Submitted to: Western Range Science Seminar Proceedings: The Range: Progress & Potential
Publication Type: Proceedings
Publication Acceptance Date: 1/19/2003
Publication Date: 1/19/2003
Citation: DERNER, J.D., HENDRICKSON, J.R., FRANK, A.B., MORGAN, J.A., THUROW, T.L., HART, R.H. DROUGHT EFFECTS ON RANGELAND ECOSYSTEMS. WESTERN RANGE SCIENCE SEMINAR PROCEEDINGS: THE RANGE: PROGRESS & POTENTIAL. 2003. Interpretive Summary: Drought, defined as the period when soil moisture availability drops to a level that adversely affects production from agricultural lands, influences the structure and function of rangelands. Drought modifies the structure of rangelands by changing vegetation composition as some plants can escape drought, other reduce water loss or maintain adequate water uptake through an extensive root system, and others tolerate drought by changing the chemical composition of internal fluids. The rate of plant recovery following relief from drought conditions is influenced by the management of these plants during drought. For example, substantial reductions in the number of grazing animals during drought conditions will accelerate recovery of plants following relief from drought. Drought modifies the function of rangelands by influenceing biomass production and the ability of these lands to effectively store carbon in soils from the atmosphere. Understanding how individual plants respond to drought and how ecological processes on rangelands are affected by drought will increase our ability to predict how management can maintain desired plant communities.
Technical Abstract: Rangeland ecosystems are event-driven, and water events are typically considered most important. Thus, understanding the dimensions of drought (duration, severity, and extent) becomes pivotal to understanding rangelands. Strong relationships between precipitation and forage production have been determined for fall precipitation and/or soil moisture as well as early spring precipitation. Because many rangelands in the Northern Great Plains are comprised of both warm- and cool-season plants, changes in the precipitation regime may alter species composition. Much of the classical work evaluating vegetation compositional responses to drought was accomplished by pioneers of rangeland ecology (e.g., Weaver, Albertson) through their monitoring efforts before, during and after the Dust Bowl years of the 1930s. One of the key lessons of this work is that the early identification of the onset of drought is critical for reducing stocking rates and preventing further rangeland degradation from loss of vegetation and soil erosion. More recently, drought research on rangeland ecosystems has addressed key ecological processes, with such efforts aimed at increasing our understanding of the functional impact of drought. Carbon flux data from a shortgrass prairie indicate that this rangeland was net sink for atmospheric carbon in non-drought years. However, severe drought in 2002 resulted in this rangeland being a net source of carbon. Additionally, grazing exacerbated carbon losses during this drought with the greatest carbon losses associated with rangeland that was heavily-grazed (targeted 75% utilization). Integration of individual plant responses with ecosystem-level processes will likely increase our predictive ability regarding management efforts to 1) maintain desired plant communities or 2) transition to another plant community.