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GL Basin Ecosystem
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1995 Midwest Oak Savanna and Woodland Ecosystems Conferences
BACKGROUNDDuring August 1995, we were able to contact natural heritage programs in six Upper Midwest states (MN, WI, IL, MI, IN, OH) to gather information on documented savanna and woodland remnants. We compiled this data so that Midwestern conservationists might more clearly recognize the relative importance of their state's savanna remnants, elements, and potentially recoverable macrosites in relation to similar communities in neighboring states. We concentrated our efforts upon the following three Upper Midwestern savanna and woodland ecosystems: Northern Bur Oak Openings, Northern Black Oak Barrens, and Northern White Oak-Bur Oak Woodland. We treated a potential fourth type, Black Oak Woodland (which others might term "Sand Woodland"), as part of the Northern Black Oak Barrens type. LIMITATIONS OF OUR DATAHistorical Extent of Savannas and WoodlandsCurrent presettlement vegetation maps underestimate the former abundance of savannas and woodlands. The former range and extent of loss of these systems will be much better understood as revised interpretations of presettlement vegetation are made. There is a great range in the accuracy and usefulness of current presettlement acreage estimates for savanna and woodland. Several states (IA, IN, IL) lack statewide estimates. Other states have statewide estimates but do not differentiate between Oak Openings, Oak Barrens, Oak Woodland or Shrub Prairies. Recognition of woodlands has received especially little attention. Woodland has not been recognized by any of the statewide presettlement vegetation maps derived from the Public Land Survey notes, including the highly detailed vegetation maps for Minnesota (Marschner 1974) and Wisconsin (Finley 1976). Only a few recent vegetational studies, conducted at a scale of one or two counties, have differentiated woodland from savanna and forest (Bowles et al. 1994, Leitner et al. 1991, Anderson 1991). New and revised analyses of the Public Land Survey Notes are necessary if we are to accurately gauge the former extent of savannas and woodlands. The Public Land Survey Notes are the only significant source of data available to estimate these presettlement acreages. Recognizing savannas and woodlands will prove challenging, and perhaps impossible in some cases, due to the coarse scale of the survey notes. Nonetheless, a regionwide analysis of the PLS data would provide a substantial improvement in our understanding of savanna and woodland distribution, and of the relative abundances of their most common components, such as the various Quercus species and Corylus americana. There are some recent efforts to reanalyze PLS notes. The state of Michigan is developing a presettlement vegetation map that includes estimated savanna acreages. This map is 75% finished at this date. Another exciting development is the computerization of PLS data for the entire state of Minnesota. Analysis of this daunting data set has yet to be undertaken. Current Extent of Savannas and WoodlandsCurrent estimates of savanna and woodland acreage and quality are limited by several factors. One is the lack of parallel nomenclature for savannas and woodlands among different states. This makes it difficult to compare acreages and quality rankings between states. Our document should help begin solving that problem. A second need is for states to recognize woodland communities and begin seeking and categorizing sites as such. Extant woodland sites are greatly underestimated. Only Minnesota has conducted a significant inventory and listing of woodland sites. Until individual states begin more thoroughly characterizing oak ecosystems, both by their canopy covers and by those diagnostic understory species that prefer woodland canopy cover levels, it will be difficult to fully characterize the extent of woodland communities. A third need is to recognize that current canopy cover by itself may not be the best means by which to classify a particular site. Sites classified as forest may be better reclassified as woodland or even savanna. Current canopy cover does not always reflect the long-term average canopy cover at a site. A site that has historically been a woodland or savanna can quickly develop a forest canopy structure once both fire and grazing have been removed. Yet the composition of such a site is likely to include understory