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.