Wildlife, Animals, and Plants
KUCHLER TYPE: Oak-hickory forest
Medium tall to tall broadleaf forests . Also, open woodlands with
prairie forbs and shrubs in the understory.
Typical deciduous trees on mesic, fairly rich soils are a maximum of 83
to 100 feet (25-30 m) tall with a nearly closed canopy. Trunk diameters
may range up to 5 feet (1.5 m). There is usually a well developed
shrub-sapling layer, but the herb and moss layer is variable, and is
usually less than 100 percent cover . Most deciduous forests have
five well-developed vertical strata: the uppermost dense canopy, an
open subcanopy of immature trees and mature small trees (such as
flowering dogwood [Cornus florida] and eastern redbud [Cercis
canadensis]), a shrub layer, an herb layer, and a surface layer of
mosses and lichens .
This write-up includes some information on transitional vegetation
(savanna) occurring at the interface between oak (Quercus spp.)-hickory
(Carya spp.) forest and tallgrass prairie. United States Public Land
Survey notes (1835) described these areas as "barrens." There is very
little agreement, however, on what constitutes a barren and the term
should be avoided . Much debate continues over the degree to which
oak savanna is "natural" [60,72]; however, most agree that it is a
fire-dependent type (a fire disclimax that is stable over time given
periodic fire). Clark  has suggested that closed oak-hickory forest
is an artifact of fire suppression. Prairie and woodland burning by Native
Americans had a great deal of influence on the extent and character of
vegetation in the prairie-forest contact region, and in the eastern
deciduous forest. The degree to which this activity altered the natural
fire regime is largely unresolved [2,15].
Oak-hickory forests occur in the central United States, ranging from
central Iowa east to southern Michigan and south to Texas. These
forests are extensive in some states, and have only local occurrences in
others. In the Southeast, oak-hickory forests are a major type in
Arkansas, Kentucky, and Tennessee and extend into Alabama, Mississippi,
and Louisiana .
In the Southeast, at the beginning of the seventeenth century, there
were approximately 1 million square miles (26 million sq km) of unbroken
forest. By 1865, 65 percent of the surface area was forested; by 1923,
less than 260,000 square miles (676,000 sq km) were left in
second-growth merchantable timber .
The U.S. Forest Service indicated that there were 36.3 million acres
(14.5 million ha) of oak-hickory forest in the north-central states in
1972 (this included Kuchler types 81, 82, 84, 89, 100, and 104) .
Oak savannas were an important feature of the midwestern landscape prior
to European settlement. Nuzzo  estimated that at the time of
settlement oak savanna covered some 28.6 to 33.8 million acres (11-13
million ha) of Minnesota, Wisconsin, Michigan, Iowa, Missouri, Illinois,
Indiana, and Ohio. This estimate includes savannas occurring in
Kuchler's oak-savanna (K081), oak-hickory forest (K100), and within the
area mapped as bluestem (Andropogon and Schizachyrium spp.)
prairie-oak-hickory mosaic (K082). There is some evidence that savannas
existed in eastern Nebraska prior to settlement, some in areas
previously thought to be exclusively tallgrass prairie . Betz 
estimated that presettlement savanna and associated sand prairie in
Indiana covered 1.68 million acres (647,000 ha). Today only remnants of
these types exist, most of which have been degraded due to various
disturbances such as grazing and altered fire regime . In 1985, 113
sites totaling 6,439 acres (2,607 ha) of relatively high-quality oak
savanna remained, approximately 0.02 percent of the original extent.
All but 100 acres (40 ha) were on sandy, rocky, or similarly droughty
STATES: AL, AR, IL, IN, IA, KS, KY, MI, MS, MO, NE, OH, OK, TN, TX
COMPILED BY AND DATE :
Janet Sullivan, 1995
LAST REVISED BY AND DATE :
AUTHORSHIP AND CITATION :
Sullivan, Janet. 1995. Oak-hickory forest. In: Remainder of Citation
Kuchler Type Index
KUCHLER TYPE DESCRIPTION
Oak-hickory forests are found on all topographic positions including dry
rocky ridges, deep coves, and well-drained valley floors . West of
the Appalachian Mountains, deciduous forests occupy areas geologically
classified as plateaus, although erosion has produced rolling to
mountainous topography .
The climate of the north-central forest region (Minnesota, Wisconsin,
Michigan, Iowa, Illinois, Indiana, Ohio, Missouri, and Kentucky) is
continental and ranges from humid to subhumid. Winters are cold and
summers hot. Temperatures differ greatly from north to south through
the region, both in summer and winter. Temperature, growing season, and
precipitation increase from north to south; at a given latitude,
precipitation increases from west to east .
In the southeastern United States along the eastern edge of the
oak-hickory forest, mean annual precipitation is approximately 45 inches
(1,140 mm); at the western edge, annual precipitation averages 39 inches
(980 mm). Lower precipitation in the western parts of this area is
exacerbated by an episodic pattern of rainfall and more frequent
drought. In southeastern oak-hickory forest, average annual
precipitation increases from 42 inches (1,060 mm) in Indiana to 55
inches (1,400 mm) in Alabama .
At the southwestern limit of oak-hickory forest, central Texas has an
average annual precipitation of 22 inches (560 mm) and mean annual
temperatures around 65 degrees Fahrenheit (18.3 deg C). In eastern
Texas mean annual temperatures are 62.6 to 66.2 degrees Fahrenheit
(17-19 deg C), and the growing season is approximately 225 days .
Oak-hickory forests occur on soils ranging from cool-moist Boralf and
Orthod Spodosols to warm-dry Millisols and Alfisols. Soils range from
clay to loam and are derived from glacial material, residual
sandstones, shales, limestones, gneisses, schists, and granites .
In southeastern oak-hickory forests, soils encompass a wide range of
physical and chemical features, ranging from shallow to deep, infertile
to rich, and high clay fraction to very little clay. Soils are formed
in residuum, primarily from limestone parent materials, but also from
sandstones and shales. Soils in oak-hickory forests are fertile
compared to other southeastern soils and represent some of the most
productive agricultural land on these uplands .
Parent materials on the Ozark plateau are predominantly limestones,
cherts, and dolomites. In Arkansas, soil parent materials in the eastern
Ouachita province are mostly shales, sandstones, quartzites, and cherts,
and in the western Ouachita province are mostly sandstones and shales .
