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Field & Street



For a long time the official state tree of Illinois was "the native oak." Purists have argued that there is no such tree, that we have many native oaks, and that if our state is going to honor one we ought to designate it properly by both genus and species. Realists have responded that getting the genus right is about as much as we can expect from the Illinois legislature.

Not long ago the legislature managed to get definite on the question by specifying the white oak, Quercus alba, as the true Illinois state tree. It's a good choice. White oaks are common throughout the state, and the species is the largest of our native oaks. Record heights are in the neighborhood of 30 meters--about 100 feet in American.

My own preference would be the burr oak, since this is the most common tree in the upland savannas that were once such a distinctive feature of the Illinois landscape. Burr oak, with its thick bark, is the most fireproof of our local oaks, a trait that gives it a competitive edge.

Both burr and white oaks are part of the white oak group, a cluster of closely related species that can be easily identified by the rounded lobes of their leaves. Leaves on trees of the black oak group have sharply pointed lobes.

All oaks belong to the genus Quercus, and all show a strong tendency to hybridize, making precise identification difficult. Through the years, books on the flora of Chicago have differed on just how many kinds of oaks we have here. The latest edition of Swink and Wilhelm's Plants of the Chicago Region lists nine full species and three hybrids.

Lately I have been leaning toward the idea that oaks are the basis of civilization as we know it. In part this thought arose from the experience of living in Seattle for a year. The Pacific Northwest has only one native oak, and the region is also very thin in the civilization department. Coincidence? I doubt it.

As partial proof of the intimate connection between oaks and civilization, consider the fact that we could use a tin pot to brew up some slop and drink it to the point of intoxication. But getting plastered in an elegant and civilized way is almost impossible without using oak. Oak barrels are absolutely essential to the creation of Chateau Latour, Nuits-St.-Georges, Maker's Mark, and grande fine champagne.

The excellence of oak--and particularly the wood of the white oak group--as a material for cooperage stems from the presence of tyloses in the conducting tissues of the wood. Tyloses are cells that scale off the walls of the vascular tubes, blocking them and effectively waterproofing the wood. Thanks to the tyloses, you can store cognac in an oak barrel for 20 years or more without losing a drop.

Tannic acid helps with the flavoring. Oak trees produce this acid--also called tannin--in substantial amounts. We have traditionally extracted it for tanning leather. It is bitter, astringent, and, in large doses, poisonous. But in small amounts it can add interest to the flavor of aged spirits. Tannic acid is also present in coffee beans. It takes temperatures in the 90 to 100 degree Celsius range to dissolve it, which is why coffee made with very hot water tastes like it has been strained through a shoe.

Tannic acid is a very effective fungicide. It is the main reason why oak is so durable and resistant to decay.

Acorns also contain tannin. Indians in California, for whom acorns were a staple food, ground the nuts into flour and then had to put the flour through an elaborate leaching process to make it palatable. Acorns of the white oak group are supposedly sweeter, and some sources say that burr oak acorns that have been through a frost can be ground, baked, and eaten without any leaching.

Of course any account of oaks and civilization could not leave out the cork oak, Quercus suber, the tree whose bark protects fine wines after they have been taken from the barrel and put into bottles. Bark is first stripped from cork oak trees at about age 20. Regeneration is rapid, and further stripping can be done every eight to ten years for the life of the tree. The bark is boiled, scraped, and dried, then cut into appropriate shapes.

Cork oak is native to areas near the western Mediterranean in both Europe and North Africa. These are places where summer drought is the usual condition, and it is a reasonable guess that the thick bark served mainly as fire protection. I wonder if anyone has ever tried to make bottle stoppers from burr oak bark?

French oak from species other than Quercus suber is the favored barrel wood of wine makers all over the world. Even California wine makers prefer imported wood over their abundant local oak.

