Shedding Light on
the North Shore Ravines

by Karen Zaworski

Look at a close-up map of Chicago’s Lake Michigan shoreline, and there they are: little wrinkles and crinkles that spread, fingerlike, into the land, starting at Winnetka and running northward to Waukegan.

They are the ravines of Chicago’s North Shore — 30 to 38 of them, depending on how you count — and they’ve become the subject of intense interest in the Chicago Wilderness region.

Spurred on by the Lake Forest Garden Club, three organizations — Openlands, the Chicago Botanic Garden, and Lake Forest Open Lands Association — banded together this past April to host a symposium entitled Reclaiming Our Ravines. The audience — about 350 area home and business owners, park district and elected officials, scientists and engineers, landscapers and developers — overflowed the auditorium, some attendees having to watch on a television in another room. The excitement that day reflected the intensity of focus over the last few years — a wave of land purchases and restoration projects — to preserve the rare and unique Illinois bluff and ravine system.

How did the ravines form?

When Dr. Michael Chrzastowski, senior coastal geologist with the Illinois State Geological Survey, explains the geologic evolution of the area, he usually has to dispel several myths about the ravines. About 14,000 years ago, he says, the Lake Michigan lobe of the Laurentide Ice Sheet began to recede, leaving rings of glacial till called moraines (piles of clay, gravel, and sand) atop the bedrock. The Highland Park moraine, destined to become incised by the ravines, extended past our current lake’s boundaries and stood over 100 feet high. (This is the first myth: not all of the Chicago area is flat.)

About 10,000 years ago, the weight of the still-retreating ice pushed down on the land so much so that it opened a lower-than-lake-level exit to the north, through Canada’s Ottawa River. The result: Lake Michigan’s water level dropped an astounding 250 feet in a very short time, exposing the older lakebed for 20 miles, to the shores of the now much smaller lake, which geologists call Lake Chippewa. Rain and melting snow quickly developed channels on the exposed lakebed floor. (Also interesting, a forest formed on the lakebed; tree stumps found at the bottom of today’s lake date to 8,300 years ago.)

About 8,000 years ago, the lakebed streams’ headward erosion reached the Highland Park moraine. As streams touched the moraine, they washed out sand and gravel, cutting a V-shaped channel into the hill. Moraine erosion continued in two directions: run-off of rain and snow in streams from the top, plus “chewing” in from the bottom from the lakebed streams. And thus the ravines began to form. (Myth #2 says that glaciers formed the ravines; actually, glaciers formed the moraines, while streams formed the ravines.) The process was quick, lasting just 5,000 years, between 8,000 B.C. and 3,000 B.C. (This dispels Myth #3, which assumes that ravines are ol d— they’re actually quite young, geologically speaking.)

As the glaciers at the northern end of the lake continued to melt, their weight decreased, allowing the land to gradually rise again, which closed off the water exits to the north. (This rebound continues today. Land around Hudson Bay continues to rise one meter per century.) Lake levels rose again, and by about 3,000 B.C., Lake Michigan had refilled close to today’s levels. Waves then chewed away at the moraine (which once extended farther east), forming the bluffs that we see today.

Scoop up a handful of sand on a North Shore beach and you are holding the sand washed down from the moraine of our last ice age. Pick up a rock and you are holding a remnant of glacial till carried here from Canada. The ravines and bluffs tell the evolution of our shoreline — and link us to our geologic past.

What should a ravine look like?

Although no two ravines are alike, the natural state of a ravine should be open and light, and shot through with color. A woodland crest gives way to a sun-dappled, gentle slope, covered with shrubs and woodland plants, and interspersed with seeps, where wetland plants and mosses grow. At the bottom, a seasonal stream leads to a beach community of plants at the mouth of the ravine, and the beach beyond.

Dr. Charles Shabica, president of Shabica & Associates, Inc. Sustainable Coastal Solutions, says healthy ravines can act as natural factories for removing carbon dioxide and pollutants from water and soil. But today our ravines are in trouble:

• Too much water is artificially directed into the ravines. Stormwater runoff from sewer systems, streets, driveways and downspouts, and too much impervious surface (concrete, asphalt) funnel water into the ravines in great torrents when it rains, accelerating erosion.
• Some ravines have been used as landfills. Fort Sheridan’s Wells Ravine (aka, Landfill #7) was the army dump for more than 100 years. It was capped in 2004.
• Nonnative trees, such as silver and Norway maples, buckthorn, and bush honeysuckle create a dense canopy that cuts off sunlight to native groundcover plants, leaving bare and easily eroded soil.
• Shade-tolerant invasive plants such as goutweed and garlic mustard crowd out the deep-rooted native species that have lived in the ravines for millennia.
• Yard waste thrown into ravines smothers the native plants and retains water.
• Currently the ravines contribute more than 10,000 tons of nitrogen and phosphorus-rich pollutants directly into Lake Michigan per year. In 2007, there were 371 beach closings on Illinois beaches.

Where these conditions prevail, heavily shaded ravines lose protective plant cover, resulting in steep and bare eroded areas, increased instability and “slump,” and fewer birds and animals.

