BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Celtis occidentalis | Hackberry 



GENERAL BOTANICAL CHARACTERISTICS : 
Hackberry is a native, deciduous small to large tree, its size varying
in response to habitat [16].  In poor, dry sites, growth is so stunted
that the plant appears as a shrub.  This drought and flood tolerant tree
grows up to 82 feet (25m) high with the larger branches 26 to 33 feet
(8-10m) above the ground [37], although on the Great Plains and on dryer
sites it usually grows to only 25 to 50 feet (7.5-15m) high with a
diameter of 8-24 inches (20-61cm) [21].  On the best sites hackberry may
reach 130 feet (40m) with a diameter of 4 feet (1.25m) [21].  The rather
thick (1 to 1 1/2 inches (2.5-4cm)), dark brown to grey bark is deeply
furrowed, checkered and warty when older; the younger branches are
mostly pubescent [16,31].  Hackberry has lateral roots which tend to be
medium deep to shallow [31,41].

Early growth of hackberry varies greatly within its range.  Height
growth may not exceed 1 inch (2.5cm)/year under a heavy overstory, but
when planted in Great Plains shelterbelts, plants average 1.3 feet
(40cm)/year during the first 6 years [34].  Maximum age attained by
hackberry is between 150 and 200 years [21].

The simple, alternate leaves are lance-ovate or deltoid from 2 to 4.5
inches (5-12cm) long and 1.2 to 2.4 inches (3-6cm) wide with a serrate
margin.  The lower surface of the leaves is paler and pubescent [16,37].
This monoecious tree has perfect, unisexual flowers which appear in the
spring as the new leaves emerge [17].  The inconspicuous, small, green
flowers are wind-pollinated [34].  Staminate flowers appear singly or in
clusters of two to three at the base of a short, green branch.
Pistillate flowers appear singly or in pairs [37].

Hackberry fruit is a round drupe with a thin, sweet, edible pulp
enclosing a bony, cream-colored nutlet.  The fruit, which is usually
variable in size, form and color [21] is dark orange or red to dark
purple or black in color, and is about 1/4 to 1/3 inch (0.5-1cm) in
diameter on a 2/3 inch (15mm) pedicel [7,16,17,37].  Hackberry produces
good seed crops each year [43].

Hackberry is host to a large number of insects and diseases, most of
which cause no serious damage.  Four gall-producing insects attack this
tree, and the entire crown may be defoliated by the spiny elm
caterpillar or the hackberry butterfly caterpillar.  The hackberry
engraver beetle attacks mostly dead or dying branches, but has been
reported to attack living sapwood as well, causing the tree to die.  A
witches'-broom caused by the mite Eriophyes spp. and a powdery mildew
fungus causes a rosette-like proliferation of the branch tips, but does
not cause serious damage to the tree [21,41].

Many ecotypes of this variable species are known to occur.  Varieties
are distinguished by such morphological charcteristics as growth form,
height, leaf size and margin, and fruit shape and color.





RAUNKIAER LIFE FORM : 
   Undisturbed State:  Mesophanerophyte
   Undisturbed State:  Microphanerophyte
   Burned or Clipped State:  Therophyte (offsite)
   Burned or Clipped State:  Chamaephyte


REGENERATION PROCESSES : 
Hackberry regenerates primarily through sexual reproduction.  This tree
produces good seed crops most years, with at least some seed produced
each year [7,21].  Although some seed may be dispersed by water, most is
disseminated principally by birds and small mammals.  The fruit, a drupe
with sweet, edible pulp [37], is consumed by many species of birds and
mammals, which then disperse the seeds in their feces [34].  Some fruit
stays on the tree through the winter, but most is consumed or falls off
before spring [34,43].

This shade tolerant species is a member of several late seral and climax
communities, reproducing even in heavy shade [11,21,35].  Hackberry
seedlings become established in existing hardwood stands, but rarely in
old fields, and seedlings and saplings have been observed growing in
heavy shade where seedlings of other overstory species did not persist
[21].  Height growth may only be 1 inch (0.5cm)/year under heavy
overstory [21].

