1993 Proceedings of the Midwest Oak Savanna Conferences
ECOLOGY AND STEWARDSHIP GUIDELINES FOR OAK BARRENS LANDSCAPES IN THE UPPER MIDWEST
Kim A. Chapman, Mark A. White
Oak barrens landscapes offer great opportunity for the restoration of large areas of savanna in the upper Midwest. Located on poor soils of outwash, lake plains and dunes, and high or irregular moraines, oak barrens consists of a complex mosaic of natural communities and vegetation structures. These include savanna and more closed-canopy woodlands and scrub, dry and moist oak sites, moist prairies, wetlands, and disjunct populations of plants of the Atlantic coastal plain. Fire and drought strongly influence vegetation structure, while local site factors (topography, soils, water bodies, wetlands) control both fire frequency and intensity, as well as species composition. Frequent low-intensity fires, probably more common historically on level ground near prairies, result in little tree death, producing a savanna or woodland structure with little woody understory. Infrequent high-intensity fires, probably historically more common in areas of rough topography, water bodies or swamps, result in much tree death, producing a dense canopy during fire-free periods, and scrub following a fire. Despite tree death, oaks persist as "grubs" due to their ability to resprout, and readily replace canopy trees during fire-free intervals. Several rare species occur in oak barrens, the most notable being the Karner blue butterfly. Degradation of oak barrens takes place when fires are prevented, hydrology is altered, land is cleared for agriculture or mined for sand, and residential and urban development takes place. Oak barrens are apparently not heavily damaged by grazing, which seems to maintain open conditions in the absence of fire. Restoration should address these factors, as well as consider the mosaic of several plant communities and vegetation structures that characterize oak barrens. Areas of 1,000-2,000 acres are perhaps minimal to encompass this variety, and provide for the habitat needs of some animal species. Recovery of disturbed lands around high quality barrens should be undertaken, given the ability of many oak barrens plant species to persist in the soil or recolonize bare ground. While fire is the most important management tool, manual cutting techniques are frequently used to accelerate removal of trees. Monitoring of canopy and understory cover, as well as groundlayer diversity, will help direct management towards goals set for an oak barrens landscape.
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 - 80% - sometimes termed a woodland physiognomy). The canopy layer is dominated by one or two of the following species: Quercus velutina (black oak), Quercus ellipsoidalis (northern pin oak), Quercus macrocarpa (bur oak), or rarely Quercus marilandica (black jack 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. The open oak barrens can be divided into two main types, Black Oak Barrens and Bur Oak - Northern Pin Oak Barrens. Northern Pin Oak Barrens of northern Wisconsin and Michigan form a variant of the Black Oak Barrens. Additional woodland types, not discussed in detail here, include White Oak - Black Oak Woodland.
The Oak Barrens occur in the prairie-forest transition region of the Midwest. Black Oak Barrens range from southern Michigan, the glaciated portions of Ohio, Indiana, Illinois, south of the tension zone through Wisconsin and southeastern Minnesota, and westward to the glaciated regions of Iowa, Missouri, Kansas and Nebraska (Fig. 1). Bur Oak - Northern Pin Oak Barrens occur in central and western Minnesota, and perhaps west-central Wisconsin (Fig. 1). Topography varies from level to gently rolling, and landforms from outwash plains to dune systems on the lake plain.
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 (Curtis 1959). Soils vary from almost pure sand to sandy loam to loamy sand. In the driftless area of Wisconsin, Minnesota, Iowa and Illinois, the communities occur on unglaciated, residual soil over sandstone bedrock.
Landscape Position, Origin and Type
Oak Barrens are dominant on portions of a) glacial lakeplains where aeolian dunes formed at old shorelines (Gordon 1969, Hanson 1976)(Fig. 2), and b) glacial outwash plains of sands and gravels, also subject to dune formation (Archambault 1987, Homoya et al. 1985) (Fig. 2). Dune ridges at southern Lake Michigan and southeast Lake Huron are closer and more regularly concentric than along the west shores of Lake Erie and Lake Huron.
