Category Archives: Trees

Why Leaves Turn Black Under Tree of Heaven

Spotted lanternfly honeydew below ailanthus tree turns black with sooty mold, Schenley, 25 Aug 2023 (photo by Kate St. John)

27 August 2023

In Schenley Park’s Panther Hollow there are only a handful of Ailanthus altissima trees (Tree of Heaven) which I rarely paid attention to until recently. A couple of weeks ago I noticed that the plants and ground beneath those trees were wet, though it had not rained. This week the leaves and ground are black. Both phenomena are a by-product of the spotted lanternfly (Lycorma delicatula) invasion.

Spotted lanternflies on a tree trunk, one egg mass below them (photo by Emelie Swackhamer, Penn State University,

Spotted lanternflies (Lycorma delicatula) are sucking insects that pierce the bark of their host plant, Ailanthus, and sip the sugary phloem that travels from the leaves to the rest of the plant. (Phloem flow is orange in the diagram below.)

Flow of xylem and phloem in plants (image from Wikimedia Commons)

Everything that eats excretes and spotted lanternflies are no exception. Their watery “poop” is called honeydew because it is full of sugar.

video embedded from Bug of the Week on Youtube

If there were only a few lanternflies we would never notice the honeydew but when a large number coat a tree the honeydew is hard to miss, especially for the consumers of honeydew: bees, wasps, hornets, ants and butterflies.

Butterfly sips on spotted lanternfly honeydew (photo by Rebekah D. Wallace, University of Georgia,
European hornet sips lanternfly honeydew (photo by Rebekah D. Wallace, University of Georgia,

Sugary honeydew eventually grows sooty mold. Everything with honeydew on it turns black.

Sooty mold is a fungus that appears as a black, sooty growth on leaves, branches and, sometimes, fruits. It is non-parasitic and not particularly harmful to plants apart from being unsightly. Potentially, it could affect the plant’s ability to use the sun for photosynthesis. If you can rub the black growth off with your fingers, it is probably sooty mold. If you cannot rub it off, it is most likely something else.

Univ of Hawaii Master Gardener Program: FAQ, Sooty mold
Sooty mold on vegetation beneath Ailanthus tree (photo by Richard Gardner,, yellow circle added
Spotted lanternfly honeydew below ailanthus tree turned black with sooty mold, Schenley, 25 Aug 2023 (photo by Kate St. John)

Eventually white mold may cover the honeydew. I haven’t seen this yet but I’m watching for it.

Spotted lanternfly honeydew grows mold (photo by Lawrence Barringer, Pennsylvania Department of Agriculture,

Will we ever be free of spotted lanternflies? Yes! Check out this blog This, Too, Shall Pass.

(photo credits are in the captions with links to the originals)

Where Is This Mosaic?

Beautiful mosaic. Where is it? (photo from Wikimedia Commons)

16 August 2023

Beautifully colored tiles. An intricate pattern. What floor, wall or ceiling holds this mosaic? Click here to see a closeup.

The photo caption at Wikimedia Commons has the answer:

Woody Dicot Stem Vascular Cylinder in One Year Liriodendron, photo from Berkshire Community College Bioscience Image Library, Pittsfield, Massachusetts.

The mosaic is made of cells in the woody stem of a one year old tuliptree (Liriodendron tulipifera), sliced thin and magnified 100 times. The colors and shapes are specific to the species and its age. The description indicates that things change at lot in a one year old tulip tree.

The mosaic slice was photographed in 2014 at Berkshire Community College in Pittsfield, MA from a sapling that probably grew in Western Massachusetts.

When a tulip tree grows up it has leaves and flowers like this.

Tulip tree leafout, Schenley Park, 28 April 2014 (photo by Kate St. John)
Tulip tree flower, 4 May 2017 (photo by Kate St. John)

Still beautiful and intricate even when not magnified.

For more information on the mosaic image see the description of the image here. It is so technical that I need a glossary to figure out what it means.

(photos from Wikimedia Commons and Kate St. John)

Pollen Season Gets Worse Every Year

Oak tree in bloom with dangling pollen flowers (photo by Kate St. John)

25 April 2023

If your pollen allergies have gotten worse there’s a good reason for it. A study of North American pollen trends in the last 30 years, led by William R. L. Anderegg, found that pollen season is starting earlier, lasting longer and has higher pollen counts than in the 1990s because of climate change.

Yale Climate Connections reports “In Anderegg’s research on pollen in North America, he saw pollen seasons starting about 20 days earlier than they did in the 1990s” and pollen concentrations increased by 21%. The higher temperatures and carbon dioxide in today’s atmosphere make plants more productive and allergies worse.