species that, although they have managed to persist under the recently developed forest canopy, characteristically establish themselves and compete best under a woodland canopy. The presence of such diagnostic species should be considered along with canopy cover when attempting to classify a particular site. Historic aerial photographs can also help determine long-term canopy conditions. Another need is to update heritage database files to reflect our current understanding of oak ecosystems. Sites previously classified as forest or prairie may now be better classified as savanna or woodland. In spite of the data limitations, we have compiled the available data for Northern Bur Oak Openings, Northern Black Oak Barrens, and Northern White Oak-Bur Oak Woodland into the following sample conservation and recovery plans. We welcome your ideas on how to expand or improve these plans. NORTHERN BUR OAK OPENINGSCommunity SummaryQuercus macrocarpa-Quercus alba-Quercus velutina/Andropogon gerardii Sparse Woodland, more often referred to as Oak Opening, is a dry-mesic to mesic community that commonly occurs on level to moderately steep, fire-prone landscapes in northeastern Iowa, southeastern Minnesota, southern and western Wisconsin, northern Illinois, southwestern Michigan, northern Ohio and possibly northern Indiana. Canopy cover ranges from 10-30% canopy. The groundlayer is dominated by graminoids, especially Andropogon gerardii and Schizachyrium scoparium, accompanied by a large diversity of forbs. Shrub cover can range widely, with Ceanothus americanus, Amorpha canescens and Rosa spp. being three of the most important shrub species. Understory species typical of oak openings require some direct sunlight throughout the growing season and are quickly reduced when heavily shaded by either tree or shrub canopy. Common shrubs in this community are adapted to the moderate fire frequencies found in oak openings, and resprout vigorously after burning. The tree layer is dominated by Quercus macrocarpa, occasionally accompanied by Q. alba. Q. velutina can also become co-dominant in Oak Openings, but only on sandier loam soils. This open-canopied community is maintained by moderate fires that are frequent enough to prevent extensive woody growth, but not so frequent to preclude saplings of canopy species from reaching fire-resistant size. Grazing by elk and bison prior to European settlement and by cattle during European settlement probably played a significant, but secondary, role in maintaining an open canopy. Without fire and/or grazing, this community is replaced by oak woodland and eventually oak-hardwood forest. (This summary is taken from The Nature Conservancy's "Community Characterization Abstract" series. The entire 13-page abstract for Northern Bur Oak Openings may be obtained by contacting Don Faber-Langendoen, The Nature Conservancy, Midwest Regional Office, 1313 Fifth St. SE, Suite 314, Minneapolis, MN, 55414-1588.) Presettlement RangeThe presettlement range of Northern Bur Oak Openings included northeastern Iowa, southeastern Minnesota, southern and western Wisconsin, northern Illinois, southwestern Michigan, northern Ohio and possibly northern Indiana. A map of this range is found at the back of this conservation and recovery plan. Presettlement AbundanceAs noted above, there are many limitations to accurately assessing presettlement acreages of Northern Bur Oak Opening. Nonetheless, we list the best estimates we could find are listed below.
Extant remnantsThe table at the back of this plan lists all inventoried Northern Bur Oak Openings remnants. These are listed by state in order of their natural quality. This list is nearly 100% complete for sites identified in or before 1993, and includes 1994-5 data for a few states. Only 21 Oak Openings sites totaling 296 acres are known to exist within the entire Oak Openings presettlement range. Four of these sites lack an acreage estimate, so assuming these sites are of comparable size to the other remnants, the total acreage of known Oak Openings may be approximately 313 acres. Oak Openings acreages by quality ranking were 42 "A" quality acres, 100 "B" quality acres, and 46 "C" quality acres. Wisconsin had the highest acreage of Oak Openings with 174 acres. Oak Openings acreage of other states was as follows: Ohio, 100 acres; Minnesota, 50 acres; Illinois, 12 acres. Current state classificationsAs noted above, each state has its own community classification system. Below are the state names for Northern Bur Oak Openings.
