Category Archives: Trees

Why Do Trees Have Buttress Roots?

Trees
Elm tree with buttress roots in Schenley Park, 21 April 2018 (photo by Kate St. John)

14 April 2026

Most trees in western Pennsylvania have trunks that taper gradually from the ground to the first large branches. Some have a few lumpy above-ground roots but our tree trunks generally look like the white oak at left below.

Buttress roots — the vertical flanges on the tree at top — are so unusual in Pittsburgh that I take photos of them. In this case it’s an American elm in Schenley Park.

Base of a white oak and an American elm in Schenley Park (photos by Kate St. John)

In some habitats buttress roots are normal, such as on bald cypresses in swamps …

Bald cypress buttress roots and “knees” at First Landing State Park, Virginia, Nov 2015 (photo by Kate St. John)

… and tropical trees like this one in Panama.

Tropical tree with large buttress roots, Panama (photo from Wikimedia Commons)

Why do tropical trees have such enormous buttress roots? Bill Sutherland answers that question.

video embedded from Bill Sutherland’s Conservation Concepts on YouTube

p.s. The name for these root structures comes from the buttresses, best seen in Gothic architecture, that hold up tall heavy walls and high vaulted ceilings. The walls would collapse outward without the added support.

The buttresses on Heinz Chapel are so beautiful that we take them for granted. There are at least three in this photo.

Buttresses on Heinz Chapel, Univ of Pittsburgh (photo from Wikimedia Commons), mark up to note buttress

Seen This Week: More Flowers and Leaves

Phenology, Plants & Fungi, Trees
Henbit blooming along Nine Mile Run Trail, Frick Park, 5 April 2026 (photo by Kate St. John)

11 April 2026

Despite temperatures that dipped into the upper 20s on Wednesday, spring is still making progress in Pittsburgh. This week I found more flowers and leaves.

Though they don’t look like flowers these yellow-orange structures are the inflorescence of bear corn (Conopholis americana, formerly squaw root), a underground non-photosynthesizing plant that is parasitic on beech and oak roots. The literature officially says “oak roots” but I always find bear corn under beech trees.

Bear corn in Schenley Park, 10 April 2026 (photo by Kate St. John)

The pawpaw trees (Asimina triloba) are blooming in Schenley Park. Their dark brown flowers have a faintly stinky smell to attract flies and beetles as pollinators. Pawpaw’s success is a good sign for zebra swallowtails (Eurytides marcellus). It is their only host plant.

Pawpaw flowers, Schenley Park, 10 April 2026 (photo by Kate St. John)

This week I finally noticed that the flowers on henbit (Lamium amplexicaule) and purple dead-nettle (Lamium purpureum) are nearly the same unusual shape — like the mouth of a tiny cave with a double landing pad at the opening. Duh! Of course they are similar. Both are in the Lamium genus, native to Eurasia.

In a patch of flowers along the Nine Mile Run Trail I found both plants in close proximity. The first photo has henbit in focus, the second focuses on purple dead-nettle so you can compare them.

Henbit (and purple dead-nettle) blooming along Nine Mile Run Trail, 5 April 2026 (photo by Kate St. John)
(Henbit and) Purple dead-nettle blooming along Nine Mile Run Trail, 5 April 2026 (photo by Kate St. John)

Jetbead (Rhodotypos scandens) has both flowers and leaves this week. Native to China and Japan it was planted in Schenley Park as an ornamental. Unfortunately it is invasive.

Jetbead in bloom, Schenley Park, 10 April 2026 (photo by Kate St. John)

Ohio buckeyes (Aesculus glabra) in Schenley Park have gone from merely leaves to blooming flowers in just one week. This tree had mild frost damage. If you look closely you’ll see a few dark green, shriveled leaves.

Ohio buckeye in bloom, Schenley Park, 8 April 2026 (photo by Kate St. John)

And yet, despite all the greenery the woods are still mostly bare. Sunlight reached the forest floor yesterday prompting woodland wildflowers to bloom.

Shadows and pale green leaves, Schenley Park, 10 April 2026 (photo by Kate St. John)

By 5 May all the trees will be leafed out and the spring wildflowers will have gone to seed.

Seen This Week: Greening Up

Phenology, Plants & Fungi, Trees
Virginia bluebells in Schenley Park, 3 April 2026 (photo by Kate St. John)

4 April 2026

Woodlots in the City are greening up with the first tentative leaves …

Schenley Park is greening up, 31 March 2026 (photo by Kate St. John)

… and full leaf on the Ohio buckeyes in Schenley Park.

