Forests for carbon sequestration or fossil fuel substitution? A sensitivity analysis

Among the proposals for mitigating the increase of atmospheric CO2 are the possibility of reforesting degraded lands to sequester C or of using sustainable forest harvests to displace fossil fuels. Storing C on-site in forests and harvesting forests for a sustainable flow of forest products are not necessarily conflicting options if we recognize that their relative merits in mitigating net emissions of C will depend on site-specific factors, such as forest productivity and the efficiency with which harvested material is used. Since the land available for reforestation or development of forest plantations is limited, the relative merits of the different mitigation strategies need to be considered. We use a mathematical model of C stocks and flows to compare the net effect on C emissions to the atmosphere for the two approaches over a range of values of forest productivity and the efficiency of product use. When sustainably-produced forest products are used inefficiently to displace fossil fuels, the greater C benefit is achieved through reforestation and protection of standing forests, and increasing the rate of stand growth yields little gain. However, when forest products are used efficiently to displace fossil fuels, sustainable harvest produces the greater net C benefits, and the benefit increases rapidly with increasing productivity.