Photo © Tom Brock, University of Wisconsin-Madison Gucker, Corey L. Quercus macrocarpa. In: Fire Effects Information System, Online. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available:. QUEMAC QUEMACD QUEMACM QUMA2 QUMAD QUMAM bur oak mossy-cup oak prairie oak The scientific name of bur oak is Quercus macrocarpa Michx. (Fagaceae) ,.

Bur oak belongs to the Quercus subgenus and section. The Quercus section has also been called the white oak, Leucobalanus, or Lepidiobalanus section ,. Two bur oak varieties are recognized by Kartesz but are considered 'clinal variants' by the Flora of North America :. Quercus macrocarpa Michx. Depressa (Nutt.) Engelm. Quercus macrocarpa Michx. Macrocarpa When the ranges of the parent species ranges overlap, bur oak may hybridize with other white oaks ( Quercus section):.

Bebb oak ( Quercus × bebbiana) C.K. Schneid., a bur oak × white oak ( Q. Alba) hybrid occurring in the Midwest ,. Quercus × bechyae Gaynor, a bur oak × dwarf chinkapin oak ( Q. Prinoides) hybrid suspected from Livingston County, Michigan ,. Quercus × burnetensis Little, a bur oak × live oak ( Q. Virginiana) hybrid reported from Texas ,.

Quercus× byarsii Sudw., a bur oak × swamp chestnut oak ( Q. Michauxii) hybrid reported from Tennessee ,. Quercus × deamii Trel., a bur oak × chinkapin oak ( Q. Muhlenbergii) hybrid common in the Midwest ,.

Quercus × guadalupensis Sarg., a bur oak × post oak ( Q. Stellata) hybrid occurring in Texas ,. Quercus × megaleia Laughlin, a bur oak × overcup oak ( Q. Lyrata) hybrid reported from Missouri ,. Quercus × schuettei Trel., a bur oak × swamp white oak ( Q. Bicolor) hybrid common in the northeastern part of bur oak's range , Bur oak has also hybridized with the nonnative, English oak ( Q. Robur) and with Gambel oak ( Q.

Bur oak × Gambel oak hybrids are a result of past introgression , and hybrids occur outside of bur oak's range in northeastern New Mexico and outside of Gambel oak's range in northeastern Wyoming ,. In northeastern New Mexico, researchers suspect that past hybridization between bur oak and Gambel oak occurred when a moister climate regime prevailed. None Tree Tree-shrub SPECIES: Quercus macrocarpa. © Elbert Little, United States Forest Service The map above illustrates bur oak's distribution in North America as of 1971.

Token Commemorating 80 Years From 1893-1973 For Mac Os X

Of the North American oaks, bur oak is the most widely distributed and ranges farthest north. General information about the potential distribution of bur oak hybrids is presented in the section.

Local distribution changes: In many parts of its North American range, the abundance of and area occupied by bur oak has decreased dramatically since European settlement. Conservation and restoration of bur oak has become a management priority for disjunct populations as well as populations within the continuous bur oak range. Agency experts in Canada consider bur oak a conservation priority because it has decreased in abundance, and its habitats are in high demand for development. In New Brunswick, bur oak populations occur about 470 miles (750 km) beyond the continuous North American distribution of the species and about 150 miles (250 km) from the nearest conspecific population in Maine. As of 2009 populations and scattered individuals occupied a combined area of less than 1.9 mi² (5 km²) in this province. All bur oak populations in New Brunswick occurred in narrow areas along floodplains and riverbanks, and many occurred on privately owned lands threatened by waterfront developments.

Bur oak savannas in the Midwest and Great Plains were ideal sites for European settlers because they provided wood for homes and fuel, and forage for livestock. Agricultural and urban development together with fire exclusion led to widespread loss of the bur oak savanna ecosystem ,. In the early 1900s, oak savannas occupied up to 32 million acres (13 million ha) in the Midwest, and in 1985, only about 6,400 acres (2,600 ha) of 'high-quality' oak savanna remained. In Wisconsin, researchers estimated that 5.5 million acres (2.2 million ha) of oak savanna existed before European settlement, but as of the late 1990s, just 500 acres (200 ha) existed (review by ).

