BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Carpinus caroliniana | American Hornbeam 



GENERAL BOTANICAL CHARACTERISTICS : 
American hornbeam is a native, deciduous small tree.  It usually grows
30 to 40 feet (9-12 m) tall [4,13,32,39].  The bark is thin, close, and
usually smooth.  The trunk is often crooked, and is usually coarsely
fluted, resembling a flexed muscle [4,7,13].  The fruit is a ribbed
nutlet 0.16 to 0.24 inch (4-6 mm) long [3,4].  It is usually described
as slow-growing and short-lived [27].

The largest American hornbeam on record for the Southeast was 75 feet
(22.8 m) tall, 21.6 (54.8 cm) d.b.h., and 67.8 inches (172.2 cm) in
circumference [42].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
The mimimum seed-bearing age of American hornbeam is 15 years [32].
Production is greatest at 25 to 50 years and probably ceases at about 75
years [6].  Large seed crops are produced at 3- to 5-year intervals
[27,32].  Seeds are are mainly dispersed by birds, and are wind blown
only a short distance [6,27].  Matlack [25] estimated the lateral
movement of American hornbeam diaspores (nut plus bracts) in a 6 mile
per hour (10 km/hr) breeze as 64 feet (19.4 m).  Seed dormancy may be
broken by stratification.  Stratification at 40 degrees Fahrenheit (4
deg C) for 18 weeks, stratification plus gibberellic acid, and
scarification of the seedcoat plus gibberellic acid all improve
germination [6,27].  The optimum natural seedbed for American hornbeam
is continuously moist, rich, loamy soil protected from extreme
atmospheric changes [6].  American hornbeam will also establish on leaf
litter seedbeds in deep shade, even when competition is present [27].
Germination occurs from April to June in the spring following seed
maturity [6].

In eastern Texas, seedling survival for American hornbeam is low the
first year, but increases substantially thereafter.  Flooding,
drought, damping off, proximity to a conspecific adult, and herbivory
were important causes of first year mortality.  Mortality tends to be
concentrated in short periods associated with particular events
(flooding, for example).  Periods of reduced flooding allowed American
hornbeam seedlings to increase in importance [36].

Regeneration of American hornbeam after a seed-tree harvest in Arkansas
consisted of new seedlings, advance reproduction, stump sprouts, and
root sprouts [27].


SITE CHARACTERISTICS : 
American hornbeam exhibits its best growth on rich, moist soils in
bottomlands, coves, and lower protected slopes.  It is also common along
the borders of streams and swamps including bay and river swamps in
Florida [6,8,27], and is also found in hydric hammocks in Florida [8].
The best sites for American hornbeam are characterized by abundant soil
moisture but sufficient drainage to prevent saturation and poor aeration
during the growing season [27].  American hornbeam is primarily found on
poorly to imperfectly drained sites, although it grows on well-drained
sites also [21].  Hook [41] rated American hornbeam as only weakly
tolerant of flooding, although it occurs on sites that have a high
probability of flooding in any given year.  He commented that mature
trees remain healthy if flooded less than 24 percent of the growing
season, but are most abundant where flooding occurs 10 to 21 percent of
the growing season [41].  In the Adirondack Mountains, American hornbeam
is found on soils derived from limestone, gneiss, shale, and sandstone
[21].  The usual soil pH range for American hornbeam sites is acidic (pH
4.0-5.6), but the tree can be found on soils as high as pH 7.4 [27].

Maximum elevation for American hornbeam is about 2,900 feet (900 m) in
the southern Appalachians [7].  Its upper elevational range is 3,000
feet (910 m) in the Great Smoky Mountains, but is more common at about
1,600 feet (490 m) [27].  In the Adirondack Mountains, New York,
American hornbeam occurs from 200 to 1,020 feet (60-311 m) elevation [21].


SUCCESSIONAL STATUS : 
Facultative Seral Species

American hornbeam is tolerant of shade [21,27].  It persists in the
understory of late seral and climax communities.  Shade tolerance is
greatest in American hornbeam seedlings and declines with age [27].
Curtis and McIntosh [5] rated the climax adaptation of American hornbeam
as 8 (10 is the maximum, usually assigned to species such as sugar maple
[Acer saccharum]).  American hornbeam responds positively to overstory
removal.  On certain southern sites, it is so aggressive that it
prevents larger species from regenerating after logging or natural
disturbance [27].  In minor streambottoms American hornbeam and other
tolerant subcanopy species are likely to capture a site once the main
canopy is removed [15].  In Connecticut, thinned northern red oak-black
oak-scarlet oak (Quercus rubra-Q. velutina-Q. coccinea) plots had a
higher proportion of American hornbeam and eastern hophornbeam than
unthinned plots [40].

In North Carolina, American hornbeam first appeared in old fields 12 to
18 years after abandonment, and appeared 25 to 40 years after
abandonment on old fields in New Jersey [27].  American hornbeam was
present on 28-, 30-, and 40-year-old old fields in western Tennessee.
It was not present on the 3- and 12-year-old sites [33].

Hupp [17] classes American hornbeam with species that do not normally
invade degraded or newly aggrading substrates (in relation to stream
channelization projects) but are tolerant of bottomland conditions and
have seed that is long-lived (up to 2 years) and dispersed by wind or
water.  These species are best suited to establish in bottomlands that
have already been stabilized by pioneer species, and occur in
abundance on undisturbed sites or on sites that are in the later
stages of recovery from channelization [17].

American hornbeam was present in the understory of a mixed hardwood
bottomland forest dominated by water oak (Q. nigra), sweetgum,
cherrybark oak (Q. falcata var. pagodifolia), and loblolly pine (Pinus
taeda).  American hornbeam seedlings and saplings dominated the
reproduction layers in this forest [18].

In Florida, American hornbeam tends to capture gaps early, but is
replaced by slower-growing and longer-lived evergreen species such as
American holly and common sweetleaf (Symplocos tinctoria) [30].


SEASONAL DEVELOPMENT : 
American hornbeam flowers from March 20 to May 6 in the Southeast, and
from April to May in the northern parts of its range, usually before the
leaves are fully grown [27].  The fruits ripen from August to October in
the same season [6,27,39].

Related categories for Species: Carpinus caroliniana | American Hornbeam