Category Archives: Trees

Kissing Trees

Fused ash trees (photo from Wikimedia Commons)

28 November 2023

If you’ve spent a lot of time in the woods chance are you’ve see trees kissing. The fusion of their trunks in what looks like a kiss is called inosculation from the Latin word for kiss.

University of New Hampshire explains how it occurs:

Inosculation happens when the friction between two trees causes the outer bark of each tree to scrape off at the point of contact. The trees respond by producing callus tissue that grows outward, thereby increasing the pressure between the two trees. This pressure, along with the adhesive nature of sap or pitch that exudes from the wounds, reduces the amount of movement at the point of contact. The cambia layers from the two trees come in contact and the vascular tissues become connected, allowing for the exchange of nutrients and water.

— UNH: Inosculation: Making Connections in the Woods

Though I’ve seen fused trees several times, I have only one photo of a pair “kissing,” fused twice at Raccoon Creek State Park in February 2015. The date is notable because that hike is also the last time I saw a long-eared owl.

Two trees “kissing” twice, Raccoon Creek State Park, 8 Feb 2015 (photo by Kate St. John)

An extreme case tweeted by Science girl @gunsnrosesgirl3 reminded me of the phenomenon. The smaller tree on the left does not touch the ground and is completely sustained by the larger one that’s holding it up. The embedded tweet below does not show that the smaller tree is cut off so click here to see a larger photo.

Some species are more likely to “fuse “kiss” because their bark is thin. Check out this list of likely suspects at Wikipedia.

(credits are in the captions)

A Yellow Carpet

The ginkgo leaves fell all at once, 22 Nov 2023 (photo by Kate St. John)

25 November 2023

On Wednesday I found a yellow carpet on Elmer Street. Ginkgo trees were shedding their leaves all at once.

The ground was gorgeous and so were the branches.

Ginkgo: Many leaves are still on the tree, 22 Nov 2023 (photo by Kate St. John)

Some trees were already bare. Some were yet to come.

Ginkgo trees dropping their leaves in a Pittsburgh neighborhood, 22 Nov 2023 (photo by Kate St. John)

But there were hazards beneath this beauty. Ginkgos are dioecious (with separate sexes) and the females produce fruits that smell like vomit. Landscapers try to plant only male trees but there was a female in this mix.

I didn’t pay attention until I stepped on a fruit and felt it pop beneath my heel. Yuck! The stinky flesh stuck in the treads of my shoe so I searched for a puddle to stomp in, too preoccupied to take a picture of the fruits. These are from Wikimedia.

Fruits and fallen leaves of ginkgo trees (photo from Wikimedia Commons)

Ginkgos were planted along Pittsburgh’s street during the Smoky City era because they’re one of the few trees that do well in polluted air. We can expect them continue for 100s of years.

In 2020, a study in China of ginkgo trees up to 667 years old showed little effects of aging, finding that the trees continued to grow with age and displayed no genetic evidence of senescence, and continued to make phytochemicals(*) indefinitely.

Wikipedia: Ginkgo biloba account

(*) Phytochemicals are chemical compounds produced by plants, generally to help them resist fungi, bacteria and plant virus infections, and also consumption by insects and other animals. Gingkos have great immune systems even when more than 600 years old.

Black Walnuts

Black walnut in shell, found in Frick Park, 19 Nov 2023 (photo by Kate St. John)

22 November 2023

The Nutty Series: Black walnut

Black walnut trees (Julgans nigra) are common in the Pittsburgh area. Their nuts are always ready to eat in time for the holidays.

In September the fruit was still on the trees while we searched for fall warblers among the leaves.

Black walnut leaves and fruit (photo from Wikimedia Commons)

By the end of October the fruit had fallen and started to look bruised. Eventually the husks turned black.

Black walnut in husk, 23 Oct 2023 (photo by Kate St. John)

But most black walnuts aren’t abandoned that long. Squirrels gather them for winter food and eat a few along the way.

Fox squirrel opening a black walnut (photo by Donna Foyle)
Fox squirrel opening a black walnut (photo by Donna Foyle)

Squirrels know that they have to open the shell on both sides to get all of the nut meat.

Black walnut shell opened by a squirrel (photos by Kate St. John)

The meat does not come out easily! It usually breaks into small pieces on the way out and is never the perfect shape of grocery store walnuts.

