A lot going on, even when you’re not thinking about it

Dr. Wendy Sue Universe

Dr. Universe,

Why do trees grow so slow?

— Ana, 7, Covert, Mich.

When you eat food, you get a lot of important nutrients that help you grow. The trees that live on our planet also need some nutrients to grow.

Trees use their leaves to help capture energy from the sun to make their own food. But as you may have noticed, a lot of trees lose their leaves during certain times of the year.

Without leaves, they can’t make nearly as much food, and without those important nutrients, they can’t grow very fast.

That’s what I found out from my friend Tim Kohlhauff, a certified arborist and urban horticulture coordinator at Washington State University. He is very curious about the lives of trees.“These trees only get to make food part of the year,” he said.

Usually, we see slower growth in these trees between March and October. Of course, maybe you are thinking about the kind of trees that do not lose their leaves, like pine trees or evergreens. When it is really hot or really cold out, these trees will also experience slower growth. They may be trying to save energy and make it through tough times.

For instance, in the redwood forests of California where some of the tallest trees on our planet live, a redwood tree might grow two or three feet a year. But if the trees are stressed or don’t have water and sunlight, they might grow just an inch per year. Trees are pretty good at adapting to changes in their environment.

Not unlike humans, a lot of trees that live in forests grow faster in their younger years, too. In the forest, it can be a bit of a race to the top. There is a lot of competition between trees to grow tall so that they can get enough sunlight. After all, that sunlight is where they get energy to make their food.

While most humans don’t grow much taller after they reach ages 18 or 20, some trees can grow for up to 100 or 200 years. One slow-growing tree is the magnolia tree, which can reach heights of about 60 to 80 feet and sometimes even 100 feet tall. These trees can grow about one foot — the length of a ruler — a year.

Meanwhile, some trees will grow slowly but may never get very big. Dogwood trees only reach about 15 to 20 feet tall and grow about a foot a year.

Some trees may grow slowly, but they don’t grow forever. At a certain point, they stop growing taller and start growing wider. Not only does the trunk itself get wider, but the branches also grow out around the tree to form its canopy.

We are still learning a lot about how thousands of species of trees on our planet grow. One thing we do know is that at least for some trees, growing slow and steady is just the right pace.

Have a science question? Ask Dr. Wendy Sue Universe, WSU’s resident science cat and writer, by email at Dr.Universe@wsu.edu, on her website at askDrUniverse.wsu.edu, via Twitter at @AskDrUniverse or at facebook.com/AskDrUniverse.

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