When describing the historical extent of bur oak savannas and a single remaining remnant savanna in southern Wisconsin, Stout called his report 'an obituary' for bur oak. In Texas, bur oak occurs on the drier sites within bottomland hardwood forests. Prior to European settlement, these forests likely occurred over 16 million acres (6.5 million ha), but as of early 2000, less than 40% of the forests remain. For more about how fire exclusion and woodland succession contribute to the loss of bur oak trees and savanna ecosystems, see. In North America, bur oak is most common at elevations of less than 3,300 feet (1,000 m) but tolerates a range of climatic and soil conditions. Bur oak occupies habitats ranging from moist woodlands and bottomland forests to prairies and sandhills.

In the western and northern parts of its range, bur oak size and growth form may vary with site conditions. In moist woodlands and on alluvial floodplains, bur oak often grows as a tree up to 160 feet (50 m) tall but on dry uplands and bluffs, it may grow as a shrub less than 16 feet (5 m) tall ,. In north-central Nebraska's Niobrara Valley Preserve, bur oak reaches only 20 feet (6 m) tall on dry sites but may reach 50 feet (15 m) tall on moist floodplains. Additional bur oak characteristics that can vary by site and distribution are discussed in the. Climate: Bur oak is one of the most cold tolerant of the North American oak species. In one of its northernmost habitats, south-central New Brunswick, bur oak abundance is greatest where the annual growing-day temperature exceeds 40 °F (5 °C) and there are about 150 frost-free days. In bur oak's northwestern range, the average growing season may be only 100 days, but in southern Illinois and Indiana, where bur oak development is considered best, the growing season is 190 days (review by ).

Bur oak tolerates a range of moisture regimes. During a severe 7-year drought in the Great Plains, researchers monitoring injury and mortality in the area reported that bur oak 'endured drought especially well'. Annual precipitation can be as low as 15 inches (380 mm) in bur oak's northwestern range, while in its southern range annual precipitation can exceed 50 inches (1,270 mm) (review by ). Soils: While bur oak tolerates harsh soil conditions, including poor, dry soils and wet, poorly drained or inundated soils , bur oak distribution is not necessarily dictated by soil characteristics. Soils in western bur oak habitats are generally Mollisols, in northern habitats are Spodosols, and in central and southern habitats are Alfisols. Although studies have related bur oak's presence and abundance to soil moisture conditions , comparing soil characteristics without information on past disturbances, land use, and successional change on all but the harshest sites may erroneously indicate bur oak-soil relationships. In a study of structure, composition, and environmental relationships in an oak savanna remnant in northwestern Ohio, researchers predicted bur oak occurrence as a function of disturbance and not of moisture or drainage regimes.

Survey records, other historical records, and soil and topographic factors in the Big Woods region of south-central Minnesota indicated that firebreaks (bodies of water and rough topography) were the primary reason for observed vegetation patterns. Bur oak dominated woodlands that experienced frequent fire regardless of soil characteristics. For more on the importance of disturbances and succession on bur oak, see. Although tolerant of some inundation, bur oak does not tolerate prolonged flooding. At Lake Oahe, South Dakota, a field trial showed that bur oak survived at least 2 weeks of growing-season inundation. However, in the northern part of the Mississippi Delta, bur oak is often killed by high water during the growing season.

Details about duration of flooding and saturation were not provided. On permanently flooded sites, bur oak trees died within 3 years (review by ). Plant communities and related site characteristics: Bur oak is often a dominant savanna or woodland species in the Great Plains and Great Lakes regions. The Society of American Foresters recognizes western and eastern bur oak forest cover types , where bur oak occurs in pure or nearly pure stands. Bur oak savannas are reported nearly throughout the Great Plains and Great Lakes regions ,. Other wide-ranging forest types in which bur oak is a dominant or codominant include northern oak-hickory ( Carya spp.) forests , and bur oak-chinkapin oak communities. In many cases, time, disturbances, and successional change are more important than climate or site characteristics in determining which type of bur oak community occurs.

