Colorado’s aspen stands are thriving, and that bodes well for fabulous leaf-peeping this fall according to one of the state’s leading forestry experts.
Dan West, entomologist for the Colorado State Forest Service and a member of the faculty at Colorado State University, spent most of the past two months flying over the state’s 24 million acres of forest. The main purpose of his annual aerial observation tour is to assess forest health, but it also gives him a unique perspective to forecast the quality of fall foliage colors.
“They look better than they’ve looked in a very long time,” West said. “Aspen look really well, even in places that over the last several years have kind of struggled.”
As a result, West also is predicting a return to normal timing for the color change.
He expects to see aspen in the northern mountains — generally north of Interstate 70 — to start turning in the middle of this month and run through the third or fourth week.
In the central mountains — including Vail, Summit County, Aspen, Crested Butte and Gunnison — he expects fall colors to emerge at the end of the month and last into the first week of October.
The southern mountains should see fall colors in the second and third week of October.
Last summer, West saw signs of recovery from years of drought stress in some forests. This year has seen drought disappear in most of the state, along with fewer days of abnormal heat.
“Going into the season, it was quite wet and I was bracing myself, thinking there was going to be quite a bit of leaf fungi that were going to be able to work their way through the aspen,” West said. “The pests that attack aspen leaves prefer wet and warm. What ended up happening, by and large, was really wet and cool. In a nutshell, the environmental conditions just weren’t conducive for some of these pathogens that attack the leaves.”
The general health of aspen and other trees that provide fall color, especially oaks and cottonwoods, is only one factor in the quality of leaf-peeping. September weather also plays a critical role.
“It’s been nice and warm and sunny, and that’s what we want during the middle of the day,” West said. “We want to burn off that chlorophyll, the green pigment, and that’s what the sun does. As the day length shortens — we’re losing about two and a half minutes every day right now — you really start to see the greens fade out. It looks like we’re shaping up beautifully right now.”
Events that could detract from great fall color include major fluctuations of temperature, early frost and heavy rain or wind events that could cause leaves to fall prematurely.
“We don’t want it to be cold,” West said. “Once it gets cold and those cells start to freeze, that pretty much ends the game, as far as the show.”
Aspen aren’t the only attraction in leaf peeping season. West says the oaks and cottonwoods appear healthy, too.
“The oaks are looking so good,” West said. “I’m already starting to see some of the oaks starting in the southern part of the state. They turn before the aspens do. We’re just starting to see some of that orange. Not quite the reds yet, but certainly the oranges are starting to come through. They look like they really might have a good year. Last year wasn’t so good, with some of the frost that happened, and they look like they’re rebounding quite well. I only mapped a couple of locations in the state that looked as though oaks were struggling a little bit. Cottonwoods also look like they’re doing really well.”
West conducts his aerial forest inspections in July, August and sometimes into the beginning of September in partnership with the U.S. Forest Service.
“We’re looking predominantly for bark beetles that are affecting conifers,” West said. “We’re also looking at aspen stands across the state, and oaks and willows and cottonwoods, to get a feel for anything affecting these particular areas so we can have early detection and a rapid response, from a forestry perspective.”
