COS 69-10
Will local or commercial natives succeed where exotic invaders fail? Cheatgrass die-offs as an opportunity for restoration in the Great Basin, USA
The exotic annual cheatgrass (Bromus tectorum) commonly occurs in dense, near-monocultures in the Great Basin, U.S.A. after diverse native plant communities have been mostly extirpated. Efforts to reestablish native species via direct seeding, typically with commercially produced, non-local seeds, are often unsuccessful. In addition to climatic factors that influence establishment, strong cheatgrass dominance impedes native establishment in highly invaded communities, and commercially produced seeds may lack important adaptive traits. The phenomenon of complete cheatgrass stand failure, or ‘die-off’, can leave areas within cheatgrass near-monocultures devoid of growth for one or more years. Such areas may represent restoration opportunities if native seeds can establish within them. This study addressed two questions within one cheatgrass die-off in northern Nevada: (1) Will native grasses establish from seed within cheatgrass die-offs, with or without modest ameliorations? and (2) Do adaptations to local conditions result in greater establishment of local genotypes, relative to commercial cultivars? In October 2012, local and commercial sources of Sandberg bluegrass (Poa secunda) and bottlebrush squirreltail (Elymus elymoides) were precision-planted in recent die-offs and adjacent near-monocultures (controls) under six treatments: litter removal, fungicide application, and no treatment; each with and without water addition.
Results/Conclusions
Emergence of native seeds was significantly lower in die-off plots, but there were significantly more actively growing seedlings of both species by the end of the first growing season in die-off plots than in adjacent control plots. Preliminary second year patterns also favor higher establishment in die-off plots. In the first growing season, commercial squirreltail (‘Toe Jam Creek’ germplasm) outperformed locally collected squirreltail, whereas local bluegrass showed higher performance than commercial bluegrass (‘Mt. Home’ germplasm). Litter removal had a positive influence on numbers of actively growing seedlings for both species in the first season, but only affected the second season establishment of bluegrass. Late autumn water addition affected emergence timing for both species and resulted in more squirreltail seedlings, but this affect was generally consistent between the controls and die-off. These results suggest that cheatgrass die-offs may support increased establishment of native species and may therefore represent valuable opportunities for restoration. Also, they indicate that local and commercial seeds differ in performance in important, but idiosyncratic, ways.