Revegetating weed-infested rangeland with niche-differentiated desirable species

Abstract

The goal of this study was to determine the potential to revegetate weed-infested rangeland by maximizing niche occupation and resource capture by desirable species. We hypothesized that as desirable species richness increases, weed establishment and growth decrease, provided that the desirable species differ in niche. Three desirable species with differing spatial and temporal growth patterns, [Agropyron cristatum (L.) Gaertn., var. Hycrest (crested wheatgrass), Elytrigia intermedia (Host) Nevski, var. Rush (intermediate wheatgrass), and Medicago sativa L., var. Arrow (alfalfa)], and 1 weed [Centaurea maculosa Lam. (spotted knapweed)], were grown in a multiple replacement series. All species were sown simultaneously in spring 1996, simulating revegetation of a site containing spotted knapweed seeds in the seed bank because of prior infestation. Desirable species richness varied among plots, while the total number of desirable seeds sown per plot was held constant. Although the desirable species were shown to differ in niche, desirable species richness or mixture did not affect soil water depletion or spotted knapweed recruitment in 1996 or 1997. These results suggest that revegetation of weed-infested rangeland must also include active control of weeds emerging from the soil seed bank. Only then can other strategies, such as maximizing niche occupation by desirable species, be expected to provide long-term success.