DED-resistant American elms

BCarley978 bcarley978 at aol.com
Mon Apr 21 17:02:03 EST 2003


"Saving the American Elm"
by Bruce Carley

http://www.elmpost.org

I have posted this article to call attention to a special project which I have
been doing since 1994 and which hopefully will be a source of inspiration for
many. Ever since some new disease-resistant varieties of purely American elm
were called to my attention, I have been hooked on raising these trees for
distribution in my home town of Acton, Massachusetts, and it did not take me
long to conceive of finding a way to have them planted on various conservation
lands, where they will always be safe from indifferent landowners. I soon
became acquainted with this town’s conservation director, who welcomed my idea
wholeheartedly and gave me the necessary permission. 

During their usual strolls along the main streets of their home towns, our
parents and grandparents gazed at the scenery around them and took for granted
a spectacular picture that is seldom observed nowadays and that few of us can
hope to see during our lifetimes. The interweaving limbs of the stately trees
that lined the streets ascended into a towering canopy with a graceful, arching
beauty unmatched by any tree that is commonly seen today, spreading
horizontally at heights often greatly exceeding 100 feet (in rare cases
attaining 140 feet with even greater spreads and 11 foot trunk diameters), and
drooping long, slender branches in abundance high above the street, blocking
all view of the sky. Along countless streets for many miles in cities and towns
throughout the tree's extensive native range in the eastern half of North
America, even as late as the early 1960's, this scene abounded, the effect of
the only species capable of giving us such majestic splendor. 

Veritably the standard against which the merits of other shade trees were
measured, the American elm provided the ultimate in stateliness and beauty,
making it the single most popular shade tree for lawns and city streets in the
eastern United States, and earning it distinction as the state tree of
Massachusetts and North Dakota. Architects even designed buildings with elm
plantings inherent in their plans. The early citizens of Portland, Maine and
New Haven, Connecticut had such a passion for the American elm that they
created elm-lined streets on practically every block and earned each city the
nickname, “City of Elms.” Once as naturally abundant as maple, oak, and pine,
the American elm was an essential part of our natural landscape and cultural
heritage throughout the first few centuries of our history, and it was in fact
the first symbol of our national independence; for a fine example had stood in
Boston as the famous “Liberty Tree,” an emblem of promise and a gathering site
for patriotic citizens intent on independence, until British soldiers destroyed
it as a final act of hostility during a hurried retreat from Boston in 1775. 

Many of us remember how painful it was for our communities to witness the
tragedy that recurred throughout the eastern states during the 1960's and
1970's. Many remember watching helplessly as countless main streets, parks,
historic sites, and neighborhoods that had been so handsomely graced with fine
elms were transformed within a few years into barren, urban-looking landscapes
devoid of trees, the result of a frighteningly efficient epidemic that had
appeared suddenly. We can imagine the profound dismay of the citizens of
Portland and New Haven as each “City of Elms” was quickly transformed into a
“City of Firewood,” necessitating almost phenomenal removal expenses. Some may
recall marveling at the futility of the “cut and burn campaigns” which were
initiated to halt the spread of an epidemic which was killing trees literally
by the millions each year. 

The cause of this pervasive syndrome of wilt and dieback was a parasitic
fungus. The spores of the fungus were being deposited into the vascular systems
of healthy elm trees through twig-crotch feeding wounds chewed by elm bark
beetles, the carriers of the disease. Once in contact with the inner bark, the
spores germinated into rapidly growing fungal threads which invaded the entire
conducting systems, clogging them and preventing the transport of water and
nutrients to the hosts' crowns, thereby killing the trees in a manner not
unlike that of the chestnut blight. Unlike the chestnut blight, however, the
elm pathogen proved efficient at destroying the root systems of its hosts,
preventing them from sending up new shoots, and it even was observed to spread
to adjacent trees through natural grafts between their roots. 

A native of Asia, the fungus first had appeared in North America in 1930 in
Cleveland, Ohio, having found its way into the continent by the same means as
the chestnut blight, through the accidental import of infested logs from a
related species. The parasite was no stranger in Europe, where it similarly had
appeared early in the century, and where its pervasive devastation of a number
of European elm species, including the esteemed Dutch elm hybrids which had
lined many streets, had given rise to its now-familiar name, “Dutch elm
disease.” 

The various elm species native to Asia, where the so-called “Dutch” elm disease
originated, are highly resistant to this disease, as healthy specimens are able
to manufacture chemicals which prevent the spores from germinating or gaining a
stronghold in the inner bark of the trees, and they consequently are able to
thrive with little or no stress in the face of generations of exposure to the
disease. In its native Asia, the disease actually serves the valuable function
of eliminating old or weakened elms to make way for new growth. The Dutch elm
disease fungus, like purple loosestrife and water hyacinth, thus provides us
with yet another classic illustration of the danger inherent in the
introduction of an organism into an ecosystem that is not its own. 

Nowadays we have to search rather painstakingly to find an occasional large
surviving American elm tree, as the pathogen's destruction of more than 100
million American elms during the last few decades has effectively depleted the
population throughout the tree's natural range. Inevitably, the continuing
pattern of destruction soon will threaten the survival of the species, for
although young saplings are still common, the current population consists
primarily of immature specimens with little chance of reaching a stately
maturity, and the large, mature examples that still are seen occasionally are
being eliminated rapidly. Like the American chestnut, which is now gone from
the forest canopy, the American elm has been declining slowly but surely ever
since the introduction of a lethal fungal blight, and although the threat of
extinction is not immediate, we cannot realistically avoid the conclusion that
the last of the sizable, wild American elms likewise will disappear within our
lifetimes. 

The development of purely American elm varieties with adequate resistance to
Dutch elm disease remains the only hope for ultimately saving the species, as
systematic injection with elm fungicide is an expensive, cumbersome, and
unnatural process. It was fortunate, indeed, that such development proved
possible and eventually yielded the American elm strains which now constitute
the essential ingredients of my project. In other words, we now have a
realistic means to ensure the ultimate survival of the American elm and to
bring about the imminent return to our landscapes of fine, stately specimens
that are likely to survive through the decades. That is the essence of my
endeavor, and it is my hope that this writing will help to sow the seeds of
this inspiration for others as well. Having obtained the wholehearted approval
of my home town's conservation director, I have been raising these new elm
varieties in quantity and have planted many of them in suitable locations in
Acton, Massachusetts. My idea of a suitable location is an open area in which a
tree always will remain safe from indifferent landowners and available for
public appreciation in a rustic setting, and that means conservation lands,
most notably the Acton Arboretum.

*** For more information, including details on DED-resistant varieties of
American elm and their availability, please visit the full version of this
article at http://www.elmpost.org



More information about the Plantbio mailing list