Bur Oak

Basic Information
Tree ID: 
Genus and species: 
The bur oak is a large, deciduous, slow-growth tree with simple leaves and a uniform crown of thick, spreading branches. Bur oaks are extremely resilient, displaying high levels of fire-resistance (thick bark), cold-tolerance, aerosol and soil salt tolerance, and drought resistance (deep taproot), surviving even in mineral-poor soil. The Bur oak has monoecious character with imperfect flowers, with a strategy of masting. This means acorns are produced in large quantities every few years in order to overwhelm consumption by wildlife. Bur oaks have a lifespan exceeding 200 years, approaching 1000 years. It has a wide distribution in North America, being native to Eastern NA. Bur oaks initial height growth is normally slow for the first 3 - 5 years, dependent on environmental conditions (sun exposure in particular). Based on the height, diameter, and growth factor, this individual is approximately 12 years old.
Reta Behnam, Michael Chen, Tony Leche
Collected Data
Tree shape: 
Wide, uniform, open, ovoid crown. Trunk supporting horizontal limbs with deep-ridged, rough bark. This is a young individual, will eventually be wider than tall.
Date of tree entry: 
4.00 m
Diameter at breast height: 
0.08 m

Bur oak bark is dark brown-gray with deep ridges and irregular sorrows. The bark is extremely thick, with an individuals around 100 years old having bark thickness of 1.6 - 2.4 in. This adds to the bur oak's fire resistance. Once they reach 12 - 15 years old, they can survive repeated burning. Insect larvae burrow into bur oak bark, and rabbits and other mammals and birds graze on the bark.
Twigs & branches
The crown consists of thick, spreading branches which droop as the tree grows. Near the base of the crown, larger branches grow horizontally and droop. Higher up, smaller branches grow vertically. Leaves alternate on twigs. The wide crown provides shade and feeding grounds for many birds and mammals.
Bur oak leaves are alternate (single at each node) and simple, typically smooth and dark green on the upper surface and slightly hairy and pale green on the underside. They display pinnate venation, being oblong and obovate (broader at the tip than the base). Length ranges from 8 - 12 in, width from 4 - 8 in. The Bur Oak is deciduous, shedding leaves annually.
Reproductive Structures
Bur oaks are monoecious, with male and female flowers occurring separately but on the same individual tree. The female flower has the appearance of a tiny narrow cone. Both female and male flowers bloom around the time of leaf development in the Spring. Dichogamous (pistils and stamens mature at different times to prevent self-fertilization). Pollen is released before the female flowers are receptive to flower such that self-pollination is rare. Weather conditions can affect the pollination success of the bur oak as rain can delay pollen shed while cold weather can reduce the production of flowers and pollen dispersal. The bur oak relies on abiotic factors such as wind for pollen dispersal. The bur oak produces large acorn and can produce them for up to 400 years of their lifespan. Bur oak acorns are a food source for a variety of birds and mammals; as a result, small mammals are the most likely dispersers of seeds for the bur oak. Bur oak seedlings can establish in a variety of conditions including in times of drought. The presence of mineral soil appears to be the most important factor for bur oak success as bur oak seedlings quickly develop taproots.
Bur oaks produce acorns which are dark brown and Ovid, approximately 1 - 2 inches in length. They are the largest of any oak. Acorns display large cups with hairs and scales. The furry, bur-like cap almost completely covers the distinct acorns. Bur oaks use a strategy of masting nut crops, meaning acorns are produced in nonconsecutive years in greater quantities in order to overwhelm the feeding capabilities of consumers. In an abundance study in Nebraska, oak trees produced large crops in two of three years, and almost none in the other year. Weather may impact acorn production, with a study showing that budding at the time of frost mitigates acorn formation. Nuts are produced in the Summer, developing from female flowers either alone or in pairs. Nuts mature in a single year, typically germinating in the following Fall.
  • Bur Oak in Winter (2/16/2022)
  • Bur Oak in Spring (4/27/2022)
  • Bur Oak in Summer (Image Courtesy of https://www.gardenia.net/plant/quercus-macrocarpa)
Natural range of distribution: 
This map depicts the bur oak's North American natural distribution as of 1971. Bur oaks are extremely cold-temperature-tolerant, drought-resistant, and can occupy a brand range of moisture regimes and soil conditions. However, the abundance of bur oak in the highlighted area has decreased dramatically in recent years. Within North America, the bur oak was commonly found at elevations of less than 3,300 feet, but had the ability to survive at a large range of climates and soil conditions. The bur oak can be found in moist woodlands, prairies, sandhills, etc. However, bur oak size and growth may vary based on the conditions of the environment. Since the bur oak is one of the most cold tolerant trees in the oak species, they can be found in the northern US states such as Ohio, Minnesota, and North Dakota. Meanwhile, the bur oak can tolerate poor, dry soils as well as wet, inundated soils. Overall, the bur oak is a dominant tree in the Great Plains and Great Lakes region.
Origin, history, and uses: 

