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Restoring Oak Savannas

by

Dane Huinker

A Paper Submitted to the

Environmental Studies Faculty in Partial

Fulfillment of the Requirements for the Degree of

BACHELOR OF ARTS

Luther College

Decorah, Iowa

2014

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Introduction

Oak savanna habitat was at one time a very prominent landscape in the midsection of the

United States. Many factors have played a role in the formation of oak savannas but to truly

understand their formation, one must first look back in history approximately one million years

ago when the uplift of the Rocky Mountains created a rain-shadow casting over everything to its

east (Kline 1997). The land in this rain shadow created by the mountains became drier, making

the environment favorable for grasses to dominate the landscape (Fig. 1) (Kline 1997).

Figure 1. Short grass, mixed grass and tallgrass prairie distribution in the U.S.

(from U.S. Department of Agriculture ND).

However, along the east edge of the tallgrass prairie zone, the moisture gradient increased and

taller grasses and trees were able to exist (Kline 1997). This created a transitional habitat

between tallgrass prairies and closed canopy forests spreading from Texas north to Canada and

from central Nebraska east to Ohio (Fig. 2) (Kline 1997).

Tallgrass Prairie Mixed Prairie Shortgrass Prairie

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Figure 2. Approximate distribution of oak savanna, barrens, and prairie

complexes in eastern United States (from Nuzzo 1986).

The natural processes determining the distribution of prairie, oak savanna, and closed

canopy forest were both fire history and short-term climate fluctuations (Kline 1997). In large

part, the amount of moisture in a landscape dictated the fire history as wetter areas were not

suitable for frequent burns thus resulting in a closed canopy forests (Kline 1997). A prairie was

the result of a dry climate and frequent fires (Kline 1997). Oak savanna habitat holds the

intermediate characteristics of both closed canopy forests and prairies. Within oak savannas,

there are three factors that determine the species composition: geographic location, soil type and

topography, and fire intensity and frequency (Kline 1997, Tester 1989). Geographic location

greatly determined the species composition with the exception of bur oaks (Quercus

macrocarpa), whose geographic range spread throughout the entire oak savanna range (Kline

1997). Species like blackjack oak (Quercus incana) and post oak (Quercus stellata) however

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where only found in the southern edges of the transitional zone while the species, pin oak

(Quercus palustris), was primarily found only in the northern zones (Kline 1997).

The soil type and topography play a significant role within each geographic zone (Kline

1997). Mesic soils (balanced moisture) support open oak savannas that contain large open-

grown bur oaks with mesic prairie grasses and forbs growing between them (Kline 1997). Wet

soils, conversely, support swamp white oak (Quercus bicolor) and bur oak with wet prairie

species growing in the open spaces (Kline 1997). Sandy soils support black oak (Quercus

velutina) or the northern pin oak (Quercus ellipsoidalis) as well as intermixed bur and white oak

(Quercus alba) with sand prairie grasses and forbs in-between (Kline 1997). Topography

differences such as a drier hillside will host bur oaks while less fire tolerant red oaks (Quercus

rubra) are normally found on steep north-facing slopes because fires do not carry across this type

of topography as frequently nor as hot (Kline 1997).

The presence of fire is the most important aspect of creating and maintaining oak

savannas (White 1992, Abrams 1992). Overall, oak species are tolerant to fire because they hold

characteristics that protect or respond to heat from fires including: thick bark, deep roots, and

resprouting (Kline 1997). Bur oaks are known to have adapted the thickest most gnarly bark

giving it the most tolerance to fire in all except for some of the youngest seedlings or shoots

(Lorimer 1985). The bark thickness in oaks from thickest to thinnest is bur oak, black oak, white

oak, red oak (Lorimer 1985, White 1986). The differences in adaptive bark thickness in oaks do

not differ coincidentally. Thicker-barked bur oak trees were usually found on drier sites where

fire frequency was usually the highest (Lorimer 1985). This is why bur oaks would be found

often at the prairie/forest border where they were subjected to almost annual prairie fires

(Lorimer 1985).

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Most oak species also have the ability to resprout from dormant buds at the base of the

tree when fire kills the above-ground portion (Lorimer 1985). If a branch of a bur oak is fire

damaged or killed, buds can be produced in response and new shoots can emerge within the

same season (Kline 1997). Both adults and seedlings of black oaks can vigorously resprout after

being top-killed by intense surface fires (Kline 1997, Lorimer 1985).

