American elms

There are elms fruiting now.  If, as you walk around the city, you look down at the pavement, or the grass, or the asphalt, you’ll see at some places papery little disks, generally less than an inch across, often quite a bit smaller – some are ciliate (they have fine hairy fringes, that is), while others have entire margins (that is, their edges are unfringed), but pretty much all of them, if the tree they come from has any hope of passing on its genes to progeny, have a seed in there.  Some have their seeds at dead center, while for others they’re positioned a bit towards the apex of the fruit, but all of them, unless their parent tree was unfortunately barren, have a seed.

These fruits are called samaras.  Samaras are fruits with wings – if you look at a maple tree, at some of them about now, the red maples for example, you’ll see another kind of samara, different from those of the elm, with these ones, those of the the maples, making the helicopters or Pinocchio noses you probably played with as a kid.  The maple samaras aren’t in the rounded and somewhat symmetrical form of the elm samara, their wing, the wing of the maple fruit, is extended in one direction, on one side of the seed, and then two are joined together to make the kind of samara that spins as it lofts towards the ground or as it is carried away to be dispersed by the wind, to new places where the seed might grow into a tree (or not).  For the maples, their wings extending outwards make for simple little machines that cause them to spin as they fly away.

For the elms, they are different.  Their samaras don’t make helicopters, their samaras are in a circular or somewhat elliptical shape, some having a notch towards the top, but all having generally a saucer shape, though sometimes uncircled and stretched in one direction to make, I guess, perhaps more of a tureen saucer than one for coffee cups, but saucer shaped nonetheless – and those samaras are all over the place now, falling to the ground beneath the elms’ spreading branches.

The ciliate samaras, the ones that are densely fringed – these rounded shaggy-margined, papery, less-than-an-inch roughly-ovals, the ones you see littering the street that look like that, these belong to the American elm.

The American elm used to be the street tree, the street tree.   Planted in long rows, in lines up and down main streets and smaller streets and all kinds of sized streets, in towns and cities across America, these plantings, they made for a beautiful effect that was somewhat architectural – the branches of the elms from opposite sidewalks meeting in the middle, forming a broad arching ceiling over the street, a covering under which horses, carriages and then ultimately automobiles traveled, and along which people walked in the shade in the summertime and under naked branches in the winter.  This was the tree of America’s streets.

The American elm was also treasured for open plantings.  With its broadly spreading branches zigzagging around and angling outward like the sides of an opening vase, this elm made for a striking shape, standing tall in a yard or park, or in the National Mall in Washington, DC, or in Harvard Yard in Cambridge, MA, or in Rittenhouse Square in Philadelphia, PA, and in places of prominence elsewhere as well.

Put simply, and to quote Andrew Jackson Downing’s Treatise on the Theory and Practice of Landscape Gardening (1841), “Let us now claim for the elm the epithets graceful and elegant.”

The elm was everywhere.  And it had always been common here.  Peter Kalm, the Scandinavian botanist who explored the new world in the late 1740s, writes of this tree as being found throughout the area in and around Philadelphia and New Jersey:

“June the 28th [1749].  The American Elm, (Ulmus Americana Linn.) grows in abundance, in the forests hereabouts.”

And back then as it is now, they flowered about this time of the year, late March:

“March the 21st [1749].  The red maple (Acer rubrum) and the American elm (Ulmus Americana) began to flower at present; and some of the latter were already in full blossom.”

[the above quotes are from John Reinhold Forster’s translation of Kalm’s “Travels into North America”, published in 1771]

And, in the city of Philadelphia, in what is now Independence Square, but was at the time called the State House Square, in the 1780s Samuel Vaughan, the man responsible for designing that square’s landscape, just after the American Revolution, was given a hundred American elms by Captain George Morgan of Princeton.  Vaughan planted them in a double allee along the main north-south path, and the founding fathers of the United States would have walked among them as they worked and lived, in their day to day lives and quotidian workdays that created much of what we live within today.

And so, from the early days of European colonization through to the constructions of the cities and towns of 20th century America, the elm was everywhere.

Then, in 1929, the Dutch elm disease arrived.  First found in Ohio, within a decade it had spread to Indiana, to Maryland, to Virginia – as far as eastern Connecticut and New York City, it had spread hundreds of miles within just ten years, according to Joseph Horace Faull, professor of forest pathology at Harvard (he spent most of his time among the trees at the Arnold Arboretum in Boston), who wrote about and studied this disease, in the 1930s.

Throughout the middle and the latter part of the 20th century, Dutch elm disease spread and spread, wiping out graceful elm plantings in yards and parks and open greens, and caving in the arched vaults formed by elms’ branches across the streets of America. The distribution of the disease rapidly became coterminous with that of susceptible elms – slippery elms (Ulmus rubra), another elm native to North America, can also catch the disease, as can the English elms (Ulmus procera) that had come over to the US from Europe.

