New tool against pollution is ancient: tree canopies

By KALEY FECH
Capital News Service

LANSING — Trees may be the answer for Michigan communities looking to reduce pollution from stormwater runoff.

For one thing, their leafy canopies work like an umbrella over the pavement, keeping rainwater from flowing across the ground and into larger bodies of water.

“Trees can reduce stormwater runoff in multiple ways,” said Heather Smith, Grand Traverse Baykeeper at the Watershed Center, Grand Traverse Bay in Traverse City.

“Trees can capture rainfall in their canopies, which can later evaporate back into the atmosphere. The roots can help promote infiltration of stormwater and the roots can also trap sediments, nutrients and other pollutants.”

The Watershed Center is working to increase the tree canopy in five communities, including Elk Rapids, Bellaire, Kingsley, Northport and Kalkaska.

Other cities are also looking for help from this leafy strategy, including Grand Rapids and Ann Arbor.

Grand Rapids has set a canopy cover goal of 40 percent, and the city is currently near 34 percent, according to Audrey Hughey, a geographic information systems specialist or Friends of Grand Rapids Parks.

Just one sugar maple tree in Ann Arbor can capture 1,763 gallons of stormwater runoff in a year, according to the city’s website.

Stormwater runoff– rainwater that falls on impervious surfaces such as parking lots, rooftops and roads — is not soaked into the ground. Instead, it flows across the ground and ends up in lakes and other bodies of water.

“When it goes over impervious surfaces like roadways and rooftops, it’s going to pick up different pollutants that may not necessarily be visible to the eye but that are invariably there,” said Jennifer Buchanan, watershed projects director at the Tip of the Mitt Watershed Council in Petoskey. “It’s coming from all kinds of different surfaces in the landscape.”

Both Buchanan and Smith said a changing climate is increasing the number and severity of rainstorms, resulting in larger amounts of stormwater runoff.

“The volume of water and the rate of runoff is an issue because it’s these big rushes of stormwater that are entering into lakes and streams,” Buchanan said. “We can’t do much about the weather, but what we can do is try to get the stormwater to soak into the ground as locally as possible.”

Smith said stormwater runoff is one of the leading causes of stormwater pollution.

“I think we’ve been thinking more about trees and other vegetation in managing stormwater in the last few decades as we realize that we can’t just pipe untreated water into the nearest lake or stream,” she said. “We need to start treating stormwater, using natural processes.”

As an area becomes more urban, the problem of stormwater runoff increases.

“As development increases, and the amount of impervious surfaces we have increases, the more stormwater becomes a problem,” said Tom Zimnicki, the agriculture policy director for the Michigan Environmental Council.

Tree canopies can  slow down rainwater and allow it to soak into the ground. Trees also hold a lot of rainwater in their leaves and bark, reducing the amount of water that reaches the ground.

“The best plants are deep-rooting plants,” said Buchanan. “Those deep roots help form channels in the soil, so they form little conduits for the stormwater to travel down into the soil. And the more root surface you have, the more nutrients that potentially can be removed.”

Smith said the positive impacts of tree canopies can be immediate and continue to increase as  trees mature.

Smith said all regions can benefit from maintaining a healthy tree canopy to help manage stormwater.

“We are encouraging individuals and communities to plant and retain a tree canopy,” she said. “We are working with our local municipalities to initiate tree planting campaigns and develop and amend ordinances that favor retaining trees or planting new trees.”

Some cities, like Petoskey, are focusing on other stormwater management practices, such as rain gardens.

With these various techniques, Hughey said she is optimistic progress will be made in reducing pollution from stormwater runoff.

“With combined efforts of increased trees, rain gardens and other runoff diversion efforts, hopefully we will see significant improvements in coming years,” said Hughey.

Buchanan said stormwater management is the responsibility of both citizens and local governments.

“I think the more we can do as citizens as far as personal properties having the trees using more of those kinds of techniques is important, she said “I think it really has to be a combination of efforts between individuals and governments.”

In Grand Rapids, residents work with the city to improve the tree canopies.

“Friends of Grand Rapids Parks has over 90 certified citizen foresters that are in the city and trained to look at the canopy and promote trees in their neighborhoods,” said Hughey. “We realize as a city and an organization that climate change will affect us in the future and we are doing our best now to plan and plant for a more sustainable and resilient city. “