Ohio buckeyes are the first to leaf out in Schenley Park, 3 April 2026 (photo by Kate St. John)

New flowers bloomed in the summer-like heat: Virginia bluebells near the Visitors Center and a star magnolia near the Westinghouse memorial.

The star magnolia’s flowers were in bud during the mid March freeze so it recovered well. Unfortunately, the forecast for Tuesday night, 7 April, calls for a low of 27°F. 🙁

Star magnolia at Schenley Park, 31 March 2026 (photo by Kate St. John)

Invasive garlic mustard leafed out on 15 March and was blooming this Friday.

Garlic mustard on 15 March and 3 April (photo by Kate St. John)

Coltsfoot went from flowers in snow on 19 March to full bloom on 3 April.

The photo below shows how many trees are greening up near the Panther Hollow Bridge which is covered in tarps for the current rehab.

What you can’t see is the female American robin carrying mud and grasses in her beak. She’s building a nest that she believes will be very safe, inside the tarp in the construction zone. The gap lets her in. Maybe the nest will be very safe. Maybe it’s a bad idea. She’ll find out.

Greening trees and a gap in the tarp at the Panther Hollow Bridge, 3 April 2026 (photo by Kate St. John)

And finally, more evidence of a bird that’s not in the photo. These track lines are small holes drilled by yellow-bellied sapsuckers. The tree heals the holes by growing more bark. Sapsuckers only visit Schenley Park on migration. I saw two yesterday.

Yellow-bellied sapsucker holes in a hickory, 31 March 2026 (photo by Kate St. John)

Seen This Week: Buds Swell and Open

Phenology, Plants & Fungi, Schenley Park, Trees
Honeysuckle from buds to first leaves, Schenley, March 8 & 13 (photos by Kate St. John)

14 March 2026

It was as hot as May at the beginning of the week as leaf and flower buds swelled and opened. Then temperatures returned to normal and it felt cold. Seen this week were ….

The first Amur honeysuckle leaves (above) and Cornelian cherry tree flowers.

Cornelian cherry flowers: buds to fully open, Schenley, March 6 to 11, (photos by Kate St. John)

Swelling buds on ginkgo trees.

Ginkgo tree buds swelling, Schenley, 13 Mar 2026 (photo by Kate St. John)

Invasive Callery pear about to bloom.

Callery pear flowers buds swell, Schenley, 13 Mar 2026 (photo by Kate St. John)

Viburnum plicatum leaf buds swelling in Frick Park. (This shrub is invasive.)

Virburnum plicatum leaf buds, Frick, 8 Mar 2026 (photo by Kate St. John)

First flowers on forsythia.

Forsythia drooping after cold night, Schenley, 13 Mar 2026 (photo by Kate St. John)

Pale green branches on the willows … tiny leaves.

Willows turning green in Schenley Park, 12 Mar 2026 (photo by Kate St. John)

First goutweed leaves.

First goutweed leaves, Schenley, 11 Mar 2026 (photo by Kate St. John)

And tree pollen allergies if you are susceptible. My husband wondered why his allergies gave him a twinge this week. American elm flowers were blooming. They are wind-pollinated.

Pixel Weather screenshot, Pollen count, 10 Mar 2026

All the tender leaves and flowers will be smacked down this coming Tuesday and Wednesday when temperatures drop into the low 20s. I cannot feel bad for half of the plants pictured here. Four of them are invasive aliens.

Seen This Week: Spring Moving Forward

Phenology, Schenley Park, Trees, Water and Shore, Weather & Sky
Dawn will be an hour later tomorrow morning (photo by Kate St. John on 2 Mar 2026)

7 March 2026

Sunrise in Pittsburgh this morning was at 6:44am. Tomorrow it will be an hour later because we’ll turn the clocks Forward to Daylight Saving Time overnight.    Sigh.

On the weather front, half the week was too wet to enjoy so I only went out when the sun was shining. Warmer at the end of the week than the beginning. On 1 March walked at Herrs Island.

Herr’s Island back channel of the Allegheny River, 1 March 2026 (photo by Kate St. John)

Way across the (finally thawed!) Allegheny River I saw a grebe-shaped water bird with a white face and chest and a black head. Even though these digiscoped photos are lousy, they confirm a horned grebe (Podiceps auritus) in non-breeding plumage.

Documentation photos of horned grebe at Allegheny River, 1 March 2026 (photo by Kate St. John)

Never abundant in Pittsburgh, most horned grebes breed in western Canada but a few stay in our area all winter if there’s open water. Here’s what they look like in a good photo by Steve Gosser.

Horned grebes, 15 Feb 2014 (photo by Steve Gosser)

Yesterday in Schenley Park we discovered that the Panther Hollow Bridge rehab project is temporarily in a VERY LOUD phase. Here are just 10 seconds of it.

