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American Elm |
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Once a very popular and
long-lived (300+ years) shade and street tree,
American Elm suffered a dramatic decline in the
1950's with the infestation of Dutch elm
disease, a fungus spread by a bark beetle. The
wood of American Elm is very hard and was a
valuable timber tree used for lumber, furniture
and veneer. The Indians once made canoes out of
American Elm trunks, and early settlers would
steam the wood so it could be bent to make
barrels and wheel hoops. It was also used for
the rockers on rocking chairs. |
Morton Arboretum accessions 604-25*1, 2 & 3, are
from grafts done 83 years ago.
| These three outstanding American
Elms display the classic vase-shape of
the species. The Morton Arboretum is one
of the largest living Ulmus collections
in the world (more than 30 species, in
addition to numerous infraspecific taxa,
hybrids, and cultivars) and has the
source of numerous elm cultivars. I
remember when the elms in Des Plaines,
Illinois all died during the 1950's. Our
walk to school along Thacker Street was
shaded by enormous elms all the way from
Wolf Road to 2nd Avenue, then the next
year they were all gone. So sad. Similar
scenarios are now playing themselves out
amongst the lodgepole pine and ash trees
of North America. |
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Leaf: alternate, simple, ovate to oblong,
3 to 5 inches long, 1 to 3 inches wide,
margin coarsely and sharply doubly serrate,
base conspicuously inequilateral, upper
surface green and glabrous or slightly
scabrous, paler and downy beneath.
This native North American tree grows
quickly when young, forming a broad or
upright, vase-shaped silhouette, 80 to 100
feet high and 60 to 120 feet wide. Trunks on
older trees could reach to seven feet
across. The six-inch-long, deciduous leaves
are dark green throughout the year, fading
to yellow before dropping in fall. In early
spring, before the new leaves unfold, the
rather inconspicuous, small, green flowers
appear on pendulous stalks. These blooms are
followed by green, wafer-like seedpods which
mature soon after flowering is finished and
the seeds are quite popular with both birds
and wildlife. Trees have an extensive but
shallow root system. |
Here is an interesting
excerpt from a scientific
paper regarding the
decomposition rate of
different tree leaves in an
aquifer:
Abstract
Dry Chinquapin oak ( Quercus
macrocarpa) and American
elm ( Ulmus americana)
leaves were placed in four
microcosms fed by groundwater
springs to monitor changes in
dry mass, ash-free dry mass, and
microbial activity over a 35-day
period. Oxygen microelectrodes
were used to measure microbial
activity and to estimate
millimeter-scale heterogeneity
in that activity. Oak leaves
lost mass more slowly than elm
leaves. Generally, there was a
decrease in total dry weight
over the first 14 days, after
which total dry weight began to
increase. However, there were
consistent decreases in ash-free
dry mass over the entire
incubation period, suggesting
that the material remaining
after initial leaf decomposition
trapped inorganic particles.
Microbial activity was higher on
elm leaves than on oak leaves,
with peak activity occurring at
6 and 27 days, respectively. The
level of oxygen saturation on
the bottom surface of an elm
leaf ranged between 0 and 75%
within a 30-mm 2 area.
This spatial heterogeneity in O 2
saturation disappeared when the
water velocity increased from 0
to 6 cm s -1. Our
results suggest that as leaves
enter the groundwater, they
decompose and provide substrate
for microorganisms. The rate of
decomposition depends on leaf
type, small-scale variations in
microbial activity, water
velocity, and the length of
submersion time. During the
initial stages of decomposition,
anoxic microzones are formed
that could potentially be
important to the biogeochemistry
of the otherwise oxic aquifer.
(4)
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Bark |
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Flower: Monoecious;
small, in drooping clusters of 3 to 5,
appear in early spring before leaf buds
open.
Fruit: Rounded, flat, pappery, wafer-like
samaras, 3/8 to 1/2 inch across, deeply
notched at apex, hairless except for margin;
ripen in spring.
Twig: Slender, glabrous, slightly zigzag,
reddish brown; buds ovate, over 1/4 inch
long, reddish brown with darker edged
scales, often placed a little to one side of
the twig.
Bark: Dark, ashy gray, flat-topped ridges
separated by diamond-shaped fissures; outer
bark when sectioned shows distinct,
titleernating, buff colored and reddish brown
patches. When young it is often quite
spongy.
Form: In the open, the trunk is usually
divided into several large, ascending and
arching limbs, ending in a maze of graceful
drooping branchlets.
--USDA Forest Service Silvics Manual
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