Black walnut shell and meat (photo from Wikimedia Commons)

The ones we buy in the grocery store that are grown in California are English walnuts (Juglans regia) which would not be possible without the life-giving participation of black walnut trees (Julgans nigra).

(English) Walnut pie (photo from Wikimedia Commons)

Non-native English walnuts are susceptible to root diseases in California so walnut farmers plant native black walnut trees to start the orchard. When the black walnuts are a year old with strong roots and vigorous base they are chopped off and an English walnut shoot is grafted to the stump.

All the trees in the orchard below show the wider stump base (highlighted in yellow) that ends at the graft point. Above the graft English walnuts produce their own delicious nuts which are harvested after they fall by sweeping and vacuuming from the ground. FLORY harvesting equipment is pictured below.

Walnut orchard in California with FLORY sweeper machine (photo from Wikimedia Commons) The trunk and treetops are Juglans regia, the stump and roots are Juglans nigra
vacuuming up walnuts in the orchard, video from Midland Tractor on YouTube

Black walnut trees can be identified in winter as a bare tree standing alone with twigs that have alternate (not opposite) small buds above large leaf scars.

Black walnut trees tend to stand alone (photo from Wikimedia Commons)
Black walnut buds and leaf scar, Schenley Park, 27 Feb 2023 (photo by Kate St. John)

Black walnut trees stand alone because …

Like other walnuts, the roots, inner bark, nut husks, and leaves [of Julgans nigra] contain a nontoxic chemical called hydrojuglone; when exposed to air or soil compounds it is oxidized into juglone that is biologically active and acts as a respiratory inhibitor to some plants. Juglone is poorly soluble in water and does not move far in the soil and will stay most concentrated in the soil directly beneath the tree.

Symptoms of juglone poisoning include foliar yellowing and wilting. A number of plants are particularly sensitive. Apples, tomatoes, pines, and birch are poisoned by juglone, and as a precaution, should not be planted in proximity to a black walnut.

quote from Wikipedia

(credits are in the captions)


Pignut with husk partly gone, Oct 2023 (photo by Kate St. John)

15 November 2023

The Nutty Series: Pignut hickory

Different species of hickory nuts look the same … but not quite. This one, partially in its husk, was a puzzle so I brought it home. Husks and shells together provide the clues so I had three nuts to work with in various stages of undress, plus a table of southwestern PA hickory husk and shell characteristics.

Pignuts in husk, shell with insect hole, partially in husk, Nov 2023 (photo by Kate St. John)
Characteristics of Southwestern PA Hickory Husks and Shells
Common NameScientific name
Shagbark HickoryCarya ovataNearly round, 1.75", thick, green, splits to baseNut has 4 ribs
Mockernut hickoryCarya tomentosaOval to pear shaped, 1.75", green, husk is thinner than shagbark's, splits to baseNut is thick-shelled with 4 ribs
Pignut hickoryCarya glabraOval or slightly pear shaped, 1.5", thin husk green to tan, maturing to da
rk brown, usually splits only partway to base
Nut has no ribs
Bitternut hickoryCarya cordiformisVery thin rough husk with 4 wings, splits only to the middle as if it is peeling off the shellNut is round, small and thin-shelled with a pointed tip

The Verdict: The photo was taken after the nuts sat indoors for three weeks. The husk is still pear shaped but has turned brown and splits completely. Hmmm. The nut, however, has no ribs so I’d say this is a pignut.

Sliced open it would look like this. I lack the tools to make such a clean cut.

Pignut sliced open (photo by Rebekah D. Wallace, University of Georgia,

Pignuts were too bitter for European settlers so they fed them to their pigs, hence the pignut name. However pignuts are prized by wildlife including chipmunks, squirrels, mice, blue jays, red-bellied woodpeckers and wild turkeys. If deer eat them they will soon disappear from the ground in Pittsburgh’s parks.

Pignut hickories (Carya glabra) range along the east coast (the original colonies) all the way to the Mississippi Valley and down to the Gulf of Mexico but don’t normally grow in northern Pennsylvania.

Pignut hickory range (map from Wikimedia Commons)

In winter they are best identified by their buds. As with all hickories, the end bud is larger than the side buds but on the pignut it is relatively small and the side buds are almost at right angles to the twig. This one is about to burst into spring leaves.

Pignut hickory buds (photo by Chris Evans, University of Illinois,

Young trees have smooth bark. Mature ones have these ridges.

