Category Archives: Trees

Fluff Like Snow in June

Pile of cottonwood fluff in the hand (photo from Wikimedia Commons)

9 June 2022

It usually “snows” in late May in Pittsburgh but this year it happened in early June.

On 3 June a light breeze carried snow-like fluff above Nine Mile Run in Frick Park. I found a source in this open catkin that had fallen on the trail.

Eastern cottonwood pods burst open, Frick Park Nine Mile Run, 3 June 2022 (photo by Kate St. John)

Another had not fully opened before it fell.

Eastern cottonwood female catkin gone to seed, Frick Park Nine Mile Run, 3 June 2022 (photo by Kate St. John)

Both came from an eastern cottonwood tree (Populus deltoides) whose leaves look like this. There are only a few of cottonwoods in the Nine Mile Run valley but their seed dispersal is prodigious.

Eastern cottonwood leaves (photo from Wikimedia Commons)

Pittsburgh is barely inside the eastern edge of the cottonwood’s range so the trees and their fluff are not common here. Read more about them in this vintage article.

(photos by Kate St. John and from Wikimedia Commons)

Invasive Princess

Princess tree (Paulownia tomentosa) in bloom (photo from Wikimedia Commons)

This gorgeous tree with large violet flowers is blooming now in Allegheny County. It grows fast, provides shade, looks beautiful and smells sweet. What could go wrong?

One paulownia blossom with my hand for size comparison, Schenley Park, 23 May 2022 (photo by Kate St. John)

The princess tree (Paulownia tomentosa), also called empress tree or royal paulownia for Anna Pavlovna of Russia (1795-1865) is — or was — popular in ornamental gardens. It was first introduced to the U.S. from China in 1840 and planted in the eastern U.S. and Washington state.

Initially it was a gardener’s dream. It is easy to grow in full sun, thrives in many soil types including disturbed soil, is tolerant of drought and pollution and grows 15 feet per year. It also reproduces like crazy. One tree can produce 20 million winged seeds that are dispersed by wind and water.

Seed pods and seeds of Paulownia tomentosa (photo from Wikimedia Commons)

And …

Paulownia tomentosa’s ability to sprout prolifically from adventitious buds on stems and roots allows it to survive fire, cutting and even bulldozing in construction areas; making it difficult to remove from established areas.

Texas Invasive Species Institute: Paulownia tomentosa

This one was chopped down but it came back stronger than ever. Notice the huge leaves.

Paulownia tomentosa sprouts from a stump. Huge leaves! (photo from Wikimedia Commons)

Eventually botanists and gardeners realized that P. tomentosa is invasive. This map of paulownia’s occurrence in the U.S. …

Distribution of Paulownia tomentosa by county in U.S. (from EDDMapS)

… nearly matches the map of its State Invasive listings. Maryland and Massachusetts have outlawed it.

State Invasive Listings for Paulownia tomentosa (map from

Years ago I knew of only one princess tree in Pittsburgh, this one next to the Schenley Bridge near the corner of Frew Street and Schenley Drive.

Princess tree next to the Schenley Bridge at Frew Street and Schenley Drive, 23 May 2022 (photo by Kate St. John)

Then a few years ago a volunteer sprouted in Schenley Park near the tufa bridge over Phipps Run. When it reached 20 feet it was cut down and its roots were dug up. However, this spring there are four paulownias near the tufa bridge. The genie is out of the bottle. Uh oh!

Learn more about the invasive princess in this video from University of Maryland Extension, posted at

p.s. P. tomentosa has been suggested as a plant to use in carbon capture projects. Nooooo! Don’t do it!

(photos from Wikimedia Commons and by Kate St. John, maps from EDDMapS; click on the captions to see the originals)

What Tree Is This?

Hosechestnut in flower (photo from Wikimedia Commons)

19 May 2022

Trees with stacks of white flowers are drawing our attention this week in Pittsburgh. Perhaps you’re wondering “What tree is this? “

Horsechestnuts (Aesculus hippocastanum) originated in Greece but have been planted around the world for their beautiful flowers. When fertilized the flowers become the familiar shiny buckeyes I played with as a child.

Fruit of the horsechestnut (photo from Wikimedia Commons)

In Pittsburgh we call the tree a “buckeye” though it is just one of many buckeyes (Aesculus) in our area including natives of North America: yellow, Ohio, and bottlebrush.

