Does Grazing Matter for Soil Organic Carbon Sequestration in the Western North American Great Plains?
Considerable uncertainty remains regarding grazing-induced influences on soil organic carbon (SOC) sequestration in semiarid grassland ecosystems due to three important complications associated with studying such effects: (1) Ecologically meaningful shifts in SOC pools attributable to grazing are difficult to detect relative to inherently large grassland SOC pools, (2) a lack of baseline (pre-treatment) data, and (3) frequent lack of or limited replication of long-term grazing manipulations. SOC sequestration rates were determined in 74-year-old grazing exclosures and paired moderately grazed sites, established across a soil texture gradient, in the western North American shortgrass steppe in northeastern Colorado. We sampled soils (0–20 cm) from 12 exclosures and paired grazed sites to measure SOC concentration and soil radiocarbon ∆14C (‰); the latter allowed us to determine turnover of the SOC pool over a 7-decade period in the presence versus the absence of grazing. Removal of grazing for more than 7 decades substantially altered plant community composition but did not affect total soil C, SOC, soil ∆14C, SOC turnover rate, or total soil N. Grazing effect also did not interact with soil texture to influence any of those soil properties. Soil texture (silt + clay content) did influence total soil C and SOC, and total soil N, but not ∆14C or SOC turnover. Results provide evidence that long-term removal of grazing from semiarid grassland ecosystems in the western North American Great Plains does not enhance long-term SOC sequestration, despite changes in the relative dominance of C3 versus C4 grasses.
Keywordscattle grazing semiarid rangeland shortgrass steppe soil carbon soil radiocarbon soil carbon turnover
We thank Nick Dufek and Matt Mortenson for leading the sampling and processing of soil samples, and Matt Mortenson for assistance with statistical analyses and developing the figures. We appreciate the provision of livestock for grazing by the Crow Valley Livestock Cooperative, Inc. Funding was provided by the USDA-Agricultural Research Service.
- Derner JD, Schuman GE. 2007. Carbon sequestration and rangelands: a synthesis of land management and precipitation effects. J Soil Water Conserv 62:77–85.Google Scholar
- Graven H. 2008. Advancing the use of radiocarbon in studies of global and regional carbon cycling with high precision measurements of 14C in CO2 from the Scripps CO2 Program. Scripps Institute of Oceanography. Ph.D. thesis. San Diego: University of California.Google Scholar
- Holechek JL, Pieper RD, Herbel CH. 2011. Range management: principles and practices. 6th edn. Upper Saddle River, NJ: Prentice-Hall/Person Inc.Google Scholar
- Lauenroth WL. 2008. Vegetation of the shortgrass steppe. Ecology of the shortgrass steppe: a long-term perspective. Lauenroth WK, Burke IC, Eds. New York, NY: Oxford University Press. pp 70–83.Google Scholar
- Sokal RR, Rohlf FJ. 1995. Biometry. New York: WH Freeman and Company.Google Scholar