Another interesting trait that may or may not be an adaptation to fire is how fallen oak

leaves curl up when they dry. The curled leaves create a loose and porous fuel load that can

easily carry fire during the dry periods of spring and fall (Lorimer 1985). Sugar maple leaves in

contrast, which are thin, easily decomposable, and lie in soggy mats after snow, resulting in a

surface that lowers fire danger levels and lowers rates of fire spreading (Lorimer 1985).

Species Composition

Oak savannas are best recognized by the various species of oak trees found there, but the

understory and herbaceous ground layer are also unique and distinguishable to oak savanna

habitat (Table 1).

Table 1. Oak savanna herbaceous ground layer species (Kline 1997).

Common Name Scientific Name

Grey dogwood Cornus racemosa

American hazelnut Corylus Americana

Leadplant Amorpha canescens

New Jersey tea Ceanothus americanus

Wild lupine Lupinus perennis

Wild rose Rosa acicularis

Stout wood reed Cinna arundinacea

Hairy woodland brome Bromus pubescens

Broad-leaved panic grass Panicum latifolium

Bottlebrush grass Hystrix patula

Virginia wild rye Elymus virginicus

Silky wild rye Elymus villosus

Long-awned wood grass Brachyelytrum erectum

Bur sedge Carex grayi

Pennsylvania sedge Carex pensylvanica

Wild Indigo Baptisia lacteal

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The list in Table 1 represents some of the species found in both prairies and closed-

canopy forests but can be found coexisting in the oak savanna habitat because they may have

certain resource preferences (Kline 1997). Generally these are prairie forbs or grasses with light

shade preferences or closed canopy forest species preferring moderate amounts of sunlight

(Kline 1997).

The unique plant life within the oak savannas provides suitable habitat for a diverse

assortment of animals as well (Table 2).

Table 2. Animal species found in oak savannas (Kline 1997).

Common Name Scientific Name

Cottontail rabbit Sylvilagus spp.

Fox squirrel Sciurus niger

Woodchuck Marmota monax

Skunk Mephitidae spp.

White-tailed deer Odocoileus virginianus

Indiana bat Myotis sodalist

Red fox Vulpes vulpes

Bison Bison bison

Elk Cervus canadensis

Wild turkey Meleagris gallopavo

Northern flicker Colaptes auratus

Red-headed wood pecker Melanerpes erythrocephalus

Great crested flycatcher Myiarchus crinitus

Eastern bluebird Sialia sialis

American kestrel Falco sparverius

Barn owl Tyto alba

Cooper’s hawk Accipiter cooperii

Sharp-tailed grouse Tymapanuchus phasianellus

Bewick’s wren Thryomanes bewickii

Bachman’s sparrow Peucaea aestivalis

Loggerhead shrike Lanius ludovicianus

Swallow-tailed kite Elanoides forficatus

Indigo bunting Passerina cyanea

American goldfinch Spinus tristis

Chestnut sided warbler Dendroica pensylvanica

American robin Turdus migratorius

Gray catbird Dumetella carolinensis

Cardinal Cardinalis cardinalis

Rufous-sided towhee Pipilo maculates

Brown thrasher Toxostoma rufum

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Oak savannas were also suitable habitat for the now extinct passenger pigeon (Ectopistes

migratorius) (Kline 1997). Insects including the Karner blue butterfly (Lycaeides melissa

samuelis) are thought to be dependent on oak savanna habitat in its larval stage due to its

dependence on the wild lupine (Lupinus perennis) (Kline 1997).

Disturbance and the Role of Humans

Oak savannas are a complex ecosystem with many important parts but the role that

disturbance plays is crucial. These disturbances include the trampling and grazing of large

animals, such as bison or elk, but most significant is the disturbance of fire (Kline 1997, Tester

1989). Just as fire is an important process in the rejuvenation of prairies, oak savannas are

dependent upon it as well (Packard 1993). Oak savannas are widely assumed to be fire

dependent and the Native Americans were very influential in forming the landscape by burning it

often (Fig. 3) (Haney and Apfelbaum 1993, Packard 1993). In addition to the millions of years

of plant communities adapting under the influence of fire, Native Americans increased fire

frequency for the past five or six thousand years in order to improve game habitat, promote

greater nut and berry production, and create easier traveling (Kline 1997). Recognizing that the

human influences in maintaining oak savannas was a natural process is essential in accepting the

restoration of these habitats (Packard 1993). When the Native Americans were forced off of

their lands upon European settlement, fire was almost completely eliminated from the landscape

(Packard 1993, Thompson 1992). Eliminating the essential role Native Americans played in the

oak savanna ecosystem resulted in the destruction of the natural community similar to the

elimination of a key predator, pollinator, or herbivore (Packard 1993).