A fungus is the causative agent of the Dutch elm disease, well two fungi, actually – Ophiostoma ulmi and Ophiostoma novo-ulmi.  Ophiostoma ulmi, arriving in the US in the early half of the 20th century, caused the first ranging of the disease, and then the more aggressive Ophiostoma novo-ulmi came on to replace that original colonizer in later years.

The fungus spreads by two routes – either via bark beetles, who carry the fungus with them as they go from tree to tree, diving into the bark to live and breed, or via root grafts.  What are root grafts?  They’re pretty much what they sound like – when elm trees grow near to each other, as you might expect, their respective roots can come into contact.  When this happens, the roots can fuse, combining together, even down to the plant’s vascular system.  This allows the fungus to spread because it can travel through this vascular system, the plant’s water transport system, the xylem.  Though the Dutch elm disease commonly spends much of its life growing as filamentous strands (=hyphae), it can also transition to a single celled form, which we call a yeast (to a mycologist, a single celled fungus is a yeast), allowing it to cruise along the xylem like a vascular highway, up and down the tree, unimpeded by bark or air, through shoots or through roots.

And so, you can imagine what this meant for those long majestic rows of elms that were planted cheek by jowl next to each other along the streets of America.  If one instance of a bark beetle arriving brought the fungus with it, the yeast of the Dutch elm disease then rapidly went from tree to tree, by the roots subterreanean vascular system, until the allee fell like a series of arboreal dominoes.

And why exactly did these trees fall?  What is it about this disease that kills the trees?  Well, imagine if you had fungi growing in your vascular system – it would become blocked up, thereby preventing the flow of nutrients to where they need to be.  The same things happen to trees infected with this pathogen – the vascular system is blocked, causing the trees to present the diagnostic early symptom of the disease, called “flagging”, where entire branches in the tree canopy exhibit drooping leaves that yellow and brown, which is then generally followed, ultimately, by the death of the tree.

There are interventions available – removal of diseased parts, insecticides to get rid of the bark beetle, fungicides to attack the fungus, cutting of the roots to inhibit spread underground – but these are intensive and require resources, both financial and in terms of labor spent on these efforts, and so replacement of the elm is generally the more viable option.

And so, through the latter part of the 20th century, American elms have become a reduced part of our urban tree community.  But they’re still there.

There are quite a few American elms in Philadelphia – there’s a large healthy one in Dickinson Square, at Tasker and Moyamensing, and there’s one in the southeast corner of Rittenhouse Square in center city, and another at the northeast corner of 22nd and Chestnut, in front of what used to be a Swedenborgian Church, and right down the street from the College of Physicians.  And if you look in the Kaskey Memorial Garden on Penn campus in west Philadelphia, or on the grounds of Friends Hospital up in Frankford, or in front of what was Lankenau Hospital, on Corinthian Avenue just south of Girard College in north Philadelphia, if you look in these places you’ll find more of the American elms that grow here in Philadelphia.  And we have English elms, too – seven enormous ones at the Woodlands Cemetery right near Penn (two of which date to William Hamilton’s time; in 1921 those two were, respectively, 10′ 1″ and 10′ 3″ around), and at Marconi Square in south Philadelphia, right along Broad Street, on the west side of Broad, there’s one with a trunk over five feet across. (and for an interesting historical record: in John Watson’s Annals of Philadelphia and Pennsylvania in the Olden Time (1899, “enlarged, with many revisions and additions, by Willis P. Hazard”), p. 373, vol. 3, he notes after a brief mention of the balloon riot that occurred in 1819 at “Vauxhall Theater, north-east corner of Walnut and Broad streets”, that “The elm that stands on Walnut street, overhanging the street, was on old tree then.” [Vauxhall was also called Vaux Hall Gardens, and had a very open parklike aspect to it, in 1819; in the 1890s, there was still a fair bit of open space in that lot, as one can see from the 1895 map here, but by 1910 it was all pretty well covered over and the elm would have been gone])

And at Independence Hall, right behind it there, along with the enormous London planes, and nearby to some little chestnuts and not far from a Franklinia, and with dozens, hundreds, or thousands of people walking under it every day, is an enormous American elm, rising high above the square.  There are other American elms there too, five in all – in that smallish square, there are multiple elms.  One, planted in 2004, is a ‘Princeton’ cultivar, a variety that, while known and planted prior to the Dutch elm disease’s incursion into America, ended up being able to co-exist with both species of Ophiostoma and therefore ended up being planted more widely, quite widely actually.  This cultivar grows well, and the example of it that is in back of Independence Hall is strong and healthy, growing  alongside its older relative that towers above the square.  These stand as a reminder of a time when American elms were the American tree, and they are the right plant to have at this historic site – trees deep in history, that are still growing tall, even though organisms that were new to them have inalterably changed their presence in the landscape, the elms stand, and grow.

To read more about elms, including Penn Treaty elms, see here;

https://growinghistory.wordpress.com/2012/02/28/some-history-of-historic-plants/