Last Wednesday afternoon, while driving home from campus, I heard a story on National Public Radio about New York City’s ongoing effort to re-plant its storm-damaged beaches with native grasses.  It turns out that seeds from those grasses have been painstakingly preserved at the city’s Greenbelt Native Plant Center on Staten Island, and those seeds are now helping restore area beaches devastated by Hurricane Sandy.

The story featured a young field taxonomist, Heather Liljengren, who spends her days traipsing through the metropolitan area’s wetlands and other natural environments, collecting seeds from native plants.  After reading comments on the NPR website, I realized that I wasn’t the only one captivated by Liljengren’s enthusiasm for her work, though I think her undergraduate degree from UMass Amherst endeared her especially to me.

But later, when I was looking at the online resources of the Greenbelt Center, I found myself drawn to other tabs on the New York City Parks and Recreation website, especially the one labeled “Trees.”  Maybe it was memories of lying on my family’s living room floor, looking at the charts and tables in the World Book Encyclopedia, which showed every major tree species in North America, complete with leaf drawings and habitat maps.  It may also have been that, over the previous weekend, family members from North Carolina had visited me here in New England and, while walking around Northampton, had asked endless question about the local flora, none of which I could answer.

Regardless of why I was drawn to it, the “Trees” website struck me as infinitely rich and fascinating.  There was a “Leaf Key,” a “Tree Census” of the five boroughs, information about municipal services like tree removal and sidewalk repair, and a section devoted to “MillionTreesNYC,” the city’s ambitious plan, announced in 2007, to plant one million new trees across all five boroughs in a decade.

It was at the MillionTreesNYC site that I first learned of the myriad benefits that urban trees provide.  Like most people, I knew there was something aesthetically pleasing about city trees – especially when laid out as they are in New York City’s Central Park mall.

But it turns out that urban trees have other benefits:

Trees purify and cool the air, reduce stormwater runoff, and conserve energy.  They increase property values, beautify neighborhoods, and improve human health and well-being.

In fact, the city estimated in 2005 that its trees have an annual benefit value of $122 million: $5.3 million in air quality improvements, by absorbing gaseous pollutants, like carbon dioxide, and capturing airborne particles, like dirt, dust, and soot; $27.8 million in energy savings, by providing shade in the summer and reducing wind speed in the winter; $754,947 in reduced carbon dioxide emissions from power plants, by lowering energy use in buildings; $36 million in reduced flooding and water pollution, by intercepting and absorbing rainwater before it becomes runoff; and $52 million in increased property values, by simply being beautiful (see the “Trees Count!” section of the New York City Parks and Recreation website).

There is lots of other research on the value of street trees in our urban ecosystems.  A much-cited paper by Dan Burden, on the “22 Benefits of Urban Street Trees,” argues that “properly placed and spaced” street trees reduce traffic speed, create safer walking environments, decrease crime, increase business, lower urban air temperatures, reduce blood pressure (!), and connect people better to nature and their own senses.

Of course street trees cause problems, too: they damage electrical lines; their branches fall – hurting people and cars; their roots destroy sidewalks and bike paths; and they require care and maintenance throughout their lives, often at high cost.  But the myriad benefits of healthy urban tree canopies clearly outweigh these disadvantages.

Unfortunately, there’s growing evidence that these benefits are unequally distributed in our metropolitan areas.  It turns out that wealthier and whiter residents of our cities and suburbs are surrounded by more trees than their lower-status neighbors, and these trees are both a cause and an effect of their relative prosperity.  Inequality in access to street trees was glaringly revealed in 2012 by Tim De Chant on his “Per Square Mile” blog.

Take these two aerial photographs of the Boston metropolitan area, one of a lower-status neighborhood in Somerville, the other, a higher-status neighborhood in Cambridge.

Clearly, if urban trees provide benefits to the people who live near them, those who live in neighborhoods with more trees will receive more of those benefits than those who do not.

In fact, the “Trees Count” section of the New York City Parks and Recreation website clearly shows that the city’s poorest borough, the Bronx, lags far behind its counterparts in terms of street trees.  The numbers on that site got me thinking about writing projects that my students might do, identifying places in their environment with impoverished tree cover but also, more generally, documenting with greater precision the natural features of their own world, and what those features might mean, practically and otherwise.

It was an article by Kaid Benfield that alerted me to the presence, across the country, of online tree inventory projects, accessible to the general public, that employ much more robust mapping programs than those on the NYC “Trees Count” website.  In the piece, Benfield highlights the San Diego Tree Map, a fascinating project conducted by “citizen foresters” in the San Diego County area who volunteer their time adding street trees to the system.  Below is a screen shot similar to one Benfield includes in his article, this one zoomed in on street trees around the University Avenue area.

I found similar street tree maps for New Haven, Connecticut:

Cambridge, Massachusetts (here focused on a honeylocust tree on Scott Street):

And, most exciting of all for me, Amherst, Massachusetts:

The screen shot above, of the Amherst map, is focused on a particular tree on Lincoln Avenue.  When I first tried out the system, I mapped Lincoln Avenue because it’s a street I know well and because it connects Route 9 with the UMass Amherst campus where I work.  The first tree listed on the street was at 24 Lincoln Ave., so I clicked on it, revealing not only its exact location but also very specific information about it.  The tree, it turns out, is an American elm (Ulmus americana) with a DBH (diameter at breast height) of 19 inches.  I was struck by the species – more on that below – and touched by the lovingly detailed attention given to this tree, which in most maps would be little more than an indistinct part of an insignificant background.  Someone studied this tree, numbered it, identified it, measured it, assessed it, mapped it.

