Category Archives: Trees

Don’t Stake That Tree

Tree staking damage (photo from Wikimedia Commons)

It’s tree-planting season and a good time to remember that trees can be damaged by our good intentions. In the old days we staked every newly planted tree but we’ve since learned that for most tree plantings, stakes are a bad idea.

Tree trunks become strong from the ground up by swaying in the wind. When a tree is staked, it “thinks” it already has strong roots where it’s staked so it puts effort into growing tall instead of establishing roots. The trunk becomes strong above the yoke and remains weak below it. In addition the yoke may damage the trunk, further weakening the tree as shown above.

If your new tree has a big root ball it probably doesn’t need to be staked, though there are exceptions quoted here from the Davey Tree blog. You should use stakes on …

  • Bare-root trees or trees with a small root ball.
  • Trees planted in areas with lots of foot traffic, like a sidewalk or street.
  • New trees that can’t stand on their own or those that begin to lean.
  • Eucalyptus trees, mesquite hybrid trees, oleander trees and acacia trees.
  • Tall, top-heavy trees with no lower branches.
  • Young trees if you live in a very windy area or if the soil is too wet or loose.”

If you use stakes make sure to remove them at the next growing season. If you don’t, the tree will grow around them like this one did at Schenley Park. See more photos at How Stakes Hurt Trees.

Tree stake was never removed so the tree grew over it, Schenley Park (photo by Kate St. John)

Still have questions? Get expert advice at Davey Tree blog, Gardening Know-how, or Northern Woodlands.

(photo credits: Wikimedia Commons (click caption for the original), and Kate St. John)

Bug Finds Food Using Infrared

Western conifer-seed bug (photo by Dawn Dailey O’Brien, Cornell University, Bugwood.org)

Back in 2008 a team of scientists made an amazing discovery: the western conifer-seed bug uses infrared sensors to find his favorite food.

Western conifer-seed bug (photo by David Cappaert, Bugwood.org)

The western conifer-seed bug (Leptoglossus occidentalis) is a North American sucking beetle that resembles a stink bug, though he’s not in the stink bug family. Ornately marked and 1/2 to 3/4 inch long (16-20 mm), he feeds on the sap of developing pine cones. This causes the seeds in the cones to wither which is only a minor problem in western forests but a big deal at pine seed orchards.

The seed bug used to be confined to temperate forests of the Pacific coast but has naturally expanded his range all the way east to Nova Scotia. In the past 20 years he’s been accidentally imported into Europe, Chile, and Japan so there’s international interest in how this bug finds pine cones at a distance.

The 2008 study led by Stephen Takács, Infrared radiation from hot cones on cool conifers attracts seed-feeding insects, found that pine cones emit infrared light at all levels and the western conifer-seed bug can “see” it.

Pine cones emit infrared light because they’re warmer than the rest of the tree by almost 60 degrees F. These photos from the study, taken in normal and infrared light, explain: “The temperature bar to the right of the paired images reveals that cones are up to 15°C warmer than foliage under high-cloud conditions.”

Conspicuousness of western white pine cones in mid-range and long-range IR spectrum thermographs. (a) visual spectrum photographs (b) thermographs (image from Royal Society Publishing 2008.0742)

To prove that the bug is attracted to infrared, researchers set up infrared emitters shaped like pine cones (photos below). Did the bug approach them? Yes, it did. Could the bug find the cones when his IR sensors were experimentally blocked? No he could not.

As the study explains:

Here, we show that the western conifer seed bug, Leptoglossus occidentalis Heidemann (Hemiptera: Coreidae), a tissue specialist herbivore that forages during the photophase and feeds on the contents of seeds within the cones of many conifers (Blatt & Borden 1999; Strong et al. 2001), uses IR radiation from developing cones as a long-range foraging cue. We present data revealing that (i) cones are warmer and continuously emit more near-, mid- and long-range IR radiation than needles, (ii) seed bugs possess IR receptive organs and orient towards experimental IR cues, and (iii) occlusion of the insects’ IR receptors impairs IR perception.

