Drift of fluffy seeds from London plane trees, 17 March 2019 (photo by Kate St. John)
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.
Like their parents — oriental plane tree (Platanus orientalis) + American sycamore (Platanus occidentalis) — London plane trees retain their dangling seed balls over the winter.
Weeping willow turning yellow, Schenley Park, 15 Feb 2019 (photo by Kate St. John)
Weeping willows (Salix babylonica) are popular landscape trees that were brought here from Asia. They’re easy to notice at this time of year because their drooping stems turn yellow in very early spring. From a distance you see a splash of yellow.
Imported species, especially those from Europe, grew up in a steady climate with few spring surprises so they’re quick to bloom in the spring and late to drop their leaves in autumn.
Meanwhile our native trees are still brown, conservative about producing tender shoots because they know that volatile spring weather can bring a killing frost in April.
Are you tired of winter? Watch for the weeping willow’s hint of spring.
Frozen sap of red oak, 10 Feb 2019 (photo by Kate St. John)
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.
Tuliptree in winter, Schenley Park (photo by Kate St. John)
The Shapes of Trees continues today with the tuliptree or yellow-poplar, Liriodendron tulipifera.
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.
This month I read Lab Girl by Hope Jahren and learned that she made an amazing discovery in 1998 during research for her doctoral dissertation: Inside common hackberry fruit is a small hard pit with a lattice made of opal.
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.
Opal is in these hackberry pits (photo by Kate St. John)
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.
In all the smoke-filled photos of the Camp Fire devastation in Paradise, California one thing stands out to me: The buildings are gone but the trees are still standing.
The town of Paradise, California (population 26,000) was destroyed on 8 November 2018 by the Camp Fire, the deadliest and most destructive fire in California history. As soon as it ignited at 6:30am, the fire raced westward on 50-70 mph winds. By 8am it reached the Paradise Town Limit six miles away. Seven towns were forced to evacuate but not everyone made it out. As of 26 November, 88 are confirmed dead, 203 are still missing and tens of thousands are left homeless.
Because the trees are still standing, the damage assessment has to be done by hand. This Washington Post article shows how the satellites can’t see through standing trees.
So why are the trees OK in this incinerated landscape? I’m sure it has to do with moisture.
Living trees contain more moisture than the dry wood in buildings. When blowing embers hit houses, they catch fire immediately. The trees’ moisture resisted. The fire moved on.
This video by Mike West shows how quickly fire consumes dry wood compared to living trees.
The scene is spooky now. Nearly everything is gone but the trees are still standing.
Snow on leaves, Schenley Park, 16 Nov 2018 (photo by Kate St. John)
On Thursday it rained. Then it sleeted. Then it snowed in the wee hours of Friday morning, especially north of Pittsburgh.
In the old days most of the trees would be bare by now, but this year many still have leaves.
Ice and snow made the leaves heavy and some of the trees came down, hitting power lines as they fell. By Friday morning KDKA reported that 65,000 households north and east of the city were without electricity. No power, no heat, and for those with well water, no water. It may take until Sunday evening to get all of the power restored..
The City is warmer than surrounding counties so Schenley Park had snow on the leaves, but no ice.
Snow on leaves, Schenley Park, 16 Nov 2018 (photo by Kate St. John)
Here’s what my favorite hillside looked like yesterday. 50% of the trees still have leaves.
Only half of the trees are bare, Schenley Park, 16 Nov 2018 (photo by Kate St. John)
The power failures wouldn’t have been so bad if most of the trees had been bare.
Witch hazel flowers catch the light after the leaves are gone, November (photo by Kate St. John)
When the leaves are gone these lacy flowers stand out in the forest.
American witch hazel (Hamamelis virginiana) blooms from late October into December in eastern North America. Its delicate yellow flowers smell like lemon.
Witch hazel flower, October in Schenley Park (photo by Kate St. John)
Since witch hazel blooms when few insects are out how are the flowers pollinated?
In 1987 Bernd Heinrich found that owlet moths come out at night to sip the flowers and thereby pollinate them.
The moths survive cold weather by hiding under leaf litter during the day, then shivering to warm up and fly at night. Click here to learn more.
Leafless bur oak, Schenley Park, 4 Nov 2011 (photo by Kate St. John)
Every year I record the date when most of the trees are bare on my favorite hillside in Schenley Park — the hill at the end of the Greenfield Bridge.
In 2008 the leaves were gone by 2 November. In 2012 Hurricane Sandy stripped them from the trees by 4 November.
Last year the changes happened much later. In 2017, the leaves were still green in late October and more than half were still on the trees on 27 November. Here’s a 2017 slideshow of autumn trees on that hillside.
26 October 2017: Lots of green at the end of October 2017.
4 Nov 2017: More than half of the trees have changed color -- mostly yellow.
12 Nov 2017: About 1/4 of the trees are bare. Some are still green, others are russet.
19 Nov 2017: Lots of ball-tree shapes on the hillside. About 1/4 of the trees are bare
27 Nov 2017: About half the trees are bare. Oak leaves are still hanging on.
This year is similar to last so I wonder … When will most of the trees be bare? November 15? 20? 30? Later?
Let me know how the trees look where you live and vote for the date “When Most of the Trees Will Be Bare” by leaving a comment below.
HINT! Two factors that affect leaf loss on this hillside: (1) More than half of the trees are oaks; oaks drop their leaves later than maples. (2) This city location is warmer than surrounding counties.
