The two enormous, stately elm trees that
towered in front of Hill Auditorium until June had lived through so
much.

One hundred years old and more than two feet thick, they had
seen the University burgeon into a major research institute. They
stood by calmly while Ann Arbor’s young soldiers enlisted for
the first, then the second, world war.

They witnessed the first Ford automobiles on Ann Arbor roads and
weathered the droughts of the Great Depression. Their leaves blew
in the wind during the protests of Vietnam.

And for years, with the help of the University’s grounds
crew, they escaped the epidemic of Dutch elm disease that, since
1930, has killed 80 percent of Michigan’s American elm
trees.

But last year, stressed by construction at the auditorium that
weakened their root systems, the trees finally succumbed to the
disease. Both were cut down this summer to prevent the fungal
sickness from spreading to other trees.

“The death certificate says ‘Dutch elm
disease,’ but I know it was the construction … that
strained the trees to the point where they could no longer fight
anything off,” said Jane Immonen, a forestry technician for
University Grounds and Waste Management.

The two lost elms typify the fight that American elms —
and the people who love their tall, vase-shaped profile —
have waged against Dutch elm disease for decades. Although
it’s too late to save Hill Auditorium’s two trees, many
preservation and restoration efforts are paying off. At the
University, elms just might be about to begin a comeback.

 

A spreading threat

 

Once considered the foremost American
shade trees for their graceful shape, large size and rapid growth,
elms used to stand in long avenues along city streets and in front
of public buildings like Hill Auditorium. The University alone had
thousands of elms on its grounds, including the Nichols Arboretum
and the Matthaei Botanical Gardens, said SNRE Prof. Burt
Barnes.

Then Dutch elm disease, introduced to the United States from
Europe in a shipment of infected wood during the 1930s, swept in.
Transmitted by unassuming little critters less than three
millimeters long called elm bark beetles, the disease has destroyed
more than half the nation’s elm trees, the U.S. Department of
Agriculture reports.

Planting practices common during the early 20th century worsened
the devastation. The close spacing of elms along city streets,
without other trees interspersed, allowed elm bark beetles to jump
quickly from one tree to the next. Also, because elm tree roots
graft, or fuse, together when they grow to a large size, infected
trees passed the sickness to neighboring trees through entwined
root systems.

Although elms seed prolifically and young elms spring up each
year, the disease prevents the trees from reaching full maturity,
Barnes explained.

“We have reduced the population of elms in nature from 200
years old to 30 years,” he said. “They used to live to
a grand old age … and now they live at most to 40
years.”

Barnes said the elm bark beetle was among the first of many
introduced pests that have threatened U.S. tree populations. These
include the chestnut blight and, most recently, the emerald ash
borer, first reported in 2002 and blamed for the ongoing deaths of
ash trees.

“We haven’t learned our lesson very well — the
lesson of invasive species,” Barnes said. “It’s
repeated over and over again.”

Dutch elm disease continues to threaten the University’s
small population of remaining elms, Immonen said, and periodically
recurs in mature trees on campus. The University currently has 153
mature elms on campus.

This year has been particularly difficult for campus elms, she
said, due to an unusually cool, rainy summer. Fungal diseases like
Dutch elm disease thrive in damp conditions and are more likely to
overcome preventive measures protecting the trees.

Also, each elm death sends a host of homeless bark beetles
scrambling for a new, nearby home.

“If they lose their food source, they’ll move on to
the next tree,” said LSA senior Valerie Ackley, who worked
with the University grounds crew to help care for elms last summer.
The Dutch elm disease that crept across a row of elms in front of
Angell Hall and killed the last elm there two years ago, she said,
could migrate to elms on the grassy corner by State Street or move
onto the Diag.

University forestry crews won’t know immediately if trees
have sickened; it may take as many as two years for Dutch elm
disease to cause symptoms, Ackley said. These symptoms include
wilting of the tree’s crown, or upper canopy, and browning of
its leaves.

No sick trees currently stand on campus grounds, Immonen said.
“Those get taken down right away because they serve as an
infection point and are also hazardous, with falling
branches,” she explained.

But Diag horticulturist Alex Sulzer pronounced a grim future for
the mature elms on campus. “With American elms, we’re
basically just prolonging their death sentence,” he said.
“They’re all going to go.”

 

The line of defense

 

It’s hard to imagine the Diag
without its 10 largest trees — all American elms that provide
shade and beauty to students studying, sleeping or throwing
Frisbees on the grass.

The University grounds crew, though, won’t give up more
trees without a fight. A small but dedicated corps of University
forestry experts works to protect campus elms and other trees.

Every other year, each elm gets its own version of a flu shot
— a vaccination by “elm doctor” Immonen. Immonen
runs insect and disease control for Grounds and Waste
Management’s forestry division, and sallies out each summer
with a student intern and a long-needled, hand-held inoculation
gun.

