City’s Street Trees Digging at the Root of Success

By Larry Caplan
Evansville, IN (October 23, 2009)- In Wednesday’s Courier & Press, there was a report that discussed the trees that line Evansville’s public streets- it didn’t look at backyard trees or others. The Indiana Department of Natural Resources gave Evansville’s trees a “grade” of C-plus- slightly better than average, but not terrific. I wanted to touch on a couple of points that people have asked me about.


First of all, our urban forest is extremely beneficial. Evansville receives more than $500,000 worth of benefits every year from our trees. They help absorb storm water, shade our homes and streets, and cleanse the air, as well as providing aesthetic value.
We were graded lowly for diversity of tree species because we keep planting the same trees throughout the city. For example, more than 20 percent of the street trees are maples and 7 percent are ash. This is important because too many closely related trees means that a single disease or insect can wipe out a majority of our urban forest. Sort of like how Dutch elm disease wiped out the American elm in the 1950s and 1960s, and how emerald ash borer is doing that with ash trees now. (By the way, the ash borer recently was found in Dubois County, Ind., in the Hoosier National Forest.)
Nearly 10 percent of our street trees are ornamental pears. Most of these are older Bradford pears, which have poor branch structure and frequently split apart during storms. We lost many of these trees over the last 12 months as a result of windstorms, ice storms and other weather events.
Even more troubling is the condition of the trees that we do have. Fourteen percent of our trees have poor pruning (they were topped, which shortens their lives and increases the likelihood that they will fall apart during storms).
Another 14 percent have conflicts with utility lines, overwhelmingly because big trees were planted too close to existing overhead lines. And almost every street tree has some form of trunk or root injury- girdling from poor planting, conflicts with sidewalks and damage from automobile accidents.
The city’s Urban Forestry Department has been working hard to improve the health and diversity of our city’s trees. For example, several years ago, we began removing the monoculture of messy and deteriorating Bradford pears from the Main Street walkway and replaced them with 30 species of trees, making this the most diverse planting in the city. We’ve been removing aging ash trees- before the borer gets here- and replacing them with a mixture of species that have good pest resistance. Most important, the city arborist and I have been working hard to educate homeowners and tree companies about the hazards of topping trees.
Every citizen in this community can help us improve our grade by matching the tree species with the property’s size and soil, planting these trees correctly, giving them proper care and not topping or otherwise improperly pruning trees.
Larry Caplan is an extension educator-horticulture with the Purdue University Cooperative Extension Service, Vanderburgh County/ Southwest Indiana. You can send e-mail to him at LCaplan@purdue.edu.
Related Resources:
Evansville Courier & Press- City’s Street Trees Digging at the Root of Success