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Globally, the combination of reforestation and afforestation activities could reduce atmosphere CO2 concentrations by as much as 30 parts per million (ppm) this century. However, this potential mitigation is limited by many factors. One is the vulnerability of forests to increased disturbances, including those caused by pathogens, droughts, fires, and storms. For example, the mountain pine beetle is projected to convert 374,000 square kilometers (km2) of pine forest from a small net carbon sink to a large carbon source in Alberta alone, liberating 1 billion tons of CO2 into the atmosphere. Climate change is another factor that could limit the potential for carbon sequestration in forests. The mountain pine beetle in Alberta is thriving in part because of warmer minimum temperatures in the winter and warmer and drier summers. A third potential limitation is landowner behavior in private-sector forestry, including decisions on what species to plant and how intensely to manage forests. Private forestry competes economically with agriculture, urban development, and other land uses. Landowner decisions will therefore dictate the success of some climate policy efforts.