[TEXT ARCHIVE WEB-PUBLISHED MAY 2001.
ORIGINAL PRINT PUBLICATION DATE: FALL 1997.]

Rebirth of the Oak Woods

The Story of the near-loss — and ongoing rescue — of a vital link in this region's chain of existence

By Sheryl De Vore

Americans agonize over the slash-and-burn destruction of the tropical rainforests and the clear cuts of old growth stands. We mourned the virtual extinction of the tallgrass prairies — now fields of corn and soybeans — and we tried to save what’s left. But when the historic oak savannas and woodlands of the Chicago Wilderness region began to disappear, no one noticed.

That’s because this was a much more subtle loss, one not nearly as recognizable as the destruction of rainforests and prairies. It was easy to overlook this change because it mostly involved growth rather than removal. Due to human practices, such as suppressing fires and bringing in new invasive plants, the once-open oak groves developed into overgrown thickets deprived of sunlight. As a result, they began losing their vast diversity of plants and animals. We thought the woods were just becoming woodier, a natural progression, perhaps. But we were wrong.

In fact, this progression from open woods to what appeared to be denser forests was an artificial one, threatening to degrade the natural landscapes to a point of no return. Luckily, scientists and land managers have discovered what’s really happening in our oak woodlands and how we can protect them.

The Post-Glacial Landscape
Midwesterners have heard stories of the first European settlers wading through grasses taller than a horse and marveling at the vast sea of prairies in Illinois and Indiana. But these settlers encountered other majestic sights. Wild turkeys gobbling. Red-headed woodpeckers flashing deep black and chalky white wings while excavating holes in oaks and hickories. Great crested flycatchers singing "Wheep" across the open woods. Blankets of white trillium, wild geraniums, and Jack-in-the-pulpits on the forest floor in spring. The soft pink flower clusters of six-foot-tall Joe-Pye weed blending with brilliant yellow sunflowers in summer. These were what we now call the oak woodlands and savannas.

Though the prairie appeared to be the prevailing natural community in northeastern Illinois in the 1820s, settlers also encountered these oak openings. Some called them "barrens" because the stands of widely scattered trees resembled the pine barrens of the east.

The author of a descriptive sketch of this particular landscape in 1837 wrote of oaks rising "from a grassy turf, seldom incumbered with brushwood, but not infrequently broken by jungles of rich and gaudy flowering plants, and of dwarf sumac. Among the oak openings you find some of the most lovely landscapes... here trees grouped or standing single, and there arranged in long avenues, as though by human hands, with strips of open meadow in between."

Changes in the Land
What the early pioneers called oak openings or barrens, ecologists now designate as savanna or open woodland. In common language, the entire continuum from open savanna through the densest maples or buckthorn can be referred to generically as woods or forest. Like the prairies, oak woods evolved over millennia under the influence of fire, those occurring naturally and those set by Native Americans. Fire acted as a fertilizer and weed killer, just as it did for prairies.

When the settlers came, however, they stopped the Native American practice of setting periodic fires and suppressed the naturally occurring ones. Settlers also unwittingly brought with them some species that were not native to the area, such as certain honeysuckles. Some of these crowded out native plant species that had lived in harmony with other natives for thousands of years.

Oak savannas, it turns out, were particularly vulnerable to these disruptions. Savannas had the timber the settlers needed and, like the prairies, these savannas contained good, rich soil, making this region the most farmable land in the nation. Thus, in an evolutionary instant, most savannas were converted to cropland. Others became pasture land. Many farmers actually burned wooded pasture to improve the grass, but when cattle grazing stopped, for instance, when these parcels were bought by a conservation agency, such sites developed unnaturally into thorn thickets.

By the end of the 19th century, most of the savanna communities had been lost. The residents of these communities — Cooper’s hawks, Edwards hairstreak butterflies, hairy gray sedge, and yellowish gentian — were dying for lack of habitat. The resultant loss of biological diversity in these communities has meant fewer varieties of plants and animals, greater soil erosion, and less soothing places for humans to experience the kind of beauty only nature can provide.

