Native northern wheatgrass range was defoliated at different frequencies (2 or 6 weeks) beginning in May, June, July or August, for 3 consecutive years to determine the effects on above- and below-ground plant yield. Defoliation reduced above-ground residual phytomass, however, plants that were defoliated earlier in the season, or more frequently, had less phytomass than those defoliated later in the season or less frequently. Clipping decreased below-ground phytomass and root and rhizome weight. However, plants clipped earlier in the season had greater below-ground phytomass when defoliated every 2 weeks, while plants clipped later in the season had greater below-ground phytomass when defoliated every 6 weeks. The authors concluded that managing northern wheatgrass mixed-prairie for multiple and/or early season defoliation would not be sustainable and suggest that a single grazing event, after July, should help to maintain productivity.
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