Clark et al. report basal area change and mortality responses of bluebunch wheatgrass (Agropyron spicatum) to 3 spring, 1 winter, and 3 spring + winter defoliation treatments. Clipping half, when the plant was at mid-boot, differed between winter grazed and non winter grazed (basal area increased 6% and 18.6% respectively). Clipping whole plants at mid-boot or inflorescence, decreased basal area (significantly more than control with winter grazing). Experiment-wide plant mortality was only 0.2%. If managed for a moderate level of defoliation, where a portion of the basal area of each bunchgrass plant is left undefoliated, livestock grazing during the boot stage should have little negative impact on the vigor and survival of bluebunch wheatgrass under environmental conditions similar to northeastern Oregon.
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