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by Michael Harrison 8 days ago in Science / Nature / Climate
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The science of overwintering as a tree!

Photo by Ian Schneider on Unsplash

I woke up this morning with the terrified realization that I had left pop cans in the garage. So is the woe of the wintery Minnesotan. For those of you who have lived in warmer climates all your lives, you might not realize this, but when cans freeze in your garage in the winter, they often times will explode, leaving a caffeinated, carbonated mess. My mind then took a sharp left, and started thinking about our loveable friends, trees. Deciduous trees (oaks, maples, things that don't have needles for leaves) all look dead and desolate over the winter, but we know they are simply dormant waiting for spring.

Why do freezing pop cans make me think of trees? Inside of trees, there is something called the xylem and the phleom. Think of them like the veins of a tree. The flow inside these veins is water based, meaning a majority of stuff in there is water! This water is prone to freezing in the winter, which provides a slew of problems for the trees. First it slows the flow of minerals and energy (that is why they go to sleep for months on end), and second, it causes the tree to expand. This is where the similarities between pop cans and trees come into play. Water expands when it freezes. In an enclosed space, there is no room for growing, or at least a very limited amount of space. As the water freezes, the space is filled in, and this can lead to things breaking, whether that is an aluminum can or a tree growing in the woods. This brings us to something I had learned a few years ago that ends up explaining a few phenomena that happen with trees. The first is sap flowing, and the second is the "lightning strike" effect.

What is sap exactly? Most of us know about it because it gives us that delicious syrup that so many of us love with our breakfast. Sap is actually a response to a wound on the tree. This is why the sap nozzles work the way they do. They are inserted into the tree, and then the sap emerges through the opening, giving the tree an easy route for the sap to flow. N0w, the reason that maple syrup season is in the spring. The oscillating temperatures are the reason for the season! As the temperatures go from warm to cold and cold to warm, the pressure inside the tree changes. As this pressure increases (when the temperature warms up, and the water inside thaws) the sap flows from the tree. So next spring, make sure to appreciate this change in temperatures since it lets us enjoy delicious maple flavors.

While I love syrup, and talking about sap flow, that is not the real reason I thought of trees freezing today. How many of you have seen a lightning strike on a tree? Most times when people see these cracks, they are not actually from lightning. They are from something called frost cracks! Frost cracks happen when the water inside a tree freezes too quickly for the tree to adjust, and snap, crackle, and POP! The bark will often crack and the actual trunk of the tree will as well. It will look like a long rift along the tree often times. It can be a small crack, or I have seen some trees where it stretches along the entire trunk, from bottom to top. Remember when I told you about water expanding, just a little bit ago? This is what causes it. That water in the trunk expanding, the tree then breaks open!

How can you tell the difference between a lightning strike and a frost crack? Well I am glad you asked. Lightning strikes will often leave a part of the tree with some "burnt" looking bark. Most times when lightning strikes hit trees, it leaves them looking much more destroyed, broken, shattered. Often I describe it as looking more rough or frayed, where as frost cracks will look more solid. Frost cracks also will be almost always vertical, as they follow the flow of water through the trunk. Lightning strikes do what they want, in a matter of speaking. What they want to do is to get to the ground, so they will follow the path of least resistance. Really it doesn't make as much of a difference if you are right or wrong about identifying the difference, its mostly just for fun! It is really just exciting to know about another phenomena that occurs in trees.

Coniferous trees! They are some of my absolute favorite trees, from their pine trees to their needles and leaves. When you picture them, what do you picture? I think of snow covered pines, frosty mornings, and red squirrels (that is another story, for another time). Water is a vital part of all life, and vital for all plants. The major task of plants is mitigating water loss, and conifers use a cool trick! This is where their needles come into play. You may notice that they never lose their leaves, thus granting the nickname evergreen trees. The needles are designed specifically for limiting water loss to the environment by their shape, and by a special covering that gives them their waxy feel. These are efficient enough for conifer trees to avoid shedding their leaves in the winter, unlike their deciduous cousins. They can also regulate some of this hydrostatic pressure by some water flow from snow in the winter. (a very simplified way of describing it, but essentially how it works).

Trees are awesome for many reasons, but I think their adaptability and ability to survive in different weather ranges is amazing. I hope you enjoyed learning something about these trees, and make sure you go and check on those cans in the garage, don't let them frost crack all over your house!

Stay adventurous, stay curious, stay wild!


About the author

Michael Harrison

Adventurer and nature enthusiast. Aspiring children's book author, novelist, and poet. Perpetual dreamer. My thoughts and ramblings are lost within the multitudes of notebooks I purchase and I don't have any hesitation in adding one more.

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