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.