Bur Oak

Basic Information
Tree ID: 
Genus and species: 
The bur oak is a large deciduous tree that possesses alternately arranged simple leaves and a wide, uniform crown. Bur oaks are among the most fire-resistant, cold-tolerant, and drought-resistant of all oak species; thus, they are distributed over a wide geographical range in North America. The plant is monoecious with imperfect flowers, a quality that reduces the chances of self-pollination and is thus advantageous for promoting genetic diversity within the population. The lifespan of bur oaks generally exceeds 200-300 years.
Alan Zheng
Collected Data
Tree shape: 
Wide, open, and uniform crown; can be wider than they are tall; crown has an ovoid/globoid shape
Date of tree entry: 
19.81 m
Diameter at breast height: 
4.17 m

The bark is dark gray with deep ridges and deep irregular furrows. In contrast, white oaks (Quercus alba) possess a light gray bark with a smoother texture. The bur oak's thick trunk contributes to its impressive fire resistance.
Twigs & branches
The bur oak possesses brown and thick twigs as well as drooped branches. In the lower crown, the branches are larger and grow horizontally. In the upper crown, the branches ascend and grow vertically.
The bur oak possesses alternately arranged simple leaves that display pinnate venation. The leaves are green in the spring/summer and turn copper/yellow in the fall. The leaf shape is characterized as oblong and obovate. The leaves of bur oaks possess 5 to 9 rounded lobes with sinuses below the middle. They are darker on the upper surface and lighter on the lower surface. The lower surface is coated with white hairs.
Reproductive Structures
The plant is monoecious with imperfect flowers, a characteristic that is advantageous for promoting genetic diversity within the population. In the summertime, male flowers are green/yellow and female flowers are red/green, and they are located on separate parts of the plant. Flowering occurs after the leaves grow back, usually from April through June. Male flowers are made up of a lobed calyx that contains 5-20 stamens. Female flowers can either be alone or clustered in bundles of 2-3. They include a pistil with red styles at the tip. Cross-pollination is much more common than self-pollination and occurs via the wind. In the summertime, fertilized female flowers mature into acorns. The seed embryo contains two cotyledons, making the bur oak a dicot.
The bur oak bears acorns, which are a brown, oval-shaped fruit with a dry/hard covering. The acorns are generally 1-seeded but can also be multiple-seeded. They are first produced at around 35 years old, and they show very little to no dormancy. In fact, they tend to germinate the same year they mature. These fruits are eaten by squirrels, rabbits, deer, blue jays, and many others. Therefore, the seeds are dispersed by animals, most commonly small mammals and less commonly birds. At least one-third, but as much as 100%, of the acorn is covered by a large cup. Bur oaks produce the largest acorns of any native oak species. The fruits generally grow from August to November. It has been discovered that acorn size generally decreases with increasing latitude.
  • Early Spring
  • Mid Spring
  • Summer - Courtesy of Walbridge (https://www.walbridge.com/project/university-of-michigan-stephen-m-ross-school-of-business-renovation-and-addition-ann-arbor-mi/)
  • Autumn - Courtesy of MLive (https://www.mlive.com/news/ann-arbor/2015/10/1_year_and_400k_later_u-m_says.html)
Natural range of distribution: 
Bur oaks are one of the most drought-resistant and cold-tolerant North American oaks; thus, they thrive in a wide range of habitats. They are located in prairies, savannas, open woods, sandy ridges, and stream edges. They generally do not thrive at elevations of more than 3,300 feet. Bur oaks prefer to be in moist soil, but because of their extensive root system, they can also tolerate soil that consists of sand or gravel. In very harsh conditions, bur oaks can adapt by growing as small trees or shrubs.
Origin, history, and uses: 

