State could use more and different urban trees

Indiana DNR Release:



Indiana could benefit by having more and different trees lining its city streets, according to a study on the trees in 23 cities done for the state's Department of Natural Resources Division of Forestry.

Bringing about such change is important, said Pam Louks, DNR's Community and Urban Forestry (CUF) coordinator, because the study also showed that Indiana’s urban forests reward Hoosiers with nearly $79 million in annual benefits. The rewards include energy savings and reducing carbon in the atmosphere.

The study, which was done for the CUF program, found that street trees throughout the state also return benefits by reducing ozone levels, volatile organic compounds such as sulfur dioxide and small particulate matter, and improve stormwater interception and reduction.

Economically, trees also make city streets look better, increase community economic vitality, increase real estate values, and give residents a sense of place, according to the study, which was done by the Davey Resource Group.

“While we are still studying the analysis, we can immediately conclude that we need to diversify our urban forest species with native trees, and, where space permits, plant large maturing trees for optimum environmental benefits," Louks said. "We also recommend to engineers, planners, and developers to plan spaces in urban areas for large maturing species of trees, as opposed to leaving small sites for so many ornamental trees that don’t offer the multitude of benefits of large ones.”

The study found that more than 850,000 vacant street tree planting sites in the state, the top six species are maple, ash, elm, oak, crabapple, and pear (with maple and ash being the predominate species), 58 percent are in good condition, 26 percent are in fair condition, 14 percent poor, and 2 percent are dead or dying.

Having such limited diversity opens many issues, which the top species listed highlight. Silver maple can cause infrastructure problems. All ash trees in Indiana are threatened with death by the emerald ash borer insect, which is and will be a financial burden for affected cities and towns. Crabapple and pear look nice but have neither the size nor canopy to produce the amount of environmental benefits many other trees offer.

Louks said the sample urban statewide inventory (SUSI) demonstrates that the urban forestry program is on track toward a solution, using the silver maple species as an example.

"The current study shows that the planting of problematic species such as silver maple is being reduced throughout the state," Louks said. "SUSI also shows that this species is our main service provider in the way of environmental benefits.

"We need to maintain the silver maple we currently have but start planting other species that have the same capability for carbon sequestration, stormwater uptake, energy conservation, and air cleaning.

"While the study shows we are making progress, it also showed that, in the 23 SUSI communities inventoried, there is approximately only one tree for every six people," Louks said.

According to recent research done by Dr. Dave Nowak of the USDA Forest Service, it takes one acre of healthy trees to support the oxygen (clean air) for eight people.

"We have our work cut out for us to help make Hoosier cities and towns green and healthy,” Louks said.

The study also found that Indiana’s urban forest is evenly balanced in age. But, Louks said, the urban forest needs to be unevenly balanced in order to ensure that the benefits derived from large, maturing trees continue without disruption.

To do the study, the consultants first inventoried the trees, then assessed and quantified the benefits of the street tree resource to estimate a net value to those benefits, after deducting the cost of purchase, planting, and maintenance over the life of each tree.

The consultants were hired by the DNR Division of Forestry using funds from three U.S. Forest Service urban forestry grants from 2007-08. The project included the same 23 cities and towns inventoried in1992 by a Purdue University study.

“The 1992 study was a baseline to guide us in the future about where we need to focus our dollars and efforts,” Louks said.

The 23 SUSI communities are being visited by the urban forest office, Indiana Urban Forest Council members, consultants, and city foresters to explain the study. For more information or a list of the communities involved in the study, call (317) 591-1170 or e-mail plouks@dnr.IN.gov.