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.

Rattlesnakes in the Quehanna

Timber rattlesnakes are awesome creatures that have a unique place in their ecosystem.

a dark-colored timber rattlesnake coiled up in brown leaves
A dark morph timber rattlesnake, there is also a light morph with lighter brown between the chevron pattern.

On a recent backpacking trip in the Quehanna Wild Area, I crossed paths with several timber rattlesnakes. Resting on the side of the trail, some of the snakes rattled, a few hissed, and others remained silent as I maneuvered around them with a wide berth. I can respect an animal’s personal space, particularly if it appears annoyed and is capable of injecting life-threatening venom. Despite their fearsome reputation, I’m quite fond of these unique and remarkable creatures.

Timber rattlesnakes are the most common of the three venomous snakes in Pennsylvania (the massasauga and copperhead also call PA home). Still, these beautifully patterned snakes are found among rocky wooded slopes in relatively uninhabited areas. Within rock crevices are winter den sites where timber rattlesnakes may brumate, or hibernate, with other snake species.

Every time that I’ve seen a timber rattlesnake in the wild, they’ve been basking on the side of a trail. The snakes mean no harm to me, they just want to safely warm up so that they can hunt again as the sun sets. Timber rattlesnakes are also a good sign for me and other hikers because they help maintain chipmunk, mice, squirrel, and rabbit populations. These snakes hunt at twilight and night using their specialized sense of smell. This predator service is important for controlling the spread of zoonotic diseases like Lyme and hantavirus.

I also don’t mind bumping into fellow travelers while I’m on the trail. While a timber rattlesnake won’t hike out too far, they do migrate during the year. Males may travel up to 5 miles from their winter den sites while reproducing females tend to stay closer to home. A timber rattlesnake seen in one area during the summer will often move on to forage or find a mate, so there’s no reason to scare them off.

Besides that, most timber rattlesnake bites occur on hands and feet, usually the result of attempted handling of the venomous snake. Only licensed venomous snake handlers should attempt to handle rattlesnakes and only when absolutely necessary.

My several encounters with timber rattlesnakes on the trail were great reminders of the wild nature of Pennsylvania. I had a moment of shock and tread more carefully the next few miles after passing a rattling tail. But, with my heart racing, I also enjoyed each moment spent in awe of the beauty and unique character of the timber rattlesnake.

One of the less welcoming timber rattlesnakes that I came across

Dame’s Rocket – Species Highlight

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

IMG_1653
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”

Across the Frozen Sky

Tundra swans’ long migration connects the isolated tundra to the urbanized mid-Atlantic.

As I laid out seed treats for wintering rodents–part of an ongoing capstone study on seed predation–a winter storm raged all around me.  Looking up, flurries of snow danced downward through the bare tree canopy around swaying tree branches in the freezing wind.  The sound of dry branches smacking and trees squealing as they rubbed against each other in the wind were the soundtrack for my hurried pace to keep warm and get out of the frigid and biting wind.

A flock of geese passed overhead, squawking against the wind.  I usually see or hear geese when I am here, likely a resident bunch that passes from crop field to crop field looking for scraps to scavenge.  A while later, I heard a different sound coming from the sky.  A soft, high-pitched ouoh ouoh sound rose from over the horizon to the North and then became louder and more distinct.  The chatter of a dozen or more tundra swans passing low over the forest filled the air and washed out the clashing and shrieking of the trees.  I heard the sound from my apartment a month before and darted out into the night, but missed any sight of them.  Now at least one flock passed directly overhead–pure white feathers against the grey winter sky.  With long necks outstretched and stroking the cold air with their wings each bird pressed on, and the V-formation of the flock sailed effortlessly out of sight.

Tundra swans, or whistling swans, are similar to most other North American swans in appearance: white feathers, a dark bill, and long neck.  Patches of yellow at the base of the bill help distinguish the tundra swan from the native trumpeter swan (with a solid black bill) and often domesticated mute swan (with an orange bill and black base).  The tundra swan’s call is much less nasal and harsh as the trumpeter swan.

Tundra swans breed in open sites across the northern edge of landmasses in the American and Eurasian Arctic.  In North America, flocks gather in large northern lakes after breeding and before embarking on a long autumnal migration across Canada.  Wintering grounds in the west include scattered large lakes, agricultural areas, and the Pacific coast.  In the east, the Great Lakes and, to a greater extent, the Chesapeake Bay regions are suitable wintering grounds.  In the winter, tundra swans feed on shellfish and grains from crop fields.  Before migrating north again in early spring, young tundra swans form mating pairs and older birds reinforce their lifelong bonds.

I marveled at the passing flock and their remarkable journey across the frozen sky.  It is inspiring to witness a few dozen creatures on their way from far-flung wild regions to the developed Atlantic coast.

While only a few months old, birds born and raised on the remote and ephemerally green tundra landscape must be ready for a migration of hundreds of miles or risk starvation and freezing.  Flying mostly in the cover of night, the swans pass over the Taiga–the great coniferous forest belt encircling the Arctic–and twinkling lights of inland cities and towns.  Their soft calls to each other are as much an encouraging cheer to press on as a distressed panting during their marathon flight.  The flocks that arrive in the Chesapeake Bay area spend their winter just offshore of the most heavily urbanized area in the United States.  Tundra swans thus connect the remote Arctic tundra to some of the most densely humanized landscapes on the planet with their migration.

Witnessing these impressive birds during their flight brings a sense of wildness to the tame eastern forests. Tundra swans’ incredible voyage is rooted in an enduring history of survival.  The nomadic lifestyle of many migratory animals–monarch butterflies, pronghorn antelope, and salmon–is only possible if stable habitats are maintained along their migration route and on breeding and wintering grounds.  For tundra swans, the isolated Arctic tundra and the urbanized coast are contrasting environments that the determined birds call home.

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”

Waning Summer, Waxing Autumn

The summer sun was nearly wasted on me.  I spent a considerable amount of time indoors at a retail job in order to pay for the enumerating costs of living as an adult. Continue reading “Waning Summer, Waxing Autumn”