Archive for the 'Winter Weeds & Trees' Category

Feb 15 2012

Winter Trees: Sycamore

From a distance this massive white tree looks like a ghost in the valley.

It’s an American sycamore (Platanus occidentalis), also called buttonwood or American planetree.  In Pittsburgh we call it a sycamore but in other countries this name can be confusing because it refers to other trees.  In Europe the “sycamore” is a maple.

American sycamores are native to eastern North America from Maine to Texas, from Ontario to Florida.  You’ll find them along creeks and rivers, in bottom land but not in swamps.  They like to be near water, but not in it, because they’ll die if their roots are submerged continuously during the growing season.

Sycamores are easily identified by their bark which flakes off in big chunks to reveal the pale new bark beneath.  They do this because their bark cannot expand as the tree grows.  Look up the tree trunk and you’ll see the characteristic ghostly white color.


In rural settings you can safely identify the flaky bark as a sycamore but in town we’ve planted London planetrees, a hybrid of the American sycamore and Oriental plane tree.  The new bark on London planetrees is greenish-beige where the sycamore is white.

The seed balls of both species stay on the tree through the winter, breaking up in early spring. Each seed has a bit of fluff attached to help it disperse by wind or water.

One way to tell the difference between American sycamores and London planetrees is to look at the seed ball stems.  On sycamores there is generally one seed ball per stem.  On London planetrees two or three hang from the same stem.


Sycamore twigs zigzag from bud to bud. The buds form underneath the petioles (leaf stems) during the growing season and don’t appear until the leaves fall off.  Each bud is encased in a single scale and surrounded by the leaf scar.


Sycamores (and London planetrees) are both noted for their very large trunks which often become hollow with age.  Champion trees have been measured at 167 feet tall with trunks 13 feet in diameter.  The oldest trees are the largest.  They can live for several hundred years.

(photos by Kate St. John)

Reminder: Meet me at Schenley Park Cafe &Visitors’ Center at 1:00pm this Saturday for a Winter Tree Walk to practice your winter tree identification skills.  So far the weather looks good (above freezing with no precipitation!).  Click here for more information.

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Feb 08 2012

Winter Trees: Black Cherry

Today’s tree is easy to identify all year simply by looking at its bark.

Black cherry (Prunus serotina) is a medium to large tree, 50 to 100 feet tall.  Mature trees have dark colored bark that looks like burnt potato chips.  The shadowy photo above accentuates the chips.

In bright light the trunk looks paler but the chips are still there, as you can see by this photo taken in full sun.


Young trees have smooth shiny bark with pale horizontal lines or lenticels.  Even the twigs have lenticels that appear as spots in the picture below.  The buds are alternate, small and scaled.  This twig looks like it wants to open its buds, proof that it’s been a weird warm winter.


Black cherries are a favorite of birds in late summer because the trees produce an abundance of small red to purple cherries, 1/3″ in diameter.  Foresters like the tree for it’s cherry-colored wood which fetches a good price.

Keep your eyes open for black cherry trees and you’ll be surprised how many you find.

(photos by Kate St. John)

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Feb 01 2012

Winter Trees: Black Locust

A friend of mine from Maryland once remarked that Pittsburgh has ugly trees.  “The gnarled ones look like devil trees,” she said.

Though she didn’t know their name I think she was referring to black locusts whose winter profile can look spooky.

Black locusts (Robinia pseudoacacia) grow in twisted shapes if they’ve been broken, badly trimmed, or invaded by the locust borer that weakens and deforms the tree.  The tree pictured above has been through at least two of these assaults.

The bark on mature black locusts is gray-brown and so deeply furrowed it looks distressed. Though a bit spooky it’s a good field mark for identifying the tree.


Up close you can see that each bud is surrounded by paired thorns, like devil’s horns.


The thorns also grow on the trunks of young trees.


Black locust flowers are such good honey-sources that they’ve been planted for this purpose in Europe, Asia and southern Africa.  If you don’t live in the black locusts’ native range — the southern Appalachians from Pennsylvania to Georgia, and the Ozarks — you might think of them as devil trees where they’ve become invasive.