Deciding to intervene and restore degraded oak savannas has been questioned by some.

Much of this controversy is created by the conflicting definitions of “nature”. Some definitions

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hold that nature is “plants, animals, geographic features, etc., or places where these exist largely

free of human interference” (Packard 1993). From the conservation and land stewardship

standpoint, this definition is impractical because oak savannas would not exist if it were not for

the influence of human activity. Packard (1993) gives a revised definition that replaces the

“largely free of humans” with “essentially free of human influence that would be so great or so

rapid that the natural processes of the ecosystem are destroyed”. In this way, it gives

communities of species in an ecosystem time to adapt in order to thrive in a changing

environment over the course of hundreds or thousands of years (Packard 1993).

Figure 3. First approximation map of presettlement fire frequency regions of the U.S. The

frequencies illustrated represent the higher fire-return intervals to be found in each landscape

unit (Frost 1998).

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The succession that is taking place in poorly managed or unmanaged oak savannas is

considered artificial selection (Packard 1993). The highly conservative species are being

outcompeted by relatively weedy species (Packard 1993). If natural succession were taking

place, relatively weedy species would be getting replaced by the more advanced successional

communities composed of native species (Packard 1993). Packard (1993) goes on to say that in

oak savannas without active management, we are preserving the “idea” of nature whereas in the

managed sites, we are preserving the natural processes and the species that nature produced.

Understanding the background of these natural processes within oak savannas is essential before

planning the laborious and time consuming restoration of these dwindling ecosystems.

Disappearance of Oak Savannas

Over the last 150 years, Midwestern oak savannas have largely been either converted to

agriculture or degraded by woody encroachment resulting from fire suppression (Brudvig and

Asbjornsen 2009, Wolf 2004, Abrams 1992). From around 1936 to today there have been

virtually no fires though oak savanna habitat (McEwan et al. 2007). Fire scar chronologies show

that between 1875 and 1936, fires occurred in oak savannas approximately every 6-7 years

(McEwan et al. 2007). Now, with the suppression of fire, oak savannas are being dominated by

shade-tolerant and fire-intolerant woody species (Brudvig and Asbjornsen 2009, Thompson

1992, Lorimer et al. 1994, Brian Fankhauser, pers. comm.). The Midwestern savannas have

been classified as critically endangered as they have been reduced by 99.98% since the mid-

1800s (Rebertus and Burns 1997). Overrun remnant oak savannas are still recognizable by large

and branchy white and bur oaks that once were able to spread out freely without closely

compacted canopies (Thompson 1992). Even though oak trees are able to produce many

seedlings, those seedlings are usually too small to compete effectively with taller saplings of

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other species (Lorimer et al. 1994). Oddly, it is fairly common to encounter young oak trees (3-5

years old) in an overrun closed canopy forest (Fankhauser, pers. comm.). However, these young

oaks’ growth quickly stagnates from the lack of sunlight and they eventually die out

(Fankhauser, pers. comm.). These young oaks are being outcompeted by shade tolerant and fire

intolerant species including: sugar maple (Acer saccharum), red maple (Acer rubrum), black

maple (Acer nigrum), basswood (Tilia americana), ironwood (Olneya tesota), chokecherry

(Aronia spp.), hackberry (Celtis occidentalis), red mulberry (Morus rubra), serviceberry

(Amelanchier spp.), and American elm (Ulmus americana), and slippery elm (Ulmus rubra)

(Lorimer et al. 1994, Thompson 1992). All of these shade tolerant species are able to form a

dense and continuous understory beneath the dominant oak canopy (Lorimer et al. 1994). Below

these shade tolerant tree species is also an invasion of dense shrubs including: prickly ash

(Zanthoxylum spp.), prickly gooseberry (Ribes montigenum), smooth sumac (Rhus glabra),

honeysuckle (Lonicera spp.), and buckthorn (Rhamnus cathartica) (Thompson 1992).

