Last week I found fluffy drifts on the sidewalks in my neighborhood. They’re the airborne seeds of London plane trees (Platanus × acerifolia), planted in Pittsburgh in the late 1800s because they’re tolerant of air pollution.
The Shapes of Trees continues today with an Asian import.
Some Pittsburghers call this tree a sumac but it’s a case of mistaken identity. Sumacs are in the genus Rhus. This tree is an Ailanthus, specifically Ailanthus altissima. Its common names include Tree-of-Heaven as it is called in China, and “Tree From Hell” because it’s so invasive in North America.
Ailanthus has a unique shape in winter with sparse, thick, crooked branches in an open crown. They’re always reaching up.
The branches look crooked from a distance because the twigs are stout and blunt and the buds are large and alternate. Each bud changes the angle of the twig. A twig can be as fat as your finger.
Ailanthus grows easily in waste places. David Sibley writes in his Guide to Trees,
Trees have been known to sprout from roots 150 feet away from the original trunk and grow over 12 feet in a year.
The weather this month has been up and down like a yo-yo: A low of 6oF on February 2, highs in the 50s and 60s for six days, then a low of 14oF on February 9. During those warm days the sap started running in the trees. I wouldn’t have noticed except …
On February 10 during a walk in Schenley Park I found flash-frozen sap on the damaged trees. At top, a fallen red oak made a red-orange waterfall. Below, a small amount of sap in a fungi-encrusted tree dripped like orange ribbons.
Sap runs and freezes inside healthy trees, too. We just can’t see it.
Tuliptrees are the tallest eastern hardwood, 70 to 190 feet tall at maturity. They’re characterized by straight branch-less trunks for most of their height because they jettison their lower branches as they grow. The crowns have arching branches and up-swept twigs(*). On mature trees some branches are bent or zigzag, but they are never as gnarly as black locusts.
The photos below show their typical shape as seen from the side and below. Notice that the trunk is straight and limbless.
Younger trees have tapered tops like candle flames.
In early winter tuliptrees are still dotted with clustered samaras that look like pale wooden flowers, but you have to use binoculars to see them.
If you’re lucky to find a twig at eye level you can easily identify the tree by its large smooth end bud, shaped like a duck’s bill.
But the mature trees have no low hanging twigs so you’ll have to use other clues.
Learn how to identify tuliptrees in winter and see photos of the bark, buds and samaras in this vintage article: Winter Trees: Tuliptree.
Now that the leaves have fallen we can see the skeletal shapes of trees. Did you know it’s possible to identify them by shape?
Seven years ago I wrote a series on identifying trees by their buds and bark but I didn’t mention shape except for this gnarly twisted tree, the black locust.
Black locusts (Robinia pseudoacacia) are easy to find in Pittsburgh because we’re within their native range and they grow well in disturbed soil. They’re often described as brittle and invasive but that’s because of what we did to them.
Locust borer larvae drill holes in the heartwood and weaken the tree. Before 1900 the bugs were in balance but that year the locust borer population exploded everywhere. Since then black locusts are usually infected and brittle so the trees rarely reach full size before they blow down.
But they do retain their distinctive shape. Here’s another example.
On Throw Back Thursday, learn more cool facts about black locusts and how to identify them in this vintage article: Winter Trees: Black Locust. Then take a walk outdoors to find their distinctive gnarly shapes.
In the next few months I’ll add more Shapes of Trees as I encounter them outdoors.
(photos by Kate St. John; map from Wikimedia Commons. click on the caption to see the original)
Hackberry fruits, pictured at top, are drupes similar to cherries and peaches with fleshy fruit surrounding a central pit. The fruit is thin and the pits are large so we rarely eat hackberries but birds love them.
The pits in cherries and peaches are made of wood (or something like it) but hackberry pits are made of stone: calcium carbonate inside a lattice framework. When Hope Jahren used Xray diffraction on the crushed lattice material its composition came up “opal.”
When I found this out I searched for the pits under hackberry trees in Schenley Park. At this time of year the fleshy purple fruit is gone, only the white pits remain. Here’s what I found, one whole, one opened. The exterior is a network of tiny raised lines.
The pits don’t look like opal and probably never will. You’d have to use acid to remove the calcium carbonate (the white stuff of seashells) and then examine the remaining latticework under a microscope. There’s a tiny bit of opal in there.
And so I wonder: How does a tree put opal in its drupes? I don’t know, but here are the raw materials:
[The rock] Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids, caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually opal is formed.
After a month of warm weather, these cherry trees were fooled into blooming in early January at Carnegie Museum.
Then last Monday the temperature dropped into the single digits and hit everything that couldn’t get out of its way. Nothing could protect those delicate pink flowers.
Unlike plants, birds can get out of the way and some of them decided to leave this week. In my neighborhood, there were many American robins in December but most of them have left since the cold snap. Did your robins leave, too?
Meanwhile, don’t be fooled by today’s warmth. Here’s a graph of Pittsburgh’s actual and predicted morning low temperatures for the first two weeks of January.