Right now in Pittsburgh we are at the height of pollen season. Recurring hot weather, 15+ degrees above normal, caused the oaks to bloom early and pollen so intense that my car turned yellow while parked at Anderson Playground for just an hour last Friday.

Allergy sufferers get a double whammy here because the pollen is added to Pittsburgh’s poor air quality making it particularly dangerous for children and people with asthma and respiratory illness.

A sneeze! Pollen allergies are in for a bad time (photo from Wikimedia Commons)

So, no, you’re not imagining it. Pollen season in North America is bad and is still getting worse.

Scientists predict that average pollen counts in 2040 will be more than double what they were in 2000.

Allergies and climate Change, Harvard School of Public Health
Shaking a pine bough, releases a cloud of pollen (photo from Wikimedia Commons)

Track the pollen count and get the daily forecast at

screenshot of pollen map on 25 April 2023 from


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

Seen This Week

Bluets, Knob Hill Community Park, 14 April 2023 (photo by Kate St. John)

15 April 2023

More flowers bloomed and more trees leafed out as hot summer weather continued this week.

I saw a few bluets (Houstonia) and spring beauty (Claytonia) at Knob Hill Community Park yesterday.

Spring beauty, Knob Hill Community Park, 14 April 2023 (photo by Kate St. John)

In Frick Park on Thursday this box elder (Acer negundo) was blooming and leafing out at the same time.

Box elder flowers and leafout, Frick Park, 13 April 2023 (photo by Kate St. John)

But many native trees still looked bare, such as the oaks on this hillside.

Progress of leafout at Frick Park, 13 April 2023 (photo by Kate St. John)

The slowness of native trees made last weekend the perfect time to see the invasive extent of Callery pears (Pyrus calleryana). Native white-flowering trees, such as serviceberry and wild cherry, were not blooming yet so the only white trees in the landscape were the Callery pears.

On 8 April at the Ridge Road interchange on the Parkway West (I-376) I found thick stands of Callery pears as far as the eye could see (first 2 slides below). The trees gained a foothold in disturbed soil after construction of the Ridge Road interchange in 2006 and Settlers Ridge shopping center in 2009. The third slide shows Callery pears in the woods at Wingfield Pines.

Callery pears were banned in PA in 2021. As you can see, we “locked the barn door after the horse got out.”

p.s. This weekend the downy serviceberries are blooming (white) and the Callery pears are growing leaves (white+green) so it’s no longer possible to pinpoint the invasive species.

(photos by Kate St. John)

Pittsburgh Redbuds 7 Years On

A redbud branch in full bloom, Frick Park, 12 April 2023 (photo by Kate St. John)

13 April 2023

Hot weather this week is speeding up spring and Pittsburgh’s redbuds are bursting into bloom. Yesterday at Frick Park I found most buds ready to burst with a few branches in full bloom.

Redbuds seem to be everywhere now but this wasn’t always the case.

Seven years ago the Western Pennsylvania Conservancy launched Pittsburgh’s Redbud Project to beautify Pittsburgh’s riverfronts. Envisioned by landscape architect Frank Dawson, the goal was to make Pittsburgh as beautiful with native redbud trees as D.C. is during the Cherry Blossom Festival.

They originally planned for 1,200 trees but by now they’ve planted three times that many along the Allegheny, Monongahela and Ohio riverfronts. The project also inspired redbud plantings in Pittsburgh’s parks and neighborhoods by Pittsburgh Parks Conservancy and Tree Pittsburgh.

Seven years ago today I wrote about the Pittsburgh Redbud Project as I was about to participate in the launch event on 19 April 2016. We gathered for tree planting on the North Shore near the Mister Rogers statue and learned why our assignment — digging holes! — was so important for a tree this size.

Pittsburgh Redbud Project: Volunteers watch how it’s done, Pittsburgh’s North Shore, 19 April 2016 (photo by Kate St. John)

The trees have now been in place for seven years and they are beautiful. This stand near the Frick Environmental Education Center drew attention yesterday even though they were still in bud.

Redbuds drawing attention at Frick Park, 12 April 2023 (photo by Kate St. John)

With temperatures in the low 80s this weekend will be the perfect time to see redbuds at their best.

Check out the Visit Pittsburgh website — Insider’s Guide: Pittsburgh Redbuds — for tips on where to go and photos of what you’ll see.

It’s definitely time to get outdoors!

(photos by Kate St. John, Pittsburgh Redbud Project logo from Western PA Conservancy)

Balsa Wood’s Environmental Paradox

Balsa canopy and trunk against the sky (photo from Wikimedia Commons)

1 March 2023

While traveling in Ecuador last month I saw balsa trees growing in the wild and learned that Ecuador supplies 95% of the world’s commercial balsa wood. The driving force behind these exports is an environmental paradox.

