Skip common site navigation and headers
United States Environmental Protection Agency
Great Lakes
Begin Hierarchical Links EPA Home > Great Lakes > EcosystemsUpland Ecosystems > Oak Savanna Conferences > 1993 Midwest Oak Conferences > Mary C. Hruska    
Aquatic Ecosystems
EPA Region 5 Critical Ecosystems
Ecosystem Funding
Great Lakes Basin Ecosystem
Great Lakes Biological Diversity
Green Landscaping
Rivers and Streams
Upland Ecosystem



1993 Proceedings of the Midwest Oak Savanna Conferences

1993 Proceedings of the Midwest Oak Savanna Conferences

Mary C. Hruska
    and Dr. John E. Ebinger
Botany Department
Eastern Illinois University
Charleston, IL 61920
Tel: (217) 832-9433




Adobe Acrobat reader logoTo view a PDF file in its entirety, please obtain the most recent edition of the free Adobe Acrobat reader.



During the Illinois Natural Areas Inventory, no intact, deep-soil, mesic savanna was found in the state, and only one high quality dry-mesic savanna was found. It is important that we start to study the remnants of these areas while some still exist, so that reconstruction efforts will have some logical basis. The present study was undertaken to develop a management plan, and start the development of a mesic savanna community at Forest Glen Preserve, Vermilion County, Illinois. The study involved a pre-burn inventory of the vegetation, and the changes that occurred after burning. It also involved post-burn survival of woody species. These studies indicated that oaks are well adapted to surviving burns by resprouting from the base or trunk. Also, most shrub species, although top-killed after fire, do resprout, as do many weedy tree species and woody exotics. A set of guidelines have been developed for savanna reconstruction.


INTRODUCTION  back to top

Defining the word savanna, as used by natural areas botanists, is a very difficult task. A broad description would be an area with open-growing trees, growing as scattered individuals or in small groves, with an herbaceous, primarily grassy understory (Bray 1955). During the Natural Areas Inventory of Illinois the definition used was based on canopy cover and soil moisture (White 1978). Canopy cover ranged from 10-80%, soil moisture was described as mesic, dry mesic, and sand. Much controversy over the definition has taken place since then. Reviewing the General Land Office survey records adds to the confusion for the surveyors did not use a standardized terminology. Different surveyors used different terminology for the same community and the same terminology to describe different vegetation types. Some of these terms were oak openings, oak barrens, oak scrub, brush prairie, scattered timber, open woodland and prairie with scattered trees (Nuzzo 1986). Anderson and Brown (1983) and Anderson (1991a), and many others, proposed that savannas are not a separate ecosystem but an ecotone between two ecosystems, prairie and forest; to elaborate, a transition zone between the western prairies and the eastern deciduous forests. When considering the transient, fluxuating nature of the savanna, this seems most appropriate, for this community is totally dependent on outside factors for it's existence. To condense this into a definition, savannas are an ecotone dominated by oaks, having between 10-80% canopy cover, with or without a shrub layer, and an herbaceous, predominantly grassy ground layer composed of species associated with both prairie and forest communities. It is fire dependent, and in the absence of fire or extreme droughty conditions will convert into a forest community.


Some of the factors that shaped or created savannas were fire, slope, climate, and soil (Anderson 1991b). The fire frequency determined whether trees would be able to grow large enough to withstand being top killed, thus growing beyond the seedling stage. In areas where fire occurs annually, few trees got past seedling stage. If fires occurred every 3-5 years some trees would be able to reach a size at which they were fire resistant. Early settlers noted that within twenty to forty years after the frequent fires were stopped, the savannas appeared as closed oak forests.

Slope, topographic relief, controlled the spread of the fire. Down hill slopes do not carry fire well. When vegetation burns there is a rising convection air current from the heat that is being produced. Fire will move up hill quickly, lifted by its own current, conversely when moving down hill the rising air current works against the fire, sometimes causing it to burn out. Also, land with greater slope tends to have more drainage (i.e. streams) than flat land. These act as fire breaks, reducing the fire frequency in the area.

Climate also works in conjunction with fire. During times of drought vegetation will be dryer especially in the fall, and will burn hotter and more completely than in a wet year. During wet years water in depressions and low lying areas causes the fire to burn out or skip areas, resulting in less complete burns and more chance for trees to grow.