Recovery and Restoration PotentialThe probability of discovering additional Oak Openings remnants appears quite small. Several states (IN, OH, MI, MN) believe that their natural area inventories have been so thorough that they are likely to find perhaps only one or two more significant Oak Openings sites (C quality or higher) within their entire state. An exception to this is Wisconsin, where it is anticipated that several small grade B and C Oak Openings might still be found in the "Driftless Area" of southwestern Wisconsin. This region has many narrow, untillable ridges, steep topography and a pre-WWII history of fire use by landowners that may have enabled the persistence of small, recoverable, moderate quality Oak Openings. But this expectation runs counter to recent findings of the natural areas inventory of Minnesota's Driftless Area, where only two significant Oak Openings sites have been documented within the six-county region over the past three years. This inventory is over 50% complete. Even more discouraging, an inventory for Oak Openings currently being conducted in northern Illinois found no significant Oak Openings remnants in 1995 (Marlin Bowles, Morton Arboretum, pers. comm.). Since there are no large Oak Openings remnants left, establishment of Oak Openings macrosites will depend upon either recovery and linkage of small, adjacent remnants, or labor-intensive effort to restore areas that have lost most of their Oak Openings composition and structure. Sites with scattered remnants that have been suggested as having high macrosite potential include the Whitewater Valley in Winona and Wabasha Counties, MN; the Mississippi and Wisconsin River corridors in WI, MN, and IA; portions of Buffalo and Pepin Counties in WI; the Southern Kettle Moraine Forest in WI; the Siloam Springs State Park area in Adams and Brown Counties, IL; and the Palos Hills area, Cook County, IL. Each of the first three sites listed above are located within the "Driftless Area" of southwestern WI, southeastern MN, and northeastern IA. As a region, this area has the greatest potential for establishment of Northern Bur Oak Openings macrosites. It is also one of the least inventoried areas within the presettlement range of Oak Openings. Only Minnesota has begun an extensive survey of the region. Other Ideas for Enhancing Recovery Plan ImplementationOne idea suggested to us was that it would be helpful to have a list of site occurrences and population sizes for species that may be modal in, or limited to, Northern Bur Oak Openings. A list of such elements needs to be developed. A few species tentatively suggested for investigation include the forbs Upland Boneset (Eupatorium sessilifolium), Purple Milkweed (Asclepias purpurascens), Wild Hyacinth (Camassia scilloides), Cream Gentian (Gentiana alba), Yellow Pimpernel (Taenidia integrima), and two butterflies, the Edward's Hairstreak (Satyrium edwardsii) and the Silvery Blue butterfly (Glaucopsyche lygdamus).
NORTHERN BLACK OAK BARRENSCommunity SummaryNorthern Black Oak Barrens have a canopy layer that ranges from a sparse, scattered canopy (generally from 5 to 30 percent cover - sometimes termed a savanna physiognomy), where the ground layer may vary from open, herbaceous dominated to scrub oak dominated, to a more closed canopy (30 to 80% cover - sometimes termed a woodland physiognomy). The canopy layer is dominated by Quercus velutina (black oak), with some Quercus ellipsoidalis (northern pin oak). Quercus alba (white oak) often occurs as a canopy tree in the eastern range, but is seldom dominant, except in woodland conditions. Tree height varies from 5 to 15 meters. A subcanopy layer composed of the preceding species, or in some cases Prunus spp., Cornus spp., Sassafras albidum, Carya spp., and Corylus americana may be present. The low shrub/scrub layer may contain ericaceous shrubs, Rosa spp., and any of the preceding woody plants. The herb layer is dominated by graminoids (e.g. Carex pensylvanica, Andropogon gerardii, Schizachyrium scoparium); forbs tend to increase as woody cover increases. Composition and structure vary in this type depending on geography, site characteristics, and disturbance history. Northern Black Oak Barrens range from southern Michigan, the glaciated portions of Ohio, Indiana, Illinois, and south of the tension zone through Wisconsin and southeastern Minnesota. Oak-pine barrens of Michigan, Wisconsin and Minnesota are not included in this type. The barrens communities generally occur on well-drained coarse textured sandy, infertile soils derived from glacial outwash, high gravelly/sandy moraines, or lake plain dune systems. Soils vary from almost pure sand to sandy loam to loamy sand. (This summary is taken from The Nature Conservancy's "Community Characterization Abstract" series. The entire abstract for Northern Black Oak Barrens may be obtained by contacting Don Faber-Langendoen, The Nature Conservancy, Midwest Regional Office, 1313 Fifth St. SE, Suite 314, Minneapolis, MN, 55414-1588.) Presettlement RangeThe presettlement range of Northern Black Oak Barrens included southern Michigan, the glaciated portions of Ohio, Indiana, Illinois, and Wisconsin and southeastern Minnesota south of the tension zone. A map of this range is at the back of this conservation and recovery plan.. Presettlement AbundanceThe best estimates we could find for Northern Black Oak Barrens are listed below.
