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Thursday, April 18, 2019
Colorado State Forest Service’s entomologist explains what bugs are threatening Summit County’s forests
The snow’s melting, the trees are shaking off a wet and wild winter and the pollen is starting to drift into the air. Spring is here, and returning with it to our forests are creatures great and small.
Among them are the tiny little bugs that have collectively ravaged Colorado forests, and they took center stage as one of the bigger threats to Colorado forests during the monthly Forest Health Task Force meeting on Wednesday in Frisco.
Dan West, Ph.D., was the featured speaker this month. West is the lead entomologist for the Colorado State Forest Service, and he knows his bugs. West’s presentation offered the state of insect infestations in Summit County and Colorado, how the infestations happen and what we can expect from the critters in the future.
West started by showing the difference in snowpack between this year, one of the wetter years in recent memory, and last year, which was one of the driest. The difference in precipitation can have a big impact on bug activity the summer after.
While bugs like the spruce beetle enjoy feeding on moist, live vegetation, the moisture also strengthens trees and their ability to ward off insects.
“The fuel load doesn’t change with the precipitation, but what does change is tree defense,” West said. “Trees defend themselves with water that turns into resin. It’s not just a mechanical defense, but there’s also chemical warfare in it with the scent they give off. It is super important for trees to have enough resin to throw at bark beetles.”
Combined with the relatively low activity of spruce beetle in Summit County’s forests, only infecting 7 acres in 2018, West anticipated the county is largely safe for the next couple of years from a mass spruce beetle infestation that could kill off much of what remains of the forest after the mountain pine beetle epidemic.
The outlook for the rest of the state, however, isn’t as rosy. The Colorado State Forest Service estimates that the spruce beetle has affected more than 1.8 million cumulative acres in the state since 2000, or about 40% of the state’s spruce-fir forests. The good news is that the spruce beetle is slowing down, as it is running out of the mature spruce trees they prefer to infect.
Despite the damage done by the spruce beetle statewide, the most common damage to the White River National Forest in Summit’s backyard has been the die-off of thousands of acres of mature subalpine fir trees. The Western balsam bark beetle and armillaria root disease, a fungus, are the main reasons for the deaths.
Those die-offs are expected to also slow down as the primary hosts — large, mature fir trees — die and provide fewer vectors for outbreak.
West provided a number of other interesting facts on forest insects, such as how spruce beetles store up glycols — basically antifreeze — in their bodies during the fall and are therefore able to withstand temperatures as cold as minus 44 degrees Celsius. Back when it got that cold, it kept beetle populations in check by as much as 10% to 20%.
West noted that Colorado hasn’t seen temperatures that cold since the ’80s, and likely never will again. That is also why climate change is a significant factor for the growing beetle outbreaks; the warmer, drier conditions over the years has weakened trees while allowing beetles to thrive.
Aside from the spruce beetle and the Western balsam bark beetle, other bugs affecting Colorado forests are the Western spruce budworm and the Douglas-fir beetle. The spruce budworm loves to feast on the new, fleshy needles on trees, making their impact extra harmful to fresh growth in spring.
West concluded hispresentationwith a prescription for improved forest health that combines forest management with realistic expectations of insect activity and tree mortality after years of unchecked growth and, in many areas, dangerous density.
“It’s up to us to manage our forests and to make our tree stands more resilient to bark beetle,” West said. “We have to be able to handle a little insect activity with smart forest management, as opposed to being so dense that the beetles are able to pick trees up one after another.”