Archive for the 'Trees' Category

Nov 20 2013

The Branches Add Up

Published by under Trees

Bare tree at sunset, Philadelphia (photo from Wikimedia Commons)

Now that the trees are bare you can do a little math on their branches.

Did you know that if you start at the trunk, gathering together all the branches and squeezing them tightly all the way to the top, the bundled branches will be the same circumference as the tree trunk?  The tree would be one big cylinder, all the same thickness as the trunk.

This principle is Da Vinci’s Rule of Trees. More than 500 years ago Leonardo wrote: “All the branches of a tree at every stage of its height when put together are equal in thickness to the trunk.”

Intuitively we can guess this is true, but the rule is very impractical to prove by hand.  A small tree could be squeezed – and sacrificed by the experiment – but a larger tree has to be measured and calculated.  As physicist Christophe Eloy of University of Provence said, “If you’re looking at big trees, there’s thousands of branches, and it takes a lot of undergrads to measure it.”

Two years ago Christophe Eloy proved Da Vinci’s Rule of Trees and the reason why it occurs by designing intricately branched trees on a computer and putting them through a virtual wind tunnel.

The designs, like the trees, were branching fractals repeated over and over.  With each design Eloy varied the thickness of the branches and subjected them to virtual wind forces that broke them.  Invariably when he found a combination that withstood the wind, it matched Da Vinci’s rule.  This not only proved the rule but showed that wind is a reason for the rule’s existence.  His findings were published in the journal Physical Review Letters in 2011.

Of course Eloy’s proof involved math and physics.  Here’s his diagram of the fractal thickness and one of his computed trees.

Tree branches and trunks follow Da Vinci's Rule (image courtesy Christophe Eloy, University of Provence)

(Image Courtesy Christophe Eloy | University of Provence)

 

But don’t take my word for it.  Read more about Christophe Eloy’s study and Da Vinci’s Rule of Trees at this link in Inside Science.

 

(photo of a bare tree at sunset from Wikimedia Commons.  Tree diagram courtesy Christophe Eloy, University of Provence linked from Inside Science.  Click on each image to see its original.)

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Nov 10 2013

Face In A Gall

Oak apple gall that looks like a face (photo by Kate St. John)

Before the oaks leafed out last spring I found this oak apple gall on a seedling at Cedar Creek Park.

When I bent down to look closely I saw the face.

Now that the leaves have fallen, look for fun features like this on the bare trees.

 

(photo by Kate St. John)

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Oct 27 2013

Wild Hickory Nuts

Shagbark hickory nuts (photo by Kate St. John)

Here’s something I literally stumbled on in Schenley Park:  shagbark hickory nuts (Carya ovata).

The big round balls, which cradle easily in the palm of my hand, are husk-covered nuts.  They’re green when ripe but turn brown with age (bottom right).  Their four sections naturally come open as the nut ages and sometimes burst when they hit the ground.

I didn’t need any special tools to open the husks, just my fingers.  At first I didn’t realize they were merely husks so I thought it was odd that they didn’t protect the nut but…

The nutshell is another story (center of the photo).  Irregularly shaped and slightly larger than a quarter, I tried to open it by cutting and other gentle means but it was impossible.  The meat inside is reputed to be sweet but I had to destroy the nut to taste it.

Hmmm.  Get out a hammer or hire a squirrel.

I got out the hammer.

The first nut had very shriveled meat inside.  Perhaps it had been attacked by a bug.

The second and third nuts looked promising except that the meats resembled dried Chinese wood ear mushrooms and they tasted like nothing.  (My photo doesn’t do this justice.)

Shagbark hickory nuts, hammered open (photo by Kate St. John)

Either I was doing something wrong — quite possible — or these nuts are not as good as described.

I wonder how many nuts the squirrels spend time opening only to find that the meat inside was not worth it.

(photo by Kate St. John)

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Oct 26 2013

Twisted Trunks

Black cherry and red oak twist around each other, Moraine State Park, Oct 2013 (photo by Kate St. John)

Last weekend I found these twisted trees in Moraine State Park.

It’s unusual to find trees like this — even more unusual when they’re two different species.

A black cherry (left at base) and a red oak (right at base) germinated next to each other.  At the ground their trunks touched and melded. As they grew they twisted around each other.

Amazing.