A close look at horsechestnut flowers reveals that some have yellow centers, others red.

Closeup of horsechestnut flowers (photo from Wikimedia Commons)

Bees see and are attracted to yellow, not red, so when a horsechestnut flower is fertilized it turns red. The flowers are …

Are there red flowers on the tree? Come back in early fall to collect the buckeyes.

(photos from Wikimedia Commons; click on the captions to see the originals)

Denuded Pine Cones

Central stem of a white pine cone missing all its seed scales, bracts & seeds, Moraine State Park, 24 March 2022 (photo by Kate St. John)

27 March 2022

On a walk last week in Moraine State Park we found a pile of pine cones in various stages of undress. Some were uneaten, some were half eaten and many were stripped bare like the stem above.

White pine cones at the red squirrel’s midden: uneaten to completely gone

The large debris pile called a midden included woody seed scales, pine straw, bract scales, and central stems but few seeds.

Close up of the midden shows many discarded seed scales, Moraine State24 March 2022

It was created while eating the seeds inside the cones.

Anatomy of a woody pine cone (image from Wikimedia Commons)

The midden was made by an individual red squirrel (Tamiasciurus hudsonicus), working alone.

We can know this because of the focus on pine cones, how the cones were denuded, and the sizeable midden. Conifer seeds make up the majority of the red squirrel’s diet and he defends his midden territory year-round against every other red squirrel.

Red squirrels are highly territorial and asocial with very few non-reproductive physical interactions. The majority of physical interactions are in male-female matings and between females and their offspring before the offspring disperse to their own territories. The non-reproductive physical interactions recorded (0.6% of all recorded behaviors in one 19-year study) were all instances of chasing an intruder from a territory.

Wikipedia Account: American Red Squirrel

The red squirrel is small and cute, but always eats alone.

Red squirrel on a tree branch (photo from Wikimedia Commons)

(photos by Kate St. John and from Wikimedia Commons; click on the captions to see the originals)

Listening to the Sap Rise?

Yellow-bellied sapsucker in Central Park, Feb 2021 (photo from Wikimedia Commons)

17 March 2022

Spring is here and tree sap is rising in western Pennsylvania. This month yellow-bellied sapsuckers (Sphyrapicus varius) are migrating through our area, pausing to drill holes in the trees to sip the welling sap.

How does a sapsucker know a tree is a good candidate for a meal? Can he hear the sap rising? Maybe so.

Seven years ago I learned that with special microphones we can hear the secret sounds of trees. Here’s an example from a Scots pine, recorded by Marcus Maeder’s trees project.

Auditory emissions of a Scots pine (recording by Marcus Maeder)

On Throwback Thursday learn more about the secret sounds of trees and listen to one in the video.

(photo from Wikimedia Commons, audio from Marcus Maeder’s trees project; click on the captions to see the originals)

Finding Food in the Cold

Snow scene on 19 January 2022

22 January 2022

I’ve often noticed that in winter there are more birds in the city than the countryside. Though we may not have “quality” birds we make up for it in quantity with large numbers of fruit-eating birds drawn to our ornamental trees.

In the past two weeks hundreds of American robins have been feasting in Oakland. Some of the fruits were inedible until the deep freeze softened them so the robins circled back to finish the Bradford pears last weekend. This week they started on pyracantha berries and the red fruits of this (hawthorn?) tree next to the Cathedral of Learning.

Was half the fruit wasted when birds and squirrels knocked it out of the trees?

Look closely and you can see that deer walked among the fallen fruit. They must have crossed Forbes or Fifth Avenue after dark to browse on the Cathedral of Learning lawn.

Nearby, the sweetgum balls were coated in snow on Monday, all melted by Wednesday.

American goldfinches arrived to pull seeds out of the balls. Some fell on the snow.

And a crow walked by to check it out.

Birds are finding food in the cold.

(photos by Kate St. John)

Guacamole and Quetzals

Resplendent Quetzal, male (photo from Wikimedia Commons)

What does the resplendent quetzal (pronounced ket ZAL) have in common with the Mexican food guacamole?

Guacamole with two chips (photo from Wikimedia Commons)

Answer: Avocados

Guacamole’s main ingredient is mashed avocado from cultivated Persea americana trees. Small fruits of wild avocado trees (Persea sp.) are the resplendent quetzal’s (Pharomachrus mocinno) favorite food.

