Colorado’s Fall Foliage: Early Colors or Drought Stress?

Reports of early fall foliage colors in Colorado have been met with skepticism by local experts, who attribute the observed changes to drought stress rather than the typical autumn transformation. Dan West, an entomologist with the Colorado State Forest Service, recently investigated claims of color changes in Summit County and Eagle County and found that the situation is not as promising as it may appear.

West’s concerns arose when he heard news reports suggesting that the fall foliage color change had already commenced. With an appreciation for the beauty of September aspen forests, he felt compelled to assess the situation firsthand. His findings confirmed his doubts: the yellowing leaves he observed were a sign of stress due to insufficient moisture, not the onset of autumn colors.

“While there is some yellowing, it’s primarily a stress response to drought conditions,” West explained. He noted the presence of what is termed “marginal necrosis,” where leaf edges turn brown as the trees lose more water than they can absorb. This phenomenon can lead to a portion of the leaf becoming yellow before ultimately turning brown.

West described the appearance of the trees: “From a distance, they might look nearly yellow, but upon closer inspection, much of the foliage is brown.” He anticipates that the actual fall color change will likely begin in two to three weeks in the northern mountains, a bit earlier than the usual timeline. The central mountains along the Interstate 70 corridor will likely follow a week later. Last year, peak foliage was observed around the third week of September.

Despite the stress observed in some aspen trees, West reassured that many still appear healthy and green. He identified areas in Breckenridge, Frisco, Silverthorne, and Vail Pass where aspen trees show signs of distress. “It’s pretty widespread along the I-70 corridor,” he noted, emphasizing the impact of drought on the region’s forests.

Walking through affected areas, West was struck by how thin some aspen trees appeared, attributing this to drought stress that prompts trees to halt growth processes earlier than usual. “There are already brown leaves falling from the trees,” he said, highlighting the immediate effects of the dry summer.

Looking ahead, West remains optimistic about the upcoming fall display. He believes there will still be vibrant colors when the actual fall foliage begins. “On the west side of Vail Pass, those aspen stands look as green as ever. That area often showcases some of the most stunning fall foliage in Colorado,” he said.

As autumn approaches, West predicts that while some trees may change color earlier than expected, others will yield softer hues. “I think a month from now, we’re going to see some stands that might go a bit earlier in color, but some may not exhibit the deep oranges and dark reds we typically anticipate,” he added.

For those eager to experience Colorado’s fall colors this season, it will be essential to monitor the ongoing drought conditions and their impact on forest health. As West highlighted, the beauty of autumn in the Rockies is still on the horizon, albeit with a few caveats.