The exception may be in extremely harsh sites, where shade-tolerant tree species fail to establish and replace bur oak. In the absence of fire or other disturbances, an oak savanna typically transitions into an oak woodland and then to a mixed-deciduous woodland. This transition is described in more detail in the section on. Some of the communities discussed below are considered 'imperiled' because of their rarity or other factors making them vulnerable to extinction (see ).

Other communities are rare because of land conversions, successional changes, and fire exclusion associated with European settlement ,. In some communities, plant associates of bur oak may now be more rare than at the time of the vegetation survey and subsequent publication. For example, Dutch elm disease and phloem necrosis have resulted in high morality levels for American elm ( Ulmus americana) , and shagbark hickory ( C.

Ovata) has been extensively harvested for fuel wood. Northern Great Plains: In the Northern Great Plains, bur oak is common in mixed-conifer forests, deciduous forests, oak and oak-hickory woodlands, oak savannas, and oak shrubland associations. Bur oak is common in bottomlands with rich soils but also occurs on open rocky hillsides with poor soils. In mixed-conifer and mixed-deciduous forest types in the Black Hills of Wyoming and South Dakota, soils are typically sandy loams to clay loams, of calcareous or igneous origin, with pH levels of 5.3 to 7.4 and organic matter contents of 3.6% to 9.5%. Bur oak stands and habitat types at the extreme western part of its range are commonly found at elevations of about 2,300 to 5,300 feet (700-1,600 m) ,. Mixed-conifer forests: The most common bur oak associate in Northern Great Plains mixed-conifer forests is ponderosa pine ( Pinus ponderosa), but in southwestern Manitoba, bur oak occurs as a shrub in a white spruce ( Picea canadensis)-deciduous forest type.

Ponderosa pine-bur oak forest types are described in Montana, Wyoming, and South Dakota , often within the Black Hills ,. In South Dakota, ponderosa pine-bur oak forests are described on very acidic soils.

Mixed-deciduous woodlands: On upper floodplain terraces, woody draws, or other mesic sites in the Northern Great Plains, bur oak is common in mixed-deciduous woodlands. Common associates include American elm , eastern hophornbeam ( Ostrya virginiana) , paper birch ( Betula papyrifera) , basswood ( Tilia americana) , quaking aspen ( Populus tremuloides) , and green ash ( Fraxinus pennsylvanica) ,. On North Dakota's Missouri River floodplain, bur oak trees, saplings, and seedlings were restricted to the outer high terraces of the floodplain where soils were the most developed and had the greatest nutrient availability, organic matter content, and water availability. In southwestern Manitoba, bur oak occupies clayey soils in cottonwood ( Populus spp.)-dominated uplands. Oak and oak-hickory savannas and woodlands: Bur oak-dominated savannas and woodlands are described throughout the Northern Great Plains.

In Manitoba, the Dakotas, and Wyoming, bur oak may be the only overstory species , or may codominate with northern pin oak ( Q. Ellipsoidalis).

In bur oak woodlands in the Black Hills of South Dakota, soils were neutral to alkaline, 19% or more clay, and sometimes more than 20% gravel. In Nebraska and Iowa, oak and oak-hickory woodlands and savannas are common along the Missouri and lower Platte rivers. Common associates include chinkapin oak, black oak ( Q. Velutina) , shingle oak ( Q.

Imbricaria) , northern red oak ( Q. Borealis) , shagbark hickory , and bitternut hickory ( C.

Cordiformis). Bur oak shrublands: In draws, riparian areas, or heavily grazed sites in the Northern Great Plains, bur oak may grow as a tree or shrub among other shrub species.

