Written by Jon Secaur, Portage County Master Gardener Volunteers
In The Wizard of Oz, the Cowardly Lion sings, “If I were the King of the Forressst!” Move over, Mr. Lion, we already have a king of the forests in Eastern North America, and it’s the oak! Ironic, isn’t it, that the largest trees are spelled with such a short name?
The massive trunk that supports those great limbs also supports the greatest number of life-forms. Nearly 900 species of insects lay eggs in and around oak trees, and the caterpillars they produce are prime food sources for baby birds. Entomologist and author Douglas Tallamy calls caterpillars “re-purposed leaves that can walk,” and they fuel the food web that oaks maintain.
Many birds and small mammals feed on the copious supply of acorns that oaks drop — three million in a tree’s lifetime — and they provide a good balance of protein, carbohydrates, and fat. A tiny worm called an acorn weevil infects some acorns, giving animals that eat those acorns an extra treat! Occasionally, and no one knows how or why, trees in a region will drop an unusually large number of acorns in what is called a mast year. How do hundreds or thousands of oaks, many miles apart, all dramatically overproduce acorns, seemingly on cue?
Besides hosting caterpillars and producing acorns, large oaks also annually drop hundreds of thousands of tough, leathery leaves that provide cover for millions of organisms to overwinter and live among the leaves. Fastidious gardeners dislike oak leaves because they decompose so slowly, the very attribute that makes them so valuable to the web of life that oaks support. Renowned ecologist Doug Tallamy urges gardeners to leave the leaves, seeing them as “priceless litter,” not something to shred, discard, or burn.
“The diversity and abundance of the little creatures that reside in the leaf litter that accumulates beneath an oak is astounding,” Tallamy writes in his book, The Nature of Oaks, “and easily exceeds counts in the millions.”
The deep roots of oaks bring water near the surface, and because they tend to go straight down and not off to the side, oaks can be planted near sidewalks and driveways without lifting the concrete. Because oaks are the kings in supporting a web of life, they are considered keystone species; without them, the ecosystem falls. As Tallamy writes, in short: “A yard without oaks is a yard meeting only a fraction of its life-support potential.”
About 435 species of oaks have been identified world-wide, and more than 90 are native to North America. Northeast Ohio hosts approximately 10 species, with more in the woodlands of Kentucky and Tennessee. Vast areas of the Great Plains and Rockies have no oaks at all, with a few species in southern Arizona and through central California.
Most of the oaks fall into two families, distinguished by the shapes of their leaves. Most are deeply lobed, and those with sharp points between the lobes belong to the red oak family, including the most common red oak, the black oak, the pin oak, and others. Leaves with rounded lobes comprise the white oak family, with the white oak, the bur oak, the chinquapin oak, and others. That’s a rough guide to the oaks found around here; many oaks have no lobes at all, but they tend to grow much farther south.
Oaks may be mighty, but they can be brought low by several tiny pathogens. The most serious causes oak wilt, a fungal infection that can kill the red oak family in a season. White oaks are more tolerant, making them simply slower to die. The agent is a fungus, Bretziella fagacearum, that clogs the sapwood fibers that carry water up the tree, blocking the flow and killing the tree from the top, down. In red oaks, especially, the internal water pressure can actually blast away a patch of bark, leaving a brown fungal mat.
The disease can be spread through the adjoining roots of trees, something that a homeowner cannot control, though if you own woods with red oaks close together, trenching to cut off roots deep below ground level can prevent new infections — a task best left to experts. However, oak wilt spreads most commonly from sap-eating beetles carrying spores from infected trees. The simple way that we can all reduce oak wilt is never to trim or prune an oak during the months that the beetles are active, April through October. The sap from a fresh wound on a healthy tree during that time attracts the beetles, possibly infecting the tree. If you must trim an oak between April and October — for example, if a storm brings down a limb — then paint the wound with latex paint. That slows the healing process, which is bad, but more importantly it seals the wound from nosy beetles, which is good!
Last year, when I had one of those ‘significant’ birthdays, I lobbied my family to plant a white oak in our yard. I liked the idea of planting a tree that would far outlive me. But closer research showed that mature white oaks produce large acorns that deer just love, and the last thing I would wish on future owners of my home is more deer! I opted, instead, for a serviceberry, a tree that is already blooming and will keep many birds happy this summer with juicy berries.
Enjoy oaks! Plant them for posterity. Respect their key role in supporting the greatest number of other critters of all sizes. And do your part in protecting them by delaying all pruning or trimming to late fall and winter — a good excuse to just sit or lie under one on a hot summer day!
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