Carya glabra (Mill.) Sweet Pignut Hickory Juglandaceae Walnut family Glendon W. Smalley Pignut hickory (Curya glabru) is a common but not -22” F) have been recorded within the range. The abundant species in the oak-hickory forest associa- growing season varies by latitude and elevation from tion in Eastern United States. Other common names 140 to 300 days. are pignut, sweet pignut, coast pignut hickory, Mean annual relative humidity ranges from 70 to smoothbark hickory, swamp hickory, and broom hick- 80 percent with small monthly differences; daytime ory. The pear-shaped nut ripens in September and relative humidity often falls below 50 percent while October and is an important part of the diet of many nighttime humidity approaches 100 percent. wild animals. The wood is used for a variety of Mean annual hours of sunshine range from 2,200 products, including fuel for home heating. to 3,000. Average January sunshine varies from 100 to 200 hours, and July sunshine from 260 to 340 Habitat hours. Mean daily solar radiation ranges from 12.57 to 18.86 million J mf (300 to 450 langleys). In Native Range January daily radiation varies from 6.28 to 12.57 million J m+ (150 to 300 langleys), and in July from The range of pignut hickory (fig. 1) covers nearly 20.95 to 23.04 million J ti (500 to 550 langleys). all of eastern United States (11). It extends from According to one classification of climate (20), the Massachusetts and the southwest corner of New range of pignut hickory south of the Ohio River, ex- Hampshire westward through southern Vermont and cept for a small area in Florida, is designated as extreme southern Ontario to central Lower Michigan humid, mesothermal. That part of the range lying and Illinois; southward through extreme north of the Ohio River is designated humid, southeastern Iowa, Missouri, and Arkansas to microthermal. Part of the species range in penin- Louisiana and parts of East Texas. The species grows sular Florida is classed as subhumid, mesothermal. eastward through Louisiana and along the Gulf Mountains in Pennsylvania, West Virginia, North Coast to Mississippi and Alabama into central Carolina, and Tennessee are classed as wet, Florida. microthermal, and mountains in South Carolina and Best development of this species is in the lower Georgia are classed as wet, mesothermal. Ohio River Basin. It is the hickory most commonly Throughout its range, precipitation is rated adequate found in the Appalachian forests. Pignut makes up during all seasons. much of the hickory harvested in Kentucky, West Virginia, the Cumberland Mountains of Tennessee, Soils and Topography and the hill country of the Ohio Valley. Pignut hickory frequently grows on dry ridgetops Climate and sideslopes throughout its range but it is also common on moist sites, particularly in the mountains Pignut hickory grows in a humid climate with an and Piedmont. In the Great Smoky Mountains pig- average annual precipitation of 760 to 2030 mm (30 nut hickory has been observed on dry sandy soils at to 80 in> of which 510 to 1020 mm (20 to 40 in) is low elevations. Whittaker (27) placed pignut in a rain during the growing season. Average snowfall submesic class and charted it as ranging up to 1480 varies from little to none in the South to 2540 mm m (4,850 ft)-the hickory with the greatest elevation- (100 in> or more in the mountains of West Virginia, al range in the Great Smoky Mountains. In south- southeastern New York, and southern Vermont (25). west Virginia, south-facing upper slopes from 975 to Within the range of pignut hickory, average annual 1050 m (3,200 to 3,445 ft) of Beanfield Mountain are temperatures vary from 7” C (45” F) in the north to dominated by pignut hickory, northern red oak 21” C (70” F) in Florida. Average January tempera- (Quercus rubra), and white oak (Q. alba). This site ture varies from -4” to 16” C (25” to 60” F) and is the most xeric habitat on the mountain because of average July temperature varies from 21” to 27” C high insolation, 70 percent slopes, and medium- to (70” to 80” F). Extremes of 46” and -30” C (115” and 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 CQ. prinus), The author is Principal Soil Scientist (retired), Southern Forest northern red oak, and pignut hickory and coincide Experiment Station, New Orleans, LA. with three shale formations (12). 198 Carya glabra ,@FJi I I,, I ”0 500 I(ILOMETERS600 950 900 800 I 1984 \ Figure l-The native range ofpignut hickory. 199 The range of pignut hickory encompasses 7 orders, Central Forest Region 12 suborders, and 22 great groups of soils (24,25). 