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1993 Proceedings of the Midwest Oak Savanna Conferences

Jean Guarino and Victor Guarino
Thatcher Woods Savanna Restoration Project 
1004 N. Oak Park Avenue
Oak Park, IL 60302
Tel: (708) 848-7175

Kathy Donahue
605 W. Madison - 4713-3
Chicago, IL 60661
Tel: (312) 902-3054 



Thatcher Woods is an oak savanna of exceptional quality. Located just 10 miles west of downtown Chicago along the Des Plaines River in the Forest Preserve District of Cook County (FPD), this 100 acre gem of mesic savanna and wet-mesic floodplain forest has a Natural Areas Rating Index (NARI) of 66.3. Close to 150 native plant species thrive in the midst of urbanization of all surrounding areas.

Discovered by local naturalist Jim Hodapp, Thatcher Woods is being restored by the Thatcher Woods Savanna Restoration Project (TWSRP), a community-based volunteer, ecological restoration group. The Project provides a lesson in urban restoration. Issues include construction of the Deep Tunnel Project on a portion of the site, litter, landscape debris, invasion of exotic plants, competition with recreationists, and safety. The Project has created a management plan to restore the site to pre-European settlement conditions, network with land management agencies and other restoration groups, and educate the public about our savanna and forest heritage. The site is presently being considered for Illinois Nature Preserve status.


INTRODUCTION  back to top

It's easy to overlook Thatcher Woods, the oak savanna nestled along the east bank of the Des Plaines River in River Forest, Illinois. For years, motorists driving down Washington Boulevard passed what appears to be dense woodlands and dismissed the area as "just another forest preserve."

Thatcher Woods is composed of two parcels owned by the Forest Preserve District of Cook County (FPD), the Grand Army of the Republic (G.A.R.) and Thomas Jefferson Woods. Together they contain such an unusually high diversity of native savanna plants that the area is considered one of the finest remnants of mesic oak savanna in the Midwest.

The north end of the site is bounded by the Northwestern Railroad tracks and the south end by Madison Street. A high school is on the southwest corner, and a cemetery at the southeast corner. The remaining borders are First Avenue on the west and Thatcher Avenue on the east. Washington Boulevard splits the area into G.A.R. Woods to the north and Thomas Jefferson Woods to the south. The total area is approximately 100 acres. 

The mesic oak savanna straddles the old Indian trail on the approximately 45 acre upland portion of the site. The wet mesic floodplain forest lies west of the trail on the Des Plaines River. A backwater in the Thomas Jefferson Woods forms a lagoon that serves as a refuge for migratory birds. The bottomland supports a variety of plant, animal, and bird species. Together they constitute another 40 to 45 acres. The backwater and bottomland lie at the southern end of Thatcher Woods, which extends another 1.5 miles north of the site to North Avenue along the river between Thatcher and First Avenues.

There are remnants of many oak savannas scattered throughout Illinois, the prairie state. What makes this savanna unique? First, the Thatcher Woods Savanna is one of a very few in Illinois that is located in the midst of a major metropolitan area (just 10 miles west of downtown Chicago). It is also unique because of the integration of wet forest and oak savanna. The good news is that it is readily accessible to local residents and the greater public to enjoy the profusion of native prairie and woodland plants and flowers. The bad news is the heavy toll development has exacted. 

Another factor that makes this oak savanna unusual is that a major portion of the land remained in the hands of a single family from the time it was purchased from the federal government in 1837 until a 55 acre tract was sold to the Forest Preserve District for $68,898.35 in 1917. Ashbel Steele, River Forest's first permanent settler and owner of the site, was not a farmer. He did not plow his land nor did he own cattle. Ashbel was a prosperous builder who constructed many of the early buildings in River Forest. Having cleared a homesite located approximately 200 feet south of where the Northwestern tracts are now and 100 feet west of Thatcher avenue for a house for his wife and nine children, he adopted a policy of benign neglect toward the rest of his homestead - a decision that allowed the area's natural ecosystem to remain intact for more than a century.

In 1989, local naturalist Jim Hodapp brought Thatcher Woods Savanna to the attention of a few area residents. He characterized the savanna as "an ecosystem poised on the verge of extinction." We believe our volunteer efforts over the past several years have been a turning point in restoring the site to its pre-European settlement state. 

