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Outdoors with Coggin Heeringa: Shady secrets and sunlit trees

Trees in a forest.

Coggin Heeringa explores the intricate relationship between sunlight and trees — from shady forests to sun-drenched yards — revealing their remarkable ability to adjust like nature's own blinds.

Singer-songwriter John Denver was in Minnesota on what he called a “dreary day, gray and slushy" in late winter, when he wrote, “Sunshine on My Shoulder.” Anyone who lives in the Upper Midwest, especially after an extremely cloudy winter, will understand why sunshine would make one happy.

Now in July, for people who live “up north,” bundled up for ten months out of the year, sunshine on their shoulders may very well give them sunburn.

Same goes for the trees, especially some of our evergreen species. They can experience tissue damage from prolonged exposure to sunlight. Arborvitae—also called white cedar—probably should get sunburned when it grows in the open, but it doesn’t.

According to the reference books, arborvitae grows in swamps or cool, shady forests. In these sites, their needles, which are oval scales arranged in branching sprays, are a rich green—almost a blue-green. The branchlets grow horizontally so that the needles can collect as much sunlight as possible.

Wind Swept Tree on Georgian Bay, a Group Of Seven inspiration.
DarleneMunro/Getty Images/iStockphoto
Wind Swept Tree on Georgian Bay, a Group Of Seven inspiration.

But in some places, arborvitae grow in direct sunlight. As an ornamental plantings in a front yard or on, say, a sand dune, arborvitae get far more sunshine than they really need.

Obviously trees don’t wander into a shady woods on a hot day. But they can readjust their branch orientation in much the same way we can adjust window blinds. By turning their branches at certain angles to the ground, trees can decrease the amount of sunlight that hits the foliage.

Several kinds of evergreens adjust their branches or needles on the beastly hot, sunny days of summer. Curiously, in much the same way, they twist their foliage in winter because sunlight reflected by snow also can give trees a sunburn.

So, although “sunlight on the water looks so lovely,” if you aren’t used to being out in the summer sun, when you go to the lake, you might want to adjust that beach umbrella, or slather on some sunscreen.

"Outdoors with Coggin Heeringa" can be heard every Wednesday on Classical IPR.