Across Southwest Colorado, juniper trees may look like they're dying, but local foresters say the situation is a lot more complicated - and puzzling - than meets the eye.
"It's very strange," said Gretchen Fitzgerald, a forester for the U.S. Forest Service based in Durango. "No one is really sure what's going on except that it seems to be potentially related to the weather."
This December, foresters in the region started to notice junipers turning from green to brown, which began internal discussions about what may be afflicting the hardy tree that grows in high desert terrain and can live for hundreds of years.
For starters, any chance of beetle kill or fungus-related diseases were immediately ruled out.
Dan West, an entomologist with the Colorado State Forest Service, was traveling through Dolores and La Plata counties last month when he pulled off the road to inspect the junipers after he noticed the abnormality.
"I didn't see anything that would indicate it was an insect or disease issue," he said. "It looks to me they're just struggling from the temperature fluctuations. It's been such a weird season."
Southwest Colorado is home to two species of junipers: the Utah, which grows at elevations between 2,000 and 8,000 feet, and the Rocky Mountain, at elevations between 5,000 and 7,000 feet.
This discoloration, foresters said, tends to be occurring to both species at an elevation band of 7,000 feet throughout Southwest Colorado, from Durango north to Gunnison.
What's confusing foresters is that the junipers don't appear to be showing the usual signs that would indicate they are dying. And, what's equally perplexing is that the juniper's ecological neighbor, the less drought resistant piñon tree, isn't showing any signs of stress.
That's led researchers to believe the junipers are adapting to the early stages of extreme stress caused by drought conditions and wildly fluctuating daytime and overnight temperatures.
Normally in the winter, junipers do turn a hue of purple as a result of the tree shutting down its system in a sort of plant-induced hibernation to save resources and energy.
This year, however, the trees appear to be turning a brownish-orange not seen in years past, which could be the result of warm daytime temperatures forcing the trees to continue to operate as if it were summer, said Todd Gardiner of the U.S. Forest Service. Then, overnight lows throw the trees' system out of whack.
"It being dry is one thing," Gardiner said. "It being dry and warm outside is a whole other thing."
In the 20 years she's worked in the region, Fitzgerald said she's never noticed junipers take this kind of turn. Her colleagues, too, say it's a first.
While the 2002 winter may be comparable in terms of the lack of precipitation in the region, this year is markedly warmer.
The warm and sunny days that have defined this winter so far can increase the amount of water lost from the needles. And with no moisture in the soil, roots are deprived of the water they need, which causes the tree to lose its green pigment.
Local foresters agree that since this is the first time they're seeing this phenomenon, there hasn't been enough research into the color shift to say this theory is definitive.
However, the numbers certainly back it up.
According to National Weather Service data, the average high in December in 2017 was 47.8 degrees, with an average low of 11.3 degrees - a change of 36.5 degrees from daytime to overnight temperatures.
The month as a whole was 3.2 degrees warmer than normal. Based on 30-year averages, December has an average high of 40 degrees and an average low of 14 degrees, which amounts to only a 26 degree spread.
Take these temperature shifts into consideration with the utter lack of precipitation - 0.02 inches recorded in December at the Durango-La Plata County Airport, 1.15 inches below normal - and the reason for the junipers' struggle becomes more clear.
Kent Grant, a forester with the Colorado State Forest Service based in Durango, said the district has received calls from residents noticing the pronounced color shift. Many people are worried the trees are dying.
"I can see why people are getting concerned," Grant said. "They are looking different than they typically do this time of year."
While the stressed junipers have warranted attention from foresters, it's too early to say whether there will be serious ramifications, such as a massive die-off, as a result of drought conditions and unusually warm temperatures.
For now, they're taking a wait-and-see approach. If winter finally arrives and brings reliably cold temperatures and moisture, it's likely the trees will rebound in the spring, Fitzgerald said.
"It's unusual, but the trees are hardy, and we think they'll bounce back," Fitzgerald said. "But we aren't sure. We won't know how this ultimately affects them until the spring."