Modelling plant growth dynamics in sagebrush steppe communities affected by fire

The EDYS model was used to simulate plant production in burned and unburned communities dominated by Bromus tectorum at the US Army Yakima Training Centre, Washington. Model results were validated with 4 years of field data obtained in experiments designed specifically for this study. Subsequently, 50-year simulations of plant production were conducted with normal precipitation for the area and with no disturbances such as grazing or military training. Our simulations of plant production were not significantly different (p>0.05) from observed results of burned and unburned communities in 90% of the comparisons, indicating that EDYS adequately simulated the dynamics of this system. Long-term simulations indicated that annual species, primarily B. tectorum, dominated burned and unburned plant communities for 13–15 years, after which, annuals were replaced by perennials. B. tectorum, however, remained five years longer in the burned than in the unburned community, suggesting that fire favors the persistence of this species in invaded areas. Although B. tectorum dominated both plant communities during the initial simulation period, its production fluctuated greatly. The main perennials that replaced B. tectorum were Chrysothamnus nauseosus, Artemisia tridentata, and Agropyron cristatum. Our long-term modelling results are supported by previous field observations in which annual species are replaced by perennials in the absence of disturbances.