name = Pignut Hickory
image_width = 240px
divisio = Magnoliophyta
classis = Magnoliopsida
genus = "Carya"
species = "C. glabra"
binomial = "Carya glabra"
Pignut hickory ("Carya glabra") is a common but not abundant species in the
oak- hickoryforest association in the Eastern United States. Other common names are pignut, sweet pignut, coast pignut hickory, smoothbark hickory, swamp hickory, and broom hickory. The pear-shaped nut ripens in September and October and is an important part of the diet of many wild animals. The woodis used for a variety of products, including fuel for home heating.
The range of pignut hickory covers nearly all of eastern United States (11). It extends from
Massachusettsand the southwest corner of New Hampshirewestward through southern Vermontand extreme southern Ontarioto central Lower Peninsula of Michiganand Illinois; southward through extreme southeastern Iowa, Missouri, and Arkansasto Louisianaand parts of East Texas. The species grows eastward through Louisiana and along the Gulf Coastto Mississippiand Alabamainto central Florida.
The best development of this species is in the lower
Ohio RiverBasin. It is the hickory most commonly found in the Appalachianforests. Pignut makes up much of the hickory harvested in Kentucky, West Virginia, the Cumberland Mountainsof Tennessee, and the hill country of the Ohio Valley.
Pignut hickory grows in a
humid climatewith an average annual precipitation of 760 to 2,030 mm (30 to 80 in) of which 510 to 1,020 mm (20 to 40 in) is rainduring the growing season. Average snowfallvaries from little to none in the South to 2,540 mm (100 in) or more in the mountains of West Virginia, southeastern New York, and southern Vermont(25).
Within the range of pignut hickory,
average annual temperatures vary from 7°C (45°F) in the north to 21°C (70°F) in Florida. Average January temperature varies from -4° to 16°C (25° to 60°F) and average July temperature varies from 21° to 27°C (70° to 80°F). Extremes of 46° and -30°C (115° and -22°F) have been recorded within the range. The growing seasonvaries by latitudeand elevationfrom 140 to 300 days.
relative humidityranges from 70 to 80 percent with small monthly differences; daytime relative humidity often falls below 50% while nighttime humidity approaches 100%.
Mean annual hours of sunshine range from 2,200 to 3,000. Average January sunshine varies from 100 to 200 hours, and July sunshine from 260 to 340 hours. Mean daily solar radiation ranges from 12.57 to 18.86 million J m± (300 to 450 langleys). In January daily radiation varies from 6.28 to 12.57 million J m± (150 to 300 langleys), and in July from 20.95 to 23.04 million J m± (500 to 550 langleys).
According to one classification of climate (20), the range of pignut hickory south of the
Ohio River, except for a small area in Florida, is designated as humid, mesothermal. That part of the range lying north of the Ohio River is designated humid, mesothermal. Part of the species range in peninsular Florida is classed as subhumid, mesothermal. Mountains in Pennsylvania, West Virginia, North Carolina, and Tennessee are classed as wet, microthermal, and mountains in South Carolina and Georgia are classed as wet, mesothermal. Throughout its range, precipitation is rated adequate during all seasons.
oils and Topography
Pignut hickory frequently grows on dry ridgetops and sideslopes throughout its range but it is also common on moist sites, particularly in the mountains and Piedmont. In the
Great Smoky Mountainspignut hickory has been observed on dry sandy soils at low elevations. Whittaker (27) placed pignut in a submesicclass and charted it as ranging up to 1480 m (4,850 ft)-the hickory with the greatest elevational range in the Great Smoky Mountains. In southwest Virginia, south-facing upper slopes from 975 to 1050 m (3,200 to 3,445 ft) of Beanfield Mountainare dominated by pignut hickory, northern red oak " Quercus rubra"), and white oak ("Q. alba"). This site is the most xeric habitaton the mountain because of high insolation, 70 percent slopes, and medium- to coarse-textured soils derived from Clinch sandstone. Mid-elevation slopes from 800 to 975 m (2,625 to 3,200 ft) are dominated by chestnut oak ("Q. prinus"), northern red oak, and pignut hickory and coincide with three shaleformations (12).
The range of pignut hickory encompasses 7 orders, 12 suborders, and 22 great groups of
soils (24,25). About two-thirds of the species range is dominated by Ultisols, which are low in bases and have subsurface horizons of clayaccumulation. They are usually moist but are dry during part of the warm season. Udultsis the dominant suborder and Hapludultsand Paleudultsare the dominant great groups. These soils are derived from a variety of parent materials- sedimentaryand metamorphicrocks, glacial till, and in places varying thickness of loess-which vary in age from Precambrianto Quaternary.
