Giants Among Us: Why Oaks Still Rule Our Forests and Our Future

This is an account of a forgetful blue jay and an acorn. It’s a funny sort of relationship, but the two have been together for the past 56 million years, when they emerged together from the Pleistocene ooze in what is now the Arctic.

That bond is important if you live in Dutchess or Columbia County and have wondered why there are so many oak trees in our forests. Oaks—their mysteries, their resilience, and the vibrant role they play in Northeastern ecosystems—were the subject of a recent presentation by Doug Tallamy at the Cary Institute of Ecosystem Studies. Our magnificent locusts and sycamores have their fans, I know, but this story concerns itself with the genus Quercus.

North America hosts 91 species of oak tree. New York alone has 16 species. According to a local ecologist, Dr. Charlie Canham of the Cary Institute, “red oaks (Quercus rubra) and white oaks have been the dominant species for nearly 10,000 years in Dutchess County and the Hudson Highlands. We know this from the pollen we dredge up from the bottom of local lakes.”

Oaks are found in nearly every ecosystem in America and are honored by humans in every one of those habitats.

That’s because oaks are awesome productivity machines, supporting a vast, interconnected web of wildlife. “Most people don’t know what’s happening in and around their oaks,” said Tallamy, an entomologist. “But they are the bread and butter of nature’s food web around here.”

A single mature oak can support more than 2,300 species, including some that would not survive without the tree, said Tallamy. These species use the tree for feeding, breeding and winter shelter. That makes them a keystone species—a plant that if it were to be removed, the entire food web would collapse.

Tallamy has a new book out on the manifold benefits of oaks. It’s called “The Nature of Oaks; The rich ecology of our most essential native trees.” He organized the book into a month-by-month guide to life around oaks. In springtime, the tree’s flowers support multiple colonies of pollinators, including bees, butterflies and hundreds of species of caterpillars with extravagant shapes and even more extravagant names — the unicorn caterpillar, the purple crested slug, the confused wood grain caterpillar, the skipmoth, the two-spotted oak punky, and more. June is cicada month. On July nights, the katydids lay their eggs on oak branches. In September, walking sticks come down off the canopies of oaks and promenade invisibly in our gardens. In October, radiantly colored wood ducks dive in our local ponds for acorns to fuel their migration south.

A single oak can produce three million acorns in its lifetime. This windfall is a key source of nutrition for hundreds of species — from fence lizards to bears, as well as animals you wouldn’t expect to benefit or may not even have heard of.

Clearly this is a tree with a deep resume.

There’s more. With their enormous size, oaks sequester more CO₂ than other trees, and because they have the most extensive root system of all local trees, they stabilize the soil. Their abundant leaf litter promotes a healthy water supply and overwinter habitat for thousands of moth and butterfly larvae.

The older the oak, the more life it is able to support. Cracks and crevices in the remaining ancient trees offer habitat for an astonishing array of creatures.

Why the biggest oaks are in fields

Many of the biggest oaks in our area are found on former fields, such as the champion burr oak near the intersection of Routes 82 and 199 that boasts a circumference of 25 feet. “Farmers never cut them down,” said Dr. Canham. “The livestock liked the shade and also ate the acorns.”

But in terms of mutualism, nothing matches oaks and blue jays. “It’s simple,” said Tallamy. “Oaks and jays really like each other.”

Jays store acorns by burying them strategically in various places around Dutchess and Columbia forests in order to eat them later. It’s a key component of their winter survival strategy. Typically the jays select only the biggest and healthiest acorns. If a jay thinks another jay has seen it bury an acorn, it will dig it up and rebury it in private. A single jay can bury 450 acorns a year.

The problem is, jays are forgetful. “They only remember where one in every four of the acorns they buried are,” said Tallamy. The forgotten acorns go on to produce many of the healthy trees we see in Dutchess and Columbia County forests. “It turns out blue jays know how to plant oaks better than we do,” said Tallamy.

Tallamy’s talk might as well have been titled “The tree of legend” for the many roles, mysteries and misunderstandings associated with the oak. Like other majestic symbols of nature, oaks have sparked more than their share of legends. The Norse god Thor trusted an acorn to grow his tree of life. Because oaks everywhere tend to be struck by lightning, Greek, Roman and Celtic mythologies associated the oak with Zeus, Jupiter and other gods of sky and thunder.

All year round, I have stared at the great pin oak in my backyard and never imagined the scale of its productivity. By comparison, we humans are slackers.

In the Middle Ages, most important books, including the Bible, were written with ink from abnormal growths on oak trees called galls that are created by gall wasps to nurture their larvae. You can find these galls with the ink inside them on Dutchess and Columbia oaks.

Oaks do not drop all their leaves in the winter, a relatively rare phenomenon called marcescence. Scientists are unsure why this is, but the prevailing theory is that the hard, bitter leaves that remain on the lower branches protect the tree from deer and other browsers from grazing on the high-nutrient young buds in the spring.

Tallamy, who admits to being “slightly obsessed” about oaks, takes the theory a step further. “In the Pleistocene, the mammoths, rhinos and giant sloths that roamed around here could reach up to 18 feet high on a tree,” he said. “That may be why most of the remaining leaves on an oak only go up 18 feet, and the top of the tree is bare.”

Oaks harbor other mysteries: Why do we see chickadees, titmice, kinglets and other birds browsing on a bare oak tree in February? “It turns out they are feeding on caterpillars on our oaks,” said Tallamy. “They are so well camouflaged we can’t see them.” In this way, oaks benefit creatures even in the dormant season.

People who work with oaks speak of them with reverence. “They really are our most majestic tree,” said Canham, who builds wooden boats and uses oak for the keels and frames. “It’s a beautiful wood to work with. And if you like wine or whiskey, you like white oaks because that’s what the barrels are made of.”

Oaks grow slowly for the first year or two. That’s because they put all their energy in growing root biomass rather than leaf biomass, said Tallamy.

In time, they become some of North America’s longest lived species. “They have 300 years of growth, 300 years of stasis, and 300 years of decline,” said Tallamy.

In the mountains of Riverside County, Calif., scientists recently identified some Palmer’s oaks that are nearly 18,000 years old. That makes Palmer’s, which survive by cloning themselves, among the oldest plants on earth. It also means these living oaks were already mature trees when mammoths and saber tooth tigers roamed the land.

Today, oaks, like so many species, are in trouble. “A biodiversity crisis is underway,” said Tallamy, who is in agreement with most scientists that the planet is in the midst of a mass extinction. Oaks are not immune. Twenty-eight out of America’s 91 native oak species are now threatened, Tallamy said. “They are not disappearing on their own,” he said. “We are killing them. Most of the old giants are already gone.” He named several culprits, including the overabundance of deer who feast on oak sprouts, prolonged droughts driven by climate change, spongy moths, and a disease called oak wilt.

The solution? Plant more oaks.

Tallamy has set himself a mission to dispel negative myths about oaks. “There are lots of excuses why people don’t plant them,” he said. Oaks grow too slowly. They can crush a house, they lift up your driveway, they create messy leaf litter — all exaggerated or untrue, he said.

Asked why he was moved to write a book about a tree, Tallamy said: “I wanted to provide a little knowledge, because knowledge generates interest, and interest generates compassion, and hopefully, compassion generates action. And we need a lot of action for the environment.”

“We can’t return the great giant oaks in our lifetimes,” he said. “But we can start the process. Plant an oak, and in a few years it will assume its role as a keystone species.”

“So plant an oak. Plant a living community.”