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Bur Oak

| Description | Products and Uses | Site Conditions |
| Regeneration | Immediate Treatments | Pests and Diseases |

Description

Range of bur oak The bur oak type occurs across Minnesota, Wisconsin, and southern Michigan (Figure 6-7). Because it tolerates a wide range of soil and moisture conditions, bur oak associates with many other trees. Northern pin oak and black oak are associates on sandy sites; white oak and hickories are found with it on other dry upland sites. Chinkapin oak and eastern red cedar are associates on hot, dry hillsides in southwestern Wisconsin. Associates on lowland sites include shagbark and other hickories, black walnut, eastern cottonwood, white ash, American elm, swamp white oak, American basswood, black ash, silver maple and sycamore. Because of its fire and drought resistance, bur oak is the most common tree on oak savannahs along the prairie-forest transition zone in Wisconsin and Minnesota.

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Products and Uses

Bur oak leafBur oak wood is commercially valuable for sawlogs and veneer, although high quality timber is not common. Their acorns are a prime food for squirrels, wood ducks, white-tailed deer, and small mammals.

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Site Conditions

Bur oak is one of the most drought resistant North American oaks. On uplands it often is associated with soils of limestone or sandstone origin. It is found on droughty sandy plains, black prairie loams, and on loamy slopes of south and west exposure. Toward the western edge of its range, it is more abundant on moist north-facing slopes than on south-facing slopes. It often dominates severe sites with thin soils, heavy claypan soils, gravelly ridges, and coarse-textured loessial hills. Bur oak is also an important bottomland species throughout much of its range.

Bur oak can survive for centuries on droughty sites, but wood quality is generally much better on moist bottomlandsOn the prairie edge it is a pioneer tree, commonly succeeded by northern pin oak, black oak, white oak, and bitternut hickory. On moist sites it is replaced by the more shade tolerant sugar maple, American basswood, and American beech. As a bottom-land species, bur oak is relatively intolerant of flooding. First-year mortality may be 40 to 50 percent if seedlings are submerged for two weeks or more during the growing season. For shorter periods of growing-season submersion, seedling mortality is only 10 to 20 percent.

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Regeneration

Bur oak is slow-growing, but commonly lives 200 to 300 years or longer. The minimum seed-bearing age is about 35 years and the optimum is 75 to 150 years. Good seed crops occur every two to three years. Acorns are disseminated by gravity, squirrels, and to a limited extent by water. Germination usually occurs soon after seedfall (August through November), but acorns from some northern trees may remain dormant through winter and germinate the following spring. Acorn germination and early seedling development is best on moist, mineral soil with no litter cover.

Bur oak stands are self-sustaining on dry sites, but planting seedlings and controlling grass and brush will aid regeneration. Bur oak will be difficult to sustain on moist bottomland sites where other species grow faster, but planting seedlings during regeneration phases will help sustain some bur oak in the species mix. Although mature bur oaks have thick, fire-resistant bark, it?fs important to prevent fires from burning over the area while trees are young.

Burning or cutting pole-size or smaller bur oaks results in vigorous stump sprouting, but sprout quality and form are poor.

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Intermediate Treatments

Bur oak is intermediate in shade tolerance. Use intermediate cuttings to manage species composition according to the site. Prairie burning on upland sites is a common practice to kill invading brush and sustain prairie grasses. Older bur oaks withstand burns quite well.

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Pests and Diseases

Bur oak is attacked by several defoliating insects, including oak webworms, oak skeletonizers, a leaf miner, variable oakleaf caterpillars, June beetles, and oak lacebugs. Oak wilt is a less serious problem in bur oak than in members of the red oak group, although the disease sometimes spreads through root grafts, killing entire groves. Bur oak is susceptible to attack by root rot, canker, and dieback diseases. It tolerates urban pollution better than most oaks. Young trees are susceptible to fire, but older trees develop thick bark that is fire resistant.

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