Krajicek [21] reports that when cut, hackberry will produce sprouts from
the stumps of small trees, but rarely from those of larger trees,
However, there is little other evidence in the literature of this
species' ability to sprout.  On the Konza prairie in Kansas, hackberry
is replacing the more heliophilous (sun-loving) bur and chinkapin oaks
(Quercus macrocarpa and Q. muehlenbergii), only where fire has been
excluded, as fire kills the seedlings and saplings [34].  This suggests
that hackberry is unable to sprout after fire or to reproduce in the
openings it creates.



SITE CHARACTERISTICS : 
Hackberry is adapted to a variety of climatic conditions.  Average
annual precipitation varies from 14 to 60 inches (35.5-155cm), and the
average frost-free season is from 120 to 250 days.  Hackberry tolerates
an annual temperature variation of 140F (60C) in the Great Plains [21].
However, the northern extension of its range is limited by late spring
frosts which destroy flowers, or by early autumn frosts which kill the
germs of immature fruits.  It grows best on moist valley soils along
streambanks and on flood plains [16] but is also commonly found on
slopes and bluffs, on limestone outcrops, on the north side of sand
dunes in western Nebraska, on upland sites in the central Great Plains
under existing oak stands on all aspects, slopes and ridges, on rocky
hillsides in open woodlands [21], and along the base of canyon walls of
the Arikaree River in Colorado [4].  In the northern Great Plains
portion of its range, where rainfall is insufficient to support upland
tree growth, hackberry is restricted to well developed river valleys,
north slopes and protected ravines, and is absent from the windswept
parts of the western river valleys [21].

Although principally a bottomland tree, sites with a permanently high
water table are unfavorable for hackberry; however, periodic flooding is
not detrimental.  In Kentucky, 46 days of flooding during one growing
season caused no apparent damage to this tree [21].  This species has
been planted frequently in the west because of its relative drought
tolerance/avoidance [31], but mesic hackberry is less successful at
coping with water stress than bur and chinkapin oaks (Quercus macrocarpa
and Q. muehlenbergii) [2].

Hackberry is tolerant of a variety of soils, but grows best on moist,
rich soils [21].  Its growth is stunted and scraggly on poor, dry sites
[31].  This species seems to prefer limestone soils [21].

Hackberry seldom occurs in pure stands, although it is prominent in the
northern phase of the sugarberry (Celtis laevigata) - American elm
(Ulmus americana) - green ash (Fraxinus pennsylvanica) forest cover
type.  It also occurs in several upland forest types in association with
sugar maple (Acer rubrum), basswood (Tilia spp.), post oak (Quercus
stellata), black oak (Q. velutina), bur oak (Q. macrocarpa), and eastern
redcedar (Juniperus virginiana) [11,21].  In the central Great Plains,
hackberry is reproducing under chinkapin oak and bur oak stands, and is
replacing the oak woodlands as the major overstory dominant [34].  

The elevational ranges for hackberry in several northern Great Plains
states are as follows [10]:

Colorado                         3,500-7,200 feet (1,067-2,195m)
Montana                          4,000-4,500 feet (1,219-1,372m)
Nebraska                         2,600-4,500 feet (792-1,372m)
South Dakota                     3,000-3,500 feet (914-1,067m)
Utah                             4,800 feet (1,463m)
Wyoming                          4,800 feet (1,463m).



SUCCESSIONAL STATUS : 
Hackberry is found in many forest types ranging from early to late
seral, making its successional position difficult to determine.
This tree is intermediate to tolerant in its ability to withstand shade
and seems to require shade for reproduction of its seedlings [21].  In
the Konza prairie of the central Great Plains where fires are excluded,
succession is progressing from oak dominated woodlands to forests
dominated by hackberry.  Abrams [1] states that on the more mesic sites
of the Konza prairie, hackberry may be the future sole dominant of what
are now oak woodlands.  Hackberry also establishes itself on river
floodplains of the central Great Plains under willow (Salix spp.) and
eastern cottonwood (Populus deltoides), and is probably the climax
species [5].  This species is also a member of several late-seral
communities [11,35].



SEASONAL DEVELOPMENT : 
Hackberry, a polygamo-monoecious tree, flowers when the leaves emerge,
or shortly after, in early April in the southern part of its range, and
in late May in the northern part.  The fruit, a drupe, ripens from
September to October, and remains on the tree throughout the winter
[7,21].  This deciduous tree drops its leaves in the fall, generally
after the first frost.

Related categories for Species: Celtis occidentalis | Hackberry