Modeling Weather Effects on Plant Production in the California Annual Grassland

Weather drives plant community assembly and seasonal plant production in most rangeland ecosystems. Previous models in the California Annual Grassland have indicated that plant production is largely determined by the thermal accumulation, or degree days, between the start and end of the growing season. These models, however, were relatively limited in spatial and temporal scope and did not include seasonal parameters commonly used in more current production-system models. The purpose of this study is to develop models that account for the annual and seasonal effects of weather inputs on plant production. Weather variables for these models included seasonal effects of accumulated degree days, total precipitation, average temperature, season length, past year's precipitation, and past year's plant production. Our results indicated that sorting precipitation years into low, moderate, and high groupings resulted in better production-model fit compared with a full-suite analysis of all precipitation years. In addition, we found that precipitation, temperature, past year's precipitation, and past plant production significantly improved model fit over models that considered only accumulated degree days and season length. Linking these models to seasonal forecasting applications across western rangeland ecosystems could significantly enhance management of grazing production systems in this environment.