Panther Hollow Bridge rehab project was VERY LOUD on 6 March 2026 (video by Kate St. John)

My guess at what’s happening: Inside the draped portion of the bridge I *think* they’re blasting off the peeling paint and rust. On the bridge deck there are two loud sucking machines that maintain negative air pressure.

Because of the noise there were almost no birds at this end of the park. We found them at the Bartlett end along with other signs of spring.

The buds look fat on this yellow buckeye (Aesculus flava).

Yellow buckeye buds in Schenley Park, 6 March 2026 (photo by Kate St. John)

Cornelian cherry (Cornus mas) buds are already opening.

Cornelian cherry buds opening in Schenley Park, 6 March 2026 (photo by Kate St. John)

The weather is warm today (77°F) but will return to near freezing on Wednesday night. Spring is moving forward in fits and starts.

Using Ice to Protect Plants from Freezing

Trees, Weather & Sky
Icicles on orange tree to protect against freezing (photo from USDA 2010 report to Congress)

15 February 2026

It’s hard to imagine that frozen water protects plants from freezing. Here’s how it works.

January was so cold in the eastern US that freezing temperatures hit Florida twice last month, on January 16 and on Jan 31–Feb 1, 2026. Florida citrus growers prepared ahead of time to save their crops and protect their trees. They …

  • Picked ripe fruit before the freeze.
  • Wrapped trees in sheets or burlap from the ground up to main branches or covered them entirely -or-
  • Mist-sprayed the trees continuously to protect against frost damage. Water must be applied continuously without interruption or this method fails.  Spraying uses so much water that it is inappropriate for drought-stricken areas.

Before the late January freeze, WPTV News visited Al’s Family Farms in Fort Pierce, Florida to talk about their preparations.

video from late Jan 2026 embedded from @WPTVNews on YouTube

On 3 February News 6 visited Showcase of Citrus in Clermont, FL to assess the damage.

video on 3 Feb 2026 embedded from WKMG News 6 Orlando on YouTube

Meanwhile the western U.S. was warmer than normal, as described here in Scientific American, so California citrus growers were spared this problem.

Seen This Week: Snow On The Rose

Plants & Fungi, Trees, Weather & Sky
Snow on the rose, Pittsburgh, 2 Dec 2025 (photo by Kate St. John)

6 December 2025

As I mentioned on Thursday, Pittsburgh isn’t usually this cold in early December and certainly not for long. But ever since it snowed Tuesday morning the temperature has not ventured above freezing, though it will finally do so later today.

On Monday it was comfortably above freezing when I saw sun shining through yellow-green willow leaves at the Beaver River in Rochester, PA.

Willow with green and yellow leaves, Rochester, PA, 1 Dec 2025 (photo by Kate St. John)

On Tuesday all the trees were coated in snow and so was the rose (photo at top). It was hazardous weather for a flower.

Snow covered trees, Cathedral of Learning, overcast sky, Pittsburgh, 2 Dec 2025 (photo by Kate St. John)
Snow-covered tree on Pitt’s campus, 2 Dec 2025 (photo by Kate St. John)

On Thursday sun lit Flagstaff Hill before the night turned quite cold.

Snow on Flagstaff Hill, Schenley Park, Pittsburgh, 4 Dec 2025 (photo by Kate St. John)

Today and tomorrow the snow will melt but then we’re heading back into a deep freeze Monday night. Terrible weather for a rose.

Seen Last Week: A Swan and Fog

Trees, Water and Shore
Immature tundra Swan at Duck Hollow, 18 Nov 2025 (photo by Jim McCollum)

23 November 2025

Just as the weather was turning foggy last week, Jim McCollum photographed an immature tundra swan at Duck Hollow. His photo, above, inspired me to go look for it but by the time I got there the swan was so far away it was a white dot in my scope. The dot might have been floating garbage except that it had a neck and it swam upstream.

Despite that disappointment Charity Kheshgi and I went to Duck Hollow yesterday morning and peered through the continuing mist.

The Monongahela River at Duck Hollow, 22 Nov 2025 (photo by Kate St. John)

The swan was there! About half as far away as before, so we waited for it to come closer.

When the swan crossed the river, a tugboat appeared upstream heading in the bird’s direction. Rather than wait at the shore the bird swam downstream — toward us! — periodically looking back at the tugboat to gauge its progress. Only one of my many digiscope attempts succeeded, below. The bird was swimming so hard that it had a wake at its prow.

Immature tundra swan at Duck Hollow, 22 Nov 2025 (photo by Kate St. John)

Charity photographed it looking our way.

