Oak savanna

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Oak savanna, California North Slope Santa Ynez Mtns.jpg
Oak savanna, California

An oak savanna is a type of savanna, or lightly forested grassland, where oaks (Quercus spp.) are the dominant trees. These savannas were maintained historically through wildfires set by lightning or humans, grazing, low precipitation, and/or poor soil.

Savanna grassland ecosystem

A savanna or savannah is a mixed woodland grassland ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of grasses.

Grassland areas where the vegetation is dominated by grasses (Poaceae)

Grasslands are areas where the vegetation is dominated by grasses (Poaceae); however, sedge (Cyperaceae) and rush (Juncaceae) families can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur naturally on all continents except Antarctica. Grasslands are found in most ecoregions of the Earth. For example, there are five terrestrial ecoregion classifications (subdivisions) of the temperate grasslands, savannas, and shrublands biome (ecosystem), which is one of eight terrestrial ecozones of the Earth's surface.

Oak genus of plants

An oak is a tree or shrub in the genus Quercus of the beech family, Fagaceae. There are approximately 600 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably Lithocarpus, as well as in those of unrelated species such as Grevillea robusta and the Casuarinaceae (she-oaks). The genus Quercus is native to the Northern Hemisphere, and includes deciduous and evergreen species extending from cool temperate to tropical latitudes in the Americas, Asia, Europe, and North Africa. North America contains the largest number of oak species, with approximately 90 occurring in the United States, while Mexico has 160 species of which 109 are endemic. The second greatest center of oak diversity is China, which contains approximately 100 species.


Map of oak savanna distribution in North America NA-savanna-map.gif
Map of oak savanna distribution in North America

Although there are pockets of oak savanna almost anywhere in North America where oaks are present, there are three major oak savanna areas: 1) California, Washington and Oregon in the west; 2) Southwestern United States and Mexico; and 3) the prairie/forest border of the Midwest. [1] [2] There are also small areas of oak savannas in other parts of the world. (See also Eastern savannas of the United States for information on pine savannas of the U.S. South.)

California oak woodland

California oak woodland is a plant community found throughout the California chaparral and woodlands ecoregion of California in the United States and northwestern Baja California in Mexico. Oak woodland is widespread at lower elevations in coastal California; in interior valleys of the Coast Ranges, Transverse Ranges and Peninsular Ranges; and in a ring around the California Central Valley grasslands. The dominant trees are oaks, interspersed with other broadleaf and coniferous trees, with an understory of grasses, herbs, geophytes, and California native plants.

Southwestern United States Geographical region of the USA

The Southwestern United States, also known as the American Southwest, is the informal name for a region of the western United States. Definitions of the region's boundaries vary a great deal and have never been standardized, though many boundaries have been proposed. For example, one definition includes the stretch from the Mojave Desert in California to Carlsbad, New Mexico, and from the Mexico–United States border to the southern areas of Colorado, Utah, and Nevada. The largest metropolitan areas are centered around Phoenix, Las Vegas, Tucson, Albuquerque, and El Paso. Those five metropolitan areas have an estimated total population of more than 9.6 million as of 2017, with nearly 60 percent of them living in the two Arizona cities—Phoenix and Tucson.

Eastern savannas of the United States

The eastern savannas of the United States covered large portions of the southeast side of the continent until the early 20th century. These were in a fire ecology of open grassland and forests with low ground cover of herbs and grasses.

Wisconsin bur oak savanna; mid-summer Bur-oak-savanna-Wisconsin.jpg
Wisconsin bur oak savanna; mid-summer

Midwestern oak savannas

The oak savannas of the Midwestern United States form a transition zone between the arid Great Plains to the west and the moist broadleaf and mixed forests to the east. Oak savannas are found in a wide belt from northern Minnesota and southern Wisconsin, down through Iowa, Illinois, northern and central Missouri, eastern Kansas, and central Oklahoma to north-central Texas, with isolated pockets further east around the Great Lakes including Ontario. [3] The bur oak (Quercus macrocarpa) is the dominant species in northern oak savannas, although black oak (Quercus velutina), white oak (Quercus alba), and Hill's oak (Quercus ellipsoidalis)are sometimes present. The dominant tree in the south is usually the black oak (Quercus velutina), although the chinquapin oak (Quercus muhlenbergii), post oak (Quercus stellata), and black-jack oak (Quercus marilandica) are also common. The flora of the herbaceous layer generally consists of species associated with tallgrass prairies, both grasses and flowering plants, although some woodland species may be present. There are also a few species that are unique to oak savannas. [4] [5] [6] Oak savannas, because of their mixture of grassland, woodland, and unique savanna species, typically have a higher plant diversity than grasslands and woodlands combined.

