Expert says wet winter is the cause of delay in fall colors

The fall colors are on delay this year, but this could be for good reason, said Fort Lewis College biology professor and forest ecology expert Julie Korb.

Every year, nearing the end of September, the aspen trees of Southwest Colorado bring shades of reds, yellows and oranges to the forests.

But this year, it appears Mother Nature is taking her time.

Korb says this is a result of last year’s moist winter.

“What we’ve seen is that we get the best color when we have a wet growing season followed by dry falls,” she said.

However, because of last winter’s moisture with a little help from late monsoon showers, Korb says the aspen leaves are losing their chlorophyll at a slower rate.

The process of the leaves changing colors involves three main factors: leaf pigment, nighttime length and weather.

“The aspen queue to the length of daytime from when they put on their first leaves,” Korb said.

When the days start to get shorter, aspen trees stop transporting water and nutrients to the leaves. However, the leaves’ pigment is determined by weather from the previous winter leading up to the spring when they start to grow back.

Korb said the intensity of the yellow color given off by the changing seasons is set from the beginning of their life cycle based on the amount of moisture the tree received during the previous winter.

But once leaves start to photosynthesize and create chlorophyll, the chlorophyll masks the yellow color.

“Normally what happens this time of year is that the nights start to get longer and the plant isn’t photosynthesizing as much,” she said.

This means less chlorophyll is being produced by the leaves, revealing the yellow color.

Because of the moisture received this year, however, the trees are healthy and continuing to photosynthesize for a longer period.

Although it was a drier summer compared to the winter, Korb said this past year’s snowfall in combination with late summer and fall storms were enough to keep the aspen trees healthy.

She reiterated that the delay in color change is not a bad thing and it’s actually positive to see the trees photosynthesizing longer.

But there are some areas like Silverton that are experiencing more color change at lower elevations compared to areas like Molas Pass and Coal Bank Pass.

Korb hypothesized that this was a result of a temperature inversion. She said the common thought is to believe it’s colder at higher elevation, which would drive the leaves to change color in higher elevations first.

However, she says cold air sinks at night, which creates an inversion of warm air at the higher elevations. Because Silverton is tucked away in a valley, it creates a cold air drainage where colder air can sit at night.

She added that it’s created by the area experiencing warm fall temperatures and that if the temperatures were colder, this wouldn’t be a factor.

“We can’t really predict. It’s basically Mother Nature’s time clock that is dictating what’s happening,” said San Juan Mountain Association Visitor Services Director J Bernite.

Bernite said peak colors could show around Oct. 8 or Oct. 9.

He suggested people check out areas between Coal Bank Pass and Silverton, Red Mountain Pass and areas near Lizard Head Pass as some the prime viewing spots.

He also said County Road 42 in Mancos State Park was another great viewing area.

The changing of the aspen leaves marks the last big surge of tourists before Southwest Colorado goes into its shoulder season before the winter.

Business Improvement District Executive Director Tim Walsworth said that downtown ambassador interactions with out-of-town visitors have been about the same this fall compared with 2022.

This likely means that the lack of color change hasn’t really impacted traffic in town.

Walsworth said that it’s been a down summer for downtown spending.

“The volume of people was high and good for summer, like we expect,” he said. “But the spending behaviors appeared different. And by different I mean that folks were not spending as much money as they had in the past on items.”

He added that fall tourism brings in a different demographic – it tends to favor older couples, he said.

This means businesses may experience different customer spending habits in the fall compared to the summer.

tbrown@durangoherald.com