Extant remnantsThe table at the back of this plan lists all inventoried Northern Black Oak Barrens remnants. These are listed by state in order of their natural quality. This list is nearly 100% complete for sites identified in or before 1993, and includes 1994-5 data for a few states. A total of 148 Oak Barrens sites have been discovered within the Oak Barrens presettlement range. Ninety-one (91) of these sites have acreage estimates which total 6, 935 acres. The other 57 sites lack an acreage estimate. Assuming that these sites are of comparable size to those sites with acreage estimates, the total acreage of known Oak Barrens may be approximately 11,279 acres. Oak Barrens with both quality and acreage estimates were compiled to give rangewide totals of 1,221 "A" quality acres, 4,041 "B" quality acres, 1,324 "C" quality acres, and 100 "D" quality acres. Illinois had the highest acreage of Oak Barrens with 3,352 acres. However, Indiana has the highest number of oak barrens sites (56) and will probably be found to have the highest Oak Barrens acreage once these figures are compiled. Oak Barrens acreages of other states were as follows: Minnesota, 2,337 acres; Wisconsin, 1,151 acres; Michigan 82 acres; Indiana 13 acres. Current State ClassificationsAs noted above, each state has its own community classification system. Below are the state names for Northern Black Oak Barrens..
Recovery and Restoration PotentialThe probability of discovering new Oak Barrens remnants varies across its range. A few states (IN, MI) feel that their natural area inventories have been so thorough that they are likely to find only a few more significant Oak Barrens sites (C quality or higher) within their state. But several states remain under surveyed. Minnesota has discovered at least 12 new Oak Barrens totaling 860 acres in the past couple of years, and will probably add that many more over the next few years of its MN Driftless Area biological inventory. The entire Wisconsin Driftless Area, which is perhaps four times the size of Minnesota's Driftless Area, remains predominantly unsurveyed. Thus it seems likely that many new sites will be discovered in this area too. In northwestern Ohio, it is estimated that some 16,000 acres of Oak Barrens and Oak Woodland remain. However, the vast majority of this acreage is highly degraded and in need of "significant restoration." (Terry Seidel, TNC-OH, Pers. Comm.). Since there are several large Oak Barrens remnants remaining, establishment of Oak Barrens macrosites would best be directed toward expanding those large sites or linking nearby medium-sized sites. Sites that have been suggested as having high macrosite potential include Illinois Beach and Dunes in Lake County, IL; portions of Kankakee and Iroquois Counties in IL; several sites within the Lake Michigan Duneland complex of northern IN; the Whitewater Valley in Winona and Wabasha Counties, MN; several sites within the Toledo Lakeplain of northwestern Ohio; Fort McCoy and surroundings in Monroe County, WI; and the Chippewa River Valley in Dunn County, WI. Other Ideas for Enhancing Recovery Plan ImplementationOne idea suggested to us was that it would be helpful to have a list of site occurrences and population sizes for species that may be modal in, or limited to, Northern Black Oak Barrens. A list of such elements needs to be developed. A few species tentatively suggested for investigation include the forbs Upland Boneset (Eupatorium sessilifolium), Sand Milkweed (Asclepias amplexicaulis), and Fame Flower (Talinum rugospermum).