Infrared radiation from hot cones on cool conifers attracts seed-feeding insects, Stephen Takács et al, Royal Society Publishing

Apparently the world looks very different to a western conifer-seed bug. For him the pine cones really stand out while the rest of the world is boring.

postscript: NOTE that the western conifer-seed bug (Leptoglossus occidentalis) is not the scourge of our western pine forests. The forests are being killed by a completely different native bug — the mountain pine beetle (Dendroctonus ponderosae) — whose larvae make galleries under the bark and kill the tree from inside. Below: Pines killed by the mountain pine beetle, Galleries under the bark, and the mountain pine beetle.

Mountain pine beetle (Dendroctonus ponderosae) and its damage (photos from bugwood; see citations and links below)

photo credits: Click on the captions to see the originals.
* Infrared images from study at Royal Society 2008.0742, Creative Commons license
* Western conifer-seed bug photos from Wikimedia Commons
* Mountain pine beetle row of photos:
#5540352: Kill at Deadman Road, CO, William M. Ciesla, Forest Health Management International, Bugwood.org, #UGA1254003, Galleries, William M. Ciesla, Forest Health Management International, Bugwood.org, #UGA1306005, mountain pine beetle, Dendroctonus ponderosae, Ron Long, Simon Fraser University, Bugwood.org

This topic was inspired by a 2008 article from Nature’s Crusaders blog: Pine Beetle Uses Infrared to Find Next Meal

Get Thee To A Shrubbery

The “ultimate green square,” Leylandii enclosing a tennis court (photo from Wikimedia Commons)

Even when a species is invasive, nurseries sell it and people plant it until it’s banned. Consider the case of Leylandii trees, sold as shrubs in the U.K.

At the garden center, the homeowners say, “I want something that grows quickly and provides some privacy.” They bring home these cute little shrubs.

Just planted, a cute little Leylandii shrub (photo from Wikimedia Commons)

But Leylandii grow three feet a year. Eventually the shrubs are so tall they have to be trimmed using ladders, like the “ultimate green square” in the photo at top.

The hedges eat the bus stop …

Leylandii eat the bus shelter (photo from Wikimedia Commons)

… and engulf the lane.

Leylandii crowd a lane (photo from Wikimedia Commons)

On Throw Back Thursday read how these “privacy” shrubs can spark fights among the neighbors in this vintage post: Plant A Shrub, Start A Fight.

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

p.s. Shakespeare fans will recognize my allusion to Hamlet’s madness.

Beat The Heat With Trees

It’s been hot in Pittsburgh lately but nothing like the heat wave that’s sweeping Europe with highs above 100 degrees F. @JeremyDBarrell tweeted a long term solution with a compelling image by Meg Caffin.

Meg Caffin is an urban forest consultant from Australia who provides guidance for cities looking to beat the heat. Her image at top used an infrared camera to show the temperature difference between a paved churchyard and the trees behind it. I’ve made a Fahrenheit translation below. Yes, it’s 113oF on the pavement and only 77oF under the trees.

Tree shade is cooler than building shade because buildings merely block the sun while the trees actually lower the temperature.

Schenley Park near Bartlett entrance (photo by Kate St. John)

Trees cool the air by transpiring. They take up water from the ground and release it from the stomata in their leaves. The release doesn’t usually drip from the leaves as shown below. Instead it evaporates and that’s what cools the air.

Transpiration droplets from a leaf (photo from Wikimedia Commons)

Evaporation — changing a liquid to a gas — uses energy. According to the Transpiration blog, “Energy is absorbed into liquid water. This reduces the temperature of the surrounding plant tissue and nearby atmosphere. To evaporate 1 gram of water 590 calories of energy is required.”

So more trees mean less heat.

If that isn’t enough reason to like trees, here’s another benefit. Trees increase your property value as shown in the EPA cost-benefit analysis below.

