The Way it Was
Presettlement Vegetation Patterns

By Karen Furnweger

The magnificent bur oak stands three hundred feet from a busy intersection in western Cook County. From its height and girth, one might deduce that this tree has witnessed several centuries' worth of changes in the landscape. But, according to Marlin Bowles of the Morton Arboretum, this tree could have served as a different kind of witness.

Between the 1820s and 1840s, surveying teams hired by the U.S. General Land Office measured northeastern Illinois into townships of 36 one-square-mile sections. A deputy surveyor systematically recorded a legal and physical description of the terrain in each section in advance of European immigrants who would purchase, settle on and farm the rich Illinois soil. To help identify these sections, the surveyor selected up to four "witness" trees closest to where section lines crossed, and an axman blazed the trees and stamped the coordinates of the intersection into the exposed wood.

The trees inscribed, the surveyor and his team trudged on. As he walked, the surveyor also made notes about the vegetation — prairie, timber, marsh, "barrens" — which would be of vital importance to settlers looking for productive farmland, building materials, and fuel.

The surveys were carried out across Illinois and the rest of the new territories. This Public Land Survey (PLS) is a nineteenth-century databank of hand-drawn maps and hand-written notebooks on which everything from property descriptions to street maps are based.

For plant conservation biologists like Bowles, the maps and first-hand descriptions of the landscape — preserved on microfilm — are also a gold mine of information on presettlement vegetation. Bowles has long been fascinated with the way local grasslands and forests "have been pushing and chewing at each other for thousands of years." In the early 1990s, with grants from the Forest Preserve District of DuPage County and the Chicago Wilderness consortium, Bowles and geographic information system (GIS) specialist Jenny McBride began mining the PLS documents covering DuPage County. They have since done the same for Will and Cook Counties.

"The most important piece of information the Public Land Survey tells us," says Bowles, "is landscape pattern: how timber and prairie were patterned across the landscape." The surveyors' field notes painted a precise picture. Each mile-long section line was measured with a 66-foot iron or brass chain consisting of 100 links, each 7.92 inches long. Eighty chain lengths equaled a mile. Using the chain and links as units of linear measure, surveyors had to record where the vegetation changed along the section line. In addition, at every half-mile, they had to rate the quality of the land for agricultural use and identify any tree species and undergrowth by common name.

On June 3, 1840, deputy surveyor William L. D. Ewing walked west on a section line in Township 38 North, Range 9 E of the 3rd Principal Meridian (part of DuPage County) and wrote:

At forty chains and seven links, he set a wooden quarter-section corner post — marking the half-mile point on the section line — and noted the distance in links and direction from the post to two witness trees, a fourteen-inch-diameter elm and a six-inch-diameter aspen. At this point he also noted: "Land — 1st-rate soil & fit for cultivation. Timber — Burr oak, lynn [basswood], hickory, elm and aspen. Hazel & hickory & oak undergrowth."

 "I have the measurement along each section line where the vegetation type changed. This was a marsh," McBride says, pointing to a Cook County map in progress on her office wall. "The notes tell me at exactly what point this marsh started and stopped." She marks the marsh on a plastic overlay of the quad map, which is affixed to a digitizing drawing board. When she has transferred all the data from the PLS records, she traces the lines on her new map with a mouse to enter it into her computer.

This savanna in Cook County's Palos forest preserves was restored to good health with guidance from the 1830s "Public Land Survey." Photo by Mike MacDonald.

Shuttling between technologies nearly two centuries apart has been an accomplishment for McBride. Just as she taught herself to use the computer software, she trained herself to decipher the handwriting in the field notes, which she reads from microfilm.

"Most of the notes I've looked at were from surveys between 1821 and 1848. They were recopied around 1850 or 1860, but they're still in this fancy old script with curlicues and the double s that looks like an f," she says. The penmanship varies from notebook to notebook, as does the depth of detail in the descriptions. "Every so often, I'll get something funny. One surveyor working in a marshy area in Cook County called it 'a complete quagmire' that wasn't fit for anything but a muskrat."

Bowles gives the surveyors credit for their overall competency in identifying trees and community types in all seasons. While no certification existed at the time, surveying was a respectable vocation for educated gentlemen. (Ewing was a land speculator who served briefly as Illinois governor and twice won the speakership of the Illinois House over Abraham Lincoln.)

The surveyors also recorded evidence of fires — one witness tree was a charred stump on a second round of surveys — and they probably recognized the role of fire in the pattern of prairie and timber.

When a warmer, drier climate set in about seven thousand years ago, prairies began replacing the oak-pine forests that dominated the post-glacial Chicago Wilderness landscape. With the prairies came great fires, naturally sparked by lightning, but also deliberately set by native Americans, who definitely influenced "presettlement" vegetation. These conflagrations also swept through wooded areas, eating up soft, thin-skinned trees like maples but barely scorching the thick, corky bark of oaks. By keeping open the woody edges — the savanna, or "scattering timber" on surveyors' maps — the midwestern prairie was gradually making inroads into the eastern forests. When settlers suppressed the fires, maples and other fire-sensitive trees, including nonnative species, slowly obliterated the oak woods, the savannas, and the grasslands.