Common associates include western snowberry ( Symphoricarpos occidentalis) , hazelnut ( Corylus spp.) , chokecherry ( Prunus virginiana) , Saskatoon serviceberry ( Amelanchier alnifolia) , and sumac ( Rhus spp.). In Manitoba and Minnesota, researchers describe a quaking aspen-bur oak-willow ( Salix spp.) shrubland type.

Southern Great Plains: In the Southern Great Plains region, bur oak is common in mixed-deciduous woodlands, oak and oak-hickory woodlands, and oak savannas. These communities are common in floodplain areas. Mixed-deciduous woodlands: A variety of associated species can occur with bur oak in deciduous woodlands in the Southern Great Plains. Hackberry ( Celtis occidentalis)-bur oak gallery forests are described in the Flint Hills of northeastern Kansas.

A bur oak-American elm-white ash ( F. Americana) floodplain type occurs in the Niobrara Valley in north-central Nebraska. In bottomlands in Webster County, Nebraska, bur oak occurs with white mulberry ( Morus alba), green ash, and silver maple ( Acer saccharinum). In Texas, bur oak is rarely dominant and is primarily restricted to floodplains, bottomlands, or other riparian areas ,. In these areas, sugarberry ( C.

Laevigata) is a typical dominant ,. Some botanists indicate that bur oak is most common in areas of Texas with limestone soils. Oak and oak-hickory savannas and woodlands: Bur oak, mixed-oak, and oak-hickory savannas and woodlands are described in Nebraska, Missouri, Kansas, and Oklahoma. In the savannas, bur oak may dominate the canopy alone or with chinkapin oak. Big bluestem ( Andropogon gerardii) is the typical grass associate ,.

In oak woodlands, bur oak often shares the canopy with other oaks such as pin oak ( Q. Palustris), swamp white oak , or chinkapin oak.

In the Flint Hills of northeastern Kansas, bur oak is most common on the most mesic lowland sites. The growth rate of bur oak was correlated with low topographic slope ( r = 0.5) and low soil nitrogen ( r = 0.7) ( P30 years).

Shade tolerance: Although bur oak is typically shade intolerant, it can tolerate some shade, in some habitats, at least in the short-term. Patterns of establishment, suppression, and release in mixed-deciduous, old-growth forests in northern Ohio were evaluated from tree core data. Researchers concluded that bur oak was intolerant of shade and became a part of the canopy only where it had established following a large-scale, canopy-removing disturbance. However, other studies report bur oak on shaded sites. Although not abundant in ground layer vegetation in red pine ( Pinus resinosa) stands in Minnesota's Chippewa National Forest, bur oak was most frequent in plots receiving a little less than 20% of full sun. Surveys of the Ozark Plateau in eastern Missouri and Arkansas conducted in 1815 showed that bur oak did not occur in open woodlands, savannas, or scrubby oak vegetation, but did occur in dense, closed-canopy forests at low frequency. In North Dakota, bur oak seedlings and saplings were reported in floodplain forests along the Missouri River.

Bur oak importance generally increased as scouring and flooding ceased and floodplain forest stand age increased ,. Seral stage: Bur oak stands have been described as early-, mid-, and late-seral as well as subclimax and postclimax, but categorizing bur oak stands into climatic seral stage communities may only be appropriate for areas with harsh site conditions.

In the Great Lakes region, bur oak communities are described as peristent vegetation maintained by frequent fire. In the Dakotas, bur oak communities have been classified as early-, mid-, and late-seral and also as subclimax and postclimax.

Along the Missouri River in South Dakota, late-seral bur oak woodlands were rare because excessive livestock grazing and/or plant disease made most woodlands early- or mid-seral communities. Cover of grasses decreased from early- to late-seral stages, and bur oak canopy, forb, and shrub cover increased from early- to late-seral communities. In the Black Hills of South Dakota, researchers considered bur oak-sumac communities to be subclimax. A bur oak-deciduous forest, which appeared to be returning to a shrubby subclimax stage was described as 'postclimax'.