Yet this is a story of the rediscovery and restoration of the remaining patches of these native communities — and of humble heroes working throughout the region to bring our oak savannas and woodlands back to health.

A Surprising Find
Healthy savannas had been lost from the landscape, and might have been forgotten altogether but for the work of Chicago-area ecologists. As it happened, a number of people reached the same conclusions — coming from different directions — at about the same time. Two of them, for instance, worked together in DuPage County. Wayne Lampa of the Forest Preserve District and Gerould Wilhelm, then of the Morton Arboretum, noticed that when they surveyed areas for ecological quality, they found high quality ratings in the prairies, in the wetlands, and in the ancient maple forests of the Indiana Dunes. But none of the region’s classic oak forests seemed comparable. They wondered why. When Lampa burned and cut brush in the oak woods at Waterfall Glen, however, the indicators of quality began to rise.

In a separate instance, the restoration of prairies led to the discovery of oak savannas. When Stephen Packard, a conservation biologist with The Nature Conservancy, began prairie restoration work in the late 1970s in small, flowery clearings in degraded thickets, he found that certain areas were not responding as other brushy prairies had. He also noted species he had never seen before, such as the savanna blazing star. Packard, Lampa, Wilhelm, and others gradually determined that these sites were not, in fact, true prairie communities but were instead the remnants of rare, ancient oak savannas.

More importantly, they found that such areas could revive — given the chance. So something happened on the way to restoring prairies: we began to rediscover the savannas and woods and all their nuances.

Fire, An Essential Element
Scientists and land managers now recognize that savannas and woodlands need occasional fires to stay healthy. Thus, throughout the region, they have been reintroducing fires as a natural process in the form of carefully controlled burns. "Everything burned for thousands of years in Lake County," says Ken Klick, a Lake County Forest Preserve District biologist. "There’s been a long record of fires here."

Studies have shown that oaks and hickories in the region are not regenerating because their seedlings cannot tolerate the excessive shade that develops in the absence of fire. Aggressive native species such as box elder and sugar maple, however, thrive in this shady environment, able to grow quickly and dominate the forests, while the oaks die. Compared with 35 years ago, Illinois forests now contain 41 percent more maples and 14 percent fewer oaks, according to data from the Illinois Natural History Survey.

"In floodplain forests along the Des Plaines River in Lake County where there are shagbark hickories, white oaks, bur oaks, and swamp white oaks, there’s no reproduction of the oaks and hickories," says Klick. "That’s because the understory is dominated by sugar maples." Thus, when a mature oak dies these days, no seedling beneath can take its place. "To control the sugar maples as well as some ashes and cherries and the buckthorn, we need fire." Those who love the brilliant autumn colors of sugar maples need not worry, Klick adds. There are still thousands of maples, both mature trees and seedlings; the maples will never all go away. In fact, Klick says, fire in the form of prescribed burns by District crews at Ryerson Conservation Area in Lake County is helping to restore the balance between oak and maple populations.

Clearing Brush, The Challenge of Invasives
Burning, however, is not always the first step in restoring areas. In degraded oak savannas, for instance, "brushy understory is often dense to the point that little if any grassy vegetation exists," says John N. Maloneya, an oak savanna researcher in southern Wisconsin.

"And the grassy herbaceous material is what is needed to create the right kind of fuel for a proper burn," Maloneya explains. So clearing away certain underbrush species, such as tartarian honeysuckle or European buckthorn, both native and non-native, is warranted. Then, as more sunlight reaches the forest floor, it triggers the growth of grassy vegetation and fire can be re-introduced.

Buckthorn was probably introduced by well-meaning landscapers for use as an ornamental hedge. It’s called an invasive species because it has so quickly taken hold — able to grow and thrive in the shade — unlike oaks which need ample sunlight to stimulate growth. Moreover, birds and deer eat its berries and deposit the seeds, thus contributing to its rapid spread. What does an area look like when buckthorn takes over? Pick a woods where it’s happened and you’ll see such a dense thicket that the forest floor consists of little more than bare soil, unable to support other plant life. Rain then gradually washes the topsoil away, taking nutrients and the seed bank with it. Soil erosion, in fact, is a serious by-product of the buckthorn invasion.

