The juniper mystery: Why is a tree that’s supposed to withstand drought suddenly dying in southern Utah?
(Courtesy photo | Kate Magargal, University of Utah)
Scientists and federal land managers are scrambling to investigate widespread juniper mortality in southeast Utah. Researchers shot this photo last month on Cedar Mesa, where junipers started dying in droves in September after the driest and warmest year on record. Foresters are stumped because juniper is seen as a drought-tolerant species.
The Utah juniper is considered the West’s most drought-tolerant and resilient conifer, withstanding even the worst dry spells while nearby pinyon and ponderosa drop their needles and die.
So it was with some alarm for Kay Shumway, a retired science educator from Blanding, when he noticed yellowing among the juniper on southeastern Utah’s Moki Dugway last spring, a time of year when these trees’ needles should carry a vivid shade of green as they ramp up their photosynthetic capacity.
“During summer, the dying junipers were such a bright yellow color. It was easy to see. You could look out over the landscape and see thousands of those dying trees. Now a lot have dropped their needles and are becoming a skeleton,” said Shumway, a former botanist who has kept himself busy as a nature photographer since retiring from the College of Eastern Utah 20 years ago. “They are dying. They are not going to come back [even if they get] some moisture.”
He frequents the Moki Dugway on the southern tip of Cedar Mesa, which provides photogenic views of the buttes and canyons falling toward the San Juan River in what was initially part of Bears Ears National Monument. Shumway has since documented dying juniper in other parts of San Juan County, which is in the midst of a severe drought.
“My first reaction was the drought was causing it. The interesting thing is the pine trees, which are the most susceptible to drought, aren’t affected. They are still green and healthy,” Shumway said. “There were more and more of [the juniper] turning yellow. By July, I went all over the county, like Mustang Mesa and Alkali Ridge [east of Blanding]. Lo and behold, it was happening there, too.”
Shumway has shared his photos and drone footage with academic scientists and forestry officials, who are now scrambling to determine the extent and causes of Utah’s latest round of tree mortality.
The Colorado Plateau just experienced its driest year on record. Bluff saw barely 2 inches of precipitation in the water year that ended Sept. 30, about a fourth of normal, according to a National Weather Service database.
But juniper should be able handle a dry year.
“You can’t look at the weather data for one year. Often the stress from drought is lagged,” said entomologist Liz Hebertson. “We would have to look at conditions back three years, six years, 10 years. When a tipping point occurs might be different between species and even individual trees.”
Other factors, working in combination with climate change, are probably at play, according to Hebertson, who works with the U.S. Forest Service’s Forest Health Protection program in Ogden.
“It could be the perfect storm of other factors,” Hebertson said. “Right now, we have a lot of questions.”
Like what is the extent of the mortality? What are the elevation profiles, soil conditions and other environmental characteristics of the affected areas? Are there signs of beetle infestation? Is the wood discolored? Are other tree species showing signs of distress?
Hebertson and her colleagues have been preoccupied this year with a new infestation afflicting forests in northern Utah, where a nonnative beetle, the balsam woolly adelgid, is decimating subalpine fir. This tree mortality is just as troubling as the one unfolding in San Juan County.
In search of clues in the juniper deaths, Hebertson is leading numerous scientists on a tour near Blanding later this month, along with Shumway, who wishes the group came earlier while the yellowed foliage was still hanging from the juniper branches.
“I’m thrilled to know there is some work being done on it,” Shumway said. “I’m going to have this group get up close and personal with these trees, though it won’t be as easy to see. You can still see there are dying trees all over the place.”
Since retiring from CEU (now part of Utah State University), where he served as dean of instruction after helping to establish the Blanding campus in 1977, Shumway has explored Bears Ears country with cameras in tow. While stressed junipers have been documented across the state line in Colorado since last year, Shumway was the first to systematically record the phenomenon in Utah.
Almost more a shrub than a tree, Utah junipers crowd valley bottoms and mesa tops all over the Beehive State. They often mistakenly were called cedars in pioneer times; hence the appearance of the word “cedar” in so many Utah place names.
Junipers, along with the pinyons they usually grow with, are the subject of vegetation-removal operations in the name of habitat improvement. But these trees play a vital ecological role, stitching landscapes together and providing habitat for countless animals.
Widespread loss of junipers would have far-reaching consequences for southern Utah’s fragile desert environments.
Among those taking a keen interest is University of Utah biology professor Bill Anderegg, who studies the impact of climate change on forest ecosystems.
“What we see is worrying and it’s mind-boggling because juniper has weathered drought. In the drought of 2002, they were not affected,” Anderegg said. “To see juniper die on a landscape scale is pretty disturbing. The pinyon don’t seem to be dying at the same rate.”
A possible factor is the Western cedar borer or cedar bark beetle, insects known to attack juniper. Shumway has pulled bark off dead trees to find larvae munching on the phloem, the critical tree tissues that conduct the fruits of photosynthesis to the root system.
But the presence of beetle larvae is just a clue, not a complete causal picture.
Last year was not only the driest on record for Utah, but it also was the second warmest. Could warm weather be compromising the trees’ health, undermining their ability to repel beetle attacks? Or could it be enabling populations of hungry beetles to explode?
“We want to know how bad is the mortality event, how prevalent it is across the Four Corners, pin down the drivers,” Anderegg said. “What are the thresholds that push junipers over the edge, and why are those thresholds being crossed now?”
Anderegg has applied for a Forest Service grant to explore such questions. At this stage, however, the extent of juniper mortality has yet to be established, much less why it might be happening, although few doubt climate change is playing some role.