by Joe Neumann

McMahon Woods is part of the Cook County Forest Preserve District's massive Palos preserve system that, in the aggregate, totals 14,000 acres. McMahon (rhymes with McPlan) itself is a mile long and a half mile wide. Even with a baseball diamond and a large model airplane field, 230 acres are left for wild nature.

As the new volunteer steward of this site, I have been entrusted with caring for the nature here. The District's Land Management staff will supervise my efforts but with 55,000 acres of natural lands to oversee, they will delegate much of the day-to-day management of the site to me. I, more than anyone else, will be the expert on McMahon.

I have been preparing to become a steward since 1990 and to become the steward of McMahon since 1997. Classes and conferences help, but mainly I have learned ecological restoration in the field. Weekend restoration sessions occur at preserves throughout the Chicago region. Volunteers and staff collect and scatter the seeds of native plants. They remove aggressive invasives like European buckthorn, a shrub that smothers all nearby plants.

A steward needs to do more than recognize restoration tasks. He or she needs to prioritize these tasks. A steward needs a sense of the habitat individual species require, an ability to assess the quality of native remnants, and a feeling for the larger landscape. "We need to make a map of McMahon's vegetative communities," District ecologist Steve Thomas tells me. Steve will examine Global Positioning Satellite (GPS) data. I will provide details that can only come from repeatedly walking McMahon. In the end, we will tour the site together.

The first feature that strikes you about McMahon is its thickets. These dense thickets are packed with European buckthorn and an aggressive viburnum shrub. In the site's interior lies a stand of old oaks, a tiny pocket of prairie and an unusual wetland. While a typical wetland is a basin, this one is narrow and long — a third of a mile long. And it is not in the lowest position in the landscape. The land to the south immediately drops off five feet. The secret of this wetland is that its water seeps down underground from the high ground to the north. It is called a fen.

This wetland is not alone in its elongated shape. This entire site is composed of strips that step upward to the northeast. The old oaks occupy a step composed of pure sand. This orderly landscape and its soils are completely different from the irregular topography and compact clay that dominate most of the Palos area. The explanation is as subtle as the difference between ice and water.

Palos's clay moraines were dumped by the glaciers. McMahon was created after the glaciers melted. Lake Chicago, the precursor of Lake Michigan, filled the entire area now occupied by Chicago and its nearby suburbs. A massive drainage river carved out the mile-wide Sag Valley that cuts across the length of Palos. The McMahon landscape began to form at the mouth of the drainage. The water flow created a sand bar. The series of terraces that step down as you walk southwest into the site correspond to various water levels. When European settlers arrived, the Sag Valley was a massive marsh. McMahon was the slope looking down on that marsh. Today the Sag Channel cuts through the area.

August 1821. Government surveyor John Walls and his crew were walking mile long lines through the rugged terrain of Palos. Settlers were eager to buy the land the Indians were vacating. If you ever wondered who laid down the outline for our modern grid of main streets, these surveyors are the people. With the precision of surveyors, they recorded where the land along their line was "swamp," "prairie," and "timber." After their survey of a six square mile township was complete, a map was made. The section containing the future McMahon Woods shows a slice of prairie wedged between timber to the northeast and marsh to the southwest. The marsh, Walls wrote, was "nearly inescapable."

April 16, 1949 was a beautiful day. I know this because I am looking right down into it from an aerial photograph. Captured in this photo is not McMahon Woods but the McMahon homestead. The windows of the farmhouse stare out blankly. The modern day model airplane field was a farm field then. Except for a single woodlot, the site was open grassland from end to end. The trees of the woodlot show in the photo as dark trunks and scraggly boughs. The leaves had not emerged yet. A dozen dark dashes mill about nearby — cattle.

This 1949 aerial photo shows what is now McMahon Woods, then a farm with row crops, grazing land, and one open savanna grove just to the left of the farmstead at bottom right.

1999 and beyond. Steve and I walk the sand ridge. Steve shows me a dune; a wind-blown sand area. I show him a section where the state threatened savanna blazing star grows. We talk about the role fire played in shaping this site. The southwest-facing slope is warmed by the sun and dried by the prevailing west wind. The presettlement fires of the Indians burned hot here. Lots of work will be required to restore this ridge. The ground cover is dominated by European garlic mustard.

We step off the sandy oak ridge and wind around through the brush until we reach the prairie pocket. A dozen native species huddle in this 50 foot patch. One species, European buckthorn, surrounds them. The prescription for reviving the prairie is this: cut buckthorn, scatter seed, and burn.

At the edge of this pocket the ground drops off again. Water seeps from the slope. As we walk west, weaving between more brush, other wet pockets appear until finally the full fen opens before us with its host of sopping sedge clumps. A brush vise chokes this wetland. To the north the former prairie is thick with brush. This thicket shades the fen edge and siphons off water.

The negative effects of weedy woodies on the fen are even more pronounced along the fen's south edge. Here a colony of box elder trees has occupied the land drained when the canal replaced the Sag Marsh. The shade cast by these trees allows only a meager ground cover to grow beneath them. Under these conditions massive gullies have developed that snake out into the fen. Steve pushes at one of the box elders that overhang a deep gully. He approves my proposal that saplings be removed from this area for erosion control. The rarest of the rare insects that inhabit the fen is the federally endangered Hines emerald dragonfly. To survive, it requires rivulets of fresh fen water, not gullies. Aiding this fen will be my first priority.

The fen sparkles with the colors, sounds, and motion of birds, butterflies, flowers, and bees. But the rich native flora and fauna of this community are shrunken to a tiny fraction of their former size. When an ecological community gets too small, its species are gradually lost. You look to the wall of brush strangling tighter and tighter. You remember sites where you've seen restoration reverse this tragedy. Then your eyes alight on the gullies cutting like protruding ribs across the fen. You have to help.

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