• Spring defoliation effects on bluebunch wheatgrass: I. Winter forage quality

      Clark, P. E.; Krueger, W. C.; Bryant, L. D.; Thomas, D. R. (Society for Range Management, 1998-09-01)
      The winter forage quality of bluebunch wheatgrass (Agropyron spicatum [Pursh] Scribn. &Smith) is generally inadequate for maintenance of wintering Rocky Mountain elk (Cervus elaphus nelsoni Bailey). Previous attempts to improve the winter forage quality of bluebunch wheatgrass by clipping and livestock grazing have achieved mixed results. We report crude protein (CP), (in vitro dry matter digestibility (IVDMD), and dry matter (DM) yield responses of bluebunch wheatgrass to 3 phenological stage/defoliation intensity treatment combinations. The study was conducted in 1993 and 1994 at 2 sites in the Blue Mountains of northeastern Oregon. Bluebunch wheatgrass was hand clipped 1 to a 7.6-cm stubble height in early June under 1 of 3 treatment combinations: 1) mid-boot/whole-plant clipped, 2) mid-boot/one-half of the plant's basal area clipped, and 3) inflorescence emergence/whole-plant clipped. Early November levels of CP and IVDMD were greater under all 3 treatments compared to an unclipped control. Mean forage quality improvement over the control was greatest in the inflorescence emergence treatment with an improvement of 1.3 percentage points for CP and 5.8 percentage points for IVDMD. Dry matter yield of the control exceeded that of all clipping treatments. Increases in forage quality resulting from forage conditioning treatments may be important to the viability of elk populations wintering on rangelands where forage quality, rather than quantity, is limiting.
    • Spring defoliation effects on bluebunch wheatgrass: II. Basal area

      Clark, P. E.; Krueger, W. C.; Bryant, L. D.; Thomas, D. R. (Society for Range Management, 1998-09-01)
      Spring livestock grazing has been suggested as a tool to improve winter forage quality of bluebunch wheatgrass (Agropyron spicatum [Pursh] Scribn. & Smith). Impacts on plant vigor and survival are important concerns associated with spring grazing. We report basal area change and mortality responses of bluebunch wheatgrass to 3 spring, 1 winter, and 3 spring + winter defoliation treatments. The study was conducted in l993 and 1994 at 2 sites in the Blue Mountains of northeastern Oregon. Basal area of individual plants was measured shortly after application of the spring treatments and again approximately 1 year after treatment. Clipping the entire basal area of bluebunch wheatgrass plants to a 7.6-cm stubble height during the mid-boot phenological stage and during the inflorescence emergence stage produced 7.0 and 7.8% declines in live basal area, respectively. Unclipped control plants and plants having only one-half their basal area clipped to a 7.6-cm stubble height during the mid-boot stage exhibited 5.2 and 18.6% increases in live basal area, respectively. Combining the mid-boot/half-plant treatment with an early winter clipping to a 2.5-cm stubble height reduced the positive live basal area response to 6.0%. No additional declines in live basal area relative to the spring-only treatments were detected for combinations of the early winter treatment with the mid-boot/whole plant treatment and the inflorescence emergence treatment. Experiment-wide plant mortality was only 0.2%. If managed for a moderate level of defoliation where a portion of the basal and 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.