Climate change: UM study finds Rocky Mountain forests losing resilience to wildfires

With the climate growing hotter and drier, the regeneration of Rocky Mountain forests after summer wildfires is expected to diminish, if they come back at all, according to research from the University of Montana and Colorado State University.

Researchers from across the Rocky Mountains analyzed data from nearly 1,500 sites in five states, including Colorado, Wyoming, Washington, Idaho and Montana. Along the way, they measured more than 63,000 seedlings growing in 52 areas burned by wildfires during the past three decades.

UM fire ecology professor Philip Higuer said they found significant decreases in tree regeneration following 21st century wildfires, a period that was much hotter and drier than the later half of the 20th century.

The research team said that with a warming climate, forests are losing their resilience to wildfires.

“While Rocky Mountain forests typically recover after wildfires, conditions are becoming increasingly stressful for tree seedlings to establish and survive,” Higuera said. “Seedlings are more sensitive to warm, dry conditions than mature trees, so if the right conditions don’t exist within a few years following a wildfire, tree seedlings may not establish.”

Higuera said the look of a forest often changes over time, yet the research team said it will take much longer for sites to re-establish forests after a wildfire, if the forests return at all.

In the warmest, driest forests, researchers found evidence suggesting that trees have stopped regeneration after wildfires, which wasn't the case in the past. The pattern was consistent across all sites reviewed in the study.

“We expect variability in how long forests take to recover after wildfires,” Higuera said, “but the decrease in tree regeneration between the late 20th and early 21st century was pretty striking, and it’s consistent with what we expect to see as climate becomes warmer and drier.”

The research team included scientists from UM, the University of Idaho, The Nature Conservancy, the University of Washington, University of Colorado-Boulder, Tall Timbers Research Station and Land Conservancy, and the Washington State Department of Natural Resources.