Poor soils, like that of sand savannas, do not support the large biomass growth that deep soils support. Fires through these areas would be less intense, allowing for trees to grow. Fires through deep soil areas that support large biomass growth would be of higher intensity, killing the trees.


Pre- and post-burn vegetation studies were done on a savanna reconstruction site at Forest Glen Preserve, Vermilion County, Illinois. Herbaceous frequency data and woody frequency and density data were taken during the summer and fall of 1991. The site was burned in March of 1992. The measurements were repeated in the summer and fall of 1992. Fisher's Exact Test was run on both the frequency and density data.

Sixty-six herbaceous species were recorded for the study area. Of these, seventeen showed significant frequency differences. Those significantly increased after the burn were: Agalinis tenuifolia, Ambrosia artemisiifolia, Cassia fasciculata, Carex sp., Desmodium glabellum, Dichanthelium acuminatum, Euthamia graminifolia, Lespedeza virginica, Potentilla simplex, Solidago juncea, Sorghastnim nutans, and Trifolium pratense.

After the burn, bare spots of soil were created where litter had been. The annuals and more aggressive species were able to colonize theses areas. Those that were significantly decreased after the burn were: Dactylis glomerata, Dianthus armeria, Eupatorium serotinum, Hypericum punctatum, and Oenothera biennis. The first four are not fire tolerant species, however the decrease of Oenothera biennis was unexpected.

Only two species of shrubs significantly increased in frequency after the fire (Table 1). These were Rubus allegheniensis (blackberry) and Rubus flagellaris (dewberry). Most of this increase was due to root sprouts. There were no significant decreases.

Trees that were less than 2.5cm in diameter at breast height were considered seedlings, those that were 2.5cm and larger were considered saplings. Juglans nigra (black walnut) was the only tree seedling which showed a significant difference in frequency, it decreased after the burn. It is not a fire tolerant species (Table 1). Both Juglans nigra and Prunus serofina (wild black cherry) decreased significantly in density after the burn. They are not fire resistant species. Sassafras albidum and Malus ioensis (wild crabapple) increased significantly in density after the burn, mainly because of root sprouts.

Only one saplings tree species showed a significant difference after the burn (Table 1). Prunus serotina was significantly deceased in frequency and density. Again this tree is not fire resistant.

The total stem numbers for the tree seedlings were not significantly different after the burn. However the stem numbers for the tree saplings greatly decreased after the burn. This reflected the number that were top killed.


During the summer of 1992, several species of trees on the savanna site were surveyed to determine their ability to survive and or resprout after the burn. This data was compiled into four categories: (1) not killed, lower limb damage sometimes occurred; (2) killed, not resprouting the next spring; (3) top-killed, resprouting the next spring from the base; and (4) top-killed, resprouting the next spring from the trunk (Table 2).

In general, the oaks were relatively resistant to the fire, particularly once the individuals reached a height of 2 to 4 m. Quercus macrocarpa (bur oak) was the most resistant, with all of the individuals over 1 m in height surviving and not being top killed. Quercus alba (white oak) individuals also survived the fire with relatively little damage once reaching a height of 3 m. Small individuals were commonly top killed, but did resprout from the base or the trunk. The remaining oak species (shingle, red and black) were less resistant, with some 4 m tall individuals being top killed.

Juglans nigra (black walnut) exhibited patterns similar to the shingle oak. Below 3m the majority were top killed resprouting from the base and trunk. At 3-4m and > 4m the individuals were not killed. This species shows a great ability to resprout and appears to be fire resistant above 3m.


During the Natural Areas Inventory of Illinois, there were no grade A, deep soil, mesic savannas identified in the state (White 1978). In fact Nuzzo reported in 1986, that to date, no intact grade A, deep soil, mesic savannas had been located in the eight midwestern states she surveyed. For this reason it is imperative that the existing remnants be restored and reconstruction efforts started. A list of ideas to be considered and steps to be taken has been compiled to help those interested in starting such efforts.

  1. Site selection - if possible choose an area with a savanna history, one with established oaks will make for a faster start. If the history of the area is not known consult General Land office survey records or maps such as Nuzzo's (1986).

  2. Herbarium collection - collect, press, mount and identify specimens of all pl&its found on the site, herbaceous and woody. This can be used for baseline data from which to monitor changes in the future. For people who are not botanists the collection can be used for study. Those involved with the project will become aware of the current and potential weedy species as well as the forest, prairie, and savanna species on the site.