(photo by Kate St. John)

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Oct 25 2013

An Alien Takes Aim At Old Treasures

Hemlock woolly adelgid at Jacobsburg (photo by Nicholas A, Tonelli via Wikimedia Commons)

Last spring the hemlock woolly adelgid (HWA) reached Cooks Forest, scary news for the old-growth eastern hemlocks there.

The pest is easy to recognize by its white egg sacs that cling to the underside of the branches.  They kill hemlocks by sucking the juice out of the needles.  Infected trees look gray-green instead of deep green and, under a heavy infestation like the one shown above, can die in only four years.  This is sad anywhere but especially unfortunate in Cooks Forest where the old growth hemlocks are over 300 years old.

It has taken a long time for the bug to reach Cooks Forest.  HWA arrived from Asia in 1924 but moved very slowly across the eastern U.S.  By 2007 it was present in 50% of the eastern hemlock’s range, unable to spread far northward because of harsh winters. Unfortunately our climate is warming so new adelgid territory opens up every year. (Notice on this NOAA plant hardiness map that the location of Cooks Forest warmed enough to change growing zones.)

HWA was first spotted in eastern Pennsylvania in 1967 but took about four decades to cross the Allegheny Front into western PA.  Slowly, slowly it crept toward Cooks Forest.  By 2010 it was in the vicinity.  This year it was there.

Knowing the imminent danger DCNR has treated the area and the old growth trees.  They use biological controls — Asian beetles that eat adelgids, though not enough of them — and soil or bole-injected insecticides on specific trees.  The poisons are systemic, similar in concept to the insecticide treatments for emerald ash borer that kill or repel all insects.  The treated trees will have fewer insects living on them.  Will this make them less useful to birds?

The question hardly matters.  Nature can’t produce a 300 year old hemlock as fast as the adelgids can destroy one.   In the case of our oldest treasures our task is clear.  Save these trees if we can.

For more information on the hemlock woolly adelgid, click here for DCNR’s report.

 

(photo via Wikimedia Commons by Nicholas A. Tonelli at Jacobsburg, Northampton County, PA. Click on the image to see the original)

 

p.s. Thanks to Kim Getz for alerting me to this news.  Because of the adelgids activity cycle, DCNR treated the old-growth trees in May and again in October.

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Oct 13 2013

Tree On Stilts

Published by under Trees

Tree on stilts, Parker Dam State Park, October 2012 (photo by Kate St. John)

During a hike at Parker Dam State Park last year I noticed this hemlock, a tree on stilts.

Hemlocks have shallow root systems and can sprout easily in moist locations.  Sometimes they sprout in the moss on top of a rock or stump and their roots follow the contour across the surface and become anchored in the earth nearby.

My guess is that this tree sprouted on a stump that decayed out from under it.  The support disappeared after the hemlock’s root system was already established but the hemlock didn’t care.  It sent down some new roots and just kept growing in place.

Hemlocks in this position are vulnerable in wind storms but this one is in the understory, surrounded and protected by many other trees.

It will probably surprise hikers on the Beaver Dam Trail for a long time to come.

(photo by Kate St. John)

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Oct 03 2013

Acorns Are Connected

Acorns of northern red oak (photo from Wikimedia Commons)

Stop and listen in Schenley Park right now and you’ll hear acorns falling, blue jays calling and squirrels scurrying.   It looks like a bumper crop for acorns in Pittsburgh. (*see p.s.)

Right now the red oaks are putting on a show.  Acorns in the white oak group mature in the same year they flower.  Acorns in the red oak group take two years to mature so those falling now were formed in the hot spring and summer of 2012, influenced by spring precipitation, summer temperatures and the date of the last killing frost.

Though we (usually*) don’t eat them, acorns are a key link in the woodland food web.  They’re so popular that oaks have evolved an abundance-scarcity strategy to throw off their consumers.  In some years acorns are so abundant that the crop overwhelms the acorn-eaters.  In other years they’re so scarce the consumers go hungry.  To further confuse things the oak groups cycle on different schedules: white oaks have a bumper crop in 4-10 years, red oaks on a 3-4 year basis.

Who eats these acorns?  Squirrels and chipmunks are the obvious consumers but plenty of other species depend on them including white-footed and deer mice, blue jays, red-headed woodpeckers and wild turkeys.  Deer, ruffed grouse, bears, mallards and wood ducks eat acorns, too.

