Grassland soil carbon is a critical piece of natural climate solutions
Grasslands store up to 20% of the world’s soil organic carbon (SOC). This pool of carbon is under constant threat of loss through land conversion and soil disturbance. The United States lost 2.4 million acres of grasslands between 2012 and 2015 as a result of demand for housing, energy, and crops such as corn and soy. The top meter of grassland soils store around 49 tonnes of carbon dioxide equivalents per acre. Once released, it takes many decades for SOC to recover if the grassland is restored from a cropland. Avoiding SOC loss in grasslands presents by far the greatest natural climate solution besides reforestation. Preventing the loss of SOC on grasslands frequently also presents opportunities to increase soil carbon sequestration rates while maintaining healthy food supply and rancher livelihoods.
Protecting against the loss of grassland soil carbon is the most critical rangeland management decision that can be made. Much attention is paid to grazing intensity and rotation, often described as a tool of regenerative agriculture. However, impacts of grazing management decisions themselves have minimal impact on SOC compared with simply keeping SOC in the ground. As described in a new study from The Journal of Soil and Water Conservation ,85% of SOC is considered “highly stable” meaning it will not be impacted unless disturbed. The other 15% of “active” carbon can be impacted by management decisions, but the magnitude of the impact is highly variable according to the literature. A meta-analysis of improved grazing studies, showed an average of 10% increase in soil carbon stock with some studies showing a 50% carbon loss to 200% carbon gain. Studies consistently show the biggest drivers of rangeland carbon stocks are the weather and soil quality. While good rangeland management, particularly adaptive rangeland management, can certainly increase SOC, it has only a minor impact on the “active” carbon pool compared to the larger pool of highly stable carbon that is at risk during land use conversion. It is critical for management plans to protect stable SOC.
The Avoided Conversion of Grasslands (ACoGs) carbon offset protocol is an excellent tool for preserving grassland SOC from being lost to conversion. Not only does it protect SOC from being released during conversion to other land uses, but requires the implementation of sustainable grazing. By encouraging sustainable grazing, further carbon sequestration gains are made. Carbon sales revenues can be used to supplement ranch income and support the rural economy. The Climate Trust, as a non-profit ACoGs project developer, has been investing up-front in grassland protection projects to assist land trusts in the purchase of conservation easements. We believe this innovative approach can have a significant impact on the pace of grassland conservation.