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Every year the Eastern spruce budworm kills multitudes of balsam fir and spruce in Minnesota, and the dead trees potentially become spectacular fuel for forest fires.
The Forest Service points out that the “Eastern spruce budworm is a native caterpillar and is the most destructive pest of sprucefir forests in eastern North America.”
In 2021 the Minnesota Department of Natural Resources reported in its Forest Health Annual Report that an infestation of spruce budworms was affecting over 380,000 acres across the state.
That same 2021 the Greenwood Fire burned 27,000 acres near Isabella in Lake County and much of that was forest affected by spruce budworm. It took three months to put the fire out and it cost the state more than $21 million.
In 2022 the DNR said spruce budworm defoliated or killed 488,838 acres of fir and spruce forests and noted in its Forest Health Annual Report that the present outbreak was in Cook, Lake, and St. Louis Counties with some scattered damage to white spruce stands in Itasca, Beltrami, Rosseau, and Lake of the Woods counties.
Cited in that report, “The majority (approximately 484,680) of those acres were defoliated, and about 4,160 acres had a mix of mortality and defoliation.”
The total in 2022 was the highest number of acres the caterpillar had impacted in Minnesota since 1955 when the caterpillars damaged 506,000 acres. Noted in the 2022 study was an “overabundance of balsam fir” had possibly prolonged the presence of spruce budworm.
Last summer, in Two Harbors, Minnesota, the National Resource Conservation Service partnered with North St. Louis County Soil and Water Conservation District on an Environmental Quality Incentives Program forestry project. The area was west on private land of Two Harbors, and the goal was to clear and mulch dead balsam that spruce budworms had killed.
The landowner wanted the dead balsam and spruce taken down because they were a fire hazard and could fall anytime. Plus, the dead trees hindered the growth of new trees, and the forest was in danger of becoming stagnant. So a Duluth logging firm was called, and the project was completed with the trees turned into mulch, future food for the new trees growing to replace the dead ones. Other private landowners have hired loggers to remove trees affected by the caterpillars to lessen the danger of wildfire affecting their property.
In 2018 an aerial survey was conducted across 15 million acres of forests in most Northern and Northwestern Minnesota and six counties in far Southeastern Minnesota, spruce budworms have defoliated and harmed an average of 323,340 acres of forest annually.
Spruce budworms mostly eat balsam fir and white spruce but can affect other tree species. The Forest Service notes, “When the budworm population is high, feeding can also occur on black spruce, tamarack, and pine.”
In most places in the country, spruce budworm infestations occur every 30 years or so and usually last 6-8 years, but the Arrowhead Region has been under attack since 1954.
The first outbreak in Minnesota occurred in 1912 and lasted into the early 1920s.
How does 2023 look for Cook County? According to the Forest Service, “The spruce budworm outbreak will undoubtedly continue to have a large impact next year as it moves farther into Cook County. In addition, as predicted by egg mass surveys from 2021, defoliation and damage are occurring in the Grand Marais area.”
While the destructive caterpillars are here to stay, some folks have been looking into uses for trees harmed by the bugs.
In 2020, a Canadian study called “Degraded Trees from Spruce Budworm Epidemics as Bioenergy Feedstock: A Profitability Analysis of Forest Operations.”
The Research Centre on Renewable Materials, Department of Wood and Forest Service Science, Laval University, Quebec City, Canada, conducted the study.
In this project, degraded trees were harvested for bioenergy alongside healthy trees used for timber and pulp.
This scenario was compared to a reference scenario in which degraded trees were left on the stump in cutover areas. “Using wood pellets as a case study, the results showed that harvesting degraded trees is not as profitable at current market prices, even with very high degradation levels.”
Maybe making the dead spruce and balsam fir into wood pellets isn’t viable now, but it might become something to consider in the future.
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