Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 19, 2004
Publication Date: January 1, 2005
Citation: Heitschmidt, R.K., Klement, K.D., Haferkamp, M.R., 2005. Interactive effects of drought and grazing on northern great plains rangelands. Rangeland Ecology and Management 58:11-19. Interpretive Summary: The potential impacts of periodic grazing during and after an intense April-June drought on native northern mixed grass rangeland were investigated over a 4-year period. Results showed that the spring drought reduced the amount of soil water readily available for plant growth during spring about 50% with only minor effects noted thereafter during the summer dry down period. The spring drought also reduced annual forage production between 20 and 40% with cool-season annual and perennial grasses being affected more so than warm-season grasses. Periodic grazing during the drought had minimal impact on forage production whereas impacts of grazing during non-drought periods varied depending upon conditions. For example, forage production was enhanced by grazing when a grazing event was followed by ample precipitation. However, no response was noted without ample post-grazing precipitation. Substantial recovery occurred the first year after drought with near full recovery realized by the end of the second year. The impacts of grazing on rate of recovery were minimal. It should be noted that the grazing regimen applied in this study were very intense, single day events applied in early May, June, and July with full uninterrupted rest between events. Thus, caution should be exercised in extending the results from this study to those that might result if grazing was season-long.
Technical Abstract: Drought is common in rangeland environments and an understanding of its impacts on the structure and function of rangeland ecosystems is paramount for developing effective management strategies. This research was the second of a series of studies investigating the impacts of varying seasonal droughts on northern Great Plains rangelands. Research was conducted on native rangeland during the 1998 through 2001 growing seasons. Study plots were twelve 5 X 10-m non-weighing lysimeters. An automated rainout shelter was used to establish drought conditions on 6 lysimeters during April, May and June of 1998 and 1999. Single day, flash grazing events were imposed at the beginning of May, June, and July. Grazing treatments were: 1) graze during the 2 years of drought and the year after; 2) graze during the 2 years of drought and rest the year after; and 3) rest all years. Results showed that the intense spring drought reduced soil water content in the upper 30 cm of the soil profile and subsequently reduced total herbage production 20 to 40% with cool-season perennial grasses being primary contributor to the reduction and cool-season annual grasses secondary. Periodic grazing during drought had minimal impact on herbage production whereas impacts on non-drought plots ranged from moderate enhancement to moderate suppression with effects varying depending upon functional group. Results also showed that substantial recovery occurred during the first post-drought year with near full recovery realized within 2 years.