Assessing the Impact of Mountain Pine Beetle in the Great Lakes Region
This story is based on an article by Assistant Professor Marcella Windmuller-Campione, published in 2018 in the Canadian Journal of Forest Research.
Mountain pine beetle has not been found in Minnesota; that is, it has not been found yet. The beetle is native to western North America where it reproduces in most native western pine species. Minnesota’s three native pines, eastern white pine, jack pine, and red pine as well as the naturalized Scots pine, are all susceptible to the beetle. Assistant Professor Marcella Windmuller-Campione is exploring the susceptibility of pines in the Great Lakes region to mountain pine beetle. She first developed a hazard rating system using the U.S. Forest Service’s Forest Inventory and Analysis (FIA) database. Next, she used the hazard rating system to quantify the susceptibility of forests in Minnesota, Wisconsin, and Michigan.
Like emerald ash borer, mountain pine beetle (MPB) is a phloem-feeding beetle, eating the part of the tree that transports sugars. If a tree cannot transport sugars from the leaves to the roots, the tree dies. “It’s like a tree dying of a million different paper cuts,” said Windmuller-Campione. Under endemic conditions, MPB acts as a natural thinning agent in forests, but changes in climate and forest structure have led to epidemic conditions of mass pine mortality in the western United States and Canada. The potential of the beetle’s range to move through Canada and down to the Great Lakes region’s 4.6 million acres of pine forest is a topic of concern among forest managers and scientists. Once limited by cold temperatures, MPB is spreading northward and eastward with warming average winter temperatures and infection of new host species.
In 2015, the Minnesota Department of Agriculture instituted a quarantine that prohibits the movement of any pine wood with bark into Minnesota from states within MPB infestation. Even with the quarantine, it is important to be aware of possible transmission of MPB into the Great Lakes region. One migration route is an eastward progression through the lodgepole and jack pine forests of Canada. These two species can hybridize, which is thought to facilitate the spread of MPB even further because this hybrid did not coevolve with MPB. The second route of transmission is through transport of infected material, either as firewood or on logging trucks.
Using her hazard rating system and FIA plots, Windmuller-Campione found that over 90% of the FIA plots with at least one pine species were classified as having a moderate to high susceptibility to MPB. More phloem means more potential food for the beetle, so plots with larger diameter trees had a higher hazard rating. Not surprisingly, stands that were denser and had higher composition of pine species showed higher susceptibility to MPB. Additionally, there was a significant difference in hazard rating among federal, state and privately owned land, with federally owned land being the most susceptible to MPB. However, compared to western states where there may be one or two species in a lodgepole or ponderosa pine stand, the pine forests of the Lake States are diverse with four to five different tree species on average. This may produce a different dynamic. Moderate and high susceptibility plots are distributed across central and northern Minnesota. These more susceptible stands are the classic even-aged stands of red pine and jack pine. However, the presence of large diameter eastern white pine does increase susceptibility with the model due to the increased amount of phloem.
What does this mean for forest managers? There is still much that is unknown about MPB, especially how it reproduces in eastern pines. While there is not an immediate need to start managing for MPB, Windmuller-Campione says “it should be on our radar.”