Impacts of defoliation on the competitive abilities of resident bunchgrasses with cheatgrass
Researchers:
Michael Reisner, Ph.D. candidate, Oregon State University, Michael.Reisner@oregonstate.edu
Paul Doescher
Dave Pyke
Study Dates:
Jan 2008-November 2009
SageSTEP Study Plots:
Hart Mountain - Rock Creek and Gray Butte Sites. Also, non-SageSTEP plots in Oregon will be used.
Study Design and Objectives:
This study will evaluate the importance of competition with resident bunchgrasses in limiting the rate of cheatgrass invasion of Wyoming big sagebrush communities, and understand the extent to which defoliation caused by herbivory impacts the outcome of these interspecific competitive interactions.
Study Objectives:
- Determine competitive ability of squirreltail
- Determine competitive impact of resident bunchgrasses on cheatgrass performance
- Determine the impacts of defoliation on the competitive ability of squirreltail and the outcome of these interspecific interactions
- Determine the level of defoliation (herbivory threshold) at which defoliation-induced reductions in the competitive abilities of bunchgrasses shifts the outcome of competition in favor of cheatgrass
The study will utilize a factorial treatment design with two factors. Defoliation of photosynthesizing biomass will be simulated by a combination of hand-clipping and weed-eater mowing using five different timing frequencies (no defoliation, single early spring, two growing season, single fall, and two fall-spring defoliation) at seven sites. Two patterns of defoliation will be used: 1) selective defoliation of only resident bunchgrasses, and 2) uniform defoliation of both resident bunchgrasses and neighboring cheatgrass.
Cheatgrass collected near the study sites will be seeded into each treatment plot, and seedling emergence will be monitored. Cheatgrass will be harvested to determine above ground biomass and seed production. Other variables, such as nitrogen and water uptake will also be measured.
Information from this study will help scientists and managers better understand cheatgrass establishment.