REGIONAL— Aerial surveys conducted by the Department of Natural Resources are continuing to show widespread insect outbreaks across northern Minnesota that are continuing to harm native forests.
One of the most significant ongoing forest health issues is damage caused by eastern larch beetle. The native beetle, Dendroctonus simplex, has caused widespread mortality in tamarack trees across Minnesota since 2001. Adult beetles are small, about 4 millimeters long, dark brown, and spend most of their lives beneath the bark of tamarack trees.
Several factors have contributed to the outbreak, including abundant mature tamarack, stress from flooding and drought, longer growing seasons associated with climate change, and the beetle’s ability to reproduce quickly. Together, these conditions have allowed beetle populations to overwhelm tamarack stands across the landscape. As a result, significant mature tamarack mortality has occurred on more than 1.2 million acres statewide.
In 2025, aerial surveys mapped 298,700 acres of eastern larch beetle damage, the highest total since 2022. About 35 percent of the affected area sustained significant damage for the first time, much of it in Koochiching County. While the outbreak may have peaked in terms of newly infested acres each year, foresters expect beetle activity to continue for several more years.
Although eastern larch beetle cannot be controlled at a landscape scale, the Minnesota Department of Natural Resources continues to manage tamarack stands to support timber salvage and long-term forest cover. In unmanaged stands studied by researchers, tamarack and other tree species are regenerating naturally. Smaller-diameter tamarack are not susceptible to the beetle, indicating the species remains well suited to Minnesota forests despite continued losses of larger trees.
Damage from eastern larch beetle is concentrated in Koochiching County and parts of far western St. Louis and Itasca counties. The extent of mortality prompted the DNR to update its forest inventory to better reflect current conditions. The agency’s Littlefork area forestry team led an effort to revise tamarack inventory data across an area representing about 76 percent of the DNR’s tamarack cover type. The update involved resetting stand age classifications based on the year trees were first observed as mostly dead in aerial imagery.
Meanwhile, other forest health threats continue to emerge. Emerald ash borer has now reached the Iron Range, having been discovered in the city of Virginia and Itasca County in 2025. Foresters had hoped that cold winter temperatures would keep the ash borer at bay in far northern Minnesota, but warming winters have allowed a number of insect pests to survive in regions where they couldn’t in the past.
Spruce budworm remains another major concern. The native caterpillar defoliates balsam fir and white spruce. Surveys recorded about 182,000 acres of damage in 2025, though that figure is believed to be a significant underestimate due to delayed surveys and reduced visibility caused by smoke from Canadian wildfires. In 2024, a record 708,000 acres of damage was mapped, the highest since 1961. Most of that damage was concentrated in Lake and Cook counties.
Spruce budworm has caused defoliation and mortality on about 1.4 million acres since 2021, primarily in northeastern Minnesota. Damage is expected to continue for another five to seven years in Lake and Cook counties.
Repeated defoliations of spruce and balsam fir can lead to tree death and the accumulation of dead balsam fir, in particular, has elevated fire danger in northeastern Minnesota in recent years. Dead balsam played a major role in escalating recent fires, including the 2021 Greenwood fire, which burned over 26,000 acres in central Lake County and the Brimson Complex fires, which burned over 37,000 acres, mostly in far eastern St. Louis County, in 2025.