We aren’t called Oakland Township in Oakland County for no reason. For thousands of years, oaks have been a keystone tree sustaining our local habitat and the people who live here. When Europeans arrived in the early 1800’s, they marveled at rolling grasslands filled with wildflowers and large oaks scattered here and there or standing in groves. An article in the Michigan Botanist journal quotes C.F. Hoffman from 1835:
Clumps of the noblest oaks, with not a twig of underwood, extending over a gently undulating grassy surface as far as the eye can reach: here clustered together in a grove of tall stems supporting one broad canopy of interlacing branches, and there rearing their gigantic trunks in solitary grandeur from the plain . . . .C.F. Hoffman 1835
What a vision, eh? If you want a taste of that landscape, visit the restored prairies at Charles Ilsley Park this spring or summer!
I decided I’d better get to know this giant among local plants. I came away impressed! My hope is that what I found will encourage you to take special care of the oaks on your own property – and if you’re without any oaks (heaven forbid!), find a corner for one this year!
What Makes Oaks So Special?
Well, of course, most of the oaks near us are big – which means that they extract huge amounts of carbon from the atmosphere and store it in their bark, branches and roots for years. How many years? White Oaks (Quercus alba), the elders of the plant family here, can keep that carbon stored for 900 years! Doug Tallamy, Professor of Entomology and Wildlife Ecology at the University of Delaware and author of The Nature of Oaks, explains that given the right conditions, oaks have a life cycle of 300 years growing, 300 years in stasis (just living!) and 300 years of decline.
During their long lifetimes, they stabilize the soil around them with huge root systems, producing ten times more biomass underground than they produce above ground! They need those roots to support them for all those long years. Their large canopies and ridged bark prevent erosion by controlling runoff in heavy rains, maintaining nearby watersheds for centuries. Their shade cools the air. Many native trees provide these services of course, but the oaks do it all on a grander scale. And that’s only the beginning of the services they provide to their surroundings.
Oaks Generously Feed the World Around Them
Throughout the centuries, and even after death, oaks literally make life possible for hundreds of species, untold thousands of individual creatures. I’m imagining that what comes first to your mind is acorns. And you’re right, but there’s more to the story.
Acorns and the Creatures that Love ’em
A single oak tree can provide three million acorns in a lifetime which feed a wide range of mammals, bird and insects. Tallamy cites squirrels, deer, mice, possums, rabbits, raccoons and foxes among our local mammals, plus many birds, including turkeys, woodpeckers, nuthatches, titmice, towhees, flickers, even wood ducks! Acorns provide them with protein and fat before and during the cold winter months – just when food is scarce and hungry creatures need to bulk up to cope with frigid temperatures.
Blue Jays and Oaks: A Match Made in Heaven
Oaks have a special friend in the crow family (Corvidae), the jays, including of course, our noisy neighbor, the Blue Jay (Cyanocitta cristata). All over the world wherever oaks shade the ground, some species of jays are planting their acorns far and wide. Our Blue Jays cache them for winter by tapping them into open soil one by one. According to Professor Tallamy, one Blue Jay can bury up to 4,500 acorns a year! Luckily, they only remember the location of about 25% of their acorns. The rest are free to grow into trees, if they germinate or aren’t eaten by other creatures. Jays can carry acorns up to a mile away which means that oaks move out into the landscape faster and farther than other trees. What a great tradeoff – food for the jays, dispersal for the oaks. (Scientists call this “mutualism”)
Oak Strategies for Outfoxing the Fox Squirrels (and other nibblers)
“Mast Years” – Overdoing It With a Purpose
Oaks have evolved a strategy for preventing those plentiful acorn-eaters from gobbling up every acorn. At random intervals, all the oaks in a given location cooperate in producing a giant crop of acorns – more than all those local munchers, like squirrels and deer, could possible eat in a season. It’s called a “mast year.” That way, chances improve for some acorns growing into oak saplings.
The population of acorn consumers increases as well-fed animals produce more young. Ah, but the next year and for several years after, the oaks somehow coordinate again in producing very few acorns, reducing the population of acorn consumers. By doing this together, but unpredictably, the oaks make it impossible for acorn lovers to plan for a mast year. They never know when a good acorn year is coming. And neither do the researchers who have yet to discover how oaks coordinate with other oaks to create a mast year! A mystery, yet to be solved! I love a good mystery…
Fending Off Bud Nibblers – A Yucky Mouthful
You may have noticed that oaks, young oaks especially, keep their dead leaves on their lower limbs until spring. It’s called “marcescence.” One hypothesis is that since oaks evolved with huge, browsing mammals, like mastodons and other megafauna, they needed to protect their tasty, nutritious buds for next year’s growth. That might explain why oak leaves as far as 18 feet up don’t drop in the autumn; that’s about as far as a mastodon could reach! Today’s browsers, like deer and moose, may be put off by a mouthful of distasteful, nutrition-poor dead leaves, just as the mastodons may have been. Or it could be that the dry leaves protect the buds from cold, maintain moisture by holding snow longer or create nutritious leaf litter in spring when most tree growth occurs. Or it may be a combination of all those factors. No one’s quite sure but it’s a distinctive feature of oaks, beeches, hornbeams and a few willows.
