Effects of Long-Term Grazing at Different Intensities on Herbaceous Biomass in Southeast Oregon Sagebrush Steppe

Abstract

Information on the effects of long-term cattle grazing at different intensities on herbage production following fire in the sagebrush steppe is lacking. We measured herbaceous biomass response to cattle grazing spanning 18 yr (2007–2024) on burned Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) steppe in eastern Oregon. Treatments were applied in a randomized complete block design, including no grazing on burned (nonuse) and unburned (control) sagebrush steppe; and cattle grazing at low (low), moderate (moderate), and high (high) stocking. All grazed treatments were by deferred rotation. Deferred rotation consisted of grazing during the active growing season (mid-May–early June) once every 3 yr followed by 2 yr of grazing during summer herbaceous dormancy (July, August, or September). Herbage was sorted by herbaceous functional group, which included an early season bunchgrass (Sandberg bluegrass [Poa secunda J. Presl]), tall perennial bunchgrasses, perennial forbs, cheatgrass (Bromus tectorum L.), and annual forbs. Both standing crop and annual net primary production (ANPP, current year’s growth) of functional groups were evaluated by repeated measures analysis. Standing crop decreased as grazing intensity increased but recovered with 1 or 2 yr of grazing rest. Herbaceous functional group ANPP did not differ among the burned treatments (grazed and nonuse), and total and perennial bunchgrass production were all greater than the control. Grazing intensity in the deferred rotation program did not affect long-term ANPP. Annual weather events account for ANPP variability measured for the various grazed and ungrazed treatments.