Recent droughts have affected forest mortality and productivity in many temperate regions. Assessments of the impacts of drought across broad ranges of forests have been limited because the temporal and spatial coverages of forest-growth data are limited. We compared annual tree-ring width data from 1,097 populations in the United States to climate data and evaluated tree responses to climate variations throughout the 20th century. For each population, we developed a climate-driven growth equation using climate records to predict annual ring widths.
Results/Conclusions
Forests within the southwestern United States appear particularly sensitive to drought and warmth. Considering various climate projections, we applied the equations to predict how tree growth will respond to 21st century climate change. Results suggest that southwestern forests will experience substantially reduced tree growth during this century. As tree growth declines, mortality rates will increase at many sites. In recent years, mortality by wildfire and bark-beetle outbreaks have been related to rising temperature and decreased precipitation. Using satellite imagery and aerial survey data, we calculate that >10% of southwestern forest area experienced mortality due to wildfires and bark beetles from 1984-2008. Knowledge of impending transitions in forest productivity, disturbance regimes, and species ranges informs efforts to manage southwestern forests.
