Smooth Hickory (Carya glabra) in prime fall color.
Hickories are a common tree of Midwestern, Southern, and Eastern Forest types. These trees are known for producing edible kernels and economically valuable timber. They support the caterpillars over 200 butterflies/moths. Indigenous people pound the nuts and separate the shell to create different food products or process them with water to release the oils and flavors. Many people know of hickory through the flavor the wood’s smoke imparts onto grilled foods. Pecans are the most well known of the hickories, though this is written from primarily an Ohio, Kentucky, Indiana experience, and does not include pecans due to lack of encountered field samples in the natural environments of these states. Hickories have the highest calorie density and fat content of almost any food outside of whale lard which is nearly pure fat, making the small kernels worth processing from a sustenance perspective. There’s certainly a promising future for Hickory expansion in Native Plant Agriculture.
In the OKI (Ohio, Kentucky, Indiana) region at least 1 hickory species finds a niche to sustain itself within all forest types outside of the most frequently flooded floodplains dominated by Sycamore, Cottonwood, Silver Maple, Box Elder Maple, and formerly Green Ash. The 6 hickories we’re describing here are all large shade trees, often 3/4th’s of the mass of Oaks in maturity though every bit as tall. So when using them in the metropolitan landscape, plan for them to reach heights of over 65 feet tall, and widths of over 40 feet. All hickory kernels are edible, but Yellowbud Hickory is like an acorn in that it must be leached of tannins before it is palatable.
This blog post will provide the specific habitat niche of each hickory species, restoration implications, and defining I.D. characteristics.
Each Hickory species has fairly variable nut expressions. This is 3 samples per species.
Two Midwestern Hickories share this similar bark, but 1 has a leaflet of 7-9, and the other is of 5.
Shellbark Hickory - Carya laciniosa - OKI Habitat/Niche
Shellbark Hickory occurs on neutral-alkaline alluvial terraces, occasionally flooded neutral-alkaline flood plains, neutral-alkaline glacial outwash, weakly acidic (6.5+PH) to alkaline glacial till or bedrock soils (residuum) of the same PH range. It is commonly associated with Blue Ash, White Ash, Chinquapin Oak, Shumard Oak, Bur Oak, Yellowbud Hickory, Black Maple, and Sugar Maple. This tree is a good indicator of a soil PH of at least 6.5 or higher. It reaches its greatest productivity on Wisconsin Glacial Till of variable drainage and glacial outwash. It is tolerant of seasonally high water tables (swampy), and has a similar flooding tolerance (river/stream flooding) as Black Walnut and Bur Oak whom are common associates with it on occasionally flooded flood plains and/or alluvial terraces.
For restoration, while it can be established in acidic soils, it is most naturally competitive in the stated PH range of +6.5, and is best kept in that range for long-term success/unassisted reproduction. This is a good tree to plant, if human-planted trees on your site are showing signs of iron chlorosis or magnesium deficiency, typically seen in Acidic soil obligate species such as Red maple, Sweet Gum, Swamp White Oak, River Birch, and Pin Oak.
Key Defining Characteristics
Bark Leaflet of 7 typically, sometimes 9, but never 5
The shaggy light gray bark of the Shellbark shares similarity only with Shagbark (Carya ovata) locally. Use the leaflet of 7, and sometimes 9 with the shaggy bark to separate it from Shagbark as Shagbark nearly always has leaflets of 5 locally. In the winter time, if you don't have access to the leaflets, use the very large nuts + Bark to separate Shagbark and Shellbark. Shagbark nuts (not husks) should not be larger than the spread of a quarter, while Shellbark should have larger, more spherically or elongated golf ball sized nuts. See first diagram for reference.
Shagbark Hickory is separated from Shellbark Hickory most easily by the leaflet of 5, not 7 or 9.
Shagbark Hickory - Carya ovata - OKI Habitat/Niche
Shagbark Hickory occurs as a common species in strongly acidic soils to near neutral PH (5-6.8PH). It is a consistent indicator of acidic soil where naturally occurring and associated with one or more these following species; Sweet Gum, Black Gum, Sassafras, Mockernut Hickory, Smooth Hickory, Pin Oak, Black Oak, Scarlet Oak, Red Maple, or Shingle Oak. It is an indicator of weakly acidic or neutral soil (6.5-7.0 PH) when associated with one or more of the following species Chinquapin Oak, Shumard Oak, Bur Oak, Kentucky Coffee Tree, or Blue Ash. Because of its preference for acidic soil and adaptability to low or high moisture availability and poorly drained soils, it finds a place in many forest types. It’s co-dominant in Acidic Forested Wetlands featuring Pin Oak, Swamp White Oak, Beech, Green Ash, Red Maple, Sweet Gum canopies; it’s also very shade tolerant in these Acidic Forested Wetlands. It can also be found in very well drained acidic soils, the common denominator is acidity, not moisture level. In restoration it should only be planted in soils of a PH less than 7.0 to mimic or match it’s original niche.
