RESTORATION OF AN OAK SAVANNA IN THE
COOK COUNTY FOREST PRESERVES:
MANAGEMENT PRACTICES AND RESULTS
In River Forest, Illinois, a Chicago suburb ten miles west of the city, are two parcels of Cook County Forest Preserves District (CCFPD) property: The Grand Army of the Republic (GAR) and Thomas Jefferson (TJ) Woods. This land is part of the Thatcher Woods corridor along the DesPlaines River, and represents a cross section of the DesPlaines River valley within the Chicago Lake Plain Section of the Northeastern Morainal Natural Division of Illinois. The restoration site encompasses approximately 85 acres on the west side of the river. This area is comprised of flood plain forest and upland savanna above 625' elevation.
The upland savanna is being managed for pre-European settlement conditions by the Thatcher Woods Savanna Restoration Project (TWSRP), a local community organization operating within the Volunteer Stewardship Network. This area, besides being geologically unique, is ecologically unique in the Chicago region because it has never been plowed, grazed, or logged, and thus has retained much of its natural ecological character. Qualitatively, the preservation value of this area lies in the human experience of its natural character in the middle of a major metropolis.
Practices used to gradually restore the savanna consist primarily of clearing the understory of woody plants, both native and non-native, by cutting, girdling, and burning. The primary invasive woods are: basswood, maple, ash, and buckthorn. Removal was done to gradually introduce sunlight to the herbaceous ground cover.
After four years of monthly three-hour work days, results of clearing are readily observable. These results are expressed in qualitative terms as affirmative answers to four questions relating to the authors' subjective observations as stewards of the site.
Management practices of the Thatcher Woods Savanna Restoration Project (TWSRP) during the period June, 1990 to June, 1994, and results to date are described.
The subject restoration site is a mesic oak savanna of approximately 45 acres of upland area occurring above 625 feet elevation. This area is within two preserves owned by the Cook County Forest Preserves District (CCFPD), the Grand Army of the Republic (GAR) to the north of Washington Boulevard in River Forest, Illinois, and the Thomas Jefferson (TJ) Woods to the south. Along the western side of the site is approximately 40 acres of bottomland wet mesic forest that drops to an elevation of 610 feet to the DesPlaines River. The site is geologically unique in that it is a portion of the only section of the DesPlaines river valley in which the river flows over the sediment of the ancient lake plain formed by the Glenwood Stage of Glacial Lake Chicago. The site is ecologically unique in that it has never been plowed, grazed, or logged since its purchased from the federal government in 1887 by Ashbel Steele, the first permanent settler of River Forest. The site's history, natural character, topographical diversity, and plant life and the formation of the TWSRP are described in recent papers (Bowels and Radke 1992; Donahue et al.1993). Our poster identifies the site in three different perspectives as follows:
The TWSRP site was first identified as a remnant oak savanna by local naturalist Jim Hodapp who observed that an existing small oak opening located approximately in the center of the GAR area had an unusually dense and diverse herbaceous ground cover of native plants under a white and red oak canopy. It was speculated that this opening existed due to occasional fires that were spread from a fireplace in a trailside concrete shelter constructed adjacent to the opening by the CCFPD in the 1930s. The shelter had deteriorated over the years, and had become a gathering place for teen-agers to light a fire and drink beer, and subsequently leaving their empty bottles and hot embers.
Fire suppression on the other hand, is accountable for the dense understory of basswood, maples, and ash in most of the upland savanna. A plant inventory conducted of the entire 85 acre site which revealed a natural area of over still rich with 150 native species, including many specifically common to the savanna landscape. A complete species list (1992 inventory) is provided in Bowels and Radke (1992) and the savanna species are identified in Donahue et al. (1993). Based on the total number of native species, the Wilhelm Natural Area Rating Index (NARI) was calculated to be 66.3, indicating that the TWSRP site is an extremely rare area in the Chicago region.
The TWSRP was fortunate to have the previously described existing oak-opening as a benchmark for future restorations. The management objective for the site was to gradually open the 45 acre upland savanna under an existing canopy of red, white, and bur oaks. This objective also is supported by the prevalent tree species on the site, the surveyor's notes of the pre-European survey of 1821 and the present native species inventory. To this end, starting in June, 1990, the following management practices, not necessarily in chronological order, were put in place and continue today.
These management practices were carried out in monthly three-hour work-day activities during past four years. It must be emphasized that the objective is to gradually introduce more sunlight to the herbaceous ground cover. We can quantify richness of the TWSRP site using the NARI computation.
In this project, restoration efforts are viewed in purely subjective terms. Four questions were developed from the authors' experience working at the TWSRP site. The affirmative answers we give to these questions are the basis on which we assert that restoration is taking effect, but it is a long continuing process. The questions are:
Bowels, M. and T. Radke. 1992. Proposal for Dedication of Thatcher, Gar, and Jefferson Woods in Cook County Illinois as an Illinois Nature Preserve. The Morton Arboretum, Lisle, IL 60532.
Donahue, K., Guarino, J. and Guarino, V. 1993. Restoration of an oak savanna within an urban Area. Proceedings of the Midwest Oak Savanna Conference, Northeastern Illinois University, Chicago, IL. In press.