The bumper crops have a ripple effect.  A 24-year study, headed by Clotfelter and Pedersen in the southern Appalachian Mountains of Virginia, followed the effects of acorn crops on rodent abundance, raptor abundance and the nesting success of ground-nesting birds.  They focused on white-footed mice, deer mice and dark-eyed juncoes and found these amazing acorn effects:

  • The population of white-footed and deer mice increases in the year after a bumper crop of acorns.
  • Rodents attract predators so the raptor population increases.
  • Too many rodents and raptors causes junco nest failure due to predation on eggs, nestlings and birds.
  • Mice eat gypsy moths so the gypsy moth population drops.
  • The number of ticks increases as white-footed mice and deer increase.

And then, this information from PLOS links acorns to Lyme disease:  Lyme disease increases predictably two years after an acorn bumper crop because white-footed mice are a main reservoir for the Borrelia burgdorferi bacteria.

Don’t blame the acorns.

Everything is connected to everything else.

 

(photo from Wikimedia Commons. Click on the image to see the original)

*p.s. Is this a bumper crop year?  I wrote about acorns because I’ve been dodging them in Schenley Park as they fall, but not all the trees are prolific.  Hmm….

*”We don’t usually eat acorns”:   Well, we can … after a lot of work.  See kc’s comment!

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Sep 04 2013

Three Sumacs And Two Imposters

Published by under Plants,Trees

Sumac fruit (photo by Kate St. John)

In July I took photos of sumacs along the Montour Trail but didn’t identify the species and assumed these first two were staghorn sumac.  Wrong!

As I started to write this article I examined the photos and noticed a big difference between them.  The red fruit spike above is fuzzy.  The one below is smooth.   Not only that, you can see that the stems on the top one are also fuzzy but the stems below are smooth.

Fruit of smooth sumac (photo by Kate St. John)

In southwestern Pennsylvania we have three common sumac species that bear pointed red fruit clusters:

  • Staghorn sumac (Rhus typhina), at top, has fuzzy fruit and stems and is named “staghorn” because the fuzzy fruit spike resembles a stag’s horn in velvet.
  • Smooth sumac (Rhus glabra), above, is smooth just like its name.
  • Shining sumac (Rhus copallina) is easily identified by its winged stems.

I haven’t seen Shining Sumac lately so here’s a photo from Wikimedia Commons.  See how the stem has wings (like wingstem) between the leaflets?

Leaves and flower of Shining Sumac (photo from Wikimedia Commons)

 

There are two more plants we call “sumac” whose leaves resemble these plants but they aren’t in the genus Rhus:

  • Poison-sumac (Toxicodendron vernix) is in the cashew family (as is Rhus) but it’s closely related to poison ivy and causes the same rash.  Its stems are smooth, like smooth sumac, but its flowers and fruit are not in dense spikes.  Fortunately poison sumac only grows in swamps and bogs so you’d have to go out of your way to touch it.  Click here for a photo.
  • And finally there’s a plant we call “sumac” which isn’t related at all.  Tree of Heaven (Ailanthus altissima) is an invasive tree from China with compound leaves that resemble sumac.  However its leaflets are notched, especially at the base, and the tree produces seeds instead of a fruit spike.  Notice the notches on the leaflets and the heavy cascade of seeds in this Wikimedia photo.   This is NOT sumac.   It grows anywhere, even in abandoned parking lots.

Ailanthus leaves and seeds (photo from Wikimedia Commons)

 

Three real Rhus sumacs and two imposters.

(photos by Kate St. John except where noted.  Click on the Wikimedia photos to see their originals)

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Aug 01 2013

Plant a Shrub, Start a Fight

Published by under Plants,Trees

Leylandii, Roman Bank, Holbeach Hurn (photo from Wikimedia Commons)

The tall square hedge in this photo is the species that launched 17,000 complaints.  It’s also been blamed for the decline of the house sparrow in the UK.

When a tree is implicated in the decline of a bird I’m compelled to find out why.

Leyland cypresses (Leylandii) are an accidental hybrid of the Nootka and Monterey cypresses (of the Pacific Northwest), first discovered in the gardens of Leighton Hall in northern Wales in 1888.  The hybrid is sterile but can be propagated by cuttings. It became popular in UK landscaping because the foliage is so thick it provides privacy from neighbors.