The cultivated avocado fruit and tree looks like this.

Cross section of a cultivated avocado (photo from Wikimedia Commons)

Botanically speaking avocados are berries and there are many species.

In Mesoamerica, Persea proliferated into many new species, and the berries of some of them constitute a valuable food supply for quetzals that live in the montane rainforests of Mesoamerica. In particular, the resplendent quetzal‘s favorite fruits are berries of wild relatives of the avocado. Their differing maturing times in the cloudforest determine the migratory movements of the quetzals to differing elevation levels in the forests. With a gape width of 21 mm (0.83 in), the quetzal swallows the small berry (aguacatillo) whole, which he catches while flying through the lower canopy of the tree, and then regurgitates the seed within 100 meters (328 ft) from the tree.

Wikipedia: Persea genus

Resplendent quetzals time their breeding to coincide with the most abundant fruit and delay breeding in poor fruit years. Here’s a male quetzal and a wild avocado tree he might visit, Persea caerulea.

Resplendent quetzal, male, Monteverde, Costa Rica (photo from Wikimedia Commons)
Aguacatillo Persea caerulea fruits and leaves (photo from Wikimedia Commons)

Watch a pair of resplendent quetzals and their (gray colored) youngster among the wild avocado trees. The fruit is just the right size for a quetzal to swallow whole.

So now when you eat avocados you can think of resplendent quetzals.

(photos from Caroline Mueller and Wikimedia Commons; click on the captions to see the originals)

p.s. This topic was inspired by Caroline Mueller’s avocado saplings which she grows from the leftover pits.

Two home grown avocado trees (photos by Caroline Mueller)

Invasive Bradford (Callery) Pear is Banned in PA

Bradford (Callery) pear trees (photo by T. Davis Sydnor, The Ohio State University,

When landscapers began planting Bradford pears in the mid 1960s in suburban subdivisions, mall parking lots and streetscapes they told us not to worry. This flowering cultivar of the Callery pear (Pyrus calleryana) was bred to be thorn-less and sterile. We thought it could not reproduce.

The trees were planted everywhere.

Callery pear cultivars (photo by Leslie J. Mehrhoff, University of Connecticut,
Callery pear cultivars flowering in suburbia, aerial view (photo by Leslie J. Mehrhoff, University of Connecticut,

We soon found out that the flowers stink, but it took a few years to discover the trees are brittle. The Bradford cultivar breaks in storms.

Bradford (Callery) pear storm damage (photo by Rebekah D. Wallace, University of Georgia,

So horticulturists went back to the lab to create stronger cultivars including ‘Aristocrat’, ‘Autumn Blaze’, ‘Capital’, ‘Chanticleer’ (also known as ‘Cleveland Select’), ‘New Bradford’, ‘Redspire’, and ‘Whitehouse. The tree was poised to become invasive.

It took a while to realize that different sterile cultivars within the reach of the same pollinating insect could cross pollinate and produce fertile fruit. The seed is a hybrid of hybrids. Birds eat the fruit and transport the seeds.

Callery pear fruit, a.k.a.Bradford pear, Nov 2012 (photo by Kate St. John)

Pyrus calleryana spreads prolifically now by seeds and roots in old fields, roadsides and disturbed soil. The invasive trees are not noticeable until early spring when they bloom before our native white-flowering trees: chokecherry, downy serviceberry (shadbush), and hawthorn.

Callery pears take over disturbed soil (photo by Britt Slattery, US Fish and Wildlife Service,

It’s gone wild in 25 states and is listed as invasive in 14. In July 2021 South Carolina banned Pyrus calleryana sale and cultivation with enforcement phased in by October 2024.

Pyurs calleryana listed as invasive in 14 states (map from

In November 2021 the PA Department of Agriculture added Callery pear (Pyrus calleryana) to the state’s list of Noxious Weeds. It cannot be legally sold or cultivated in our state though you may see it in nurseries while enforcement is phased in through February 2024.

In the meantime, if you are offered a Callery pear cultivar as a landscaping choice, don’t buy it.

(fruit photo by Kate St. John, remaining photos and map from bugwood; click on the captions to see the originals)

p.s. Did you know that some of hybrid wild trees revert to their thorny ancestry? Don’t be confused if you see thorns in the wild.