Judd also described a bur oak community in the badlands of western North Dakota as 'postclimax'. A review of survey records, other historical records, and edaphic and topographic features of the Big Woods of south-central Minnesota indicated that firebreaks were the primary factor in controlling vegetation patterns. Bur oak represented a persistent vegetation type maintained by fire. Succession in the absence of fire: Prairies: It is common for bur oak to establish throughout a prairie if the time between fires extends to 10 years or more. Bur oak may also establish as scattered individuals in safe sites during shorter fire-free periods. Bur oak functions as a 'pioneer along the prairie border'. In the prairie-deciduous forest ecotone that occurs from Minnesota to Texas, bur oak and other woody species invade the prairie at an average rate of 1 foot (0.3 m)/year without frequent fire.

In Kansas, bur oak increased its range during a time of decreased fire frequency in prairie habitats. In the Wolf Road Prairie in Cook County, Illinois, researchers compared the composition and structure of vegetation over time. Before 1955, the area supported a bur oak savanna.

In the next 10 years, a period without fire, the density of bur oak stems increased dramatically. Bur oak grubs, which are burl-like woody structures that develop on the soil surface as young bur oak stems or sprouts are repeatedly top-killed by fire, were released during the fire-free period and produced an abundance of stems. By 1995, the area was dominated by a dense 30-year-old subcanopy of bur oak and northern pin oak. Gaps in the subcanopy were rare. Oak savannas and woodlands: Once bur oak reaches the stage at which it can tolerate repeated fire (12 years or older), it persists indefinitely in savannas or open woodlands with frequent fire.

Without fire, bur oak savannas and woodlands are replaced by other deciduous species that are intolerant of fire but tolerant of shade. Changes in bur oak savannas in Wisconsin in the absence of fire were well described by Curtis. After about 10 years without fire in prairies and bur oak savannas, woody saplings and other shrubs become established. After 25 to 30 years without fire, dense oak forests develop. Large, mature bur oaks in the savannas can survive overtopping by other species for about 80 years, at which point they become weakened by wood-rot fungi in the shade-killed lower branches. Most bur oak trees in dense woodlands are snapped by wind storms after 100 to 110 years.

Survey records from 1837 to 1840 in Lake County, Illinois, indicated that bur oak was the most common tree species, and bur oak savannas were the most common vegetation type. Surveys in the late 1940s and 1950s showed that, with the exclusion of prairie fires, bur oak savannas were heavily invaded by other woody vegetation. As of 1978, the bur oak savannas of presettlement time in this area were extinct. A comparison of survey records for Stewart's Woods in Wisconsin showed that the area changed from a bur oak-dominated savanna in 1834 to a dense woodland where bur oak was only a minor species in 1946. After evaluating the histories of land use, climate, and diseases, researchers concluded that European settlement and the end of frequent burning by American Indians facilitated the successional change.

For a summary of studies documenting changes from open oak savannas and oak-pine woodlands in early land surveys to dense, closed-canopy, mesophytic forest types in more contemporary surveys, see Nowacki and Abrams. The succession from bur oak savanna or woodland to dense, mesic stands has been described in many areas. In his study of vegetation and successional change in Wisconsin, Curtis reported that bur oak fails to reproduce successfully once canopy cover reaches 75%. Climax species that often replace bur oak include sugar maple ( Acer saccharum), basswood, and hackberry. The bur oak-chinkapin oak community type that occurs along the Mississippi River drainage system from Kansas and Nebraska to Wisconsin is replaced by sugar maple and basswood in absence of fire or other major disturbances. In southern and western Wisconsin, researchers described a vegetational continuum in upland forest stands.

Drought-tolerant, shade-intolerant species such as bur oak, bigtooth aspen ( Populus grandidentata), and black oak were first to invade prairie vegetation. Climax species included eastern hophornbeam and sugar maple. In the absence of major disturbances over a 50-year period in the David-Purdue Research Forest in east-central Indiana, bur oak importance decreased and density of American elm and sugar maple increased. After European settlement in about 1840 around the Konza Prairie in northeastern Kansas, the extent, frequency, and/or severity of fires in the area decreased.

