Climate Change Impacts on Future Carbon Stores and Management of Warm Deserts of the United States
Climate change is a pressing environmental issue that requires measuring the exchange of greenhouse gases between terrestrial systems and the atmosphere. Reductions in atmospheric carbon dioxide concentration through enhanced terrestrial carbon storage may help slow or reverse the rate of global climate change. As a result, federal land management agencies, such as the USDA Forest Service, are now beginning to implement management policies to increase carbon storage. Throughout the southwestern United States, climate models project increased aridity and seasonal shifts in precipitation, along with more extreme precipitation events. Information regarding how these elements of climate change might affect the balance between carbon dioxide uptake and loss is lacking in forms available to land managers on semiarid rangelands. Forest Service scientists published a summary of studies that focused on key components of carbon exchange including photosynthesis, soil respiration and plant productivity across the warm deserts of North America to determine if common trends exist that can be utilized in management. They also provided an overview of how management practices can influence carbon sequestration in this region. Since desertification is projected to increase in the future, management strategies that increase carbon sequestration or decrease carbon loss are especially important. Xeric rangelands [lands adapted to a dry environment] tend to be in carbon balance or are small carbon sources, whereas more mesic rangelands [lands adapted to an environment having a greater supply of moisture] function primarily as carbon sinks. When warm desert rangelands do function as carbon sinks, it is for relatively short periods following adequate rainfall. This requires managers to consider management practices that do not impede carbon sequestration during critical times. The scientists provided an overview of how management practices influence carbon sequestration and discussed the USDA Forest Service Climate Change Scorecard, which addresses carbon sequestration and provides fundamental questions for managers to address when reporting on their accomplishments towards developing land management strategies in the context of climate change.
They also found that ungrazed desert grasslands remain carbon neutral over the long-term. This neutrality occurs because carbon is sequestered during infrequent high precipitation monsoon seasons, and is then slowly respired (released back into the atmosphere) over subsequent years. Shrub-dominated areas, including areas recently encroached by shrubs, tend to store carbon annually, even during a sequence of dry years that likely represent future patterns of climate change.
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