Pyrus calleryana thorns in the wild (photo by John D. Byrd, Mississippi State University,

The Leaves Lingered

Though most trees are bare, the hilltop oaks still have leaves on 30 Nov 2021 (photo by Kate St. John)

4 December 2021

Last weekend many homeowners in Pennsylvania were annoyed that they had to rake leaves after Thanksgiving. A decade ago this would never have happened because the trees were bare by 5 November. Nowadays the leaves linger. Our warmer climate keeps them on the trees.

The delay in leaf drop has been increasing for at least a decade. In 2008-2012 most of the trees were bare by 2 or 4 November. In 2017-2021 the trees waited until 25-30 November. (*)

Meanwhile the height of fall color is later and lackluster. Twenty years ago we used to go leaf peeping on Columbus Day. This year the height of color in Schenley Park was on 13 November and not particularly breathtaking.

Fall color at Westinghouse Memorial in Schenley Park, 13 Nov 2021 (photo by Kate St. John)

Trees need a particular weather combination to trigger fall colors and leaf drop.

The timing and quality of color changes depend on a combination of temperatures, precipitation and sunlight. The best fall color displays occur after sunshine-filled days and cooler nights, following healthy doses of rain in the summer.

Washington Post: Fall foliage flopping: How climate change is dulling and delaying your leaf peeping

But it was way too warm in October. In fact it was the world’s fourth warmest on record.

U.S. Temperature Outlook for October 2021 issued 30 Sep 2021 by National Weather Service

The leaves lingered and finally by 30 November 2021 most of the trees were bare. Note that this date and all dates mentioned above are assessments of this same hillside in Schenley Park.

More than half of the trees are bare, Schenley Park, 25 Nov 2021 (photo by Kate St. John)

Read more about the disappointment of this fall’s foliage — and the economic impact — at the Washington Post: Fall foliage flopping: How climate change is dulling and delaying your leaf peeping.

(photos by Kate St. John, map from the National Weather Service)

Seen This Week

Ginkgo turning yellow at Schenley Park, 13 Nov 2021 (photo by Kate St. John)

20 November 2021

This week we had a last blast of fall color, a partial lunar eclipse and a surprising confirmation of pigeon fertility. Here are a few scenes from 12-19 November.

The ginkgo trees (Ginkgo biloba) turned yellow and will probably drop their leaves in a single day. Red oaks and hickories made a bright splash of color at Phipps’ outdoor garden on Monday.

Red oak at Phipps garden, 15 Nov 2021 (photo by Kate St. John)

Some beech leaves were already brown though the leaf veins were still yellow. Beech leaves cling to the smaller trees all winter, becoming paper thin and rattling in the wind.

Beech leaves turn brown though the veins are still yellow, Schenley Park, 15 November 2021 (photo by Kate St. John)

On Wednesday 17 November four of us drove north hoping for water birds but were disappointed by the lack of bird activity, particularly after the clouds moved in. Colorful leaves were scarce in Crawford County, especially at Conneaut Outlet swamp where high water killed the trees. This scene says “November in western Pennsylvania.”

Conneaut Outlet, Crawford County, 17 Nov 2021 (photo by Kate St. John)

On 18 November I saw a pigeon feeding two babies at its nest on Filmore Street near the Cathedral of Learning. Yes, nesting in November! Feral rock pigeons (Columba livia) breed year round if there’s enough food — and there is at this pile of birdseed on the corner.

Birdseed for pigeons at S. Dithridge & Filmore, 18 Nov 2021 (photo by Kate St. John)

As expected the partial lunar eclipse was obscured by clouds in Pittsburgh at 4am on 19 November. Only a tiny bright uneclipsed sliver is visible. The clouds are lit from below by the city lights.

Partial lunar eclipse obscured by clouds. Only the bright sliver shows in Pittsburgh, 19 Nov 2021 (photo by Kate St. John)

More leaves fell this week but most of the trees are not yet bare. Here’s a week’s worth of change at Schenley Park, 12 and 19 November.

Maples are bare, oaks are red, Schenley Park, 12 Nov 2021 (photo by Kate St. John)
Not yet. Most of the trees are Not bare. Schenley Park, 19 Nov 2021 (photo by Kate St. John)

The leaves are hanging on about two weeks longer than they used to. When will most of the trees be bare in Pittsburgh? Soon.

(photos by Kate St. John)