Researchers in the Northern Plains have been studying how changes in the atmosphere might impact rangelands throughout the region. With this research under our belt, we can begin strategizing how to adapt our rangeland and grazing management practices to future conditions. The following highlights some of the research project's findings and recommendations.
Impacts of Elevated CO2 and a Warming Climate on Forage Production and Forage Quality in the Mixed-Grass Prairie
Summary by Dr. David Augustine, USDA-ARS:
We conducted a field experiment to examine how increasing C02 concentration in the atmosphere (from the current 400 parts per million [ppm] to a simulated future level of 600 ppm) and increasing temperature (by 1.5°C during the day and 3°C at night) affect the productivity and quality of forage for livestock in the northern mixed-grass prairie.
Our study was conducted in southeastern Wyoming, near Cheyenne, beginning in 2007 and continuing through 2013. The grassland we studied is dominated by two cool-season grasses (needle and thread grass, and western wheatgrass) and one warm-season grass (blue grama), but it also has >20 plant species that are commonly grazed by cattle.
On this northern mixed-grass prairie, we measured the production of forage plants, and the degree to which these plants can be digested by cattle. Each year, we collected forage plants from the experimental plots when they reached peak biomass in July. We then measured the rate at which they could be digested.
We found that, with increased atmospheric CO2 and warming, total forage production increased (by an average of 38% over the 7-year study period). Yet forage quality declined. Dry matter digestibility of western wheatgrass declined from an average 63% to 61%, and crude protein content of western wheatgrass declined from 7.8% to 6.5%.
These changes could significantly reduce the rate at which individual cattle gain weight during the growing season.
Given expected increases in forage productivity, decreases in forage quality could potentially be mitigated by increasing stocking rates. Other management practices, such as prescribed burning, fertilization at low rates, and legume interseeding, could also potentially enhance forage quality.
Augustine, D.J., D.M. Blumenthal, T.L. Springer, D.R. Lecain, S.A. Gunter, and J.D. Derner. 2018. Elevated CO2 and warming induce substantial and persistent declines in forage digestibility and protein content in mixed-grass prairie. Ecological Applications 28:3 721-735.