Balsa (Ochroma pyramidale) is a pioneer tree of tropical forest clearings, native to Central and South America. It is so fast growing that it can grow 6-9 feet a year and reach full height of about 100 feet in only 10-15 years. The trees are short-lived, lasting only 30-40 years.

Mature balsa tree in Colombia (photo from Wikimedia Commons)

Inside the living wood the cells are large, thin-walled and full of water so that the tree stands upright. When cut and kiln dried the wood is very lightweight and sturdy.

In the wild balsa trees are widely spaced at about one tree per acre (2-3/hectare) but to meet commercial demand balsa is grown in plantations containing 400 trees/acre (1000/hectare). Plantation trees are cut at 6-10 years old because much of the wood in older trees — the core and outer layers — is commercially useless.

Balsa plantation (photo from both Forestry Journal UK and WR Carpenter PNG)

Most of us are familiar with balsa wood in toys and woodworking.

Boy flies a balsa wood airplane (photo by Liz Henry via Flickr Creative Commons license)

This balsa wood bridge won a physics contest in 2006. It weighs only 60.95 grams (0.134 pounds) yet it supported 14.51 kg (31.989 pounds).

Balsawood bridge contest at Whitmore Lake High School, 2006 (photo from Wikimedia Commons)

Ecuadorans made ocean-going rafts of balsa logs long before the Spanish arrived in the 1500s and it is still used for rafts today. (Balsa is the Spanish word for raft.)

Pre-Colombian balsa rafts in Ecuador circa 1565 and two modern balsa rafts next to a kayak (images from Wikimedia Commons)

But none of these uses are the driving force behind increased Ecuadoran balsa exports.

Balsa wood is a component in wind turbine blades. According to GE which manufactures wind turbine blades at Castellon, “Workers make the blades from fiberglass fabric and balsa wood. Then, the blade is covered with an airtight foil and the team installs a network of tubes that pumps in and distributes the resin that will hold it together.”

Wind turbine blades in transport, I-80 in Iowa (photo from Wikimedia Commons)

In the past decade when the Chinese government eliminated taxes for the alternative energy industry, it prompted a boom in wind turbine production. The majority of Ecuador’s balsa exports go to China.

Chuanshan Wind Turbine Field, 2015-04-11 02 (photo from Wikimedia Commons)

Plantations provide 60% of Ecuador’s balsa wood but the remaining 40% is coming from wild trees in the rainforest. Using satellite images and on-the-ground followup Mongabay and Global Forest Watch have documented deforestation in Ecuador, especially east of the Andes in the Amazon watershed. According to Mongabay:

The Pastaza River Basin is one of the areas most affected by the balsa industry. There, the Pastaza, Bobonaza, Curaray, Villano, Copataza and other rivers are used as logging access routes, with satellite imagery showing their banks increasingly pockmarked by deforestation. Sources tell Mongabay Latam that the logging has been so intense that balsa has been completely removed from some areas.

…[And now] loggers are starting to harvest other timber species in areas that have been denuded of balsa.

“The same loggers and traders that one year ago arrived from [the cities of] Quevedo, Esmeraldas or Guayaquil are now arriving to look at what else is there,” Páez said.

“There is an ongoing process of deforestation of valuable tree species in Indigenous territories” with no monitoring by the authorities, she added.

Mongabay, August 2021: Indigenous Amazonian communities bear the burden of Ecuador’s balsa boom

The deforestation shows up as pink dots in Global Forest Watch’s map, below left. Are these places where birders go? The eBird map of Ecuador hotspots at right is red at sites where birders reported more than 500 species. There seems to be overlap south and east of Quito.

Screenshots of Global Forest Watch map of Ecuador integrated deforestation alerts + eBird map of Ecuador hotspots

The environmental paradox of balsa wood is this: To create renewable energy quickly, we are cutting down the rainforest.

Read more in this article from Mongabay and this from World Rainforest Movement.

NOTE about the eBird map: eBird maps show where birders have found birds and reported them on eBird. The blank spots on the Ecuador map do not indicate an absence of birds but instead an absence of birders or an absence of Internet access.

(photo and map credits are in each caption; click on the captions to see the originals)

Seen This Week

Woodland crocus or Tommasini’s croscus, 21 Feb 2023 (photo by Kate St. John)

25 February 2023

For seven days this week the temperature stayed above freezing and hit 71 degrees F on Thursday. At 26 degrees above normal, flowers opened on plants and trees.


