Spruce beetle, western spruce budworm, and Douglas fir tussock moth outbreaks in Colorado mountain forests increased in 2015, according to forest health aerial survey results released on Jan. 28.
The annual survey of insect and disease infestations is a joint project of the U.S. Forest Service Rocky Mountain Region and the Colorado State Forest Service. They work together each year to monitor forest health conditions on millions of acres.
"Spruce beetle outbreaks caused widespread tree mortality for the fourth consecutive year," the report says. That affected higher elevation stands of Engleman spruce. Beetle infestations were detected on 409,000 acres in 2015, expanding onto 182,000 acres of previously unaffected forests. Since 1996, these outbreaks have affected 1.5 million acres in the state, with varying degrees of mortality.
The report also cites blowdown events, long-term drought, warmer temperatures and big dense stands of older spruce trees as a contributing factor.
In the San Juan National Forest, the survey shows that the spruce beetle infestation has grown to a total of more than 120,000 acres. To address this and other forest-health issues, the San Juan National Forest is working on several proposals that will include public involvement and environmental analyses this year.
On the Columbine Ranger District, an integrated forest-health project across several thousand acres north of Highway 160 between the Piedra River and the Vallecito area is investigating the potential for salvage sales in dead forests, resilience treatments in live spruce and aspen forests, as well as fuels reduction and prescribed burning.
On the Pagosa Ranger District near Wolf Creek Pass, a small salvage sale is being prepared for approximately 100 acres of dead spruce in 2016. A nearby planning effort is investigating the future salvage of additional dead spruce that can be accessed from the Wolf Creek and Falls Creek roads. Both proposals focus on the harvest of dead merchantable trees, retention of live green trees, and using timber sale revenue to promote reforestation in areas of heavy mortality. Dead spruce trees can remain standing for several decades and retain value as commercial timber for up a decade or more.
In the Dolores Ranger District, a timber sale is being considered for about 900 acres of mixed spruce and aspen in the Taylor and Stoner Mesas area to improve resilience of spruce forests not yet affected by the beetle outbreak but already experiencing spruce budworm activity. Thinning green stands can improve forest health by adding diversity of size and age class and encouraging natural regeneration, but cannot stop the spread of insects.
For information on the San Juan National Forest timber program, contact Travis Bruch, 970 385-1317.
The western spruce budworm is the most widespread forest defoliator in Colorado, the forest health report says. Affected areas increased from 178,000 acres in 2014 to around 312,000 acres in 2015. The budworm typically feeds on developing buds and new needles of fir, Douglas fir, and spruce in Southern Colorado.
Another major defoliator, the Douglas fir tussock moth, damaged Douglas fir, white fir, and spruce on the Front Range, especially in the South Platte Basin and areas west of Colorado Springs. One hopeful sign: "Ground surveys have documented the presence of a naturally occurring virus among Douglas fir tussock moth caterpillars, which has historically been a key indicator of imminent population collapse," the report says.
Trees weakened by these defoliators may become susceptible to the Douglas fir beetle which can kill the trees.
The report says mountain pine beetle activity has subsided and remains low, with 5,000 acres affected statewide. "The epidemic has ended in many areas of Colorado as mature pine trees have been depleted in the core outbreak areas," the report says.
Colorado State Forest Service Director Mike Lester said, "The lesson we can take away from the extensive insect and disease damage we've seen in Colorado over the past two decades is the need for proactively taking care of our forests. The best time to take actions to address long-term forest health is before a major outbreak starts, and not after."
In 2015, CSFS treated more than 17,000 acres, mainly on private or state lands, as part of forest management and wildfire mitigation efforts.
CSFS has quick guides to the spruce beetle and Douglas fir tussock moth, and a brand new release on the Douglas fir beetle, at www.csfs.colostate.edu/csfspublications.
The U.S. Forest Service treated around 51,000 acres in Colorado in 2015 through timber sales, thinning, and prescribed fire. There was a joint landscape restoration project in the San Juan National Forest, in collaboration with the National Resources Conservation Service (NRCS).
CSFS and USFS signed a master Good Neighbor Agreement last November to work across land ownership boundaries onto USFS lands. "Both agencies are working to identify eligible projects to protect water supplies, manage insect infestations, reduce wildfire risk, and meet other forest management objectiives," the news release says.
The 2015 aerial detection survey highlights and maps are at http://www.fs.usda.gov/goto/USFSR2ForestHealth.