40 Post Oak-Blackjack Oak About two-thirds of the species range is dominated 44 Chestnut Oak 45 Pitch Pine by Ultisols, which are low in bases and have subsur- 46 Eastern Redcedar face horizons of clay accumulation. They are usually 52 White Oak-Black Oak-Northern Red Oak moist but are dry during part of the warm season. 53 White Oak Udults is the dominant suborder and Hapludults and 55 Northern Red Oak Paleudults are the dominant great groups. These 57 Yellow-Poplar soils are derived from a variety of parent materials- 59 Yellow-Poplar-White Oak-Northern Red Oak sedimentary and metamorphic rocks, glacial till, and 64 Sassafras-Persimmon in places varying thickness of loess-which vary in 110 Black Oak age from Precambrian to Quaternary. Southern Forest Region A wide range of soil fertility exists as evidenced by 75 Shortleaf Pine soil orders-Alfisols and Mollisols which are medium 76 Shortleaf Pin+Oak 78 Virginia Pine-Oak to high in base saturation to Ultisols which are low 79 Virginia Pine in base saturation (24). Pignut hickory responds to 80 Loblolly Pine-Shortleaf Pine increases in soil nitrogen similarly to American 81 Loblolly Pine beech (Fagus grandifolia), sugar maple (Acer sac- 82 Loblolly Pine-Hardwood charurn), and blackgum (Nyssa sylvatica) (15). These 83 Longleaf Pine-Slash Pine species are rated as intermediate in nitrogen deficiency tolerance and consequently are able to Because the range of pignut hickory is so exten- grow with lower levels of nitrogen than are required sive, it is not feasible to list the associated trees, by “nitrogen-demanding” white ash (Fraxinus shrubs, herbs, and grasses, which vary according to americana), yellow-poplar (Liriodendron tulipifera), elevation, topographic conditions, edaphic features, and American basswood (Itlia americana). Hickories and geographic locality. are considered “soil improvers” because their leaves have a relatively high calcium content. Life History Associated Forest Cover Reproduction and Early Growth Hickories are consistently present in the broad Flowering and Fruiting-Hickories are monoe- eastern upland climax forest association commonly cious and flower in the spring (3). The staminate called oak-hickory, but they are not generally abun- catkins of pignut hickory are 8 to 18 cm (3 to 7 in> dant (18). Locally, hickories may make up to 20 to 30 long and develop from axils of leaves of the previous percent of stand basal area, particularly in slope and season or from inner scales of the terminal buds at cove forests below the escarpment of the Cumberland the base of the current growth. The pistillate flowers Plateau (23) and in second-growth forests in the appear in spikes about 6 mm (0.25 in) long on Cumberland Mountains, especially on benches (14). peduncles terminating in shoots of the current year. It has been hypothesized that hickory will replace Flowers open from the middle of March in the chestnut (Castanea dentata) killed by the blight southeast part of the range to early June in New (Cryphonectria parasitica) in the Appalachian High- England. The catkins usually emerge before the pis- lands (10,121. On Beanfield Mountain in Giles Coun- tillate flowers. ty, VA, the former chestnut-oak complex has changed The fruit of hickory is pear shaped and enclosed in to an oak-hickory association over a period of 50 a thin husk developed from the floral involucre. The years. This association is dominated by pignut hick- fruit ripens in September and October, and seeds are ory with an importance value of 41.0 (maximum dispersed from September through December. Husks value = 300), northern red oak (36.01, and chestnut are green until maturity; they turn brown to oak (25.0). White oak, red maple (Acer rubrum), and brownish-black as they ripen. The husks become dry sugar maple are subdominant species. at maturity and split away from the nut into four Pig-nut hickory is an associated species in 20 of the valves along sutures. Husks of pignut hickory split 90 forest cover types listed by the Society of only to the middle or slightly beyond and generally American Foresters for the eastern United States (6): cling to the nut, which is unribbed, with a thick shell. Northern Forest Region Seed Production and Dissemination-P&put 53 White Pine-Chestnut Oak hickory begins to bear seed in quantity in 30 years, 200 Carya glabra 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; frost can 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 germina- tion. Pignut seed, averaging 440/kg (200/lb), is lighter than the seed of other hickory species.