BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Carya glabra | Pignut Hickory 



GENERAL BOTANICAL CHARACTERISTICS : 
Pignut hickory is a slow-growing deciduous tree which reaches 65 to 98
feet (20-30 m) in height and 11 to 39 inches (30-100 cm) in diameter
[10,17,27,54].  On extremely favorable sites, individuals may reach 131
feet (40 m) in height [11].  Pignut hickory is characterized by a narrow
oblong crown and somewhat pendulous branches [54].  The gray bark is
shallowly ridged and furrowed [10,17].  Plants generally possess a
pronounced taproot but few laterals [51].

Pignut hickory is monoecious [51].  Pistillate flowers are borne in two-
to five-flowered spikes [27,54], which develop on the shoots of the
current year [51].  Slender, staminate catkins averaging 2 to 3.1 inch
(5-8 cm) in length are borne from the axils of leaves on the previous
season or from the inner buds of terminal scales on the current year's
growth [17,27,51].  The fruit of pignut hickory is a hard, pear-shaped
nut [10,45].  The nut is thick-shelled and approximately 0.6 to 1.4
inches (1.5-3.5 cm) in length [27,54].  The husk splits about halfway to
the base [10,45].  The small kernel is sweet to bitter [17,54].

Characteristics which distinguish varieties of pignut hickory are as
follows [54]:

      var. megacarpa - larger leaves and fruit.
      var. hirsuta - obovoid fruit; lower leaflets; densely pubescent.
      var. glabra - usually five leaflets; husk indehiscent or splitting
                    to the middle.


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Phanerophyte (megaphanerophyte)
   Undisturbed State:  Phanerophyte (mesophanerophyte)
   Burned or Clipped State:  Chamaephyte
   Burned or Clipped State:  Hemicryptophyte
   Burned or Clipped State:  Cryptophyte (geophyte)


REGENERATION PROCESSES : 
Pignut hickory regenerates through seed and by vegetative means.

Seed:  Pignut hickory begins producing seed at approximately 30 years of
age; maximum seed production generally occurs between 75 and 200 years
of age [2,51].  Maximum age of seed production is approximately 300
years [51].  Good seed crops occur at 1- or 2-year intervals, but may be
reduced by frost, insects, and seed-eating birds and mammals.  Seed is
dispersed by gravity and by birds and mammals [51,57].  Mammals such as
squirrels and chipmunks are typically more effective dispersal agents
than birds [57].

Germination:  Seeds of pignut hickory exhibit embryo dormancy that can
be broken by stratification at 33 to 40 degrees F (1-4 deg C) for 30 to
150 days [2].  Seeds rarely remain viable in the forest floor for more
than one winter [51].  Early seedling growth is typically slow.

Vegetative regeneration:  Pignut hickory sprouts from the root or stump
after plants are cut or top-killed by fire.  Smalley [51] reported that
sprouting "is not as prolific as in other deciduous tree species but
sprouts that are produced are vigorous and grow rapidly in height."
Sprouts may be killed by drought, frost, fire, or herbivory, but roots
often survive and sprout from dormant buds located near the root collar
or lower part of the stem [48].  Smaller diameter pignut hickories
typically sprout more frequently than do larger trees.  Sprouts that
originate at or below the ground level tend to be less subject to decay
than those that originate higher on the trees [51].


SITE CHARACTERISTICS : 
Pignut hickory grows in mesic to xeric mixed woodlands, bottomland
woodlands, wet hammocks, on stable dunes, and rocky hillsides
[10,11,17,40].  It is a common component of southern mixed hardwood
forests, flatwoods, and eastern redcedar (Juniperus virginiana)
[18,40,42].  It is also common but rarely abundant in oak-hickory
forests [51].

Plant associates:  Various oaks, including post oak (Quercus stellata),
southern red oak (Q. falcata), black oak (Q. velutinus), northern red
oak, white oak, chestnut oak (Q. prinus), and blackjack oak (Q.
marilandica), are common overstory associates [18,45]. Shortleaf pine
(Pinus echinata), loblolly pine (P. taeda), bald cypress (Taxodium
distichum), sweetgum (Liquidambar styraciflua), and water tupelo (Nyssa
aquatica) also grow with pignut hickory [50].  Southern magnolia
(Magnolia grandiflora), cabbage palmetto (Sabal palmetto), and redbay
(Persea borbonia) are particularly common overstory associates in the
South [8,50], whereas sugar maple (Acer saccharum), red maple (A.
rubrum), black birch (Betula lenta), and yellow birch (B.
alleghaniensis) frequently grow with pignut hickory in the northern
portion of its range [15,24,59].

Understory associates of pignut hickory are both numerous and diverse
and vary according to site and location [51].  In portions of the South,
flowering dogwood (Cornus florida), sourwood (Oxydendrum arboreum),
muscadine grape (Vitus rotundifolia), blueberries (Vaccinium spp.),
rhododendron (Rhododendron spp.), and common greenbrier (Smilax
rotundifolia) are common associates [5].

Climate:  Pignut hickory occurs in a humid climatic regime [51].

Soils:  Pignut hickory grows best on light, well-drained, loamy soils
[41].  Soil fertility is variable [51].  It occurs on soils derived from
a variety of metamorphic and sedimentary parent materials including
limestone, granitic-basic and mica schist-phyllite, glacial till, and
shale [17,18,51].

Elevation:  Generalized elevational ranges by geographic location are as
follows:

Elevation                     Location                Authority

> 2,952 feet (> 900 m)        s Appalachians          Duncan and Duncan 1988
< 2,500-3,000 feet (763-915 m)Great Smoky Mtns.       Whittaker 1954
up to 4,850 ft (1,480 m)      Great Smoky Mtns        Smalley 1991


SUCCESSIONAL STATUS : 
Pignut hickory is tolerant of shade in the Southeast, but relatively
intolerant in the northeastern portion of its range [51].  It grows as a
common codominant in climax communities of the North Carolina Plain [43]
and occurs in climax hammock communities of Florida [14,53].  In parts
of Florida, early seral pine-oak-hickory forests are replaced by mature
oak-hickory stands [30].  Species such as southern magnolia, beech,
cabbage palmetto, and redbay may ultimately assume prominence, but
long-lived dominants such as pignut hickory commonly persist in climax
stands [9].  Pignut hickory grows in climax white oak-hickory forests of
southwestern Ohio, in old-growth oak-hickory forests of southern
Michigan, and in low-elevation climax stands in parts of the southern
Appalachians [4,21,59].

Heavy-seeded species such as pignut hickory are generally slow to invade
new areas [18].  However, pignut hickory, along with various oaks
(northern red oak, black oak, white oak), may replace early seral gray
birch (Betula populifolia)-eastern redcedar stands in oldfield
communitites of New York [47].  More shade-tolerant species such as red
maple (Acer rubrum) may ultimately replace oak and hickory.  In some
portions of the Appalachian Highlands, hickory may ultimately replace
chestnut killed by chestnut blight [51].


SEASONAL DEVELOPMENT : 
Across most of its range, pignut hickory flowers in April or May [2].
Staminate flowers typically develop before the pistillate flowers [51].
Fruit ripens during September or October as the husk splits part way to
the base [2,27].  Seed dispersal occurs from September through December
[51].  Flowering and fruit ripening dates by geographic location are as
follows:

Location    Flowering         Fruiting          Authority

se U.S.     April-May         ----              Duncan & Duncan 1988 
SW          April-May         Sept.-Oct.        Vines 1960
New England May 17-June 23    ----              Seymour 1985
NC, SC      April-May         October           Radford and others 1968

Related categories for Species: Carya glabra | Pignut Hickory