Oak Barrens were present, but less common, in c) ice-contact (kettle-kame) and gravelly/sandy end moraines, where the ice sheet melted in place, piled unsorted materials in knobs and ridges, and created kettleholes where chunks of ice were buried, then melted (Archambault 1987, Chapman 1984). While the hydrological interactions in Oak Barrens are not well understood, seasonally high water plays an important role in lower areas (Cole and Pavlovic 1987). Oak Barrens on upper slopes may provide important locations for infiltration and creation of subsurface flow of water to lower, moister portions of the mosaic (S. Apfelbaum pers. comm.).
Location of plant communities in the oak barrens landscape mosaic
b) Lower dune ridges, lower slopes, dry flats between ridges, and north slopes support white oak or white-black oak woodland and savanna with bracken fern and Baptisia spp. in the east, changing to northern pin oak woodland and bur oak savanna west of south-central Wisconsin (Archambault 1987, Cole & Pavlovic 1987, Chapman & White pers. obs., Bakowsky 1988). Red oak may occur, particularly on north slopes. Clay lenses or mineral cementations often occur within the B soil horizon, improving soil moisture (Grigal et al. 1974, Archambault 1987).
c) Moist dune valleys and sand flats just above maximum flood level support moist sand prairie (Cole & Pavlovic 1987, White & Madany 1978) with characteristic composition (e.g., Scleria triglomerata, Hypericum kalmianum, Liatris spicata, Polygala sanguinea, Aletris farinosa, Baptisia spp., Spiraea spp.). Depth to water table on lakeplains January to April is 0.15-0.45m (Stone et al. 1980), in June 1.1-1.5m (Cole and Pavlovic 1987). This community diminishes inland from the Great Lakes and westward from central Wisconsin. Populus tremuloides readily occupies sites of moist sand prairie because of a water table near the surface (Cole and Pavlovic 1987, Grimm 1984). In southeastern Michigan outwash plains, black oak woodland exists on moist sand prairie (Archambault 1987).
d) Wet prairie, wet meadow, and marsh occupy channels and depressions in lakeplain dune formations and in outwash (Moran 1978, Cole & Pavlovic 1987, Chapman & White pers. obs.). Sites are flooded in spring (Grigal et al. 1974, Cole & Pavlovic 1987). Marshes occupy the deepest portions of channels anddepressions. In Minnesota outwash, water in marshes was 0.5-1.5m deep throughout the year (Grigal et al. 1974). Government land surveyors recorded depths of most marshes on the lakeplain in the Chicago region at 0.3-0.9m. June water table in lakeplain wet prairie was 0.5-1m below the surface (Cole & Pavlovic 1987). Quercus palustris (Pin oak) and Populus tremuloides occupy the highest sites in wet prairie (Cole & Pavlovic 1987, Chapman & White pers. obs.). Pin oak flats are found in southern Michigan and southwestern Ontario, but disappear northwest of Illinois.
Other communities: Water levels in wetlands fluctuate in these outwash plains and sandy glacial lake beds. Consequently, some gently sloping shorelines harbor communities of plants, many of them annuals, which respond favorably to cyclic flooding and draw-down, including species associated with the Atlantic Coastal Plain, carried here by migration along glacial lakeshores and waterfowl transport (Keddy & Reznicek 1982, McLaughlin 1932, Peattie 1922).
In southern Michigan, southern Wisconsin, and east-central Minnesota, peatlands supporting bog, bog forest, and fen can occupy depressions in outwash plains, to the exclusion of wet prairie and marsh.
In the prairie-forest transition zone the climate can support prairie, forest, or barrens vegetation. Vegetation pattern is most closely correlated with variation in physical factors of the landscape: topography, edaphic factors and their influence on disturbance regime (Anderson 1983). The variation in composition and structure of Oak Barrens is related to topographic and edaphic variability which influence nutrients, soil moisture, humidity, insolation, and to the effects of adjacent fire resistant communities on the movement of fire. These factors along with macroclimate affect fire frequency and intensity (Grimm 1984).