Immature tundra swan on the Monongahela River, Duck Hollow, 22 Nov 2025 (photo by Charity Kheshgi)

Lest you think the entire week was foggy, I happened to capture a moment of sun. A blue house, a blue sky, and a bare ginkgo on Yew Street.

Ginkgo street tree on a sunny day in Bloomfield, Pittsburgh, 17 Nov 2025 (photo by Kate St. John)

Bare Trees Reveal Summer’s Secrets

Insects, Spiders, Mammals, Nesting & Courtship, Trees
Squirrel dreys in bare trees, Wellesley, MA (photo from Wikimedia Commons)

19 November 2025

Now that most of the trees are bare(*) we can see nests that were hidden by summer leaves. Among them are those built by hornets, birds, and squirrels.

Papery hornet nests dangle like hanging raindrops or upside-down cones from a sturdy branch.

Hornet nest silhouetted against the sky in Schenley Park, Nov 2023 (photo by Kate St. John)
Hornet nest in Indiana (photo from Wikimedia Commons)

Newly revealed bird nests come in all sizes, from the small hanging nests of red-eyed vireos that dangle from the fork of a small branch …

Red-eyed vireo nest in bare tree (photo by Dianne Machesney)

… to the large nests of American crows built high in the trees.

American crow nest in bare tree (photo by waferboard via Flickr Creative Commons license)

Squirrel nests — actually called dreys — look like misshapen leaf balls with a few twigs poking out.

A drey is the nest of a tree squirrel, flying squirrel or ringtail possum (in Australia). Dreys are usually built of twigs, dry leaves, and grass, and typically assembled in the forks of a tall tree. They are sometimes referred to as “drey nests” to distinguish them from squirrel “cavity nests” (also termed “dens”).

— Wikipedia: Drey

Squirrels use dreys as nests in spring-summer and shelters in the winter. Before the leaves fall they are busy biting off leafy branches and carrying them up to the winter drey. It takes a lot of effort to keep their shelter warm and waterproof. Brrrr!

In the top photo there are three dreys in three trees and one in the fork of a tree in Schenley Park, below.

Squirrel drey in the crotch of a tree, Schenley, 11 Dec 2016 (photo by Kate St. John)

How can we tell whether it’s a squirrel’s drey or a large bird nest?

Large bird nests, such as the crow nest below, are built of sticks. Squirrels use leaves, especially on the outside.

Crow nest (photo by Wanderin’ Weeta via Flickr Creative Commons license)

(*) Most of the trees are bare: For many years I’ve kept track of leaf-off in Schenley Park. Sometimes it’s early, sometimes it’s late. This year most of the trees were bare on or before Friday 14 November 2025. Here’s what the park looked like on that date.

Most of the trees are bare, Schenley Park, 14 Nov 2025 (photo by Kate St. John)

Seen This Week: Yellows and Gold

Phenology, Schenley Park, Trees
Ginkgo leaf with beads of water, 14 Nov 2025 (photo by Kate St. John)

15 Nov 2025

After my 11 November article about The (Pittsburgh) Ginkgo Map I kept my eye out for local ginkgo trees (Ginkgo biloba) but I was already too late to see them drop their leaves.

That afternoon I went back to photograph the Garetta Street trees, shown in my article from 11 November 2017.

Ginkgo trees at Jewish Association on Aging, Garetta Street as seen from JHF Drive, 11 Nov 2017 (photo by Kate St. John)

But the 11th of November was too late this year. All the leaves had fallen and the landscaping crew was sucking them into the red truck (at right, below). Oh no! I was just in time to see part of their yellow carpet.

Ginkgo trees at Jewish Association on Aging, Garetta Street as seen from JHF Drive, 11 Nov 2025 (photo by Kate St. John)

On Friday I photographed the ginkgo leaf carpet at Phipps Conservatory’s lawn. Someone had picked up a bunch of leaves and made a smaller pile in the distance. I picked up one leaf beaded with water, above, and took its photo.

Carpet of ginkgo leaves at Phipps Conservatory lawn, 14 Nov 2025 (photo by Kate St. John)

Ginkgos weren’t the only yellow.

Witch-hazel (Hamamelis virginiana) is blooming in Schenley Park. Its pale yellow flowers are fertilized at night by owlet moths that survive cold weather by hiding under leaf litter during the day. They shiver to warm up and fly at night.

Witch-hazel in bloom, Schenley Park, 14 Nov 2025 (photo by Kate St. John)

The wind made waves in Panther Hollow lake on 13 November, turning the sunlight from yellow to gold.

video by Kate St. John, 13 Nov 2025
Light reflects on wavy surface of Panther Hollow Lake, video by Kate St. John, 13 Nov 2025