Emerald Ash Borer
Background
Emerald ash borer (EAB, Agrilus planipennis) is an invasive species that has spread throughout the United States and into Minnesota. The insects spread through human-assisted transportation (like in infected wood) or through flight (only about three kilometers at a time). In its larval (newly hatched) stage, they can kill an ash tree (Fraxinus spp.) by eating the living tissue that transports nutrients and water, effectively starving the tree. Ash trees can be infected by EAB long before they become reproductively mature, and so EAB is particularly destructive to a population. Minnesota has especially large populations of ash trees, and thus our ecosystems are highly vulnerable to an invasion of EAB. When ash trees die, they leave gaps in the forest for other trees to take over. Native trees like sugar maple or elm have been known to grow in place of the fallen ash, but aggressive or invasive species like buckthorn can also begin to take over.
In 2016, EAB had yet to reach the Natural Lands. A St. Olaf student decided to study a collection of forest plots to help land managers predict how EAB will affect which tree species are dominating the forests. With an idea of how EAB will change the species composition, managers can work toward preventing total ecosystem destabilization.
The Study
Emma Burck (Class of 2017, B.A. Environmental Studies) took data on the size and characteristics of mature trees in four sections of the Natural Lands. Two sections had low concentrations of ash trees and two sections had high concentrations of ash trees. Using data from a previous study in 2015, Burke also calculated the growth rates of the ash trees in the plots.
The Findings
The study calculated the growth rates of the mature trees using data from a study in 2015 and comparing it to the 2016 data. Ash trees and non-ash trees appeared to have similar growth rates. The species composition of all of the plots was very different, with the low ash plots being dominated by bur oak and black walnut, and the high ash plots being dominated by white ash. Burck emphasized the need for more data to improve the accuracy of the growth rate estimations and overall temporal changes. Data collection on the composition and growth of these plots was continued in 2017 and 2021 by two more St. Olaf students. Burck predicts that sugar maples and boxelder will likely take over the canopy after the anticipated ash-dieoff, but invasive buckthorn is likely to spread as well.
Relevance
Managing the effects of EAB is a priority for land managers in the Natural Lands. As of now (2024), infected ash trees that are threatening infrastructure are the primary focus. This includes trees that are within falling distance of trails, trees that affect other management activities, and trees that may endanger desirable trees. Data like this contributes to a long-term understanding of forest growth and change amidst EAB.
Learn more about current EAB management from the DNR.
Citation
Burck, E. 2016. Potential impacts of the emerald ash borer (Agrilus planipennis) on ash trees (Fraxinus spp.) and forest composition in the St. Olaf College natural lands (Northfield, Minnesota). St. Olaf College Local Ecology Papers. https://wp.stolaf.edu/naturallands/files/2017/03/Burck_2016_Forest.pdf