Black locusts thrive in old fields, disturbed woodlots and along roadsides because they tolerate pollution and poor soil.  They make their own fertilizer through a process called nitrogen fixation.  As members of the legume family, their roots have a symbiotic relationship with Rhizobium bacteria.  The bacteria enters the root hairs and the plant makes tumor-like growths to surround it.  This protects the bacteria which in turn takes in nitrogen and converts it to a form that fertilizes the plant.

With beautiful flowers and an ability to make fertilizer, they don’t deserve to be called devil trees.

(photos by Kate St. John)

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Jan 25 2012

Winter Trees: White Oak

Continuing the oak theme, today’s tree is the Eastern White Oak (Quercus alba).

As I said last week, Pittsburgh’s natural habitat is the oak-hickory forest.  In this part of North America oak species fall into two groups: reds and whites.  Red oaks are typically found in oak-dominated forests.  White oaks are so versatile they can grow in many habitats and have one of the widest ranges of any tree on the continent.

White oaks are majestic trees — as much as 150 feet tall, four feet in diameter, and 600 years old.  Like all oaks they produce acorns and have clusters of buds at their twig tips.  You can distinguish them from red oaks because their leaves have rounded lobes, their buds are smaller and blunter, their acorn cup scales are paler, knobby and the cup is not hairy inside, and their bark is paler, scaly and sometimes peeling.

The blunt buds, clustered at the twig tip, are pictured above.  As you can see, a few dried leaves remain on the tree in the winter.

The bark at the base of the tree is a good hint to this tree’s identity because it looks as if part of it was rubbed off.  Here are two examples.  (It’s easier to see the “rubbed off” appearance in real life than in photos.)

Look up the tree trunk and you’ll see paler, slightly peeling bark and a few dried leaves.

White oaks are famous for producing bumper crops of acorns every 4-10 years.  A single tree can produce 2,000 to 7,000 acorns so you can imagine the effect in an area with a lot of white oaks.  One fall in the Laurel Highlands there were so many acorns that I found it hard to hike without slipping on them!

Squirrels eat acorns from both red and white oaks but they treat them differently.  They bury red oak acorns and eat the white oaks’ right away.  Red oak acorns are full of tannin (less palatable) and don’t sprout until their second spring.  White oaks have less tannin and sprout in their first spring.  Burying reds and eating whites makes sense.  Red oak acorns can be placed in underground storage.  White oaks would sprout before the squirrel could get back to them.  Smart squirrels, eh?

(photos by Kate St. John)

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Jan 20 2012

Winter Tree Walk at Schenley Park, Feb 18, 1:00pm


Here’s a chance to practice the winter tree identification skills I’ve been blogging about on Wednesdays.

On Saturday, February 18, 1:00pm – 3:00pm, I’ll lead a Winter Tree Walk in Schenley Park.

Meet me at the Schenley Park Cafe and Visitor Center at 1:00pm and we’ll walk the trails to see some of the trees I’ve highlighted.

Bring a field guide or the Winter Tree Finder, binoculars or a hand lens so you can see the details, and quarters for the parking meter (unmetered parking is a bit of a walk).  Prepare for cold weather and dress warmly.  We’ll be moving at the speed of botany (slowly!) so expect to be standing out in the cold.

For directions to the Visitor Center, click here and scroll down to the heading: “Directions to Schenley Park Cafe and Visitor Center, 101 Panther Hollow Road.”  The Visitor Center is open from 10am to 4pm with food and hot chocolate.  Come early and eat lunch.  Here’s the menu.

I hope February 18 will be as nice as the day in December when I took this photo.  Watch my blog on the morning of February 18 for final details.

Hope to see you then.

(photo by Kate St. John)

p.s. If you have questions, leave a comment.  I moderate the comments so I’ll be able to read and respond privately.

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Jan 18 2012

Winter Trees: Red Oak

If you’ve traveled around the country you may have noticed there’s a different mix of trees outside of Pittsburgh.  Compared to other parts of North America, southwestern Pennsylvania has few pines and spruces, no white birches (unless planted) and no mangroves.  But we do have a lot of oaks and hickories.

