Getting to the root of white oak decline

in northern Illinois

A Q&A with Roz Remsen about her white oak study

|  Story by Cindy Wojdyla Cain |


Roz Remsen noticed something unusual a few years ago when she was working for a private tree care company in northern Illinois.

The white oak trees she was called to treat were dying. She could see the bare tips of branches, which is called stag-horning for the way the tips resemble stag antlers, which was a symptom of the decline.

Remsen had graduated with a forestry degree before she took the job. When she decided to get her master’s degree in soil science from the University of Wisconsin Stevens Point and needed a thesis study, she quickly thought of the struggling oaks.

She examined the soil around oaks in the Forest Preserve District of Will County’s properties and other sites this year and is working on lab and data analysis. She will work on her thesis in 2024.

Here is a Q&A with Remsen about her white oak study:

Oak trees with fall color.

Describe your study?

We are studying the pattern of oak decline that can be seen across the Chicago region. Oak decline is not a single disease, but a gradual spiral of decline, often leading to death of oak trees. This is caused by many factors driving decline, including recently dry summers and insects and diseases that take advantage of stressed trees. Once trees get put in a high state of stress, every opportunistic pest and pathogen will start jumping onto that tree. My research focuses on what site or soil differences may be influencing this pattern of decline. I am comparing the characteristics of healthy white and bur oaks to declining ones on the same sites to see what may be related to decline. We also hope this information will help us find if there's anything we can do to better manage our oaks to prevent losses of our mature oak trees. I am collaborating with the Morton Arboretum to also investigate if certain root rot diseases are playing a significant role in this pattern. Hopefully, we can find site and soil characteristics to manage for and treatments for diseases to stop mortalities.

Is this a local study, regional or national?

My research is regional, covering 32 sites spread over the seven-county region of Chicago.

Roz Remsen collecting soil samples.

What are you searching for in the soil samples?

I use a bucket auger to determine drainage as well as soil structure, or how the soil naturally aggregates or clumps together. This affects water availability and how well tree roots can live in that soil. You want aggregates that can hold onto water and nutrients, but you don’t want a massive aggregate because that tends to trap water and not let it infiltrate down through the soil. If it’s compacted, the soil clumps become smooshed and the water will get stuck at the top or it will run right off. We also are testing the soil samples for pH, salt content, compaction, carbon, phosphorus and potassium.

A soil sample.

What have you learned so far?

The pattern of oak decline is continuing to spread over the region. I am returning to sites that I used to work at as an arborist and seeing even more decline on a site than there was two years ago. Unfortunately, on many sites I had a hard time finding completely healthy groves of trees. I am also learning how invested homeowners, park managers, and forest preserve employees and visitors are in preserving their mature oak trees. It is refreshing to hear everyone's stories about their oaks and the value they see in them.

Damaged white oak tree bark.

White oak tree bark showing carpenter ant “frass,” which includes wood debris and is a sign of damage to the tree.

What is the goal of the research you are conducting?

To determine what site and soil factors may be driving white oak decline so we can improve management recommendations for preserving mature oaks and understand what treatment options may help slow the pattern. This information may also inform future plantings of white and bur oaks to replace the recent losses.

How will this research help the environment?

Mature oak trees are 100-200 years old and provide valuable services to our communities. These services include reducing stormwater runoff, reducing local temperatures, ecological diversity, food sources for wildlife and many more. By investigating what may be causing this decline, we may be able to preserve more of these oak trees and help them continue to improve our quality of life and environment every day.

Roz Remsen standing in front of a white oak tree.

Anything else you would like to add about your research?

Large trees need to be watered, too, when there's a drought! They may not wilt immediately in the same way our small annual flowers do, but drought stresses can impact large tree health and potentially start decline spirals such as the oak decline we're seeing. If it hasn't rained at all in over a week, please consider giving your large trees a long, slow soak near the base of the tree in the morning or evening. A properly installed mulch ring will also be a huge help to your trees as well.

Remsen also noted that the white oak is the state tree of Illinois. And she said it’s her favorite tree.

“White oaks are such stately and majestic trees, especially in their structure and the way they hold their branches,” she said. “If they’re in the right position they can become the dominant tree in a landscape. They provide so many services. And white oaks have a personality to them. They are a little finicky and they don’t like their soil or roots being messed with. They like everything to be just right, which is why they are declining.”

Remsen's research is funded by Davey Tree Expert Co. and The Garden Club of America. 

Photo credits: Stephanie Adams, Roz Remsen and Anthony Schalk

Back to Top