Classification: There is much debate over the most useful
classification for the eastern deciduous forests including oak-hickory
forest. Oak-hickory forest is not uniform across its range; dominants
vary with climatic and edaphic conditions. The many differing
interpretations of oak-hickory forest are probably a function of its
vegetational complexity . The most extensive area of unequivocal
oak-hickory forest is found in the Ozark Mountains, where it covers most
upland sites . Hicks and Chabot  described oak-hickory forest
that is largely equivalent to Kuchler's oak-hickory type, but Braun 
characterized the central and eastern portions of K100 as western
mesophytic forest. She defined the oak-hickory forest as the most
westerly part of the deciduous forest region. Some authors use a
definition of oak-hickory forest that is broader than either Kuchler's
or Braun's, and include all forests dominated by oaks and having at
least some hickory component as oak-hickory. These definitions usually
include Kuchler's oak-hickory forest (K100), oak-hickory-pine (Pinus
spp.) (K111), Appalachian oak forest (K104), and Braun's mixed
mesophytic forest [37,81].
Monk and others  divided the eastern deciduous forest into three
regions: the northern region, occupied by eastern hemlock (Tsuga
canadensis), eastern white pine (Pinus strobus), and northern hardwood
forests; the central region which included oak-hickory; and the southern
region, occupied by pine and oak-pine forests. They defined oak-hickory
as inclusive of Braun's oak-hickory, oak-chestnut (Castanea spp.), and
about half of her western mesophytic forest; this definition is
inclusive of Kuchler's oak-hickory forest but somewhat broader .
The Forest and Range Ecosystems of Garrison and others  include FRES
15, the oak-hickory ecosystem. This ecosystem includes Kuchler's
oak-hickory but also the mosaic of oak-hickory and bluestem prairie
(K082), Cross Timbers (K084), Appalachian oak (K104), oak-pine-hickory
(K111), and oak savanna (K081) types .
This write-up includes mostly information about communities within
Kuchler's  oak-hickory forest region as it was mapped, with the
major focus on oak-hickory communities in the Ozarks. Communities
further north (in Wisconsin and Michigan) are included where information
is deemed relevant. An oak savanna type was mapped by Kuchler as a
potential type for Wisconsin and Michigan (K081), but forests of similar
structure and containing mostly the same species occurred widely in
presettlement times throughout the prairie-forest interface. Savannas
in the central states are therefore included because of their relevance
to the fire ecology of oak-hickory forests.
Other classifications describing oak-hickory forest include the following:
The central hardwood forest 
Plant geography--with special reference to North America 
Ordination and classification of western oak forests in Oklahoma 
A classification of the deciduous forest of eastern North America 
The study of plant communities 
Classification and evaluation of forest sites in the Cumberland
The natural vegetation of North America 
Flora: Oak-hickory forests as described by Kuchler  are dominated
by white oak, black oak, northern red oak, bitternut hickory (Carya
cordiformis), and shagbark hickory (C. ovata). Other trees in
alphabetical order of scientific name include pignut hickory (C.
glabra), white ash (Fraxinus americana), black walnut (Juglans nigra),
black cherry (Prunus serotina), chinquapin oak (Q. muehlenbergii), and
basswood (Tilia americana). In the northern parts of the oak-hickory
forest, other components are northern pin oak (Q. ellipsoidalis), and
shingle oak (Q. imbricaria). In the southern parts of the oak-hickory
type, forest tree species include black hickory (C. texana), mockernut
hickory (C. tomentosa), southen red oak (Q. falcata), overcup oak (Q.
lyrata), blackjack oak (Q. marilandica), Shumard oak (Q. shumardii),
and post oak (Q. stellata) . Occasional eastern white pine and
eastern hemlock also occur .
Burkman and others  described oak-hickory forests as the largest and
most diverse forest type in the eastern United States. Cover types
include post oak-blackjack oak, bur oak (Q. macrocarpa), bear oak (Q.
ilicifolia), northern pin oak, chestnut oak (Q. prinus), white oak-black
oak-northern red oak, white oak, black oak, and northern red oak .
Oak-hickory forest sensu Kuchler is approximately equivalent to the
Society of American Foresters white oak (Q. alba)-black oak (Q.
velutina)-northern red oak (Q. rubra), white oak, and northern red oak
forest cover types .
Braun's description of the oak-hickory forest flora resembles Kuchler's.
In northern stands, bur oak has great prominence. Northern pin oak is
confined to the northern division. Flowering dogwood is a common
understory tree. Blueberries and huckleberries (Vaccinium spp.) are
abundant shrub layer components, as is ceanothus (Ceanothus spp.). The
herb layer often contains poverty oatgrass (Danthonia spicata),
bird's-foot viola (Viola pedata), Appalachian mountainmint (Pycnanthemum
flexuosum), stone-mint (Cunila origanoides), clasping aster (Aster
patens), flax-leaved aster (A. linariifolius), and legumes including
downy trailing lespedeza (Lespedeza procumbens), round-leaved
tick-trefoil (Desmodium rotundifolium), wild sensitive plant
(Chamaecrista nictitans), goat's rue (Tephrosia virginiana),
pencil-flower (Stylosanthes biflora), and Sampson's snakeroot (Orbexilum
The Texas Plant and Wildlife Department published a list containing
current information on the stability and distribution of plant
communities occurring in Texas. They listed a post oak-black hickory
series and post oak-blackjack oak series which occur within Kuchler's
oak-hickory forest. In each of these community types, woody species
diversity is highest to the east, where closed canopies may form. Post
oak-black hickory forms open woodlands over deep sands in the western
portion of its Texas range; species composition varies with soil texture
and depth and herbs have higher species diversity than stands farther
east. Components of this type include white oak, southern red oak,
blackjack oak, pines, other hickories, flowering dogwood, yaupon (Ilex
vomitorium), and beautyberry (Callicarpa americana). Common components
of the post oak-blackjack oak series include cedar elm (Ulmus
crassifolia), southern red oak, yaupon, beautyberry, water oak (Q.
nigra), black hickory, eastern redbud, and deciduous holly (I. decidua),
but composition is variable .
Savanna: Some authors define oak savanna as open-grown oaks with 10 to3
80 percent crown cover, with or without a shrub layer, and with a ground
cover of grasses and forbs . The understory vegetation of savanna
is a mixture of both prairie and forest species, with prairie forbs and
grasses more abundant in areas of high light, and forest forbs and woody
species more abundant in areas of low light [13,69]. Early descriptions
of Missouri savannas are of very open woodlands with ground covers of
grasses and forbs and no underbrush or small timber .
The herb layer in oak savannas consists mostly of bluestem prairie
species, namely big bluestem (Andropogon gerardii), little bluestem
(Schizachyrium scoparium), Indian grass (Sorghastrum nutans),
switchgrass (Panicum virgatum), and many prairie forbs . In Indiana
typical savanna herbs include little bluestem, butterfly weed (Asclepias
tuberosa), flax-leaved aster, and yellow sedge (Carex pensylvanica) .
