Air Quality Benefits and Disbenefits of Forests under Future Environmental Stressors

Air quality in the U.S. has improved greatly in the past half century, due to environmental policies such as the Clean Air Act (CAA) focused on controlling anthropogenic point and mobile sources. As the contributions of anthropogenic sources decrease and environmental stressors, such as wildfire, increase, forests are becoming increasingly important diffuse sources and sinks of atmospheric compounds. Indeed, forests impact several air quality programs, yet stressors are modifying these forest-compound interactions. To characterize how forests may impact current and future air quality, we reviewed studies on environmental stressors affecting forest interactions with key air pollutants regulated under the CAA. Long-term temperature trends and changes in precipitation, as well as disturbances such as wildfire, pest outbreaks and drought are among the stressors considered. Overall, increasing stressors on forests are generally worsening air quality. Indeed, the increase in wildfire is one of the main contributors to current declines in air quality. Other effects were bidirectional or there were information gaps, especially in predicting multistressor impacts. Forests are fundamental to life and environmental stressors are shifting their impact on air quality. As a result, it is imperative to understand the benefits and disbenefits of forests to better predict and manage future air quality.