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One of the perks of my position with the School of Earth, Society, and Environment at the U of I is an office in the Natural History Building on Green Street. My colleagues and I will be moving to temporary quarters soon as renovations here begin, but for now the view out my window includes a magnificent bur oak, a tree I used to cross campus just to check on now and then. [Photo by author.]How big is “magnificent”? I recently measured my tree at 13’7” around at chest height, which makes it bigger than just about any other tree on campus, although that’s still on the small side compared to the Illinois state champion bur oak, which is more than 23 feet in circumference. In characteristic bur oak fashion, my tree’s massive lower limbs grow almost horizontally; by my measurement, conducted in cooperation with coworker Lana Holben, they span 114 feet at their widest point.
It can be difficult to know for certain how long a tree has lived, but last year Gene Himelick, Professor Emeritus of Plant Pathology at the U of I, calculated that my tree is between 183 and 188 years old.
As bur oaks go, 180-some years is no record—they may live to be three or four hundred—but that still makes this one the oldest living organism on campus. (Insert your own joke about old professors here if you must.)
Like others of its kind, my oak provides all manner of benefits to wildlife. Squirrels feast on its abundant acorns, and they build their leafy nests among its limbs. Migrating songbirds also flock to it, attracted by the caterpillars of moths and butterflies it hosts. Among the many birds that distracted me from work this past spring were American redstarts and blackburnian warblers, blue-headed vireos and ruby-crowned kinglets.
This year’s extraordinarily warm March prompted my oak to flower and leaf out four weeks earlier than normal, which means the birds found a diminished food source when they arrived on schedule in late April and early May. An occasional warm spring won’t undo the age-old association between oaks in the Midwest and the long-distance bird migrants that depend on them, but ornithologists anticipate that the long-term trend toward earlier leaf-out could have that effect, to the great detriment of the birds.
Bur oaks were the signature tree of the wooded groves that here and there graced the landscape of east central Illinois when tallgrass prairie was the dominant landcover. Their thick, corky bark, which grows on even their smallest branches, enabled them to survive prairie fires better than other trees.
The species name for bur oak, “macrocarpa,” translates as big seed, and refers to the size of its acorns, which can be two inches long. The “bur” in the common name refers to another characteristic of the acorns, their heavily fringed caps, which reminded people of chestnut burs.
In one of my favorite tree books, twentieth-century botanist and writer Donald Culross Peattie cites studies suggesting the root system of a bur oak mirrors its above-ground growth in its mass and extent. If that’s so, the parking lots near my tree are already encroaching on its roots. But I know it has friends, too; someone from Facilities & Services kept it well-watered through the drought this summer. Similar consideration for this natural treasure will be important as construction to bring the Natural History Building up to date begins.
