Rangeland sequestration potential assessment (Final Report)

Authors: SPANGLER, LEE - Montana State University; VANCE, GEORGE - University Of Wyoming; SCHUMAN, GERALD - Retired ARS Employee; Derner, Justin

Submitted to: Scientific and Technical Review
Publication Type: Government Publication
Publication Acceptance Date: 8/20/2011
Publication Date: 9/1/2011
Citation: Spangler, L., Vance, G.F., Schuman, G.E., Derner, J.D. 2011. Rangeland sequestration potential assessment (Final Report). Acarology International Congress Proceedings. DOE: DE-FC26-05NT42587.

Interpretive Summary: Rangelands have capacity to store additional soil carbon through management actions, and though the rate of this storage is low on a per unit land area basis, there is a large area of rangelands (50% of the Earth’s surface area). Here, we conducted a literature review to identify sustainably management practices that conserve existing pools of soil carbon in rangelands, as well as potential to increase potential for carbon sequestration. The intensity of grazing appears to be a major factor in controlling dynamics of soil carbon. In addition, climatic effects (weather patterns, drought) impact soil carbon levels, and therefore carbon sequestration. For example, drought reduces levels of soil carbon with more losses of carbon in pastures that were heavy grazed compared to lightly grazed. This suggests that light to moderate grazing is beneficial compared to heavy grazing with respect to soil carbon under drought conditions.

Technical Abstract: Rangelands occupy approximately half of the world's land area and store greater than 10% of the terrestrial biomass carbon and up to 30% of the global soil organic carbon. Although soil carbon sequestration rates are generally low on rangelands in comparison to croplands, increases in terriestrial carbon in rangelands resulting from management can account for significant carbon sequestration given the magnitude of this land resource. Despite the significance rangelands can play in carbon sequestration, our understanding remains limited. Researchers conducted a literature review to identify sustainably management practices that conserve existing rangeland carbon pools, as well as increase or restore carbon sequestration potentials for this type of ecosystem. The research team also reviewed the impact of grazing management on rangeland carbon dynamics, which are not well understood due to heterogeneity in grassland types. The literature review on the impact of grazing showed a wide variation of results, ranging from positive to negative to no response. On further review, the intensity of grazing appears to be a major factor in controlling rangeland soil organic carbon dynamics. In 2003, researchers conducted field sampling to assess the effect of several drought years during the period 1993-2002. Results suggested that drought can significantly impact rangeland soil organic carbon (SOC) levels, and therefore, carbon sequestration. Resampling was conducted in 2006; results again suggested that climatic conditions may have overridden management effects on SOC due to the ecological lag of the severe drought of 2002. Analysis of grazing practices during this research effort suggested that there are beneficial effects of light grazing compared to heavy grazing and non-grazing with respect to increased SOC and nitrogen contents. In general, carbon storage in rangelands also increases with increased precipitation, although researchers identified threshold levels of precipitation where sequestration begins to decrease.