Replanting Trees Following Emerald Ash Borer Infestation Reduces Stormwater Runoff, Improves Lake Michigan Water Quality

Project Summary: Fifty trees planted along roads to partially replace the ash trees lost following an emerald ash borer infestation are decreasing runoff into Lake Michigan.

A green ash that has been infested and consumed by emerald ash borer larvae. Photo from Wikimedia Commons.

Location: Wilmette, Illinois

Description: Ash trees are adaptable to many soil types and grow relatively quickly, making them a popular tree to plant alongside roads or to beautify neighborhoods. Unfortunately, ash trees have been decimated by a non-native insect—the emerald ash borer—whose larvae consume and kill ash trees. In 2006, the village of Wilmette discovered an infestation of emerald ash borers. For a community that takes pride in its status as a Tree City USA, and in which 15 percent of its tree population was ash, this was devastating. From 2006 through 2014, the village had to remove over 2,000 dead or infected ash trees from public property alone. Many of these trees had been planted between streets and the Lake Michigan shoreline, where they helped retain stormwater and filter out pollutants. Removing the ashes significantly increased the flow of sediment and suburban contaminants such as car oil solvents, pesticides, and fertilizers into Lake Michigan.

Recognizing their importance, Wilmette began to replace the lost trees, guided by a principle that every tree lost should be replaced. Thanks to a grant from the Great Lakes Restoration Initiative, the village was able to plant 50 new trees in 2015. The trees were supplied by a local nursery and were composed of eight different species—river birch, sweet gum, a couple varieties of oak, bald Cyprus, American elm, catalpa, and tulip tree—

Once matured, this newly planted oak will mitigate stormwater impacts and protect Lake Michigan’s water quality. Photo courtesy of Kevin Sorby.

chosen for their hardiness and their preference for the moist soils and stable temperatures along the Lake Michigan shoreline. Replacing the removed ash trees with eight different species also increases the diversity of Wilmette’s tree population, making it less susceptible to any one parasite or pathogen in the future. All fifty trees were planted within a mile of the shoreline along parkways and roads, reducing the flow of stormwater and pollutants into Lake Michigan and improving water quality. For the next several years, the village will regularly inspect the trees to monitor their health. They will also provide extensive watering and mulching to encourage the redevelopment of the root system and help the trees acclimate to their new sites.

Approximate cost of project: $8,000, provided by the Great Lakes Restoration Initiative.

Resource challenges addressed: Tree loss, stormwater discharge, and invasive species.

Key partners (public and private): The Village of Wilmette, Acres Group Nursery.

Types of jobs created: Contractors, foresters, interns, and general labor.

Results and accomplishments: Once the trees have matured, they will prevent the discharge of almost 40,000 gallons of untreated stormwater into Lake Michigan each year. This will significantly improve water quality for the village and throughout the Lake Michigan watershed. Wilmette has also been recognized by the Arbor Day Foundation for their efforts to raise awareness about emerald ash borer management for other Midwestern communities and groups.

Website: http://www.wilmette.com/engineering-public-works/forestry/

Originally published on June 7, 2017

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