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?
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.
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.
This one was chopped down but it came back stronger than ever. Notice the huge leaves.
Eventually botanists and gardeners realized that P. tomentosa is invasive. This map of paulownia’s occurrence in the U.S. …
… nearly matches the map of its State Invasive listings. Maryland and Massachusetts have outlawed it.
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.
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!
Trees with stacks of white flowers are drawing our attention this week in Pittsburgh. Perhaps you’re wondering “What tree is this? “
Horsechestnuts (Aesculushippocastanum) 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.
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.
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)
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.
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.
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)
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.
The cultivated avocado fruit and tree looks like this.
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.
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.
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.
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.
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.
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.
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.
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.
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.”
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.
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.
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.
The leaves are hanging on about two weeks longer than they used to. When will most of the trees be bare in Pittsburgh? Soon.