Category Archives: Phenology

Buds About To Burst

Yellow buckeye buds about to burst, 1 April 2019 (photo by Kate St. John)

Yesterday I found these buds about to burst in Schenley Park.

Yellow buckeyes (Aesculus flava) are one of the first trees to leaf out in the spring, unfurling their dramatic palmate leaves. They’re such a welcome splash of green that I photograph them nearly every year. This is the first time I noticed the bud at this stage. I didn’t expect it to be red.

Over the years my buckeye photographs have documented the vagaries of spring in Schenley Park. In cooler years — such as 2015 — the buds weren’t this far along in mid-April. Here’s a closed bud on 15 April 2015.

Closed bud on 15 April 2015 (photo by Kate St. John)

In hot years — such as 2012 — the buds opened weeks ahead of schedule. This buckeye was completely leafed on 19 March 2012.

Yellow buckeye tree 19 March 2012 (photo by Kate St. John)

This year appears to be a “normal” spring … whatever that means these days.

(photos by Kate St. John)

Late March in Schenley Park

  • Cornelian cherry (Cornus mas), 28 March 2019 (photo by Kate St. John)

Spring is coming at a good pace this year. Unlike hot years, such as March 2012, there’s time to appreciate each new leaf and flower before the next set appears.

My photos above show a selection of leaves and flowers at Schenley Park this past week. Most were taken on March 28 but the real surprise was coltsfoot blooming on St. Patrick’s Day. That flower hid for ten days and appeared again last week.

Unfortunately, all of these plants are alien and some are invasive. Their ability to spring ahead of the local plants gives them an advantage all year long.

Click here for that same honeysuckle branch, bud-to-leaves on March 11, 16.

(photos by Kate St. John)

The Trees Are Snowing

Drift of fluffy seeds from London plane trees, 17 March 2019 (photo by Kate St. John)

Last week I found fluffy drifts on the sidewalks in my neighborhood. They’re the airborne seeds of London plane trees (Platanus × acerifolia), planted in Pittsburgh in the late 1800s because they’re tolerant of air pollution.

Like their parents — oriental plane tree (Platanus orientalis) + American sycamore (Platanus occidentalis) — London plane trees retain their dangling seed balls over the winter.

London plane tree fruit in autumn (photo from Wikimedia Commons)

Then in the first warmth and light of spring the seed balls disintegrate and the seeds blow away. You’ll find drifts near American sycamores, too.

London plane tree fruit disintegrating (photo from Wikimedia Commons)

In March the trees are snowing.

(seed drift photo by Kate St. John; remaining photos from Wikimedia Commons, click on the images to see the original)

Weeping Willows Hint of Spring

Weeping willow turning yellow, Schenley Park, 15 Feb 2019 (photo by Kate St. John)

Weeping willows (Salix babylonica) are popular landscape trees that were brought here from Asia. They’re easy to notice at this time of year because their drooping stems turn yellow in very early spring. From a distance you see a splash of yellow.

Imported species, especially those from Europe, grew up in a steady climate with few spring surprises so they’re quick to bloom in the spring and late to drop their leaves in autumn.

Meanwhile our native trees are still brown, conservative about producing tender shoots because they know that volatile spring weather can bring a killing frost in April.

Are you tired of winter? Watch for the weeping willow’s hint of spring.

(photo by Kate St. John)

Watch for Witch Hazel

Witch hazel flowers catch the light after the leaves are gone, November (photo by Kate St. John)

When the leaves are gone these lacy flowers stand out in the forest.

American witch hazel (Hamamelis virginiana) blooms from late October into December in eastern North America.  Its delicate yellow flowers smell like lemon.

Witch hazel flower, October in Schenley Park (photo by Kate St. John)

Since witch hazel blooms when few insects are out how are the flowers pollinated?

In 1987 Bernd Heinrich found that owlet moths come out at night to sip the flowers and thereby pollinate them.

The moths survive cold weather by hiding under leaf litter during the day, then shivering to warm up and fly at night. Click here to learn more.

(photos by Kate St. John)

When Will Most Of The Trees Be Bare?

Leafless bur oak, Schenley Park, 4 Nov 2011 (photo by Kate St. John)

Every year I record the date when most of the trees are bare on my favorite hillside in Schenley Park — the hill at the end of the Greenfield Bridge.

In 2008 the leaves were gone by 2 November.  In 2012 Hurricane Sandy stripped them from the trees by 4 November.

Last year the changes happened much later. In 2017, the leaves were still green in late October and more than half were still on the trees on 27 November.  Here’s a 2017 slideshow of autumn trees on that hillside.

  • 26 October 2017: Lots of green at the end of October 2017.

This year is similar to last so I wonder … When will most of the trees be bare?  November 15?  20?  30? Later?

Let me know how the trees look where you live and vote for the date “When Most of the Trees Will Be Bare” by leaving a comment below.

HINT!  Two factors that affect leaf loss on this hillside:  (1) More than half of the trees are oaks; oaks drop their leaves later than maples.  (2) This city location is warmer than surrounding counties.

(photo by Kate St. John)

Gentian Gone To Seed

Bottle or closed gentian (Gentiana andrewsii) blooms in September in western Pennsylvania.  By the end of October it’s gone to seed.

In bloom this gentian’s tightly closed petals prevent most insects from reaching its nectar, though bumblebees can force their way in. 

Bottle gentian in bloom, September 2015 (photo by Kate St. John)

Carpenter bees take a shortcut. They drill a hole in the petals to access the pollen and nectar. Once there’s a hole, honeybees and other small insects use it, too.

When I found the faded gentian shown above, I plucked a dried flower to examine the seeds.  Aha!  The closed petals have two holes in them.  The seed pod also has two curled knobs at the top.

I pulled the knobs apart to reveal the seeds …

… and scattered them nearby. 

I hope they’ll become new gentians next year.

(photos by Kate St. John)