Utah’s towering ponderosa pines are tough customers.
They can live for hundreds of years, surviving harsh conditions at high altitudes. But even giants have a breaking point.
This winter was Utah’s warmest on record, and statewide snowpack has cratered to new record lows. That’s likely to leave a mark, said Justin DeRose, an associate professor of applied forest ecology at Utah State University.
“2026 is shaping up to be a marker year in the tree ring record.”
DeRose leads USU’s tree ring lab. His team reads the history of forests based on cross-section samples that show a tree’s layers of growth. It’s a field of science called dendrochronology.
When a tree produces a wide ring, that tells DeRose it was a year with good growing conditions. A narrow ring points to a lean year. Scientists can match those marker years with similar patterns on nearby trees to create a timeline.
Other bad snow years, such as 2002, 1977 and 1934, all left their mark in Utah’s tree ring history, but forests were able to bounce back.
What’s troubling, DeRose said, is that bad marker years seem to be showing up more often. Utah trees produced noticeably narrow rings in both 2018 and 2021, and another is likely to be added this year.
“We look for those marker years every couple of decades or so,” DeRose said. “But if they're becoming more frequent, what is that telling us about what's changing in the climate?”
Scientists agree that climate change, driven by greenhouse gas emissions, has made many extreme events like droughts and warm spells more intense and more likely. If trees don’t have enough average or good years to catch their breath, that’s bad news for the health of forests that cover some of the state’s most beloved landscapes.
“At some point, trees that continually get knocked down without being able to recover are going to grow less,” DeRose said. “They're going to be less competitive. They're going to be unable to resist the kinds of things that like to kill trees.”
After a couple of consecutive dry seasons, he said forests could dry out and increase the area’s wildfire risk. Eventually, some ponderosa pine stands could die off and be replaced by a different species, such as juniper.
Conditions will likely continue to make things harder on forests as climate change continues, said Marcos Robles, lead scientist with The Nature Conservancy in Arizona. A century of wildfire suppression hasn’t helped, either.
“The climate is having an overarching impact that is reducing resilience, making these trees more vulnerable to drought and pathogens,” he said. “But also, we've had tremendous change in the forest conditions over the past 100 years.”
Tree rings show that the Southwest’s forests used to burn every five to seven years, he said. Those natural fires removed seedlings and saplings. Ring records also indicate stands of ponderosa pine historically had just 10 to 20 trees per acre.
Without fires sweeping through regularly, forest density now reaches thousands of trees per acre, Robles said, making the environment even more challenging.
“Not only do you have a warmer climate, you also have more competition, as you have more trees that have their roots into the ground.”
While individual forest managers may be limited in their ability to bend the curve of climate change globally, he said, there are things people can do to give trees a better chance.
His team has partnered with the U.S. Forest Service on a long-term restoration project across nearly 2 million acres of Arizona. Over the past 15 years, they’ve thinned forests by removing hundreds of thousands of trees. The results so far show that this practice can significantly increase trees’ resilience to climate change, he said.
Additional research his team is working on indicates that thinning ponderosa forests also improves snowmelt. When an area is packed with trees, snow is more likely to fall on branches and sublimate — get sucked into the atmosphere without becoming a liquid — before it ever reaches land.
Their preliminary findings suggest that thinning the number of trees leads to a 10-30% increase in the amount of snowmelt and extends the snowmelt period by up to 10 days.
“Reducing the drought risks through forest restoration not only has benefits for the forests themselves, but also for downstream communities,” Robles said. “That can have a big impact on the drinking water supply for millions of people across the West.”
Disclosure: The Nature Conservancy is a financial sponsor of KUER.
