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).
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.