Oaks
(Quercus spp.)
General Information
Oak trees genus Quercus are found throughout much of the United States with the highest densities lying in the eastern and southeastern US. Oaks can be found in both the upland and floodplain forests on FLMR but are more abundant and dominant species in the upland forest.
Oaks are typically divided into two varieties, red oaks and white oaks. This can be confusing as there are also specific species called Red Oak (Quercus rubra) and White Oak (Quercus alba). The main differences between red and white oak varieties can be seen in leaves and bark. Red oaks are generally smoother in appearance in their bark and the leaves tend to have small points on the tips. White oaks tend to have rougher bark with deeper furrows and the leaves tend to be more lobed and lacking points (4, 9). This is the first step in identifying which oak species you have.
After determining which variety of oak, identification comes down to comparing slight differences in leaves, bark, and acorn fruits that determine which is the best match for your unknown tree. Note that leaves on a singular tree can be quite variable and may require the observer to look at leaves from different areas of the tree canopy. Below is a brief list of some of the frequent oak species found on FLMR and a brief description of each to aid in identification.
RED OAKS
Red Oak (Quercus rubra) can grow to heights of 110 feet. Leaves are alternate and sized around 5-8 inches long. Red Oak is unsurprisingly a red oak variety and possesses bristle tips numbering 7 to 11. The sinuses typically reach ½ to 1/3 of the distance to the midvein or midline of the leaf. Acorns are almost completely round to slightly oval and measure ¾ to 1 inch long. Caps are thick and flat and cover the acorn about ¼ or less. Scales are compressed with no loose edges and are generally diamond in shape. Bark of the red oak is generally smooth with flat-topped ridges and shallow furrows that have been described as ski tracks. Furrows can appear somewhat reddish depending on the size of the tree (4, 9).
Pin Oak (Quercus palustris) can grow to heights of 110 feet. Leaves are alternate and sized around 3-6 inches in length. Pin oaks are part of the red oak variety and possess 5-9 bristles at the tips of each lobe. Sinuses are highly variable in depth and can extend nearly all the way to the midvein or midline of the leaf. Pin oak leaves are visually very pointed and have less surface area than most other oaks. Acorns are very round and measure around ½ an inch in length one of the smaller acorns. The cap is thin and has been described as saucer-like with scales that are somewhat broad, flat, and compressed onto the cap. The bark is gray-brown, thin, and smooth throughout the lifetime of the tree. Furrows are shallow and may present a reddish color (4, 9).
Black Oak (Quercus velutina) grow to heights around 90 feet. Leaves are alternate and are sized around 4-10 inches long. Being a red oak variety leaves possess bristle tips usually numbing 5-7. Sun leaves tend to have deeper sinuses between lobes while shade leaves may not have as deep sinuses. Acorns are generally oval in shape and measure ½ to ¾ of an inch long. The caps cover around 1/3 to ½ of the acorn with scales that are somewhat loose and relatively broad. The bark is gray and relatively smooth compared to white oak varieties with medium-deep furrows that run vertically with rounded ridges. When the outer bark is peeled back it reveals a deeply orange-red inner bark high in tannins that to the taste is extremely bitter (4, 9).
WHITE OAKS
Bur Oak (Quercus macrocarpa) grows to heights of 100 feet. Branches are sprawling and generally more horizontal than other oaks. Leaves are alternate and sized around 6-12 inches in length. Bur oaks are part of the white oak group and possess 2-3 lobes per side of the leaf which lack bristles. Sinuses are variable in depth but are typically quite deep nearing the midline of the leaf. Acorns of the bur oak are quite large measuring up to 2 inches in length. The caps of the acorns typically cover 1/3 to 2/3 of the nut with knobby scales that turn to hair-like fringes at the tips. The bark is grayish brown with deep furrows and large flat ridges (4, 9).
White Oak (Quercus alba) grows to heights of around 110 feet. Leaves are alternative and sized around 5 to 9 inches in length. White oak as the name would suggest is part of the white oak group and lacks bristles at the end of the 3-6 lobes per side. Lobes are lightly rounded and are deeply sinuses nearly reaching the midline. Acorns are ¾ to 1 inch in length. Acorn caps cover roughly ¼ of the nut and possess scales that are flat and tight against the cap. The bark of the white oak is light gray with shallow furrows and blocky flat plate-like ridges (4, 9).
Chinkapin Oak (Quercus muehlenbergii) grow to heights of 80 to 90 feet. Leaves are alternate and sized 4 to 8 inches in length. Unlike most other oaks that possess lobes Chinkapin oak leaves have 8 to 14 teeth per leaf side and are part of the white oak family and lack leaf bristles. Sinuses between teeth are shallow and the leaf comes to a sharp point. Acorns measure ½ to ¾ of an inch in length and typically occur in clusters when still on the tree. Acorn caps cover around ½ of the nut and possess scales that are flat and tight against the cap. The bark is gray in color with shallow fissures and short ridges that are flaky (4, 9).
Post Oak (Quercus stellata): grows to heights of around 100 feet. Leaves are alternate and sized around 4 to 7 inches in length. Post oaks are part of the white oak group and lack bristles at the end of the 1-3 lobes per leaf side. Lobes are rounded and sinuses are relatively deep reaching 1-2cm from midline. One of the field marks for identification of the post oak is the lobes for a cross shape. Acorns of the post oak measure ½ to ¾ of an inch in length. Acorn caps cover ½ to 1/3 of the nut and possess scales that are flat and tight against the cap. The bark of the post oak is gray to dark brown with deep fissures and flat blocky ridges.
