T. Anne Cleary Walkway Ash Trees lining walkway

UI and the Emerald Ash Borer

Over the past years, you may have noticed the University of Iowa's changing landscape in regard to the campus trees.

On February 1, 2016, the UI Landscape Services tree crew discovered a larva of the emerald ash borer in an ash tree in Gibson Square Park. The discovery of the emerald ash borer on the UI campus was the first in Johnson County, making it the 30th Iowa county with a confirmed emerald ash borer presence. The larvae of this invasive species feed on the inner bark of the tree and destroy the tree's ability to transport nutrients from the ground to its branches. Infested ash trees dry out quickly and as a result become brittle and dangerous to pedestrian and vehicular traffic.

Due to the pervasiveness of the infestation, nearly all of the UI's roughly 700 ash trees have been removed from campus. Landscape Services replaces the removed trees by planting approximately 300 new trees each year from a diverse tree portfolio.

Emerald Ash Borer

How the Emerald Ash Borer Impacts Campus Trees

Native to Asia, the metallic-green emerald ash borer was first discovered in North America in Michigan in 2002 and has now been detected in 35 U.S. states. The adult female lays her eggs on the outer bark of the tree, and the larvae feed on the inner bark, disrupting the tree’s ability to transport water and nutrients, killing the tree within two to four years. An infested tree should be removed soon after symptoms appear because the wood will lose its structural integrity and begin to fall apart, posing a hazard to pedestrians and property. After weighing management options and the pervasiveness of emerald ash borer infestations, nearly all of the UI campus's roughly 600 ash trees are scheduled for removal.

Fortunately, ash trees make up a small percentage (7%) of the university’s tree inventory so even in a worst-case scenario, 93 percent of the campus’ shade trees will survive. Scott Gritsch, Associate Director of Landscape Services, says ash trees have not been planted on the campus for more than 10 years. Instead, about 300 new trees of varying species are planted each year to increase the campus’ tree biodiversity and keep potential future pest or disease infestations from causing too many casualties.

As a result, the loss of infected ash trees has had a minimal visible impact on the broader campus. But areas where ash trees were heavily concentrated, such as the T. Anne Cleary Walkway, the west end of Iowa Avenue, and along Washington and Market streets, all of which were shaded by canopies of mature ash trees, have been noticeably impacted.

Tree Planting

Progress on the Five-Year Removal Plan

After the discovery of the first emerald ash tree borer larva on the UI campus in 2016, Landscape Services began working on a five-year plan to remove infested ash trees on the UI campus. This intensive process to remove approximately 700 ash trees was developed to help protect public safety on the UI campus. Infected ash trees quickly dry out and lose structural integrity, causing the wood to fall apart and posing a risk to people and property on the UI campus.

To date, approximately 95% of the roughly 700 ash trees managed by FM have been removed with about 60-70% of tree replacement to date. Landscape Services had been replacing removed ash trees in the early stages of the five-year plan but prioritized removal for a period of time as the remaining trees became brittle and posed safety concerns. Replanting a more diverse tree canopy resumed in the spring of 2021.

Trees to be considered as replacement species of the ash must be tolerant of urban soils and other stresses associated with planting in an urban forest, not be a host for any serious pests or disease, should be long lived with low-maintenance demands, non-invasive and preferably free of fruit. Some species Landscape Services have used–but are not limited to–'State Street' Miyabe Maple, 'Princeton' Ginkgo, 'Espresso' Kentucky Coffeetree, Hardy Rubber Tree, Columnar Norway Maple, Silver Linden, Zelkova and Thornless Honeylocust.