DED-resistant American Elms

BCarley978 bcarley978 at aol.com
Sun Jan 21 23:50:52 EST 2001


From: "Saving the American Elm," by Bruce Carley
http://users.aol.com/BCarley978/elmpost.htm

QUINTESSENTIAL MAIN STREET

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 wider 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 Massachusetts state
tree. Architects even designed buildings with elm plantings inherent in their
plans. The early citizens of Portland, Maine had such a passion for the
American elm that they created elm-lined streets on practically every block and
earned their 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 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 chopped it down as a final act of hostility during a
hurried retreat from Boston in 1775.

THE FALL FROM GRACE

Many of us remember how painful it was for our communities to witness the
tragedy that recurred throughout the eastern states, mostly during the 1960'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 as
their “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 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, gumming them up 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 was even observed to spread to
adjacent trees through natural grafts between their roots.

A native of Asia, the fungus had first appeared in North America in 1930 in
Cleveland, Ohio, having found its way into the continent by the same means as
the chestnut blight, namely, through the accidental import of infested logs
from a closely related species. The parasite was no stranger in Europe, where
it had similarly appeared early in the twentieth century, and where its
pervasive devastation of a number of European elm species, including the highly
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 are consequently 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 very real 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 elm tree, as the pathogen's destruction of more than a hundred
million American elms during the last few decades has effectively depleted the
population throughout the tree's natural range in North America. Inevitably,
the continuing pattern of destruction will soon 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 specimens that are still seen
occasionally are rapidly being eliminated. Like the American chestnut, which is
now gone from the forest canopy, the American elm has been slowly but surely
declining 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 will likewise
disappear within our lifetimes.

THE SOLUTION

The development of purely American elms 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 varieties 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 by the dozen
and planting them in suitable locations around Acton, Massachusetts. My idea of
a suitable location is an open area in which a tree will always remain safe
from indifferent landowners and available for public appreciation in a rustic
situation, and that means conservation lands, most notably the Acton Arboretum.

[snip]
************
This article continues with instructive information on CULTIVATION,
PROPAGATION, and AVAILABILITY of the new, purely American elm varieties,
"Valley Forge," "New Harmony," "Princeton," and "American Liberty," and
provides quality photographs and links to research data and other informative
sites, including information on successful and promising development of highly
blight-resistant American chestnut strains. For further information, please
visit:

http://users.aol.com/BCarley978/elmpost.htm






More information about the Plant-ed mailing list