Bur oaks in winter

Bur oaks in winter

By Rod Myers

By Rod Myers

Without its chlorophyll clothing, a bur oak tree (Quercus macrocarpa) in winter cannot hide its unique form. Its thick, twisted, arthritic-looking branches make it easy to spot. A good place to see one is out in the middle of a farm field. When you find one, odds are it’s a lone tree, and it was probably spared the ax because the farmer used it for precious shade during hot work days gone by, although bur oaks are not the best of shade trees.

Before white farmers worked the land, a lone bur oak tree smacked of prairie. Both bur oaks and prairies were products of fire. Fires regenerated prairies by destroying competition, thatch, and returning nutrients to the soil. If a bur oak acorn sprouted, then avoided being burned for 15 or 20 years, it may have been big enough to survive when the prairie fires returned. At this point, the leaves are high enough off the ground, and a cork-like material under the bark makes the tree fireproof if the fire is not too intense. After the tree is big enough to withstand fires, the fire becomes its ally by killing its competition and feeding its roots with nutritionally packed prairie ashes.

Bur oaks love glacial alluvial prairie-enriched hill soil. Have you ever ridden a sled down a hill dotted with bare bur oaks? We called it Dodge Bur, and you had to steer carefully lest your blood would feed the big roots when the snows melted.

Speaking of melted snow, bur oaks south of North America’s glaciated areas grow in the rich soil of flood plains. Kentucky’s flood plain bur oaks are the biggest. Missouri’s are slightly smaller, but these have a 2 1/2-inch acorn that will dent your sled helmet. This flood plain sprouting tree is a subspecies of our area’s bur oak, and its range spreads all the way to Texas. And remember, don’t take your sled helmet off when you’re resting on the flood plain beneath the steep hill.

If you can get close enough to a naked bur oak, notice the fine gray hairs on the thickish leaf-bearing twigs. The hairs reduce the tree’s moisture loss. Canescens is a name given to the gray hairs, and it means “wolflike.” The leaf-bearing twigs are not as thick in number in the crown area, but others of this type reside on the big interior branches and even on the trunk. Because the canopy is less thick, it lets in more light, allowing the leaves on the inner branches and trunk to photosynthesize. This allows maximum use of light, making the bur oak a shade tree of a lesser God, but a gardener will choose the bur oak to plant under because of the light that reaches the ground. Even a minority of prairie plants will grow under bur oaks, and you know how much prairie plants love the sun.

Go out and find a big bur oak after the next snowstorm. You’ll find the arthritic-looking branch design reduces snow and ice accumulation, thus preventing portions of the tree from breaking from too much weight. Lowered wind resistance is another plus for the haunting shape of the tree’s branches, reducing wind damage.

The bur oak is the genius result of evolution, and my little article is not worthy of such a bio giant. As such, I am ending my words with a little lighthearted ethereality. There’s a very old two-acre bur oak hill forest in southern Wisconsin, and because the branches are shaped as they are, the forest looks very haunted without leaves. Every January, a pair of great horned owls take over an old hawk’s nest to start a late-winter family in the forest. In the cold of winter, the owls believe their hoots to be the scariest sounds of this haunted woods. However, the owls pale compared to the subtle creaks, groans, squeals and moans of thick bur oak branches dirty dancing in a strong, gusty wind without one stitch—not even a stem—of chlorophyll clothing.

Rod Myers is a local resident with an interest in nature and the environment. He is a member of the Rockford Amateur Astronomers Club, the Sinnissippi Audubon Society, Wild Ones Natural Landscapers and the Planetary Society.

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