A wide range of soil fertility exists as evidenced by soil orders-
Alfisolsand Mollisolswhich are medium to high in base saturation to Ultisols which are low in base saturation (24). Pignut hickory responds to increases in soil nitrogen similarly to American beech (" Fagus grandifolia"), sugar maple (" Acer saccharum"), and blackgum (" Nyssa sylvatica") (15). These species are rated as intermediate in nitrogen deficiency tolerance and consequently are able to grow with lower levels of nitrogen than are required by "nitrogen- demanding" white ash (" Fraxinus americana"), yellow-poplar (" Liriodendron tulipifera"), and American basswood (" Tilia americana"). Hickories are considered "soil improvers" because their leaves have a relatively high calciumcontent.
Associated Forest Cover
Hickories are consistently present in the broad eastern upland
climaxforest association commonly called oak-hickory, but they are not generally abundant (18). Locally, hickories may make up to 20 to 30 percent of stand basal area, particularly in slope and cove forests below the escarpmentof the Cumberland Plateau(23) and in second-growth forests in the Cumberland Mountains, especially on benches (14). It has been hypothesized that hickory will replace chestnut (" Castanea dentata") killed by the blight (" Cryphonectria parasitica") in the AppalachianHighlands (10,12). On Beanfield Mountainin Giles County, Virginia, the former chestnut-oak complex has changed to an oak-hickory association over a period of 50 years. This association is dominated by pignut hickory with an importance value of 41.0 (maximum value = 300), northern red oak (36.0), and chestnut oak (25.0). White oak, red maple (Acer rubrum), and sugar maple are subdominant species.
Pignut hickory is an associated species in 20 of the 90 forest cover types listed by the
Society of American Forestersfor the eastern United States (6):
Northern Forest Region
White Pine- Chestnut Oak
Central Forest Region
Post Oak- Blackjack Oak44 Chestnut Oak45 Pitch Pine46 Eastern Redcedar52 White Oak- Black Oak- Northern Red Oak53 White Oak 55 Northern Red Oak 57 Yellow-Poplar59 Yellow-Poplar-White Oak-Northern Red Oak 64 Sassafras- Persimmon110 Black Oak
outhern Forest Region
Shortleaf Pine76 Shortleaf Pine- Oak78 Virginia Pine-Oak 79 Virginia Pine 80 Loblolly Pine- Shortleaf Pine81 Loblolly Pine 82 Loblolly Pine- Hardwood83 Longleaf Pine- Slash Pine
Because the range of pignut hickory is so extensive, it is not feasible to list the associated
trees, shrubs, herbs, and grasses, which vary according to elevation, topographic conditions, edaphicfeatures, and geographic locality.
Reproduction and Early Growth
Floweringand Fruiting- Hickories are monoeciousand flower in the spring (3). The staminate catkinsof pignut hickory are 8 to 18 cm (3 to 7 in) long and develop from axils of leaves of the previous season or from inner scales of the terminal buds at the base of the current growth. The pistillate flowers appear in spikes about 6 mm (0.25 in) long on peduncles terminating in shoots of the current year. Flowers open from the middle of March in the southeast part of the range to early June in New England. The catkins usually emerge before the pistillate flowers.
fruitof hickory is pearshaped and enclosed in a thin husk developed from the floral involucre. The fruit ripens in September and October, and seeds are dispersed from September through December. Husks are green until maturity; they turn brown to brownish-black as they ripen. The husks become dry at maturity and split away from the nut into four valves along sutures. Husks of pignut hickory split only to the middle or slightly beyond and generally cling to the nut, which is unribbed, with a thick shell.
eed Production and Dissemination
Pignut hickory begins to bear
seedin quantity in 30 years, with optimum production between 75 and 200 years (16). The maximum age for seed production is about 300 years. Good seed crops occur every year or two with light crops in other years; frostcan seriously hinder seed production (22). Usually less than half of the seeds are sound (2,3), but 50 to 75 percent of these will germinate. The hickory shuckworm ("Laspeyresia caryana") can seriously reduce germination. Pignut seed, averaging 440/kg (200/lb), is lighter than the seed of other hickory species. The nuts are disseminated mainly by gravity, but the range of seeding is extended by squirrels and chipmunks.
Hickories exhibit embryo dormancy which is overcome naturally by overwintering in the
duffand litter or artificially by stratification in a moist medium at 1° to 4°C (33° to 40°F) for 30 to 150 days. In forest tree nurseries unstratified hickory nuts are sown in the fall and stratified nuts are sown in the spring. Hickories are hypogeously germinating plants, and the nuts seldom remain viable in the forest floor for more than one winter (22).
