Submitted to: Ecological Society of America Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2006
Publication Date: 8/7/2006
Citation: Derner, J.D. 2006. Grazing-induced modifications to the productive capacity of northern mixed-grass prairie. p. 94. In: Proceedings of the 91st annual meeting of the Ecological Society of America. Abstract. Interpretive Summary:
Technical Abstract: Selective grazing can modify the productive capacity of rangelands by reducing competitiveness of productive, palatable species and increasing the composition of more grazing-resistant species. A stocking rate (light, moderate and heavy) X grazing system (season-long continuous and short-duration rotational grazing) study was initiated in 1982 on northern mixed-grass prairie that was previously very lightly grazed. Peak standing crop, harvested in late July/early August, ranged from 56 to 2299 kg•ha-1 over the 22 year study period (1982-2003). Mean peak standing crop was greater under light (1512±80 kg•ha-1, mean±1SE) compared to moderate (1298±81 kg•ha-1) and heavy (1130±64 kg•ha-1) stocking rates across years with season-long continuous grazing. No differences were found among stocking rates in years with dry springs. Peak standing crop did not differ between season-long continuous and short-duration rotational grazing systems for either moderate (1272±55 vs. 1170±49 kg•ha-1, season-long continuous vs. short-duration rotational) or heavy (1106±42 vs. 1127±42 kg•ha-1) stocking rates. April+May precipitation was a robust predictor (r2 > 0.51) of peak standing crop across stocking rate and grazing system treatments with greatest robustness (r2=0.67) observed for the light stocking rate. This long-term study illustrates the importance of stocking rate rather than grazing system affecting productive capacity of the northern mixed-grass prairie as 16-34% less forage was produced with moderate and heavy stocking rates compared to light. This reduced productive capacity is attributed to changes in species composition with increasing stocking rate as the less productive, warm-season perennial shortgrass blue grama (Bouteloua gracilis) increases at the expense of more productive, cool-season perennial mid-height grasses. Land managers may need to substantially modify management to offset these losses in productive capacity which has altered the structure and function of this rangeland ecosystem.