Key Defining Characteristics
Bark-See above Picture Leaflet-of 5
What separates Shagbark from all other hickories except for Shellbark Hickory is the mature form of it's bark. In the growing season, use the leaflet of 5 paired with the bark to separate it from Shellbark. In the winter, use the nut size comparisons shown in the opening picture + bark, though nut comparison is less reliable to the inexperienced eye.
Mockernut Hickory is nearly always found in acidic soil naturally, like Shagbark and Pignut.
Mockernut Hickory - Carya tomentosa - OKI Habitat/Niche
Mockernut Hickory is overall less common than Shagbark Hickory, but occurs in very similar habitats. It is an occasional species in Acidic Wetland forests, though in my observation, its often directly associated with White Oak, Beech, and Sugar Maple which are less high water table tolerant as Swamp White Oak and Red Maple, indicating that it may be occurring in slightly better drained portions of Acidic Wetland Forests. It’s been observed increasing in dominance on slopes of over 3% on high water table acidic glacial till plains where drainage is better supporting acidic well drained soil associates such Black Oak and Pignut Hickory. Mockernut Hickory’s other niche is well drained acidic soil, whether from acidic bedrock (residuum) in unglaciated regions or acidic glacial till deposits in glaciated regions. Restoration is fairly straight forward, stick to acidic soils that are better drained than the most poorly drained high water tables, and it should be able to regenerate-long term. If drainage is questionable, but you know it’s acidic, use it on a slope of 3% of greater.
Key Defining Characteristics
Leaflet of 7 to 9 Nut (see original diagram) Bark (see picture above)
The leaflet of 7 to 9 narrows it down to being Shellbark, Mockernut, Sweet Pignut, or Bitternut Hickory. The nut clearly disqualifies Red Hickory, and Yellowbud. The Bark will clearly separate it from Shellbark Hickory as it doesn’t shag. The buds are also the largest of these 6 hickories, and they can be seen from the forest floor like the buds of a Buckeye. As you see more and more mockernut, you’ll also notice the twigs are less numerous and more proportionately thicker to support the heavy nuts, like walnuts, bur oaks, and buckeyes.
Yellowbud Hickory is the only PH generalist of these 6 described hickories.
Yellowbud Hickory - Carya cordiformis - OKI Habitat/Niche - aka Bitternut Hickory
Yellowbud Hickories are the most widely adapted of our hickory trees, more generalist; less specialized. It will occur in soils within a PH range of 5-7+, and is the most commonly regenerated hickory of neutral to alkaline soils. They can occur on occasionally flooded flood plains with Shellbark Hickory, Black Walnut, and Bur Oak, or they can occur on thin bedrock soils the same. The two niches they do not occur in often are frequently flooded flood plains and forested wetlands. The nuts are high in tannins, like acorns, and are left much of the winter by wildlife until needed, choosing to eat less tannic nuts first if they are available. Humans can leach the tannins from these just like acorns are leached by indigenous people, and the reward being a hickory kernel that has a much higher nut meat to wood/shell ratio than the other 5 mentioned hickories in this post. Through pressing, a high quality hickory nut oil can be obtained, that also lacks the bitter/tannic quality of the unpressed kernels. This is the fastest growing hickory out of these 6 mentioned, and is one of the more shade tolerant (in its youth) of the bunch.
Key Defining Characteristics
The leaflet is most often 7-9, never 5, the wings on the husk of the nut are also a consistent, defining feature which separates it from all of the other 5 described. The terminal buds are yellowish, which is unique to Yellowbud. The bark can sometimes look like Red Hickory bark at certain stages, it can also look like Mockernut bark in some expressions, the bark only easily separates it from Shellbark and Shagbark Hickories. You should be able to I.D. Bitternut with the leaflet of 7 to 9 plus terminal bud or the winged husk on the nut. With enough observation you’ll be able to recognize Bitternut based on the bark alone in most cases.
Pignut Hickory is the most thin soil/drought tolerant of these 6 described, restricted to acidic soils naturally.
Smooth HIckory - Carya glabra - OKI Habitat/Niche - aka Pignut Hickory
Smooth Hickory is a less dominant hickory in our region compared to the other hickories. It’s restricted to acidic soils like Mockernut Hickory and Shagbark Hickory but it does not occur in seasonally high water tables, and tends to stick to rocky acidic residuum soils and acidic glacial till deposits on slopes greater than 5% (well drained). Where soils are acidic and drought prone due to lack of depth and/or steep sloped, it seems Pignut has an competitive advantage though it appears as a minority species in deep acidic, well drained soils too. For restoration, we strongly recommend excluding Smooth Hickory from neutral and/or alkaline soil plantings as in all of our field studies it is always absent from this PH range, while showing an increase in frequency the more well drained and acidic the soil becomes. I’d also avoid seasonally high water tables, as it’s also completely absent from our field observations in these winter/spring saturated soils. Side note, Smooth Hickory may have the most magnificent fall color of all of the hickories listed here, from bright gold to orangish gold. It’s also a myth that all smooth hickories taste bitter or bad. Every Smooth Hickory we’ve consumed had no bitterness and is on the same Pecan flavor spectrum that all hickories are on, bitter or not.
