Forest Preserve District of Cook County, Illinois
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The Bur Oak
Nature Bulletin No. 708   March 9, 1963
Forest Preserve District of Cook County
Seymour Simon. President
Roberts Mann, Conservation Editor

THE BUR OAK
The state tree of Illinois is the "native oak". It should be the Bur Oak. As Aldo Leopold discerned: "When school children vote on a state bird, flower, or tree, they are not making a decision; they are merely ratifying history". Ergo, when the first settlers gazed westward across the vast prairies of Illinois, bur oaks were the burly trees on knolls and ridges which stood like ships in a sea of grass.

Those oak openings, as they are called, were remarkable features of the tall grass prairies in Indiana, Illinois, and the prairie peninsulas that extended northward into Michigan and Wisconsin. Many early travelers wrote lyrical descriptions of those park-like openings "without a twig of underbrush". . . "where deer grazed leisurely like sheep"...."so open that a cabriolet could have been driven through them for miles".

They existed because a bur oak is the only tree that can be swept by a roaring prairie fire and still live. It is insulated, even on the twigs, by a crust of corky bark. On the trunk of a huge patriarch its deeply furrowed bark may be four inches thick. On a sapling the stem, branches and twigs are covered with weird assortments of corky ridges and excrescences.

Although most numerous in the Middle West, the bur oak is distributed from Nova Scotia to Manitoba and south to Delaware, Tennessee and Central Texas. In Illinois it grows throughout the state -- probably in all of the 102 counties originally. Here in Cook county, and as a rule, it is most common on deep rich soils that are moist but well-drained. However, the species is surprisingly adaptable. It frequently flourishes on gravelly moraines and sandy ridges underlain by water bearing strata and some of the largest bur oaks in Illinois -- giants more than 350 years old and 5 or 6 feet in diameter -- grew on such soils. On the other hand, in LaSalle and adjacent counties, bur oaks are found on dry uplands in company with hickories and white, red and black oaks.

This tree is one of the largest and, next to the white oak, most majestic of American oaks. Its stiff gnarled branches and stout, frequently crooked, branchlets with corky wings along them are distinctive. Ordinarily, it is seldom more than 80 feet high and 3 feet in diameter but, in favorable locations such as the Wabash river basin, giants 170 feet tall and 7 feet in diameter have been known. a forest it develops a tall clear trunk but, growing in the open, we have seen some with short massive trunks, huge lower branches almost horizontal, and a spread of 80 feet or more.

Its leaves, largest of all the oak leaves, are from 6 to 12 inches long, 3 to 6 inches broad in the upper portion, with from 5 to 7 lobes which, since it is a member of the white oak group, are rounded. The central lobes are separated by wide bays or sinuses that reach almost to the midrib. Those thick leaves are dark green above but silvery green and downy underneath. In autumn they become dull yellow or tan and, unlike other oaks, all drop off.

The Latin name for all oaks is Quercus. The scientific name for the bur oak is Quercus macrocarpa, meaning large-fruited. The common names -- bur or mossy cup -- refer to its distinctive acorn. Egg-shaped and from 3/4 to 2 inches long, it is held in a deep scaly cup which has a fringe of elongated scales and sometimes covers more than half of the acorn. Its white kernel is sweet and edible.

The wood -- hard, strong, tough and close-grained -- is almost as heavy as white oak and equally valuable for many purposes such as lumber, veneers, furniture, interior trim and flooring. Because of its durability in contact with the soil, bur oak is frequently used for piling, railroad ties and structural material.


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