Category Archives: Trees

A Big Year For Acorns

Acorns litter a sidewalk on Tennyson Ave, Pittsburgh, 27 Sept 2020 (photo by Kate St. John)

1 October 2020

When Rob Protz mentioned last week that a pin oak near his home is producing more acorns than he’d ever seen before I started paying attention in my neighborhood. Yes, there are lots of acorns in Oakland. It looks like a masting year for red oaks in southwestern Pennsylvania.

Acorns litter the grass in Oakland, Pittsburgh PA, 27 Sept 2020 (photo by Kate St. John)

Oaks are one of many trees that irregularly cycle their fruit production to insure that predators don’t eat everything. They boom or bust by synchronizing seed production. White oaks have a bumper crop in 3 years, red oaks on a 4 year basis. The bumper crops are called masting years.

Acorns in the red oak group take two years to mature so those falling now were formed in the spring and summer of 2019, influenced by spring precipitation, summer temperatures, the last killing frost, and each other.

North Oakland has a lot of oaks (duh! it’s the neighborhood name) so of course we have acorns on the streets. They make a hollow “ponk” sound when they fall on parked cars.

Check out the acorn crop in your own neighborhood. Is it a masting year where you live?

p.s. In masting years you’ll see more acorn predators — squirrels, blue jays and deer — as we did in the big acorn year of 2013.

(photos by Kate St. John)

Tiny Jumping Beans

Jumping oak galls, Neuroterus saltatorius (photo by Donald Owen, California Department of Forestry and Fire Protection via bugwood.org)

24 July 2020

There’s a cool thing happening in California right now that we never see in Pennsylvania. In neighborhoods with white oaks there are tiny “jumping beans” in the gutters.

Here’s that they look like, recorded a week ago by Mary K Hanson.

They’re even better in slow motion, recorded by Mark Eagleton in Woodland, California.

Though they resemble the moths called “Mexican jumping beans” (Cydia deshalsiana) these galls are the agamic (asexual) second generation of tiny Neuroterus saltatorius wasps that mature on white oak leaves and fall to the ground.

Neuroterus saltatorius 2nd generation galls on back of oak leaf (photo by Steve Katovich via bugwood.org)

The larvae are tightly packed inside the galls so when they move the galls jump up to 3 cm. That’s 30 times the size of the gall!

In the fall the larvae become adult wasps inside the galls and overwinter to emerge next spring.

Neuroterus saltatorius are native to western North America from Texas to Washington state and up to Vancouver Island, Canada. That’s why we don’t see them in Pennsylvania.

Learn more at the University of Florida’s Department of Entomology: Neuroterus saltatorius.

(photos from Wikimedia Commons and bugwood.org; click on the captions to see the originals. videos embedded from YouTube)

Oh, Christmas Tree

If you have a live Christmas tree, it’s probably one of sixteen species of fir, spruce, pine, cypress or cedar. Many people prefer firs for their soft needles, but firs dry out quickly and drop their needles fast. One year our tree dropped its needles before Christmas!

One species, the Scots or Scotch pine (Pinus sylvestris), doesn’t lose its needles even when it’s completely dry. I’ve seen Scotch pines put out for trash collection in January that looked as if they were freshly cut. There’s a down side though, as described at The Spruce:

You’ll want to wear gloves when decorating a Scotch pine since its needles can be sharp as pins!

The 10 Best Christmas Trees You Can Buy — The Spruce

If the tree was sheared closely there’s no room to insert your hand or an ornament. Ouch, Christmas tree!

However Scotch pines have this advantage, and so do other live trees: If you feed birds in your backyard, place your old Christmas tree near the feeders to provide winter cover for birds.

(photos from Bugwood.org and Wikimedia Commons; click on the captions to see the originals)

Trees Remember Their Lives As Seedlings

New red oak leaves, April 2015 (photo by Kate St. John)

Just as our own experiences shape our response to the future, trees remember their lives as seedlings and it shapes their responses to environmental stress.

Arborists had long suspected a “nursery effect” in which transplanted trees of the same species seemed to respond differently to the same environment depending on the nursery where they were grown. A 2011 study by the University of Toronto at Scarborough used poplar tree nursery stock to examine this theory.

Poplar trees (Populus sp) are propaganted clonally so a cutting grown from a parent tree is genetically identical to the parent. The study obtained stem cuttings from the same parent poplar tree regrown in widely separated nurseries in Alberta and Saskatchewan. They then regrew the trees in Toronto under identical conditions with half exposed to drought, the other half well watered.

Putting down roots: an acorn puts out a shoot, April 2017, Ohiopyle (photo by Kate St. John)

Amazingly the clones from Alberta responded differently than those from Saskatchewan. They even used different genes in their response.

“The findings were really quite stunning,” said Malcolm Campbell, lead author of the study. “Our results show that there is a form of molecular ‘memory’ in trees where a tree’s previous personal experience influences how it responds to the environment.”

Red oak seedling, April 2019 (photo by Kate St. John)

That’s why it’s unwise to transplant a tree grown in Somerset County, PA to a backyard in Pittsburgh. The origin and destination climates are too different. The tree’s triggers are incorrectly set for its new life. (Somerset is zone 5b, Pittsburgh is 6b, on the Plant Hardiness Map).

USDA Plant Hardiness Zone map for Pennsylvania as of May 2018 (map from USDA.gov)
USDA Plant Hardiness Zone map for Pennsylvania as of May 2018 (map from USDA.gov)

This applies to forest trees too, even though they aren’t transplanted. Their previous experience could help their survival in the face of climate change, diseases and pests.

As winter arrives this week, watch the trees respond with their own history as a guide.

Resources: Lab Girl by Hope Jahren and Forest trees remember their roots from Science Daily

(photos by Kate St. John, map from USDA)

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.