Shagbark Hickory

Shagbark Hickory

(Carya ovata [Mill.] K. Koch)

Description

The shagbark hickory (also known as shellbark or scalybark hickory) is a deciduous hardwood from the walnut family (Juglandaceae). They are easily recognizable due to their unique bark structure – rough and gray in color, it forms fissures in the trunk due to its tendency to form long, loose-fitting plates. These striking trees have an average height between 60 to 80 feet (although much larger specimens have been observed in the wild), supported by an average trunk diameter of 2-3.5 feet. This is complemented by an ovular crown with a common spread of 25-35 feet, consisting of crooked branches with odd-pinnately compound leaves. Once matured, these leaves are 8-14 inches long and contain five leaflets, each varying in size (3-8 inches long) and shades of green (with the first pair of leaflets being the lightest and the terminal leaflet being the darkest). All leaflets are oblong in shape with serrated margins with a pale underside. Both male and female flowers are produced during spring, meaning that the shagbark hickory is capable of self-pollination. The male flowers cluster in groups of 3 (known as catkins) at the tips of twigs, whereas female flowers form short green spikes at the tips of shoots. In trees that are 40 years or older, female flowers produce clusters of small fruits during the summer. These fruits mature by the end of autumn, forming a thick, brown, ribbed husk  encasing an edible core1,5.  Illustration of shagbark hickory flowers, leaves, and fruits. Leaves are compound, a dark green with a lighter green underside, pinnately veined with a toothed magin. Flowers are clusters of light green growing below the leaves. Fruit is spherical, brown, and smooth exterior, dehiscing into four carpels, with a white seed separated into four faces by raised ridges.

Diagrams of shagbark hickory.  Clockwise from left:  pinnate leaves and male catkins, mature fruit, immature fruit, female flowers to scale and female flowers enlarged.  @ P. Nelson, Missouri Department of Conservation 14. 

Fruits of the shagbark hickory grow, with a few leaves attached near the same node, on a deep brown knobby tree branch. Leaflets are deep green with prominently yellow veins and a serrated leaf margin. Underside of leaflets are much light green and matte, compared to the shiny and darker green adaxial side. Two fruits sit in the center of the photograph, both with leathery smooth light green exteriors, one of which has part of the exterior of the fruit removed exposing the bright white seed of the interior.

Mature fruit of shagbark hickory showing thick husk.  @ P. Wray, Missouri Department of Conservation 14.

A tree trunk stands prominently in the center of the photograph against a light green forested background of leaves and other trees. The bark of the tree subject is light brown and stripping away from the trunk in long thin sheets, giving the tree trunk a shaggy look.

Shagbark hickory bark.  @ J. Brighton, 2010*, Maryland Plant Atlas 15.

Distribution 

The shagbark is extremely hardy for a hickory, able to withstand temperatures as low as -40° F and as high as 115° F. As such, it is commonly found throughout Eastern United states (with an exception to Southeast America, along the Gulf coastal plains)5,8. The tree is found in both high and low elevations, and though it has adapted to rainfalls as low as 24 inches and as high as 79 inches per year, it prefers humid areas with moist acidic soil. Given these characteristics, shagbark hickory is most abundant in the central regions of Maryland where these living conditions are regularly met5,6.  It is capable of withstanding a variety of light conditions from full sun to full shade and is commonly found scattered throughout a forest consisting of other species with little disturbance due to their lack of fire resistance1,2,7.

A white and gray map of the eastern United States, with the native range of this species emphasized in a dark gray shading. This range includes most of the eastern half of the U.S., from Missouri, Arkansas and Iowa all the way east to the coastal states, but exclude those areas closes to the coast of the Gulf of Mexico and the Atlantic Ocean. The range goes north into New England, but stops shy of Vermont, excludes the northern half of New Hampshire, and most of Maine.

Native range of shagbark hickory.  USDA 5.

Wildlife Importance 

The edible portion of this tree’s nuts is a key part of many animals’ diet, including small mammals such as birds, squirrels, and chipmunks. This, in turn, makes the tree an important hunting zone for predators such as foxes and even bears. Invertebrates are also dependent upon the species – large amounts of larvae burrow into the tree’s wood to feed upon its juices in addition to caterpillars and beetles that often feed on its foliage and shoots. The unique bark structure also provides nesting habitats for many smaller organisms, including endangered species such as the Indiana bat1,4,7. 

Economic Importance 

The shagbark hickory has two economic contributions: its wood and nuts. The former is exceptionally strong and resistant to impact and physical strain, making it well-suited for usage in construction tool handles. The wood is also prized as charcoal and fuel due to its unique aroma4,8. The nuts of the tree are equally important – known for their sweet taste, the edible innards of the shagbark’s fruits are widely eaten both on their own and processed into oil for pastries9.

 Threats 

Shagbark hickories, despite their resilience to environmental factors, suffer from several natural threats, most notably hickory bark beetles. These pests burrow small holes into the tree, digging tunnels and feeding on terminal growth, both of which cause defoliation and stunted growth. Serious infestations are extremely common in shagbarks that are already weakened from other factors, resulting in girdled branches, severance of conductive tissues, and eventually death without intervention3,10.  Canker rot also poses a serious, albeit less common, threat to the tree, as the infection enters through dead or broken branches and causes widespread wood rot and defoliation11. Hickories are also sensitive to natural disturbances, most notably fires – these disasters often scorch large portions of the tree, weakening it to other threats¹. 

Interesting Facts 

  • The wood of the shagbark hickory is extremely durable – so much so that it has previously been used in the wheels of wagons, carriages and even automobiles4. 
  • Andrew Jackson, infamous U.S. Army Major General and 7th president of the United States, earned the nickname “Old Hickory” due to his determination and toughness – both of which reminded many of the unbreakable hickory tree12. 
  • Shagbark hickory’s wood is still to this day used for firewood; not only does it have a pleasant aroma, but it holds the second highest heat potential of all firewood behind black locust5.
  • The largest shagbark hickory within the United States is located within Anne Arundel, Maryland; standing at 104 feet tall with a crown spread of 99 feet, it dwarfs the average size of 60-80 feet13. 

References 

  1. Illinois Wildflowers:  Shagbark hickory
  2. National Wildlife Federation:  Shagbark hickory
  3. University of Florida, IFAS Extension:  Carya ovata
  4. USDA, Forest Service, FEIS:  Carya ovata
  5. USDA – Forest Service Silvics Manual, Vol. 2 Hardwoods
  6. USDA, Agricultural Research Service:  Carya ovata
  7. Lady Bird Johnson Wildlife Center:  Carya ovata
  8. USDA Plants; Carya ovata
  9. University of Arkansas, Division of Agriculture: Carya ovata
  10. University of Georgia, Bark and Wood Boring Beetles
  11. Connecticut Agricultural Experimental Station: Hickory
  12. National Park Service;  Andrew Jackson gins his nickname
  13. American Forests.  Champion Tree National Register:  Shagbark hickory
  14. Missouri Department of Conservation: Shagbark hickory
  15. Maryland Plant Atlas:  Carya ovata

 *  Imaged used with permission of photographer.

Contributed by M. Perry

Towson University Glen Arboretum

Towson University