The roundheaded pine beetle continues to ravage drought-stricken ponderosa pine forests on the San Juan National Forest in Dolores County, according to recent aerial surveys.
The outbreak in the Glade area near Narraguinnep Canyon began in 2013 with about 1,500 acres of forest impacted, and the beetles’ destructive path grew at a startling rate.
By 2018, the area of dead, dying or damaged trees in Dolores County had grown to 27,000 acres, or 45 percent of the 60,000 acres of ponderosa pine forest in Dolores County, according to new research by the Colorado State Forest Service and U.S. Forest Service. The infestation grew by 59 percent from 2017, when 11,000 acres had been affected.
The impacted area is nearly 30 percent of the 90,000 acres of ponderosa forest in the Dolores Ranger District of the San Juan National Forest.
The duration of the infestation in Southwest Colorado is unusual, experts say.
Outbreaks of the native roundheaded beetle in nearby New Mexico typically last three to four years, then taper off, said Dan West, an entomologist with the Colorado State Forest Service.
The persistence of this infestation is related to the ongoing exceptional drought, the most severe category, combined with an overgrown forest.
“The conditions have weakened the ponderosa’s defenses, basically a calling card for the roundheaded beetle that targets the tree,” West said. “The area impacted has almost doubled every year and is moving northward.”
A healthy ponderosa fights off beetles by flushing them out with resins, preventing them from feeding and laying eggs, West said.
But when there is a severe lack of moisture over time, resins are not adequately produced, allowing infestations of beetles to penetrate outer and inner bark layers, which damages or kills the tree.
West said it would take more than one or two years of good winter snowpack for the trees to recover and start resisting the beetle. In an extended drought, fine feeder roots that deliver moisture to produce defensive resins, die off, and they take several years to grow back once precipitation conditions improve.
The outbreak’s impacts vary and do not always cause total tree mortality in the area affected, West said.
More thinning of the ponderosa forest in that area would improve the microclimate and help deter beetle outbreaks, he said. A less crowded forest creates less competition for water, and the spacing allows for more sunlight and winds that disrupts beetle activity. Acres of dead or damaged ponderosa also raise the risk for more extreme wildfire.
To try and stop the beetle spread, the San Juan National Forest has partnered with Montrose Forest Products on a large-scale commercial logging project to thin out ponderosa forests ahead of the infestation.
The trees will be shipped to the company’s Montrose mill to be made into construction lumber. Logging is expected to begin in 2020 and continue for several years.
Beetle-kill ponderosa have found a local market. When milled, the lumber has distinct blue-gray stain created by a fungus brought in by the beetle.
Aspen Wall Wood, of Dolores, has been logging beetle kill ponderosa and is having success selling blue-stain paneling.
“We are taking what was thought to be waste timber and turning into a really nice product,” said owner David Sitton.
The drier wood of beetle kill is also ideal for making mine shaft cribbing used in the coal industry. Westfork Lumber Co., a mill west of Dolores, has milling blue-stain ponderosa for that purpose and to make fence posts.
Outbreaks of different species, the spruce beetle, has also continued to expand in Colorado, according the state and national forest survey. The beetle has caused widespread tree mortality for the seventh consecutive year, affecting 178,000 acres of high elevation Engelmann spruce in 2018. Acreage annually affected has been declining for the past four years.
The aerial survey also revealed that Douglas fir beetle populations continued to impact low-elevation forests in the central and southern portions of the state, at levels similar to what was observed statewide in 2017. Outbreaks of western spruce budworm declined in 2018, compared with the prior year, although the budworm still defoliated 131,000 acres of spruce and fir in the state. “Colorado’s forests are important to the ecological and economic health of our state,” said Mike Lester, state forester and CSFS director. “Our efforts in partnership with the U.S. Forest Service ensure that we understand the condition of our forests, so we can design the best treatments to enhance forest health.”