Oak barrens is a fire-dependent savanna type dominated by oaks, having between 5 and 60% canopy, with or without a shrub layer. Black oak (Quercus velutina) and white oak (Q. alba) typically dominate the scattered overstory. The predominantly graminoid ground layer is composed of species associated with both prairie and forest communities. Oak barrens are found on droughty soils and occur typically on nearly level to slightly undulating glacial outwash in southern Lower Michigan.
County Distribution Map
Global Rank: G2? - Imperiled (inexact)
State Rank: S1 - Critically imperiled
Oak barrens occur on well-drained, nearly level to slightly undulating sandy glacial outwash, and less often on sandy moraines or ice-contact features. It is found in the southern Lower Peninsula in the driest landscape positions, such as ridge tops, steep slopes, south- to west-facing slopes, and flat sandplains. Oak barrens typically occur in bands surrounding prairie and grade into dry sand prairie on one edge and dry forest on the other.
Characteristic soils of oak barrens are infertile, coarse-textured, well-drained sand or loamy sand with medium to slightly acid pH and low water-retaining capacity. The drought soils contain little organic matter and lack the fine-textured illuvial horizon associated with the richer and more productive soils of the oak openings.
Oak barrens likely originated when prairie fires spread into surrounding closed oak forest with enough intensity to create open barrens. Repeated low-intensity fires working in concert with drought, frost, and windthrow maintained oak savanna ecosystems. Fires prevented canopy closure and the dominance of woody vegetation. Fires in oak barrens and prairie typically occur during the spring, late summer, and fall. Flammability peaks bimodally, in the spring before grass and forb growth resumes and in the late summer and autumn after the above-ground biomass dies. Infrequent, high-intensity fires kill mature oaks and produce barrens covered by abundant, scrubby oak sprouts (i.e., oak grubs). Park-like barrens with widely spaced trees and an open grass-dominated ground flora are maintained by frequent, low-intensity fires that occur often enough to restrict growth of oak grubs into overstory trees.
Numerous biotic factors influence the patterning of vegetation of oak barrens. In addition to widely distributed overstory trees, barrens are characterized by scattered ant mounds. Mound-building ants play a crucial role in soil development of prairies, savannas, and barrens; ants mix and aerate the soil as they build tunnels and bring soil particles and nutrients to the topsoil from lower soil horizons. Herbivores can limit woody establishment and growth. With their flammable properties, grasses and forbs help maintain the annual fire regime. Open canopy conditions are also preserved by the development of a dense herbaceous litter, which limits tree seedling establishment. Overstory trees influence vegetative composition by affecting the distribution of nutrients, light, and moisture.
The canopy layer generally varies from 5 to 60% cover and is dominated or codominated by black oak and white oak. These species of oak are also prevalent as multi-stemmed shrubs of stump-sprout origin, especially in areas of high fire intensity. In addition, red maple (Acer rubrum), black cherry (Prunus serotina), big-toothed aspen (Populus grandidentata), quaking aspen (P. tremuloides), and northern pin oak (Q. ellipsoidalis) are often found in the overstory and subcanopy of this community. Northern pin oak is especially common on excessively well-drained, infertile sites. Prevalent species of the subcanopy layer include hickory species (Carya spp.), dogwoods (Cornus spp.), cherry species (Prunus spp.), and sassafras (Sassafras albidum). Characteristic shrubs include serviceberry (Amelanchier spp.), bearberry (Arctostaphylos uva-ursi), New Jersey tea (Ceanothus americanus), sweetfern (Comptonia peregrina), dogwoods, American hazelnut (Corylus americana), beaked hazelnut (C. cornuta), hawthorn species (Crataegus spp.), wintergreen (Gaultheria procumbens), huckleberry (Gaylussacia baccata), wild plum (Prunus americana), choke cherry (P. virginiana), sand cherry (P. pumila), dwarf chinquapin oak (Quercus prinoides), shining sumac (Rhus copallina), pasture rose (Rosa carolina), northern dewberry (Rubus flagellaris), prairie willow (Salix humilis), and low sweet blueberry (Vaccinium angustifolium). The ground layer is dominated by graminoids and forbs. Common species include little bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardii), and Pennsylvania sedge (Carex pensylvanica), with Pennsylvania sedge often replacing the bluestems in shaded areas and fire-suppressed communities. Other prevalent herbs of the oak barrens include hair grass (Avenella flexuosa), false foxglove (Aureolaria spp.), tickseed (Coreopsis lanceolata), slender sand sedge (Cyperus lupulinus), poverty grass (Danthonia spicata), panic grass (Dichanthelium implicatum), flowering spurge (Euphorbia corollata), woodland sunflower (Helianthus divaricatus), porcupine grass (Hesperostipa spartea), June grass (Koeleria macrantha), false dandelion (Krigia biflora), white pea (Lathyrus ochroleucus), hairy bush clover (Lespedeza hirta), rough blazing star (Liatris aspera), dwarf blazing star (L. cylindricea), wild lupine (Lupinus perennis), wild bergamot (Monarda fistulosa), wood betony (Pedicularis canadensis), black oatgrass (Piptochaetium avenaceum), prairie heart-leaved aster (Symphyotrichum oolentangiense), goats-rue (Tephrosia virginiana), and birdfoot violet (Viola pedata). The flora of this community is a mixture of prairie and forest species, with prairie forbs and grasses more abundant in areas of high light and forest forbs and woody species in the areas of low light. The invasive plants spotted knapweed (Centaurea stoebe) and common St. John’s-wort (Hypericum perforatum) are becoming increasingly common, especially along roadsides and trails through the community.
