Vegetation response to seven grazing treatments in the Northern Great Plains

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 (28.8 AUD ha 1 year ) of cattle using 3-pasture summer rotation, season-long, highintensity low-frequency, short-duration, 3-pasture winter rotation, and spring calving systems. The final treatment was severe growing-season grazing (108.2 AUD ha 1 year ). 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) (674 186 kg ha ; P > 0.69), other perennial C3 grasses (102 156 kg ha ; P > 0.77), perennial C4 grasses (178 111 kg ha ; P > 0.22), and shrubs (13 34 kg ha ; P > 0.57) were similar across grazing treatments. Severe grazing produced more forbs (142 16 kg ha ; P < 0.01) than moderate stocking (67 16 kg ha ). Annual C3 grasses increased (P < 0.01) from 131 55 kg ha 1 on pastures grazed after May to 362 55 kg ha 1 on pastures grazed before June. Cacti also increased (P < 0.03) from 47 to 187 52 kg ha 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. Published by Elsevier B.V.