Iowa State University forestry professor helps Iowans prepare for decline of ash trees

AMES, Iowa – As the specter of the emerald ash borer continues its seemingly inevitable spread across the state, an Iowa State University professor is working with communities and homeowners to prepare for life without ash trees.
The emerald ash borer, an invasive beetle that attacks and kills ash trees, has been confirmed in six Iowa counties, putting city officials and property owners across the state on high alert for signs of the small green pests.
Jan Thompson, a professor of natural resource ecology and management and the Harmon Family Professor of Forestry, said upwards of 240 Iowa communities have begun systematic inventories of the trees that populate parks and other public spaces as a first step in determining what eventually will replace ash trees.
Thompson said she’s advising those communities to get a head-start on the ash borers by filling in existing empty spaces with a diverse array of tree species. She said diversity is key to protect against future pests that target a particular species, like the emerald ash borer does with ash trees.
“Hedge your bets and plant some of everything,” she said. “Diversity is critical because you don’t know what the next pest will be. Mix it up.”
Thompson estimated that about 15 percent of the trees in Iowa parks and public spaces are ash trees.  They’re popular because of their large canopy, a feature that provides a number of advantages such as shading structures, absorbing water during wet weather and storing carbon.  
Species that offer a similar canopy and are suited to environmental conditions in Iowa include American basswood, honeylocust, sugar maple, black maple, red oak, white oak, bur oak, and sycamore trees, she said.
But Thompson stressed that choosing a tree species also depends on the specifics of the site and other qualities like drought and flood tolerance, mature tree height and spread, as well as growth rate.
Thompson said some municipal forestry departments are considering the preemptive removal of ash trees before the appearance of emerald ash borers, but she said it’s probably not necessary for homeowners with ash trees to take such a precaution.
That holds especially true if the tree is in good health and providing shade and other important functions, she said.  In that case, homeowners may want to investigate treatment options that can protect the tree from the borer.
“If you have old and damaged ash trees, or a tree that’s likely to become a hazard, it might be good to have it removed,” she said. 
She also encouraged Iowans to be on the lookout for signs of emerald ash borers, including small D-shaped holes in tree trunks and splits in the bark.