The researchers found rising death rates across a wide variety of forest types, at different elevations, in trees of all sizes and among major species including pine, fir and hemlock.
"Wherever we looked, mortality rates are increasing," said Nathan Stephenson, a study co-author and USGS research ecologist.
The study concludes that the most likely cause of the increased mortality is warming temperatures. At NRDC, we've long been concerned about the increasing impact of global warming on forest communities. Many tree species act as "foundation" species, defining entire ecosystems. If these tree species decline or disappear, entire biological communities can be lost. Dying forests can also lead to a vicious positive-feedback climate loop--non-forest ecosystems, such as grasslands, sequester less carbon dioxide than forests and forests can even become net carbon emitters as the number of dead and decaying trees increase.
Because of a combination of pine beetles (whose outbreaks are exacerbated by global warming) and blister rust (an introduced pathogen) one of the foundation tree species farthest down this grim road is the white bark pine. Last month NRDC petitioned to protect white bark pine under the Endangered Species Act. Given the implication's of the Science study, how the U.S. Fish and Wildlife Service and the U.S. Forest Service react our petition, and the problem of disappearing forests in the wake of global warming pollution more generally, is likely to become an increasingly important piece of finding solutions to global warming and enacting meaningful federal legislation to deal with climate change.