Basalt milkvetch: Candidate species for rangeland restoration in the western USA

Astragalus filipes Torr. ex A. Gray (basalt milkvetch) is a native legume that may have potential in restoration in western North America. A total of 67 populations (accessions) of basalt milkvetch from California, Nevada, Utah, Idaho, Oregon, and Washington were evaluated in 2005 and 2006 in two common garden experiments in northern Utah (Evans Farm and Millville). Accessions from north central Oregon exhibited greater biomass yield in summer and fall in both years at both sites and greater seed yield at Millville in both years. Accessions from Nevada, Washington, and Utah, and some accessions from Oregon and Idaho showed poor biomass and seed production in both summer and fall. Forage quality characteristics (neutral detergent fiber and acid detergent fiber) were positively correlated with biomass, and crude protein concentration was negatively correlated with biomass only in 2005. Seed weight per 100 seeds varied among basalt milkvetch accessions, and accessions with high biomass yields tended to produce heavier seeds. Significant seed predation was observed in 2006, but not in 2005. Insect predators did not prefer seeds of one accession over another. High correlations between number of stems and biomass and between number of stems and seed yield indicated that number of stems is a good predictor of biomass and seed production in basalt milkvetch. Accessions from lower elevations produced greater biomass and seed yields than those from higher elevations. Accessions from north central Oregon have the most promise for plant improvement efforts.