Publications:

Literature in Review

Coachella Valley milkvetch

Astragalus lentiginosus var. coachellae

USFWS: Endangered
CDFG:

Background

Distribution, Abundance and Trends. The Coachella Valley milkvetch occurs in dunes and sandy flats, along the disturbed margins of sandy washes, and in sandy soils along roadsides, in areas formerly occupied by undisturbed sand dunes. Within the sand dunes and sand fields, this milkvetch tends to occur in the coarser sands at the margins of dunes, not in the most active blowsand areas. As this species is strongly affiliated with sandy substrates, it may occur in localized pockets where sand has been deposited by wind or by active washes. It may also occur in sandy substrates in creosote bush scrub, not directly associated with sand dune habitats. In the Plan area, populations are known from the Snow Creek area (in the sandy areas on either side of Snow Creek Road east toward Windy Point and scattered along Tipton Road, north of Hwy. 111), on the Whitewater River Floodplain Preserve, the Edom Hill-Willow Hole Preserve/ACEC, and the Coachella Valley Preserve. Other concentrations of the species occur along Gene Autry Trail near the airport in Palm Springs, on and around Flat Top Mountain, along Varner Road at the base of Edom Hill, and in scattered locations in the southern parts of Desert Hot Springs (including at the wastewater treatment plant). In the area of the Big Dune, populations have been much reduced by roads, fragmentation, and disturbance (Barrows 1987, CNDDB 1997). Though suitable habitat appears to be present in the Indio and La Quinta areas, this species has not been recorded there. Within the Plan area, the easternmost known location for the Coachella Valley milkvetch that is still extant is on the Coachella Valley Preserve.

The Coachella Valley milkvetch was first described by Rupert Barneby in Shreve and Wiggins (1964) based on a collection made by Alice Eastwood in 1913 near Palm Springs, Riverside County. Barneby (1964) had previously identified this specimen as Astragalus lentiginosus var. coulteri in the description of that taxon in 1945. Extensive dune systems, which once occurred at the base of the Santa Rosa Mountains in what are now the cities of Palm Springs, Cathedral City, Rancho Mirage, Palm Desert, Indian Wells, and La Quinta, provided suitable habitat for the Coachella Valley milkvetch.

This species is known from locations from One Horse Spring near Cabazon to the sand dunes off Washington Avenue, north and west of Indio, in a longitudinal west to east range of approximately 33 miles. The distribution of this species is restricted to the Coachella Valley in Riverside County, between Cabazon and Indio, with the exception of six outlying occurrences within a 5-mile area along the Rice Road in the Chuckwalla Valley north of Desert Center (Dice, pers. comm.). These Desert Center "outliers", most recently observed in March 1998, are not within the Plan area. While the overall range of this species may not be significantly reduced from the historical distribution, the number of known locations has declined dramatically (Barrows, 1987).

This federally-listed endangered species is an erect winter annual, or short-lived perennial, which blooms from February to May, producing pink to deep magenta-colored flowers. It is distinguished in part from other milkvetches by its strongly inflated, two-chambered, mottled pods. These pods, when dried, fall to the ground and are blown along the dunes. In good years, 100's to 1000's of individuals have been described in a population, but often reports are of less than 20 plants. Specific data on population size and dynamics are not available for this species. The factors controlling population size through effects on seed germination, seedling establishment, and plant longevity have not been studied, but presumably involve moisture availability and soil and air temperatures (Sanders 1995).

Threats and Limiting Factors. The primary threat to the Coachella Valley milkvetch is habitat destruction due to continuing urban development, including the direct effects of habitat conversion. Other impacts to the species are from increased human activity, including off-road vehicle use, trampling, and the introduction of non-native plants, including Russian thistle (Salsola tragus) and Saharan mustard (Brassica tournefortii). Development of wind energy parks has impacted this species, although the plants can persist associated with wind parks as long as disturbance to the species' sandy habitat is minimized. These sand dune areas where this milkvetch occurs have now been developed, been stabilized by adjacent development, or fragmented by urbanization. Each of the impacts described relates to the sand dune ecosystem and the interference with the windblown sand transport system. These ecosystems require a source of new sand to be maintained over long periods of time and a wind corridor to maintain dune dynamics. Though Coachella Valley milkvetch does not appear to require, or even prefer, active blow sand dune habitats, the species does appear to be dependent on sand dune ecosystems.

The annual variation in population size that has been observed in this species, associated with drought conditions and the occurrence of seasonal rainfall, is also of concern. The small size of populations in drought years could leave this milkvetch vulnerable to extinction from stochastic events. The number of individuals of this species in known locations can vary dramatically from year to year, depending on available soil moisture and other factors. For example, during the course of a biological survey for the Army Corps of Engineers at the Cabazon Windpark site in May 1979, 209 individuals were observed (Wright and La Pre 1979); a survey of this same area in May 1987 (Barrows 1987), a dry year, recorded only six Coachella Valley milkvetch.

Special Considerations. Within the Plan area, other species of concern whose habitat overlaps with that of the Coachella Valley milkvetch include flat-tailed horned lizard, Palm Springs pocket mouse, Palm Springs ground squirrel, Coachella giant sand treader cricket, Coachella Valley Jerusalem cricket, and burrowing owl.