Savanna trees are oak-hickory dominants; bur oak is common in northern
savannas and post oak and blackjack oak are dominant in southern
savannas. In Texas junipers (Juniperus spp.) and mesquites (Prosopis
spp.) are common associates . Indiana black oak sand savannas are
dominated by black oak and white oak. Understory trees include black
cherry, sassafras (Sassafras albidum), shining sumac (Rhus copallina),
and smooth sumac (R. glabra) .
No species is known to be endemic to oak savannas, and relatively few
species are modal (i.e., have their highest occurrence in this habitat)
. In Wisconsin only six species are considered modal in oak savanna
(K081): sunflower-everlasting (Heliopsis helianthoides), kitten-tails
(Besseya bullii), cancer-root (Orobanche uniflora), smooth phlox (Phlox
glabberima), thick-root buttercup (Ranunculus fascicularis), and
mountain deathcamas (Zigadenus elegans) .
Geographic Trends: Major vegetational trends from east to west include
an increasing importance of oaks, particularly post oak, and a reduction
in canopy tree species diversity. Mesic sites and vegetation are more
restricted in the western part of the range, particularly with decreased
precipitation and increased incidence of drought and fire. Pines
increase in importance from north to south . Oak-hickory merges
with oak-hickory-pine (K111) in eastern Texas, grades into post
oak-blackjack oak savanna (Cross Timbers [K084]) farther south and west
in Texas, and alternates with tallgrass prairie on the western edges of
its distribution (within the region mapped as mosaic of bluestem prairie
and oak-hickory forest) .
Birds: Few bird species can be considered distinctive of oak-hickory
forests. Species frequently encountered in oak-hickory forests include
red-bellied woodpecker (Melanerpes carolinus) and cerulean warbler
(Dendroica cerulea) . Avian species richness is well documented
within the southeastern portion of the oak-hickory forest. Breeding
bird communities within southeastern oak-hickory forests range from
about 120 species in western Tennessee to about 93 species in the
southern extreme . Dominant members of the avifauna of southeastern
oak-hickory forests include downy woodpecker (Picoides pubescens),
great-crested flycatcher (Myiarchus crinitus), red-bellied woodpecker,
eastern wood-pewee (Contopus virens), tufted titmouse (Parus bicolor),
Kentucky warbler (Oporornis formosus), red-eyed vireo (Vireo olivaceus),
and summer tanager (Piranga rubra) in the Bluegrass region of Kentucky.
On the Highland Rim and Knobs of Kentucky and Tennessee, dominant
avifauna also include ovenbird (Seiurus aurocapillus), black-throated
green warbler (Dendroica virens), black-and-white warbler (Mniotilta
varia), blue jay (Cyanocitta cristata), red-eyed vireo, wood thrush
(Hylcichla mustelina), Carolina chickadee (Parus carolinensis), hairy
woodpecker (Picoides villosus), and eastern wood-pewee. In the Central
Basin, Tennessee, dominant avifauna include most of the abovementioned
species and yellow-billed cuckoo (Coccyzus americanus). In the Ozark
Plateau blue-gray gnatcatcher (Polioptila caerulea) and northern
cardinal (Cardinalis cardinalis) occur in addition to previously
mentioned species; on the Coastal Plain additional species include
Carolina wren (Thryothorus ludovicianus), northern parula (Parula
americana), and hooded warbler (Wilsonia citrina). In lowland
communities the avifauna is dominated by prothonotary warbler
(Protonotaria citrea), American redstart (Setophaga ruticilla), wood
duck (Aix sponsa), red-eyed vireo, American woodcock (Scolopax minor),
yellow-throated vireo (Dendroica dominica), northern parula, hooded
warbler, Acadian flycatcher (Empidonax virescens), pileated woodpecker
(Dryocopus pileatus), white-breasted nuthatch (Sitta carolinensis),
Carolina chickadee, and tufted titmouse .
Probst  summarized oak forest bird communities for the eastern
United States, including both oak-hickory forests and oak-pine forests.
The blue jay and the brown-headed cowbird (Molothrus ater) are species
of generalized habitat requirements that are found in almost every
stand, regardless of age or structure. However, most birds require
particular habitat features. Five categories of birds that are present
in oak-hickory forest, based on response to habitat feature include: 1)
bark foragers such as northern flicker (Colaptes auratus),
white-breasted nuthatch, downy woodpecker, and hairy woodpecker, 2)
active gleaners feeding in the tree canopy such as chickadees (Parus
spp.), tufted titmouse, and red-eyed vireo, 3) pursuers feeding in tree
canopy with a sit-and-wait hunting strategy such as flycatchers
(Empidonax spp.) and tanagers (Piranga spp.), 4) ground species
associated with shrub and sapling layers such as thrushes (family
Muscicapidae), rufous-sided towhee, and ovenbird, and 5) species
associated with dense growth of saplings and small trees, mostly
warblers (Emberizidae) .
Mammals: Southeastern oak-hickory forests generally are low in
mammalian species richness with the exception of bats (Chiroptera).
The limestone-based geology of the region has fostered a rich cave fauna
including little brown myotis (Myotis lucifugus), big brown bat
(Eptesicus fuscus), and pipistrelles (Pipistrellus spp.). The
white-footed mouse (Peromyscus leucopus) is very common in southeastern
oak-hickory forest; other common species include short-tailed shrews
(Blarina brevicauda and B. carolinensis), eastern chipmunk (Tamias
striatus), eastern gray squirrel (Sciurus carolinensis), eastern fox
squirrel (S. niger), gray fox (Urocyon cinereoargenteus), raccoon
(Procyon lotor), opossum (Didelphis virginiana), striped skunk (Mephitis
mephitis), and white-tailed deer (Odocoileus virginianus) .
Reptiles: The garter snake (Thamnophis sirtalis) is very common in
oak-hickory forests of the Southeast; other common reptiles include
black racer (Coluber constrictor), black rat snake (Elaphe obsoleta),
five-lined skink (Eumeces fasciatus), fence lizard (Sceloporus
undulatus), rough green snake (Opheodrys aestivus), ring-necked snake
(Diadophis punctatus), eastern hognose snake (Heterodon platyrhinos),
and eastern box turtle (Terrapene carolina). Reptile species richness
generally increases to the south and east of the southeastern
Amphibians: Moist sites within oak-hickory forest support amphibians,
most commonly slimy salamander (Plethodon glutinosus), dusky salamander
(Desmognathus fuscus), American toad (Bufo americanus), Fowler's toad
(B. woodhousei), spring peeper (Hyla crucifer), and gray treefrogs (H.
versicolor and H. chrysoscelis) .
