A Simulation Model for Grassland Primary Producer Phenology and Biomass Dynamic

Abstract

The two primary producer submodels described in this chapter, plant phenology and carbon flow, are components of the grassland ecosystem model, ELM. The objectives of these submodels are to simulate biologically realistic phenology and growth responses to conditions varying from drought to irrigation and fertilization. These submodels simulate five primary producer groups and interact extensively with each other and the other ELM submodels. The phenology submodel simulates phenological change in each producer group. The rate of phenologic change is determined from maximum air temperature, insolation, soil- water potential, soil temperature, day length, and shoot weight. The carbon submodel simulates dynamics of live shoots, dead shoots, live roots, seeds, and crowns for each producer group. One litter and three dead-root state variables are represented for all producers. The processes modeled for each producer group are growth, respiration, and death of shoots, roots, and crowns, gross photosynthesis, seed produc- tion and germination, and the fall of standing dead shoots. Comparison between observed data and simulations suggest the model to be most sensitive to the belowground system, the fall of standing dead, and the relationship between phenology and environment, and that these areas need additional refinement.