Hints of Stress Early in Boulder County Foliage Season
Nederland Town Marshal Larry Johns glanced outside his window earlier this week to look at the aspen — and noticed they seemed “more grey-black than green.”
Welcome to the onset of foliage season 2018, which in some areas appears to be starting early, but might not be quite the stuff of picture postcards, at least as compared to some other years.
“We are seeing some yellowing, but not any real change,” Johns said. “It looks like, to me, we are seeing drying of the leaf ends. I don’t think it’s going to be a good leaf season.”
But those who took to the high country across the state over Labor Day weekend were treated to broad tapestries of brilliant orange and yellow, as many mountainsides beyond the Front Range were alive with a brilliance that appeared to be running a shade ahead of the calendar that Mother Nature typically keeps for Colorado.
“I think that perception is right on,” said Bill Bowman, a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado. He also is director of CU’s Mountain Research Station, located off Colo. 72, north of Nederland.
“It does seem to be an early season. And locally, it looks as if there are some stressed trees as well. We’re seeing trees that are pale green, with some spots, and my guess is that they’re responding to the early summer drought that we had,” he said.
Told of Johns’ observation of seeing “gray-black” aspen leaves, Bowman said, “I think that’s a fairly accurate description. They are really pale green, or a gray-green.
“The leaves respond to a combination of environmental cues. And that can include the drought; day length is usually the thing that starts to trigger — actually the length of the night is what triggers the start of the coloration. But that can go earlier, if the trees are stressed.”
Adding that the confluence of factors driving the color change is something that is still not fully understood, Bowman said, “There is concern about aspen health across the state, anyway. There has been a lot of death of aspen stands in the southwest over the last decade. That was a response to dry conditions, to drought, and unfortunately, that’s something that’s going to continue as well, with climate change.”
Dave Sutherland, an interpretive naturalist for Boulder’s Open Space and Mountain Parks department, said he had not been in the mountains recently to see what is happening there — or what is not.
“One thing that could have an impact is if it is really dry in the weeks leading up to peak color change, some of the leaves might start to start to change, then shrivel up and die, and you won’t get as nice a fall color display, if we have super nasty drought condition.”
A “neat thing” to mention about aspen, Sutherland said, is that they grow as clones; due to shoots and suckers arising from its long lateral roots, a grove will produce many genetically identical trees.
So in looking at a swath of aspen, Sutherland said, “There may be 20 or 30 trees but they are all actually the same organism. So they are all responding to climate cues the same way. And one big clonal patch may be reacting differently than the one next to it, more orange or more yellow.
“So as you look, you can try to identify the clone boundaries — like jigsaw pieces.”
Nederland Town Administrator Karen Gerrity was in the Lake City area over Labor Day, and found “that whole area is full of yellows, oranges and reds. And along (U.S.) 285 you could see patches of yellow up on the mountains. They’re changing here (near Nederland), but not as much. They’re just starting to change.”
The peak of foliage season is still a few weeks away, but it’s something those in mountain towns such as Nederland eagerly anticipate — not only for the aesthetic enrichment, but the dollars it deposits in the local cash registers from those coming to enjoy it.
“We call it ‘peeper weekend,’” Gerrity said. “There’s more than one. We usually get two, sometimes three. Hopefully, people still get to have an enjoyable leaf-peeping experience.”
Charlie Brennan: 303-473-1327, email@example.com or twitter.com/chasbrennan