Estimating impacts of Eastern larch beetle (Dendroctonus simplex LeConte) induced mortality on tamarack (Larix laricina (Du Roi) K. Koch) harvest amounts in Minnesota

Background/Question/Methods

Since first being detected in northern Minnesota in 2000, Eastern larch beetle (Dendroctonus simplex LeConte) or ELB, infestation of tamarack (Larix laricina (Du Roi) K. Koch) has been increasing over the past 13 years.  As of 2012, it is estimated this native pest has caused mortality of tamarack trees on 165,411 acres.  In 2012 alone, it was estimated mortality had occurred on 42,275 acres.  Once thought to be a “secondary” or “non-aggressive” pest, it is now probably a “primary” or “aggressive” pest, capable of killing healthy trees.  As part of a larger analysis identifying the tamarack resource and markets, an analysis was conducted to project how different assumed rates of infestation over the next 50 years would impact potentially available harvested tamarack species volume on Minnesota DNR lands.  Four scenarios were modeled.  A Current scenario where the rates of mortality remain status quo at 15,000 acres per year, Double, where the amount of infested acres increases to 30,000 per year, Insect Collapse, where rates remain constant over the next 5 years but then ELB is assumed to collapse and no further infestation occurs, and No Future Infestation where no further infestation occurs beyond that detected over the past 13 years.

Results/Conclusions

If ELB collapses in the next 5 years and harvesting practices remain essentially as they are, the impact on annually harvested volume will be minimal.  However, assuming harvesting practices basically remain as they are, if infestation rates remain constant and especially if they double, the impacts on annually harvested volume could be large.  We estimate that if infestation rates double that annually harvested tamarack species volume could decrease by as much as 42,000 cords 50 years into the future.