Soil Characteristics and Topographic Factors
Cole and Pavlovic (1987) demonstrated that elevation and slope aspect class differentiated dry oak woods from mesic oak woods. The highest elevation sites were all dry oak woods. High westerly slopes had the lowest stem density, while northern exposures had the highest basal area composed of Acer rubrum, Q. alba, and Sassafras albidum. Shrub cover changed with differences in slope aspect and insolation: exposed slopes were dominated by Vaccinium pallidum, V. angustifolium, and Gaylussacia baccata, while northern exposures had high cover of Prunus serotina, Cornus foemina, and Toxicodendron radicans.
Climate and Drought
Climate, particularly the periodic occurrence of drought, has played a role in the distribution and persistence of oak barrens. Kline and Cottam (1979) suggested that climate shifts in the last 500 years may have affected the persistence of some oak systems. Whitford and Whitford (1971) indicated that droughty conditions on sandy soils may be a more significant factor maintaining oak barrens in central Wisconsin than fires. Faber-Langendoen and Tester (1993) found that drought, perhaps in combination with rapid moisture changes, probably caused high mortality rates for mature oak trees in parts of the barrens at CCNHA that had sparse canopy cover.
Landscape Patterns and their Effects on Disturbance
In Minnesota, almost exclusively Indian-set fires swept entire landscapes in spring or fall, except in fire-safe areas behind rivers, streams, lakes, and rough topography (Grimm 1984). Presettlement vegetation on the Anoka Sand Plain in east-central Minnesota illustrates the influence of landscape patterns and adjacent plant communities on the distribution of oak barrens. i) Oak barrens sites next to fire-resistant portions of the landscape (e.g. open water, tamarack-cedar swamps) were described by government surveyors in 1854-56 as "Oak Brush", "Grub Oak", "Brushland," and "Brushy Prairie." ii) Away from these fire sinks, but next to marshes and wet meadows (which burned easily only in the fall), oak barrens sites were described as "Black Oak with Grub Oak understory", "Scattering Black Oak with Scrub Oak" and "Timber scattering Black and Bur Oak and Oak Brush." iii) Next to level prairie with few marshes or wet meadows (a fire source that always burned), oak barrens sites were described as "all of line in Prairie w/scattered Bur and Black Oak", "Bur Oak Openings" and "Bur Oak and a Few Black Oak, no Underbrush."
Conversely, small wetland sites in a matrix of oak barrens were mapped by surveyors as marsh and wet meadow. But marsh and wet meadow sites adjacent to fire-resistant plant communities sometimes supported tamarack swamp.
Disturbances: Fire Effects
The role of fire in oak barrens has been documented and investigated in numerous studies (e.g., Curtis 1959, White 1983, Anderson and Brown 1983, Henderson and Long 1984, Grimm 1984, Tester 1989, Faber-Langendoen and Davis 1995). In general fire maintains open canopy, and depending on frequency and intensity either open or scrubby understory. In the absence of fire Oak Barrens may succeed to closed dry forest (Curtis 1959, White 1986).
White (1983, 1986) determined in a central MN oak barrens (CCNHA) that low intensity prescribed fireat 1 to 3 years intervals removed woody cover in the sapling and shrub layers but had little effect on large canopy trees (>30 cm dbh). Graminoid and forb species increased in importance with this fire regime. Quercus ellipsoidalis peaked on unburned sites, while Quercus macrocarpa peaked on burned sites. Tester (1989) examined the effects of fire frequency on vegetation at the same site. Tree density and basal area decreased with greater burning frequency, and most of the reduction occurred in the 5 to 25 cm dbh size classes. Species richness increased with fire frequency. Results suggested that 2 year burn intervals produced the greatest ground layer diversity. Percent cover of true prairie species (graminoids, forbs, and shrubs) tended to increase. Introduced grasses and forbs as a whole showed no significant change in cover with respect to the number of burns. However, initial cover values were less than 1% at most sites.
