Tamarack Trees in fall along a Northern MN lake.

MN Impact: DNR promoting management and harvesting to help protect Northern forests from the effects of eastern larch beetle

June 16, 2020

Issue

The outbreak of eastern larch beetles in Minnesota began in 2001 and shows no signs of slowing down. Foresters believe the nearly 500,000 acres of affected tamarack trees may never recover, thus changing the broader ecosystem in the northern parts of the state.

What has been done

Eastern larch beetles are not new and, in fact, are native to Minnesota. They are found everywhere tamaracks grow, but throughout history, the beetles never posed a great threat and were largely ignored by forest entomologists. What has changed?

University researchers have shown that populations of eastern larch beetles increase when warm, extended growing seasons permit two generations of insects to develop within a summer. Increased numbers of insects, in concert with warmer and dryer years, are likely facilitating these continued outbreaks. In Minnesota, tamaracks typically grow in bogs, swamps and other areas too wet for most trees to survive. As large tamaracks die off in high numbers, the water table rises and could lead to young trees being flooded out.

Results

Studies from the Minnesota Department of Natural Resources (DNR) and the University of Minnesota have shown when tamaracks are just left for the beetle; young saplings left behind are less likely to survive. By one estimate, the survival rate is about 100 new trees per acre. When foresters clear and reseed before the beetle kills them off, the area can replenish with about 800 to 1,000 new saplings per acre.

In response, the DNR is working to speed up tamarack timber auctions in hopes they can harvest some trees while still standing and the wood is useful. Additionally, harvesting opens up the area so young sapling and other species can grow and replace them, thus hopefully protecting the fragile ecology of the forests