Pittsburgh’s habitat type is the oak-hickory forest, the widest ranging deciduous forest type in eastern North America.  Oak-hickory forests are dominated by oaks and hickories (of course) and are home to birds and animals who eat the acorns and nuts: blue jays, wild turkeys, gray squirrels,  fox squirrels and eastern chipmunks.

The northern red oak (Quercus rubra) and eastern black oak (Quercus velutina) are indicator species for the oak-hickory forest.  Both are in the red oak group, are very similar and even hybridize. For purposes of this simple tree guide I’ll help you recognize “red oaks.”

All oaks produce acorns and have a cluster of buds at the tip of the twig. In eastern North America oaks fall into one of two groups: reds and whites. Here are the differences between them:

  • Red oak group:
    • Leaves have pointed or bristly tips on each lobe
    • Buds have pointed tips and are larger than white oaks’ buds
    • Acorn cup scales are brownish and flat; the cup is hairy inside
    • Bark is generally dark, smooth or ridged but not peeling
  • White oak group:
    • Leaves have rounded lobes
    • Buds are blunted, rounded and generally smaller
    • Acorn cup scales are knobby and paler; cup is not hairy inside.
    • Bark is paler, peeling from higher trunk and branches, looks as if it was rubbed off at the base of the tree.

Notice in the photo above how the buds are clustered at the tip and are pointed.

Red oak bark is dark and doesn’t peel.  Even though it has ridges, the ridge tops still have a smooth appearance.


Oaks have bumper crops of acorns every few years on a cycle that’s determined by species.  Red oaks cycle every 3-4 years; white oaks every 4-10 years.  This abundance and scarcity causes a fluctuation in those who eat the acorns, too.

Sometimes you can recognize oaks from afar because their crowns are massive, wide and spreading.  Here’s a red oak seen from a distance in Schenley Park.


Interestingly, the red oak is the dominant oak in Schenley Park and often has a reddish tinge in the bark’s furrows or on the surface.  I’m not sure why or even if this tinge is diagnostic.  (See the slight reddish tinge in the bark furrows above.)

(photos by Kate St. John)

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Jan 11 2012

Winter Trees: Norway Maple

No discussion of western Pennsylvania’s trees would be complete without including the Norway maple (Acer platanoides).

As its name suggests this tree is native to Europe, growing as far north as Norway, south into Greece and Iran, east into Russia.  It was brought to North America as an urban shade tree because it survives well in compacted soil and air pollution.

Unfortunately it survives too well.  The Norway maple naturalized on this continent and easily became invasive because it releases chemicals in the soil that inhibit the growth of underbrush and native saplings.  In addition, native animals and insects prefer to eat North American maples more than this import. With these competitive advantages it’s no wonder you can find pure stands of Norway maples with bare ground beneath them.

Normally I recognize Norway maples by their twigs and buds.  The buds are opposite on the stem, reddish and turban-shaped with a slightly larger end bud.  In the photo above, taken in Schenley Park in November, the twig is green with reddish turban-shaped side buds and an end bud that looks like it’s opening.  The twig below conforms more closely to the typical description of Norway maple buds.  There are many cultivars in Schenley Park including a variety with purple leaves so my photo may differ for that reason.


Norway maple seeds are easy to recognize because the samaras are nearly 180 degrees apart.  Other maples have “wings” that droop.  You’ll see some of these seeds and their stalks on the trees in the winter.


The bark on young Norway maples looks almost smooth, just faintly striped.


On older trees it has narrow stripes and shallow furrows.

Norway maples are easiest to recognize in late fall because they’re out of synch with our seasons.  They retain their yellow leaves into mid or late November and lose them only after our native maples are bare.

(photos by Kate St. John except UGA0008518 by Paul Wray, Iowa State Univ and UGA5306048 by Steve Hurst, USDA, both from

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Jan 04 2012

Winter Trees: Bitternut Hickory

This one is easy.

It’s the only tree in Pennsylvania with a very long yellow end bud (and alternate small yellow buds).  It’s the bitternut hickory (Carya cordiformis).

