Noticed an explosion of color this year in aspen forests throughout the Gunnison Basin — including orange and red hues highlighting the golden landscape? Does the change seem earlier than usual?
There’s reason. Drought is to blame for disrupting the timing of this year’s change of the seasons — and, perhaps, even the colors.
Western Colorado University biology professor Jonathan Coop explained that it’s all part of the processes taking place within the plant.
“Basically, leaves are supposed to drop when they’re no longer producing enough return to make up for their expense,” Coop said.
During the course of a growing season, there comes a point when photosynthesis is not occurring to a great enough degree for it to be worth a tree keeping those leaves.
“What we know is that in some situations even in the middle of summer, leaves can turn color and fall off because maybe a branch got damaged or parts of a plant are drought stressed,” he said. “You’ll see that happen even if it’s not fall.”
But during fall, the decrease in intensity and duration of sunlight paired with cooler temperatures cause the leaves to stop their food-making process. The chlorophyll breaks down. The green color disappears, and yellowish colors already in the leaf become visible.
“What seems like is happening is when you add drought stress on top of that, leaves seem to be changing earlier,” Coop said. “It’s just this one additional complicating factor.”
According to U.S. Drought Monitor, most of Gunnison County is currently under “extreme drought,” with the western portion of the county under even more severe “exceptional drought.”
Additionally, Coop noted that drought could change the colors of leaves in fall — or how much color trees exhibit.
“What I’m seeing is a lot of red out there,” he said. “I think that when trees are producing a lot of those red colors, it’s thought to be a mechanism that actually helps protect the leaf as it undergoes this really complex process called senescence.”
Coop said that during his 11 years in the Gunnison Basin watching aspens change, he’s noticed a typical “peak” of late September or early October.
“My sense is things are happening a little earlier this year, and that’s consistent with drought stress that’s going on out there,” he explained.
Also, Coop noted that with climate change one would expect the growing season to be longer — and leaf senescence to occur later.
“There’s evidence of that in some parts of the world,” he said. “Here, we have this interesting thing. It’s been really warm, but it’s also been really dry. Those forces are going to be pulling plants in two different directions.”
(Will Shoemaker can be contacted at 970.641.1414 or at firstname.lastname@example.org.)