Can Sainfoin Improve Conditions for Establishment of Native Forbs in Crested Wheatgrass Stands?

Abstract

Concerns about wildlife habitat quality in western North America has stimulated interest in diversifying Agropyron cristatum (crested wheatgrass) stands. Four main obstacles make it difficult to establish native forbs in stands of A. cristatum. First, adult A. cristatum plants are fierce competitors with native seedlings. Second, A. cristatum seedlings emerging from a long-lived seedbank can crowd out native species. Third, A. cristatum control may facilitate secondary invaders rather than the desired native species. Fourth, potential soil modification by A. cristatum may impede establishment of diverse native plant species. A “bridge species” that is compatible with A. cristatum control and improves conditions for native species establishment could facilitate A. cristatum stand diversification. We compared native forb growth in soils of former A. cristatum stands preconditioned by A. cristatum, Bromus tectorum (cheatgrass), and Onobrychis viciifolia (sainfoin), a glyphosate-tolerant legume. Soils preconditioned by O. viciifolia had the greatest P and K availability. Although total plant biomass was similar among treatments, native forbs had greater root colonization by arbuscular mycorrhizal (AM) fungi, less root colonization by non-AM fungal, and lower root-shoot ratios when grown in O. viciifolia-conditioned soils, suggesting improved soil microbe and nutrient conditions for native forb establishment. We conclude that O. viciifolia may be a useful bridge species for improving soil conditions while allowing for weed control during restoration of A. cristatum stands.