Climate profoundly shapes forests. Forest species composition, productivity, availability of goods and services, disturbance regimes, and location on the landscape are all regulated by climate. Much research attention has focused on the problem of projecting the response of forests to changing climate, elevated atmospheric carbon dioxide (CO2) concentrations, and nitrogen deposition, deepening our understanding since the publication of the last forest sector assessment (Ryan et al. 2008). We have many new examples of how changes in climate over the period 1971-2000 have affected forest ecosystems, including long-term monitoring data on forest change, multifactor experiments that document the potential interactions between temperature and elevated CO2, and new modeling approaches that project the effect of projected changes in climate on forest ecosystems, their goods and services, and their disturbance regimes. Climate projections are being done on a finer spatial scale, and global climate models include more detail and feedbacks with terrestrial processes. Downscaled estimates from these models are more readily available and have been used for more regional and local assessments. Despite the large amount of new research, this new information has not substantially altered the primary projections made in the last assessment (Ryan et al. 2008). In this assessment, we have added more detail about the effects covered in the last assessment (especially altered disturbance regimes and potential effects on hydrologic processes), provided more information about regional effects, and covered additional topics.