Henderson and Long (1984) examined the recent fire history of two black oak woodlands in northern Indiana and determined that fire frequency and intensity strongly influenced composition and structure. Infrequent, high intensity fires created an open overstory and a scrubby sapling layer of black and white oak and high cover of herbaceous species. More frequent low intensity fires were associated with higher canopy cover, higher density, lower basal area and lower herb and shrub cover. Curtis (1959) hypothesized that scrub oak barrens were subject to infrequent catastrophic fires which removed the canopy and created a dense scrub oak structure.
Anderson and Brown (1983) studied the effects of a prescribed fire in an open oak barrens and adjacent closed forest in Northern Illinois. They found no mortality or damage to large, isolated trees in the barrens while in the closed forest tree mortality was high. Tree mortality in the forest was attributed to high fuel accumulations. They hypothesized that isolated trees in a savanna are in part protected by 1) shade which inhibits graminoid and forb productivity, resulting in low fuel loads, 2) oak leaves are swept away by wind leaving small amounts of leaf fuel. Anderson and Brown (1986) proposed that the maintenance of closed forests in fire susceptible areas was precluded by fuel buildups of quantities sufficient to allow fires to cause high tree mortality and convert closed forest to savanna. However, isolated trees may be more susceptible to drought effects (Faber-Langendoen and Tester 1993).
Disturbance: Grazing Effects
White and Chapman (1989) found a strong correlation between species distribution and canopy cover in oak barrens and oak woodland in northern Ohio. Species composition changed from dry site, disturbance-adapted species to those characteristic of shaded, mesic sites along gradients of open to closed canopy and dry todry-mesic soil moisture.
In general, species characteristic of dry open habitats and of more closed mesic sites are distributed in oak barrens stands relative to canopy cover, site moisture status and disturbance history.
Presettlement Vegetation Descriptions
Recently a new model has emerged which describes a more variable physiognomy for oak barrens. Grimm (1981) determined that the prevailing physiognomy for oak barrens in the Big Woods region of Minnesota was scrub oak. He described the vegetation as dense thickets of brush and scrub oak, where scrub oak patches occurred in a mosaic with grassland. "True savanna" (widely spaced trees with a grassland understory) was present but was not widespread.
Grimm (1981, 1984) examined studies of presettlement vegetation from other areas in the prairie-forest border region and determined that oak barrens formed a heterogeneous vegetation group. In this model, most trees were small, as few reached sufficient size to resist stem killing by frequent fires. Trees weakened by fire were susceptible to pathogens. Sprouts grew from oak grubs in the understory. Frequent fires kept oak sprouts low in stature, but increased numbers of sprouts. A few years without fire might lead to formation of dense thickets with scrub oak overtopping herbaceous vegetation.
An examination of land survey records of extant oak barrens and other areas supports the view of a heterogeneous physiognomy. Survey line descriptions from CCNHA in central Minnesota cited earlier [Landscape patterns and their effects on disturbance regimes] provide a good example of this: "scattering black and burr oak, oak brush", "black oaks with scrub oak understory", "burr oak and few black oak, no underbrush", "brushy prairie". Bacone et. al. (1979) provided these descriptions of presettlement Oak Barrens in northern Indiana: "shrubby yellow and jack oak barrens" 'white and yellow oak barrens" "rolling with oak". In southern Michigan descriptions ranged from open park like savanna with large scattered trees to small scrub oak barrens (Chapman 1984). Descriptions from the Kitty Todd preserve in northern Ohio refer to "scrub oak, oak brush, soil 3rd rate" (Huffman 1989, pers. comm.).
