The species is essentially a bottom-land species and is often found on river terraces and second bottoms. Land that is subject to shallow inundations for a few weeks early in the growing season is favorable for shellbark. However,8=> (UTC) the tree will grow on a wide range of topographic and physiographic sites.
Shellbark hickory commonly grows in association with American (Ulmus americana), slippery (U. rubra), and winged elms (U. alata), white (Fraxinus americana) and green ash (F pennsylvanica), basswood (Tilia americana), American hornbeam (Carpinus caroliniana), red maple (Acer rubrum), blackgum (Nyssa sylvatica), sweetgum (Liquidambar styraciflua), and cottonwood (Populus deltoides). It is found in association with four other hickories-shagbark, mockernut, bitternut (Carya cordiformis), and water (C. aquatica), and numerous oak species, including swamp white Quercus bicolor), pin Q. palustris), white (Q. alba), Shumard (Q. shumardii), water (Q. nigra), Delta post (Q. stellata var. paludosa), swamp chestnut (Q. michauxii), and Nuttall (Q. nuttallii).
The herbaceous stratum includes numerous sedges and grasses. The shrub and small tree layer may be composed of painted buckeye (Aesculus sylvatica), pawpaw (Asimina triloba), flowering dogwood (Cornus florida), eastern redbud (Cercis canadensis), possumhaw (Ilex decidua), poison-ivy (Toxicodendron radicans), and trumpet-creeper (Campsis radicans).
Seed Production and Dissemination- Shellbark nuts are the largest produced by any hickory. The number of cleaned seed per kilogram ranges from 55 to 75 (25 to 35/lb). Hickories show embryo dormancy. Shellbark hickory seeds require from 90 to 120 days of cold stratification before they will germinate. The minimum tree age for seed production is about 40 years, with the most seed produced between 75 and 200 years. Thrifty trees may produce 70 to 105 liters (2 to 3 bu) of nuts in a good year, and good crops are produced about every second year (2).
The seed is dispersed from September to December by gravity, birds, and animals. Squirrels and other rodents are the principal dispersal agents (7).
Seedling Development- Shellbark hickory requires moist soil for good germination and establishment. Germination is hypogeal. Seeds germinate from late April to early June. The seedlings rapidly develop a long taproot, but shoot growth is initially slow. Shellbark hickory seedlings grow faster in height than most of the other hickories (7).
Shellbark hickory is shade tolerant in early life and reproduces under forest conditions. Under light shade height growth may be slow. In the Ohio Valley, seedlings were only 11 cm (4 in) tall after 1 year and 56 cm (22 in) tall at the end of 5 years.
Vegetative Reproduction- Shellbark hickory sprouts readily when cut, and coppice management has been recommended for this and other hickories. It is a persistent sprouter following fire and/or grazing. Although more difficult to propagate by grafting and budding than fruit trees, this species can be reproduced by these techniques with good success. It is not known whether shellbark hickory will root from cuttings.
Rooting Habit- Shellbark hickory develops a large taproot that penetrates deeply into the soil. Lateral roots emerge at nearly right angles to the taproot, spreading horizontally through the soil. No distinct major lateral roots develop. In Illinois, root growth was rapid in April, slowed during July and August, increased again in September, and ended in late November.
Mycorrhizal associations are formed when trees are young. The only specific fungus identified from shellbark hickory roots is an ectotrophic mycorrhiza, Laccaria ochropurpurea.
Reaction to Competition- Shellbark hickory is very shade tolerant, exceeded only by sugar maple (Acer saccharum) and beech (Fagus grandifolia). It grows slowly under a dense canopy, however. In stands with only partial shade, it reproduces well. It is a very strong competitor in most of the species associations in which it is found.
Under forest conditions, shellbark hickory often develops a clear bole for half its length and has a narrow, oblong crown. Open-grown trees have egg-shaped crowns (7). Heavy release sometimes results in epicormic branching.
Damaging Agents- Although numerous insects and diseases affect hickories, shellbark hickory has no enemies that seriously threaten its development or perpetuation as a species. Seed production can be reduced significantly, however, through attack by several insects. Two of the most important are the pecan weevil (Curculio caryae) and the hickory shuckworm (Laspeyresia caryana).
The hickory bark beetle (Scolytus quadrispinosus) feeds in the cambium and seriously weakens or even kills some trees. Adults of the hickory spiral borer (Agrilus arcuatus torquatus) feed on leaves, but the larvae feed beneath the bark and can be very destructive to hickory seedlings. The flatheaded appletree borer (Chrysobothris femorata) likewise is a foliage feeder as an adult, but its larvae feed on the phloem and outer sapwood.
The living-hickory borer (Goes pulcher) feeds in the trunks and branches of trees. A twig girdler (Oncideres cingulata) can seriously affect reproduction by killing back the tops of seedlings and sprouts. Both standing dead trees and freshly cut logs are highly susceptible to attacks by numerous species of wood borers.
A large number of insect species feed on hickory foliage. None of them cause serious problems for shellbark hickory, although they may be responsible for some stem deformity and growth loss (1).
Shellbark hickory is free of serious diseases, but it is a host species for a variety of fungi. More than 130 fungi have been identified from species of Carya. These include leaf disease, stem canker, wood rot, and root rot-causing fungi. Specific information for shellbark hickory is not available (4).
Shellbark hickory is susceptible to bole injury from fire, and fire injuries are often invaded by wood rot fungi. It is resistant to snow and ice damage but is susceptible to frost damage.
(Silvics of North America; volume 2: Hardwoods, United States Department of Agriculture Forest Service Agriculture Handbook 654, 1990).