Impact of management practices on the tallgrass prairie

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Abstract
The ELM ecosystem-level grassland model simulates the flow of water, heat, nitrogen, and phosphorus through the ecosystem and the biomass dynamics of plants, consumers, and the decomposers. This model was adapted to a tallgrass prairie site in northeastern Oklahoma, USA, the Osage Site of the U.S. International Biological Program Grassland Biome. Several range management manipulations were simulated by the model and the results compared to field data and literature information: (1) altering the grazing intensity, grazing system, and grazing time period; (2) adding nitrogen and phosphorus to the grassland; (3) adding water during the growing season; and (4) spring burning of the prairie. The model showed that cattle weight gain per head, above-ground and belowground plant production, transpiration water loss, standing dead biomass, and the net nitrogen balance decrease with increasing grazing intensity, while soil water content and bare soil water loss increase. A moderately stocked year-round cow-calf grazing system is more beneficial to the grassland than a more highly stocked seasonal steer grazing system because the former increases the aboveground and belowground primary production and the plant nutrient uptake rates. Range manipulations, such as fire, which stimulate uniform grazing of a pasture, increase primary production, cattle weight gains, and nutrient uptake of plants and animals. Model results indicated that adding fertilizer was the best strategy for increasing cattle weight gains per head, while adding water would produce the greatest increase in primary production. Simulation of yearly and triennial spring burns suggests that these treatments increase primary production, plant nutrient uptake, and cattle weight gain per head. Burning increases the nitrogen losses from the systems; however, these losses are greater with annual burns. The model results also suggest the spatial grazing pattern of cattle must be considered to correctly represent the impact of grazing on the prairie. The model is used to describe the behavior of the tallgrass prairie ecosystem, evaluate alternative management strategies, and identify future scientific research and management studies.