ECOLOGICAL RELATIONSHIPS :
Species Distribution: Oak-hickory associates tend to clump together on
ridges and upper slopes. In grassy openeings and on steep slopes and
other dry exposures oak-hickory associates cooccur with plant species
such as eastern redcedar (Juniperus virginiana) that are tolerant of
xeric conditions . On the Ozark Plateau dry ridges and south-facing
slopes are usually occupied by open communities of post oak and
blackjack oak. Locally, shortleaf pine (Pinus echinata) may form mixed
stands with the oaks. White oak is usually more abundant on
north-facing slopes, entering some ridge forests. In the western border
area, deep ravines and gorges are occupied by mesophytic species; sugar
maple (Acer saccharum), white oak, and northern red oak are abundant.
Open forests of low-statured trees with sparse herbs occur on xeric
plateaus . On the Ozark Plateau in southeastern Missouri,
ordination of forest stands showed a clear separation of upland forests
into two groups. Acid upland stands were dominated by black oak, black
hickory, and white oak. Other stands (intermediate in elevation and
soil acidity) tended to be dominated by chinkapin oak, sugar maple,
eastern redcedar, and basswood. White ash and slippery elm (Ulmus
rubra) were sometimes present .
The eastern deciduous forest reaches its western limit in the central
portion of Oklahoma as oak forest and oak savanna. Farther west,
occasional stands occur in sandstone canyons in west-central Oklahoma
and in the Wichita Mountains of southwestern Oklahoma . These
forests are attributed to climatic fluctuations which favored the
westward migration of eastern species . Prior to European
settlement oak savanna was common in western Oklahoma; these stands now
have a closed canopy developed with the advent of grazing and fire
suppression. Ordination of forests in this area demonstrated that the
vegetation pattern corresponded to a complex moisture gradient. Post
oak and blackjack oak codominated forests occuping the xeric end of the
gradient, post oak dominated stands located in the middle (slightly more
mesic), and forests at the mesic end of the gradient included sugar
maple, elm, and Shumard oak-dominated stands . Post oak and black
hickory appear to require relatively high levels of nutrients and
moisture, while blackjack oak is tolerant of drier, less fertile sites
Phenology: The understory herbs begin growth earliest in spring; the
herb stratum is dominated by species that overwinter as rosettes or
underground perennating organs .
Disturbance and Succession: Oak-hickory forests have a long history of
disturbance; the presettlement pattern was a mosaic of seral stands,
many due to Native American activities. Continuing and overlapping
disturbances in the range of oak-hickory forest arise from the high
value of the land for agriculture . In some regions in the eastern
United States, current oak dominance is similar to and is related to the
importance of oaks in presettlement forests. In other regions,
particularly in the Midwest, the current distribution of oaks exceeds
that of presettlement vegetation . Much development of oak forests
has occurred through a variety of ecological pathways and disturbance
patterns . In northern Michigan sites on upland sandy soils that
were dominated by eastern white pine, red pine, or mixtures were
converted to northern red oak stands after disturbance by logging and
fire . In Missouri stands that were oak-pine or pine at the turn
of the century are now dominated by scarlet oak (Quercus coccinea) and
black oak following heavy cutting of the pine and post-harvest fires
Most oaks are considered early to mid-successional species; there is
recent evidence of a widespread potential for oak replacement by more
shade-tolerant tree species in mature forests [53,68]. This phenomenon
seems to be more prevalent on mesic than on xeric sites [1,2]. There is
a strong successional trend to shade-tolerant species such as sugar
maple and American beech (Fagus grandifolia) on moist sites . The
persistence of relatively shade-intolerant oaks in mesic forests may be
related to cycles of synchronous tree death similar to the fir (Abies
spp.) waves seen in New England, or shifting mosaic conditions caused by
climate changes and/or large-scale disturbance . Changes in fire
frequency have had an impact on the species composition and structure of
many forests . For further discussion, see FIRE ECOLOGY AND
Old-field Succession: Species composition and the successional role of
species may vary geographically. Generally, the first 3 years following
the last crop are dominated by herbaceous members of the Asteraceae such
as fleabanes (Erigeron spp.), asters (Aster spp.), ragweeds (Ambrosia
spp.), and goldenrods (Solidago spp.), and grasses such as crabgrasses
(Digitaria spp.), bristlegrasses (Setaria spp.), threeawns (Aristida
spp.), and panic grasses (Panicum spp.). In many instances, woody
species such as persimmon (Diospyros virginiana), elms (Ulmus spp.),
hackberries (Celtis spp.) and junipers seed in but are not dominant for a
number of years. Broomsedge (Andropogon virginicus) is a common
dominant from the fourth year on, and may be a component for over 20
years. On limestone soils, eastern redcedar is a major old-field
inhabitant. Oak-hickory and dry open forests of post oak, junipers,
blackjack oak, and black hickory eventually develop on at least 50
percent of the relatively dry uplands. Other forest types develop in
mesic coves and in bottomlands .
Old-field succession occurred on abandoned fields in western Illinois
following a period in which the area was heavily cultivated and suffered
severe erosion, then converted to pasturage and hay fields. Early
succession was dominated by cool-season grasses including Kentucky
bluegrass (Poa pratense). Early establishing woody species included
boxelder (Acer negundo) and elms. Trees with heavy seeds only later
invaded the edges of fields. The most rapid tree development took place
in gullies .
Savanna Vegetation: Depending on local conditions including fire
regime, climate, and settlement patterns, very different descriptions of
the same area were sometimes recorded within a few years . The
structure of most savannas is highly dependent on fire frequency;
savannas are converted to more closed forest in less than 50 years
without fire. Further discussion of the relationship of savanna and
fire is in FIRE ECOLOGY AND MANAGEMENT .
Nuzzo  distinguished between open savanna and scrub savanna. Open
savanna is a parklike community with widely spaced trees, virtually no
shrub layer, and an herbaceous ground layer. Scrub savanna is made up
of moderate to dense thickets of oak sprouts within a prairie matrix,
with a few fairly dwarfed open-grown trees. Open savannas usually occur
on flatter, usually mesic areas, and scrub savannas are generally
located on the dry to dry-mesic areas of steeper topography,
particularly hillsides, dunes, and ridges. Both kinds of savanna vary
in structure through time and space, depending on fire occurrence .
