochortiana December 2012 Number 1 RECOVERY PLAN ACTIONS Completed Actions 2006-2008 In 2006, recovery plan actions for the species began. Grand Canyon NP has completed annual monitoring of the Maricopa Point population each year (2006-2008) and performed a complete census of the Maricopa Point population in 2008. We installed permanent photopoints in all three populations in summer 2008. Grand Canyon NP and the Arboretum at Flagstaff collected 2600 seeds from 74 individuals in the summer of 2008 (Figure 3). The Arboretum at Flagstaff completed seed germination studies, initiated greenhouse seed production. established an ex situ population, and conducted mycorrhizal studies of the species. Grand Canyon NP completed parking lot removal, trail rerouting and shuttle bus stop relocation from Sentry milk-vetch habitat adjacent to the Maricopa Point population to allow habitat restoration and population augmentation and expansion (Figure 4). In addition, two suitable areas for artificial population establishment were selected in Spring 2008. Planned Actions 2009-2013 Recovery plan actions planned for 2009-2013 include restoration of disturbed habitat and completion of seeding and planting trials at Maricopa Point. Acquisition of a passive solar greenhouse in 2009 will provide a dedicated facility for seeding trials, seed and plant production for introduction trials at Maricopa Point, and will create an ex situ Sentry milkvetch population. Through these trials we plan to develop techniques for creation of artificial populations, increase the number of individuals at Maricopa Point, and establish new pilot populations in suitable areas near Maricopa Point (Figure 5). A discovery survey of the westernmost portions of the south rim will be completed in 2009. Soil seed bank studies and ecological observations to determine pollinators will be conducted in 2009-2010. Additionally, interpretative materials will be developed and displayed at the Grand Canyon Visitor Center. Cooperating agencies in planned recovery actions include Grand Canyon National Park, US Fish and Wildlife Service, The Arboretum at Flagstaff, Grand Canyon Association, National Park Service, Center for Plant Conservation, Northern Arizona University Environmental Monitoring and Assessment (EMA) and Coconino National Forest. LITERATURE CITED Allphin, L., N. Brian, and T. Matheson. 2005. Reproductive success and genetic divergence among varieties of the rare and endangered Astragalus cremnophylax (Fabaceae) from Arizona, USA. Conservation Genetics 6: 803-821. Figure 3. Seed collection, summer 2008. Figure 4. Parking lot removal adjacent to population, September 2008, readied the site for restoration to be completed in 2010-2012. Figure 5. Suitable area selected for Sentry milkvetch artificial population. 107
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December 2012 Number 1 - Utah Native Plant Society

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