Identifying Oak Savannas

Historically, oak savannas could be loosely defined as communities with a continuous

herbaceous layer dominated by grasses and forbs and a discontinuous layer of trees or shrubs, up

to 25-50 percent cover (Peterson and Reich 2001, Wolf 2004). However, when an oak savanna

has been eliminated or degraded, it is difficult to judge a piece of land as having been oak

savanna or not. Arial photography from the 1930s can be useful in understanding the general

canopy cover of an area not too long before fire was eliminated from the landscape (Fankhauser,

pers. comm.). Without the aid of historical photography, making use of knowledge about where

oak savannas thrive can be helpful. Understanding that south and west-facing slopes and flats

provided enough dry soil and light to stimulate oaks is important (Fankhauser, pers. comm.). In

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contrast north and east-facing slopes are often too cool and moist which do not suit well for oak

savanna but rather closed canopy-forest species. The age of the existing tree cover in a forest

can also indicate if the area has been oak savanna or forest. Many of the oak savannas are dotted

with large oaks and intertwined with young shade-tolerant and fire-intolerant species

(Fankhauser, pers. comm.). The difference in herbaceous species and shrubs can be especially

useful to differentiate oak savannas from closed canopy forests. If shrubs like hawthorn

(Crataegus mollis) and prairie crab apple (Malus ioensis), forbs such as feverwort (Triosteum

perfoliatum), and grasses like bottle brush grass (Hystrix patula) are found, the area was most

likely oak savanna (Fankhauser, pers. comm.). If spring ephemerals such as blood root

(Sanguinaria canadensis) and dutchman's breeches (Dicentra cucullaria) are found, the area can

be distinguished as closed canopy forest because these species have adapted to flower in the

spring before the dense tree canopy can block sunlight from reaching the forest floor

(Fankhauser, pers. comm.).

Savannas Types

Most oak savanna habitat has been completely eliminated by human-driven development,

fire suppression, public campaigning against forest fires, and habitat fragmentation (McEwan et

al. 2007). However, some remnant oak savannas are still holding on while battling the

continuous invasion of shade-intolerant/fire-intolerant woody growth. Even though some of

these transformed oak savannas appear to be permanently changed to closed canopy forest, there

is still hope for the restoration and recovery of these oak savanna remnants. Across the varying

moisture gradients in the oak savanna geographical range, there are different types of oak

savannas that require different management techniques. This is not only because they have

different species compositions, but also because the successional changes they have undergone

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has occurred at different rates, thus requiring more or less aggressive management tactics (Haney

and Apfelbaum 1993). The two main oak savannas of the Midwest can be classified as mesic

and dry. Apart from land use changes, mesic oak savannas have been so quickly invaded by

successional change and exotic species that they are hardly recognizable. Mesic savannas are

characterized by bur oak, white oak northern red oak, and swamp white oak. In contrast, dry

savannas have fewer invaded exotic species (Haney and Apfelbaum 1993). Dry savannas are

characterized by black oak, Northern pin oak, blackjack oak, and post oak (Haney and

Apfelbaum 1993).

Mesic: Clay-Loam Savannas

Within the mesic savannas there are clay-loam savannas, floodplain sand savannas, and

mesic loam savannas (Haney and Apfelbaum 1993). The dominant tree of clay-loam savanna is

the bur oak and these savannas are among the rarest and most diverse (Apfelbaum and Haney

1993). They have poorly drained soil derived from lake or glacial deposits and occur throughout

Northern Illinois, Southern Wisconsin, Iowa, parts of Michigan, and Southern Minnesota (Haney

and Apfelbaum 1993, Curtis 1959). The herbaceous layer consists of sedges (Corix spp.),

bluejoint reedgrass (Calamagrostis canadensis), bottle-brush grass (Elymus patula), and in

moister areas Virginia wild rye (Elymus virginicus) and wood reed (Cinna arundinacea) (Haney

and Apfelbaum 1993). Many of these ecosystems that were not able to be tilled were quickly

invaded by European buckthorn (Rhamnus cathartica) with the lack of fire and grazing (Haney

and Apfelbaum 1993). Restoring these savannas requires a combination of mechanical thinning

and repeated prescribed fires (Haney and Apfelbaum 1993).