Seedling growth of hickories is slow. The following height growth of pignut hickory seedlings was reported in the Ohio Valley in the open or under light shade, on red
Hickories sprout readily from stumps and
roots. Stump sprouting is not as prolific as in other deciduoustrees species but the sprouts that are produced are vigorous and grow fairly rapidly in height. Root sprouts also are vigorous and probably more numerous than stump sprouts in cut-over areas. Small stumps sprout more frequently than large ones. Sprouts that originate at or below ground level and from small stumps are less likely to develop heartwooddecay. Pignut hickory is difficult to reproduce from cuttings.
apling and Pole Stages to Maturity
Growth and Yield- Pignut hickory often grows 24 to 27 m (80 to 90 ft) tall and occasionally reaches 37 m (120 ft), with
d.b.h.of 91 to 122 cm (36 to 48 in). The bole is often forked. Height and diameter by age are shown in table 1 for selected locations. Diameter growth of pignut hickory (along with chestnut oak, white oak, sweet birch (" Betula lenta"), and American beechis rated slow. Since hickories constitute 15 percent or less of the basal area of oak-hickory forest types, most growth and yield information is written in terms of oak rather than oak-hickory. Yields of mixed oak stands (5,7,19) and of hickory stands (2) have been reported. Tree volume tables are available (2,19).
----¹Second growth. ²Virgin forest.
Pignut hickory tends to develop a pronounced
taprootwith few laterals and is rated as windfirm (21). The taproot develops early, which may explain the slow growth of seedling shoots. Taproots may develop in compact and stony soils.
Reaction to Competition
The hickories as a group are classed as intermediate in shade tolerance; however, pignut hickory has been classed as intolerant in the Northeast and tolerant in the Southeast. In much of the area covered by mixed oak forests, shade-tolerant
hardwoods (including the hickories) are climax, and the trend of succession toward this climax is very strong. Although most silvicultural systems when applied to oak types will maintain a hardwood forest, the cutting methods used affects the rapidity with which other species may replace the oaks and hickories (17,18,26).
Pignut hickory is easily damaged by fire, which causes stem degrade or loss of volume, or both. Internal discolorations called mineral streak are common and are one major reason why so few standing hickories meet trade specifications. Streaks result from
yellow-bellied sapsuckerpecking, pin knots, worm holes, and mechanical injuries. Hickories strongly resist ice damage and seldom develop epicormic branches.
The Index of Plant Diseases in the United States lists 133
fungiand 10 other causes of diseases on Carya species (4,9). Most of the fungi are saprophytes, but a few are damaging to foliage, produce cankers, or cause trunkor root rots.
The most common disease of pignut hickory from Pennsylvania southward is a trunk rot caused by "Poria spiculosa". Cankers vary in size and appearance depending on their age. A common form develops around a branch wound and resembles a swollen, nearly healed wound. On large trees these may become prominent
burl-like bodies having several vertical or irregular folds in the callus covering. A single trunk canker near the base is a sign that the butt log is badly infected, and multiple cankers are evidence that the entire tree may be a cull.
Major leaf diseases are
anthracnose("Gnomonia caryae") and mildew("Microstroma juglandis"). The former causes brown spots with definite margins on the undersides of the leaf. These may coalesce and cause widespread blotching. Mildew invades the leaves and twigs and may form witches' brooms by stimulating bud formation. Although locally prevalent, mildew offers no problem in the management of hickory.
canker("Nectria galligena") produces depressed areas with concentric barkrings that develop on the trunk and branches. Affected trees are sometimes eliminated through breakage or competition and sometimes live to reach merchantable size with cull section at the canker. No special control measures are required, but cankered trees should be harvested in stand improvement operations.
A gall-forming fungus species of "Phomopsis" can produce warty excrescences ranging from small twig
galls to very large trunk burls on northern hickories and oaks. Little information is available on root diseases of hickory.
More than 100
insects have been reported to infest hickory trees and woodproducts, but only a few cause death or severe damage (1). The hickory bark beetle("Scolytus quadrispinosus") is the most important insect enemy of hickory, and also one of the most important insect pests of hardwoods in the Eastern United States. During droughtperiods in the Southeast, outbreaks often develop and large tracts of timber are killed. At other times, damage may be confined to the killing of a single tree or to portions of the tops of trees. The foliage of heavily infested trees turns red within a few weeks after attack, and the trees soon die. There is one generation per year in northern areas and normally two broods per year in the South. Control consists of felling infested trees and destroying the bark during winter months or storing infested logs in ponds.