Mature bark on a pignut hickory (photo by Rebekah D. Wallace, University of Georgia,

The tree’s compound leaves have 5-7 serrated leaflets …

Pignut on the hickory tree (photo by Franklin Bonner, USFS (ret.),

… which turn a beautiful golden color in the fall.

Pignut hickory in autumn (photo by T. Davis Snydor, The Ohio State University,

But now the trees are bare.

Bare pignut hickory (photo by T. Davis Sydnor, The Ohio State University,

Bonus! Did you notice the clean hole in the center nut in my three-nut photo? It was probably made by a pecan weevil (Curculio caryae). The weevil drills a hole to lay its eggs inside developing hickory nuts, including pecans.

Pecan weevil drilling into a husk (photo by Jerry A Payne, USDA Agricultural Research,

How does she drill into the nuts? Check out this video of acorn weevils drilling and mating.

Read more about pignuts at the Glen Arboretum.

(credits are in the captions)

A Wasp, An Oak, and Indelible Ink

Screenshot from Making Manuscripts: Oak Gall Ink (source video below from the British Library on YouTube)

12 November 2023

Nowadays it’s rare to write anything by hand unless it’s the size of a Post-It note. When we really want to say something we use keyboards and touch screens to generate digital text read on screens or, less often, on paper. Our writing equipment becomes obsolete so rapidly that our computers and cellphones are replaced within a decade. (Who among us is still using the same cellphone since 2013? Do we even remember what model it was?)

So consider this: Humans used the same writing tool, the same indelible ink, from the 5th to the 19th century. When applied to parchment, it is readable 1,700 years later. The ink is easy to make by hand from natural ingredients and is still used in calligraphy today. To make iron gall ink, the process starts with a wasp and an oak.

When a cynipid wasp lays an egg in a developing oak leaf bud, the hatched larva secretes a substance that makes the oak surround it with a gall. The wasp (Andricus kollari) and the oak marble gall below are from Europe but similar wasps and oak galls occur in North America(*).

The outer shell of the gall is rich in tannins whose presence protects the wasp from predation.

Oak marble gall on white oak forced by Andricus kollari (photo from Wikimedia Commons)

When crushed and soaked in water the galls’ tannins give color to the ink.

Oak marble galls on the twig, forced by Andricus kollari (photo from Wikimedia Commons)

Two more ingredients transform the ink for final use: Iron sulfate dissolved in water makes the ink black.

Iron sulfate crystals (photo from Wikimedia Commons)

Gum arabic dissolved in water makes the ink sticky enough to hold onto parchment or paper.

Gum arabic in lumps and powder (photo from Wikimedia Commons)

This video from the British Library shows how iron gall ink is made.

(video embedded from the British Library on YouTube)

Eventually we used paper instead of parchment, even for important documents, and iron gall ink fell out of favor because the acid in iron sulfate makes the paper disintegrate. To solve that problem we invented paper-friendly inks and then computers.

Iron gall ink has oxidized the cellulose, causing the paper to disintegrate (from Wikimedia Commons)

Medieval manuscript creation used natural products from animals, plants and minerals. See the process from parchment to ink to binding in this 6-minute video from the Getty Museum.

video embedded from the Getty Museum on YouTube

Read more at Making Ink From Oak Galls: Some History & Science.

(*) p.s. The amount of tannin varies by type of gall and the tree species the gall came from. Galls with the most tannin work best.

(credits are in the captions)

Seen This Week

Eastern screech-owl, Frick Park, 7 Nov 2023 (photo by Charity Kheshgi)

11 November 2023

Songbird migration is quiet now and birds, when they’re found, are in mixed species flocks.

On 7 November, Charity Kheshgi and I encountered agitated golden-crowned kinglets, tufted titmice and dark-eyed juncos but it took us a while to find what they were upset about. This red morph screech-owl was hiding above our heads in a small oak.

Golden-crowned kinglet, Frick Park, 7 Nov 2023 (photo by Charity Kheshgi)

An exception to the mixed species flocking rule is our “murder” of crows. My guess is that Pittsburgh’s winter crow flock is 90% American and 10% fish crows, but who can tell? They look alike.

In late afternoon crows stage in the trees in Shadyside and Squirrel Hill, then head west at sunset. 6,000 to 10,000 pass by my building on their way to the roost.

Crows staging in Squirrel Hill just before dusk, 10 Nov 2023 (photo by Stephen Tirone)

At sunset black birds in a darkened sky are impossible to photograph but it’s another story at sunrise. Click on the photo below for a closeup of crows in the brightening sky.