The persistence of some high-quality savannas may be related to the
droughty soils on which they occur. Some savannas, in particular those
located on thin soil or rocky substrates, have survived moderate
grazing, exclusion of fire, and competition with alien and woody
species. Light grazing may have helped maintain the savanna. Some
stands have survived because they have been burned relatively frequently
The roots of savanna trees may show morphological responses to growing
in dry soils; bur oak taproots are at least 13.2 feet (4 m) deep in dry
soils but are not as deep in moist soils .
KUCHLER TYPE VALUE AND USE
KUCHLER TYPE: Oak-hickory forest
FORESTRY VALUES :
Forests dominated by oaks comprise the largest type of commercial
hardwood forest land in the United States. Collectively the red and
white oaks comprise 38 percent of the total hardwood sawtimber volume in
the United States. Oak wood is strong, hard, and tough. It has good
working characteristics and is used extensively for furniture, flooring,
paneling, ties, and cooperage. Oak manufacturing residues and low-grade
stems not suitable for lumber have been increasingly used for pulp
RANGE VALUES :
Livestock grazing is incompatible with timber production in most of the
north-central states; forage production is low and cattle damage tree
reproduction and compact forest soils. Grazing on Federal land in this
region is minimal. Forest range suitable for grazing is grassland
adjacent to or within forested areas, or savanna .
WILDLIFE VALUES :
Oaks are important to wildlife species for both cover and food. Young
oaks with branches close to the ground provide foliage browse long into
the winter months, and often provide the only brushy cover in dense pole
stands. Dried oak leaves are important in the winter diet of
white-tailed deer in some areas. Different parts of oak trees are
consumed by 186 different kinds of birds and mammals; the geographic
distribution of many animals coincides with or depends on the range of
oaks [84,94]. Acorn production is of primary importance to many birds
and mammals. For example, in the Ozarks of Missouri acorns comprise 37
percent of the yearlong diet of wild turkey (Meleagris gallopavo) and 54
percent of white-tailed deer diets . Many mammals consume acorns,
including white-footed mouse, eastern chipmunk, eastern fox squirrel,
eastern gray squirrel, red squirrel (Tamiasciurus hudsonicus), flying
squirrels (Glaucomys spp.), and deer mouse (Peromyscus maniculatus).
Acorns (particularly of northern red oak) are an important food for
northern bobwhite (Colinus virginianus), red-headed woodpecker,
red-bellied woodpecker, blue jay, tufted titmouse, common grackle,
white-breasted nuthatch, sapsuckers (Sphyrapicus spp.), quail
(Phasianidae), ruffed grouse, and various waterfowl including common
golden-eye (Bucephala clangula), gadwall (Anas strepera), mallard (A.
platyrhyncos), wood duck (Aix sponsa), hooded merganser (Lophodytes
cucullatus, and others [57,94].
Black oak has high cavity value for wildlife . Cavity nesters are
an important component of oak-hickory forests. Cavity nesters comprise
the 10 most frequent bird species in all 7 sampled vegetation types,
most of which are oak-hickory forest types in the Missouri Ozarks .
Current land use patterns that decrease forest cover and increase herb
cover result in an increased abundance of grassland bird species such as
dickcissel (Spica americana) and horned lark (Eremophila alpestris)
Many animals that depend on Illinois savanna or open woodlands are
decreasing in abundance due to forest closure caused by fire exclusion.
Examples include Kirtland's snake (Clonophis kirtlandii), Cooper's hawk
(Accipiter cooperii), and silvery blue butterfly . Sharp-tailed
grouse (Tympanicus phasianellus) habitat in the eastern United States
includes oak savanna and recently burned areas .
Nine species of terrestrial vertebrates on the Endangered and Threatened
Wildlife and Plants list occur in oak-hickory forest: gray bat (Myotis
grisescens), Indiana bat (M. sodalis), Ozark big-eared bat (Plecotus
townsendii ingens), eastern cougar (Felis concolor couguar), Bachman's
warbler (Vermivora bachmanii), bald eagle, peregrine falcon (Falco
peregrinus ssp. anatum and F. p. ssp. tundrius), and Kirtland's warbler
(Dendroica kirtlandii) . Branson and others  listed 81 species
of terrestrial vertebrates with ranges in oak-hickory forests in
Kentucky that are considered threatened, endangered, of special concern,
or of undetermined status because of lack of information. A summary of
state lists of rare, threatened, or of special concern was prepared by
Meredith  and included many species occurring in oak-hickory
OTHER VALUES :
Forests in the north-central states offer a wide variety of recreational
opportunities. All nine north-central states have both State and
Federal forest-oriented recreation facilities. Activities include
picnicking, camping, hiking, hunting, and fishing .
Forests in the north-central states provide habitat for most big game,
and many small game animals including game fish. There were 26,400
deer, 474 bear, 151 moose, and 1,927 wild turkey taken on National
Forest land in 1974 (National Forest land is only a small portion of the
available hunting areas in this region) .
MANAGEMENT CONCERNS :
Diverse vegetation is important for maintaining wildlife species
diversity in oak-hickory forests. Mature stands are high in cavity and
den value. Regeneration cuttings in even-aged stands create openings
and edge habitat. Regeneration areas provide browse, sapling stands are
good habitat for certain bird species, and pole, immature sawtimber, and
sawtimber stands are good habitat, providing mast and cover for many
Removal of culls and snags from oak-hickory forest stands has
detrimental impact on cavity nesting species. Even-age management of
eastern deciduous forests creates cull-free, young, fast-growing stands
that have very few cavities available to cavity nesting species. For
high quality bird habitat clearcuts should be kept small and planned so
that each management unit contains diverse stand age classes. Leaving
dead snags and trees with heart rot during regeneration cuts and
subsequent thinnings may maintain habitat for cavity nesting species.
On medium-quality sites, killing unwanted trees and leaving them
standing also provides habitat for cavity nesters .
Oak regeneration has become a subject of concern in oak-hickory forest
management; in many areas oaks are being replaced after harvest by mesic
hardwoods such as sugar maple [20,54,55,81]. Oak stands on sites with
adequate soil moisture usually have high densities of mesophytic species
in the understory, which often outcompete oak regeneration, even after
timber harvesting [15,55]. In Wisconsin planted oak seedlings showed
excellent (>90%) survival on plots in which tall (>5 feet [1.5 m])
understory vegetation was removed; on control plots where tall
understory vegetation was left intact more than 70 percent of planted
oak seedlings died within 5 years. Natural seedlings were also more
abundant on opened plots . Merrit  indicated that the present
mature oak stands originated when woodlands were subjected to severe
cutting, grazing, and fire; these conditions have largely been
eliminated from current management practices . Northern red oak was
favored by frequent fires and/or heavy cutting because of its sprouting
ability. In Indiana, however, both even- and uneven-aged silvicultural
practices have converted many stands containing large proportions of oak
sawtimber-sized trees to species such as sugar maple and yellow-poplar
(Liriodendron tulipifera) .