Our volunteer group was organized in the spring of 1990. During our formative months we were fortunate to have the assistance of Ross Sweeny who, at that time, was a regional steward for the Volunteer Stewardship Network representing the North Branch Prairie Project. He guided us through these early days, providing tools and encouragement. Jean Guarino, a local author and history columnist, published several articles in the local papers calling attention to this jewel that existed in our community. She set up a telephone hotline and served as coordinator to enlist volunteers from the community. Subsequently, the Thatcher Woods Savanna Restoration Project (TWSRP) was formed. 

Today, business meetings are held the first Monday of each month in the Oak Park Village Hall. Work at the savanna site is conducted the Saturday following the first Monday of each month, from 9:00am to 12:00 noon.

Basic tools were initially purchased with financial support from the Garden Club of Oak Park and River Forest and later a $500 grant from First United Church of Oak Park. Today, we have a core of 20 workday volunteers and a mailing list of 32. Jean and Victor Guarino serve as stewards of the site. Dennis Nyberg is the science advisor. Jim Hodapp is an enthusiastic and knowledgeable guide for the Scout troops who have, from the early days, participated in our workdays. He also guides other groups who periodically request a tour and is a guide in our community outreach program. For example, in the summer of 1991, we brought a group of children from Rockwell Gardens, the Chicago Housing Authority project in Chicago, for a visit to Trailside Museum, a picnic, and a nature walk. We hope to repeat this activity.

PLANT LIFE  back to top

Thatcher Woods Savanna has a rich and diverse plant assemblage. To date, 37 tree species (33 native), 31 shrubs and woody vine species (28 native), 23 species of grasses and sedges (20 native), and 136 forbs (108 native) have been identified. This diversity can be quantified and related to the quality of the site as a natural area.

Wilhelm (1979) created a rating scale which assigns values of 110, 15 or 20 to species based on degree of conservatism. A higher number means a species indicative of a natural area. Using the Wilhelm scale, the Thatcher Woods site has a Natural Areas Rating Index (NARI) of 66.3 without age points, greater than 70 with age points. (Introduced/non-native species are not included when calculating NARI.)

Establishing that the site is an example of an oak savanna community involves examining available pre-European settlement data on herbaceous and woody vegetation. While surveyors' notes of the site provide information regarding type and abundance of tree cover, relatively little information is available regarding herbaceous species.

The following comparison was made regarding the changes in woody vegetation using 1821 surveyor notes and the results of a 1991 study of the site. A comparison between plant species lists from surveyors and the present was then used to compare this site to other identified oak savannas. Changes have occurred in basal area, species dominance, species composition, and size class frequency of trees on the site since the time of the original survey in 1821. Comparison of data indicates a move from an open savanna community to a more heavily wooded site. Since 1821, there has been a 28-fold increase in basal area overall. While basal area of the oak savanna species of the white oak group (white, bur and swamp oak) has risen from 2.53 m2/ha in 1821 to 43.02 m2/ha in 1991, a non-typical species, the ash, has increased from 0.12 m2/ha to 42.24 m2/ha. This places the ashes, once the lowest basal area species, on par with the oaks, originally the most dominant tree species with respect to basal area. The number of trees per hectare has also risen dramatically from 6.71 in 1821 to 337.46 in 1991.

These dramatic changes in tree cover are a result of the cessation of fire since European settlement. Further supporting this idea are the number of tree species that were not noted in the surveyors' records. Trees include hackberry, box elder, hawthorn, sugar maple, and choke cherry.

The plant species list for the site can be compared with those species lists of the oakopening/savanna ecosystems compiled by Dr. Mead (1846), Curtis (1959), and Packard (1985, 1986). Twenty of the 98 plant species on Dr. Mead's list are found in Thatcher Woods (Table 1). Twenty-two of the 65 plant species on Curtis' list are also found here (Table 2). And finally, similarities occur between the TWSRP plant species list and Packard's (1985) list, which he compiled from a variety of sources, including Curtis and Mead. His work stems from the restoration of oak savannas along the north branch of the Chicago River. Of 113 species found on Packard's list, 38 are found at Thatcher Woods (Table 3).

It is of interest to note the tree species found on the TWSRP site that were not included in the other lists (Table 4). Of these species, Quercus rubra, Carya lacinosa, and Carya ovata are probably the only savanna species. The other 13 tree species are indicative of the changes that have occurred since the area was surveyed in 1821.