But Oaks Sustain Life with an Even More Plentiful Food Source than Acorns!
Oaks provide another much more impactful way of feeding a park, a forest or my yard (which is surrounded by Black Oaks.) It all centers around the creatures that the famous entomologist E.O. Wilson once called “the little things that run the world” – insects! Insects are a basic food group for countless creatures. Stop a second and think of all the creatures around us that eat insects: fish, reptiles, amphibians, spiders, and especially birds!
Some mammals also include insects in their diet, like possums, raccoons, bears, bats, and moles to name a few. Plants eat insects, too. Here are three local species: Sundew (Drosera anglica), Pitcher Plant (Sarracenia purpurea) and Common Bladderwort (Utricularia vulgaris).
Even insects eat other insects! My list includes dragonflies, praying mantises, ladybugs, and crickets, but no doubt there are many more.
Insects also pollinate about 80 to 90 percent of all plants on the earth. What a huge service for life! Without pollinated plants, we’d all go hungry since even human meat-eaters dine on plant-eating creatures. Insects also act as essential decomposers of dead plants and animals.
But what’s just as crucial about insects is their young – those squiggly caterpillars. As the largest class of animals on earth, they feed countless creatures. The massive number of caterpillars in any given area feed a greater number and wider variety of creatures than any other animal that eats plants – more than deer or even elephants!
E.O. Wilson once observed, “If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed 10,000 years ago. If insects were to vanish, the environment would collapse into chaos.” See what he meant when he said they “run the world”?
And What Makes Oaks So Special When It Comes to Insects?
Well, wherever oaks grace the landscape, they are the undisputed champions at housing and feeding caterpillars. They support over 900 species in North America. Here’s just a tiny selection among the more than 500 species that oaks support around here in Michigan. Aren’t they amazing?
We don’t even know most of these small caterpillars exist (at least, I didn’t!), because most of them are so small and live high in the trees. Caterpillars largely eat at night in order to avoid birds and other daytime predators. Many adult moths, which make up a huge percentage of the more than 500 species of lepidoptera (butterflies and moths) in our oaks, pollinate at night as well. No wonder we don’t see them! Their presence generally presents no problem for oaks and the leaf damage is not really noticeable to us from the ground. So even if we don’t see them, they’re up there, along with the young of other insects like katydids, beetles, and praying mantises among many others.
According to Jim McCormac, former field botanist at the Ohio Department of Natural Resources, only a tiny percentage of insect eggs, caterpillars and pupae survive to produce the next generation. The vast majority become food for other creatures. Doug Tallamy uses our friendly Black-capped Chickadees (Poecile atricapillus) to demonstrate the gigantic quantity of insect offspring needed each year.
To feed a clutch of their young, two Chickadee adults must catch 6,000 to 9,000 caterpillars each season to feed their young just while they’re in the nest! Then they feed their fledglings outside the nest for another 21 days. And those numbers don’t include the frozen insect eggs and caterpillars that Chickadees rely on to survive the winter.
Migrating birds flock here each spring because our native trees and plants produce such a flush of nutritious caterpillars. Imagine the numbers of caterpillars required to just feed the birds in your yard. Then imagine the number required in one of our parks, or in a national forest – in every season, all over the country and the world! Insect numbers are in drastic decline worldwide due to insecticides and habitat loss. But we can help by planting and preserving oaks, the trees that host the largest number of caterpillars in their leaves, their bark and their roots – even in their leaf litter!
Most caterpillars native to North America can’t eat the leaves of non-native plants, or if they do, they can’t reach maturity by eating those leaves. They didn’t evolve with plants from far away, so they can’t properly digest the leaves. That’s why native flowers, shrubs and plants are so crucial to preserving life everywhere. Pollinator gardens are wonderful at feeding adult insects, but unless they also have a significant percentage of native plants, even they can be a desert for butterfly offspring.
Would You Consider Planting One? Hmmm?
Now I know what you’re thinking, or at least I think I do. See if I’m right and if I can give you a somewhat acceptable answer.
- You believe that they grow too slowly? They don’t really. The first few years they develop slowly above ground because they’re developing the root system that has to support and feed them for hundreds of years. In one of his presentations (cited below), Tallamy shows yearly photos of a White Oak that he planted from an acorn that grew to 45 feet tall in 20 years with a canopy spread of 30 feet! That’s a lot of cooling shade! Of course, that amount of growth assumes: a) the oak is planted where its roots can grow deep, i.e. no interference from sewer lines, foundations, compacted soil; b) that it’s not fertilized. North American trees grow best on the nutrient poor soils left by glaciation. Weird, eh?
- Looking for a somewhat smaller oak? Yes, we have some! Dwarf Chinkapin Oaks and Pin Oaks might work in your yard here in the township. Across the state and the country, there are other smaller varieties. Ask a native nursery or landscaper.
