Monday, March 26, 2012


Arthur Plotnik writes in The Urban Tree Book:

 …most tree species are out of their element in the urban scene.  Between pollutants, drought, compacted soil, poor drainage, salt spray, bugs, dogs, heat, construction, vibrations, vandalism, and opportunistic diseases, many trees simply give up the ghost.

On my worst days, I can’t tell if Plotnik is talking about trees or citybillies.

There’s no doubt about it: trees have it tough here in the city, no thanks to that long list of obstacles quoted above. 

I’d add two more to the list.  

The first would be solitary confinement.  Only on a city street or a mall parking lot will you see trees plotted out in perfect alignment, each one confined to a small quarter of a sidewalk square, every one equally spaced between the next one down the block.  Trees don’t grow like that in the wild, and for good reason.  Healthy competition among trees encourages healthy trees.

The second obstacle is even more heartbreaking, far more dangerous and damn near impossible to control or change…and it originates from one of the most sinister, lifeless settings you’ll ever find on this spaceship Earth: a committee. 


Back in the 1960s, the war against one of America’s favorite trees, both urban and suburban, was finally nearing its tragic end.  The fungus won and the American elm was defeated. 

Spread by the bark beetle, the fungus known as the Dutch elm disease was first noticed in Europe around 1910 and was accidentally shipped to New England in 1928, where it migrated, at a rapid pace, to the entire native range of the North American elms, in the kind of pattern you see on a doomsday map at the beginning of those disease-outbreak movies.

Dutch Elm Disease Outbreak
The fungus had one key advantage in the war: monoculture.  The elm was one of the most beloved and popular street trees, gracing the avenues and boulevards of small towns, suburban neighborhoods and big cities up and down the entire megalopolis.  With all those trees planted right in a row, the fungus easily hopped from tree to tree, street to street, town to town, city to city and finally state to state…from New England all the way south to the Shenandoah Valley, all the way west to the bison and tipi country of the Great Plains.  Man’s monoculture was the bark beetle’s clear path to victory.

By 1970, over 77 million elms had fallen, worldwide, and both Main Streets and Wall Streets alike needed a new tree.  In City Halls all across America, the big brains behind their big desks found their substitute: the callery pear.

And another monoculture was afoot.


There’s actually a lot to like about the callery pear.

In its youth, it has a pleasant crown in the shape of a perfect spade that casts a cool shade on the sidewalk, perfect for city walking.

It has a slender, straight trunk and it starts branching five or six feet up from its base.  Plus, all of its branches grow upwards.  Those two attributes make it a perfect tree for curbside parking.

Wallace Street, between 19th and 18th Street

Without a doubt, though, the best part of the callery pear have to be those pretty white flowers that first bloom in early spring.

These flowers pop.  They are small but they grow in tight clusters, each cluster surrounded by its own wreath of hairy gray buds or bright green leaves, either one the perfect backdrop for those phosphorescent flowers.  I especially enjoy them at night.

All the pretty little pear trees all lined up in a row…it was probably a very easy decision.  It was probably very easy to approve: take the callery pear and plant it along the streets, and plant it some more, and keep planting it and keep planting it until, now, it is one the most ubiquitous trees in all of Philadelphia.

Yo.  Not a good idea.


The callery pear has a short life span, averaging only 25 years.  It does not age gracefully.

As it gets older, that perfect conical shape goes awry. 

The branches keep growing upwards but, as they get bigger and need more space, they start extending further and further away from its trunk and out into the street.

These trees require selective pruning using an expert, discerning eye but, with so many planted in so little time, there was never enough city staff available to properly manage their growth.

Within a few years, their huge branches hang over the streets above the cars at precarious angles.

Because the bigger branches begin at the same point along the trunk, the tree cannot handle all that weight.  The tree starts to split.  

What was once a perfect, dense, spade-shaped crown is now a teetering, tottering mess, branches splayed in all the wrong directions and so much space in between the splitting crown that you lose all that precious shade.  

What's worse?  Those heavy branches are just one good gust of wind or one bad ice storm away from crashing down on your car, I don’t care how good a parking spot you got.

They've also proven to be an invasive species, which should've been obvious to the original planters.  Quick growers, easy adapters, able to handle lots of stress and drought, and planted in such sheer numbers, it was really just a matter of time before they would inch their way into the little woods and forests left in the big city.  

That time has already come.  

According to the Pennsylvania Department of Conservation and Natural Resources, the callery pear is now an invasive, exotic plant and they offer, on their website, this sage advice: "Do not plant callery pear."

But the absolute worst aspect of the callery pear is its frightening reminder that we never learn from our past.  We planted too many of the same kind of tree.  Again.  It’s just one good fire blight, one strong pest, one hungry fungus away from being wiped out completely, in the same manner as the elm.  We replaced one monoculture with another monoculture and now we wait, enchanted by pretty white flowers, for the trees to fall again.

With my luck, I'll be parked underneath.

1 comment:

  1. Is it safe to say someone suggests these species to a committee? Someone with a background in horticulture or silvics? I'd imagine someone suggested this tree, but who?

    So after the inevitable demise of the Callery Pear in Philly, what tree would you suggest to replace it?