If you travel the deserts of the American Southwest, you will see many piñon pines and junipers. The two types of trees are so prevalent in places, those landscapes are referred to as piñon-juniper or PJ woodlands. These slow-growing species are well adapted to heat and dryness.
But the mega-drought of the past two decades is proving to be a challenge even for them. Many piñon pines succumbed to an invasion of bark beetles driven by drought in the early 2000s. Now, junipers are dying in places scattered across the Four Corners region.
Bradley Lalande is a forest pathologist with the U.S. Forest Service in Gunnison, Colorado. Although piñon-juniper woodlands aren’t common on national forest lands, the Forest Service works with the Bureau of Land Management, tribal communities, states, and other entities. Lalande says the high juniper mortality we are seeing now has been attributed to conditions back in 2018.
“Although we’ve been in this drought for 20 years, it was like the peak of the drought," he says. "Those high temperatures and lack of precipitation really stressed the junipers out.”
And it takes pretty severe drought to stress out a juniper. They evolved to be one of the most drought-tolerant of trees.
“They are able to withstand drought because they have really deep root systems,” Lalande says.
He also says they are also able to shut off their photosynthesis. But even junipers have their limits.
“When there’s just no water over so many years, they can’t withstand any more,” he says.
According to Lalande, neither insects nor pathogens are the primary cause of the juniper die-off.
“People who work with insect diseases and forest health really want to attribute it to an insect or disease and we’re not finding it.”
What this means for the future of PJ landscapes is uncertain. In a worst-case scenario, sagebrush, grasses and invasive species may replace piñons and junipers. This in turn would harm the birds and other animals that depend on those trees and their berries.
But there is still hope. Junipers may rebound if significant precipitation returns. Woodlands have survived droughts in the past.
"Although we will lose a substantial portion of our current stands, as long as we have regeneration our stands will persist into the future,” he says. “I’m definitely a glass-half-full kind of guy.”
Lalande says young junipers can replace the mature ones, which are more susceptible.
“We have thousands upon thousands of seedlings in the understory.”
But junipers and piñons grow slowly. The effects of severe drought don’t usually show up on the trees until the next year. For example, if 2022 stays hot and dry, the resulting die-off will be seen in 2023.
“In 2019 we had some precipitation in Utah, so mortality actually subsided. So they are reacting well to some precipitation. But this year we don’t have any. If there is drought this year we will see mortality in 2023.”
So far, 2022 has been warm and dry in the Four Corners. This is having an impact on all types of trees, from junipers in the lower elevations to spruce and firs at higher altitudes.
“Until we get rain every single tree will be a concern associated with drought and it’s scary,” Lalande says.