I couldn’t help but seek the fellow out.  Here it is – the American elm of 24 Lincoln Avenue in Amherst, Massachusetts.

Unfortunately, there’s no tree inventory for Northampton, Massachusetts, where I live.  I realized, however, that one neighborhood in my town has mapped its trees with some care, though not with the precision of the GIS-based tree maps shown above.  That neighborhood is Smith College, which has a detailed “tree guide” to its campus, complete with map and walking tour including nearly forty of its most unique and noteworthy trees.

When I looked closely at the map, I was drawn immediately to #33, a tree on Chapin Lawn between Neilson Library and the Campus Center.  It’s probably my favorite tree in Northampton.  Here’s what it looks like as you walk north from the library.

And here it is from the opposite direction, the Campus Center looking south:

The best view of the tree, however, is from underneath it.

It’s a tree I have sat under many times – I once had a memorable conversation with a friend here.  I’ve pointed it out to family and friends.  It’s also a tree I look at when I sit on the second floor of the Campus Center, studying:

When I read the key provided with the Smith College tree map, I realized that #33 was, like the tree on Lincoln Avenue in Amherst, an American elm (Ulmus americana).  And indeed, there’s a small plaque on the tree itself:

Its leaves also match those associated with the elm in standard reference works:

Elaine Chittenden, the manager of living collections at the Smith College Botanic Garden, told me that the tree, measured recently, is 22.7 meters tall, 1.44 meters in diameter (at breast height), and 34.6 meters in spread – it is, in other words, a tree wider than it is tall.  Unfortunately, there appears to be no good estimate of the tree’s age, though the plaque on the tree suggests that it was added to the Smith College collection in 1918 (but how old was it then?).

She also confirmed something I had already discovered online: the tree has Dutch elm disease.  The following note appeared in the Botanic Garden’s “Landscape Update” of July 11, 2011:

Last week the Botanic Garden’s Landscape Manager and Arborist Jay Girard noted a yellow branch tip on the old majestic American elm on the Chapin lawn. After Chief Arborist John Berryhill climbed the tree to get a sample, it was confirmed that one branch had Dutch elm disease. Experts from C.L. Frank & Co. (professional arborists) were called in and the limb was removed well below the point of infection. While the removal was significant, it is hoped that this type of surgery combined with injections of a fungicide will prevent the spread of the disease, which is caused by a fungus that travels through the water conducting vessels in the limbs and plugs them up. The initial infection is transmitted by a beetle that carries the fungus from tree to tree. If untreated the disease is always fatal. Surgery and fungicide treatment can prevent the further spread of the disease but there is never a guarantee with Dutch elm disease. The tree is also being recabled to reduce the effects of high wind on limb integrity. We will do all that is possible to save this tree, but wanted the campus community to be informed of the situation.

There was something oddly moving about that last sentence.  Having known the tree for some time now, and having spent an afternoon with it recently, I felt like I was hearing sad news about an old friend.

But who was I to this tree?  True, I have walked about it.  I have pointed it out to family and friends.  I have sat beneath it.  And every spring and fall, I have watched students lounge around it.  But I didn’t know it was sick.  I didn’t even know it was an American elm.

When I was young, my father told me that a disease had killed most of the elm trees in this country.  He said that the eastern part of the United States, from Maine to Florida, had once been covered by elms – tall, majestic, spreading.  But within the span of a few decades, they had been almost totally wiped out.

He was born in Elm City, North Carolina.

I grew up thinking of the American elm (Ulmus americana) as a ghost.  But here I was, in 2013, and I had discovered, on the same day, by an odd serendipity, two living elm trees in my midst, trees carefully mapped by others, which I had passed numerous times but never bothered to truly get to know.

Of course, the most famous elm tree in Northampton is long gone.  It was a true “street tree.”  Sometime in the early eighteenth century, in front of his house on King Street, right around the corner from where I live today, the famous preacher and theologian Jonathan Edwards planted an elm tree that survived for nearly two hundred years.  To this day, although it’s only a memory, it’s referred to in Northampton as the “Edwards Elm.”  Here’s a depiction of it from early in the twentieth century, just a few years before it toppled over from its own weight.

King Street today is an ugly gateway to Northampton, largely bereft of healthy, “properly placed and spaced” street trees.

Wouldn’t it be nice to see an urban forest again growing along this thoroughfare: slowing traffic, cooling temperatures, drinking rainwater, cleaning air, and lowering blood pressure?

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Postscript: Feb. 23, 2014: Today’s New York Times includes a lovely article by Guy Trebay about the elms of Central Park, the most famous of which are the ones that flank Literary Walk and that line the west side of Fifth Ave. from 59th to 110th St., considered by some the longest continuous stand of American elms in the world.

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For the NPR report on NYC’s efforts to replant its beaches with native grasses, click here.

For the Greenbelt Native Plant Center on Staten Island, click here.

For the NYC Street Tree Census, including a discussion of the benefits of street trees, click here.

For Kaid Benfield’s “Case for More Urban Trees,” click here.

For Dan Burden’s “22 Benefits of Urban Street Trees,” click here.

For Tim De Chant’s “Income Inequality, As Seen from Space,” click here.

For Emily Badger’s “The Inequality of Urban Tree Cover,” click here.

For the San Diego Tree Map, click here.

For the New Haven Street Tree Inventory Map, click here.

For the Cambridge Tree Inventory, click here.

For the Amherst Street Tree Inventory, click here.

For the Smith College Tree Guide, click here.

For the USDA’s page on Ulmus americana, click here.

For the Arbor Day Foundation, click here.