Leylandii are huge trees that grow three feet per year and can reach 130 feet tall, but they’re used as hedges and therein lies the problem.

When planted as cute little “shrubs,” people imagine their Leylandii will look like this…

Well-trimmed Leylandii in Chilwell (photo from Wikimedia Commons)

…but that tidy look takes constant trimming.  Instead the hedgerow turns into this…

Leylandii hedgerow (photo from Wikimedia Commons)

…and can engulf nearby buildings.

For instance, Snarestone Pumping Station was visible from the road in 1994 before Leylandii were planted at the perimeter.  By 2010 only the top of the smokestack can be seen above the trees.  (Notice the little red car at the right side of the right hand photo.  These trees are huge!)

Snarestone pumping station before and after Leylandii, 1994 & 2010 (photos from Wikimedia Commons)

Leylandii block views and create very dense shade.  Neighbors ask owners to trim them.  The disputes begin.

By 2005 there were 17,000 disputes, prompting Parliament to pass an “anti-social” law to settle them.  When neighbors object to Leylandii they must first try to settle the dispute privately.  If this fails they can ask local Council to intervene and pay a fee to begin.  Council can rule that the trees be trimmed to 2 meters (6 feet).  Failure to comply can result in a £1000 fine.

Here’s an example of a dispute in Plymouth, complete with a video that shows the neighborhood.  The trees completely obscure the owner’s house.  Notice that the neighborhood has no plantings for birds either.

How do house sparrows figure into this?  House sparrow population studies have shown they thrive where there are deciduous trees, not evergreens.  House sparrows are declining.  Leylandii are oppressive evergreens.  Voilà!

(photos of Leylandii from Wikimedia Commons.  Click on the images to see the originals)

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Jul 30 2013

Oak Wilt Strikes Again

Published by under Schenley Park,Trees

Oak wilt in Schenley Park, 5 July 2013 (photo by Kate St. John)

I love trees so much that I jump at the chance to learn more about them.

Back in February 2011 I learned about the threats facing 60% of our city park trees when the Pittsburgh Parks Conservancy presented a public event called Preserving Pittsburgh’s Trees: Action and Recovery.   I was already familiar with emerald ash borer since I first saw it in Schenley in May 2010 but I learned about something I’d never seen before: oak wilt.

While Schenley Park had been coping with the death of all its ash trees, the other three big parks — Frick, Highland and Riverview — had experienced oak wilt as well.

Oak wilt is caused by a fungus that doesn’t spread easily but can kill a tree in 30 days.  The fungus travels in the oak’s vascular system and when the tree detects it it blocks those vessels.  The blockage kills the tree. It’s the arboreal equivalent of a stroke.  Watch the 13 minute video here to see how this happens.

After the conference I began to watch Schenley’s oaks with new interest.  Two years passed.  Early this month I could tell something wasn’t right at Prospect Circle.  I emailed this and other photos to Phil Gruszka, Director of Park Management and Maintenance at the Pittsburgh Parks Conservancy, and he confirmed that oak wilt had struck again.  He also started the ball rolling to eradicate it.

Fortunately the fungus spreads slowly and that’s the key to stopping it.  It’s either carried into an open wound by sap-eating beetles (this is harder than you think) or it travels from oak to oak via root grafts.  Amazingly, the roots of adjacent oaks graft to each other when they touch underground.  In a pure oak stand they become one huge vascular system.

There is no cure but future deaths can be prevented by cutting down the affected trees, trenching the perimeter to prevent uninfected roots from entering the danger zone, and medically treating the oaks just outside the perimeter.

In the not too distant future a large patch of dead and dying oaks will be chopped down at Prospect Circle.  This will look ugly at first but will save all the other beautiful oaks along the road and hillside.

For more information about oak wilt, read these Pittsburgh Parks Conservancy blogs about the episode in our parks in 2010:

 

(photo of the oak wilt trees in Schenley Park, July 2013, by Kate St. John)

 

p.s. Learn more about the trees in our city parks at this link on the Pittsburgh Parks Conservancy website.

UPDATE on 18 October 2013 from the Pittsburgh Parks Conservancy –> click here.

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