GRAND JUNCTION — Abundant Colorado snowpack helped reduce 2019 bark beetle activity impacting trees, but the following wet spring contributed to tree defoliation, a new report said.
The findings were part of an annual U.S. Forest Service and Colorado State Forest Service aerial survey evaluating forest health impacts from insects and disease, The Daily Sentinel reports.
There was a decline in tree mortality in 2019 due to bark beetles compared to 2018, but “large epidemics of spruce beetle and roundheaded/western pine beetles in Colorado continue to expand,” the report said.
The cold, wet spring followed by warm rains led to fungi germinating on aspen leaves and causing kill spots, the report said.
The heavy snowpack in winter 2019 followed the 2018 season when Colorado experienced its second driest winter on record dating back to 1895.
Last year was “a good year for trees, which means reduced acreage in bark beetle activity,” said Dan West, a state forest service entomologist.
Additional moisture enables trees to produce sap, which is a defense against insect infestation, although West said it takes more than one year of significant precipitation for trees to return to full health after drought.
Spruce beetle outbreaks have been a major concern in Colorado in recent decades, causing tree mortality on about 2,900 square miles since 2000 and affecting about 41% of spruce-fir forests.
Aspen health is a matter of interest due to factors ranging from tourism to summer shade for elk. Fungal defoliation does not raise concerns about aspen mortality unless it occurs over multiple years, West said.
Aspen defoliation caused by fungal and other factors affected 100 square miles in Colorado last year.