Natural History
There are around 90 species of oaks (Quercus spp.) found in North America with the group largely being considered a keystone species thanks to how many other species of organisms are supported by the oaks.
One of the most important roles of the Oaks in forests where they are one of the dominant species is the production of their fruit or nuts which are a major food source for a plethora of organisms. The nuts are considered hard mast nuts and oaks at large are considered mast-producing trees (7). The interesting part of acorn production is the phenomenon of boom and bust years. In boom years oaks synchronize larger than normal production of acorns resulting in abundant food for various species. This abundance directly results in major effects on the ecosystem at various levels of the food web locally. Organisms that rely on acorns for their diet benefit and so do their predators and parasites. In bust years there is a normal or less than normal number of acorns produced. This too has major effects on the local ecosystem. With fewer acorns, there is more pressure on organisms to seek other sources of food, potentially leading to reductions in the population (8).
When it comes to a specific example of relationships with oaks this can be observed on base with the Southern Flying Squirrel (Glaucomys volans). The Southern Flying Squirrel is listed as a species in need of conservation according to the Kansas Department of Wildlife and Parks. Thanks to efforts by Fort Hays State University in collaboration with Kansas State University the existence of Southern Flying Squirrels has been reconfirmed at FLMR. The nests of SFSs are quite specific with preferences for mast-producing trees like oaks. They nest in cavities of standing dead trees and are active at night (11). Oaks and hickories make up the majority of the diet of the SFS (5). Without an appropriate amount of oaks and hickories southern flying squirrels would not be able to exist making the old-growth forests of FLMR a good stronghold for SFSs.
There are two main groups of oaks in the US, white and red oaks. Each group has specific characteristics. For example, members of the red oak group possess bristles on the tips of the lobes of their leaves while members of the white oak group lack these bristles. Additionally, members of the red oaks pollinate and gestate differently from members of the white oaks. Red oaks generally take around a year after the pollen has reached the flower for the seed to germinate. White oaks typically germinate within the same season that pollen reaches the flower (6).
Historical and Indigenous Uses
There are many colonial uses of the genus Quercus. One of the most common and well known is their uses for various woodworking products. Some of these include veneer, cabinetry, shipbuilding, ornamental trim, and flooring. Red Oaks have been found to have better mechanical strength than White Oaks.
Oak bark is high in tannins or tannoids that serve to protect trees from predation thanks to their unpalatable flavor. These tannins have been historically used in Europe for tanning leathers (3).
For indigenous peoples many of the oak species held many uses. The nuts of various species have been ground down into meal or flower and made into bread and other food products (1). The Cherokee tribe used bark to treat symptoms of dysentery and as an antiseptic (2).
Citations
1) Bean, L. J., & Saubel, K. S. (1972). Temalpakh: Cahuilla Indian knowledge and usage of plants. Malki Museum.
2) Chiltoskey, M. U., & Hamel, P. B. (2002). Cherokee Plants and Their Uses -- A 400 Year History. Cherokee Publications.
3) Clarkson, L. A. (1974). The English Bark Trade, 1660–1830. The Agricultural History Review, 22(2), 136–152. http://www.jstor.org/stable/40273608
4) Haddock, M. J., & Freeman, C. C. (2019). Trees, shrubs, and Woody Vines in Kansas. University Press of Kansas.
5) Helmick, K. R., Barrett, T. L., & Barrett, G. W. (2014). Dietary resource preference of the southern flying squirrel (glaucomys volans). The American Midland Naturalist, 171(2), 371–374. https://doi.org/10.1674/0003-0031-171.2.371
6) Hipp, A. L., Manos, P. S., & Cavender-Bares, J. (2024, February 20). How oak trees evolved to rule the forests of the Northern Hemisphere. Scientific American. https://www.scientificamerican.com/article/how-oak-trees-evolved-to-rule-the-forests-of-the-northern-hemisphere/
7) Hutchinson, Jay G., ed. Central hardwood notes. St. Paul, MN.: U.S. Dept. of Agriculture, Forest Service, North Central Forest Experiment Station. 9.12
8) Koenig, W. D., & Knops, J. M. H. (2005). The Mystery of Masting in Trees: Some trees reproduce synchronously over large areas, with widespread ecological effects, but how and why? American Scientist, 93(4), 340–347. http://www.jstor.org/stable/27858609
9) Kurz, D. R., Nelson, P., Ritter, T., Chasteen, B., & Porter, M. (2009). Trees of Missouri: Field guide. Missouri Dept. of Conservation.
10) Liebhold, A., Sork, V., Peltonen, M., Koenig, W., Bjørnstad, O. N., Westfall, R., Elkinton, J., & Knops, J. M. (2004). Within‐population spatial synchrony in mast seeding of North American oaks. Oikos, 104(1), 156–164. https://doi.org/10.1111/j.0030-1299.2004.12722.x
11) Taulman, J. F. (1999). Selection of nest trees by southern flying squirrels (sciuridae: glaucomys volans) in Arkansas. Journal of Zoology, 248(3), 369–377. https://doi.org/10.1111/j.1469-7998.1999.tb01036.x