BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Ulmus americana | American Elm 



GENERAL BOTANICAL CHARACTERISTICS : 
American elm is a deciduous, fast-growing, long-lived tree which may
reach 175 to 200 years old with some as old as 300 years [5,27,53].  In
dense forest stands, American elm may reach 100 to 200 feet (30-36 m) in
height and 48 to 60 inches (122-152 cm) in d.b.h.  Heights of 80 feet
(24 m) are common on medium sites but on very wet or very dry soils, the
species is often 40 to 60 feet (12-18 m) tall at maturity [5,44,54].  In
the forest American elm often develops a clear bole 50 to 60 feet (15-18
m) in length.  Open-grown trees fork 10 to 20 feet (3-6 m) from the
ground with several erect limbs forming a wide, arching crown [29,56].
The alternate, double-toothed leaves are 2 to 5 inches (5-10 cm) long
and 1 to 3 inches (2.5-7.5 cm) wide.  The dark gray bark is deeply
furrowed (9,15).  The perfect flowers are borne in dense clusters of
three or four fascicles.  The fruit is a samara consisting of a
compressed nutlet surrounded by a membranous wing [7,29].

The root system of American elm varies according to soil moisture and
texture.  In heavy, wet soils the root system is widespreading, with
most of the roots within 3 to 4 feet (1.0 - 1.2 m) of the surface.  On
drier soils, American elm develops a deep taproot [29].


RAUNKIAER LIFE FORM : 
   Phanerphyte


REGENERATION PROCESSES : 
Seed production and dissemination:  American elm seed production may
begin as early as age 15 but is seldom abundant before age 40.  When
mature, American elm is a prolific seed producer.  Trees as old as 300
years have been reported to bear seed [5].  In closed stands, seed
production is greatest in the exposed tops of trees.  The winged seeds
are light and readily disseminated by the wind.  Although most seeds
fall within 300 feet (90 m) of the parent tree, some may be carried 0.25
mile (0.4 km) or more.  In riverbottom stands, the seeds may be carried
by the water for miles.  Cleaned, unwinged seeds average 70,900 per
pound (156,000/kg) [28,46,53].

Seedling development:  Germination in American elm is epigeal.  Seeds
usually germinate soon after they fall, although some seeds remain
dormant until the following spring.  Germination is usually 6 to 12 days
but may extend over a period of 60 days.  Dormancy may be overcome by
stratification in sand for 60 days at 41 degrees Fahrenheit (5 deg C).
The seeds germinate best with night temperatures of 68 degrees
Fahrenheit (20 deg C) and day temperatures of 86 degrees Fahrenheit (30
deg C).  The germination capacity averages about 65 percent
[7,10,29,46].

Vegetative reproduction:  American elm will reproduce fairly vigorously
by stump sprouts from small trees.  Large trees 150 to 250 years old
seldom sprout after cutting [29].  Observations in undisturbed
bottomlands of Minnesota suggest that replacement of American elm may be
by root suckering [5].


SITE CHARACTERISTICS : 
American elm is common on wet flats and bottomlands but is not
restricted to these sites.  In the southern bottomland regions, it
commonly occurs on terraces and flats but not in deep swamps.  At higher
elevations in the Appalachians it is often limited to the vicinity of
larger streams and rarely occurs at elevations above 2,000 feet (610 m).
In the Lake States and Central States, it is found on plains and moraine
hills as well as the bottomlands and swamp margins.  Along the
northeastern edge of its range, it is usually restricted to valleys
along waterways except where it has been planted on the uplands
[29,42,50].

American elm grows best on rich, well-drained loams.  Growth is poor on
dry sands and where the summer water table is constantly high.  In
Michigan, on loam and clay soils, growth is good when the summer water
table drops 8 to 10 feet (2.4-3.0 m) below the surface.  In the South,
American elm is common on clay and silty-clay loams on bottomlands and
terraces.  Growth is medium on wetter sites and good on well-drained
sites.  In the arid western end of its range, American elm is restricted
to silt or clay loams in river bottoms and terraces.  American elm most
commonly grows on soils of the orders Alfisols, Inceptisols, Mollisols,
and Ultisols [5,29,41].

In addition to those species mentioned in SAF Cover Types, common
associates of American elm include balsam fir (Abies balsamea), silver
maple (Acer saccharinum), sycamore (Platanus occidentalis), pin oak
(Quercus palustris), black tupelo (Nyssa sylvatica), white ash (Fraxinus
americana), sweetgum (Liquidambar styraciflua), hackberry (Celtis
occidentalis), boxelder (Acer negundo), birch (Betula spp.), and hickory
(Carya spp.) [4,19,43,50].


SUCCESSIONAL STATUS : 
Faculative Seral Species.

American elm is classed as intermediate in tolerance among eastern
hardwoods [50].  It usually responds well to release.  Once it becomes
dominant in a mixed hardwood stand, it is seldom overtaken by the other
species.  It can persist for years as an intermediate but will be
replaced by tolerant hardwoods such as sugar maple (Acer saccharum) or
beech (Fagus grandifolia) if suppressed.  Although American elm is not
listed as a key species in the climax types on moist sites, it is
usually one of the associated species [29,32].


SEASONAL DEVELOPMENT : 
The time of flowering, seed ripening, and seed fall varies by about 100
days between the Gulf Coast and Canada.  The flower buds swell early in
February in the South and as late as May in Canada.  The trees are in
flower 2 to 3 weeks before the leaves unfold.  The fruit ripens as the
leaves unfold or soon afterward.  The seed is dispersed as it ripens and
seed fall is usually complete by the middle of March in the South and by
the middle of June in the North [3,7,29].

Related categories for Species: Ulmus americana | American Elm