Great Plains broad expanse of flat land west of the Mississippi River and east of the Rocky Mountains in the United States and Canada

The Great Plains is the broad expanse of flat land, much of it covered in prairie, steppe, and grassland, that lies west of the Mississippi River tallgrass prairie in the United States and east of the Rocky Mountains in the U.S. and Canada. It embraces:

Minnesota State of the United States of America

Minnesota is a state in the Upper Midwest, Great Lakes, and northern regions of the United States. Minnesota was admitted as the 32nd U.S. state on May 11, 1858, created from the eastern half of the Minnesota Territory. The state has a large number of lakes, and is known by the slogan the "Land of 10,000 Lakes". Its official motto is L'Étoile du Nord.

Wisconsin A north-central state of the United States of America

Wisconsin is a U.S. state located in the north-central United States, in the Midwest and Great Lakes regions. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin is the 23rd largest state by total area and the 20th most populous. The state capital is Madison, and its largest city is Milwaukee, which is located on the western shore of Lake Michigan. The state is divided into 72 counties.


Before European settlement, the oak savanna, a characteristic fire ecology, was extensive and was often a dominant part of the ecosystem. Fires, set by lightning or Native Americans, ensured that the savanna areas did not turn into forests. Only trees with a high tolerance for fire, principally certain oak species, were able to survive. On sandy soils, black oak ( Quercus velutina ) predominated. On rich soils bur oak (Quercus macrocarpa) was the major tree in Midwestern North America. These savanna areas provided habitat for many animals, including American bison, elk, and white-tailed deer.

Fire ecology scientific discipline concerned with natural processes involving fire in an ecosystem and the ecological effects

Fire ecology is a scientific discipline concerned with natural processes involving fire in an ecosystem and the ecological effects, the interactions between fire and the abiotic and biotic components of an ecosystem, and the role as an ecosystem process. Many ecosystems, particularly prairie, savanna, chaparral and coniferous forests, have evolved with fire as an essential contributor to habitat vitality and renewal. Many plant species in fire-affected environments require fire to germinate, establish, or to reproduce. Wildfire suppression not only eliminates these species, but also the animals that depend upon them.

Forest dense collection of trees covering a relatively large area

A forest is a large area dominated by trees. Hundreds of more precise definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing and ecological function. According to the widely used Food and Agriculture Organization definition, forests covered 4 billion hectares (9.9×109 acres) (15 million square miles) or approximately 30 percent of the world's land area in 2006.

<i>Quercus velutina</i> tree species

Quercus velutina, the eastern black oak or more commonly known as simply black oak, is a species in the red oak group of oaks. It is widespread in eastern and central North America, found in all the coastal states from Maine to Texas, inland as far as Michigan, Ontario, Minnesota, Nebraska, Kansas, Oklahoma, and eastern Texas.

The most fire-tolerant of the oak species is the bur oak ( Quercus macrocarpa ), which is especially common in hill-country savannas in the Midwest.

<i>Quercus macrocarpa</i> species of plant

Quercus macrocarpa, the bur oak, sometimes spelled burr oak, is a species of oak in the white oak section Quercus sect. Quercus, native to North America in the eastern and central United States and eastern and central Canada. This plant is also called mossycup oak and mossycup white oak.

Fire-tolerant bur oak savanna in Wisconsin hill country Bur-oak-savanna.jpg
Fire-tolerant bur oak savanna in Wisconsin hill country

European settlers cleared much of the savanna for agricultural use. In addition, they suppressed the fire cycle. Thus surviving pockets of savanna typically became less like savannas and more like forests or thickets. Many oak savanna plant and animal species became extinct or rare.

Prescribed burn; Wisconsin bur oak savanna Fire-sav-S-slope-3720.jpg
Prescribed burn; Wisconsin bur oak savanna


With the rise in interest in environmental conservation, restoration and preservation of surviving areas of oak savanna began. Low intensity, spring prescribed burns have been used since 1964 at the Cedar Creek Ecosystem Science Reserve in Minnesota in an attempt to restore the area to an oak savanna. [7] Burned areas are now more savanna like (having greater grass and forb and lower shrub and lower tree representation) than unburned areas but still have higher overstory densities than apparently existed in presettlement times. Restoration work began in the 1970s in Illinois, followed by work in Wisconsin, Indiana, Iowa, Missouri, and Minnesota. [8]

Cedar Creek Ecosystem Science Reserve

The Cedar Creek Ecosystem Science Reserve is an ecological research site located primarily in East Bethel, Minnesota in the counties of Anoka and Isanti on the northern edge of the Minneapolis-Saint Paul metropolitan area. Encompassing 5,400 acres (22 km2) of native upland forests and prairie and lowland swamps and meadows, the site contains over 900 plots of long-term experimental research which evaluate plant competition and biodiversity. The herbivory research division examines animal and plant relationships. Led by prominent American ecologist G. David Tilman, the University schedules more than 130 faculty, post-doctoral researchers, graduate students, staff, and undergraduate researcher interns to the site as of 2006.

