Modeling growth and competition of a multi-species pasture system
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abstract
Pastures are often a mixture of different plant species. The growth patterns of these mixtures are determined by the interactions and competition among the coexisting species, as well as their response and interactions with the environment. Grassland management for economic and environmental sustainability should be based on the integrated view of the pasture system and the understanding of the processes involved. Computer models are ideal to study such complex systems. Most modeling efforts have focused on binary combinations of an agronomic crop and a major weed species in agricultural systems. In this research, the GRAzing SImulation Model (GRASIM) was extended to account for growth and interspecies competition among a mixture of plant species, including grasses, legumes, and weeds. In the multispecies GRASIM, a user-specified number of species grow separately on a daily time step, competing for light, soil water, and nitrogen. Forage experiments were conducted on a naturalized pasture at the Pennsylvania State University Beef Research Farm (University Park, Pa.). The pasture was divided and rotationally stocked at two intensities (high and low). Forage biomass data from 1998 and 1999 were used to develop and evaluate the multispecies GRASIM model. The nuiltispecies GRASIM reasonably simulated the growth dynamics of multiple species on two grazing treatments across two seasons, despite the high variability of the pasture. The model-simulated and observed biomass data for the dominant species across the two treatments and the two growing seasons gave regression coefficients of determination (R 2) ranging from 0.25 to 0.98. Model limitations and directions for future efforts are outlined and discussed. The multispecies GRASIM can be used to help evaluate coexisting species interaction and their response to the environment and provide insight into the complex mixed-species pasture ecosystem.