Oak barrens and surrounding prairie habitat once supported a rich diversity of invertebrates including numerous species of butterflies, skippers, grasshoppers, and locusts. Mound-building ants and numerous grassland birds also once thrived in barrens and prairies. The fragmented and degraded status of Midwestern oak barrens, savannas, and prairies has resulted in the drastic decline of numerous insect and bird species associated with these habitats and their host plants. The now extinct passenger pigeon (Ectopistes migratorius) was likely a keystone species in oak ecosystems, roosting in oaks by the thousands. Where large herbivores were abundant, grazing may have helped inhibit the succession of oak barrens to woodland or forest.
- Agalinis gattingeri (Gattinger’s gerardia, state endangered)
- Androsace occidentalis (rock-jasmine, state endangered)
- Arabis missouriensis var. deamii (Missouri rock-cress, state special concern)
- Aristida tuberculosa (beach three-awned grass, state threatened)
- Artemisia ludoviciana (western mugwort, state threatened)
- Aster sericeus (western silvery aster, state threatened)
- Astragalus canadensis (Canadian milk vetch, state threatened)
- Astragalus neglectus (Cooper’s milk vetch, state special concern)
- Baptisia leucophaea (cream wild indigo, state endangered)
- Botrychium pallidum (pale moonwort, state special concern)
- Bouteloua curtipendula (side-oats grama grass, state threatened)
- Buchnera americana (blue-hearts, presumed extirpated from Michigan)
- Carex gravida (sedge, presumed extirpated from Michigan)
- Carex richardsonii (Richardson’s sedge, state special concern)
- Celtis tenuifolia (dwarf hackberry, state special concern)
- Cirsium hillii (Hill’s thistle, state special concern)
- Commelina erecta (slender day-flower, presumed extirpated from Michigan)
- Cuscuta indecora (dodder, state special concern)
- Cuscuta pentagona (dodder, state special concern)
- Dalea purpurea (purple prairie-clover, presumed extirpated from Michigan)
- Dasistoma macrophylla (mullein foxglove, state threatened)
- Dennstaedtia punctilobula (hay-scented fern, state threatened)
- Eupatorium sessilifolium (upland boneset, state threatened)
- Euphorbia commutata (tinted spurge, state threatened)
- Gentiana flavida (white gentian, state endangered)
- Gentiana puberulenta (downy gentian, state endangered)
- Geum triflorum (prairie-smoke, state threatened)
- Gillenia trifoliata (Bowman’s root, state threatened)
- Helianthus hirsutus (whiskered sunflower, state special concern)
- Helianthus microcephalus (small wood sunflower, presumed extirpated from Michigan)
- Helianthus mollis (downy sunflower, state threatened)
- Hieracium paniculatum (panicled hawkweed, state special concern)
- Houstonia caerulea (bluets, state special concern)
- Ipomoea pandurata (wild potato-vine, state threatened)
- Kuhnia eupatorioides (false boneset, state threatened)
- Lactuca floridana (woodland lettuce, state threatened)
- Lechea minor (least pinweed, state special concern)
- Lechea stricta (erect pinweed, state special concern)
- Lespedeza procumbens (trailing bush-clover, presumed extirpated from Michigan)
- Linum sulcatum (furrowed flax, state special concern)
- Linum virginianum (Virginia flax, state threatened)
- Onosmodium molle (marbleweed, presumed extirpated from Michigan)
- Paronychia fastigiata (low-forked chickweed, state special concern)
- Penstemon calycosus (smooth beard tongue, state threatened)
- Penstemon pallidus (pale beard tongue, state special concern)
- Phlox bifida (cleft phlox, state threatened)
- Prunus alleghaniensis var. davisii (Alleghany plum, state special concern)
- Scutellaria incana (downy skullcap, presumed extirpated from Michigan)
- Silene stellata (starry campion, state threatened)
- Silene virginica (fire pink, state threatened)
- Sisyrinchium strictum (blue-eyed-grass, state special concern)
- Solidago bicolor (white goldenrod, state special concern)
- Sporobolus clandestinus (dropseed, state special concern)
- Tradescantia virginiana (Virginia spiderwort, state special concern)
- Trichostema dichotomum (bastard pennyroyal, state threatened)
- Triplasis purpurea (sand grass, state special concern)
- Ammodramus savannarum (grasshopper sparrow, state special concern)
- Atrytonopsis hianna (dusted skipper, state threatened)
- Catocala amestris (three-staff underwing, state endangered)