Sunrise with crows, 2 Nov 2023 (photo by Kate St. John)

Leaves littered the ground this week and the air was filled with the sound of leaf blowers. 🙁

Fallen red maple leaf, 7 Nov 2023 (photo by Kate St. John)

Most of the trees were bare in Schenley Park by Friday 10 November.

Bare tree touched by sun, Schenley Park, 3 Nov 2023 (photo by Kate St. John)
Most of the trees are bare, 10 Nov 2023 (photo by Kate St. John)

And finally, a reminder that the rut is still in progress and deer are crossing roads. This duo showed up at a Squirrel Hill polling place on Election Day at a place surrounded by roads. So watch out.

Deer at the polling place on Election Day, 7 Nov 2023 (photo by John via Mardi Isler)

(credits are in the captions)

Bitternuts, Butternuts

Bitternut hickory nuts (photo by Kate St. John)

8 November 2023

The Nutty Series: Bitternut Hickory & Butternut

Though their names differ by only one letter bitternuts and butternuts are not the same at all.

Bitternut hickory (Carya cordiformis) is one of the most common hickories in southwestern Pennsylvania and easy to identify by its slender sulfur-yellow buds.

Bitternut hickory buds, April 2022 (photo by Kate St. John)

Bitternuts are closely related to pecans and also share the hickory genus with shagbark hickories, pignuts and mockernuts. Unlike the pecan the bitternut tree is rarely cultivated.

The fruit is a very bitter nut, 2–3 cm (0.75 – 1.25 in) long with a green four-valved cover which splits off at maturity in the fall, and a hard, bony shell.

Wikipedia: Bitternut hickory

The “green four-valved cover” turns brown after the nut lies around for a while (see middle nut at top) and indeed the shell is hard and bony. I had to use a hammer to open this one and damaged the perfect nutmeat in the process. You’ll have to imagine it was shaped like a short squat pecan.

Bitternut hickory nut, opened (photo by Kate St . John)

I can tell you from taste-testing that the nut is bitter and astringent. Squirrels avoid these nuts though Wikipedia says that rabbits eat them.

Butternuts (Juglans cinerea), on the other hand, are prized because the nuts taste good.

Butternut in its soft furry husk, similar to a black walnut (photo by Kate St. John)

Butternuts are in the same genus as black walnuts and sometimes called “white walnuts.” The leaf arrangement is so similar that I didn’t realize that I was looking up at a butternut tree — to see warblers — until I saw the nuts on the ground.

Butternut bark and leaves (photo from Wikimedia Commons)

Notice how similar the husks are: butternut on the left, black walnut on the right below. The butternut husk is oblong and fuzzy.

In the husk: Butternut (oblong and fuzzy) next to black walnut (rather smooth) – photos by Kate St.John

As the husk deteriorates (at left) the lumpy nutshell is revealed.

Butternut husk and nut at various stages (photos by Kate St. John)

A cross section of the nut shows the rough exterior and nutmeat inside.

Cross section of butternut with nutmeat inside (photo from Wikimedia Commons)

The butternut’s natural range runs from Maine and southern Ontario to southeastern Missouri and is smaller than the bitternut hickory’s. While the bitternut thrives, the butternut is declining and listed as threatened in some U.S. states and endangered in Canada. Its biggest threat is a fatal disease, butternut canker, caused by a fungus imported with the Japanese walnut. Ironically butternuts are partly threatened by too-easy hybridization with Japanese walnut trees.

Like black walnuts, butternuts are shade intolerant and thrive only when they’re at the top of the canopy or in an open space. Now that I know what a butternut looks like, I’ll pay more attention.

(credits are in the captions)


American beech nuts, Oct 2023 (photo by Kate St. John)

1 November 2023

The Nutty Series: American beech

If you find a small spiny capsule on the forest floor that opens to reveal two to three nuts (in this case two are nicely packed together) you’ve found beechnuts. Without even looking up you can be sure you’re near an American beech (Fagus grandifolia).

American beech fruit capsule with nuts, Oct 2023 (photo by Kate St. John)

The fruit [of Fagus grandifolia] is a triangle-shaped shell containing 2–3 nuts inside, but many of them do not fill in, especially on solitary trees. Beech nuts are sweet and nutritious, can be eaten raw by wildlife and humans, or can be cooked. They can also be roasted and ground into a coffee substitute.