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Mesic: Floodplain Savannas

Floodplain savannas are dominated by swamp oak, white oak, and bur oak and they are

also one of the more rare savanna types (Haney and Apfelbaum 1993). They have alluvial soils

and are found in similar geographic regions as clay-loam savannas minus Central and Western

Iowa (Haney and Apfelbaum 1993). Cottonwoods (Populus spp.) are also commonly found in

this ecosystem. These ecosystems have common ground cover species such as Virginia wild rye

and wood reed, among many types of sedges and forbs (Haney and Apfelbaum 1993). Periodic

floods and fires maintain these savannas and when floods and fire disturbances are reduced,

invasions of green ash (Fraxinus pennsylvanica), boxelder (Acer negundo), red elm (Ulmus

rubra), prickly ash (Zanthoxylum spp.), buckthorn (Rhamnus cathartica), bitternut hickory

(Carya cordiformis), red maple (Acer rubrum), and river birch (Betula nigra) increase to form a

closed forest (Haney and Apfelbaum 1993).

Mesic: Loam Savannas

Loam savannas contain dominant trees including white oak, Northern red oak, and black

oak (Haney and Apfelbaum 1993). They have moderate to well drained loam and clay-loam

soils ranging from Ohio through Southern Michigan to Northern Illinois and through Southern

Wisconsin into Eastern Iowa (Haney and Apfelbaum 1993). Many of these mesic loam savannas

are found on bluffs or ridges or on morainal deposits in soil developed in loess (Haney and

Apfelbaum 1993). In the absence of fire or grazing sugar maple (Acer saccharum), black maple

(Acer nigrum), shagbark hickory (Carya ovata), basswood (Tilia americana), ironwood (Olneya

tesota), boxelder (Acer negundo), and red elm (Ulmus rubra) dominate the understory (Haney

and Apfelbaum 1993). Mesic savannas on loess bluffs are more stable to successional changes

than most mesic savannas but they are still invaded by shade tolerant species like prickly ash

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(Zanthoxylum americanum), honeysuckle (Caprifoliacaea spp.), and garlic mustard (Alliaria

petiolata)(Haney and Apfelbaum 1993). The shade-tolerant species can form such a dense

canopy and understory that it makes reintroduction of fire very difficult, especially in the spring

because there is so little litter to serve as fuel (Haney and Apfelbaum 1993). Mechanical cutting

of woody plants can provide enough fuel to support fires (Haney and Apfelbaum 1993). The

large older oaks, in overgrown savannas often have wide crowns that indicate the once open to

semi-open nature of these savannas (Haney and Apfelbaum 1993).

Dry: Eastern Sand Savannas

The dominant trees in Eastern sand savannas are black oak (Quercus velutina) and white

oak (Quercus alba) with intermittent pin oak (Quercus palustris) in steep hydrologic gradients

and some bur oaks in less well drained areas (Haney and Apfelbaum 1993). The soils are often

sandy and very well drained and are found in Northwestern Indiana and Southern Michigan

(Haney and Apfelbaum 1993). Jack pines (Pinus banksiana) can be found intermixed with black

oaks in the Indiana Dunes which marks the southern-most extension where jack pines are located

(Haney and Apfelbaum 1993). These savannas were known to carry intense fire which gave

them their barrens community type with most trees reduced to shrubs leaving a prairie matrix of

grasses and forbs (Haney and Apfelbaum 1993). They range from almost zero percent tree cover

after intense fire, to nearly 100 percent in the absence of fire for more than 50 years (Haney and

Apfelbaum 1993). Without fire, black cherry (Prunus serotina) and black oaks (Quercus

velutina) increase in frequency while the leaf litter accumulates resulting in loss of grasses and

forbs (Haney and Apfelbaum 1993). If moderate to light fires are carried, tree and shrub cover

may only be reduced by 10 to 30 percent but it can increase plant species richness and increase

forb and grass cover (Haney and Apfelbaum 1993). The year after a moderate to hot fire, about

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30% increase in species richness can be found (Haney and Apfelbaum 1993). Because black

oaks are moderately tolerant to fire, higher fire frequency and intensity favor them over the other

tree species in the Eastern sand savannas (Haney and Apfelbaum 1993).

