Response of Vegetation of the Northern Great Plains to Precipitation Amount and Grazing Intensity

Abstract

Changes in basal cover of vegetation were predicted in response to variation in precipitation and grazing intensity. Multiple regression analysis was used with basal cover as a dependent variable and precipitation parameters as independent variables to develop predictive equations. Predicted cover values were used to develop three dimensional response surfaces which describe individual species responses to fluctuating precipitation and different grazing intensities. Results indicate that each species reacts to precipitation regimes and grazing pressure in a unique manner. Continual changes in basal cover can be expected in the plant community as the precipitation regime changes. Moderate grazing intensity, approximately 0.92 ha (2.3 acres) per AUM, appears to be most conducive for maintaining vegetative cover that is desirable for livestock production. However, stocking rate changes need to be anticipated and planned to coincide with available forage because of large fluctuations in cover due to varying precipitation. Climate appears to be the major factor controlling plant growth in the Great Plains. Whitman et al. (1943) stated that drought is the primary influence of vegetational change. Reed and Peterson (1961) Hurtt (1951) and Clark et al. (1943) stated that major trends in vegetation are primarily determined by fluctuations in climatic conditions, and that changes within these major trends are influenced by grazing intensity.

Interactive Effects of Drought and Grazing on Northern Great Plains Rangelands

“…7) are in agreement with previous findings showing that precipitation is the principal factor altering productivity of these rangelands (Whitman et al 1943;Hurt 1951;Reed and Peterson 1961;Olson et al 1985;Biondini and Manske 1996;Biondini et al 1998;. Similarly, results from this study (as well as those studies cited above) show that grazing consistently reduces herbage standing crops (Fig.…”

Stocking Rate and Weather Impacts on Sand Sagebrush and Grasses: A 20-Year Record

“…Purple sandgrass increased during the first wet period, but not the second. These temporal changes are examples of nondirectional dynamics driven by individualistic species responses to environmental variability, a phenomenon also observed by Olson et al (1985). Illius and O'Conner (1999) felt that vegetation response would be more tightly coupled to grazing intensity during periods of higher precipitation.…”

“…Illius and O'Conner (1999) countered that vegetation response is coupled to grazing intensity even in ecosystems with highly variable precipitation, but the strength of the coupling is greater for more productive sites within a grazing unit and during high precipitation periods. Olson et al (1985) concluded climatic effects were dominant but that the responses of individual species to climate were mediated by stocking rate. Fuhlendorf et al (2001) found that stocking rate determined the long-range trajectory of grassland succession but that climatic fluctuations could either strengthen existing trajectories or promote alternate trajectories.…”

Journal of Range Management, Volume 55, Number 5 (September 2002)

“…Olson et al (1985) suggested, however, that each species reacts to precipitation and grazing in a unique manner. Grazing often results in a shift in composition from tall to short species, and in selection for prostrate growth forms within a species (McNaughton 1983(McNaughton , 1984, producing a greater uniformity in the horizontal distribution of biomass than is found on nongrazed sites .…”

“…Intensive grazing may reduce the negative effect of drought by reducing transpiring leaf area, thereby conserving soil moisture Detling 1986, Day andDetling 1994). The effects of grazing intensity on plant responses to drought are species specific (Olson et al 1985), suggesting that the interaction between drought and grazing could significantly affect botanical composition of rangelands.…”