By Michael Caduto
From appreciating their beauty and form to understanding their role in storing and sequestering carbon to mitigate climate change—trees are having their moment. Here in the Green Mountains, much of the attention goes to Vermont’s State Tree; our arboreal rock star, the sugar maple. According to iNaturalist.org, however, there are some 75 species of tree found in Vermont, ranging from tulip to black gum, and from silver maple to eastern hemlock. Among these, red oak is one of the more common, less-heralded and ecologically significant trees.
Back in the mid-1970’s, I conducted a botanical study of the hybridization between red and black oaks in the Foster Tract of the Audubon Society of Rhode Island’s George Parker Woodland. During one particular springtime field trip, when the oaks were in full bloom, I stopped to eat lunch in a mixed stand of white pines and oaks that stood 60-70 feet tall. Wanting to see the oak flowers first-hand, I found a pine with low-hanging branches and began to climb.
After some long minutes of climbing, during which I contorted my body to wriggle through the thick, uneven limbs, my head rose up into another world. The crowns of pine and oak intermingled and gently danced to a moderate breeze. As it turned out, the topmost leader of the pine I climbed had been broken off some decades ago, and the wound had healed over entirely with a smooth layer of bark sporting a small depression shaped like a saddle. I climbed onto the bark seat, locked my legs into the branches on either side and rode the top of the swaying pine like a sailor minding the crow’s nest of a schooner, rocking in a sea of green tree flowers. I was reminded of the kinship between the sound of a breeze through the branches and waves gently breaking on the seashore.
Another sound was in the air; thousands of insects buzzed from flower-to-flower amid the oaks, gathering an early harvest of spring pollen, including many small wasps, some wasp-like tachinid flies and hundreds of honeybees. What would the world in the treetops look like through the multi-faceted eyes of a wasp or bee—viewed through those mosaicked windowpanes and interpreted by the ganglia of an insect’s intelligence?
That wing-born symphony of six-leggeds hummed the notes of my epiphany. From nature walks to natural history books and botany classes, I had been taught that our early tree flowers—including oaks, maples, birches and hickories—were wind-pollinated. And while wind may be their chief means of pollination, insects obviously played a vital role. The acorns that speckle the ground each autumn—a promise for the next generation of oaks and means of winter survival for a multitude of squirrels and mice—owe their existence to the wind and the ravenous vernal appetites of airborne insects.
While it is not as celebrated as the sugar maple, the red oak, Quercus rubra, is one New England’s most abundant and stalwart trees. Mature individuals rise on graceful arching trunks, sheathed in bark sporting long ridges that intertwine like ski trails running down a mountain slope. In springtime, each individual tree is festooned with dangling male catkins whose pollen fertilizes minute female flowers that take two years to mature into large, classic, glossy acorns with shallow cups—a favorite food of everything from squirrels to chipmunks, white-footed mice, raccoons, white-tailed deer and black bears. On hot summer days, the red oak’s broad, thick, bristle-tipped leaves cast a deep, cool shade. When autumn arrives, the leaves turn a rich crimson or golden-yellow.
Roots intermingle with beneficial fungi in the soil where roughly half the biomass of each red oak resides. Roots can even discern whether fungi are hurtful, or helpful. Detrimental fungi are attacked as soon as they invade root tissues. But when the root senses a beneficial mycorrhizal fungus, the plant suppresses its counterattack and allows the fungal threads to penetrate and absorb carbohydrates from the tree. The reciprocal aspect of this relationship occurs as the strands of the mycorrhizal fungus expand the root’s ability to absorb water and mineral nutrients from the soil. A tree whose roots are associated with mycorrhizal fungi is more vigorous; it can better withstand the vicissitudes of drought and disease.
One mycorrhizal fungus—whose growing soil strands, or hyphae, intermingle with the roots of oak trees—produces the agaric mushroom, Lactarius camphoratus. The small, reddish-brown fruiting bodies of this fungus are 2-inch tall mushrooms that smell like maple syrup or burned sugar.
In a mature forest ecosystem, oaks and other species of tree are joined underground by a woody web of roots that become grafted together as they grow in contact with one another. This intertwining system of roots weaves together with the vast symbiotic network of mycorrhizal fungi. In this way, a forest evolves into one giant organism. Although our own arboreal experience is largely confined to the parts of individual trees that grow above the soil horizon, the expansive web of life that permeates the cool, moist subterranean world is one of the most important symbiotic relationships that any given tree has with other living things.
Red oak leaves. Photo: Michael J. Caduto.
WHAT YOU CAN DO: Explore trees and their ecological roles in such books as Finding the Mother Tree: Discovering the Wisdom of the Forest by Suzanne Simard and The Hidden Life of Trees: What They Feel, How They Communicate by Peter Wohlleben.
