Environmental Almanac: A view of the oldest living thing on campus

One of the perks of my position with the School of Earth, Society and Environment at the University of Illinois is an office in the Natural History Building on Green Street. Unfortunately, we'll all be clearing out for a large-scale renovation to begin within the next year. But for the time being, the view out my window includes a magnificent bur oak, a tree I used to cross campus just to check on now and then.

How big is "magnificent"? I recently measured my tree at 13 feet, 7 inches 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 co-worker Lana Holben, they span 114 feet at their widest point.

A couple of years ago, I attended a 200-year birthday party for my tree, orchestrated by Bruce Hannon, Jubilee Emeritus Professor of Geography and Geographic Information Science, whose conservation efforts have produced so much good in East Central Illinois over the years. When, after the celebration, photographs uncovered by UI archivists called into question that age for the tree, new borings were used to recalculate it in 2011.

That calculation, by Gene Himelick, professor emeritus of plant pathology, gave an age of between 183 and 188.

As bur oaks go, an age of 180-some years is no record —they may live to be 300 or 400 — 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.

Of more interest to me, migrating songbirds flock to it, attracted by the plentiful 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 2 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, "A Natural History of Trees: of Eastern and Central North America," 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 and 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.

Environmental Almanac is a service of the University of Illinois School of Earth, Society and Environment, where Rob Kanter is communications coordinator. Environmental Almanac can be heard on WILL-AM 580 at 4:45 and 6:45 p.m. on Thursdays.

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