Effects of annual weather variation on peak herbaceous yield date in sagebrush steppe

Authors: Bates, Jonathan - Jon; JOHNSON, DUSTIN - Oregon State University; Davies, Kirk; SVEJCAR, TONY - Oregon State University; Hardegree, Stuart

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2022
Publication Date: 8/17/2023
Citation: Bates, J.D., Johnson, D., Davies, K.W., Svejcar, T., Hardegree, S.P. 2023. Effects of annual weather variation on peak herbaceous yield date in sagebrush steppe. Western North American Naturalist. 83(2):220-231. https://doi.org/10.3398/064.083.0207.
DOI: https://doi.org/10.3398/064.083.0207

Interpretive Summary: Inter-annual climate variability impacts forage yield in semi-arid rangelands, but also affects the timing of peak yields. Knowledge of peak standing crop or yield dates would be useful when planning field work for various research or management activities and of potential value for developing more accurate models linking herbage production to climatic variables. Herbaceous yield was measured every two weeks (April-August), over an 8-year period, in a big sagebrush steppe community in southeastern Oregon. Peak yield dates for the herbaceous response variables were strongly correlated to annual climatic variation, usually a combination of early growing season precipitation (March to May 15) and March and April potential evapotranspiration, with correlation coefficients ranging between 0.79 and 0.92. For planning field work, estimates of peak yield date can be used to more accurately sample peak yields for herbaceous species, functional groups and the total community.

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.