In the gallery forests, there are old, large bur oaks and chinkapin oaks, but there has been very little oak recruitment for over 50 years. Hackberry dominates the young size classes on moist sites and eastern redbud ( Cercis canadensis) on dry sites. Other factors affecting succession: While the forest succession described above may be most common, different successional patterns and drivers are also possible.

On calcareous soils at Lake Itasca in Minnesota, bur oak is a mid-seral species. Early-seral forests are dominated by quaking aspen, birch ( Betula spp.), and jack pine ( Pinus banksiana). In the mid-seral, hardwood-eastern white pine ( P. Strobus) forest, bur oak is common before sugar maple becomes dominant.

Climax forest species include white spruce ( Picea glauca) and balsam fir ( Abies balsamea). In central Kentucky, dendrochronological analyses indicated that an oak savanna, where bur oak was common, developed from a closed-canopy forest. Historical growth rates and growing conditions estimated from dendrochronologies suggested that savanna trees exhibited suppressed growth rates early in life and were part of a closed-canopy forest.

Closed-canopy forests may have developed because American Indian populations in the area suffered extensive losses from pandemics, particularly small pox. Rapid tree growth coincided with Euro-American settlement, which involved extensive land clearing to create pastures.

In xeric savannas invaded by nonnative common buckthorn ( Rhamnus cathartica) in southeastern Wisconsin, bur oak reproduction is generally lacking. Invasion by common buckthorn coincided with European settlement and fire exclusion. Conditions from 6.6 feet (2 m) above ground to ground level were shadier in invaded than in uninvaded areas , which likely limited bur oak recruitment. On some harsh sites, bur oak may be a late-seral species or may persist for longer periods in the absence of disturbance because successional change occurs slowly on these sites.

In Riding Mountain National Park, Manitoba, bur oak forest stands are replacing themselves on excessively drained, gravelly, sandy soils. Researchers doubted that many other tree species could tolerate the dry site conditions.

In the Upper Midwest, bur oak often dominates dry calcareous savanna, where soils are shallow or excessively drained. A lack of herbaceous fuel build up on the harsh sites limits the chance of intense fires. Although the density and cover of woody vegetation have increased without fire, harsh soil conditions allow for the persistence of remnant savannas. In the absence of large disturbances in Wisconsin, bur oak typically dominates for just a single generation before being replaced by more shade-tolerant species, but bur oak dominates longer without disturbances on hot, dry sites, where soil organic matter and water retention increase slowly. In south-central Wisconsin, bur oak persisted in the absence of disturbance only in open stands on the most xeric sites. Bur oak may respond to stress from abundant moisture in central Illinois. On mesic sites, bur oak is a pioneer species and is replaced by sugar maple as shade levels increase, but in wet-mesic and floodplain forests, bur oak generally replaces itself and persists through succession.

In some areas, researchers think that climate has more influence than fire on succession in bur oak communities. Researchers suggested that climate rather than American Indian fires were responsible for development of oak savannas in southern Ontario, where bur oak occurred but was not dominant. After reviewing current site conditions, historical climate evidence, time since last fires, and European settlement records, researchers suggested that the prevailing climate in Minnesota from 1812 to 1825 was conducive to forest invasion of the prairies and savannas.

Although lack of fire was considered important to the succession from prairie or pine-oak savanna to sugar maple-basswood forests, researchers concluded that climate was the most influential factor. Old field succession: Bur oak establishment is slow in old fields, even if an adjacent seed source exists.

The following studies suggest that bur oak is unlikely in old fields abandoned less than 30 years. Bur oak did not occur in fields abandoned for 19 to 24 years in southeastern Ontario, even though bur oak occurred in forests adjacent to the fields. In southwestern Ohio, bur oak was uncommon in a 90-year-old field but was not reported in 2-, 10-, 50-year-old fields. On the Anoka Sand Plain in east-central Minnesota, bur oak did not occur in a hayfield abandoned for about 20 years.