If you live in the southern U.S. the yellow buds resemble the pecan to which the bitternut is closely related.  Both are members of the Walnut family but the pecan produces tasty nuts and the bitternut produces very bitter nuts, so bitter that squirrels avoid them.  Hence its name.

In his 1985 Thornapples essay, A Nut-Gatherer’s Compendium, Charles Fergus tells of his excitement at gathering wild nuts before he knew how to identify hickories.  He collected a bucketful of nuts and hammered them open.  Fortunately he tasted one before he spent much time at this activity.  He’d collected a bucket of bitternuts.  So bitter!!

In areas where both trees grow, such as the Mississippi valley, you can distinguish between the two twigs by the bitternut’s very long end bud.  Pecan buds are small.

Don’t worry that you’ll mistake the nuts.  Bitternuts are small and round (one inch diameter) with a pointed tip.  Pecan nuts have the familiar smooth pecan color and oblong shape.

Like all hickories the bark on young bitternuts is gray-brown and smooth but it lacks the stripes found on young shagbarks that will split to become shaggy later in life.

Here’s young bitternut bark found in Schenley Park:


The bark on mature bitternuts is said to be thin and tight with interlacing ridges.  This description applies to several other hickories so I didn’t illustrate it.  It’s so confusing!

Don’t bend your brain trying to identify this tree by its bark.  Look at the yellow end bud.  It’s easy.

(photos by Kate St. John)

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Dec 31 2011

Green Aliens

It’s winter.  Mostly.  The plants are dormant but there’s no snow to brighten the ground.  With temperatures in the 40’s and overcast skies the landscape is brown in Pittsburgh.

But what is this?  A spot of green on this last day of 2011.  What plants are braving the cold in Schenley Park?

Two alien invasives:


… and Garlic mustard.

Perhaps it’s not wintry enough for them.

(photos by Kate St. John)

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Dec 28 2011

Winter Trees: Tuliptree

The tuliptree (Liriodendron tulipifera) is easy to identify by its leaves, flowers, fruits and seeds but more of challenge when you’re limited to twigs and bark.

In early winter, look up and you’ll find the tree dotted with upright, drying fruits shaped like flowers.  Each one is a seed cluster of samaras attached at the base of the “flower.”


As time passes, the fruits dry and the samaras blow away from the tree or fall to the ground below.  They look like rounded skis with a lump at the toe.


In the absence of these clues examine the twigs, trunk and bark.

The reddish-brown twigs are less than 1/2 inch thick and have alternate leaf buds with a single large end bud shaped like a duck’s bill.  This shape is your big clue that it’s a tuliptree.  I’ve read that this bud encloses the nascent leaves until the frosts are past, then the leaves unfurl like wings.  Also notice the stipule scar that surrounds the twig where the leaf used to be.

I’ve seen both reddish-dark-gray and deep-red end buds in Schenley Park.  Dark gray is shown in the first photo, deep red below:


Identifying the tree by its bark is another story.  The best clue is the shape of the trunk.  It’s very straight and tall with no lower branches because these trees grow so fast.  Tuliptrees are shade intolerant and put all their energy into the trunk during their surge to the sun.  Along the way they drop their lower branches and leave a big upside down smile on the bark where the branch used to be.  This is noticeable on younger trees whose bark has flat-topped ridges with lighter furrows, shown here:


On older trees the ridges look less flat-topped, the furrows aren’t as light and the smiles are hard to find, though you will see horizontal line breaks in the bark:


When tuliptrees reach the top of the canopy, their crowns are shaped like candle flames which they resemble in late November.  At that point they retain just a few fluttering yellow leaves while the rest of the forest is brown and bare.

Perhaps this fluttering gave them the alternate name of yellow-poplar because they flutter like poplars.  But the tuliptree is not a poplar.  It’s in the magnolia family and will have beautiful flowers in the spring.

(Buds and older bark photos by Kate St. John.  Fruits, samaras and younger bark from Wikimedia Commons. Click on the Wikimedia photos to see the originals.)

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