Current distribution

Presettlement there was approximately 50,000,000 acres of oak savanna in Midwestern United States, all of it being exclusively in a wide strip stretching from southwestern Michigan to eastern Nebraska and from southern Manitoba to central Texas. After Europeans arrived, fire suppression and settlement diminished the oak savannas to a fraction of their former expanse, which currently exist in many fragmented pockets throughout its native range. Many sites are protected and maintained by government bodies or non-profit organizations such as The Nature Conservancy, the Wisconsin and Minnesota Departments of Natural Resources, and the Iowa Natural Heritage Foundation. Examples include the Neal Smith Wildlife Refuge near Prairie City, Iowa, the Indiana Dunes National Lakeshore in Indiana, numerous State Natural Areas in Wisconsin, the Lake County Forest Preserve District, Cook County Forest Preserve District and Iroquois County State Wildlife Area in Illinois, the Oak Openings Preserve Metropark in Ohio, and Pinery Provincial Park on Lake Huron in Ontario. An excellent example of a restored oak savanna is Wisconsin's Pleasant Valley Conservancy State Natural Area. [9]

Related Research Articles

Prairie ecosystems considered part of the temperate grasslands, savannas, and shrublands biome

Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the dominant vegetation type. Temperate grassland regions include the Pampas of Argentina, Brazil and Uruguay, and the steppe of Ukraine, Russia and Kazakhstan. Lands typically referred to as "prairie" tend to be in North America. The term encompasses the area referred to as the Interior Lowlands of Canada, the United States, and Mexico, which includes all of the Great Plains as well as the wetter, hillier land to the east.

Tallgrass prairie ecosystem native to central North America

The Tallgrass prairie is an ecosystem native to central North America. Natural and anthropogenic fire, as well as grazing by large mammals, were historically agents of periodic disturbance, which regulates tree encroachment, recycles nutrients to the soil, and catalyzes some seed dispersal and germination processes. Prior to widespread use of the steel plow, which enabled conversion to agricultural land use, tallgrass prairies expanded throughout the American Midwest and smaller portions of southern central Canada, from the transitional ecotones out of eastern North American forests, west to a climatic threshold based on precipitation and soils, to the southern reaches of the Flint Hills in Oklahoma, to a transition into forest in Manitoba.

Nichols Arboretum Ann Arbor campus of the University of Michigan

Nichols Arboretum, locally known as the Arb, is an arboretum operated by the University of Michigan. Located on the eastern edge of its Central Campus at 1610 Washington Heights in Ann Arbor, Michigan, the Arboretum is a mosaic of University and City properties operated as one unit. The arboretum is open daily from sunrise to sunset with no charge for admission. The Huron River separates a northern section of the arboretum's floodplain woods; the railroad marks the northern border.

University of Wisconsin–Madison Arboretum

The University of Wisconsin–Madison Arboretum is a teaching and research facility of the University of Wisconsin–Madison and the site of historic research in ecological restoration. In addition to its 1,260 acres (5 km2) in Madison, Wisconsin, the Arboretum also manages 520 acres of remnant forests and prairies throughout Wisconsin.

Prairie restoration type of habitat conservation

Prairie restoration is a conservation effort to restore prairie lands that were destroyed due to industrial, agricultural, commercial, or residential development. For example, the U.S. state of Illinois alone once held over 35,000 square miles (91,000 km2) of prairie land and now just 3 square miles (7.8 km2) of that original prairie land is left.

Spread Eagle Barrens State Natural Area

Spread Eagle Barrens State Natural Area is a 7,155-acre (2,896 ha) protected area just off of U.S. 2 in Florence County, Wisconsin, USA. The nearest unincorporated community is Spread Eagle, Wisconsin, but the closest large city is Iron Mountain, Michigan; 6 miles (10 km) away. The Spread Eagle Barrens is owned by the Wisconsin Department of Natural Resources and the Wisconsin Energy Corporation, and was designated a State Natural Area in 1995.

Pre-Columbian savannas of North America

Pre-Columbian savannas once existed across North America. These were created by both natural lightning fires and by Native Americans. The arrival of European settlers caused the death of most Native Americans in the 16th century. Surviving natives continued using fire to clear savanna until European colonists began colonizing the eastern seaboard two hundred years later. Many colonists continued the practice of burning to clear underbrush, reinforced by their similar experience in Europe, but some land reverted to forest.

