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.

A Year Under an Oak: The Start and End of an Acorn

The little patch of forest in Schenley Park has been aging. Years of relatively easy growing conditions have allowed some of the city park’s oaks, maples, and beeches to grow immensely large and heavy-branched. A summer of windstorms, heavy rain, and periodic drought has taken down a few of the giants.

A three-foot-wide tree trunk recently blocked my path home, its full crown of branches blocking another trail across a stream. The red oak lay prostrate with a summer’s worth of fresh green leaves, still full of life but impossible to mend. The tree wasn’t the only casualty, however, because on the hillside where it grew was a rich ecosystem woven in its branches and tangled in its roots. Now those organisms must find some way to carry on without the red oak.

No tree exists alone, even if it grows as a standout specimen in a grassy lawn. Instead, a tree is first part of the soil that it lives in. Most oaks start out life by burying a taproot in soil. The taproot seeks out water and nutrients, but it encounters other organisms in the soil. Fungal threads called mycellium fan out through the soil while burrowing mammals like mice, voles, shrews, and moles seek out buried insects, roots, and seeds.

The tree is also part of the forest floor just above the soil. The canopy of the red oak offered shade from the blistering summer sun. Shade might damper the growth of many plants, but some prefer the moist soil under an oak. The tree also offers an annual blanket of leaves which protects dormant animals and plants from the cold of winter.

The tree is finally a part of the forest canopy. When given the opportunity, usually in the form of a canopy opening, a tree reaches up toward available light. At its full height, the tree can spread branches and fill a canopy gap in the forest. The leaves several meters in the air are not safe from all harm, however. An army of caterpillars–joined by aphids and other insects–find the green forest roof irresistible. Luckily for the trees, a fleet of birds and parasitic wasps hunt the caterpillars and other leaf browsers.

Of the trees in Schenley Park, oaks are dominant. Northern Red Oak is the most widespread and White Oak takes up a few stands among them. Also common are red maple, sugar maple, basswood, beech, and tuliptree. The changing forest dynamic will promote the growth of maples, beech, and basswood in some parts of the forest. Other parts may see the rise of hemlock, while still other areas may become dominant in oak. The mosaic of trees within the forest is ever-changing as the older, larger trees age out and younger trees take their place (as in the case of the recently fallen red oak).

Grey squirrels are seed predators, particularly for acorns and hickory nuts.

In order to better understand the changing forest–and the existing forest community–I’ve selected a small area in and around a mature white oak to examine. I want to visit this oak to explore the surrounding community of organisms as a representation of the forest. What I find likely won’t be a perfect slice of life from this ecosystem. For one, I’ll be within the city limits where this park was, generations ago, a cleared field for crops. I’ll also still be within a heavily human-influenced area–roads, trails, a golf course, human dwellings, and businesses all within a 1/2 mile radius. Despite the settings, the forest here still changes and grows and adapts through seasons, age, and with the influence of man.

Dame’s Rocket – Species Highlight

A new species highlight on dame’s rocket, one of the prettiest invasive species out there.

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A patch of dame’s rocket in North Park, Allegheny County, PA.

From May to July, the roadsides in my area are often graced with pinkish, purple, and white clusters of flowers.  The showy display is a sure sign of the coming summer.  The dame’s rocket (Hesperis matronalis) is responsible for these splashes of color. Continue reading “Dame’s Rocket – Species Highlight”

Snow Drops

Sixty degree weather in February has created some unique opportunities for me this year.  While it’s not quite late enough for much of anything to be growing or flowering, there are some typical early bloomers that appear almost out of place without a blanket of snow on the ground and nippy air on the nose. Continue reading “Snow Drops”

Trout Lily and Bloodroot

I decided recently to take a walk in an unfamiliar place and it paid off!  If you are tired of browsing through your local park try looking at conservancy or land trust properties.  The places I visited were less crowded and garden-like.

New Growth

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Spring Crocus (Crocus vernus) with a honeybee (Apis mellifera)

 

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Common chickweed (Stellaria media)–a common garden weed

I’ve been venturing out here and there throughout the past couple weeks Continue reading “New Growth”

Spring Wildflowers at Irwin Run

May 16 2015 190

 

In nature nothing exists alone.
     –Rachel Carson, Silent Spring

 

 

 

I park my car near a small lake in the local park and decide that I will follow a stream–Irwin Run. Continue reading “Spring Wildflowers at Irwin Run”