Carya glabra

Pignut hickory
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Fagales
Family:	Juglandaceae
Genus:	Carya
Section:	Carya sect. Carya
Species:	C. glabra
Binomial name
Carya glabra Miller
Natural range of Carya glabra

Carya glabra, the pignut hickory, is a common, but not abundant species of

is used for a variety of products, including fuel for home heating. Its leaves turn yellow in the Fall.

Habitat

Native range

The range of pignut hickory covers nearly all of the eastern United States. The species grows in central Florida and northward through North Carolina to southern Massachusetts. It also grows north of the Gulf Coast through Alabama, Mississippi north to Missouri and extreme southeastern Iowa, and the Lower Peninsula of Michigan.

The best development of this species is in the lower

.

Pignut hickory is also found in

area along western Lake Ontario, and southward along the northern shore of Lake Erie and pockets of extreme southwestern Ontario.

Pignut hickory grows in a

(25).

Within the range of pignut hickory,

from 140 to 300 days.

Mean annual

relative humidity

ranges from 70 to 80 percent with small monthly differences; daytime relative humidity often falls below 50% while nighttime humidity approaches 100%.

Mean annual

). 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.

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

formations.

The range of pignut hickory encompasses 7

.

A wide range of soil fertility exists as evidenced by soil orders-

content.

Associated forest cover

Hickories are consistently present in the broad eastern upland

, 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 Foresters for the eastern United States (6):

53

40 Post Oak-Blackjack Oak
44

45 Pitch Pine
46 Eastern Redcedar
52 White Oak-Black Oak-Northern Red Oak
53 White Oak
55 Northern Red Oak
57 Yellow-Poplar-Tulip tree
59 Yellow-Poplar-White Oak-Northern Red Oak
64 Sassafras-Persimmon
110 Black Oak

75 Shortleaf Pine
76 Shortleaf Pine-Oak
78 Virginia Pine-Oak
79 Virginia Pine
80 Loblolly Pine-Shortleaf Pine
81 Loblolly Pine
82 Loblolly Pine-Hardwood
83 Longleaf Pine-Slash Pine

Because the range of pignut hickory is so extensive, it is not feasible to list the associated

features, and geographic locality.

Hickories are

. The catkins usually emerge before the pistillate flowers.

The

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.

Seed production and dissemination

Pignut hickory begins to bear seed in quantity in 30 years, with optimum production between 75 and 200 years. The maximum age for seed production is about 300 years. Good seed crops occur every year or two with light crops in other years; frost can seriously hinder seed production. Usually less than half of the seeds are sound, 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

germinating plants, and the nuts seldom remain viable in the forest floor for more than one winter.

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 clay soil (2):

Age	Height
(yr)	(cm)	(in)
1	8	3.0
2	15	5.8
3	20	8.0
4	30	12.0
5	43	17.0

Hickories sprout readily from

.

Sapling and pole stages to maturity

Pignut hickory often grows 24 to 27 m (79 to 89 ft) tall and occasionally reaches 37 m (121 ft), with

-hickory forest types, most growth and yield information is written in terms of oak rather than oak-hickory. Yields of mixed oak stands and of hickory stands have been reported. Tree volume tables are available.

Diameter and height of pignut hickory in selected geographic areas (adapted from 2)

Age	D.b.h.	Height
	S. Indiana and N.Kentucky¹	Ohio Valley¹	Northern Ohio¹	Cumberland Mountains²	Mississippi Valley²
(yr)	(cm)	(m)	(m)	(m)	(m)
10	2	2.7	2.1	1.8	1.8
20	5	5.8	6.1	4.3	5.8
30	8	9.8	10.7	7.3	8.2
40	11	12.8	14.6	9.8	10.4
50	14	15.5	18.6	12.2	12.2
60	17	17.7	21.0	14.6	14.0
70	21	19.5	22.6	16.8	15.8
80	25	21.0	--	18.9	17.7
(yr)	(in)	(ft)	(ft)	(ft)	(ft)
10	1.0	9	7	6	6
20	2.0	19	20	14	19
30	3.2	32	35	24	27
40	4.4	42	48	32	34
50	5.5	51	61	40	40
60	6.8	58	69	48	46
70	8.4	64	74	55	52
80	10.0	69	--	62	58

---

¹Second growth. ²Virgin forest.

Rooting habit

Pignut hickory tends to develop a pronounced taproot with few laterals and is rated as windfirm. The taproot develops early, which may explain the slow growth of seedling shoots. Taproots may develop in compact and stony soils.

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

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.

Damaging agents

Pignut hickory is easily damaged by

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

.

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

(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.

The stem canker (Nectria galligena) produces depressed areas with concentric bark rings 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 wood products, but only a few cause death or severe damage. 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 drought periods 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

) 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 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 Phylloxera caryaecaulis, Caryomyia holotricha, C. sanguinolenta, and C. tubicola.

Hickories provide food to many kinds of wildlife. The nuts are relished by several species of squirrel and represent an estimated 10 to 25 percent of their diet. Hogs were observed consuming the nuts in colonial America, lending the species its common name.^[2] Nuts and flowers are eaten by the wild turkey and 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 deer occasionally 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 calcium contents are generally moderate to low. Crude fiber is very low.

Pignut hickory makes up a small percentage of the biomass in 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

because of its size and difficulty of transplanting, although it has spectacular orangey-red fall colors.

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.

Carya glabra (Mill.) Sweet var. glabra distinguishes the (typical) pignut hickory from red hickory (C. glabra var. odorata (Marsh.) Little). The taxonomic position 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. 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.

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 size and shape of its nuts and is possibly a

analyses of hickory nut oils.

Carya glabra is a 64 chromosome species that readily hybridizes with other hickories, especially C. ovalis.^[3]

One hybrid, C. x demareei Palmer (C. glabra x cordiformis) was described in 1937 from northeastern Arkansas.

• 
  Bud
• 
  Bud break
• 
  Leaves
• 
  Female flowers
• 
  Maturing fruit
• 
  Carya glabra in fall

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10. Keever, C. 1953. Present composition of some stands of the former oak-chestnut forests in the southern Blue Ridge Mountains. Ecology 34:44-54.
11. 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.
12. 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.
13. 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.
14. Martin, W. H. Personal correspondence. 1981. USDA Forest Service, Silviculture Laboratory, Sewanee, TN.
15. 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, Massachusetts. 94 p.
16. 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.
17. 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.
18. 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.
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20. Thornthwaite, C. W. 1948. The climates of North America according to a new classification. Geographical Review 21:633-655.
21. 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.
22. 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.
23. U.S. Department of Agriculture, Forest Service. 1978. Unpublished data. Silviculture Laboratory, Sewanee, TN.
24. 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.
25. U.S. Department of the Interior, Geological Survey. 1970. The National Atlas of the United States. Washington, DC. 417 p.
26. 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.
27. Whittaker, R. H. 1956. Vegetation of the Great Smoky Mountains. Ecological Monographs 26:1-80.

 This article incorporates public domain material from Smalley, Glendon W. (1990). "Carya glabra". In Burns, Russell M.; Honkala, Barbara H. (eds.). Hardwoods. Silvics of North America. Vol. 2. Washington, D.C.: United States Forest Service (USFS), United States Department of Agriculture (USDA) – via Southern Research Station.

External links

• Carya glabra images at the Arnold Arboretum of Harvard University Plant Image Database
• Friedman, William (Ned). "Shadows and highlights in the Arboretum." Posts from the Collection, Arnold Arboretum of Harvard University website, 19 November 2016. Accessed 21 May 2020.