Upper Midwest forest-savanna transition

The Upper Midwest forest-savanna transition is a terrestrial ecoregion that is defined by the World Wildlife Fund. An oak savanna plant community located in the Upper Midwest region of the United States, it is a ecotone between the tallgrass prairies to the west and the temperate deciduous forests to the east. A part of the Upper Mississippi River basin, it is considered endangered with less than 5% of the original ecosystem remaining intact, due mostly to overgrazing and conversion to agriculture.

Central tall grasslands

The Central tall grasslands are a prairie ecoregion of the Midwestern United States, part of the North American Great Plains.

Whiterock Conservancy is a 501(c)(3) land trust located in west-central Iowa that stewards over 4,000 acres of contiguous land located in the Middle Raccoon River watershed, and an additional 1,000 non-contiguous land located in the Brushy and Middle Raccoon River watersheds. The Whiterock landscape almost exclusively made possible by an extraordinary planned land gift from the Garst family to Whiterock Conservancy. The landscape is a mosaic of agricultural land, wetlands, preserved prairie and oak savanna, riverine woodlands, and upland forest. The land is also home to the historic Roswell and Elizabeth Garst Farmstead, which hosted Soviet Premier Nikita Khrushchev in 1959, and is now on the National Register of Historic Places. The land is used for recreation, environmental conservation, and for the production of agricultural products, and is managed as a working landscape where cultural, environmental, agricultural, and recreational land uses are held in equal importance.

Interior Low Plateaus physiographic province in the United States

The Interior Low Plateaus are a physiographic region in eastern United States. It consists of a diverse landscape that extends from north Alabama across central Tennessee and Kentucky into southern Illinois, Indiana, and Ohio. Its natural communities are a matrix of temperate forests, woodlands, and prairies.

Oak woodland

An oak woodland is a plant community with a tree canopy dominated by oaks. In terms of canopy closure, oak woodlands are intermediate between oak savanna, which is more open, and oak forest, which is more closed. Although the community is named for the dominance of oak trees, the understory vegetation is often diverse and includes many species of grasses, sedges, forbs, ferns, shrubs, and other plants.

Northern mixed grasslands

The Northern Mixed Grasslands is one of 867 terrestrial ecoregions defined by the World Wide Fund for Nature. This ecoregion includes parts of the Canadian provinces of Saskatchewan and Manitoba, north-central and eastern North Dakota, most of east South Dakota, and small portions of western Minnesota in the American Great Plains. The United States Environmental Protection Agency (EPA) defines this ecoregion as the Northern Glaciated Plains.

Bur oak blight (BOB) is a fungal disease that is relatively new to the plant pathogen landscape. BOB started to appear in Midwestern states in the 1990s. The first few diagnoses pointed to a common fungus, Tubakia dryina, as the culprit. However upon further research BOB was said to be caused by a new unnamed species of Tubakia, later named Tubakia iowensis T.C. Harr. & D. McNew sp. nov. ‘’ BOB has severe symptoms and is a serious new problem amidst the plant pathology world.

Remnant natural area

A remnant natural area, also known as remnant habitat, is an ecological community containing native flora and fauna that has not been significantly disturbed by destructive activities such as agriculture, logging, pollution, development, fire suppression, or non-native species invasion. The more disturbed an area has been, the less characteristic it becomes of remnant habitat. Remnant areas are also described as "biologically intact" or "ecologically intact."

Stephen Packard (1943–) is an American conservationist, author, and ecological restoration practitioner active in the Chicago area.


  1. McPherson, Guy R. 1997. Ecology and Management of North American Savannas. University of Arizona Press, Tucson.
  2. Anderson, Roger A., Fralish, James S. and Baskin, Jerry M. editors.1999. Savannas, Barrens, and Rock Outcrop Plant Communities of North America. Cambridge University Press.
  3. Nuzzo, V.A. 1986. Extent and status of Midwest oak savanna: presettlement and 1985. Natural Areas Journal 6: 6-36.
  4. Penfound, W.T. (1962). "The savanna concept in Oklahoma". Ecology. 43: 774–775. doi:10.2307/1933481.
  5. Abrams, M.D. (1992). "Fire and the development of oak forests". BioScience. 42: 346–353. doi:10.2307/1311781.
  6. Packard, Steve. Just a few oddball species: restoration and the recovery of the tallgrass savanna. 1988. Restoration and Management Notes 6:1, 13-22
  7. Research Paper NC-266. St. Paul, MN: U.S. Dept. of Agriculture, Forest Service, North Central Forest Experiment Station
  8. Stevens, William K. 1995. Miracle Under the Oaks: The Revival of Nature in America; New York. Pocket Books
  9. "Pleasant Valley Conservancy".