Savannas on Walpole Island in Lake Erie have been burned annually for the past 100 years. These stands have both the classic scattered canopy structure with large widely spaced oaks and an understory of prairie species, as well as woodland structure. Oak grubs are present but remain small as a result of the annual fires (Bakowski 1989, pers. comm.).
In summary, oak barrens growing on dry, infertile soils were heterogeneous, ranging from dense scrub oak to open, scattered canopies, depending on the fire regime. The fire regime was influenced by fire breaks, topo-edaphic factors, climate, and native American activities (Grimm 1981, 1984, Anderson and Brown 1986).
Panzer (1988) suggests that prairie-restricted insect species are extinction prone because of fluctuating population, poor dispersal, and patchy distribution. Competition, changes in habitat that decrease its quality, predation and excessive burning can contribute to their extirpation. Timing and frequency of burning may be important for maintaining invertebrate fauna.
Oak barrens represent important habitat for a number of rare Lepidoptera. The following rare Lepidoptera are characteristic of oak barrens habitat and deserve special management concern: Lycaeides melissa samuelis (Karner blue), Incisalia iris (Frosted Elfin), Erynis persius (Persius Dusky Wing), Viola pedata (Regal Fritillary). A recent publication by Andow et al. (1994) brings together information on the biology, status, and management of Karner blue. For information on species composition of other invertebrates see Panzer (1987, 1988), Panzer and Gnaedinger (1986), and Panzer and Stillwaugh (1987).
The herb layer of oak barrens is generally resistant to grazing. Curtis (1959) noted that prairie was most resistant to grazing at wet and dry extremes and most susceptible to replacement at the mesic center. Tilman (1987) suggests that cool season exotics have higher nitrogen requirements than dry prairie grasses and thus are limited by low nitrogen levels on dry, infertile sites. Overgrazing may weaken native grasses and allow increased abundance of cool season exotics such as Poa pratensis and P. compressa.
Beaver may not have occupied certain lakeplain barrens that lacked flowing streams (Cole & Pavlovic 1987). But Hubbard (1838) was told by Indians that beaver, abundant on the southeast Michigan lakeplain but gone by 1807, created wet prairies by damming streams. On lakeplains and outwash plains with streams, beaver would dramatically influence the landscape by i) expanding wetland area, and ii) creating barriers to fire. Because flooding creates and maintains wet prairie and moist sand prairie, beaver benefited these communities. Since active impoundments contain some open water year-round and even abandoned dams retain spring meltwater, fires could not cross beaver-influenced wetlands easily, and perhaps not at all in spring.
Alteration of hydrology in barrens landscapes by removal of beaver, ditching and tiling may not seriously affect Oak Barrens per se because they are located higher on the landscape (Cole and Pavlovic 1987, Archambault 1987). However, oak barrens landscapes are studded with moist sand prairies, wet prairies, wet meadows, and marshes. These communities co-occur with specific soils, depths to water table, and perhaps amount of organic matter (Cole and Pavlovic 1987, Huffman pers. obs.). Early accounts indicate dramatic increases in woody cover on prairie portions of the landscape mosaic following ditching and drainage (Davis 1908).
Agriculture and Sand Mining
Studies at CCNHA on old fields which were formerly oak barrens indicate low nitrogen levels may be responsible for slow invasion of abandoned fields by oaks (Tilman 1987). Documentation of the rapidity of invasion of oaks on other abandoned farmlands would be of interest.
Borrow pits and sometimes other sand-mining operations are found in oak barrens landscapes. This is more likely to occur in lakeplain systems where dunes are larger. Oak barrens on southeast Lake Michigan sand dunes have been destroyed by sand mining (Chapman pers. obs.). Portions of Kitty Todd Preserve were mined (Huffman pers. obs.).