What’s growing there?

The unusual terrain of a ravine harbors an unusual climate. Temperatures are typically 10 degrees cooler inside a ravine than on the bluffs or the beach, as lake breezes pour into the exitless ravines. Susanne Masi, manager of regional floristics at the Chicago Botanic Garden, explains that, despite degradation, significant pockets of native plants survive in both Bartlett and McCormick ravines. With the dramatic changes in topography, from crest to slope to seep to beach, “every few meters you’re in a different microsystem,” says Masi. Plants more typical of Wisconsin and Michigan are at home in the ravines’ cooler spots — notably paper birch (Betula papyrifera). Other rare finds include:

• Poke milkweed (Asclepias exaltata) — “only a few” — and blue lobelia (Lobelia siphilitica) in the floodplain of McCormick Ravine’s stream.
• Black-seeded rice grass (Oryzopsis racemosa) below the ravine crest, “which is wonderful,” says Masi, “because it’s a slope-holder that binds the soil. It’s a plant that has a lot of potential as a stabilizer in restorations.”
• Buffaloberry (Shepherdia canadensis), an attractive shrub with silvery-green leaves, on the bluff in Bartlett Ravine.
• Smooth blue aster (Aster laevis) at the top of the beach and American beach grass (Ammophila breviligulata), sea rocket (Cakile edentula), and seaside spurge (Chamaesyce polygonifolia) on the beach.
• And an unexpected surprise: mid-slope seeps where wetland sedge meadows have taken hold and skunk cabbage (Symplocarpus foetidus) can be found.

Masi especially appreciates the ravines’ understory trees. “The shrub layer is especially nice,” she explains. “In many of our woods the shrub layer isn’t strong — bush honeysuckle and buckthorn have replaced them — but I’ve seen beautiful shrubs like witch hazel, hazelnut, and three dogwood species, including pagoda dogwood (Cornus alternifolia) and round-leaf dogwood (Cornus rugosa), all on one walk.”

Together with volunteers from Plants of Concern and Lake Forest Open Lands Association, Masi is working to put a well-designed monitoring program into place. “The ravines are unique and special,” she says. “Any site that natural — a remnant of an original system — is worth preserving and restoring.”

Who’s working on what?

The symposium took place against a background of restoration work. Ownership and stewardship are complex issues in the ravines: ten towns, six townships, two counties, several park districts, the federal government, and even the United States Army Corps of Engineers all have authority over different parts of this narrow strip of land — plus, 70 percent of Lake County’s ravine property is privately owned. Still, in part because the ravines drain naturally into Lake Michigan, they affect everyone. Restoration work is already underway. A few highlights:

Turning a once-in-a-lifetime opportunity into a dramatic ravine turnaround, the Lake County Forest Preserve District continues to restore and develop the 250-plus acres of the Fort Sheridan Forest Preserve, land deeded to them after the United States Army’s closure of Fort Sheridan in 1993. Following an action plan developed with Conservation Design Forum, the district opened the 1.3-mile Lake Michigan Trail in 2006 (the first public access to that property since 1887) and restored the wooded Hutchinson Ravine. Now it’s turning its attention to erosion issues and habitat restoration in Janes Ravine.

With nearly ten acres of lake bluff habitat and twenty acres of ravine habitat in its four lakefront parks, the Park District of Highland Park has also begun restoration. At selected sites, Norway maple and black locust have been removed to open up the canopy, though some dead trees have been left as habitat for red-headed woodpeckers and the other 39 resident and 69 migratory species of documented birds. The district reintroduced fires to clear leaf litter and invasive plants, and hydro-seeding (a mix of water and native plant seeds) has returned native species to the bluffs. Huge amounts of buckthorn were removed from the beach at Rosewood Park — and here the first baby sand dunes are beginning to form.

Openlands has started restoration of the Bartlett Ravine, formerly part of Fort Sheridan. To some, the degraded ravine, with its layers of debris and asphalt road covering the former stream channel, would seem a poor candidate for restoration. Dr. Scudder Mackey, an environmental consultant with Habitat Solutions NA, describes Bartlett as “a ravine that’s no longer natural. There is no open or active ravine channel in the system, and no stream habitat. But,” he stresses, “the ravine’s slopes are very stable. And that means the potential for bio-systems.” Openlands has leapt at the task. Trees have been assessed and inventoried, invasive trees removed, and layers of debris, including chunks of concrete, have been hauled out. Despite degradation, five very rare species have been identified.

Because the upper section of Lake Forest’s McCormick Ravine was used as a dump, the lower section remained intact and is probably the best natural ravine in the area. In this fragile and beautiful place, education has taken root. Lake Forest Open Lands Association has put Lake Forest College students to work as citizen scientists, monitoring plant populations and water quality; high school classes clean up the beaches; scouts participate in garlic mustard pulls; third graders learn about the forces of nature. In the quiet, cool, and vegetated world at the bottom of McCormick, one gets the sense of what a healthy ravine feels like.