Submitted to: Eastern Oregon Agricultural Research Center
Publication Type: Experiment Station
Publication Acceptance Date: 1/1/2004
Publication Date: 6/29/2004
Citation: Bates, J.D. 2004. Interannual productivity in burned and unburned wyoming big sagebrush-grassland. Eastern Oregon Agricultural Research Center. Range Field Day Report 2004: Current Forage and Livestock Production Research. Special Report 1052. p. 17-23. Interpretive Summary: Interannual climate variability has a huge impact on forage production in the sagebrush steppe of the northern Great Basin. Forage production tends to be positively correlated with higher crop year (Sept. ' May) precipitation, but other factors are also important. Temperature, timing of precipitation, and soil nutrient availability also influence forage production. In this study, herbaceous production was evaluated in burned and unburned sagebrush steppe over a 6-year period. Herbaceous production was estimated every two weeks by harvesting using grass clippers. By clipping frequently we were able to track current years production trends and develop a better understanding of how peak production fluctuates at the community and functional group (e.g. perennial grasses, perennial forbs) level. As expected, dry years generally produced less forage than years with above average precipitation. However, we also recorded higher productivity in a drought year than in a preceding year when precipitation was above average. Clearly, other environmental factors are interacting with precipitation to affect productivity in the sagebrush steppe. In the dry years, peak production tended to occur earlier in the growing season than in years when precipitation was above or near average. The burn increased herbaceous production when compared to the unburned treatment in the 2nd and 3rd year after fire. However, during the drought years (4th ' 6th after fire) differences in productivity were minimal between the burned and unburned plant communities.
Technical Abstract: Herbaceous production in the sagebrush steppe is highly variable across years. The variability is linked to the amount and timing of precipitation received over the winter and early spring (Sneva 1982). Past work has focused on the relationship of total peak production and crop year (Sept-May) precipitation. Total peak production is assumed to occur when perennial bunchgrasses are in flower. Because of the focus on bunchgrass productivity, relationships between precipitation and other species and functional groups are not as well quantified. Because of differing phenological development, peak production of other plants in the community may be undervalued. In this study, we monitored herbaceous productivity every 2 weeks during the course of 6 growing seasons (Apr-Aug). Determining productivity through the growing season provided an index of not only peak community production but peak production for other plant functional groups as well. We placed plants into functional groups based on plant type and growth cycles. We separated current year's growth from total standing crop to quantify year effects to annual productivity. We also compared productivity between burned and unburned treatments.