However, despite the changes and following just three years of restoration and management, Thatcher Woods is, in the authors' opinion, grade "A" quality oak savanna. Continued management will further enhance the quality and diversity of the plant communities present.

LAND MANAGEMENT  back to top

Thatcher Woods Savanna management plans include the following activities:

  • Controlled management burning to clear away brush and promote understory vegetation;
  • Selected removal of sugar maples, ash, bass, common buckthorn (Rhamnus cathartica), and bush honeysuckle (Lunicera tatarica) to allow more sunlight to filter through;
  • Control by hand pulling of herbaceous exotics such as garlic mustard (Alliaria petiolata) and periwinkle (Vinca minor); 
  • Collection and seeding of plant species from richer areas to areas burned or cleared of trees and brush;
  • Continued inventory of the flora and fauna;
  • Prevention of alteration of hydrologic conditions;
  • Control of vehicle access;
  • Prevention of dumping as well as removal of debris; and,
  • Restoration of the Deep Tunnel construction site.

From the outset the TWSRP was organized to manage the site as a community group in partnership with the Forest Preserve District. Today, we work in close cooperation with Chet Ryndak, Director of Conservation of the FPD, to develop near-term, mid-term, and long-term goals as part of an overall site strategy. The FPD helps fund our ongoing expenses such as purchase of new equipment, photography costs, and postage for our monthly newsletter. The FPD also arranges to have the debris that is collected during workdays picked up.

Because no one knew of the high natural quality of the area, human activities were detrimental. Yard waste and other debris was dumped by homeowners, contractors, and passersby. The Northwestern Railroad dumped railroad ballast. The drainage practices of the Water Reclamation District at the

Deep Tunnel construction site caused serious erosion of the river bank. Also, the area had become a gathering place for rowdy teenagers and gangs. The first near-term goal, therefore, was to concentrate our efforts on finding solutions to these human problems. To hinder dumping, the FPD helped in securing

from the railroad a durable steel gate with lock to block unauthorized vehicular entrance to the access road that runs along the north border. "No dumping" police order signs were installed at strategic locations.

The dumping of ballast in a secondary floodplain area of the property was brought to the attention of the U.S. Environmental Protection Agency and the Army Corps of Engineers. Concurrently, contacts with railroad officials and the FPD real estate division have resulted in a cessation of the dumping and the removal of the existing hill of ballast by the railroad.

Additionally, we contacted each resident along the east boundary on Thatcher Avenue to ask their cooperation in policing the area directly in front of their homes. They have agreed to immediately call the FPD police should any illegal dumping be observed.

The FPD also assisted us in getting the Deep Tunnel Project to drain its construction shaft by connecting a 3inch hose from the drainage pump to run directly into the river. Previous practice was to discharge the pump directly to the surrounding soil. This flooded a large area of native plants adjacent to the river embankment. It also caused serious erosion of the bank which resulted in a precipitous drop from the trail into the river.

Regarding the problem of rowdies, the FPD removed a dilapidated concrete shelter that was present on the trail in G.A.R. Woods since the 1930's. This helped to eliminate a gathering point. Our continued presence in restoration efforts and other activities such as Earth Day and Scout tours together has diminished their presence. Because our activities have been well published in local newspapers, and since a large, attractive sign identifying the area as the Thatcher Woods Savanna and outlining the restoration activity was installed, there has been a noticeable increase in the use of the savanna by families and other area residents.

Parallel with these initial near-term goal efforts, we began working on midterm goals which concentrated on solutions to the biological problems of invasives and exotics, restoration of the Deep Tunnel site, and wider recognition of the area as high quality by the State of Illinois Conservation Department.

Foremost in achieving midterm goals was a comprehensive inventory of plant life and a needs analysis. This was principally accomplished by examining the species list and conducting the ratings analysis presented above. To supplement the species list we started a photographic documentation of the plants. A color slide presentation was developed that is available to local groups for educational purposes.

The invasives and exotics are not a major problem at the site today. We were able to remove essentially all of the mature European buckthorn and bush honeysuckle. We were also able to remove most of the small sugar maple trees that were concentrated under the oaks in two sections of the savanna. Selected small ash and bass trees have been girdled in the process. The garlic mustard problem is generally confined to the outer boundaries of the site. These plants are pulled out at the roots and removed from the site in plastic bags to prevent reseeding. Remaining problems include removing scattered patches of periwinkle and day lilies that were planted in years past.

