Aspen color change peak has begun at high elevations
Aspen trees and Gambel oak begin to change to fall colors on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald file)
The vibrant shimmering leaves of Southwest Colorado’s aspen stands have begun to transition, once again, from summer’s green hues to fall’s trademark yellows, oranges and velvet reds.
As days fall shorter and the trees’ chlorophyll production dips, the green that shades the leaves fades, revealing a sequential panoply of colors.
Colors are expected to hit their peak in Southwest Colorado at the end of September and into the first week of October, although stands at higher elevations will generally turn sooner.
The U.S. Forest Service’s annual regional report on forest insect and disease conditions, released every March, noted that “Heavy defoliation was observed near Durango, Colorado near Purgatory ski resort,” in 2023. (Jerry McBride/Durango Herald)
Despite climate-related threats to the health of aspen stands, it is shaping up to be an excellent season for leaf peepers, foresters say.
“I think we’ll have a very good color change this year, based on some conditions, as far as a wet growing season, wet spring and summer, particularly,” said Ryan Cox, lead forester with the Colorado State Forest Service’s Durango Field Office.
This ranch, one of the most photographed places along U.S. Highway 550 north of Durango, once had the most beautiful aspen groves. The stands in the area have been defoliated by Western tent caterpillar but are making a comeback. (Jerry McBride/Durango Herald)
The recent cool nights followed by warmer days is expected to produce vibrant colors, he added.
In the early 2000s, researchers noticed landscape-scale dieback of aspen trees, a phenomenon named sudden aspen decline, or SAD. The trend was attributed to the trees’ heightened susceptibility to insects and pathogens brought about by drought conditions.
Although trees in certain pockets of the Southwest are still suffering, aspens are, by and large, in a relatively healthy state, said San Juan National Forest Forester Travis Bruch.
In stands near Purgatory Resort, Western tent caterpillars that cling to aspen branches have caused defoliation in places – but San Juan National Forest Forester Travis Bruch said the species’ population tends to swell and die off before causing widespread harm. (Jerry McBride/Durango Herald)
“For the most part, we don’t really see any SAD, or it’s in really small places at this point in time,” he said.
In stands near Purgatory Resort, Western tent caterpillars that cling to aspen branches have caused defoliation in places – but Bruch said the species population tends to swell and die off before causing widespread harm.
The U.S. Forest Service’s annual regional report on forest insect and disease conditions, released every March, noted that heavy defoliation was observed near Purgatory in 2023.
In general, trees stricken by drought are less resilient and cannot defend against pathogens and insects as well as they otherwise might.
A Western tent caterpillar makes its cocoon with eggs in it on the end of an aspen tree branch near the Needles area west of U.S. Highway 550. (Jerry McBride/Durango Herald file)
But stands are considered a single organism, and a hardy one at that. The trunks of trees in a single stand grow from one root system, making each a clone with the same genetic composition. And even when pathogens or insects wipe out a clone’s trunks, the root systems will sometimes still survive and regenerate with force if given adequate moisture.
“It’s not something that, you know, we expect to kill tens of thousands of acres of aspen,” he said. “But I mean, all in all, when you go around and look at the aspen, it’s in decent health.”
Stephanie Weber, the executive director of the San Juan Mountains Association, is urging visitors to be smart.
“Please don't stop in the middle of the highway,” she said. “Please find a pull off. Don't impede traffic.”
rschafir@durangherald.com
Aspen tree leaves begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Gambel oak begins to change to fall colors on Tuesday along Missionary Ridge north of Durango in the 2002 Missionary Ridge Fire burn area. (Jerry McBride/Durango Herald)
Pine cones cut from the tree by squirrels for their winter stash on Tuesday along Missionary Ridge north of Durango. (Jerry McBride/Durango Herald)
Aspen tree leaves begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Gambel oak and aspen trees begin to change to fall colors on Tuesday along Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Aspen trees and Gambel oak begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Aspen trees and Gambel oak begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Aspen trees and Gambel oak begin to change to fall colors on Tuesday as clouds move through Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
A wild rose blooms as fall colors begin to appear on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Gambel oak begins to change to fall colors on Tuesday along Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Rose hips begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Aspen tree leaves begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Aspen tree leaves begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Gambel oak begins to change to fall colors on Tuesday along Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Fireweed begins to change to its red fall colors on Tuesday along Missionary Ridge north of Durango. (Jerry McBride/Durango Herald)
Fireweed begins to change to fall colors on Tuesday along Missionary Ridge north of Durango. (Jerry McBride/Durango Herald)
Aspen tree leaves begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Pine cones cut from the tree by squirrels for their winter stash on Tuesday along Missionary Ridge north of Durango. (Jerry McBride/Durango Herald)
Foliage begins to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Gambel oak and aspen trees begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
Aspen trees and Gambel oak begin to change to fall colors on Tuesday on Missionary Ridge north of Durango in the burn area of the 2002 Missionary Ridge Fire. (Jerry McBride/Durango Herald)
