Parton W J, Risser P G
Natural Resource Ecology Laboratory, Colorado State University, 80523, Fort Collins, CO, USA.
Department of Botany and Microbiology, University of Oklahoma, 73019, Norman, OK, USA.
Oecologia. 1980 Jan;46(2):223-234. doi: 10.1007/BF00540130.
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.
ELM生态系统层面的草地模型模拟了水、热、氮和磷在生态系统中的流动以及植物、消费者和分解者的生物量动态。该模型适用于美国俄克拉荷马州东北部的一个高草草原地点，即美国国际生物学计划草地生物群落的奥色治地点。该模型模拟了几种牧场管理措施，并将结果与实地数据和文献信息进行了比较：（1）改变放牧强度、放牧系统和放牧时间段；（2）向草地添加氮和磷；（3）在生长季节补充水分；（4）春季焚烧草原。模型显示，随着放牧强度的增加，每头牛的体重增加、地上和地下植物产量、蒸腾失水量、立枯生物量和净氮平衡都会下降，而土壤含水量和裸土失水量会增加。全年适度放养的母牛-小牛放牧系统比放养密度更高的季节性公牛放牧系统对草地更有益，因为前者能提高地上和地下初级生产力以及植物养分吸收率。诸如火灾等牧场管理措施能促进牧场均匀放牧，增加初级生产力、牛的体重增加以及动植物的养分吸收。模型结果表明，添加肥料是增加每头牛体重增加的最佳策略，而补充水分会使初级生产力增加最多。对每年和每三年春季焚烧的模拟表明，这些处理会增加初级生产力、植物养分吸收和每头牛的体重增加。焚烧会增加系统中的氮损失；然而，每年焚烧时这些损失更大。模型结果还表明，必须考虑牛的空间放牧模式，才能正确反映放牧对草原的影响。该模型用于描述高草草原生态系统的行为、评估替代管理策略以及确定未来的科学研究和管理研究。