During our first years we gradually began fire management activities. These fires were limited to small areas in order to allow for training of volunteer personnel, and to establish the necessary public relations with local residents and fire and police departments. Both fall and spring burns have been tried, leading to planning for annual burns of the total area on a rotational type schedule.

Regarding the restoration of the Deep Tunnel construction site, we submitted a modification to the Metropolitan Water Reclamation District (MWRD) architect's plan to the FPD. We proposed planting a combination of 8 bur and white oaks having a spacing of 17 feet on this .16 acre site. We have native woody plants bordering the access road to the site, and in place of Kentucky bluegrass we proposed the use of native grasses. The plan calls for the MWRD to grade the site and provide top soil, and the FPD to provide the oak trees. The TWSRP provided seeds for woody plants and grasses which are being cultivated by the FPD and by Dennis Nyberg at the University of Illinois at Chicago. Planting is scheduled to take place in the summer of 1993.

Finally, to achieve our long term goals of full restoration and preservation, we need to have ongoing protection of the site at as high a bureaucratic level as possible, and we need continuing education and appreciation of our native plants by future generations. To this end, detailed documentation regarding the historical significance, quality of plant life, and ecological importance as the best of its kind in the Des Plaines River valley in Cook County was submitted to the Illinois State Department of Conservation for nomination for placement on the Illinois Natural Areas Inventory. Although the application was denied at the time the information gathered, along with a strong recommendation by the review committee, served as the basis for the FPD's application for Nature Preserve status.


Table 1.  Plant species found on TWSRP site   back to top
that are also listed in plant list of Dr. Mead

  • Allium triroccum
  • Campanula americana
  • Carya cordiformis
  • Dioscorea villosa
  • Dodecatheon meadia
  • Hypericum punctatum
  • Lonicera prolifera
  • Lysimachia eiliata
  • Quercus bicolor
  • Ranunculus abortiuns
  • Ribes missouriense
  • Solidago ulmifolia
  • Taenidia integerrima
  • Zanthoxylum americanum
  • Bromus purgans
  • Cinna arundinacea
  • Hystrix patula
  • Leersia virginica


Table 2.  Plant species common to TWSRP site   back to top
and oakopenings as discussed in
Curtis, Vegetation of Wisconsin, 1959

  • Quercus macrocarpa
  • Q. alba
  • Q. ellipsoidalis
  • Prunus serotina
  • Fraxinus pensylvanica
  • Ulumus rubra
  • Acer negundo
  • Tilia americana
  • Tuglans nigra
  • Fraxinus americana
  • Ulmus americana
  • Amphicarpa bracteata
  • Desmodium glutinosum
  • Fragaria virginiana
  • Galium sp. 
  • Geranium maculatum
  • Physalis sp.
  • Poa pratensis
  • Polygonatum canaliculatum
  • Rhus radicans
  • Simlacina racemosa


Table 3. Plant species found on TWSRP site   back to top
which are included in Packard's (1985)
savanna species list

  • Agrimonia pubescens Scrophularia marilandica
  • Amphicarpa bracteata Silene stellata
  • Aster sagittifolius Smilacina stellata
  • Camassia scilloides Smilax lasioneura
  • Cirsium altissimum Solidago flexicaulis
  • Convolvulus sepium Solidago ulmifolia
  • Crataegus sp. Taenidia integerrina
  • Desmodium glutinosum Triosteum aurantiacum
  • Dioscorea villosa Verbena urticifolia
  • Galium concinnum
  • Helianthus divaricartus
  • Helianthus hirsutus
  • Hypericum punctatum
  • Lonicera prolifera
  • Orobanche uniflora
  • Penstmon digitalis
  • Polygonatum canaliculatum
  • Pyrus ioensis
  • Quercus bicolor
  • Q. ellipsoidalis
  • Q. macrocurpa
  • Sanicula gregaria


Table 4. Trees found on TWSRP site   back to top
but not mentioned in Mead, Curtis, Packard   

  • Acer platanoides
  • A. saccharinum
  • A. saccharum
  • Carya lacinosa
  • C. ovata
  • Celtis occidentalis
  • Gymncladus dioica
  • Juglans cinerea
  • Morus alba
  • Populus alba
  • Ostrya virginiana
  • Populus deltoides
  • Prunus virginiana
  • Quercus rubra
  • Robina pseudoacacia
  • Salix nigra

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