Trees increase property value far beyond cost of maintenance (EPA)

Plan to plant a tree this fall or plan to keep one. It’s cheaper to keep an existing tree than to plant a new one and mature trees increase property value even more.

Meanwhile if you’re feeling hot right now, visit a local park.

Schenley Park Upper Trail, July 2017 (photo by Kate St. John)

Beat the heat among the trees.

(embedded Tweet from Jeremy Barrell; infrared heat image by Meg Caffin for the City of Geelong, Australia (Fahrenheit added); transpiring leaf from Wikimedia Commons; photos of Schenley Park by Kate St. John)

A Beautiful Success Story

Kentucky yellowwood flowers, Schenley Park, 20 May 2019 (photo by Kate St. John)

This flowering tree is a native North American but was so rare that few people ever saw it until botanists fell in love with it.

Originally found in small patches from Arkansas to Kentucky and Tennessee, the Kentucky yellowwood’s (Cladrastis kentukea) beautiful flowers, mid-story height, and tolerance for full sun in urban settings makes it the perfect ornamental.

Original range of the Kentucky yellowwood tree (map from Wikimedia Commons)

Planted in eastern North America for over 200 years, it became naturalized in scattered locations from Ohio to Massachusetts. Allegheny County is one of the few new places where Kentucky yellowwood grows wild.

On Sunday in Schenley Park, our group was awed by the profusion of vanilla-scented flowers at the Visitors Center. We didn’t recognize the species so I went exploring yesterday and found it both cultivated and wild.

Kentucky yellowwood at the Schenley Park Visitors Center, 20 May 2019 (photo by Kate St. John)

Here are some other cool facts about Kentucky yellowwood:

  • It’s called yellowwood because “a clear yellow dye is obtained from the heartwood.”
  • It is the only Cladrastis native to North America.
  • The flowers are attractive to bees. Narratives say the tree is attractive to birds.
  • Flowering varies from year to year with heavy blooming every 2-3 years, particularly after a long hot summer. 2019 is a big year for Kentucky yellowwood in Pittsburgh.
  • Every description says the tree flowers in June, but blooming started here in mid May — two+ weeks early, probably due to climate change.

Once I started looking I found the tree in many out of the way places in Schenley Park, probably growing wild. Kentucky yellowwood is a beautiful success story in Pittsburgh.

They Fold Their Leaves

Black locust, young leaves (photo from Wikimedia Commons)

Now that black locusts (Robinia pseudoacacia) are leafing out in Pittsburgh we can watch their leaves do exercises.

According to Wikipedia black locust leaves fold together at night and during wet weather, a trait of the Legume family called nyctinasty. I’ve often seen nyctinasty in clovers but have never noticed it in black locusts because I haven’t been paying attention. This month I plan to take a look.

It will be a good week to get close to black locusts. They’re blooming now with a sweet grape-like scent. See photos and read more about them in last year’s article: The Sweet Smell of Trees.


Tiny Hemlock Pest Has Hatched

Hemlock woolly adelgid nymphs (photo by Elizabeth Benton, University of Georgia, Bugwood.org)

A week ago I received a message from the USA National Phenology Network that hemlock woolly adelgids would hatch very soon in Pittsburgh and the southern Appalachians. This is worrisome because the nymphs are the active phase of this forest pest.

Hemlock woolly adelgid hatch announcement from USA NPN

Originally from Japan, hemlock woolly adelgids (Adelges tsugae) kill eastern hemlocks in 4-20 years by locking on where the needle meets the stem and sucking the lifeblood out of the tree (closeup at top).

The adults are sedentary, attached to a tree. The nymphs, however, are tiny and mobile. They blow on the wind and hitchhike on clothes, equipment, birds and animals. They spread very easily just after they’ve hatched.

The message above says “You should see active nymphs” but you won’t. At 1/100th of an inch they’re smaller than a grain of sand, almost microscopic. And yet, their effect is devastating.