NORTHERN WHITE OAK-BUR OAK WOODLANDCommunity SummaryQuercus albaQuercus macrocarpaQuercus rubra/Corylus americana Woodland is a dry-mesic woodland that occurs on flat, gently rolling or hilly landscapes subject to fires of low frequency and variable intensity. Its geographic range is southeastern Minnesota, southern and western Wisconsin, northern Illinois, southwestern Michigan and possibly northern Indiana, northern Ohio and eastern Iowa. Canopy cover ranges from 30 to 80% canopy. The groundlayer is codominated by shrubs and tree grubs, forbs and graminoids. Shrub cover is usually high (30-50%) with some stands forming impenetrable thickets (MN Natural Heritage Program NHP 1993, Bowles et al. 1994). The tree layer is dominated by Quercus alba and Q. macrocarpa on drier soils and occasionally co-dominated by Q. rubra on more mesic soils. This community is maintained by a fire regime that is frequent enough to prevent full canopy closure and sapling establishment of fire-sensitive tree species, but infrequent enough to allow saplings of fire-tolerant tree species to reach fire resistant size. The groundlayer dominance by shrubs in many oak woodlands, especially hazelnut (Corylus americana), a high-light requiring, highly fire-tolerant species, suggests that many woodlands were maintained by fires of low frequency but high intensity that periodically consumed the overstory and stimulated Corylus, oak grubs and other fire-tolerant shrubs to resprout vigorously (Bowles et al. 1994, MN NHP 1993, Anderson 1991). In the absence of fire and/or grazing, this community is replaced by oak-hardwood forest and eventually by maple-beech-basswood forest. (This summary is taken from The Nature Conservancy's "Community Characterization Abstract" series. The entire 12-page abstract for Northern White Oak-Bur Oak Woodland may be obtained by contacting Don Faber-Langendoen, The Nature Conservancy, Midwest Regional Office, 1313 Fifth St. SE, Suite 314, Minneapolis, MN, 55414-1588.) Presettlement RangeThe presettlement range of Northern White Oak-Bur Oak Woodland included southeastern Minnesota, southern and western Wisconsin, northern Illinois, southwestern Michigan and possibly northern Indiana, northern Ohio and eastern Iowa. A map of this range is found at the back of this conservation and recovery plan. Presettlement AbundanceAs noted above, there are many limitations to accurately assessing presettlement acreages of Northern White Oak-Bur Oak Woodland. Nonetheless, we list below the best estimates we could find.
Extant RemnantsThe table at the back of this plan lists all inventoried Northern White Oak-Bur Oak Woodland remnants. These are listed by state in order of their natural quality. This list is nearly 100% up-to-date for Minnesota, the one state that has clearly defined and identified Oak Woodland separately from Oak Openings and Oak Forest. Forty-eight (48) Oak Woodland sites totaling 3,768 acres have been discovered within the presettlement range of Northern White Oak-Bur Oak Woodland. One site of three acres is located in Michigan; all other sites are located in Minnesota. Oak Woodland acreages by quality ranking consist of 1,281 "B" quality acres, 1,939 "C" quality acres, and 545 unranked acres. Current State ClassificationsAs noted above, each state has its own community classification system. Below are the state names for Northern White Oak-Bur Oak Woodland.
Recovery and Restoration PotentialThe probability of discovering new Northern White Oak-Bur Oak Woodland remnants appears significant. Except for Minnesota, no Midwestern state has even begun classifying Oak Woodlands as a separate community intermediate between Oak Opening and Oak Forest. It is probable that many sites currently listed by state natural heritage inventories as Oak Forest are best reclassified as Oak Woodland, particularly when diagnostic understory plant species are taken into consideration. The recent findings of numerous Oak Woodlands in the MN Driftless Area suggest that numerous new woodland sites are also likely to be discovered in the Driftless Area of Iowa and Wisconsin when these areas are more thoroughly inventoried. Thus the Driftless Area, with its clusters of Oak Woodland remnants, harbors the most promise for future establishment of Oak Woodland macrosites. Other Ideas for Enhancing Recovery Plan ImplementationOne idea we received was that it would be helpful to have a list of site occurences and population sizes for species that may be modal in, or limited to, Oak Woodland. A list of such elements needs to be developed. A few species tentatively suggested for investigation include the forbs Great Indian Plantain (Cacalia muhlenbergii), Ohio Horse Mint (Blephilia ciliata), Bracted Tick-Trefoil (Desmodium cuspidatum), and Heart-Leaved Skullcap (Scutellaria ovata).
ACKNOWLEDGEMENTSWe would like to thank the following persons for helping us compile the above plans: Marlin Bowles, Pat Comer, Hannah Dunevitz, Eric Epstein, Mike Homoya, Greg Schneider, Terry Seidel. Our apologies if we failed to acknowledge anyone. We hope you all will find these compilations useful! |
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