Advance regeneration in oak-hickory forest is poor [19,20,23,82].
Underlying causes may be related to fire exclusion. Fire may have a
beneficial influence on oaks by reducing competition from more
fire-sensitive tree species in the sapling layer . Fire reduces the
amount of litter under a stand, which, according to Lorimer , may
discourage rodent predation of acorns. Fire may indirectly influence
rodent populations as well, by reducing available nest sites and food
Oak-hickory forests in the northeastern United States have notable pest
problems. Gypsy moth larvae have caused widespread defoliation
contributing to oak decline and mortality in many areas, and oak wilt is
widespread in the central states and in some eastern states .
Butternut canker has caused widespread losses of butternut (Juglans
cinerea), and dogwood anthracnose has caused serious losses throughout
its range .
A widespread decrease in oak vigor and growth rate and an increase in
mortality have recently been attributed to high atmospheric levels of
sulfur dioxide and other pollutants .
In the central United States, savanna has declined drastically since
settlement. In Wisconsin and other northern areas, most savanna trees
were cut within 25 to 30 years after settlement. Savanna that was
protected from fire developed into dense forest .
KUCHLER TYPE FIRE ECOLOGY AND MANAGEMENT
KUCHLER TYPE: Oak-hickory forest
FUELS, FLAMMABILITY, AND FIRE OCCURRENCE :
Fuels and Flammability: In the Sand Prairie Scrub Oak Nature Preserve,
Illinois, estimated fuel loads were highest in closed forest, moderate
in savanna, and lowest in prairie. When blackjack oaks in savanna reach
sufficient size, grass growth under their crowns is reduced and wind
action sweeps away litter; this reduces the amount of fuel near the tree
trunk and prevents fire from reaching the tree base. Following a spring
prescribed fire, a study of patterns of fuel consumption around isolated
blackjack oak savanna trees showed that fire never reached their bases.
In closed forest, tree mortality was high, and trees experienced more
scorch at stem bases than trees on the forest-prairie edge .
In hardwood stands in the north-central states, fire danger is high in
both the spring and fall and low in the summer months when the
vegetation is green . At Indian Creek Nature Center, Iowa,
prescribed fires were conducted in spring under moist conditions in
grassland and adjacent oak-hickory woodlots. In the woods, fires were
generally patchy and left large areas unburned .
Oak leaf litter affects the likelihood of fire and increase fire
intensity . Oak leaves crinkle up when they dry and are therefore
held above the ground surface creating a loose, porous fuel bed that
carries fire easily [54,73]. In contrast, leaves of locust (Robinia
spp.), maple, and elm lie flat, stay damp, and do not burn well .
Oak leaf litter is easily carried by wind; burning leaves can ignite
spot fires and increase fire spread. Dead leaves of black oak often
remain on the tree, creating deep layers of dry fuels in young stands
. Wildfire hazard has increased due to fuels buildup and fire
exclusion on the Hercules Glades Wilderness Area in southwestern
Missouri since its designation as wilderness. Management-ignited fire
and prescribed natural fire have been recommended .
Fire Occurrence: It is widely accepted that along the western boundary
of the deciduous forest Native Americans set many fires that kept
oak-hickory forests open, helped determine the grassland-forest
boundary, and limited the range of maple-basswood forests [73,97].
Nearly every acre in the Midwest probably experienced at least
occasional fire . There are numerous reports of Native Americans
burning Missouri savannas and grasslands on an annual basis, usually in
the autumn after leaf-fall [22,56]. Northern Missouri was virtually
fire-free soon after settlement; southern Missouri continued to be
burned by early settlers, but fires were of lower severity than
presettlement, aborigine-set fires. In 1936, the state Conservation
Commission began a concerted effort to suppress fire throughout the
state . In the Missouri Ozarks, fire history of a post oak savanna
growing on a ridge was reconstructed for 1734 to 1991 using tree ring
analysis. The mean fire return interval from 1740 to 1850, the period
of greatest fire frequency, was 2.8 years. After 1850, the fire return
interval increased to 24 years .
In southern Wisconsin (the area mapped by Kuchler as oak savanna [K081]
but containing virtually the same species as oak-hickory forests and
bluestem prairie-oak-hickory mosaic), oak savannas were widespread and
common in presettlement times and disappeared rapidly as soon as fires
ceased. It was therefore estimated that presettlement fire frequency
was very high and in some areas fire occurred annually .
In the north-central states, there were more than 11,000 fires reported
between 1970 and 1972. Many fires were caused by debris burning
(approximately 33%), many were incendiary (20%), and only a very few
(1%) were started by lightning. More than 50 percent of the fires
burned in hardwood stands . Boerner and Cho  estimated fire
return intervals for heavily forested sites in southeastern Ohio from
1923 to 1978. They calculated an average fire return interval of 643
years given current conditions. Average fire intervals of 900 years
were estimated for the Shawnee National Forest, Illinois .
FIRE EFFECTS ON SITE :
In Missouri seasonal rates of nonsymbiotic nitrogen fixation in surface
soils of oak-hickory forests were measured on plots exposed to 30 years
of annual or periodic prescribed fire. Fire treatments had no
influence on fixation rates, which averaged 0.1 kg/ha/year, or on the
proportion of samples showing nitrogen fixing activity .
In Missouri annual fire in oak-hickory forests may reduce nutrient
availability and water infiltration. Burning significantly reduced
quantities of extractable ammonium in the soil; annual burning resulting
in lower amounts than burning every 4 years . In Missouri, oak
forests were prescribed burned annually or periodically (every 5th year)
in spring. Annual fires were patchy and of low severity due to lack of
surface fuels. Soils of annually burned plots became increasing
compacted and had little or no earthworm and insect activity compared to
unburned soils and litter. After seven annual fires, water infiltration
rates were 4.5 times faster on unburned soils than on burned soils .
Arend  reported reductions in infiltration rates after prescribed
fire for some soils under mixed upland oaks in Missouri.
FIRE EFFECTS ON VEGETATION :
Fire is an important factor in establishing and maintaining vegetation
patterns in the Ozark Mountains [2,74]. The closed-canopy oak-hickory
forest that now predominates in the Missouri Ozarks is thought by some
authors to be an artifact of fire suppression and other anthropogenic
disturbances. People travelling in the area in presettlement times
described a wide variety of plant communities ranging from grassland, to
oak savannas, to oak-pine forests . Repeated fires create open,
parklike stands of oak .
