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Vegetation response to seven grazing treatments in the Northern Great Plains

Vermeire, Lance T., Heitschmidt, Rodney K., Haferkamp, Marshall R.
Agriculture, ecosystems & environment 2008 v.125 no.1-4 pp. 111
grasslands, grazing, grazing management, rangelands, range management, dry matter accumulation, botanical composition, crop yield, stocking rate, drought, grasses, perennials, Pascopyrum smithii, C3 plants, C4 plants, forbs, annuals, cacti and succulents, seasonal variation, rotational grazing, functional diversity, Montana
Grazing systems may alter botanical composition and productivity of grasslands through differential use in time, space, or intensity. Seven simulated grazing treatments were applied six years in eastern Montana, USA to determine effects on plant community composition and standing crop. Treatments were moderate stocking (28.8AUDha⁻¹ year⁻¹) of cattle using 3-pasture summer rotation, season-long, high-intensity low-frequency, short-duration, 3-pasture winter rotation, and spring calving systems. The final treatment was severe growing-season grazing (108.2AUDha⁻¹ year⁻¹). Treatments were randomly assigned to 14, 6.1-ha pastures. Post-treatment grass and total standing crops were 54 and 58% of their pre-treatment measures because of extended drought. No single grazing system affected standing crop of any herbage component. Standing crops of Pascopyrum smithii Rydb. (Love) (674±186kgha⁻¹; P >0.69), other perennial C₃ grasses (102±156kgha⁻¹; P >0.77), perennial C₄ grasses (178±111kgha⁻¹; P >0.22), and shrubs (13±34kgha⁻¹; P >0.57) were similar across grazing treatments. Severe grazing produced more forbs (142±16kgha⁻¹; P <0.01) than moderate stocking (67±16kgha⁻¹). Annual C₃ grasses increased (P <0.01) from 131±55kgha⁻¹ on pastures grazed after May to 362±55kgha⁻¹ on pastures grazed before June. Cacti also increased (P <0.03) from 47 to 187±52kgha⁻¹ on early-grazed pastures. Greater total standing crop on pastures grazed before June (P <0.03) was accounted for by increases in annual C₃ grasses and cacti. Rotational and continuous grazing strategies produced similar effects on all vegetation components. Grazing systems were not effective in altering standing crop or functional group composition one year after six years of treatment. Standing crop changes over time and limited shifts in forbs, cacti, and annual C₃ grasses indicate northern mixed prairie is most responsive to weather, with stocking rate and timing of grazing contributing minor influences.