McBride's witness tree map shows high tree densities and fire-sensitive species such as sugar maple, basswood, and ash on the eastern side of rivers and other natural barriers to the eastward-moving prairie fires. Prairies, barrens, and savannas, occupied mainly by fire-tolerant white, bur, and red oaks, grew on the western, windward side of landscape firebreaks.

These patterns reinforce existing knowledge about presettlement vegetation, but from the old notes, McBride injected new precision and exquisite detail into the picture. And there was "one wonderful surprise," says Bowles.

"What Jenny found in the surveyors' notes for DuPage County was that the majority of the section lines in timber had woody undergrowth. About 50 percent of the savanna areas also had woody undergrowth," he says.

"Until we started working on these Public Land Survey notes, the general concept of our native presettlement oak woodlands was that there was no undergrowth," Bowles says. "Into the mid-1990s, restoration ecologists and land managers thought that if they were going to restore something to presettlement structure, it would be a two-tiered community: oaks and ground-layer vegetation. So this helped reshape our concepts about management and restoration."

The notes revealed that American hazelnut was the most abundant woody understory species, occurring on 90 percent of the timber and savanna section lines. "This information tells us that if we want to try to restore these communities, we've got to have American hazelnut," Bowles says.

From McBride's maps, Bowles calculated species abundance, tree density at section corners and the relative size of trees in a given stand. From this, he ranked the relative "importance value" of each tree species in timber, savanna, barrens, and prairie. White oak dominated, except in the barrens, where stunted red oaks and hickories persisted more successfully through repeated fires. In the other communities, bur oak was the second most abundant tree, although in varying ratios to white oak.

Bowles and McBride's studies reinforced and clarified the critical role of fire in shaping the entire landscape. "We found that fire probably structured timber throughout the landscape except in the very most fire-protected pockets, such as the east sides of major rivers," Bowles says. "But even there, oaks were present, and it's most likely that during drought years, fire swept through those areas."

But restoring natural areas to match the surveys is not necessarily the goal — or even a possibility. "It's impossible to manage for presettlement conditions," says Marcy DeMauro, superintendent of planning and development for the Forest Preserve District of Will County. "The landscape is extremely modified."

Still, she says, "Most of the properties we own are large sites, so we look at restoring them on a landscape scale." Raccoon Grove, for example, is a true prairie grove — six hundred acres of savanna and forest surrounded by prairie. "We try to manage for the historically natural processes that were operating at a landscape scale. Marlin's work gives us a good sense of that."

From Bowles and McBride's findings, DeMauro realized that the prairie being managed at Hickory Creek was really barrens. "We were having a lot of trouble with shrub growth, so we took a step back to figure out what was going on. Marlin's work suggested we had a barrens habitat here. All the species were there, along with soils, topography. and general landscape." Management efforts shifted from shrub removal and prairie-scale burns to hazelnut reintroduction and lighter burns.

"It's not the only piece of information we rely on when we make a decision on what we're going to do with a particular property," says DeMauro, "but I couldn't imagine doing management planning without it."

Bowles acknowledges that it's difficult to re-create sustainable presettlement plant communities in a heavily fragmented landscape. "No longer do we have what I call an infinite landscape, where you start a fire here and it burns for fifteen miles until it hits a firebreak. Now, it has to cross three interstates and four shopping centers to get from stand A to stand B — and, of course, it doesn't.

Sometimes, Bowles says, you get lucky, and the presettlement vegetation pattern is right in front of you, alive and pretty well. "Wolf Road Prairie is the one place where you can look at a line drawn by the Public Land Survey people in the 1820s and then go there and still see the same prairie-timber boundary that they saw. That gives me goose bumps."

Into the 1960s, local kids unknowingly perpetuated the management practices of the Potawatomi by periodically torching the prairie. The fires kept grassland and woodland in edgy equilibrium, with the lightly wooded oak savanna at the center of the turf war. But since the landscape-scale fires stopped, the savanna has started filling in. Experiments with manipulating the canopy by trimming tree limbs or removing certain trees could help redefine the slipping savanna, Bowles says.

On a visit to the prairie, Bowles stands on a triangle of grass at Thirty-first Street and Wolf Road and points to one of several ancient bur oaks. Is this a witness tree?

There are two ways to prove it, he says. The first is to stand in the middle of the intersection, measure the exact distance to the tree and take a compass reading. If the distance and compass reading match exactly with those taken by surveyors in the 1820s, that would be "pretty good, but still circumstantial" evidence that the massive oak is a witness tree. He and McBride did just that. "The tree was pretty close, but it wasn't exact. We don't know how good survey instruments were in those days." He does know that the surveyors weren't dodging cars as they worked. Bowles would like to measure again some time, preferably early on a Sunday morning.

"These communities are bits of our natural heritage that we have inherited from the past. If we want them to persist, we've got to replicate the ecological processes they were living with in the past," Bowles states. "It's never going to be quite the same, but the research gives us a framework for trying to restore the processes that allow us to take care of them now and into the future."