Description and habitat

Bitternut Hickory (Carya ovata) is a large deciduous tree in the Walnut Family (Juglandaceae), reaching 20-40 m tall at maturity. It is one of Long Point’s four hickory species – the other three species are the commonly observed Shagbark Hickory (Carya ovata) and the much rarer Red / Pignut Hickory (Carya glabra) and Shellbark Hickory (Carya lacinoisa). This species is named for it’s fruit – which has a much more bitter taste than Ontario’s other hickory species. It is most closely related to the Pecan Hickory (Carya illinoinensis) of the southern United States. The bark of Bitternut Hickory is usually described as fissured, with narrow, intersecting ridges (narrower than those of Tuliptree, Liriodendron tulipifera, or White Ash, Fraxinus americana, which it sometimes is confused with). On many trees, especially younger individuals, the bark is smooth in texture, and appears brown, grey, or even slightly greenish.

This tree grows across the portion of Ontario south of the Canadian Shield. The largest populations are found in southwestern Ontario, especially the Lake Erie Region (Carolinian Life Zone), where it is a typical component of moist forests and riparian forests. In Central Ontario, it is found around Lake Ontario and the Kawartha Lakes, though it is absent from the high moraines and escarpment formations that dominate Bruce and Grey counties. It is found on the Canadian Shield in the Cataraqui (Frontenac) Region, and Gatineau in Quebec, common in the Ottawa River Lowlands of eastern Ontario. In the United States, this tree is distributed from Minnesota to Texas east to Florida’s panhandle and almost everywhere in between.

The foliage of Bitternut Hickory is alternately arranged, and pinnately compound, emerging late for an Ontario hardwood tree, in mid-May. In total, each leaf measures 15-40 cm long (smaller than Shagbark Hickory), divided into 7-11 leaflets narrowly elliptical leaflets with finely toothed margins. Understory leaves are larger and broader than canopy leaves – an adaption to lower light levels, and are usually obovate – the upper part of the leaf is wider than the lower part near the leaf base. In the autumn, the leaves turn a golden yellow or a vibrant orange. Bitternut Hickory grows at a moderately fast rate for an Ontario tree. One of the most important identifying characteristics of Bitternut Hickory are the buds, which are elongated, and a distinctive sulfur to yellow in colour. This contrasts well with the brown, red, or grey buds of Ontario’s other tree species.

Bitternut Hickory occurs on a wide diversity of habitats, as long as there is ample moisture. It is a common component of Sugar Maple (Acer saccharum) and Beech (Fagus grandifolia) forests, having a similar niche to White Ash and Tuliptree. It is also observed growing alongside Basswood (Tilia americana), Red Oak (Quercus rubra), Yellow Birch (Betula lutea), Red Maple (Acer rubrum), Black Cherry (Prunus serotina), and Butternut (Juglans cinerea), and American Chesnut (Castanea dentata) in such systems. In riparian forests, it is usually observed as a canopy component with other tolerant hardwoods, such as Black Maple (Acer nigrum), Shagbark Hickory, White Ash, Blue Ash (Fraxinus quadrangulata), Basswood, though it also associates with Hackberry (Celtis occidentalis), Black Walnut (Juglans nigra), and Burr Oak (Quercus macrocarpa). The understories of hickory forests often have a rich diversity of shrubs, ferns, and native wildflowers, though species composition widely depending on the ecosystem type – it can be upland or riparian.

Wildlife importance

When trees are at least 10 years old, medium-sized nuts ( 2-3 cm) are produced by Bitternut Hickory, though optimal production is not attained until 30 years of age (sometimes much layer, if saplings are suppressed in a shaded understory). Hickory nuts are a valuable resource for wildlife, including small mammals, especially squirrels (Sciuridae), and seed-eating birds. Nut production varies widely each year – similarly to oaks, most nut production occurs during “mast years” with favourable conditions, a mechanism to control herbivore and insect populations, especially nut weevils (Curculionidae). The leaves are a source of food for insects, especially beetles and moths. Bitternut Hickory foliage is a food resource for Luna Moths (Actias luna), Royal Walnut Moth (Citheronia regalis), Hickory Hairstreak Butterfly (Satyrium caryaevorus), Hickory Tussock Moth (Lophocampa caryae), and several species of Underwing Moths (Catocala species). Luna Moth caterpillars grow up to 6.5 cm before over wintering in a cocoon and emerging as an adult moth with a wingspan of up to 10.5 cm, arguably one of North America’s most beautiful moths. Adult Luna Moths are short-lived, with a lifespan of ~10 days, which is primarily focused on reproduction.

Fun facts 

• Bitternut Hickory is fast growing in full sunlight, but slow growing in shade. This makes it well-suited for understory conditions, growing at an accelerated rate when canopy gaps allow sunlight to penetrate the forest understory.
• The bitter taste of hickory nuts from this species is caused by a high concentration of tannins. It is not preferred by squirrels for consumption. This is beneficial to Bitternut Hickory, as the tannins at as a herbivore deterrent, increasing the chances of successful germination without predation.
• Many types of caterpillars and larvae prefer feeding on Bitternut Hickory. This include the Hickory nut weevil (Curculio caryae), which commonly infests the fruit, especially during low-production years. However, a large presence of insects makes Bitternut Hickory an important species for breeding songbirds, which consume large amounts of insects.

 

Written by Matthew Palarchio, HBSc in Environmental Sciences, Western University.

All photos are provided by Matthew Palarchio

 

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