December 2012 Number 1 - Utah Native Plant Society

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Utah Native Plant Society Pod shape, longitudinal section (podsl): 1. seculate & abruptly acute apically; 2. seculate & attenuate apically; 3. elliptic, narrowly elliptic, lunate & acute apically; 4. oblong, narrowly oblong & attenuate apically; 5. linear; 6. lanceolate, widest at base & attenuate apically; 7. oval, ovoid, broadly ovoid; 8. obovoid, broadly obovoid; 9. subglobose; 10. clavate-oblanceolate. Pod shape, cross section (podsc): 1. subterete, dorsiventrally compressed, when obcordate, the suture shallowly sulcate; 2. obcordate & laterally compressed, broadly to narrowly (obcompressed), suture deeply sulcate; 3. didymous & dorsi-ventrally compressed, broadly to narrowly; 4. cordate & dorsi-ventrally compressed, broadly to narrowly; 5. cordate & laterally compressed, broadly to narrowly. Pod orientation on raceme (podro): 1. ascending, erect & beak & 1/2 pod curved inward; 2. ascending to spreading, straight; 3. spreading, declined & beak to 1/2 pod recurved; 4. spreading & slightly curved inward from middle (lunate, falcate); 5. spreading & beak to 1/2 pod incurved to 180° (hamate). Pod orientation, degree of pod incurve, coded range (podpi): 1.
Calochortiana December 2012 Number 1 Ecology of Rusby’s Milkvetch (Astragalus rusbyi), a Rare Endemic of Northern Arizona Ponderosa Pine Forests Judith D. Springer, Michael T. Stoddard, and Daniel C. Laughlin, Ecological Restoration Institute, Northern Arizona University, Flagstaff, AZ Debra L. Crisp and Barbara G. Phillips, Coconino National Forest, Flagstaff, AZ Abstract. Rusby’s milkvetch (Astragalus rusbyi Greene) is endemic to basaltic soils northwest and west of Flagstaff, Arizona. Recent interest in this species is due in part to its addition to the U.S. Forest Service Region 3 sensitive species list in 1999 and its occurrence in ecological restoration projects and proposed fuels reduction projects that involve tree thinning and prescribed burning. Some of its habitat has been subjected to large wildfires over the last few decades, and other areas have undergone ecological restoration treatments, while much of its range in ponderosa pine forest is slated to undergo such treatments in the near future. In a ponderosa pine restoration study area northwest of Flagstaff, A. rusbyi was an indicator species of remnant grass patches and increased following tree thinning and prescribed burning. However, in an area less than 3 km away, there appeared to be no relationship to restoration treatments, trees per ha, pine basal area, or canopy cover, but A. rusbyi did appear to be sensitive to an extreme drought event in 2002 and may have remained dormant in that year, a pattern that has been observed in other rare Astragalus species. A. rusbyi has a foliar nitrogen content of 4.4% and a foliar C:N mass ratio of 11. It is classified as a competitive ruderal species, meaning it is able to compete well with other understory species, but is not very tolerant of stresses, such as deep shade. We currently do not have a thorough understanding of the ecology of this species, or the effects of ecological restoration or fuels reduction treatments. In this paper we will discuss ecology of other members of the genus Astragalus and explore the relationships of A. rusbyi to moisture, vegetation treatments and overstory mortality. Astragalus is believed to be the largest genus of flowering plants in the world, with over 2500 species worldwide and over 400 species in North America alone, primarily in arid regions of the western U.S. The highest diversity in North America is centered in the Great Basin and on the Colorado Plateau (Barneby 1989, Sanderson 1991). Astragalus species are often found in marginal habitats or on specialized soil types, and their geographic ranges are strongly skewed towards narrow endemism (Barneby 1964, 1989; Sanderson 1991). Along with a limited dispersal ability possessed by many members of the genus, there is widespread local differentiation and geographic speciation, particularly in the areas of the western U.S. where it achieves the highest levels of diversity (Sanderson 1991, Lesica et al. 2006). However, due to restricted ranges and habitats, some Astragalus species may exhibit low genetic variability and reduced fitness from inbreeding depression (Karron et al. 1988, Allphin et al. 2005, Breinholt et al. 2009). Neoendemism is common in the intermountain regions of North America where there are large numbers of both widespread, recently evolved species, as well as narrowly endemic species, which are often associated with extreme edaphic conditions and reduced competition from dominant species (Lesica et al. 2006). Lesica and his co-authors suggest that restricted ranges and high local abundances of neoendemic species may be due more to patterns and processes of speciation than to ecological tolerance. The small ranges exhibited by many Astragalus species in the western U.S. may be due to recent speciation and an insufficient amount of time for these species to have increased their ranges significantly (Lesica et al. 2006). Reticulate evolution may not be widespread in the Astragalus genus, for many members of the genus appear to exhibit allopatry (geographic isolation) along with high levels of local endemism and little hybridization (Sanderson 1991). The type specimen of A. rusbyi was collected by Henry Hurd Rusby on July 2, 1883 on Mt. Humphreys, near Flagstaff Arizona (Welsh 2007) and was first described by Edward Lee Greene in 1884 (Greene 1884). A. rusbyi is a slender perennial averaging 15-40 cm in height. It also has a fairly deep taproot (D.C. Laughlin, personal communication, 2008). It grows primarily in meadows in ponderosa pine forests and in aspen groves (Barneby 1964, Welsh 2007), but it also may be found in moderately dense ponderosa pine forests. Populations are mainly concentrated on basaltic soils in two areas in northern Arizona: around the San Francisco Peaks 157
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December 2012 Number 1 - Utah Native Plant Society

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