Logs and dying trees of several hardwood species including pignut hickory are attacked by the
ambrosia beetle("Platypus quadridentatus") throughout the South and north to West Virginia and North Carolina. The false powderpost beetle ("Xylobiops basilaris") attacks recently felled or dying trees, logs, or limbs with bark in the Eastern and Southern States. Hickory, persimmon (" Diospyros virginiana"), and pecan ("C. illinoinensis") are most frequently infested, but other hardwoods also are attacked. Healthy trees growing in proximity to heavily infested trees are occasionally attacked but almost always without success. Hickory and persimmon wood (useful in the manufacture of small products such as shuttle blocks, mallets, and mauls) is sometimes seriously damaged.
Hickory is one of several host species of the twig girdler ("Oncideres cingulata"). Infested trees and seedlings are not only damaged severely but become ragged and unattractive. A few of the more common species of gall-producing insects attacking hickory are "
Phylloxeracaryaecaulis", " Caryomyiaholotricha", "C. sanguinolenta", and "C. tubicola".
Hickories provide food to many kinds of wildlife (8,13). The nuts are relished by several species of
squirreland represent an estimated 10 to 25 percent of their diet. Nuts and flowers are eaten by the wild turkeyand several species of songbirds. Nuts and bark are eaten by black bears, foxes, rabbits, and raccoons. Small mammals eat the nuts and leaves; 5 to 10 percent of the diet of eastern chipmunks is hickory nuts. White-tailed deeroccasionally browse hickory leaves, twigs, and nuts.
The kernel of hickory seeds is exceptionally high in crude
fat, up to 70 to 80 percent in some species. Crude protein, phosphorus, and calciumcontents are generally moderate to low. Crude fiber is very low.
Pignut hickory makes up a small percentage of the
biomassin low-quality upland hardwood stands that are prime candidates for clearcutting for chips or fuelwood as the first step toward rehabilitation to more productive stands. Hickory has a relatively high heating value and is used extensively as a home heating fuel.
Pignut hickory is an important
shade treein wooded suburbanareas over most of the range but is seldom planted as an ornamental tree.
"Carya glabra" var. "megacarpa" (Sarg.) Sarg., coast pignut hickory, was once recognized as a distinct variety but is now considered to be a synonym of "C. glabra" (Mill.) Sweet. "C. leiodermis" Sarg., swamp hickory, has also been added as a synonym of "C. glabra" (11).
"Carya glabra" (Mill.) Sweet var. "glabra" distinguishes the (typical) pignut hickory from red hickory ("C. glabra" var. "odorata" (Marsh.) Little). The
taxonomicposition of red hickory is controversial. The binomial "C. ovalis" (Wangenh.) Sarg. was published in 1913 for a segregate of "C. glabra". It was reduced to a synonym of "C. glabra" in Little's 1953 checklist but was elevated to a variety in the 1979 edition (11). The principal difference is in the husk of the fruit, opening late and only partly, or remaining closed in "C. glabra" but promptly splitting to the base in C. ovalis. However, many trees are intermediate in this trait, and the recorded ranges are almost the same. The leaves of "C. ovalis" have mostly seven leaflets; those of "C. glabra" have mostly five leaflets. The two can be distinguished with certainty only in November. Since the two ranges seem to overlap, the distributions have been mapped together as a Carya glabra-ovalis complex (11).
"Carya ovalis" has also been treated as an interspecific hybrid between "C. glabra" and "C. ovata". "C. ovalis" was accepted as a polymorphic species especially variable in the size and shape of its nuts and possibly a hybrid. The relationships may be more complex after a long and reticulate
phylogeny, according to detailed chemicalanalyses of hickory nut oils.
One hybrid, "C." x "demareei" Palmer ("C. glabra" x "cordiformis") was described in 1937 from northeastern
*Baker, Whiteford L. 1972. Eastern forest insects. U.S. Department of Agriculture, Miscellaneous Publication 1175. Washington, DC. 642 p.
*Boisen, A. T., and J. A. Newlin. 1910. The commercial hickories. USDA Forest Service, Bulletin 80. Washington, DC. 64 p.
*Bonner, F. T., and L. C. Maisenhelder. 1974. Carya Nutt. Hickory. In Seeds of woody plants in the United States. p. 262-272. C. S. Schopmeyer, tech. coord. U.S. Department of Agriculture, Agriculture Handbook 450. Washington, DC.