Hemlock woolly adelgids have already killed up to 80% of the hemlocks on parts of the Blue Ridge Parkway and in Shenandoah National Park. They are eating their way through the Great Smoky Mountains, shown below, and they’re killing hemlocks in Pennsylvania.

Tree death from Hemlock woolly adelgid in the Great Smoky Mountains (photo by Ignazio Graziosi, University of Kentucky, Bugwood.org)

We won’t know how far they’ve spread this spring until they reveal their presence next fall when the females deposit woolly egg sacs on the undersides of hemlock branches.

Hemlock woolly adelgid eggs covered in white “wool” (photo by Steven Katovich, USDA Forest Service, Bugwood.org)

Right now the nymphs are spreading.

Read more about hemlock woolly adelgids at the USA National Phenology Network.

(photos from Bugwood’s invasive.org, message and map from USANPN. Click on the captions to see the originals)

Not A Nice Flowering Tree

Callery pear gone wild (photo by Richard Gardner, Bugwood.org)

Yesterday I noticed white flowering trees on the hills and swales near Robinson Town Centre (I-376 West). “How nice,” I thought, “Who planted those trees in the empty places?” No one. They’re invasive.

April is the perfect time to see the invasive extent of callery pears (Pyrus calleryana) because they bloom before our native white-flowering trees: chokecherry, downy serviceberry (shadbush), and hawthorn.

Originally imported from China in the early 1900s as root stock for pear orchards, USDA bred them as landscape trees in the 1950s and came up with a winning cultivar, the thorn-less sterile “Bradford pear.”

From 1960 to the 1990s callery pears were wildly popular as street trees in suburbia. They’re pretty in early spring, colorful in fall, and they grow well in the full sun and disturbed soil found in new subdivisions. The Bradford cultivar is also brittle so commercial plant breeders created other cultivars. That’s when the genie came out of the bottle.

In a single cultivar population the fruits are sterile but if two different cultivars are planted near each other, or even grafted together, insects cross-pollinate them and the trees produce fertile fruit. Birds eat the fruit and disperse the seeds. The trees escape to the wild.

Callery pears grow anywhere. A patch can start with a single tree that becomes a thicket in several years. Dense thickets push out all native species. To make matters worse, the wild trees can have 3-inch thorns! The best field-scale control measure is to brush-hog and then mow every year. They still come up!

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

Callery pears now grow wild from Texas to New York and Massachusetts. They’re listed as invasive in eight states including our own: Pennsylvania, Maryland, Virginia, South Carolina, Georgia, Alabama, Tennessee, and Illinois.

You’ll see them this month on open hillsides and fields along the interstate, near shopping centers, and at the edges of subdivisions.

Don’t plant callery (Bradford) pears. They are not nice flowering trees.

(photos by Richard Gardner and Britt Slattery via bugwood.org; click on the captions to see the originals)

Red Maples Are Complicated

Male red maple flowers fallen from the tree, 10 April 2019 (photo by Kate St. John)

This week the hillsides turned faintly red as red maples (Acer rubrum) bloomed across southwestern Pennsylvania. The city’s maples bloom sooner than the suburbs so I’ve had a preview of what’s to come.

In Schenley Park the ground under some red maples is carpeted with fallen flowers (above) while others retain flowers that are setting seed (below).

Female red maple flowers on the tree, developing samaras, 10 April 2019 (photo by Kate St. John)

That’s because red maples are sexually complicated. They are polygamodioecious which means some trees have only male flowers, some have only female, and some have both (i.e. hermaphroditic). And they can even switch back and forth:

Under the proper conditions, the tree can sometimes switch from male to female, male to hermaphroditic, and hermaphroditic to female.

Wikipedia Acer Rubrum

Watch your local red maples to see what they’re up to. The one in my backyard dropped its flowers a few days ago. This year it’s a male. 😉

p.s. For more on maple phenology, read Chuck Tague’s blog post: Maples In Spring: A Study in Diversity.

(photos by Kate St. John)

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)