The bur oak was given its name because the cup of the bur oak acorn bears a resemblance to the bur of a chestnut. Bur oak were plentiful within the North American range, but its presence in the region dramatically decreased after the settlement of Europeans. Bur Oak savannas in the Midwest and Great Plains were ideal sites for the European settlers because the bur oak provided sources of wood to be used for homes and fuel. In addition, bur oak wood was used as forage for livestock. As a result of agricultural and urban development, there was a widespread loss of the bur oak savanna ecosystem. In the early 1900s, it was estimated that 32 million acres of oak savannahs existed in the Midwest. As of 1985, there are only 6,400 acres that remain.

The bur oak serves as a food serve for many wildlife species such as deer, rabbits, racoons, and rodents among others. As the bur oak reaches maturity, the tree can provide nesting for numerous species of birds. In addition, the bur oak is often used as material for cabinets, flooring, and barrels due to its durability.

The Bur oak is deciduous, shedding its leaves each Fall and blossoming in the late Spring into early Summer. Pollination occurs during this time, with acorn formation happening in later Summer into Fall, in most but not all years in the masting process. Acorns take a year to mature, typically germinating in the following Fall.

Frett, J. (No date provided). Bur Oak (Quercus macrocarpa). College of Agricultural Sciences, University of Delaware. http://www.museum.state.il.us/muslink/forest/htmls/trees/Q-macrocarpa.html

Gilman E.F. & Watson D.G. (1994). Quercus macrocarpa: Bur Oak. Fact Sheet ST-551. USDA Forest Service. https://hort.ifas.ufl.edu/database/documents/pdf/tree_fact_sheets/quemac…

Gucker, C.L. (2011). “Quercus macrocarpa”. Fire Effects Information System. U.S. Department of Agrigulture, Forest Service, ROcky Mountain Research Station, Fire Sciences Laboratory. https://www.fs.fed.us/database/feis/plants/tree/quemac/all.html

Illinois Wildflowers. (No date provided). Bur Oak: Quercus macrocarpa: Beech family (Fagaceae)https://www.illinoiswildflowers.info/trees/plants/bur_oak.htm

Johnson, P.S. (No date provided). Bur Oak: Quercus macrocarpa Michx. USDA Forest Service. https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/quercus/macrocarpa…

Scianna, J.D. (2009). BUR OAK: Quercus macrocarpa Michx: Plant Fact Sheet. USDA NRCS Plant Materials Program. https://plants.usda.gov/DocumentLibrary/factsheet/pdf/fs_quma2.pdf

Other information of interest: 

The Bur oak plays a key role in relevant food webs and communities. The leaves provide a food source for many native caterpillars (such as the Hairstreak family) and moths (including Dagger moths and Underwings), with the bark also acting as a food source for Long-Horned Beetles as well as other insects. These insects are likewise consumed by many birds, which also use the acorns of the Bur oak as a food source. Acorns also are an important food source for many mammals, including the Black Bear, Raccoon, Squirrel, Chipmunk, and other rodents. The branches and cavities provide nesting habitats for squirrels and many birds including the Red-Tailed Hawk and Screech Owl.

Media and Arts

Our creative element is a drone video turned Tiktok! This was filmed earlier in the semester.