• Predicting big sagebrush winter forage by subspecies and browse form class

      Wambolt, C. L.; Creamer, W. H.; Rossi, R. J. (Society for Range Management, 1994-05-01)
      Improved regression models were developed to predict winter forage production from big sagebrush (Artemisia tridentata Nutt.) through consideration of the subspecies variation among mountain big sagebrush (A.t. ssp. vaseyana [Rydb.] Beetle), Wyoming big sagebrush (A.t. ssp. wyomingensis Beetle and Young), and basin big sagebrush (A.t. ssp. tridentata). Changes in shrub morphology from browsing were also accommodated in our models. Colinearities among some variables used in previous studies were found and avoided in our models. Models used easily measured objective variables of which major axis and average cover of shrubs were most useful. Multivariable models without colinearities were evaluated on the basis of their R2a values which increased by an average of 10% to near 0.90, with taxa and browse form class included, compared to a model ignoring these differences.
    • Tiller defoliation patterns under frontal, continuous, and rotation grazing

      Volesky, J. D. (Society for Range Management, 1994-05-01)
      An investigation was conducted to characterize the intensity and frequency of tiller defoliation in 'Plains' Old World bluestem (Bothriochloa ischaemum (L.) Keng) under frontal, continuous, and 2-paddock rotation grazing systems. Frontal grazing allows cattle a continuous opportunity to graze fresh forage via a livestock-pushed sliding fence that allocates and controls grazing within a pasture. Nearly 100% of frontal grazing tillers were defoliated at least once during a 3-hour period as the frontal fence was advanced over the transect ares. The initial defoliation intensity of tillers under frontal grazing was also significantly higher and remaining tiller height less than that of tillers under rotation or continuous grazing (P < 0.05). Tillers under frontal grazing were defoliated at a faster rate compared to rotation or continuous grazing, but cattle had access to them for only 6 to 8 days of the entire grazing season. Season-long defoliation frequency was estimated to be 2.4, 4.6, and 4.7 times for frontal, continuous, and rotation grazing, respectively. Tillers that originated from the perimeter of a tussock were initially taller than those arising from the center (P < 0.05); however, frequency and intensity of defoliation was similar for both tiller locations. Significant relationships were also described between defoliation frequency and stocking rate and between defoliation frequency and herbage allowance. Defoliation frequency increased linearly as stocking rate increased; and conversely, defoliation frequency decreased quadratically as herbage allowance increased. Data from this study suggest that the pattern of tiller defoliation under frontal grazing enhanced forage production which allowed the maintenance of higher stocking rates.