Drought is the primary agent controlling the frequency and severity of
fire and the impact of fire on trees in oak-hickory forests. Drought
contributes to low fuel moistures and therefore high fireline intensity,
resulting in more severe fire. Individual trees stressed by drought are
more susceptible to pathogens after fire wounding and sprout less
vigorously after top-kill. Stands affected by insects or pathogens also
have high amounts of fine fuels .
Species Responses: Most oaks are resistant to fire to some extent; fire
resistance generally increases with stem diameter [54,78]. Most oaks
sprout from dormant basal buds after top-kill. Sprouting species are
favored over other hardwoods by occasional fires . Boerner and Cho
 hypothesized that large, emergent oaks in an old-growth forest in
southeastern Ohio were established following one or more large-scale
disturbances such as fire or windstorm. After oak establishment on good
sites, severe fire maintains oak dominance .
Rouse  listed the following oaks in order of decreasing bark
thickness: chestnut oak, black oak, northern red oak, and white oak.
Lorimer  rated upland oaks slightly differently in order of
decreasing bark thickness: bur oak, black oak, white oak, and northern
red oak. The thinner bark of northern red oak may acount for its
susceptibility to top-kill by fire. Bur oak and white oak are often
maintained in oak savannas, whereas frequent fire reduces northern red
oak to shrubby clumps of sprout origin.
Black oak is a short-lived (less than 150 years) tree, intermediate in
shade tolerance. It sprouts after injury or top-kill. Susceptibility
to fire is intermediate in larger individuals and high in young
seedlings and sprouts . Both mature  and young black oak
seedlings sprout .
Fire-caused basal wounding provides entry for wood-rotting fungi and
insects . Loomis  published a method for predicting tree
mortality and estimating basal wound size for surviving trees.
Mortality equations were derived for black oak, white oak, post oak, and
scarlet oak. The black oak formula also applies to hickories and to
northern red oak. Mortality depends on tree species, diameter at breast
height, height of bark blackening, and the width of bark blackening at 1
foot above the ground .
Prescribed spring fire in grasslands and adjacent woods in Iowa resulted
in a great increase in flowering of forbs, and reduced woody species such
as common prickly-ash (Zanthoxylum americanum), black locust, barberry,
buckthorns, and maples .
Survival of lichens after fire in a Michigan oak savanna was summarized
by Wetmore . Many species showed lower cover after fire on the
part of tree trunks closest to the soil; cover reduction was less
pronounced high on the tree trunks, even at high fire frequencies .
Effects of Fire on Species Composition: Fire influences species
composition towards oak-hickory and away from maple-beech dominated
forest . After a severe wildfire in West Virginia, oaks increased
from 9.3 percent of the dominant trees to almost 30 percent of the
total, mostly due to top-kill of mesic hardwoods . Frequent fire
reduces tree and shrub cover in favor of prairie species. In the
Driftless Area (Wisconsin and Minnesota), almost pure stands of northern
red oak occur on moist sites that would be suitable for sugar maple.
These are even-aged stands that probably established after severe fires
. In many oak-hickory forests, sugar maple and other shade-tolerant
and fire susceptible species are increasing in number and cover.
Evidence that this is a result of fire exclusion includes the tendency
of sugar maple and other fire-susceptible species to co-occur on
protected sites that show no evidence of past fire . In southern
Wisconsin oak forests (which experienced fire in presettlement times but
have not burned recently), oak regeneration is scarce. McCune and
Cottam  suggested that since none of the understory species in
southern Wisconsin (hackberry, boxelder, American elm, butternut, black
cherry, and red maple) are true climax species, the absence of
disturbance is an historic anomaly and the future composition of these
forests is unclear.
Henderson  compared two black oak stands in Indiana with differing
fire histories. The stand which had experienced frequent, low-severity
surface fires was dominated by black oak and a few northern red oak, and
there were few other woody species. The stand that had experienced more
severe fire less frequently was also dominated by black oak, but had
less fire-tolerant species present as well: red maple (Acer rubrum),
sassafras (Sassafras albidum), and black tupelo (Nyssa sylvatica) .
In Illinois grassy openings with few trees were burned annually with
prescribed fire from 1969 to 1973. They were not burned again until
1990, 1991, and 1992. With annual fire, prairie forbs increased and
woody species declined. In the 15-year fire-free interval, the number of
shrub species increased. When prescribed fire was resumed, prairie
willow (Salix humulis) and silky dogwood (Cornus amomum) sprouted
vigorously after fire; prairie forbs also increased .
Effects of Fire on Stand Structure: Fire was important in maintaining
oak savannas at the forest-prairie ecotone. There are numerous
historical references to the rapid conversion of savanna to oak forest
following European settlement and cessation of fire . Anderson and
Brown  proposed that the mosaic of presettlement vegetation types was
strongly influenced by fire patterns that tended to limit closed forests
to areas protected from most fires. In Tennessee annual and periodic
prescribed surface fires were conducted in upland oak-dominated
vegetation. Upland stands were mostly post oak-blackjack oak, southern
red oak-scarlet oak, or white oak . After 25 years, understory
cover of woody plants was irregular but more or less constant in
annually burned plots. Overstory cover was open, with few trees per
acre. In periodically burned plots, woody understory cover increased
irregularly. In unburned control plots, woody understory plant cover
first decreased but then increased over the 25-year period .
In presettlement Indiana grass-dominated openings were maintained by
annual burning after autumn frost. These frequent fires prevented the
growth of trees and "permanent vegetation". In less than 50 years
without fire, former openings were converted to forest . Repeated
fires are thought to be responsible for scrub oak lands (stands of
scrubby oaks of sprout origin) in the Midwest .
In the Sand Prairie Scrub Oak Nature Preserve, a March 1977 prescribed
fire in closed forest consumed 95 to 99 percent of the surface litter in
study plots. Numerous trees had fire scars up to 3.3 feet (1 m) above
the ground. In the savanna the fire did not reach within 1 foot (30
cm) of the base of any of the 14 trees. Surface area burned ranged from
7.1 percent to 52.4 percent in different plots. None of the savanna
trees showed any deterioration in 3 years after the fire even though
some had scorching of the lower branches .
Black oak sand savannas at Hoosier Prairie Nature Preserve, Indiana, are
maintained by prescribed fire. One area has been burned four times in 8
years, three times in the spring, and once in the fall. The number of
woody stems increased after the first fire, but decreased thereafter.
