Forests

Forestland, and thus forest carbon, has changed substantially in North America over the last several hundred years. In the United States, for example, forestland amounts to an estimated 72% of the area that was forested in 1630, with roughly 120 million ha converted to other uses (mainly agricultural) primarily from 1850 to 1910 (Smith et al., 2009). National assessments of forest land area and carbon dynamics have been conducted in Canada, Mexico, and the United States, but the motivation for these reports and the methods and data sources they use differ substantially among countries. In recent decades, official government estimates of forest land area, forest carbon stocks, and stock changes have been compiled following guidelines from the Intergovernmental Panel on Climate Change (IPCC 2003, 2006). However, the methods for estimating carbon stocks and their changes (e.g., stock difference versus gain-loss) still differ based on country-specific circumstances, but estimation approaches have evolved as new and better information has become available in each country. Of the numerous key findings SOCCR1 identified on the role of forests in the North American carbon cycle, many (e.g., land-use change) continue to be relevant 10 years later, along with several emerging topics (e.g., climate feedbacks).