Short Duration, Perennial Grasses in Low Rainfall Sites in Montana: Deriving Growth Parameters and Simulating with a Process-Based Model

Rangeland grasses in the arid western U.S. grow quickly, set seed, and senesce in a relatively short timeframe enabling them to survive and reproduce when the limited soil moisture is available. In addition, rangeland management in arid sites can benefit from process-based simulation tools to optimize grazing timing, intensity and duration and for assessing impacts of invasive species and of climate change. In this study, over three growing seasons, we derived the needed growth parameters for the ALMANAC model to simulate three common cool season grasses and one warm season grass in Montana. The parameters were then used with the model to simulate plant growth on three typical ecological sites near Miles City. Model parameters such as radiation use efficiency and potential leaf area index showed expected trends with the four grasses. Once the parameters were used with the ALMANAC model, simulations showed reasonable agreement with published NRCS grass yields for normal years, wet years, and dry years. Thus this process-based model and parameters such as those described herein will be valuable for assessing various management scenarios and climate variables in these types of low rainfall, western U.S. ecological sites.