Climatic viability for the persistence of mountain pine beetle in pine forests of the western Great Lakes region

Background/Question/Methods

Mountain pine beetle (Dendroctonus ponderosae) has killed millions of pines in western North America. Its potential eastward spread across the continent is a serious concern. Climate suitability has played a role in recent expansion north and east of its historical limits in western Canada. Mountain pine beetle is now reproducing in mature jack pine (Pinus banksiana) of the boreal forest, a corridor for unassisted spread to the east. Eastward movement may also occur inadvertently in transport of green logs originating from states within its range. In this study we examine whether several climatic conditions known to facilitate mountain pine beetle persistence and outbreak are met in the pine forests of Minnesota, a gateway to pine forests of eastern North America. Fifty years of temperature records (1962-2012) were collected and analyzed from locations throughout the pine forests of Minnesota.

Results/Conclusions

Minnesota has a climate that is becoming increasingly suitable for mountain pine beetle. Degree days needed for the completion of a univoltine lifecycle and 50% egg hatch in the fall were consistently above the minimum thresholds throughout the state. In addition, average temperatures during the flight season were sufficient for host-seeking adults to continue to fly. Finally, high winter mortality across the region is becoming less likely. At several locations, particularly around Lake Superior and in the southern extent of the state’s pine range, temperatures have not reached the point of 100% mortality for overwintering larvae of mountain pine beetle in 50 years or more. In those locations which had previously experienced these temperatures regularly, the frequency of years experiencing extreme temperatures is decreasing.