By Izabela Zaluska 

Matt Dannenberg, an assistant professor in the Department of Geographical and Sustainability Sciences, knew he wanted to study forests after a backpacking trip to Rocky Mountain National Park as a teenager. 

The multi-day hike and camping trip sparked Dannenberg’s love for the outdoors and ecology.  

Now, as a faculty member in the College of Liberal Arts and Sciences, Dannenberg studies ecosystem responses to climate change, especially changes in the water cycle. Dannenberg, who joined the faculty in 2019, looks at impacts on the growth, photosynthesis, and water use of plants. He conducts field work every summer in states around the country, including Montana, Arizona, Nebraska, Iowa, and more. 

“Part of what I enjoy is that it’s my job now to go to beautiful places and study them,” Dannenberg said. “Plus, the process of discovery is fun and intellectually stimulating. I get to test my ideas about how ecological systems respond to climate change for a living.” 

Dannenberg recently received three grants to further his research and teaching. Learn more about his work. 

Projecting how tree growth will change as rainfall changes because of climate change

Dannenberg received a $324,677 National Science Foundation grant to use tree rings and dendrometers, which measure tree diameter changes every 10 minutes, to understand how growth responds to extreme precipitation and to contextualize current climate change and future projected changes, specifically in wet extremes. He is collaborating with Erika Wise, a faculty member at University of North Carolina at Chapel Hill. 

Trees are generally better at reconstructing dry extremes than wet extremes, and there’s a long history of tree rings being used to reconstruct past histories of drought, he said. Dannenberg learned, however, that water managers at the U.S. Army Corps of Engineers wanted to better understand the wet extremes, which is what led to the project.

Dannenberg is using a combination of measurements and models to understand how tree growth changes as rainfall frequency and intensity change, as well as how these wet extremes have changed in the recent past and are likely to change because of warming. 

“One of the things we know about how climate change will affect our water cycle is it’s quite likely that extreme rainfall events will get larger but separated by longer periods of time,” Dannenberg said. “Figuring out how those changes compare to changes in the past and figuring out if we can improve the ways that we reconstruct the histories of those wet extremes is going to be an important part of preparing for and understanding climate change.” 

Dannenberg installed new instruments this past August to measure tree growth fluctuations every 10 minutes. When a rainfall event comes, the team will be able to see in real time how much this stimulates plant growth, for how long, how quickly after rainfall growth starts to decline, and more. 

Examining impacts of drought on tree growth using tree ring records 

Dannenberg’s second grant is $398,756 from the U.S. Department of Energy. He is collaborating with scientists at the University of California, Los Angeles and the Pacific Northwest National Laboratory. 

The team will use tree ring records from across the United States to examine how tree growth responds to different types of drought and how those responses vary across different climates and among different tree species.  

Researchers will focus on how both physiological traits and tree size affect drought responses, specifically soil drought and atmospheric drought, Dannenberg said. 

Soil droughts happen when there’s low soil moisture, and atmospheric droughts happen when there’s high evaporative demand, he added. 

"Usually, we think of drought as low rainfall,” Dannenberg explained. “That's what we usually call a meteorological drought. But it's not just rainfall per se that plants respond to. What plants respond to directly is how much soil moisture there is, and how dry the atmosphere is, which demands more water from the plant in the soil.” 

The team will examine how trees respond to soil droughts, atmospheric droughts, and their combination, as well as if the drought effects are longer lasting for one type over the other, Dannenberg said. 

Using plant growth chambers to further research and teaching 

The $348,015 grant from the Roy J. Carver Charitable Trust was used to purchase eight growth chambers for controlled experiments on plants. These chambers will simulate multiple aspects of climate change to learn how they affect plant growth. 

The project is a collaboration between Dannenberg and Susan Meerdink, also a faculty member in the Department of Geographical and Sustainability Sciences. The funds are paying for the equipment, and the goal is to start proposing new research grants using the growth chambers, as well as using them in the classroom with undergraduate and graduate students. 

“There's a lot of ways the Earth system is changing due to human activity,” Dannenberg said. “Warming, changes in the distribution of rainfall events, increases in atmospheric CO2, and many others. All of those changes interact to affect plants in potentially pretty severe ways.” 

The growth chambers—which are roughly the size of a large refrigerator and meant for potted plants—will allow controlled experiments on plants that simulate these various changes to see how they will affect plant growth now and in the future. Dannenberg and Meerdink will be conducting experiments on potted saplings, especially those native to the Midwest like oaks and maples. 

Dannenberg and Meerdink will also use the growth chambers while teaching their various courses to students. 

"The goal is that these will be used both for classroom teaching and to support undergraduate and graduate research, whether that's student summer research, independent studies, or for honors and graduate theses,” Dannenberg said.