Dry: Northern Sand Savannas

Northern sand savannas comprised about 20,000 km² in presettlement time and the

dominant tree were Northern pin oak (Quercus ellipsoidalis), jack pine (Pinus banksiana), and

bur oak (Quercus macrocarpa) (Vora 1993, Haney and Apfelbaum 1993). The soil is much the

same as Eastern sand savannas and these savannas range from South Central Wisconsin north

into the Upper Peninsula of Michigan and west into Minnesota (Haney and Apfelbaum 1993,

Grimm 1984). One of the major distinguishing characteristics that differentiate Northern sand

savannas from Eastern sand savannas is the presence of Northern pin oak and the absence of

black oak (Haney and Apfelbaum 1993). It is difficult to determine the transition between these

two ecosystems because black oak and Northern pin oak can hybridize (Haney and Apfelbaum

1993, Curtis 1959). Black cherry (Prunus serotina), serviceberry (Amelanchier arborea),

chokecherry (Prunus virginiana), blueberry (Cyanococcus spp.), huckleberry (Ericanceae spp.),

hazelnut (Corylus americana), rice grass (Oryzopsis hymenoides), and bracken fern (Pteridium

aquilinum) are all more common in Northern sand savannas than in Eastern sand savannas

(Haney and Apfelbaum 1993, White 1986). Similar to Eastern sand savannas, fire intensity and

frequency was historically very high which helped to maintain the barrens community type with

shrub dominated areas and dominant herbaceous plants (Haney and Apfelbaum 1993). Over the

past 80 to 90 years, fire suppression has developed these barrens into closed canopy forests of

Northern pin oak, jack pine, black cherry, quaking aspen (Populus tremuloides), and scattered

understory of serviceberry and hazelnut (Haney and Apfelbaum 1993). This ecosystem change

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has greatly affected these savannas as the forb and grass cover becomes outcompeted for light

and nutrients (Haney and Apfelbaum 1993, Tilman 1984). Fire is very important in this

ecosystem because it releases nutrients and stimulates plant productivity which has shown to

increase the herbaceous ground cover dramatically (Haney and Apfelbaum 1993, Vogl 1965). In

Chequamegon National Forest, woodland thinning followed by burning resulted in the presence

of the rare temate grape fern (Botrychium ternatum) and dwarf bilberry (Vaccinum cespitosum)

which is a host plant for the rare Naboror’s blue butterfly (Lycacides idas nabokovi) (Haney and

Apfelbaum 1993, Vora 1993).

Dry: Southern Oak Savanna

Southern oak savannas are dominated by post oak and backjack oak and they lie on older,

clay-loam soils, sandy soil, or shallow soils over limestone or other rock outcrops (Haney and

Apfelbaum 1993). On deeper soils, white oak (Quercus alba) and Chinkapin oak (Quercus

muehlenbergii) occur on alkaline sites Texas (Haney and Apfelbaum 1993). They range from

Southern Indiana across Central and Southern Illinois through Missouri to Oklahoma and Texas

(Haney and Apfelbaum 1993, Stritch 1990). Southern oak savannas frequently were interspersed

with prairie openings, especially on the south facing slopes where sun exposure helped create

dryer habitat which increased fire frequency and intensity (Haney and Apfelbaum 1993). In the

absence of fire these savannas are invaded by winged elm, hickory, black maple (Acer nigrum)

and sugar maple (Acer saccharum), and Eastern red cedar (Juniperus virginiana) (Haney and

Apfelbaum 1993, Anderson and Schwegman 1990).

Effects of Prescribed Fire

Simulating the natural effects of fire with prescribed burns is the goal for many land

conservationists in order to restore the stability of the oak savanna ecosystem (Anderson and

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Brown 1986). Peterson and Reich (2001) were able to provide some very useful analysis over

the course of 32 years of prescribed burning in the Cedar Creek Natural History Area in east-

central Minnesota as well as follow up on some of the results from two other studies at the same

location by White (1986) and Tester (1989). The effects of fire resulted in apparent changes in

the forest structure and plant communities as more grasses and forbs were seen in burned units

(White 1986). However, they found no distinguishing characteristics between burn regimes to

indicate which one would be better suited for the oak savanna restoration. The study tried burn

regimes such as annual burns, 2:2, 4:2, 3:3, and 2:1 cycles (White 1986). Tester (1989) did find

a relationship between fire frequency and restoration quality. Species richness was highest when

2 consecutive years of burning were followed by 2 years without which allowed for the build-up

of fuel so that the subsequent burn was more likely to be hotter to better control forest species

(Tester 1989, Anderson and Brown 1986). The second fire most likely serves to further deplete

the food reserves stored in the invasive or woody species root systems which result in decreased

strength or death (Tester 1989). A common finding is that prescribed fire cannot alone restore

oak savannas. Mechanical thinning in overrun savannas is as important as fire in most locations

(Peterson and Reich 2001, White 1989, Fankhauser, pers. comm.). However, removing

competitive understory brush alone shows very little affect on oak seedling growth (Buckley et

al. 1998). The most effective thinning takes place in the canopy (Buckley et al. 1998).