- You’re worried that they’re expensive? Get the smallest oak sapling you can find. Small oaks won’t have such heavily pruned root systems. Large nursery saplings need to spend many years re-growing their previously cut roots, but a small sapling can establish and start growing right away. Or simply pick up an acorn right after they fall. There’s a section at the back of Tallamy’s book, The Nature of Oaks, called “How to Plant an Oak.”
- Too many leaves? It’s best if you can find a spot where the leaf litter can just be left below the oak tree – no raking or mowing. Leaf litter keeps the soil moist, slowly returns nutrients to the soil and nurtures many moth caterpillars. Some moth caterpillars stick their cocoons to the bark of a branch or trunk. But others drop to the ground, burrow into the soil and pupate there – or spin a cocoon in the fallen leaves to overwinter there. But if leaving fallen oak leaves is impossible in your yard, consider planting ferns, sedges and/or wildflowers beneath your tree. They’ll make for a soft, safe landing for little caterpillars.
- Too many acorns? Remember that mast years occur periodically but not every year. And you can handle the acorns from one or two trees. Oaks in the Red Oak group have mast years less often than White Oaks do. Maybe consider sharing some acorns with neighbors along with planting instructions?
- You’re afraid a tree might fall on your house? If you have room, plant a grove of oaks, or a mix of oaks and other species, so that their roots interconnect and support each other. And by the way, oaks don’t lift sidewalks or driveways because they grow deep enough not to bother hardscape on the surface. The pavers near our black oaks do just fine. Also, don’t panic about old, hollow oaks. Like a pipe, all the strength of any tree is in its outer ring; the interior is softer, dead material. So unless it poses a danger to structures or you often walk beneath it, don’t cut it down. It’ll survive for a long time and continue feeding the habitat around you.
How’d I do? Are you persuaded? If you still have other concerns about planting an oak in your location, consider leaving me a question in the comments and I will try to find an answer.
Protect Your Oaks!
It’s important that you don’t prune your oaks or damage their bark in any way from mid-March to November. Wait until late fall or winter to trim your oak trees, and avoid attaching signs, bird houses, or anything else to your trees. In warmer weather, a deadly, non-native fungus called Oak Wilt can be carried by native beetles that adore the smell of broken oak bark. They can arrive at your damaged tree within 20 minutes! Keep a can of clear shellac around; if damage happens, quickly spray it on the wound. Currently there’s no reliable cure for oak wilt. Trees in the Red Oak group can spread the disease to other oaks through their interconnected roots. We don’t have much oak wilt in our area yet. Let’s keep it that way!
Also be aware that occasional infestations of non-native Spongy/Gypsy Moths (Lymantria dispar) can severely defoliate oaks and other trees. The trees usually survive and re-sprout, even if defoliated for repeated years. But if you’re concerned, here’s Michigan State University’s web page on identifying and dealing with them. Please don’t confuse them with the native silk web caterpillars, Eastern Tent Caterpillars or Fall Web Worms, which cause only minimal damage. Remember, spraying an oak can kill over 500 species!
A Brief Guide to Oak Identification
I’ve only included leaf shapes here. I’m trying to learn bark patterns for winter ID’s but have a long way to go before I master it. Consult a tree ID app or guide book for more complete information. Lots of acorns look very much alike, but I love the distinctive fringed, stocking-cap-look of Bur Oak acorns that make identifying them so easy!
Our oaks fall into two groups, White Oaks and Red Oaks. Here’s a quick look at leaves of the most common species in our area.
The leaves of the White Oak group have rounded lobes. This group includes species such as White Oak, Swamp White Oak, Chinkapin Oak, and Bur Oak. The leaves of Swamp White Oaks and Chinkapin Oaks are slight more pointed but don’t have bristles at the tips like the Red Oak family.
Each lobe on the leaves of the Red Oak group has a sharply pointed tip ending in a bristle. The Red Oak group in our area includes species such as Northern Red Oak, Pin Oak, Red Oak, and Black Oak.
So, What Do You Think? Can You Host an Oak in Your Yard?
I know not everyone can plant an oak, but I’m hoping many of you can. More than any other native tree, the mighty oaks provide life support for the whole, intricate web of life that surrounds each of us. All of our native trees host some native caterpillars; our insects evolved with them after all. But if we want to make a big difference with just one tree, the oak’s our best bet. And just think, it will be standing right where you planted it for hundreds of years after you and I are gone. Such a great legacy to leave for the future!
- Michigan Botanist, 2008, Vol 47 “PRAIRIE AND SAVANNA IN SOUTHERN LOWER MICHIGAN: HISTORY, CLASSIFICATION, ECOLOGY” by Kim Alan Chapman and Richard Brewer. Quote from Hoffman, C.F. (1835). A winter in the west. Michigan History Magazine 9:221–228; 9:413–437 (1925)
- Bringing Nature Home and The Nature of Oaks by Professor Doug Tallamy
- Doug Tallamy’s online presentation for the Washtenaw Conservation District. The first section is an interesting piece on how to help oaks regenerate in forests. Doug’s section on the nature of oaks begins 27 minutes in.