Residential and Industrial Development
Animal populations may not persist, however. As discussed above, characteristic butterflies of oak barrens have declined over most of their ranges. Schweitzer and Rawinski (1987) note that small community occurrences almost always have degraded Lepidoptera fauna in northeastern pine-oak barrens. They also note that even sites larger that 1000 acres have lost species. The decline of Lepidoptera in oak barrens is related to: 1) loss of larval food plants because of increased shading resulting from fire suppression (cf. Shuey et al. 1987) 2) barriers to migration (e.g., highways, fences, parking lots) (Panzer 1988). Persistence of butterflies over the last 100 years is linked to larger areas where mixture of open and closed canopy is found. Panzer (1988) makes3 general recommendations for maintaining populations of restricted insect species 1) eliminate unnatural landscape features, 2) maximize habitat diversity, noting that because of dichotomous life histories insects often require habitat mosaics, 3) burn with restraint.
An assessment of area needed for preserves can be done using minimum viable population estimates. Assuming a minimum viable population 200 interbreeding adults, and with or without an additional 600 other individuals, the density per acre of animals can be used to calculate a minimum acreage needed for population persistence. Although these are gross estimates they give some indication of preserve sizes needed to maintain some types of faunal diversity:
The essence of an oak barrens is its variable physiognomy in time and space. As has been shown, before settlement this dynamic resulted from the complex interplay of fire frequency and intensity, fire source areas and fire barriers, woven into the landscape mosaic and played out over vast expanses. That pattern of diversity no longer exists, and oak barrens preserves are less secure as a result. Mimicking the landscape diversity pattern is possible. It may require areas of 1000 to 2000 acres for management units large enough to achieve a physiognomy and composition suitable for some targeted animals.
Increasing Preserve Size using Degraded Lands
Restoration of barrens landscapes has greater potential for rapid success than for most other Midwest ecosystems. The recovery potential of degraded barrens is good. Moreover, large blocks of degraded barrens often abut high quality oak barrens, or lie next to abandoned fields and other disturbed areas where oak barrens groundlayer species persist.
Building on a high quality core, preserve design should strive for integration of large blocks of closed oak barrens with refugia of barrens groundlayer species. It should also strive for restoration around a high quality core of large blocks of degraded barrens showing good recovery potential (diagnostic or constant species of barrens are present, albeit rare and struggling).
Results of management treatments on degraded oak barrens in the Midwest indicate good potential exists to restore natural community composition and structure. Little is known about the recovery potential of faunal populations.
Recovery with Fire
Results from Kitty Todd Preserve, northern Ohio (Huffman unpublished data), central Wisconsin (Blewett 1978, Holtz and Howell 1982), and northern Wisconsin (Vogl 1961) indicate rapid change in herb layer composition toward barrens species with fire and/or cutting treatments.
A catastrophic fire in 1971 turned oak woods into dense oak-aspen scrub at Kitty Todd Preserve. In 1987, 96% of the area was covered by oaks, aspen, and 15-foot cherries. Greenbriar dominated the understory. After a fall 1987 burn, 45 barrens understory species were recorded, and canopy cover was reduced to 41% (Huffman unpubl. data).
In degraded barrens these barrens species may originate from 1) perennial plants present as rhizomes in the soil or as understory plants of low vigor, 2) viable seeds dormant in the seedbank until canopy and litter cover are removed, and 3) a seed source located nearby in stands of high quality barrens vegetation.
Recovery After Soil Disturbance
Disturbance of the soil which removes litter and underbrush can restore groundlayer species in oak barrens. An aspen thicket, bulldozed in 1985, was later purchased by TNC and found to harbor the highestconcentration of rare species in the Kitty Todd Preserve (Huffman 1988). A fire-break bulldozed through another aspen thicket next to an abandoned field at Kitty Todd produced populations of Lupinus perennis, Tephrosia virginiana, Comandra umbellata, Asclepias tuberosa and Helianthemum sp. Populations of the rare butterflies Erynnis persius and Incisalia iris colonized lupine in this fire-break the next year (Shuey et al. 1987).