Regeneration Challenges

The largest challenge conservationists are having with oak savannas restoration is oak

recruitment and regeneration. It is hard to understand why such a prominent historical landscape

requires so much effort in re-stabilization (Lorimer et al. 1994). A number of studies have tried

to find the most productive restoration techniques in stimulating new oak growth. There do seem

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to be some successes, but the findings often will only truly apply to the particular region where

the study was conducted. In addition to location, the amount of time elapsed, since the start of

the relatively recent restoration studies, has not been significant enough to make certain claims

about their findings. Brian Fankhauser (pers. comm.) has found that increased regeneration is far

more likely after establishing more direct sunlight to the forest floor. This requires the thinning

of fire intolerant/shade tolerant species followed by the reintroduction of fire. The fire helps to

burn away the heavy duff build-up that accumulates quickly in the absence of fire. When the

duff is removed, acorns have better soil contact to enhance germination (Fankhauser, pers.

comm.). In addition, with the removal of the duff layer, the soil is able to dry out which provides

an optimal environment for oak seedlings to thrive (Fankhauser, pers. comm.). Fankhauser was

part of an oak restoration in Iowa that saw remarkable oak regeneration which followed three

consecutive years of burning. Inadvertently, the timing of the third burn happened to be on a

mast year for the oaks. Fankhauser (pers. comm.) noted that in order to allow the oak seedlings

to not get top-killed by continuous annual burns, a two to three year absence of fire is needed.

Brudvig and Asbjornsen (2005) conducted a study on oak regeneration in Central Iowa

comparing mechanical thinning with no thinning. They found that canopy thinning appeared to

be a necessary restoration step before white oak seedling could increase significantly in size.

Their study did not include prescribed fire but still had promising results for oak regeneration. In

Central Virginia, oak regeneration benefited from fire treatments which were done in the winter,

spring, or summer (Brose et al. 1998). The large tap root of oaks gave them a competitive

advantage over yellow-poplar as they can store more reserves for shoot and leaf growth after

fires (Brose et al. 1998). Before prescribing the first burn, it was critical to allow oak seedlings

to develop for several years after mechanical thinning so that they could form relatively large

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root systems (Brose et al. 1998). Giving oak seedlings this small time interval before burning

also allowed for the stored yellow-poplar seeds on the forest floor to germinate, making them

more vulnerable to surface fires (Brose et al. 1998). Spring also proved to be the best season for

the prescribed burns as the warm temperatures, lower humidities, sunny days, and southerly

winds were suitable for frequent opportunities for medium-high and high intensity fires (Brose et

al. 1998).

Restoring Remnant Oak Savanna in Northeastern Iowa

Within Northeast Iowa, there is a lot of variation in oak savannas. Variation is caused by

dissimilar soil types and quality, size, fire history, and species composition quality. There are

oak savannas that have been invaded by Eastern red cedars (Juniperus virginiana), or European

buckthorn (Rhamnus cathartica), or garlic mustard (Alliaria petiolata), or all of the above. A

helpful way to begin any oak savanna restoration is to examine an aerial picture from the 1930s

to get an idea for the percentage of tree cover and composition. A very common comparison

between 1930s and presents day aerial photography shows how the open canopy gaps have

gradually filled in with Eastern red cedars or other invasive woody species.

The next step would be to thin the invasive trees in order to let sunlight reach the ground

layer. Leaving a few invasive trees should make the restoration transition more gradual to

prevent a sudden disruption for any dependent wildlife. Another way to gradually thin woodland

is by either girdling or frilling invasive trees (Solecki 1997). Using a chainsaw, two rings need

to be cut that penetrate the phloem and cambium layers completely around the tree, which

effectively cuts off any nourishment the tree tries to send down to the roots (Solecki 1997).

Some tree species are able to resprout in response to the girdling; in which case frilling becomes

a better option (Solecki 1997). The only difference between frilling and girdling is the herbicide

20

treatment on the lower ring, ensuring tree faster kill (Fankhauser pers. comm.) Thinning may or

may not prove to be essential in oak savanna restorations, but it will aid the process more rapidly

than prescribed burns alone.

Roundup (glyphosate) has proven to be an effective herbicide to control any resprouting

of fire tolerant/shade tolerant species after being mechanically removed (Solecki 1997).