*Campbell, W. A., and A. F. Verrall. 1956. Fungus enemies of hickory. USDA Forest Service, Hickory Task Force Report 3. Southeastern Forest Experiment Station, Asheville, NC. 8 p.
*Dale, M. E. 1972. Growth and yield predictions for upland oak stands 10 years after initial thinning. USDA Forest Service, Research Paper NE-241. Northeastern Forest Experiment Station, Upper Darby, PA. 21 p.
*Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Society of American Foresters, Washington, DC. 148 p.
*Gingrich, S. F. 1971. Management of young and intermediate stands of upland hardwoods. USDA Forest Service, Research Paper NE-195. Northeastern Forest Experiment Station, Upper Darby, PA. 26 p.
*Halls, Lowell K., ed. 1977. Southern fruit-producing woody plants used by wildlife. USDA Forest Service, General Technical Report SO-16. Southern Forest Experiment Station, New Orleans, IA. 235 p.
*Hepting, George H. 1971. Diseases of forest and shade trees of the United States. U.S. Department of Agriculture, Agriculture Handbook 386. Washington, DC. 658 p.
*Keever, C. 1953. Present composition of some stands of the former oak-chestnut forests in the southern Blue Ridge Mountains. Ecology 34:44-54.
*Little, Elbert L., Jr. 1979. Checklist of United States trees (native and naturalized). U.S. Department of Agriculture, Agriculture Handbook 541. Washington, DC. 375 p.
*McCormick, J. F., and R. B. Platt. 1980. Recovery of an Appalachian forest following the chestnut blight or Catherine Keever-you were right! American Midland Naturalist 104:264-273.
*Martin, A. C., H. S. Zim, and A. L. Nelson. 1961. American wildlife and plants: a guide to wildlife food habits. Dover Publications, New York. 500 p. Unabridged republication of 1st (1951) edition.
*Martin, W. H. Personal correspondence. 1981. USDA Forest Service, Silviculture Laboratory, Sewanee, TN.
*Mitchell, H. L., and R. F. Chandler, Jr. 1939. The nitrogen nutrition and growth of certain deciduous trees of northeastern United States. Black Rock Forest Bulletin 11. Harvard University, Cambridge, MA. 94 p.
*Nelson, T. C. 1965. Silvical characteristics of the commercial hickories. USDA Forest Service, Hickory Task Force Report 10. Southeastern Forest Experiment Station, Asheville, NC. 16 p.
*Roach, B. A., and S. F. Gingrich. 1968. Even-aged silviculture for upland central hardwoods. U.S. Department of Agriculture, Agriculture Handbook 355. Washington, DC. 39 p.
*Sander, Ivan L. 1977. Manager's handbook for oaks in the North Central States. USDA Forest Service, General Technical Report NC-37. North Central Forest Experiment Station, St. Paul, MN. 35 p.
*Schnur, G. Luther. 1937. Yield, stand, and volume tables for even-aged upland oak forests. U.S. Department of Agriculture, Technical Bulletin 560. Washington, DC. 87 p.
*Thornthwaite, C. W. 1948. The climates of North America according to a new classification. Geographical Review 21:633-655.
*Tourney, J. W. 1929. Initial root habits in American trees and its bearing on regeneration. In Proceedings, International Plant Science Congress. 1926. p. 713-728.
*Trimble, G. R., Jr. 1975. Summaries of some silvical characteristics of several Appalachian hardwood trees. USDA Forest Service, General Technical Report NE-16. Northeastern Forest Experiment Station, Upper Darby, PA. 5 p.
*U.S. Department of Agriculture, Forest Service. 1978. Unpublished data. Silviculture Laboratory, Sewanee, TN.
*U.S. Department of Agriculture, Soil Conservation Service. 1975. Soil taxonomy: a basic system of soil classification for making and interpreting soil surveys. U.S. Department of Agriculture, Agriculture Handbook 436. Washington, DC. 754 p.
*U.S. Department of the Interior, Geological Survey. 1970. The National Atlas of the United States. Washington, DC. 417 p.
*Watt, Richard F., Kenneth A. Brinkman, and B. A. Roach. 1973. Oak-hickory. In Silvicultural systems for the major forest types of the United States. p. 66-69. U.S. Department of Agriculture, Agriculture Handbook 455. Washington, DC.
*Whittaker, R. H. 1956. Vegetation of the Great Smoky Mountains. Ecological Monographs 26:1-80.
("Silvics of North America; volume 2: Hardwoods", United States Department ofAgriculture Forest Service Agriculture Handbook 654, 1990).
Wikimedia Foundation. 2010.