Postfire sprouting of smooth sumac occured at the same rate through four
fires, but black oak and prairie willow sprouting rates declined.
Another area of oak savanna at Hoosier Prairie was burned five times in
8 years. Allowing plots to rest from fire for least 2 years resulted in
an increase in the numbers of woody stems, but the number of woody stems
decreased after two consecutive fires .
FIRE EFFECTS ON RESOURCE MANAGEMENT :
Few instances of direct mortality from fire have been recorded for
wildlife species in oak-hickory forests. In Oklahoma, Bigham and others
 observed many dead eastern box turtles immediately after severe
fires in post oak-blackjack oak woods and adjacent pasture and range.
They also observed living turtles, snakes, northern bobwhites, and a
rabbit on the burned area 4 days after the fire .
FIRE USE CONSIDERATIONS :
Moore  published a method for field measurement of fuel moisture to
assess burning conditions in oak-hickory forests.
FIRE MANAGEMENT CONSIDERATIONS :
Fire was once an important factor in the oak-hickory ecosystem and
maintained the open character of most stands in the Midwest [15,54].
Many historians and ecologists feel that the midwestern oak-hickory
forests evolved with frequent fire and remain fire-dependent .
Prescribed fire is useful for maintaining the diversity of oak-hickory
forests, and is being used in Indiana, Illinois, Missouri, Wisconsin,
and Iowa with good results. Prescribed fire use continues in hardwood
and mixed forests as a wildlife management tool  and to modify
understory composition or size class structure [35,99].
Unfortunately, few short- or long-term ecological studies of fire
perturbations have been conducted on oak-hickory forests .
Implications for fire in management of currently existing closed-canopy
forests are unclear. Regeneration problems associated with these
forests are similar to problems occurring in forests farther east.
Prescribed fire is being considered as a silvicultural tool in oak
forests. It seems likely that several low- to moderate-severity
prescribed fires will reduce the number of shade-tolerant competitors,
and it is possible that such fires may encourage establishment of oaks.
A single fire will have little lasting impact, and in some cases may be
detrimental to oak regeneration. Several fires are probably necessary
to select against less fire-resistant competitors . Lorimer 
commented that experiments with medium-severity fire are to be
encouraged; low-severity fire may not kill competing species at rates
high enough to be beneficial to oak regeneration. In some areas
silvicultural approaches may be as least as successful as prescribed
burning programs  because basal wounding by fire allows entry of
fungi and insects and reduces the value of timber trees .
In an attempt to improve oak regeneration in an upland hardwood forest
in northern Alabama, a prescribed fire was conducted in 4- to 6-year-old
oak stands that appeared to be in danger of replacement by other
species. One fire in these stands did not substantially alter the trend
to replacement of oaks by other species. Stands recovered rapidly from
fire; density of browse species and herb cover increased, resulting in
improved wildlife habitat .
With increasing age of forests, regeneration of oaks after disturbance
tends to decrease. Sprouting tends to decrease with age. Established
shade-tolerant species in the understory and subcanopy are more
competitive than low-vigor oak sprouts .
In the Midwest many savanna and grassland areas have been prescribed
burned on a regular basis. These fires have been prevented from
spreading into adjacent forests, with the result that there are no
transitional areas. Under presettlement conditions, grassland fires
sometimes spread into adjacent oak-hickory forests, depending on local
conditions. These fires maintained savanna and ecotonal communities in
irregular mosaics. It has been recommended, therefore, that prescribed
fires for grassland maintenance be allowed to burn into adjacent forest
and reestablish savanna vegetation and ecotones .
In Indiana fire management policies are based on the premise that oak
savanna and prairie communities will best be maintained by a fire
interval of 2 to 8 years, depending on unit history and specific goals.
Annual fires are not recommended for either restoration or maintenance
of oak savanna because there is usually not enough fuel to carry fire,
and annual fires may damage some herbs. Remnants of oak savanna prairie
need to be burned at least every 15 years or they will develop into dense
forest. Spring fires are thought to be the most effective .
In Indiana black oak sand savannas, maintenance and restoration of
vegetational mosaics was initiated with prescribed fire. Plots were
burned biennially, three times in the spring and once in the fall, for a
total of four times in 8 years .
On the Grand Prairie, Illinois, U.S. Forest Service personnel are
attempting to restore the transition landscape (as savanna) by allowing
firewood removal until approximately 10 trees are left per acre (25
trees/ha); tree removal is followed by annual prescribed fire .
There has been some debate over the choice of sites and appropriate
methodology for restoration of presettlement vegetation including
savannas [60,72]. Mendelson and others  contend that savanna
vegetation represents an ecotonal and therefore not unique vegetation
type and should not be created by artificial means. Packard  and
his colleagues believe that, since the presettlement vegetation has been
grossly disturbed by humans, drastic measures (i.e., prescribed fire
and tree thinning) are necessary to restore savanna and other
presettlement vegetation types.
REHABILITATION OF SITES FOLLOWING WILDFIRE :
KUCHLER TYPE: Oak-hickory forest
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2. Abrams, M. D. 1992 
3. Anderson, R. C. 1982 
4. Anderson, R. C.; Brown, L. E. 1983 
5. Anderson, R. C.; Brown, L. E. 1986 
6. Anderson, R. C.; Schwegman, J. E. 1991 
7. Bacone, J. A.; Post, T. W. 1986 
8. Betz, R. F. 1978 
9. Bigham, S. R.; Hepworth, J. L.; Martin, R. P. 1964 
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Goll Woods, an old-growth forest remnant in northwestern Ohio. Bulletin
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others]. 1981. Endangered, threatened, and rare animals and plants of
Kentucky. Transactions of the Kentucky Academy of Science. 42(3-4):
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Philadelphia, PA: Blakiston Books. [pages unknown]. 
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14. Brown, James H., Jr. 1960. The role of fire in altering the species
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19. Carvell, Kenneth L. 1979. Factors affecting the abundance, vigor, and
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22. Clubine, Steve; Davis, Maurice. 1993. Missouri grasslands and fire.
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23. Crow, T. R. 1988. Reproductive mode and mechanisms for self-replacement
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25. Curtis, John T. 1959. The vegetation of Wisconsin. Madison, WI: The
University of Wisconsin Press. 657 p. 
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oak-hickory ridgetop in the Missouri Ozarks. American Midland
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27. Cutter, Bruce E.; Lowell, Kim E.; Dwyer, John P. 1991. Thinning effects
on diameter growth in black and scarlet oak as shown by tree ring
analyses. Forest Ecology and Management. 43: 1-13. 
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