  3. Herbaceous and woody data - quadrats and transects are your friends! Take frequency and density data, if unfamiliar with these techniques contact a local environmental group such as The Nature Conservancy. They will know someone who can teach these techniques. Again this can be used as baseline data to monitor changes in the future.

  4. Eliminate exotic shrubs and woodies - methods for elimination of such species are cutting, burning, girdling, and herbiciding (if acceptable), this should be started as soon as possible since it may take several growing seasons to achieve this goal. Some species are excellent resprouters so this will be an ongoing project.

  5. Burn - if using fire for weedy/exotic species control do burn several consecutive years. If small oaks are already present or have been planted, spray with water immediately before the burn for protection, and rake liner away from the bases to reduce the intensity of the fire as it passes. Once the weedy/exotic species are under control only burn every 3-5 years to allow the oaks time to grow.

  6. Prepare seed bed - methods used can be plowing, discing, herbiciding, and after burns, bare spots can be seeded by hand. Plowing can turn up weedy seeds that are buried in the soil but it is sometimes necessary if the soil is extremely hard or if the area is covered with non-native grasses that are hard to kill, (for example brome and fescue can out-compete many native species). Discing will turn up less soil so less weed seed, and it can be used with herbicide for a better kill of non-natives. Areas can be tilled once a month for an entire growing season to eliminate the non-natives. If time permits, this offers the least amount of competition for the new native plants.

  7. Herbaceous layer - the first thing that must be done before acquIring any plants or seeds is to research what species were native in the specific area (do your homework), this can be done by visiting local prairies and forests, talking to local botanists, and using local plant lists if available. Always use local genotypes, they will be best suited for the conditions in that area. There are several sources for seeds and plants; many nurseries are specializing in native plants, seed may be collected for unattended road ditched, and seed can be collected from local preserves or established areas, but you must GET PERMISSION FIRST! FOLLOW THEIR RULES! The steward for the area may already have plans for that year's seed but it may be available in future years. Get to know these people, they may be a source of information and assistance. If the trees are small or have to be planted start with herbaceous species that can tolerate full sun, add the more shade tolerant species later when there is shade.

  8. Shrub layer - shrubs were a major component of many savannas, (hazelnut, plum, blackberry, raspberry, and dewberry). Some of these will be brought in by birds, others can be purchased.

  9. Woody layer - oaks are the tree of choice with the species depending on location. If the site has established oaks, collect these acorns for use in more open areas, if the oaks are old they will probably be local genotypes. If there is an area that has a high concentration of small trees, use a tree digger to move these to less populated areas. Again acorns can be collected from local woods but find out if you need permission to collect. Small trees can be purchased from the Department of Conservation.

  10. Threatened and endangered species - it is not advisable to attempt the introduction of these species during the early stages of restoration projects. These species typically have special habitat requirements which are available only in natural systems or well-developed restorations. Also these species are controlled by state and federal regulations. For this reason their introduction should be attempted only in the later stages of restoration, and then only in compliance with the previously mentioned regulations.

  11. Give it time to grow - restoration projects take time. If at the end of the first growing season the prepared seed beds are full of foxtail and other annuals, do not worry, the natives take a few years to grow, but they will be able to out compete the non-native annuals.


Anderson, R. C. 1991a. Savanna concepts revisited. BioScience 41:371.

Anderson, R. C. 1991b. Presettlement forests of Illinois. Pages 9-19 in G. V. Burger, J. E. Ebinger, and G. S. Wilhelm, eds. Proceedings of the oak woods management workshop. Eastern Illinois University, Charleston, Illinois.

Anderson, R. C. and L. E. Brown. 1983. Comparative effects of fire on trees in a midwestern savanna and an adjacent forest. Bulletin of the Torrey Botanical Club 110: 87-90.

Bray, J. R. 1955. The savanna vegetation of Wisconsin and the application of the concepts of order and complexity to the field of ecology. PhD Thesis. Univ. Wisconsin, Madison, WI.

Nuzzo, V. A. 1986. Extent and status of midwest oak savanna: Presettlement and 1985. Natural Areas Journal 6:6-36.

White, J. 1978. Illinois natural areas inventory technical report, VoL I: Survey methods and results. Illinois Natural Areas Inventory, Urbana, Illinois. xix+426p.


Begin Site Footer

EPA Home | Privacy and Security Notice | Contact Us