A strip that removed two to four inches of soil was bulldozed through thick underbrush in an oak barrens on the Saginaw lakeplain northeast of Bay City, MI in 1978. In 1982, Asclepias tuberosa, Comandra umbellata, Salix humilis, Helianthus spp., and Aster spp. were observed growing in the bulldozed strip beneath the closed oak canopy, but not elsewhere (Chapman pers. obs.). Whether a comparable effect could be induced by fire on these sites is not known, nor is it clear to what degree only certain barrens species may benefit from bulldozing.
Sand pits at Kitty Todd and Oak Openings Metropark provide habitat for species associated with shallow ponds with fluctuating water levels, a minor but significant community of oak barrens landscapes (Huffman pers. obs.). Plant species include those disjunct from the Atlantic Coastal Plain. Sand pits expose the water table and provide suitable habitat for species which have disappeared from their former habitat because regional water tables have been lowered.
Powerline right-of-ways, roadways, firebreaks, and even bulldozed areas are refuges for shade-intolerant barrens plants (Huffman and Chapman pers. obs.).
Biological monitoring is needed to assess effectiveness of management treatments and progress toward stated goals. Goals are developed by comparing present vegetation composition and structure with a "model" of the natural community. Divergence from the model directs management. For example, a natural community model may indicate that a site should have an open canopy structure with low woody cover and density, but the site currently has 80% canopy cover and 40% subcanopy cover. The intent of management is to reduce canopy cover less than 30% and subcanopy to 10% cover. Monitoring would focus on measuring movement toward these goals.
Objective 1: Create and maintain very open (savanna) and open understory (woodland) conditions on dry or fire prone sites. For monitoring management accomplishments in oak barrens use the following:
For the herb layer estimate cover of constant and diagnostic species in a 5x20 m subplot in the center of the 20x25m plot, or use 15-25 0.5x1.0 m (or 0.25x0.5 m) microplots systematically located within either a single 20x25 macroplot or, if a larger plot size was used, spread over the entire plot.
Objective 2: Create and or maintain scrub oak barrens on sites prone to low frequency, high intensity fires, with low canopy cover (5 to 30%), high cover of oak species in tall shrub/sapling and low shrub layers (30%), and high graminoid cover (75%).
Biological Monitoring Programs
1) What are fire effects on rare faunal populations? A number of rare lepidoptera have host plants occurring on barrens. We need more information on the biology, ecology and the effects of standard management practices on these species.
2) What are the effects of different burn intervals, intensities and seasons on vegetation and rare fauna? Fire history of oak barrens is essential.
3. a) What is the nature of seasonal water changes? What is the role of seasonal high water tables on the vegetation mosaic? How does the water table fluctuate seasonally? Models of hydrologic systems are needed for individual preserves.
b) What is the nature of annual water changes? What is the role of periodic droughts?
4) What roles do seedbanks, vegetative reproduction, and external seed sources play in restoration of degraded oak barrens?
5) How rapidly do barrens species recolonize abandoned agricultural land? How does the kind and degree of disturbance influence recolonization?
6) Information is needed on minimum viable population size, and area/habitat requirements for characteristic barrens animal species.
Oak barrens should be managed using natural processes that shaped them--fire and water. In managing barrens diversity, the location, number and size of each kind of barrens physiognomy and composition should be considered. Wetland patches in the barrens landscape should also be brought into the equation as integral "filters" of the regional fire pattern. Barrens management should restore good numbers of large patches which represent different barrens physiognomies. This approach provides habitat for shade-tolerant and light-demanding plant species, and large blocks of different kinds of uniform habitat for animals.
Application of different intensity fires, in fall and spring, under cool and hot fire conditions, creates the necessary diverse physiognomies. Infrequent, canopy-replacing fires in dense woody cover may produce scrub; annual running ground fires in woodland with heavier graminoid groundlayer may produce open, scattered tree canopy. Intermediate conditions arise from intermediate prescriptions.