- Cryptotis parva (least shrew, state threatened)
- Dendroica discolor (prairie warbler, state endangered)
- Elaphe o. obsoleta (black rat snake, state special concern)
- Erynnis p. persius (Persius duskywing, state threatened)
- Hesperia ottoe (ottoe skipper, state threatened)
- Incisalia henrici (Henry’s elfin, state special concern)
- Incisalia irus (frosted elfin, state threatened)
- Lepyronia gibbosa (Great Plains spittlebug, state threatened)
- Lycaeides melissa samuelis (Karner blue, federal endangered and state threatened)
- Microtus ochrogaster (prairie vole, state endangered)
- Oecanthus pini (pinetree cricket, state special concern)
- Orphulella p. pelidna (barrens locust, state special concern)
- Papaipema sciata (Culver’s root borer, state special concern)
- Prosapia ignipectus (red-legged spittlebug, state special concern)
- Pygarctia spraguei (Sprague’s pygarctia, state special concern)
- Pyrgus centaureae wyandot (grizzled skipper, state special concern)
- Schinia indiana (phlox moth, state endangered)
- Schinia lucens (leadplant flower moth, state endangered)
- Scudderia fasciata (pine katydid, state special concern)
- Sistrurus c. catenatus (eastern massasauga, federal candidate species and state special concern)
- Speyeria idalia (regal fritillary, state endangered)
- Terrapene c. carolina (eastern box turtle, state special concern)
Biodiversity Management Considerations
Fire is the single most significant factor in preserving the oak barrens landscapes. Where remnants of oak barrens persist, the use of prescribed fire is an imperative management tool for maintaining an open canopy, promoting high levels of grass and forb diversity, deterring the encroachment of woody vegetation and invasive species, and limiting the success of dominants. Fire intervals of one to three years bolster graminoid dominance, increase overall grass and forb diversity, and remove woody cover of saplings and shrubs. Burning at longer time intervals will allow for woody plant seedling establishment and persistence. Where rare animal species are a management concern, burning strategies should allow for ample refugia to facilitate effective post-burn recolonization. When feasible, fire management of oak barrens should include burning adjacent communities as well, including dry sand prairie, dry southern forest, oak-pine barrens, coastal plain marsh, intermittent wetland, bog, prairie fen, and southern wet meadow.
Degraded barrens that have been long deprived of fire often contain a heavy overstory component of shade-tolerant species, which can be removed by mechanical thinning or girdling. Restored sites will need to be maintained by periodic prescribed fire and may require investment in native plant seeding where seed and plant banks are inadequate.
Historically, Native Americans played an integral role in fire regimes of oak savanna and barrens ecosystems, intentionally and/or accidentally setting fires. Oak barrens have been cleared for sand mining, agriculture, and residential and urban development. Alteration of historic fire regimes has shifted most barrens types into woodlands and forest. Wildfire suppression policies instituted in the 1920s in concert with road construction, expansion of towns, and increased agriculture caused a dramatic decrease in fire frequency and intensity. The reduction of fire in the landscape resulted in the succession of open oak barrens to closed-canopy forests dominated by black and white oaks with little advanced regeneration of oaks and a vanishing graminoid component. In addition, timber exploitation of oaks in the 1920s destroyed or degraded oak barrens across Michigan. Many oak barrens fragments are currently completely dominated by black oak as the result of selective harvest of canopy white oak. In addition to simplified overstory structure, these communities are often depauperate in floristic diversity as the result of fire suppression and subsequent woody encroachment, livestock grazing, off-road vehicle activity, and the invasion of non-native species. Ground layer vegetation of barrens remnants has been inhibited by low levels of light filtering through the dense overstories and impenetrable understories (often dominated by invasive shrubs) and by the thick litter layers that have accumulated from nearly a century of fire suppression.
