|Hart, Richard - RETIRED - ARS|
Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: September 15, 2004
Publication Date: February 5, 2005
Citation: Derner, J.D., Hart, R.H. 2005. Grazing-induced modifications to the productive capacity of northern mixed-grass prairie: effects of grazing system and stocking rate. Society for Range Management Meeting Abstracts. V. 58:80. Technical Abstract: Selective grazing by large herbivores can modify the productive capacity of rangelands by reducing competitiveness of productive, palatable species and increasing the composition of more grazing-resistant species. A grazing system (continuous season-long, C, and short-duration, SD) X stocking rate (moderate and heavy) study was initiated in 1982 on northern mixed-grass prairie that was previously ungrazed. Short-duration pastures had 4 grazing cycles with 2-, 3-, 5-, and 7-day grazing events per grazing season (early June to mid-October). Peak standing crop (PSC), harvested from 8, 0.18 m2 quadrats per treatment each year in late July, except for 2000 when a severe drought occurred, ranged from 91 to 2055 kg ha-1 over the 22 years (1982-2003). Grazing system did not affect PSC across years (C=1189, SD=1147 kg ha-1), but moderately stocked pastures were 10% more productive compared to heavy stocked pastures (1226 vs. 1117 kg ha-1). Stocking rate effects were evident only during years of above-average annual precipitation as stocking rate effects were reduced in below-average precipitation years. Grazing system did not interact with stocking rate to affect PSC, indicating that the grazing-induced modification to PSC was driven by stocking rate only. These results suggest that northern mixed-grass prairie stocked at high stocking rates has a diminished productive capacity that is likely attributable to changes in species composition resulting from the increase in the warm-season perennial grass Bouteloua gracilis (blue grama) at the expense of the more productive cool-season perennial grasses.