The bur oak is so named because the cup of its acorn bears a slight resemblance to the spiny bur of a chestnut. Bur oaks are native to North America and can thrive in a host of environmental conditions. Because of its extensive root system, the bur oak can adapt to adverse soil conditions, and thus it has become the dominant oak species of the prairie. Because of its thick bark, it is the most fire-resistant of all oak species. It extends farther north (Canada) than does any other oak species due to its ability to tolerate cold weather. Historically, many Europeans preferred to settle in bur oak savannas because the wood from bur oaks could be used for constructing homes and for providing fuel. Moreover, the wood could be used to feed livestock. Unfortunately, widepsread agricultural and urban development throughout the 20th century resulted in a huge loss of bur oaks in the Northern Hemisphere. In the early 1900s, there were an estimated 32 million acres of oak savannas, whereas by 1985, just 6,400 acres of oak savanna remained. 

Because of their durability, bur oaks are used to build various objects such as cabinets, barrels, fence posts, and hardwood floors. The tree is commonly planted for shade at local parks, and it can also be planted for ornament and shelter belts. An interesting fact is that Native Americans used bur oak for medicinal purposes, particularly when caring for those afflicted by heart ailments, broken bones, diarrhea, and even bleeding wounds. Bur oaks are not just important for humans, however. The acorns they bear are a vital food source for many different animals, including the wood duck, raccoon, pileated woodpecker, and greater prairie chicken, among many others. Not only that, they harbor animals such as treehoppers, plant bugs, and leaf beetles, all of which feed on the tree. 

As mentioned above, bur oaks blossom between April and June. Pollination also happens in the spring. Fruiting occurs as early as August and as late as November. The bur oak's leaves are green in the spring/summer and yellow during autumn. Being a deciduous tree, the bur oak loses its leaves in late autumn and grows them back in the spring.

Allen, J. (2015, October 30). 1 year after $400K move, U-M says 250-year-old bur oak tree transplant was a success. MLive. 1 year after $400K move, U-M says 250-year-old bur oak tree transplant was a success - mlive.com

Dolan, M. (2016, October 21). U-M celebrates $135M business school expansion. Detroit Free Press. U-M celebrates $135M business school expansion (freep.com)

Friends of the Wild Flower Garden, Inc. (2015). Bur Oak, Quercus macrocarpa Michx. Bur Oak, Quercus macrocarpa Michx. (friendsofthewildflowergarden.org)

Illinois State Museum. (n.d.). Quercus macrocarpa. Quercus macrocarpa (state.il.us)

Illinois Wildflowers. (n.d.). Bur Oak (Quercus macrocarpa). Bur Oak (Quercus macrocarpa) (illinoiswildflowers.info)

Kalman, M. (2014, October 26). Historic Ross tree moved after months of planning. The Michigan Daily. Historic Ross tree moved after months of planning | The Michigan Daily

Lady Bird Johnson Wildflower Center. (2015, November 6). Quercus macrocarpa (Bur oak) | Native Plants of North America. Quercus macrocarpa (Bur oak) | Native Plants of North America (wildflower.org)

Nesom, G. (n.d.). Quercus macrocarpa. United States Department of Agriculture. Quercus macrocarpa (usda.gov)

Samilton, T. (2014, October 26). Lifted on Giant Inner Tubes, An Old Tree Moves In Michigan. NPR. Lifted On Giant Inner Tubes, An Old Tree Moves In Michigan : NPR

University of Michigan. (2014, October 7). University of Michigan: Ross Tree relocation [Video]. YouTube. University of Michigan: Ross Tree relocation - YouTube

USDA Forest Service. (n.d.). Quercus macrocarpa. Quercus macrocarpa (fs.fed.us)

Other information of interest: 

Many careful and calculated measures were taken in preparation for the tree relocation. The first step involved calculating the diameter of the root ball and then severing the roots so as to allow for root regeneration before the lifting process. In doing so, new roots were given the opportunity to sprout from the root ball prior to the tree being lifted. The second step included digging deep trenches and inserting pipes below the tree; these pipes would act as the platform during the lifting process. The third and final step entailed placing rubber bags below the pipes and then inflating them to uplift the tree. 

Media and Arts
Animation of Ross Tree Relocation (Courtesy of the University of Michigan)