A comparison of modeled and measured impacts of resource manipulations for control of Bromus tectorum in sagebrush steppe

The EDYS (ecological dynamics simulation) model was used to simulate vegetation growth resulting from different experimental treatments for Bromus tectorum control at Yakima Training Center, Washington. The treatments tested in the field for 4 years were seeding, sucrose application, and a combination of seeding and sucrose application. These treatments included burning to favor their implementation. A control plant community with no manipulations was also monitored in the study. The simulations of plant production were not significantly different from the observed field results in 90% of the comparisons, supporting the validity of the model. In long-term simulations, the population of B. tectorum ceased to dominate the plant community in about 12 years regardless of the treatments. Subsequently, the successional patterns were affected by the treatments. The control and sucrose treatments produced similar successional trends dominated mainly by shrubs (Artemisia tridentata and Chrysothamnus nauseosus). In contrast, both seeding treatments, including the one with sucrose, produced successional trends dominated by grasses, which reflected the seed mix composition. Seeding had more lasting effects than sucrose application. However, the seeded species only started to dominate the seeded areas when the dominance of B. tectorum was reduced. The long-term simulations provided projections that were difficult to envision solely based on the results of the 4-year field experiment.