DENVER—Having spent the past two months flying over all 24 million acres of Colorado’s forests to assess their health, one of the state’s leading forestry experts foresees a good-to-great year for fall foliage, with peak colors starting in mid-September.
Dan West, the state forest entomologist for the Colorado State Forest Service, who also teaches at Colorado State University, said some forests are showing signs of recovery from stress caused by years of drought.
Another key factor for fall colors could be September weather. The current 30-day forecast by the National Weather Service calls for above-normal temperatures across the state, with below-normal precipitation in the northern half and equal chances of above or below normal moisture to the south. Those conditions should enhance the color transformation process while preventing frosts or early snows, which can curtail leaf-peeping season.
“The forecast is favorable for aspens and fall color in general,” West said. “That’s almost the ideal condition. We want cool nights, not cold, and we want really warm, sunny days.”
When the shortening days of late summer trigger the fall color change, trees burn off the chlorophyll in their leaves which gives them their green pigment. As it dissipates, other pigments that were there all along become visible.
“We want as much sunshine as we can get to burn off the green,” West said. “That leaves us with those yellows and oranges and reds. And, cooler temperatures [at night] with warmer days produce those red pigmentations that we all love.”
In the northern third of the state, West expects peak fall colors to occur in mid- to late September. Subsequent peaks should occur in late September in the central part of the state, with the peak in the southern third of the state coming in late September to early October. If his suspicion is accurate, that would mark a return to normal patterns.
“In recent years, it’s been creeping sooner; we’ve seen those colors happening a little earlier,” West said. “But I think this year, it’s looking like we’re going to be on average, barring storms and early snow.”
Forests in the central part of the state were hit hard by a late-spring frost which occurred after they had already begun to produce leaves. Aspen stands around Kenosha Pass and Fairplay also were damaged by pest infestations, so West doesn’t expect great fall colors in those areas. Elsewhere, the outlook is better.
“I’ve really noticed that some aspen stands look really green and beautiful,” West said. “For the trees that were able to survive that [frost], or had enough resources to get new leaves to push out and flourish, it looks like it’s going to be a wonderful season.
“If I were to rate this, sitting here at the end of August, I would say the northern portions of the state are looking like it’s going to be a great season. Looking at things from the Front Range through Summit County, it looks like there will be some areas that will be not as great and some areas that are going to be good. In one drainage it might be wonderful while the next drainage might not be so great.”
West spends the last week in June, all of July, and all of August conducting annual surveys of the state’s forests from the air for the purpose of assessing their vitality and identifying areas that need attention from forestry crews to address pest infestations or other maladies. He was pleasantly surprised by what he found this summer.
“In the past couple of years I’ve had a question mark of, ‘Man, aspens across the state are not looking real great,'” West said. “Last year, there were so many aspen stands that looked brown in August because of the drought. The margins [edges] of the leaves were dried up and had started to die back. From afar, those stands looked brown. They weren’t, entirely, but they had this off-tinge to them. I haven’t seen that this year at all. And it seems like the weather patterns have been really favorable for a lot of our aspens this year, aside from the early cold frost.”
He was especially encouraged by what he observed in the southern part of the state, which was hit hard by severe and extreme droughts in recent years.
“Honestly, flying over some of those stands, they look really great,” West said. “In the areas where we were experiencing extreme and severe drought conditions, they’re not nearly as bad as we’ve seen in years past. I didn’t notice any defoliations, so a lot of that area looks like it’s going to be quite good for fall colors. Perhaps this year there could be a bit of a rebound in the southwest, or the southern third of the state.”
One species that figures to be disappointing during leaf-peeping season this year is narrow-leaf cottonwoods, which typically are among the first to change.
“A lot of our low-elevation waterways are lined with those narrow-leaf cottonwoods,” West said. “Narrow-leaf cottonwoods throughout a good portion of the state have been dealing with the cottonwood leaf beetle that has been causing them to have a very brown tinge. I anticipate a lot of the narrow-leaf cottonwoods will end up dropping a lot of their leaves.”
Although West’s countless hours inspecting forests from 1,000 feet above makes him arguably the state’s best source to speculate on the quality of an upcoming leaf-peeping season, identifying threats to state forests is the primary focus of his summer work.
Ground crews then address those problems by using insecticides, cutting down infested trees, or utilizing semiochemicals, which confuse pests that react to chemical signals from others.
“We’ve figured out how bark beetles communicate through chemistry,” West explained. “We can put up the ‘No Vacancy’ sign that tells them, ‘We don’t want to infest this tree because there’s no more room for our offspring.’ We can use chemical sprays as tools in some places. We can use mechanical removal in places, before the adult beetles emerge and attack adjacent trees.
“All we’re doing is trying to buy time so Mother Nature can catch up,” West said. “We do a lot of these management activities so we can get through the window of where trees are extremely stressed or drought-stricken so they can start to fend off attacks when the [moisture] comes back. We want to have forests for future generations. We want to be good stewards of the land, not just let everything sit and get taken by bugs.”