• Mississippi National River and Recreation Area


    National River & Recreation Area Minnesota

Bur Oak

This is the tree that is most associated with the savannas of our area. The thick, corky bark of mature trees insulated the living tissues within from the grass fires that frequently swept the savanna. For further protection from fire the bur oak leafs out fairly late--usually after the spring fire season--compared to other trees, thus protecting vulnerable leaves from heat and smoke damage. Other tree species, being less well adapted to fire, are often excluded from fire dominated ecosystems such as grasslands.

These “open-grown” bur oaks may grow 50-80 feet tall and have thick trunks with widely-spreading, often crooked branches. The acorn is large and has a “burry” cap, from which this oak gets its name. The leaf has rounded tips on its lobes, but with a deeply incised “waist,” a characteristic it doesn’t share with other oaks in our area. The bark is gray and deeply furrowed in older trees. Twigs are both thick and blunt compared to many other trees.

Fascinating Facts

Savanna is among our rarest plant communities, yet they are among one of our most popular places to visit. City parks, essentially grasslands with widely spaced trees, are modeleds after savannas.

In much of the Midwest, savannas are also called “oak openings,” as there are many small, grassy openings among the groves of oak trees.

As the Mississippi River corridor was settled in our area, grass fires became less frequent and fire intolerant trees grew up around the bur oaks. These lesser trees block light to the lower branches of the bur oaks. When branches no longer have access to light, the tree often “self-prunes” letting those useless branches die so valuable resources can be used on those branches that still have access to sunlight. Look for open grown bur oaks with dead lower branches that were once located in what was savanna, but is now forest.

A line of bur oaks trees leafless against a blue sky.
Notice the nearly horizontal lower branches of these bur oaks. These trees are often referred to as "open-grown."

Bur Oak
Quercus macrocarpa

Find It
Bur oaks may be found on the bluff tops of Crosby Farm and Indian Mounds Regional Parks. A beautiful stand of bur oaks graces the lawns of the Highway 10 rest stop northwest of Anoka.

Tell Us
Have you found this plant at other locations within the Mississippi National River and Recreation Area (map)? If so, let us know the location by e-mail. Put the word "Plant" in the subject line.

Did You Know?