A Year Under an Oak: Freaky Fungal Friends

I explore the fungi underneath the oak and delve deep to understand their relationship with trees.

“In nature, nothing exists alone.”

Rachel Carson, Silent Spring

In the forest, autumn flowers in a strange way. Cool nights and soaking rains trigger a bloom of small parasols among the forest’s crumpled brown leaves. Mushrooms spring up all over and unfurl their gills or spongy undersides for a brief time before melting into a pile of dark, slimy goop on surrounding leaves. The mushrooms seem to appear and then vanish as if by magic (perhaps the origin of the idea of mushrooms being magical). The truth about fungi is less magical yet still very fascinating.

On a rainy day, I took stock of the mushrooms sprouting underneath the white oak tree. I’m admittedly not very good at identifying mushrooms, but I could tell that at least 8 species were now fruiting underneath the oak. The mushroom itself is really a simple spore-delivery service–much like how an apple helps spread seeds. The rest of the fungus that the mushroom belongs to lives underground, in the soil. Fungi require moisture, so life in the soil is perfect, but spreading spores underground is nigh on impossible.

In fact, the soil is filled with life. Moles, mice, chipmunks, and other mammals burrow through the dirt to build underground highways and homes. Some insects, like wasps, ants, and bees build colonies underground and venture out for food. Other insects live most of their lives as larvae in the soil–like beetles, flies, and cicadas–munching on roots or decomposing organisms. Worms, large and small, play out their lives in the soil. The well-known earthworm helps break down decomposing matter and is preyed upon by the ruthless hammerhead worm. Beyond these creatures are microscopic bacteria, rotifers, nematodes, protozoans, and more. Add in the tangled web of roots from trees, ephemeral flowers, mosses, and ferns.

Then there are the fungi, weaving through the roots and spreading thread-like filaments called mycelium into tiny pore spaces of soil clumps. The mycelium of fungi are far thinner and better equipped for tightly packed soils than thick and clumsy tree roots, but mycelia don’t store carbohydrates like tree roots do. So a mutual partnership formed between some soil fungi and their plant neighbors. What plants can make with leaves–energy in the form of carbohydrates–the plants share with fungi. In exchange, fungi share the resources they can access in soil–nitrogen, phosphorus, and other minerals. This symbiosis increases the reach of a tree’s root system with the cost of some of the energy a tree creates from sunlight.

A similar relationship formed between fungi and algae to form what we know of as lichen. Lichen is typically one or more fungi and an alga or cyanobacterium which live as one composite organism. The two, or three, separate organisms are actually inseparable. I often wonder if such a relationship could exist between the white oak tree and its fungal partners in the soil?

The forest fungi here are not just symbiotic partners, some are decomposers. Some forest fungi use enzymes secreted by the tips of the mycelial threads to break down organic matter. Nearby logs also house hungry fungi that work their way into the wood from the outside in. Without these fungi, the forest might be a mess of leaves and branches. No other organisms are quite as capable as fungi of decomposing the forest’s waste products.

As I leave the canopy of the white oak, I noticed a nearly perfect circle of mushrooms. This fairy ring seemed staged, but I could find no evidence of an artist’s hand. Natural fungal growth can take bizarre shapes and sizes. The little ring of mushrooms reminds me that I can still be surprised by the ordinary in a familiar place.

A Year Under an Oak: The Great White Oak

Throughout most of the forested temperate eastern North America Quercus alba, the white oak grows. The white oak is not the tallest, widest, or most handsome tree. Instead, it is robust and adaptable. White oaks in the eastern forests grow to hundreds of years old and often outlive many trees that might grow in their shade, waiting for a canopy opening. I’ve always been fond of the white oak’s habit of growing a wide, open crown, and with age, they become a grizzled old veteran of the changing forest around them.

The forest white oak’s branches spread about 50 feet wide.

The white oak has a light grey bark that flakes and sheds on upper branches and from the trunk. White oak acorns start growing the same season that they reach the ground. A long taproot emerges and anchors the seedling. The first leaves emerge the following spring.

In Schenley Park, there are several white oaks. Though not as numerous as the red oak, they are adaptable to many soil conditions. Some are planted and pruned on green, grassy lawns and others are residents of the more dense forest where close neighbor trees compete for the available light several meters up. This leads to different growth forms depending on the available light.

In the forest, where the bright summer sun comes mostly from overhead, most trees grow fairly straight upward. As they grow taller, lower branches are naturally pruned when taller branches shade them out. A tree won’t waste energy growing a branch full of leaves if there isn’t enough of a benefit to compensate for the growth and maintenance. Tall and rather straight oak trees are the result of years of work to fill in a canopy gap.

A white oak growing on a golf course in the open. This oak’s branches spread about 100 feet.

In an open area a tree has room to grow. This is really where the form, or growing habit, of a tree is obvious. A white oak, for instance, has a round, wide shape. An elm is usually vase-shaped with branches spreading widest at the top. Spruce and fir are typically pyramid-shaped, like the classic Christmas tree. The forest oak will grow taller than the oak in the open, but there isn’t much of a benefit to gaining height in the open area where there is no competition from neighboring trees.

The oak I have chosen to observe is a forest oak. It is tall and slender, not a giant by any means, but it grows in a small grove of seven or eight other white oak trees. This is no monoculture, of course. The trees are threatened by neighboring red oaks, sugar maples, and hickories. These other species are saplings of 10-15 feet, but if enough of a canopy gap is available, they’ll easily shoot up to fill it and become competition for the white oak.

The forest floor is typical for a dry wooded slope. Some grasses are presenting seedheads, white snakeroot is showing glamorous white umbels of flowers, and modestly adorned wood asters are in bloom. Here and there are remnants of the spring wildflowers–the leafed stalks of solomon’s seal take in the last of the summer’s sun.

Despite the bustle of Saturday hikers, bikers, and joggers in the park, I can also hear the rustle of chipmunks and squirrels. Chickadees and titmice chatter in the treetops, skimming insects from leaves and branches. Piles of green acorn husks are a sure sign that summer is waning and the time to prepare for winter is here.

Spring Greening

Humanity is exalted not because we are so far above other living creatures, but because knowing them well elevates the very concept of life.
— Edward O. Wilson, Biophilia

It’s May already.  I feel like the last few months of winter and the first of Spring blend and meld and then suddenly it’s ninety degrees Fahrenheit and everything is green.  I have been busy and all together not so busy–work and life and dirty dishes.  I still walk through nature often enough. Continue reading “Spring Greening”

Becoming a Naturalist

I only went out for a walk, and finally concluded to stay out till sundown, for going out, I found, was really going in.
–John Muir

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As a youth I had a dream of becoming an astronaut.  I even made a T-shirt with the space shuttle on it using acrylic paint–I wanted to be the first man on Mars.  I grew up more in high school and thought that I wanted to be a Jack Kerouac or a Christopher McCandless. Continue reading “Becoming a Naturalist”