“We do trunk injections with fungicides,” Immonen
explained. “That we have any elm trees standing is
attributable to the fact that we do fungicide treatment.”

Immonen also uses sticky traps to monitor elm bark beetle
populations on campus. A small vial on the traps releases a
pheromone, or scent chemical, which “smells like a female
bark beetle looking for a date,” Immonen said. The scent
attracts male beetles, which stick to the otherwise harmless
surface of the trap. Immonen then counts how many beetles lie
within small circles drawn on the trap, and plugs the number into a
statistical calculation that tells her when the beetle population
becomes active that year.

Pesticide sprays once helped control beetle populations, but
now, environmental considerations prevent widespread spraying. The
federal government banned the pesticide DDT, once used on campus
elms, in 1972 for its detrimental effects on wild birds.
Methoxyclor, another pesticide, is no longer used at the University
due to toxicity concerns, Immonen said.

Instead of pesticides, non chemical measures are used to protect
elms from disease. Sulzer said extra efforts go into preventing
construction from hurting large trees like the elms in front of
Hill Auditorium. Trees are watered more frequently, pylons are
driven in around them to prevent soil compaction around their roots
and compost is added to the soil to provide nutrients.

But, Sulzer admitted, “it’s always kind of a crap
shoot whether that tree will survive.”

Also, to keep the campus green, construction companies working
near a large tree must compensate the University by planting 10 or
12 new trees if the tree dies, Sulzer said.

The best way to preserve tree cover at the University, explained
Grounds and Waste Management director John Lawter, is to plant many
different tree species. “We try to diversify so that no one
bug can come and wipe us out.”

 

From the ground up

 

Two rows of spindly saplings stand in the
grass in front of Angell Hall, sporting chicken wire around their
trunks to prevent squirrels from gnawing their bark. Close
inspection of their leaves reveals the trees are elms.

Immonen said she obtained the trees from the Elm Research
Institute, an organization that has developed a strain of American
elm resistant to Dutch elm disease.

“The research institute spent years collecting seeds and
cuttings from trees all over the country, looking for trees that
were resistant,” she said.

The New Hampshire-based institute calls its final result the
“Liberty Elm.” According to the institute’s
website, Liberty Elms are clones of six genetically-different,
Dutch elm-resistant trees. The trees are visually identical in
shape and size to the classic American elm.

“We’re now in the 20th year and (our) trees are out
there in great number and great height,” Institute director
John Hansel said. “They’re on many campuses across the
nation and we’re very proud of them.”

Denny Townsend, a research geneticist at the U.S. National
Arboretum in Washington, said several other strains of American elm
are considered tolerant to the disease. He listed the Valley Forge,
New Harmony and Princeton elms as tolerant in laboratory tests.
Both the Valley Forge and New Harmony were developed at the
Arboretum.

Townsend explained that while no elm is completely immune to the
disease, “in the natural environment, we don’t see
symptoms in these trees.”

A lively controversy has sprouted regarding the different
strains of resistant elm. Townsend said the Liberty Elm showed more
symptoms in laboratory tests when inoculated with Dutch Elm disease
than the Valley Forge, New Harmony and Princeton elms.

He added, however, that laboratory tests do not mimic the
natural environment. “We ran our tests under unnatural
conditions, in that we injected each tree with half a million
spores of the fungus.” In nature, he said, elms are exposed
to far fewer spores. “Under natural conditions, the Liberty
Elm might do just fine.”

In turn, Hansel criticized the National Arboretum and other
distributors of resistant elms for not tracking their trees after
distribution to determine their success in nature.

“Don’t duck the responsibility of tracking your
trees,” he said. “The last thing we need … is
another failure. The country would be the loser as the American elm
went down for the last time.”

The Liberty Elm Institute assigns a serial number to each tree
it distributes and offers a warranty under which any tree lost to
Dutch elm disease is replaced. Extensive field testing and tracking
of Liberty Elms, Hansel said, has shown that less than 1 percent
have succumbed to the disease.

Meanwhile, the young elms in front of Angell Hall, unaware of
the controversy, are slowly gaining girth.

“They’re doing well,” Immonen said.
“Elms grow pretty fast … but for them to reach big
tree size is going to take a few decades.”

If the elms survive, they’ll eventually join the ranks as
some of the University’s most valuable trees. A large, mature
elm in a prominent location can be valued at as much as $27,000,
said Marvin Pettway, a forester with Grounds and Waste
Management.

For Sulzer, this value indicates far more than just the work
involved in planting and protecting campus elms.

“They’re part of the fabric of the campus —
the history and heritage,” he said. “They’re
massive, beautiful old trees.”

With any luck, American elms like these will shade the
University for at least a few centuries more.

 

View this page:
“http://www.michigandaily.com/vnews/display.v/ART/416fb49af28ae”>October
15, 2004: Taking Root

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