Key Defining Characteristics
Leaflet of 5 Bark (bark is quite variable from smooth to deeply furrowed)
Nuts (Essential to I.D.)
The leaflet of 5 will narrow it down to Shagbark Hickory, Red Hickory Hickory, or Smooth Hickory. The bark will separate it from Shagbark Hickory. Red Hickory most commonly has leaflets of 7, but sometimes has populations that have leaflets of 5, where as Smooth Hickory is nearly always leaflets of 5….but sometimes 7. The only way to definitively separate Smooth Hickory (Carya glabra) from Red Hickory (Carya ovalis) is the husk of the nut. If you look at the link we attached, Smooth Hickory husks do not dissect from the top to bottom on all sides, so the husk remains on the nut throughout the winter and rots away. Red Hickory husks, like Shagbark, Shellbark, and Mockernut, do have these creases/dissection lines that run from the top of the nuts to the bottom which causes them to release the nut fully as they dry out and mature. This is the most reliably defining characteristic, though as stated before, commonly, Red Hickory have leaflets of 7 and Pignuts have leaflets of 5.
Sweet Pignut aka Red Hickory (Carya ovalis) shows a niche difference compared to Pignut (Carya glabra).
Red Hickory - Carya Ovalis - OKI Habitat/Niche - aka Sweet Pignut Hickory
Sweet Pignut aka Red Hickory is about as common as Smooth Hickory locally, but has a wider range of adaptability. While Smooth hickory is completely restricted to acidic soils, Red Hickory has been found numerous times regenerating on Ordovician Limestone/Shale residuum soils of +6.8PH. Red Hickory also appears to be more common in the 6 PH range than Smooth Hickory, especially when studying forest regeneration on the Wisconsin Glacial Till Plains of SW Ohio and SE Indiana. However we don’t consider Red Hickory a PH generalist like Bitternut Hickory as it disappears in the higher alkalinity soils such as of Glacial Outwash parent materials; where only Shellbark (alkaline adapted) and Yellowbud (True PH Generalist) have proven adapted. Glacial Outwash soils are generally more alkaline than Ordovician Limestone/Shale soils where Red Hickory has proven adaptation. The fall color ranges from yellowish to plain brown, where as locally observed Carya glabra ranges from golds to orangish golds. Red Hickory, like Smooth Hickory, has not expressed itself in wetland forests of any PH range. For restoration, Red Hickory should regenerate long-term in moderately well drained soils in the PH range of upper 4 to 7.2. It is likely more adapted to acidic soils than neutral soils, it’s the most dominant hickory in the canopy of Lake Hope State Park in Ohio, where the residuum bedrock produces acidic enough soil to support Sourwood, in the 4 to 5 PH range.
Key Defining Characteristics
Terminal Bud (not yellow like Yellowbud, not large like Mockernut) Bark (never as shaggy as Shagbark or Shellbark) Leaflet of 7 (commonly 7, but some populations have leaflet of 5) Nuts (Full dissection lines from top to bottom on all sides unlike Pignut)
Most Red Hickories have leaflets of 7, but some populations consistently have leaflets of 5. If your hickory has a leaflet of 7, the bark will definitively I.D. it as Shellbark or Red Hickory based on the provided bark picture links. But Mockernut also commonly has leaflets of 7, compare the difference in nut size and the difference in terminal bud size to separate these two. Mockernut has large enough terminal buds to be seen from the forest floor like you can see Buckeye buds, where as sweet pignut buds are comparatively small. If it has a leaflet of 5, but lacks the shaggy bark of Shagbark hickory, it could be Smooth Hickory or Red Hickory. To repeat, sometimes Red Hickory has leaflets of 5 like Pignuts, so in this case in comes down to the husks of the nuts. Copied from the Smooth Hickory (Carya glabra) section; The only way to definitively separate Smooth Hickory (Carya glabra) from Red Hickory (Carya ovalis) is the husk of the nut. If you look at the link we attached, Smooth Hickory husks do not dissect from the top to bottom on all sides, so the husk remains on the husk throughout the winter and must rot away. Red Hickory husks, like Shagbark, Shellbark, and Mockernut, do have these creases/dissection lines that run from the top of the nuts to the bottom which causes them to release the nut fully as they dry out and mature.
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