About 20 percent of France is still covered with forest, and about 25 percent of that is oak woods. The French have been managing their oak woods since about 1000 AD. They use a coppice system that involves making partial cuts that leave scattered trees to serve as seed sources. Oak stumps produce many sprouts that grow into trees, but trees grown from sprouts tend to develop heart rot at an earlier age than trees grown from acorns. So the French system alternates generations. After a cut the relatively fast-growing sprouts provide a new crop in a relatively short time. Then the slower-growing trees produced by acorns become large enough to cut. Since this system has been successful in maintaining both the woods and a continuing yield of timber for about 1,000 years, it seems reasonable to believe that the French are on to something.

The ability of oaks to sprout from stumps or from the roots themselves played an important role in sustaining the genus in fire-prone areas such as the midwest. In Vegetation of Wisconsin John Curtis suggested that once oaks had become established in an area, fire could not remove them. Oak grubs--which is to say the root systems--could survive the mightiest fire and send up new sprouts the following spring.

The biggest, oldest oaks in the Chicago area almost all began growing at roughly the same time, about 1830. This is the time when settlers began to protect the land hereabouts from fire, so the sprouts produced in that decade were not incinerated. With well-established root systems to support them, the sprouts grew rapidly, and lands that were considered prairie in 1830 became oak woods in a very short time.

When glaciers covered Chicago the oaks retreated far to the south, but when the ice left the oaks started coming back. The speed of their northward advance, reconstructed from fossilized pollen and other evidence, averaged 350 meters or less per year.

Oaks are not the sorts of trees that can easily pioneer in new ground. Cottonwoods, which produce millions of very tiny seeds that can be blown miles by even a moderate breeze, are ideal for that sort of role. It would take a hurricane to blow an acorn any distance at all, so how did the oaks manage their inexorable march from the gulf coast to the midwest?

The answer may well be blue jays. We know that blue jays cache acorns, and that they often don't return to eat what they have cached. And that they may carry the nuts for up to a mile before caching them.

So upon the wings of blue jays the oaks advanced into the midwest. Here they encountered the civilization of the Native Americans. And here was created one of the world's many symbioses between humans and oaks.

Our attitudes toward oak trees are an interesting piece of social/scientific history. Until recently scientists treated our oaks as just another tree of the forest, like maples and basswoods. Then prairie restoration began, and oaks assumed a somewhat villainous role. They were trees, and invading trees destroyed prairies by covering their sun-loving plants with shade.

But as prairie-restoration work proceeded, it became obvious that oaks belonged in re-creations of our native landscape. They were not just another tree in the forest, and they certainly weren't villains. They were, it seems, a major part of the landscape, dominants in a biome that ranged from treeless prairie to prairie with a few scattered oaks to open oak groves to true oak woodlands. Restoring the presettlement landscape meant restoring oaks as well as northern dropseed grass or lead plant.

Then we took our thinking a step further. Why were all these oaks here? We knew that fire favors oaks. That it drives out maples and basswoods and other fire-sensitive competitors. And we knew from early travelers and from tribal traditions that the native peoples deliberately set fires. And anyone who cared to look could see that tribes are still using fire as a deliberate management tool on reservation land.

We also know that oak woods are very productive when it comes to game animals. Deer, turkey, and quail are all very fond of acorns, and the open character of an oak woods favors these important game animals. And we know that contemporary Native Americans measure the value of an oak woods by the number of game animals it can support--just as medieval Frenchmen calculated the worth of a woods by the number of pigs it could feed.

But it took us a long time to make the logical inference: that the prairie/savanna landscape of Illinois was to a considerable extent a human creation. Its ecosystems had been continuously shaped by human intervention, perhaps for as long as people had existed in this place.

This is not a comfortable idea for many Americans. We like to imagine America as an empty continent, a primeval wilderness that we shaped into a home for ourselves. If the place was empty, then we don't have to think about what we did to the people who lived here. And if we do think about them, it is much more comforting to imagine them as ignorant savages than as sophisticated ecologists who knew centuries ago things we are only now beginning to learn.

But if we examine this idea it is full of hope for our expanding efforts to restore our native plant and animal communities. After all, if humans could shape this landscape once, perhaps we can do it again.

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