Spring burns carry irregularly through areas of the barrens landscape influenced by high spring water table. Patchy fire leaves refugia for invertebrates, other species, and may permit oak seedling establishment. Late spring and summer burns probably do greater harm to woody plants than fall or early spring burns. Many wetlands, moist sand prairie, pin oak flats, and other low areas may be too wet for spring burning. Schwegmanand McClain (1985) observed that fall fires burn wet prairies and marshes which are often too moist to burn in the spring. Analysis of weather conditions at the Kitty Todd Preserve indicate that fire weather occurs most frequently in the fall (Huffman pers. comm.). Fall may have been the typical burn season in northwest Ohio (Aldrich 1888). An historical account reported an Indian-set fire in a snowless December and another author indicated Indians set fires in fall in southern Michigan (Chapman 1984). Schwegman and McClain (1985) state that presettlement fires in Illinois occurred frequently in the fall. However, in southern Wisconsin, where cool/wet falls are frequent, this may not be the case (R. Henderson 1989, pers. comm.).
Because data on the response of barrens to different fire treatments is scanty, all new information is useful and should be recorded and reported. Managers should take detailed records on each burn, such as weather conditions before and after the burning, fuel characteristics, and fire behavior parameters. Fire observations must be coupled with information on vegetation response. If possible, a monitoring station should be established within the treatment area before the first treatment and a second station could be established in an areas not to be treated.
To produce barrens structure without a brushy understory, successive low-intensity burns are necessary. Use annual burns during the restoration phase of management until the height and density of woody sprouts meets a stated goal. For more rapid results on badly degraded sites, cutting may be required to augment annual burning. Sprouts allowed to grow a full season are able to develop larger and larger root systems each year, aggravating a woody plant problem. Once a structural goal is met, fire return interval can be relaxed to once every 1-3 years.
To produce scrub barrens with a graminoid understory, high-intensity fires at long intervals are necessary. A single fire under extreme conditions set at Jasper-Pulaski State Fish and Wildlife Area (IN) removed virtually all oaks from an almost closed canopy, producing a mosaic of dense oak scrub and graminoid patches (White & Chapman pers. obs.). Intervals between fires may be as great as 15 years.
Fire breaks should be clear of dead fuels. (Leaf blowers have been used successfully for leaves and mowed fine fuels.) In barrens, snags within falling distance of fire breaks should be knocked or sawed down to ensure burn crew safety. Barrens fires can require long hours of mop-up; dead limbs high in old trees may ignite unexpectedly and throw sparks into non-burn units. Old snags can smolder throughout the growing season (A. Steuter pers. comm.) If fire management is successful, live woody cover is converted to downed heavy fuels, which can accumulate and require intensive fire break preparation and mop-up.
Burn crews should be properly equipped with hardhats, Nomex suits, and radios in burn units large enough to lose sight of crew members. Burns must be carefully planned and executed according to all applicable guidelines established by the managing agency.
Figure 1. Distribution map for the two major types of open oak barrens in the Upper Midwest: Bur Oak -Northern Pin Oak Barrens (western type - primarily MN) and Black Oak Barrens (eastern type). Within the Black Oak Barrens type, two areas on glacial lake plain are outlined separately. Location of high-quality sites that are nominated (dots) and dedicated (circles) National Natural Landmarks are shown: 1) Agassiz Dunes, 2) Cedar Creek-Helen Allison, 3) Chippewa River sites, 4) Ft. McCoy, 5) Illinois Beach, 6) Kankakee Sand Plains site, 7) Indiana Dunes, 8) Allegan, 9) Shakey Lakes. Other site (triangle): 10) Toledo Metroparks-Kitty Todd.
Figure 2. Position of plant communities in barrens landscapes in outwash plains (top figure) and glacial lake plains (bottom figure). a) dune and ridge tops and slopes, b) lower dune ridges, lower slopes and dry flats, c) moist dune valleys and sand flats just above maximum flood level, d) channels and depressions where sites are flooded in spring.
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