PA Environment Digest

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Penn State Extension: Planting Trees Is A Green, Cost-Effective Way To Reduce Stormwater Runoff

By Vincent Cotrone, Penn State Extension Urban Forester

What we do on the land, or what we cover it with, affects the quantity (volume) and quality (pollutant levels) of the rainfall that enters our waterways-- what many call stormwater. Reducing and managing stormwater can be a real challenge for many municipalities, especially those designated as MS4 [Stormwater Pollution Prevention] communities.

So, how do municipalities begin to reduce stormwater runoff and the pollution associated with it?

Well, they can increase the size of underground pipes and the capacity of their sewage treatment plants which might cost billions of dollars.

Or they can begin to look for some greener and cheaper solutions.

Have you ever thought about planting or protecting the existing trees in your community? It is amazing how much rainfall (potential stormwater) is intercepted in the canopies of large shade or street trees throughout your community.

Think of them as large green, leafy umbrellas that capture rainfall before it hits the street or sidewalk.

Average interception by deciduous trees (trees that lose their leaves in the fall) can range from 1,000 to 2,000 gallons per year, depending on their size, while an evergreen can intercept more than 4,000 gallons per year.

Large canopy trees such as Oak, Maple, or London Planetree planted over impervious surfaces (streets and parking lots) will provide more benefit with time.

Compare a 20 year-old crabapple that intercepts an average of 144 gallons of stormwater each year with a 20 year old Hackberry that intercepts an average of 1,300 gallons each year.

Some Pennsylvania communities are conducting street tree inventories or urban tree canopy assessments and using USDA Forest Service research-based applications called iTree to quantify the multiple benefits provided by trees.

Stormwater reduction is just one of the measurements that is calculated. Others include energy conservation, carbon sequestration, and air pollution removal.

Just this summer, the Municipality of Kingston, in Luzerne County conducted a partial street tree inventory with the help of DCNR Bureau of Forestry, Penn State Extension and the Pennsylvania Outdoor Corps (a DCNR program for youth).

Five two-person crews spent a week measuring trees and collecting data on iPads into PATreeMap from the field.

About a third of Kingston’s streets were inventoried with 1,876 trees identified, measured and photographed, and 842 potential planting spaced tallied. Collectively these trees that line Kingston’s streets reduce stormwater runoff by 4.2 million gallons each and every year.

That number will surely increase as we complete the inventory next summer and as the shade tree commission works to plant the vacant street side planting spaces.

Communities that are interested in using PATreeMap to measure the ecosystem benefits their trees provide, especially stormwater, can visit the PATreeMap webpage (several towns and cities are already mapped and completed) and contact a local DCNR Service Forester for their county or Penn State Extension Urban Forester to discuss tree inventories.

For homeowners that are curious about the benefits provided by trees around their home, use the online National Tree Benefit Calculator.

Planting trees along our community streets and in parking lots, are one of the cheapest ways to reduce stormwater, and their benefits extend much further as they increase property values, reduce summer temperatures, clean and filter the air, and provide healthy livable communities.

Urban forests are finally being viewed by some as part of the "green infrastructure" solutions required by our communities to improve water quality and control stormwater.

Designated MS4 communities can now receive nutrient reduction credits for tree plantings and the TreeVitalize program is helping to finance the planting of trees in many communities.

For more information about trees and stormwater visit Trees & Stormwater: Know Your Community or for information about planting and caring for community trees visit the Penn State Extension Urban Forestry website.

(Reprinted from Penn State Extension Watershed Winds newsletter. Click Here to sign up for your own copy and other updates from Extension.)

More Forestry Resources

Apply now for these grants and assistance--

September 30: Prequalified groups can apply for DCNR/PennVest Buffer Grants

October 1: Landowners Can Volunteer Their Land For Keystone 10 Million Trees Tree Planting

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