Catherine joined The Nature Conservancy in 2021 as a Bailey Conservation Fellow. For her fellowship, Catherine is analyzing spatial patterns of forest regeneration and health in the Northwoods region (northern Michigan, Wisconsin and Minnesota) for dominant forest types. By analyzing associations of tree species distribution and diversity with driving factors (abiotic, biotic and human-mediated), this research can inform management and conservation priorities.
Catherine earned her Ph.D. (2022) at Michigan State University as a dual student in the Department of Forestry and the ecology, evolution and behavior program. Her dissertation research focused on the regeneration and recruitment stand dynamics of managed northern hardwood forests in Michigan. Catherine also holds a B.S. (2014) in ecology and environmental science from Duke University. Catherine lives in Lansing, Michigan with her partner, Chad. Her hobbies include sourdough bread baking, reading, equestrian sports and running.
How do trees survive the winter?
In the winter months, Michigan is often blanketed in snow. While we all bundle up in layers of warm clothing, trees are relying on their own layers to protect themselves from the chill.
“I’m freezing!” How often do you say or hear those words during a Michigan winter? While people have the comfort of retreating to a warm home, or animals to a protective nest or den, trees are rooted in place. How do trees survive the long, cold Michigan winter?
To answer that question, we need to first step inside of a tree to understand how trees grow and survive. Many people are familiar with naming the outer components of a tree—for example, bark, leaves, trunk, branches and twigs. But inside each tree are different layers, each with its own purpose.
Let’s move through a tree—from the outside in.
Outer bark: Think of this like a suit of armor. Bark protects the tree. This is the part you can see!
Inner bark: This is a thin layer responsible for moving tree food (called sap) throughout the tree. Hence, the need for a suit of armor!
Cambium: This is how a small tree becomes a big tree. This is the area which is actively growing—adding on new cells each year.
Sapwood (or xylem): This is how trees move water and minerals from the roots to the leaves. Leaves are thirsty!
Inner wood (or heartwood): The storage and structural support of the tree. This part of the tree doesn’t move any water or food.
How do trees not freeze?
In the late summer and early fall, shortening day length—which means less time to absorb energy from the sun—and cooling temperatures are a warning sign to trees of winter to come. Growing more slowly, they build smaller and smaller cambium cells. We call this “late wood” since it’s late in the growing season. This period of limited growth is known as early rest.
Eventually, low temperatures encourage trees to enter true dormancy or winter rest, and they totally stop their cambium growth. By stopping their growth and resting, trees can survive freezing temperatures and harsh winter conditions. Some dormant trees can withstand temperatures as low as -360˚ F! However, not all types of trees enter true dormancy, and some just stay in a version of early rest. Trees that enter true dormancy are considered hardier, or less sensitive, to the cold.
What happens after the winter rest?
Though it may seem far off now, trees will soon be entering post-dormancy, or after rest, in the spring. During this time, growth begins again. And eventually, in the summer the cambium cells get bigger, forming what we call “early wood.”
When looked at with the human eye (often with the help of a microscope!), latewood (from the late summer/early fall) appears dark, and the earlywood appears light. This is why we can count tree rings for trees growing in parts of the world where cold temperatures in winter cause growth to slow down and stop once a year.
On some winter days, we might want to be like the trees—resting and hibernating. But other times, we may heed the quiet call of the winter woods with a hike, snowshoe or cross-country ski excursion among these hibernating giants. Check out one of our preserves for your next adventure in Michigan’s winter wonderland!
Barnes, B.V., Zak, D.R., Denton, S.R., and Spurr, S.H. 1980. Forest Ecology. 4th edition, New York: John Wiley & Sons, 1998.
Speer, James H. 2010. The Fundamentals of Tree Ring Research. Tuscon: The University of Arizona Press.
Webinar: Walking in a Winter Wonderland
Watch Bailey Conservation Fellow Catherine Henry explore how trees survive winters during this Facebook live recording.
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Catherine R. Henry, Michael B. Walters, Andrew O. Finley, Gary J. Roloff, Evan J. Farinosi (2021). Complex drivers of sugar maple (Acer saccharum) regeneration reveal challenges to long-term sustainability of managed northern hardwood forests. Forest Ecology and Management, 479 (0378-1127). https://doi.org/10.1016/j.foreco.2020.118541
Catherine Henry and Kate Carter (2021). Communicating Climate Change Content in Small and Mid-Sized Museums: Challenges and Opportunities. Journal of Museum Education, 46(3), 321-333. https://doi.org/10.1080/10598650.2021.1937791