Weather effects on herbaceous yields: Wyoming big sagebrush steppe, southeastern Oregon

Authors: Bates, Jonathan - Jon; Copeland, Stella; Hardegree, Stuart; Moffet, Corey; Davies, Kirk

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2023
Publication Date: 5/22/2024
Citation: Bates, J.D., Copeland, S.M., Hardegree, S.P., Moffet, C., Davies, K.W. 2024. Weather effects on herbaceous yields: Wyoming big sagebrush steppe, southeastern Oregon. Western North American Naturalist. 84(1):89-106. https://doi.org/10.3398/064.084.0108.
DOI: https://doi.org/10.3398/064.084.0108

Interpretive Summary: We investigated the effects of weather on herbage yields on sagebrush steppe of eastern Oregon from 2003-2012 using linear and multiple regression methods. Crop year (e.g. October - May, September - May) and spring precipitation and RET all provided significant predictive models for the functional groups and total herbage. Spring precipitation provided the strongest predictors of perennial bunchgrass (March - May & June; R2 = 0.91), perennial forb (May; R2 = 0.79), annual grass (March; R2 = 0.79) and total herbage (March - May; R2 = 0.83) yields. Yields of P. secunda and annual forbs were most strongly associated RET October - May (R2 = 0.86) and October – April (R2 = 0.79), respectively. The results found a greater influence of late winter and spring precipitation than models developed several decades ago where crop year precipitation provided more accurate herbage forecasts.

Technical Abstract: Interannual climate variability impacts forage yield in semiarid rangelands, but it also affects the timing of peak yields. Knowledge of peak standing crop or yield dates would be useful when planning fieldwork for various research or management activities and for developing more accurate models linking herbage production to climatic variables. In this study, herbaceous yield was measured every 2 weeks (April–August) over an 8-year period in a Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) community in southeastern Oregon. Date of peak yield (Julian day) was calculated for morphological groups (tall perennial bunchgrasses, perennial forbs, annual forbs), Sandberg bluegrass (Poa secunda J. Pressl), and total herbaceous yield. Linear and multiple regression analyses were used to correlate date of peak yield of herbaceous morphological groups with spring precipitation, reference evapotranspiration (RET), and air temperature. Peak yield dates for the herbaceous response variables were strongly correlated to annual climatic variation, commonly a combination of early growing season precipitation (March to 16 May) and March through May RET. Depending on morphological group, peak yield date varied by 3 to 7 weeks during the growing season. The best regression coefficients for peak yield date of perennial bunchgrasses, perennial forbs, Sandberg bluegrass, annual forbs, and total herbaceous vegetation alone or with various combinations of precipitation, temperature, and RET were 0.97, 0.82, 0.86, 0.90, and 0.98, respectively. For planning fieldwork, estimates of peak yield date can be used to accurately sample for yields of herbaceous morphological groups and community production potentials.