Increasingly Severe Droughts Could Transform U.S. Forests, Study Says

Severe drought conditions in the southwestern U.S. in recent years could become normal in the years to come, a shift that could trigger increased tree mortality and ultimately transform the region’s forests, a new study says. In an analysis of tree-ring data from conifer trees dating back to A.D. 1000, a team of scientists concluded that while the region endured several “mega-droughts” over the last 1,000 years, the long-term drought that began in the late-1990s could end up being the worst yet and may portend even drier periods in the future. After modeling the level of stress caused by droughts on forests — and considering other factors caused by these changes, including bark-beetle outbreaks and wildfires — the researchers calculated that tree mortality over the next four decades will be worse than at any time over the last 1,000 years. “With increasing drought stress, our forests of tomorrow will hardly resemble our forests of yesterday,” said Henri Grissino-Mayer, a geography professor at the University of Tennessee, Knoxville and one of the authors of the study published in the journal Nature Climate Change.