An annual report on forest health in Colorado revealed the spruce beetle epidemic continues to rapidly expand in the San Juan Mountains, killing trees on 12,000 newly identified acres in 2016.
This year, they observed 36,000 acres where the beetle is active in the San Juan National Forest. To date, 237,000 acres in the forest have been impacted since the infestation began more than two decades ago – nearly 12.6 percent of the approximately 1.878 million-acre San Juans.
In Colorado, the teams surveyed 28 million acres, and for the fifth consecutive year, the spruce beetle was the most destructive insect pest in Colorado. It impacted 350,000 acres of high elevation Engelmann spruce across the state in 2016.
The largest infestations, the report says, were in southern and central Colorado, “with more than one-third of those acres ‘new’ or not previously impacted.”
Since 1996, the spruce beetle epidemic has been a scourge on Colorado forests. The beetles attack mostly Engelmann spruce trees, which usually grow above 9,000 feet in elevation, killing off trees on more than 1.7 million acres throughout the state.
In the San Juan Mountains, the outbreak started in the late 1990s, and has been slowly making its way westward through Wolf Creek Pass, decimating Colorado’s largest wilderness area, the Weminuche Wilderness.
On Sunday, The Durango Herald reported that forestry experts within the last year or so found evidence of the beetle finally crossing the alpine tundra near Silverton that had acted as a natural barrier between the east and west side of the Weminuche Wilderness.
As a result, popular areas along the Durango-to-Silverton corridor show signs of die-off, with predictions that the epidemic will start in full force this summer.
“I tell people all the time: You need to get up there before it starts to look different,” Kent Grant, a Durango-based district forester with the Colorado State Forest Service, previously said. “Already, it’s increasingly more obvious. It’s just around the corner.”
In Dolores County, the roundheaded pine beetle, which has been present in the area for several years, affected nearly 7,000 acres of ponderosa pines in 2016. The report notes the insect has been found only in Southwest Colorado, and though its spread tends to be slower, the expansion in Dolores County is “notable.”
Western spruce budworm activity decreased from last year but still defoliated 226,000 acres, most notably in the San Juan and Rio Grande national forests, among others areas.
Douglas-fir beetle populations continued to expand on the Western Slope, with 19,000 new acres impacted. This beetle’s outbreak tends to occur in smaller pockets, rather than outwardly spread like the spruce beetle.Mountain pine beetle, which has hit nearly 3.4 million acres across the state over 20 years, continued its decrease in activity, with fewer than a thousand acres impacted statewide. Yet, the report notes the Beaver Creek Fire that burned more than 38,000 acres in Jackson County was in a beetle kill zone.Declines in impacted acreage were observed in Douglas-fir tussock moth and fungal leaf diseases of aspen firstname.lastname@example.org