Wikipedia account: American beech, Fagus grandifolia
American beech seed capsule with nuts inside, Oct 2023 (photo by Kate St. John)

Beechnuts can be eaten raw? Well, it’s complicated. Foraging Beech Nuts explains that it’s best to let the capsules dry out for 2-3 weeks and then cook the nuts because some people get throat irritation from the raw seed coating.

In Pittsburgh’s parks beechnuts can be hard to find because they are so popular with deer and squirrels. Looking for a beech without looking up? Here’s another clue.

Beech drops (Epifagus virginiana) are parasitic on beech tree roots so if you see these well camouflaged plants you are definitely near an American beech. Read about them at On The Beech.

Beech drops (photo by Scott Zona via Flickr Creative Commons license)

Looking up at American beech trees this month you’ll see brown beech leaves clinging to the branches.

American beech leaves, 15 Nov 2021 (photo by Kate St. John)

Its buds are distinctive: long, pointed and golden brown like its fall leaves.

American beech buds and autumn leaf (photo by Kate St. John)

The trunk has smooth gray bark.

Bark of American beech, Nov 2011 (photo by Kate St John)

And at the end of winter, small American beeches have pale, rattling leaves that make them stand out in the forest.

Forest with young beech tree in February (photo by Kate St. John)
Forest with young beech tree, February 2018 (photo by Kate St. John)

All the beechnuts will be eaten or hidden by the end of winter.

p.s. If you’re my age you probably remember Beech-Nut chewing gum. Were there beech nuts in it? No, that was the name of the company. The gum’s claim to fame was its peppery peppermint zing.

Whatever happened to the candy? The candy division of Beech-Nut went defunct in 1976. Read about the Beech-Nut company here.

(photos by Kate St. John except for the beech drops photo by Scott Zona via Flickr Creative Commons license)

Autumn Beauty in the Woods

Beautiful autumn in the woods, 26 Oct 2023 (photo by Kate St. John)

28 October 2023

The last full week of October brought beautiful weather and fall foliage to Southwestern Pennsylvania. Early mornings were chilly but warmed up quickly. Here are a few scenes from the week.

  • Frick Park is beautiful in early morning sunlight on 26 October. With Charity Kheshgi.
  • American beech leaves in Schenley Park show three color stages: green, yellow, brown.
  • Sugar maple leaf is red at SGL 203, Marshall Twp
  • The arching trunks of a mature Norway maple in Shadyside, City of Pittsburgh.
  • Fall colors reflecting on Lake Arthur at Moraine State Park.
  • Beautiful sunrise on 26 October. Three crows pass by on their way from the roost.
American beech changing color, Schenley Park, 21 Oct 2023 (photo by Kate St. John)
Sugar maple leaf, SGL 203, 22 Oct 2023 (photo by Kate St. John)
Norway maple in yellow, Shadyside, Pittsburgh, 23 Oct 2023 (photo by Kate St. John)
Fall foliage reflection at Moraine State Park, 24 Oct 2023 (photo by Kate St. John)

Golden yellow is a them from leaves to sky.

Sunrise with three crows, 26 Oct 2023 (photo by Kate St. John)

(photos by Kate St. John)

You Can Tell A Tree By Its Nuts

Red oak acorns on the branch, August 2023 (photo by Kate St. John)

25 October 2023

By late October leaves and nuts are underfoot and still falling. Red oak acorns that were green on the branch in August litter the footpaths and sidewalks now.

Red oak acorns on the ground, Sept 2020 (photo by Kate St. John)

Underneath black walnut trees it’s hard not to misstep on the yellow husked nuts. You may even be hit by a black walnut detached and dropped by a squirrel gathering nuts above you. Squirrels save time by crawling all over the tree and detaching lots of nuts. Then they scurry down to collect them. Ouch!

Black walnuts in the husk (photo from Wikimedia Commons)

Keep looking down and you may find unusual nuts and seeds like these.

Magnolia cucumber tree lea and seeds, Sept 2011 (photo by Kate St. John)

Even without leaves, you can identify the trees above you by knowing the nuts at your feet. This fall I’ll run a series on identifying nuts found in western Pennsylvania.

Meanwhile to kick it off …

Adam Haritan explains a few trees you can identify without even looking up in this 15-minute Learn Your Land video.

video from Learn Your Land on YouTube

(credits are in the captions)