Roundup is most effective when the plant is sending its energy down to the root system

(Fankhauser pers. comm.) Roundup is also effective when attacking large patches of garlic

mustard, especially during the spring or fall when many of the native ground layer species are

dormant (Solecki 1997). However, spraying may do more harm in areas with a diverse native

plant community, thus hand-pulling is preferred in some areas. Aside from herbicide, large

patches of garlic mustard can be controlled by scything the plants at ground level when they are

in full flower (Solecki 1997). After scything, the stems have to be removed to avoid the chance

that viable seed is still produced. In general, garlic mustard control can be best handled by a

combination of spring burns, hand-pulling, and scything flowering plants (Solecki 1997). For

less concentrated infestations, hand-pulling works well if the plants are removed from any soil

contact (Solecki 1997). Buckthorn invasions can be controlled by repeated spring and fall burns

for up to six consecutive years (Solecki 1997). However, buckthorn invasions usually prevent

adequate fuel loads, resulting in the need for herbicide treatments on cut stems; optimal in the

fall (Solecki 1997).

In order to promote oak seedling germination, the long term burn regime should be

delayed for two to three years after thinning treatments or other invasive species control

management. Each burn should occur late in the spring in order to clear the fuel load and

replenish the soil with nutrients. Although conditions for burning may be optimal in early

21

spring, a later spring burn may be more beneficial if it occurs after some of the invasive cool

season species have started to emerge. If a burn is done too early, some of the opportunistic

invasive species will be able to take advantage of the nutrients created by the fire (Solecki 1997).

At this stage in the restoration, management involves monitoring for persistent invasive species

to prevent further spread. It is also crucial to monitor the native plant species diversity. If the

native species have not responded to the restoration, interseeding may be required. In deciding

which seed types to use, observe the native plant species found in a high quality oak savanna

remnant with similar species of oaks (Packard 1997). Seed mixes should be prepared beforehand

to match the specific sites within the restoration. These seed mixes should be suitable for

specific shade and moisture gradients; wet, mesic, and dry (Packard 1997). If the seeds are

broadcasted by hand-seeding, they need to be incorporated into the soil, otherwise the risk of

losing seeds to birds or by wind becomes too great (Packard 1997). In order to achieve this,

seeding should be done after a spring or fall burn, which removes the leaf and duff layer, and

right before a rainstorm (Packard 1997). However, on steeper sloped oak savannas, seeding after

a rainfall can wash away the seeds (Packard 1997). In this case, broadcast seeding during the

late fall after a burn, but before winter, will not only create better seed to soil contact, but the

gradual freezing and thawing helps to churn up the soil (Packard 1997).

Along with the reintroduction of a six to seven year burn interval, further monitoring of

plant, animal, and insect species diversity and abundance should be done to see if the restoration

has been successful (Packard 1997). On smaller sized restoration areas, attentive monitoring of

invasive species is necessary to prevent the inward spread of colonies forming on the degraded

outskirts of the restoration (Packard 1997).

22

Conclusions

It appears that there is no “one size fits all” approach to oak savanna restoration.

However, there appear to be some common trends among oak savanna restoration practices.

Thinning followed by prescribed fire followed by the absence of fire until oaks are developed

enough to tolerate fire again (Buckley et al. 1998, Brose et al. 1998, Rebertus and Burns 1997,

Tester 1989, Fankhauser, pers. comm.). Spring fires are also more beneficial for oak

regeneration purposes as they provided more intense burns to remove the encroachment of other

woody species and possibly aid in the reduction of acorn predation by insects (Brose et al. 1998,

Fankhauser, pers. comm.).

Humans have had as much to do with the formation of oak savannas as they have had to

do with their destruction. Today, only 1% of remnant oak savannas remain in the Midwest

(Brudvig and Asbjornsen 2009). Oak savannas will not exist if we do not continue to play an

integral role in managing them. Oak savannas are unique and diverse ecosystems and there are

many questions yet requiring more research to be done on them. A more comprehensive

understanding of the complex natural processes and history of oak savannas is critically

important in knowing the best way to restore and conserve these unique native ecosystems.

Acknowledgements

I was fortunate enough to learn a lot from Brian Fankhuaser with the Iowa Natural

Heritage Foundation. His experienced insight on oak savannas was invaluable to this paper. I

also want to thank Dr. Kirk Larsen for not only providing valuable literature, but also for

directing and editing this paper.

23

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