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”

The Herbarium: Mounting

October 2, 2017

Dr. J,

Last week, I continued to sort through various Polygonaceae family members.  I ran across several from arctic regions including Koenigia islandica, whose name suggests a warmer climate than the Alaskan archipelago where it is native.  Another, Oxyria digyna, is a unique little plant that can be found both in the arctic regions of the north and in alpine habitats further south.  This makes sense as the two habitats are similar, yet the plant can be seen exhibiting different growth forms between the two habitats.  Arctic plants are more likely to reproduce asexually and alpine plants tend to produce more seed.  Perhaps this difference is related to the number of pollinators available in Arctic vs. alpine regions in California and Colorado.

I met one of the mounters on Thursday.  Bonnie walked me down to the lower herbarium—the collection is kept in two rooms on two separate floors—to meet Helen and witness the mounting process.  Helen stood at a table with a paintbrush in her hand hunched over a specimen sheet.  An AM/FM radio tuned to WQED station was blasting classic music just loud enough to disturb the neighbors (if they were any).  Helen is an 85-year old retired jeweler and has been working with the herbarium for many years.  A flat school lunch tray held a pool of diluted Elmer’s glue which Helen dabbed onto thin strips of adhesive paper.  These strips held the pressed plant to the specimen paper.  She also dabbed some glue on loose ends of the plant and pressed these against the paper.  Helen is meticulous.  She carefully glues down every bit of plant so that a strong gust of wind would fail to loosen even a leaf.  She showed me the appropriate way to lay the leaves—so that at least one leaf underside would show.  Her attention to detail as well as the pace at which she worked were impressive.

Helen told me that she got her start as a volunteer and that eventually she was asked to work for pay a few days per week at the museum.  The mounting process seemed fairly straightforward, but it does require a certain level of diligence.  Helen would take the loose bits of leaf, stem, and seed that were dislodged from the specimen and pack them into a miniature envelope.  The envelope was then attached to the appropriate specimen paper.  Helen remarked that saving these small pieces is important.  Her dedication to the herbarium is something that I admire.

Having volunteers and personnel with particular skills, such as Helen, is important to institutions like the museum and herbarium.  Helen may not have the skills required to collect and identify specimens, but she can provide for the herbarium by mounting collected specimens.  After sifting through specimens that she may have mounted, I’m glad that I had the chance to meet Helen and witness her skills in use.

Regards,
Aaron

Postscript:  Helen’s technique is commonly seen in many of the specimens at the museum, but I have also seen other ways of fashioning specimens to herbarium paper (a heavy duty paper 11 x 16 inches).  Wire poking through the paper can be an effective fastener and may be good for an artistic use of pressed plants in temporary displays.  The type of glue used varies, however, thicker hot-glue may be too unyielding for a specimen and cause stems and leaves to crack.  Elmer’s and paper strips seem like a good option and are easy to find and cheap to purchase.

The Herbarium: Invasive Migrations

September 26, 2017
Dr. J,

Bonnie mentioned going into the field to collect plants in the near future.  I’m sure the process of pressing plants isn’t very complex or exciting, but I am excited to learn about it. Continue reading “The Herbarium: Invasive Migrations”

The Herbarium: Intern vs. Polygonaceae

Prologue:
My internship is counted for credit with Chatham, so I have to do some sort of check-in with an advisor at my university.  I chose my academic advisor, Dr. J, because she is very cool and she is a botanist.   Continue reading “The Herbarium: Intern vs. Polygonaceae”

The Herbarium: Hidden Science at the Museum

I stood in the main foyer of the museum staring out into a courtyard where some smart-looking people sat drinking coffees and having a chat.  I was waiting for Bonnie Isaac, the herbarium collection manager at Carnegie Museum of Natural History. Continue reading “The Herbarium: Hidden Science at the Museum”

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”

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