Forest health survey shows impacts of beetles, diseases
Summit County has increased likelihood of widespread, destructive forest disturbances
In its annual aerial forest health survey, the Colorado State Forest Service examined forested land and cautioned that beetle and disease activity combined with drought is likely to lead to more destructive wildfires.
The survey, which is conducted in collaboration with the U.S. Forest Service, was scaled back in 2020 due to limitations presented by the pandemic. Normally, the survey covers the majority of forested land in the state, about 44 million acres. Last year, the survey covered 23 million acres, focusing primarily on high-priority areas, including Summit County, where there is an increased likelihood of widespread, destructive forest disturbances, according to survey results.
State forest entomologist Dan West said as the 2021 survey is getting started this week, he expects the whole state to be surveyed again this year.
West said the Summit County survey results were similar to years past, with an endemic, or background level, of bark beetles. That means there are small pockets of trees, groups of anywhere between three and 10, that are affected by various bugs.
“If we were in an area where there was no epidemic, you’re always going to have bark beetles that are going to recycle trees that have been struck by lightning or that have breakage or an issue with their roots or whatever,” West said. “So years where drought really is compacted or compiled year after year, we pretty much start to see bark beetles pick off those trees and continue the cycling of nutrients.”
West added that Summit County sits in the middle of two pockets of spruce beetles, which remain the most damaging forest pest in the state for the ninth consecutive year. Populations have worked their way south from Steamboat Springs down through Rocky Mountain National Park and into the northern end of Grand County, just to the north of Summit.
In the southwest corner of the state, West said a spruce beetle outbreak started around 2004 in the Rio Grande National Forest. Spruce beetle populations have started to make their way northeast since, most recently moving into Pitkin County just to the southwest of Summit.
The most prominent disturbance seen in Summit County is the presence of western balsam bark beetle, which often appears in conjunction with root disease. According to the Forest Service, these beetles have been detected on 8,000 acres of subalpine fir in Colorado and Wyoming.
In years of drought, balsam beetles will attack otherwise healthy trees that have been predisposed to a reduced defense response due to a lack of precipitation — as was the case in 2020, according to the survey. This in turn sets the stage for increased activity in 2021.
“That’s a bark beetle that we never worry about as far as large, widespread damage because it doesn’t move in a wave across the forest …” West said. “It really continues to just work in little small pockets or individual trees.”
When these trees are killed by beetles, they become much more likely to sustain large forest fires.
Tree canopies fade from green to red in the few years after a beetle attack as the trees die. When that happens, the tree canopies can fuel wildfire as it travels through tree crowns, according to the survey. This is known as an active crown fire, which was responsible for quickly consuming vast acreages of forest during Colorado’s record-setting 2020 wildfire season.
Summit County forester Ashley Garrison said one of the biggest diseases affecting lodgepole pines in the area is dwarf mistletoe, which is a native parasitic plant that makes trees more susceptible to drought and insects.
Despite the presence of bugs and diseases, Garrison said wildfires and windthrow, or trees being uprooted by wind, are the greatest risks to Summit County forests right now.
“We work to balance out those effects by doing field treatments, forestry treatments, having a diversity of age classes, a diversity of tree density and diversity of different species,” Garrison said.
The goal is to alter fire behavior to make it easier for firefighters to control, Garrison said.
“We want to alter the fuel so that it’s not a catastrophic wildfire, so that it can actually have some benefit and not be so damaging,” she said.
West said it’s important for communities to be on the lookout for beetle activity as it has a strong linkage with forest fires.
“Mitigating our property, of course, for private landowners is paramount, especially on the tails of such a bad wildfire season,” West said.
Justin Conrad, fire management officer for the eastern half of the White River National Forest, also said the amount of dead and downed trees in the county contributes fuel to wildfires.
As the state endures an ongoing drought, dry trees not yet attacked by beetles become more susceptible as they are less able to defend themselves. Healthier trees can build stronger defenses, making it harder for beetles to bore into the trunk. Bark beetles aren’t able to live for a long period of time outside of a tree, meaning beetle populations would likely decrease in healthy forests with the help of birds and other predators, West said.
West said Summit forests received plenty of precipitation this spring and that if rainfall continues throughout the year, trees could start to build a better defense. He said trees typically need two seasons or more to recover from a drought.
While West said it’s too early to predict whether spruce beetles will make their way to Summit County, it’s possible.
“Should there not be enough precipitation, we would consider them still on the move and consider them still to be at higher risk to increasing their footprint across Colorado state forests,” West said.
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