Tree of the Month: Bur Oak
The majestic bur oak tree is a beautiful symbol of environmental health and durability! This gigantic, long-lived oak is an important ecological species and is widely adaptable as a landscape specimen. Here, we’ll go over the features of bur oak trees and their environmental needs while highlighting their contributions to the local ecosystem.
How to Identify a Bur Oak Tree
The bur oak tree gets its common name from the soft, furry burs on its acorns, whose large size also informs its scientific name: Quercus macrocarpa, or “large-fruit oak.” The acorns can be up to two inches in length, placing them among the largest of acorns. Nuts of the bur oak are an important source of nutrients to mammals like deer and squirrels, as well as large birds like turkeys, geese, and ducks. Bur oaks are sometimes known as “mossy cup oaks” due to their acorns’ scaly, warty caps.
It's not only the bur oak’s acorns that are big; the tree itself is among the tallest growing, with wavy branches that reach upwards and outwards to form a wide crown, resulting in the shape of a horizontal oval at maturity. Due to their height and spread, bur oaks are wonderful shade trees!
The leaves have the classic oak fiddle shape, with numerous lobes and deep sinuses. As a member of the white oak family, the bur oak’s leaves have rounded tips. In the fall, the bur oak’s foliage turns golden yellow before dropping off. During the winter months, the silhouette of the tree casts an interesting figure, with its wide, waving branches. The tree’s light brown bark is on display, with an interesting vertical pattern made of straight and intersecting ridges.
Like many other types of oak trees, the flowers of the bur oak are catkins—long, yellowish-green bunches of tiny flowers that release pollen into the wind during the spring to pollinate nearby oaks. This can sometimes lead to natural hybridization (when one species of oak successfully reproduces with another).
Bur Oaks in Nashville
Bur oak trees are native to North America and are one of the furthest north-reaching oaks. In fact, Nashville is about as far south as these trees reach east of the Mississippi, giving them a unique cold hardiness compared to other trees in the south. The tree’s preference for moist but well-drained soil allows it some flood tolerance in addition to drought tolerance, which works well in Nashville’s sometimes wet, sometimes dry climate. This also means it will do well in the city's urban landscape, whose impermeable surfaces (like streets and buildings) create temporary flood conditions in times of heavy rainfall.
The oak’s wide crown reflects an extensive root system as well, which helps these trees stay in place in stormy weather while holding the soil in place and preventing erosion. These big trees will even absorb some of the water that may saturate a yard’s ground, further helping manage stormwater!
While the tree can tolerate some flooding like it experiences naturally in lowland areas, the bur oak also grows in dry uplands, sandy plains, and grasslands. The bur oak does well in limestone soil, which is prevalent in the Nashville area. These trees prefer to grow in neutral to slightly alkaline soil (7-7.5 pH). However, they can tolerate a range of soil types, from sand to clay or slightly acidic. The tree’s versatility makes it a good option for urban environments with variable weather and some pollution.
As a native oak tree, bur oaks provide an essential habitat for many kinds of local caterpillars, insects, birds, and mammals, in addition to providing food in the form of leaves and acorns. In terms of ecosystem services, the bur oak is a pillar of ecological stability.
How Fast Does a Bur Oak Grow?
While a bur oak can grow to be one of the biggest trees around, it needs time to become that size. It’s a slow-growing tree, taking on less than 12 inches annually. However, a specimen can reach up to 80 feet on average, and some bur oaks have been known to live for 400 years. Considering the importance of the first few years of the life of a tree, planting oak trees today and caring for them as they grow can have implications for Nashville’s canopy hundreds of years on!
Plant a Bur Oak Tree
The bur oak is a wonderful tree to plant, especially in big, open areas where it can stretch its roots and branches (be sure to consider water lines and house foundations on your property when selecting a location for such a big tree!). Check out our listing for the bur oak on the NTCC’s tree sale page. If you’d like to help us plant trees around the city, sign up to volunteer, and to stay updated on the latest tree news in Nashville, subscribe to our email newsletter!