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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. The effect of annual precipitation on Agropyron cristatum suppression of bromus tectorum. In: Society for Range Management Meeting Abstracts, January 31-February 6, 2015, Sacramento, CA. 68:255. Interpretive Summary: Technical Abstract: The ability of established crested wheatgrass (Agropyron cristatum) to suppress cheatgrass (Bromus tectorum) is well documented. Many studies that examine the competition between these two species usually do so at the seedling phase. We do not consider decreased performance between two seedlings as an appropriate use of the term “suppression” as it relates to weed management. We define cheatgrass suppression as an established perennial grass having a negative effect on the density of cheatgrass. This is noted by the absent of plants in the adjacent area around a mature crested wheatgrass plant, resembling a bare ring appearance. We have observed that in years of high precipitation, these rings of suppression reduce in diameter with cheatgrass growing proximate to crested wheatgrass plants with no apparent signs of “suppression”. We designed an experiment adding simulated precipitation at bi-monthly intervals (March-May) to crested wheatgrass stands that averaged 4.26 plants/m2 in order to measure suppression effects. We hypothesized that increased precipitation would decrease crested wheatgrasses ability to suppress cheatgrass. Cheatgrass seed banks were measured prior to the study and cheatgrass seeds were added where needed so that all treatments were equal. Treatment 1 received an added 4.57cm of simulated precipitation, treatment 2 received an added 1.52cm of simulated precipitation, and treatment 3 was treated with Glyphosate and to kill the crested wheatgrass plants. Treatment 1 plots averaged 101 cheatgrass plants/m², treatment 2 plots averaged 23 cheatgrass plants/m², and treatment 3 plots averaged 20 cheatgrass plants/m². Cheatgrass mortality did however occur during the Glyphosate application which decreased the overall cheatgrass density in that treatment. Also, cheatgrass plants in treatment 3 were significantly larger than the other treatments and control plots as soil nitrogen increased from 5ppm to 14ppm. Control plots average 8 cheatgrass plants/m² and received the natural precipitation of 2.36cm from March through May. Overall, we find the results support our hypothesis but acknowledge there are many other interacting factors. Suppression is seldom “complete” with cheatgrass seed banks ever-so- present and awaiting a disturbance or other favorable conditions to gain dominance. Management to preserve and enhance perennial grass stands is critical in the suppression of cheatgrass densities and fuel loads. |