Monitoring and control efforts to detect and remove invasive species are critical to the long-term viability of oak barrens. Invasive species that threaten the diversity and community structure include common St. John’s-wort, spotted knapweed, black swallow-wort (Vincetoxicum nigrum), white swallow-wort (V. rossicum), Canada bluegrass (Poa compressa), ox-eye daisy (Leucanthemum vulgare), hawkweeds (Hieracium spp.), sheep sorrel (Rumex acetosella), hoary alyssum (Berteroa incana), Oriental bittersweet (Celastrus orbiculatus), common buckthorn (Rhamnus cathartica), bouncing bet (Saponaria officinalis), autumn olive (Elaeagnus umbellata), Eurasian honeysuckles (especially Lonicera morrowii, L. tatarica, and L. xbella), and multiflora rose (Rosa multiflora).
The oak barrens community is a heterogeneous savanna vegetation type with variable physiognomy in time and space. Structurally, oak barrens range from dense thickets of brush and understory scrub oak within a matrix of grassland to park-like open woodlands of widely spaced mature oak and virtually no shrub or subcanopy layer above the open graminoid and forb ground flora. The physiognomic variations, which occur along a continuum, are the function of the complex interplay between fire frequency, fire intensity, and site conditions. Scarlet oak may be present in oak barrens on the southeast Lower Michigan lakeplain, where the community is limited to dry beach ridges.
Similar Natural Communities
- Anderson, M.D., and L.E. Brown. 1983. Comparative effects of fire on trees in a Midwestern savannah and an adjacent forest. Bulletin of the Torrey Botanical Club 119(1): 19-28.
- Bowles, M.L., and J.L. McBride. 1998. Vegetation composition, structure, and chronological change in a decadent Midwestern North American savanna remnant. Natural Areas Journal 18(1): 14-27.
- Chapman, K.A. 1984. An ecological investigation of native grassland in southern Lower Michigan. M.A. thesis, Western Michigan University, Kalamazoo, MI. 235 pp.
- Cohen, J.G. 2001. Natural community abstract for oak barrens. Michigan Natural Features Inventory, Lansing, MI. 8 pp.
- Faber-Langendoen, D. 1993. A proposed classification for savannas in the Midwest. Background paper for the Midwest Oak Savanna Conference. 18 pp.
- Faber-Langendoen, D., and M.A. Davis. 1995. Effects of fire frequency on tree canopy cover at Allison Savanna, eastcentral Minnesota, USA. Natural Areas Journal 15(4): 319-328.
- King, R. 2000. Effects of single burn events on degraded oak savanna. Ecological Restoration 18(4): 228-233.
- Minc, L.D., and D.A. Albert. 1990. Oak-dominated communities of southern Lower Michigan: Floristic and abiotic comparisons. Michigan Natural Features Inventory, Lansing, MI. Unpublished manuscript. 103 pp.
- Nuzzo, V. 1986. Extent and status of Midwest oak savanna: Presettlement and 1985. Natural Areas Journal 6(2): 6-36.
- Peterson, D.W., and P.B. Reich. 2001. Prescribed fire in oak savanna: Fire frequency effects on stand structure and dynamics. Ecological Applications 11(3): 914-927.
- Tester, J.R. 1989. Effects of fire frequency on oak savanna in east-central Minnesota. Bulletin of the Torrey Botanical Club 116(2): 134-144.
- White, A.S. 1983. The effects of thirteen years of annual prescribed burning on a Quercus ellipsoidalis community in Minnesota. Ecology 64(5): 1081-1108.
- Will-Wolf, S., and F. Stearns. 1999. Dry soil oak savanna in the Great Lakes region. Pp. 135-154 in Savannas, barrens, and rock outcrop plant communities of North America, ed. R.C. Anderson, J.S. Fralish, and J.M. Baskin. Cambridge University Press, Cambridge, UK. 480 pp.
For a full list of references used to create this description, please refer to the natural community abstract for oak barrens.
Kost, M.A., D.A. Albert, J.G. Cohen, B.S. Slaughter, R.K. Schillo, C.R. Weber, and K.A. Chapman. 2007. Natural Communities of Michigan: Classification and Description. Michigan Natural Features Inventory, Report No. 2007-21, Lansing, MI.