Trees in the West are remarkably flexible — they endure extended droughts, sweltering summers and subzero winters as part of a wildly variable climate. Even so, this year’s snow drought is going to leave a mark.
Without a winter snowpack to convert into spring runoff, trees will shift into very low gear, growing little and leaving narrow bands in their tree-ring records. In really bad years there is no growth, and no ring, at all. Justin DeRose, dendrochronologist from the Department of Wildland Resources is buckling up this year for that possibility.
2026 will be a “tree-ring marker year” in Utah and likely the West, he believes.
DeRose isn’t necessarily one for hand-wringing — he takes the long view. The year’s snow total is spectacularly bad, he said, but he’s seen worse: in 1934 during the Dust Bowl; and around 1580 when tree rings recorded a catastrophic drought from Mexico to the Rocky Mountains that had civilization-altering consequences for Indigenous populations.
But he is paying close attention this year all the same, because very bad snow years seem to be cropping up more often than they did in the past.
DeRose and Ryan Jess, a senior technician in the Applied Forest Ecology lab at Utah State University, use cross sections of trees to match ring sequences to calendar years. The practice adds to researchers’ understanding of what climate patterns have looked like over the very long term.
The first thing they look for are certain visible markers that appear in many, if not all tree samples from a region: rings that are especially narrow (indicating drought), fire scars, white rings (from defoliation or frost damage) or especially wide ones (good growing conditions). It’s the key to where that particular tree fits into climate history.
Drought marker years, DeRose said, used to be separated by multiple decades (1902, 1934, 1977). Now they are happening only years apart (2002, 2018, 2022, and potentially 2026). It’s true that Western forests evolved under fairly dramatic wet and dry cycles, he said, but lately the rhythm of drought is accelerating.
If extended drought years continue to stack up against forests, it could mean trouble for their health.
“It’s like a boxing match,” Jess said. “Trees can take one, or several, blows from dry years and keep on growing. But when stress stacks against them again and again, over multiple years, that can lead to more widespread mortality.”
The consequences of these stacked blows are reshaping the ecology of the West. Trees are being pushed past critical thresholds. Cumulative stress has triggered massive mortality events across the region, such as the 2012 to 2016 California drought that claimed over 100 million trees.
And drought years often go hand-in-hand with wildfire — narrow rings are often corroborated by fire-scars. When a large region of the West has drought, we are more likely to have more widespread and typically larger fires, DeRose said.
Weaker trees also lose other natural defenses.
“Drought-stressed trees can’t produce the resin and chemical defenses to repel bark beetles,” he said. “That gives an opening for insects to devastate millions of additional acres.”
Drought stress is driving a long-term shift in what Utah’s forests look like. Drought-vulnerable species like pinyon pine and aspen can succumb in dry years. The loss of forest canopy creates a feedback loop for the region’s water problems. Without shade to protect the winter snowpack, the snow melts and evaporates faster, which means less predictable runoff for the reservoirs and communities downstream.
Utah weather has been directly recorded over the last 120 years, but that is too short a time to understand Utah’s climate trajectory. Using the patterns recorded in tree rings, researchers can look back over two millennia to help predict future changes in the climate by seeing how forests survived, or succumbed to, past mega-droughts, DeRose said.
It’s one of the reasons that he partners with the Utah Forest Restoration Institute.
“These forests were built to handle variability — but this pace of change is tough on them,” said Larissa Yocom, director of the institute. “Our job now is to help them persist through conditions they haven’t had to face before.”
Years from now, forests may record 2026 as one more narrow ring, but the real story will be how closely it sits beside others, what that pattern reveals about a changing climate and how managers today chose to respond to changing forest ecology.
