Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/20/2014
Publication Date: 1/31/2015
Citation: Harmon, D.N., Clements, D.D. 2015. Evaluating perennial grass competition as a management tool. In: Society for Range Management Meeting Abstracts, January 31-February 6, 2015, Sacramento, CA. 68:251.
Technical Abstract: Evaluation of plant competition is highly dependent on life stage and cycle. One of the largest problems that Great Basin rangelands face is the competitive nature of the exotic and invasive annual grass, cheatgrass (Bromus tectorum). Advantages of cheatgrass are often attributed to large seed production, the ability to carry persistent seed banks, fall germination, and plasticity. However, the measurement of a “successful” competitor is often reported in terms of biomass. Biomass represents the negative effect of competitor “A” on competitor “B” through resource limitations and therefore judging competitor “A” as the winner in many cases. This relationship is often reported by authors as “suppression”. We limit the term “suppression”, in regards to management, for use only at the population level for densities, not individual plant biomass. The target goal for cheatgrass suppression is the absence of plants and significant decrease in seed production, not just smaller plants. While biomass is related to seed production, annuals exist at high densities producing an excess abundance of seed. It is unfounded that decreased biomass would have significant effects on cheatgrass dominance due to its ability to produce more seed than is needed to sustain the population. For a perennial grass we hypothesized that competing with cheatgrass at the seedling phase is best evaluated by survival (drought tolerance) not biomass or seed production. Biomass and seed production are an artifact of species and resource limitations. In efforts to rehabilitate rangelands the first concern is establishing a desirable density of seeded species, not the biomass or seed production of said plants. Productivity after all cannot be measured without establishing plants first. From previous research we found that the greatest indicator of seedling failure was desiccation. With this research we focused on what separates cheatgrass from the other perennial grasses observed and likely leads to its competitive dominance. This research examines which indices of competitiveness relate to survival. We conducted a 3-year study measuring biomass, germination, emergence, drought tolerance, and seed production of cheatgrass, squirreltail (Elymus elymoides), bluebunch wheatgrass (Pseudoroegneria spicata) and crested wheatgrass (Agropyron cristatum). Plants were seeded at high intra and inter-specific competition densities in replicated soil boxes (9m3). Biomass was a poor indicator, as cheatgrass had less biomass yet was more dominant. Germination corresponded to seedling drought survival as cheatgrass germinated first followed by crested wheatgrass, bluebunch wheatgrass and squirreltail. There was no significant difference between germination and emergence as all species emerged very close to germination rates. While all indices contribute to perennial failures, seedling drought survival was fundamental for evaluating success. Seeding perennials with the highest seedling drought tolerance should be a primary principal in rehabilitation efforts.