Climate Change Making Forests Less Resilient to Wildfires

The Peekaboo fire burns in Colorado in summer 2017 (Mike Smith, U.S. Forest Service via Inciweb)

(CN) – After years of warmer, drier conditions, forests in the West are losing their ability to bounce back after wildfires, according to a new study from Colorado State University.

Forests of the Rocky Mountain West historically have been resilient to wildfire and able to regenerate successfully after blazes, but researchers found that seedlings planted after wildfires in the last 30 years are having a tough time establishing themselves. Researchers found significant decreases in tree regeneration following 21st century wildfires, a period markedly hotter and drier than the late 20th century.

The study authors analyzed about 1,500 replanted forests in Colorado, Wyoming, Washington state, Idaho and Montana, and studied more than 63,000 seedlings growing in 52 areas burned by wildfires over the past three decades. Researchers set out to find how changing climate has affected post-fire tree regeneration – a key indicator of forest resilience.

“While Rocky Mountain forests typically recover after wildfires, conditions are becoming increasingly stressful for tree seedlings to establish and survive,” study co-author Philip Higuera, of the University of Montana, 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.”

The researchers said their findings are consistent across the five states they studied.

“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.”

About 30 percent of the forests that researchers studied after major fires had no forest regeneration, according to Higuera.

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

While the news may seem dire for forests in the West, certain wildlife species actually benefit from these types of fires, according to Dr. Michael Schwartz, a researcher with the U.S. Forest Service.

A “super scooper” plane collects water from Lake Koocanusa during the Gibralter fire in northwest Montana in summer 2017. (U.S. Forest Service)

“Many species are impacted by wildfires either directly or indirectly,” Schwartz said. “Some species may actually benefit from fire, while others are negatively affected. To complicate matters, some species are initially negatively impacted in the short-run, but then have long-term benefits as the habitat recovers.”

Black-backed woodpeckers are one species that benefits from a fire, as they make their nests in post-fire habitats, according to Dr. William Block, a U.S. Forest Service researcher.

How well wildlife recovers from fire varies among species and the forest type, Schwartz said. Wildfire can be especially harmful for species whose populations are already at historically low numbers or with isolated populations, Schwartz said.

After decades of a warmer, drier climate, forest fires of the last several years are uncharacteristic of longer-term historical fire patterns, Schwartz said. “The severity and extent are greater than of those existing in the past,” he said. “These recent fires provide novel conditions, from the stand to the landscape, which we are only beginning to study.”


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