The area was dominated by bur oak savannas before conversion to agriculture, but the abundance of bur oak in the woodlands surrounding the field was not reported. In the Cedar Creek Natural History Area on the Minnesota sandplain, bur oak was generally absent from fields less than 15 years old ; bur oak seedlings and saplings were scattered near the woodland margin of a 48-year-old field; and bur oak seedlings were common but saplings were rare in 60-year-old fields. In east-central Minnesota, researchers surveyed the forest-field margins of 18 fields abandoned less than 65 years. Bur oak was extremely rare in fields less than 31 years old. Abundance in fields increased with increasing abundance of bur oak trees in adjacent forests. In an old field adjacent to mixed-hardwood-oak forests in Ottertail County, Minnesota, bur oak established within 30 years of abandonment. Disturbance-related succession: Large canopy gaps appear necessary for bur oak colonization.

Single-tree canopy gaps did not encourage bur oak recruitment in the Brownfield Woods in Champaign County, Illinois. Between 1925 and 1975, the open oak woodland dominated by bur oak and chinkapin oak was being replaced by a closed-canopy woodland dominated by sugar maple. In areas where slippery elm ( Ulmus rubra) was killed by disease, sugar maple colonized. During a study of the structure, composition, and environmental relationships of an old-growth remnant in northwestern Ohio, researchers found bur oak trees with DBH greater than 3 feet (1 m) but none with DBH less than 15.8 inches (40 cm). Historical disturbance patterns suggested that bur oak established after 1 or more large disturbances that were more extensive than single- or multiple-tree falls. Occurrence of bur oak was a function of disturbance and not simple edaphic relationships.

Bur oak recruitment occurred in canopy gaps created by a 'catastrophic windthrow' event in northern pin oak but not in eastern white pine forests in Minnesota. Density of bur oak (1 inch (2.5 cm) DBH) was 64 stems/ha before and 92 stems/ha 14 years after the storm.

Browsing: Livestock and native ungulates can limit bur oak survival and recruitment. Several studies suggest that browsing can maintain open conditions in oak savannas and woodlands. Bur oak seedlings and saplings are commonly browsed by livestock and deer. On a coal mine restoration site in Kansas, bur oak stems within the reach of cattle were nearly browsed to the ground each year. In the Little Missouri National Grasslands, bur oak survival 5 years after planting was 44% in areas grazed by cattle and 82% in protected areas. In ponderosa pine-bur oak forests in the Black Hills of Wyoming and South Dakota, livestock exclusion is suggested to encourage bur oak regeneration.

See for more on the utilization and palatability of bur oak. Researchers suggest that loss of large carnivores, introduction of livestock, and browsing by native ungulates limited recruitment of bur oak in Wind Cave National Park, South Dakota. Tree core analyses showed that bur oak recruitment peaked in the 1870s but was nearly nonexistent after the 1890s. Loss of recruitment coincided with large carnivore removal and rapid increases in livestock abundance. When the Park Service removed livestock, however, bur oak recruitment did not improve, likely because of continued heavy browsing by unchecked native ungulate populations. Bur oak trees with a DBH of less than 20 inches (51 cm) were restricted to areas with physical barriers restricting large mammal access.

In an upland 230-year-old red pine forest in Itasca State Park, Minnesota, protection from deer browsing allowed for some recruitment of bur oak into the larger size classes. Researchers reported that moderate to high deer browsing levels slowed woody encroachment and succession ,. Density (stems/ha) of bur oak stems by size class inside and outside exclosures in a red pine forest in Minnesota , Size class (height, unless otherwise reported) 0.15-2.1 m 2.1-4.3 m 4.3 m overstory ( ≥20 cm DBH) in. out in out in out in out 1969 17 0 5 0 0 0 0 0 1984 15 20 15 0 5 0 0 0.Exclosures constructed in 1937. Many studies suggest that grazing can maintain open conditions in bur oak habitats in the absence of fire. In the Sheguiandah Township on Manitoulin Island in Ontario, bur oak savannas have remained open because of almost continuous livestock grazing.

