The public locking a bicycle to a tree can damage the trees protective bark and the delicate cambium layer just below the bark. Photo by Eleanor Revelle

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On hot summer days, Evanstonians may feel more appreciative than usual of the community’s rich urban forest. Trees shade Evanston homes from the summer sun, provide a leafy canopy over families out for a walk, shelter parked cars and cool the air through evapotranspiration.

Less noticeable are some of the other benefits of trees. They capture and store carbon, helping to slow the build-up of global warming pollution in the atmosphere. They remove air pollutants and improve air quality. They reduce storm-water runoff, provide important habitat for birds and other wildlife, add beauty, improve health and increase property values.

Maintaining This Valuable Resource

According to City forestry officials, there are some 33,000 trees on public land in Evanston – and twice that many on private property. But this valuable urban forest is under intense pressure. The changing climate is bringing hotter, drier summers and more frequent heavy storms with damaging high winds. Exotic invasive insects and diseases – such as Dutch elm disease and, more recently, the emerald ash borer – pose additional threats.

Evanston’s urban forest needs proper care if it is to survive and thrive under these challenging conditions. RoundTable readers can help by caring for the trees in their own yards and on their parkways. Here are three important tree-care best practices:

• Water, especially during hot, dry periods. Trees need 15-25 gallons of water every week in spring, summer, and fall. The actual amount required depends on local site conditions, but trees need to be watered if natural rainfall is less than one inch per week. One method is to let a hose run slowly for 30 minutes within the “dripline” of the tree, the area under the tree’s outermost branches. The aim is to water deeply rather than frequently so the water can reach the tree’s roots.

• Mulch, but avoid mulch “volcanoes.” Mulch holds moisture, discourages weeds, and keeps tree roots cool in summer. A 3-to-4-inch layer of wood chips or hardwood mulch in a 3-foot-wide area around the base of the tree is ideal, but the mulch should be kept away from the trunk. Free wood chips are available at James Park (accessible by the drive at 300 Dodge Avenue. Enter the area via the driveway at the Levy Center at Mulford at Dodge Ave. and continue back past the baseball fields to the wood bins). Note that turf grass is not a substitute for mulch as it will compete with the tree for moisture and nutrients.

Protect the bark. Lawn mowers, weed whackers, car doors, and bicycle locks can all damage a tree’s bark. “Lawnmower blight” is a leading cause of tree death in urban settings. Mulching can help keep mowers away.

 Expanding Evanston’s Urban Forest

Evanston has lost thousands of public and private trees in recent years due to invasive insects and disease as well as storm damage. Residents can help remedy this loss and even expand the City’s important tree canopy.

• Plant new trees. Updated tree-selection information is available to property-owners who have lost a tree – or who have a suitable space in their yard – and are ready for a new tree. In view of the changing climate, trees suitable for this area will be those that are tolerant of warmer weather and drier conditions and resistant to invasive insect pests and diseases. Another factor to consider: A slow-growing tree will generally live longer than a fast-growing species and often will have deeper roots, making it more drought resistant.  

The Chicago Botanic Garden has a list of Illinois Best Plants, and the City’s Forestry Division has an “approved species list” for parkway planting that is also helpful in selecting trees for private property. The City’s list was developed with an eye to improving species diversity so that no single species will represent more than 10 percent of Evanston’s street-tree population. This will help to minimize the incidence of species-specific infestations. 

• Request a parkway tree. Property owners whose parkway has space for a tree can contact the Forestry Division to put their address on the list for a new tree.

• Contribute to the Reforestation Fund. After severe storms destroyed many trees in 2011, the City established a reforestation fund to help maintain Evanston’s park and parkway trees. The fund is helping to replace the many ash trees destroyed by the emerald ash borer. Donations may be made online on the main Forestry webpage.

Green Drinks Program

Caring for Evanston’s Urban Forest will be the topic of the July 10 Green Drinks program sponsored by Citizens’ Greener Evanston. Panelists will discuss the challenges to Evanston’s urban forest, what is being done to manage Evanston’s public trees, and what residents can do to help keep Evanston’s urban forest healthy.

Panelists will include Paul D’Agostino, Evanston superintendent of Parks, Forestry and Facilities Management; Josh Behounek, Davey Resource Group; and Wendy Pollock, treekeeper #1050.

This free learning and networking opportunity will take place July 10 from 7-9 p.m., at the Firehouse Grill, 750 Chicago Ave.

All are welcome.