Mass proliferation of invasive species is poised to alter local forests.
by Roger Klein // Photography by Roger Klein
Swaths of dead ash trees are the skeletal remains of a forest that once dominated the Silver Creek Wetland. A small, metallic green insect known as the emerald ash borer (EAB) is to blame. Ash borer larvae feed on a tree’s vascular cambium under the bark, which ultimately “girdles” and kills the tree.
The invasive insect was first discovered in Ontario in 2002 after it crossed into Canada from Michigan. The emerald ash borer is an Asian species native to China, Japan, Taiwan, Korea and Mongolia. Since its arrival here, the ash borer has spread through Southern Georgian Bay’s forests and fencerows, leaving a path of destruction. It also opened the door for the proliferation of an invasive shrub called European buckthorn.
Research by Western University’s Centre for Environment and Sustainability published in the Canadian Journal of Forest Research confirms that a secondary invasion is now underway. “We find evidence that EAB-induced ash mortality facilitates European buckthorn through the creation of canopy gaps,” researchers concluded after a statistical analysis of six deciduous forest stands within urban and agricultural landscapes surrounding London, Ontario.
European buckthorn (common buckthorn) is a tenacious shrub native to Eurasia that was introduced to Ontario to help with erosion control in the late 1800s. Buckthorn is one of the first shrubs to leaf in early spring. It also retains its green leaves well into the fall (November in some areas), when nearly all other species are leafless. The seeds are spread by birds and animals that eat, then excrete the seeds away from the parent shrub, enabling the plant’s widespread invasion. The seeds can remain viable in the soil for up to five years.
Buckthorn seedlings spread quickly across the forest floor, preventing other species, including native plants, from growing and surviving. Buckthorn can even change soil chemistry in a way that makes it harder for other species to compete. These traits make this invasive species particularly harmful to hardwood forests and challenging for land managers trying to promote healthy forest succession in the long term.