According to early surveys, these savannas resulted from a 'catastrophic fire' in 1865. None of the savannas had burned since 1865, and in areas protected from grazing, a closed woodland has developed. A similar situation was reported in another study in Ontario and the Barton Woods of north-central Illinois. An open-canopy bur oak woodland changed to a closed-canopy forest with an abundance of other deciduous species after 50 to 60 years without grazing. On continually grazed sites, canopy trees, primarily bur oak, were often 39 to 79 feet (12-24 m) apart and sometimes 164 feet (50 m) apart. In the TL Davis Preserve in southwestern Douglas County, Nebraska, just 2 bur oak trees established before 1895 and nearly all other bur oak and other woody species established after 1968. Reasons for the 70- to 80-year gap in tree establishment were not known, but grazing was suspected because of the fencing remnants observed.

In 1850, the bur oak-dominated cover was estimated at 23%, and by 2003, it was 99%. Although many suggest that grazing may inhibit bur oak establishment, others suggest the opposite may be true. In western Iowa, periodic overgrazing of prairies during settlement of the area was suggested as the main reason for 'spectacular forest advances'. SPECIES: Quercus macrocarpa. Photo © Tom Brock, Universtiy of Wisconsin-Madison: Mature bur oak trees are not typically damaged by fire, and bur oak trees only 3 feet (1 m) tall may survive fire ,. Bur oak seedling establishment varies on burned sites and is limited on repeatedly burned sites ,. Survival of bur oak acorns on burned sites and heat tolerance of acorns were not reported in the literature.

Generally, acorns produced by the white oak group have little to no dormancy and typically germinate or are removed by predators soon after falling, so establishment from soil-stored seeds on burned sites is unlikely (see, and ). : Tree with buds, a sprouting, and/or Tall shrub, buds and/or a sprouting (off site, initial community) Based on prescribed fire studies in the Cedar Creek Natural Area and a review of other fire studies, Peterson and Reich reported that bur oak is a fire 'resister'.

Bur oak typically survives low-severity fire. It is long-lived and persistent at maturity. Bur oak maintains the potential for population growth when spatial or temporal variability in fire allows for seedling establishment or release of.

Bur oak is well adapted to survive fire, and frequent fires are necessary for bur oak persistence in many habitats. Because the of mature bur oak trees insulates their cambium from high temperatures , mature trees rarely suffer any fire damage ,. Young bur oak trees are typically only top-killed by fire ,. Once bur oak trees reach 12 to 15 years old, they can survive repeated burning. Thick bark: Many sources indicate that bur oak trees produce very thick, fire-resistant bark ,. Large bur oak trees in eastern Nebraska produced bark about 1.5 inches (5 cm) thick. In Funk's Grove in McLean County, Illinois, open-grown bur oak trees 111 to 140 years old, with DBH measurements of 37 to 68 inches (93-172 cm), had bark thicknesses of 1.6 to 2.4 inches (4-6 cm).

Photo © Paul Wray, Iowa State University, Bugwood.org In plantations and natural areas in Illinois, researchers evaluated the physical and protective characteristics of bur oak bark. Bark thickness increased with increasing DBH ( r² = 0.93), and relatively high rates of bark thickening occurred with radial growth. Maximum bark thickness was 2.9 inches (7.4 cm) for a bur oak with a DBH of 52.9 inches (134.3 cm). Bark moisture was greatest in the summer and lowest in the fall, but differences were not statistically significant. Using a technique designed to mimic conditions produced by low-severity surface fire, researchers found that the average cambial temperature of bur oak during the fire was 134.8 °F (57.1 °C). Cambial temperature exceeded 140 °F (60 °C) for an average of 3.1 minutes in just one bur oak tree ,. Exposure to temperatures of 140 °F (60 °C) for at least 60 s is typically required to kill vascular plant tissue, but tissue can survive 140 °F (60 °C) temperatures for a longer time when moisture content of the tissue is high.