Invading pests down in some forests, surging in others
A wetter-than-average year helped Santa Fe National Forest boost its defenses enough to hold steady against pests, according to the U.S. Forest Service.
Aerial surveys show the bark beetle had a higher mortality rate in ponderosa pines, piñon and
Douglas fir in 2019 due to higher precipitation, strengthening the trees’ ability to fend off the pests, the Forest Service said in a news release late last week.
However, fewer beetles died off when infesting spruce and other fir species. And they did well when invading dead or dying Douglas firs near the 10,000 acres charred during the 2013 Jaroso and Pacheco fires in the Jemez Mountains and San de Cristo range, the Forest Service said.
Pests tend to feed on trees weakened by fires or a prolonged drought. Last year’s heavier precipitation supplied moisture that the trees required to make resin within their bark to repel bugs, said Dan West, forest entomologist at the Colorado State Forest Service.
In 2018, the region had the second-driest year on record, leading to pests wreaking widespread destruction in the forests, West said.
“We see the pendulum swinging from very, very dry to wetter than average,” West said, adding that scientists don’t know yet
whether this will be a long-term trend.
A severe drought can shrivel a tree’s root system, which isn’t reinvigorated from one damp year, West said.
Other pests fared better than the bark beetle. Defoliators such as the western tent caterpillar stripped the leaves from aspen trees, most noticeably along Hyde Park Road. These trees are expected to regain their leaves in time for a bright gold display in autumn, the Forest Service said.
The piñon needle scale, a sap-sucking bug, invaded 9,000 acres of piñon trees on the Interstate 25 corridor. The bug by itself seldom kills trees but can increase tree mortality rates when combined with bark beetles and drought.
The Janet’s looper caterpillar, which emerged in high-elevation firs in 2017 and 2018, appears to be in retreat, affecting 5,650 acres in 2019 compared to almost twice that acreage in 2018.
Although last year’s wetter season offered relief from an extreme drought, the temperatures remained about the same, West said, adding that the weather needs to cool as well. “We want below-average temperatures with above-average precipitation,” West said. “We’ll see if that plays out.”