PELLSTON, Mich. — Footsteps crunch fallen leaves as Dr. Inés Ibáñez’s research team finds their trees.
A forest ecologist and tree demographer, Ibáñez has been conducting research throughout the University of Michigan Biological Station’s 11,000 acres for 16 years.
This fall she’s setting up an experiment — an eight-month “tracer” study — that targets an increasingly important question: What happens underground during the winter and how does it impact summer growth? This project aims to learn if trees take up nutrients, specifically nitrogen, in the winter.
That’s where the decomposing leaves come into play.
“Nitrogen is the most limited resource that plants have because it’s not in the soil. It’s coming from the decomposition of organic matter,” Ibáñez said. “We think if plants are taking any nutrients, it’s going to be nitrogen.”
On Tuesday, Oct. 15, the professor in the University of Michigan School for Environment and Sustainability (SEAS) and co-instructor of the Forest Ecosystems course at UMBS got down on her hands and knees on the forest floor to insert resin strips into the soil next to the chosen trees marked with orange flags.
She and the U-M undergraduate and graduate student researchers on her team set up this experiment in two different types of forest at the campus in northern Michigan using oak, pine and maple trees. They repeated this same process in southern Michigan near Ann Arbor.
They’ll split up to visit each tree once a month through June 2025, removing one resin strip each month.
“Usually when we look at forests in these kinds of biomes that are very cold in the winter, we assume that everything is happening in the summers — when they are growing, when they are reproducing,” Ibáñez said. “But we also see is that there is a climatic signature of winters that is really affecting productivity during the summer.”
The assumption is that trees are dormant in the winter, but it’s possible they may be active underground.
“They still may be respiring and taking nutrients,” Ibáñez said. “And maybe these winter conditions are what are really driving what may be happening in the summer. We want to make a prediction of how these forests may function in the future.”
Changing Winters
The lab of Dr. Aimée Classen, director of UMBS, set up a publicly accessible snowpack sensor last winter as increasing weather events like rain-on-snow events reduce snowpack and wash away nutrients from soils to our streams and lakes.
Classen is collaborating with Ibáñez on the field work for the new nitrogen experiment and joined the tree research team on the fall excursion along Douglas Lake as colors peaked on trees throughout campus.
“The University of Michigan Biological Station is beautiful year round but there’s something really special about the fall here,” Classen said. “The transition from summer into fall and fall into winter is particularly spectacular. We have a large number of research groups up here right now conducting research to think about how these transitions into fall and winter change the ecosystems in northern Michigan.”
Historic Harvest
Collecting data at what are known as the DIRT plots at UMBS, Karin Rand continuously rams a hammer corer into the ground until it reaches a depth of 30 centimeters.
“This tool has a lot of oomph in which we can core really deeply down into the soil, and it packs it into a core,” Rand said. “We’re interested in not just the top 10 centimeters where a lot of things happen. This is a long-term experiment so we might start to see these signatures of the treatments all the way down to 30 centimeters.”
The manager of Classen’s lab collected soil samples on Oct. 15 that can tell a story spanning two decades. It’s all about soil carbon stability, the capacity of soils to accumulate and store, or “sequester,” carbon.
“Today we are doing a 20-year soil harvest,” Rand said. “It has happened every five years from the beginning of the project. Treatments started in 2004, so we’re 20 years in. The goal is to look at long-term inputs and removals of carbon sources in the forest — both leaf litter and roots that makes up for above- and below-ground carbon inputs.”
DIRT is comprised of a global network with more than a dozen sites in North America, Europe and Asia. Other U.S. sites include the University of Wisconsin and Harvard University, among others. The landmark international project was started by Dr. Knute Nadelhoffer, a former UMBS director.
At UMBS, the only location in Michigan, researchers steward 27 experimental, 5-by-5-meter plots. They’re partitioned off by combinations of whether they have leaves, roots, wood or fertilizer in the soils, or none of the above.
“DIRT is a really exciting project,” Classen said. “Fundamentally, it’s interested in thinking about: do the leaves on trees when they fall impact soils? Do the roots that grow in soil impact how soils develop? Or does wood when a tree falls down impact how soils develop?”
The research also can be used as an analog to think about the future.
“As our forests change and they change how much leaves they have falling into the soil or how many roots are growing in because of how trees are changing the way that they grow, we can answer questions about soils and what soil development might look like,” Classen said.
As a 20-year study, DIRT researchers are starting to see long-term impacts. They’re excited to look at what they dug up this time.
Rand’s hammer corer separated the historic soil samples into 10-centimeter chunks. She bagged them up and took them back to her laboratory in Ann Arbor. That’s where she’ll next analyze the carbon and nitrogen components in the soil.
“When we think about climate change and the scale at which it’s acting in a forest and the scale at which a forest is responding, 20 years actually gives us a scope into that appropriate time scale,” Rand said. “We’re hoping to understand how forests are changing under global change and how they might respond to different scenarios so that we can better manage forests for the future.”
A New Forest?
Rand and Ibáñez don’t overlap when it comes to location or scope, but both researchers at UMBS are focused on the forests and the future.
“We are studying how global change may affect these forests,” Ibáñez said.
Researchers at UMBS are looking at a wide variety of questions — how pollution changes in the landscape, the introduction of new pests or other species, how climatic changes may change these forests.
“We want to know if they are going to be functioning in the same way with the same kind of productivity,” Ibáñez said. “We want to know if the same species are going to be able to persist or if we are going to see a replacement of a species and have a new forest.”
To learn more about the DIRT plots that Rand is managing, read this UMBS news story put together during the 15-year harvest.
Scroll below to watch a video about this research as well as view a photo gallery of fall scenery including fungi.
Founded in 1909, the U-M Biological Station is one of the nation’s largest and longest continuously operating field research stations.
Laboratories, classrooms and cabins are tucked into more than 11,000 acres along Douglas Lake to support long-term science research and education.
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