At Old School Forest Preserve in Lake County, workers recently cleared a 50-acre oak forest of buckthorn and honeysuckle. "The measures appear quite drastic when you see a freshly cleared area," says Klick. "But in the end, it’s a much richer habitat. People need to realize that restoring health to natural communities takes time. Forests don’t seem to heal as quickly as prairies. There has been a lot of soil loss with no vegetation to hold it in place. The canopy has been closed for 80 years or more and there’s still a dense canopy," he says, "so it might be difficult to stimulate the seed bank." Sometimes crews plant seeds to help the revival.

Garlic mustard, a low-growing herb, is another alien species that spreads swiftly in degraded areas outcompeting native plants. In spring, teams of volunteers comb the area’s woodlands pulling garlic mustard before it sets seed, to prevent an even bigger crop from sprouting the next year.

More to Learn
Much remains to be learned about the effects of restoration and various land management techniques. Some birders, for example, became upset when the Cook County Forest Preserve District cut buckthorn at a popular birding site. Clearing the dense layers of buckthorn removed habitat for blue-winged warblers, an avian species that requires thickets and brushy overgrown fields for nesting.

Land managers acknowledge the delicate balance they seek to achieve. If such areas were just left alone, Ken Klick says, we’d lose both the shrubland and the open oak woods, both important bird habitats.

"The main goal of restoration is to maximize the biological diversity of plants and animals," says veteran ecologist Wayne Lampa who helped to develop a management plan for natural areas in DuPage County and who has worked to restore degraded areas for many years. At Waterfall Glen, for example, where 25 acres have been restored, researchers have recorded an increase in butterfly and wildflower species, as well as "a dramatic increase in breeding bird species," Lampa says. "Before we burned, there were just a few woodpeckers and maybe a few wood thrushes. But now, we find great crested flycatchers and Cooper’s hawks. The place just came alive with birds." Twenty new nesting bird species have been observed there since the restoration, he says.

"Ample sunlight is the key," says Lampa. In fact, light is so crucial to the regeneration of woodland communities that Lampa, through the Conservation Research Institute in Naperville where he now works, is studying the relationships between tree species, flora on the forest floor, and the availability of light in several high-quality woodlands in DuPage County. Volunteers and forest preserve staff are learning how to use light meters to survey plant life in areas with various light readings. "You can use the meter readings as measuring sticks," Lampa explains, "to learn how much light is needed for certain species to thrive."

"At Indiana Dunes National Lakeshore, we’re looking at black oak sand savannas and how canopy cover affects biodiversity," says Noel Pavlovic, a plant ecologist with the Lake Michigan Ecological Research Station in Indiana. "We’re studying plants, birds, beetles, and butterflies, and we’re doing the work at open- and closed-canopy sites and those in between," he says. This means studying areas where the land is mostly covered with trees — the closed-canopy sites — as well as areas where the land is only 10 percent covered with trees.

Research has shown that the male of the endangered Karner blue butterfly prefers open sunny sites while the females use a broader range of canopy covers. "To preserve habitat for them, you have to have a fairly heterogeneous understory," says Pavlovic, which means a mixture of healthy woodland and forest communities. But even that’s not the whole story. The Karner blue butterfly overwinters as eggs in the leaf litter. "So when you burn an area of their habitat," Pavlovic says, "you potentially kill the eggs. However, if you vary the fire intensities and burn in patches instead of the whole area at once, then the eggs will survive."

Scientists are retrieving new pieces of the complex puzzle of our oak woods with each new discovery they make. The collaboration among scientists, land managers, and thousands of volunteers engaged in the effort to restore these natural areas is a story of inspiration and hope. As birders, botanists, nature-lovers, and prairie and woodland specialists work together, sharing their knowledge and expertise, they can salvage these rare and beautiful communities — our ancient oak woodlands.

Sheryl De Vore is an award-winning environmental journalist for Pioneer Press Newspapers, the Chief Editor of Meadowlark, A Journal of Illinois Birds, and Assistant Editor of Chicago Wilderness. She recently won the prestigious national Harry E. Schlenz Medal for excellence in environmental education and journalism.