My favorites were the early crocuses. Native to Bulgaria, Hungary, Albania and the former Yugoslavia, these woodland crocuses (Crocus tommasinianus) are often seen in gardens but someone in my neighborhood planted them in a grassy front yard. Because the flowers bloom before the grass grows they are in no danger of being mowed.

Tomasini’s crocuses blooming in the grass, Neville Ave, 21 Feb 2023 (photo by Kate St. John)

On Pitt’s campus Cornelian cherry trees (Cornus mas) produced yellow flowers.

Flowers of Cornelian Cherry, 20 Feb 2023 (photo by Kate St. John)

Red maples (Acer rubrum) bloomed next to Carnegie Museum …

Red maple flowers near Carnegie Museum, 20 Feb 2023 (photo by Kate St. John)

… and at Frick Park the maple branches looked thick with tiny flowers, including yellowish pollen-bearing ones.

Maple trees against a blue sky. Branches look thick with small flowers and pollen anthers, Frick Park, 23 Feb 2023 (photo by Kate St. John)

This week, tiny leaves opened on jetbead (Rhodotypos scandens) and a few honeysuckle bushes. Unfortunately invasive plants are first to leaf out.

New leaves opening on jetbead, Frick Park, 23 Feb 2023 (photo by Kate St. John)

The coming week will be like a wet blanket: above freezing, gusty wind, lots of rain.

(photos by Kate St. John)

Seen This Week

Sunrise, 11 Jan 2023 (photo by Kate St. John)

14 January 2023

The sunrise was gorgeous and cold last Wednesday when a group of us decided to walk at Jennings in Butler County. We saw few birds but there were ice heaves, buttress roots on an elm, and the seeds of old man’s beard (Clematis drummondii).

Ice heave at Jennings, Butler County 11 Jan 2023 (photo by Kate St. John)
Elm tree with buttress roots, Jennings, Butler County, 11 Jan 2023 (photo by Kate St. John)

When old man’s beard is in bloom it’s called virgin’s bower, transforming it from a young woman to an old man in a matter of months.

Seeds of Virgin’s bower, a.k.a. Old man’s beard, Jennings, Butler County, 11 Jan 2023 (photo by Kate St. John)

My friends who live north of the city have not seen many dark-eyed juncos at their feeders this winter, but juncos are definitely present at the Frick Park Environmental Education Center. Charity Kheshgi posted photos of our recent trip to Frick.

(bird photos by Charity Kheshgi embedded from Instagram, all other photos by Kate St. John)

A Few Things Seen

A red oak felled at Anderson Playground in Schenley Park, 30 Dec 2022 (photo by Kate St. John)

7 January 2023

This week’s rain dampened outdoor activities but there were still some things to see.

Chainsaw tree “trimming” continues in the city. This red oak had a hollow core so it was chopped down in late December at Anderson Playground in Schenley Park. Can you count the rings and determine its age?

On 3 January rain flecked the camera as Ecco stopped by for a visit. Notice how wet his head is!

On 4 January the rain finally stopped and the moon shone at 8pm.

When the cold snap ended on 28 December the ice thawed and the creeks began running again. Listen to the sound of Panther Hollow Run in Schenley Park on 30 December 2022.

(nest photos from the National Aviary snapshot camera at Univ of Pittsburgh, all other photos and video by Kate St. John)

Deer Density at a Glance

Tall columnar arborvitae along an alley in Kutztown, PA, 27 Nov 2022 (photo by Kate St. John)

12 December 2022

At Thanksgiving in Kutztown, PA I was stunned to see a solid wall of arborvitae bordering a neighborhood. In Pittsburgh’s East End, arborvitae is always bare from the ground to 4-5 five feet up, eaten by our overpopulated deer. Here’s a row of arborvitae at Schenley Park golf course.

Deer damage on arborvitae at Schenley Park golf course, 11 Dec 2022 (photo by Kate St. John)

Why didn’t deer browse the Kutztown trees? My guess is that they are the Green Giant variety of Western arborvitaes. Davey Tree explains:

Deer don’t care for Western arborvitaes, like green giant, steeplechase or spring grove. So, if you plant these, they may leave them alone.

Though, when deer are starving, they become less picky and will eat almost anything, including those deer-resistant arborvitaes. If deer are a big problem in your yard, avoid arborvitae altogether. Stop Deer from eating Arborvitae trees (even Emerald Green)

There are so many deer in Pittsburgh that indeed they eat almost anything. They even nibble on poisonous milkweed!

Kutztown has far fewer deer per acre.

The trees show deer density at a glance.

(photos by Kate St. John)