Minnesota’s oak-hickory forest type
Northern red oak, white oak, bur oak, black oak, northern pin oak, and various hickories make up an oak-hickory forest. Associated species include red and sugar maple, black cherry, American basswood, black walnut, white pine, and white and green ash. If left undisturbed, an oak-hickory stand in the Upper Midwest will shift toward more shade-tolerant species.
Oaks grow best on north- and east-facing, gently sloping, lower slopes where soils are at least 36 inches deep. Medium-quality sites have moderately deep soils (20 to 36 inches) on upper and middle slopes facing north and east. Oaks survive but grow poorly on narrow ridgetops or south- and west-facing, steep, upper slopes where soil is less than 20 inches deep. Oaks survive better than most other tree species on dry sites, but they do not produce much merchantable timber on such sites. On the best sites there is fierce competition among tree species, so oaks are difficult to regenerate there.
Range of northern red oak.
Products and Uses
Oak is valued in furniture, flooring, paneling, ties, cooperage and fuelwood. Hickory, a wood of great strength, has much less market demand but is used for furniture, tool handles, high-strength specialty items, flooring, plywood, fuelwood, and charcoal.
The oak-hickory forest is home to many game animals such as white-tailed deer, turkey, gray and fox squirrels, and ruffed grouse. Raccoon, opossum, red fox, bobcat, skunk, and many birds also take advantage of this forest type.
Oaks commonly reproduce from acorns. Northern red oaks producegood acorn crops at 2 to 5-year intervals; however, seedlings are abundant only following years when there are excess acorns not damaged by acorn weevils or consumed by wildlife. Acorns usually are disseminated by blue jays, squirrels, and gravity. Best germination occurs in mineral soil under a light covering of leaves.
Northern red oak and white oak are intermediate in shade tolerance. In stands with a dense understory or overstory, there will be few oaks in the understory.
Oaks may live for several hundred years. However, for timber production in this region, stands on moderate to good sites can be regenerated when the oaks are 60 to 90 years old and trees average 18 to 24 inches in DBH. A stand also may be ready for harvest and regeneration if it is greatly understocked or most trees are poor quality or undesirable species.
Natural oak regeneration is most reliable where there is plenty of advance regeneration. The number of oak seedlings needed to successfully stock the next stand depends on seedling size prior to the harvest. The larger the seedlings, the more likely they are to survive to harvestable size. For example, you need 15,435 seedlings per acre if they are less than 1 foot tall. If they all are more than 4 feet tall, you need just 514 per acre.
Stands that are well stocked with advance regeneration and that have relatively little competition from undesirable understory trees, shrubs, or other vegetation may be clearcut and usually regenerated successfully. A clearcut should be at least 1/2 acre and preferably at least 2 acres in size; otherwise, shade from the surrounding timber will suppress oak seedling growth. For regeneration purposes there is no maximum size for clearcuts.
If there is a seed source present but few seedlings, the problem often is too much shade. Acorns may germinate and the seedlings may survive for 4 or 5 years beneath heavy shade, but advance oak regeneration will not accumulate over a long period.
To resolve this problem, start by reducing shade produced by the understory of shade tolerant hardwood trees, shrubs, or ferns. Cut or treat vegetation with herbicide, depending on the species to be controlled. If dense shade is produced by a high canopy, also remove 20 to 40 percent of the canopy in a shelterwood harvest, leaving species and individual trees that you want to provide seed for the next generation. Harvest carefully to avoid damaging residual timber.
Following a shelterwood harvest and understory removal, you may need to wait several years before clearcutting the stand to ensure that a satisfactory number of oak seedlings are present. You may need additional understory control if the oaks take more than 5 years to regenerate.
An alternative to the shelterwood harvest is to wait until there is a good acorn crop, then clearcut and disturb the soil after the acorns drop but before the ground freezes. Soil disturbance helps to bury the acorns and uproot competing vegetation.
Because of the risk and possible delay involved when relying on natural regeneration, you may want to plant seedlings. Planting enables you to supplement natural regeneration, to use genetically superior stock when it is available, and to choose the species. Seedlings may be planted immediately following a shelterwood cut or a clearcut. Before planting, control undesirable trees and shrubs by cutting, bulldozing, or treating with herbicide.
The best oak seedlings have a fibrous root system and a stem at least 3/8-inch in diameter. If large seedlings appear difficult to handle during the planting operation, just prior to planting clip the tops of the seedlings, and the roots if necessary, leaving each about 8 inches long. You may need to plant 200 to 800 seedlings per acre, depending on their size and the amount of advance reproduction already in the stand. Control weeds around the oak seedlings for 1 to 2 years. Herbicides are often effective and economical for weed control.
Control undesirable tree species that compete with crop trees when stand height averages at least 25 feet (10 to 20 years old). When growing trees for timber production, thin sprouts growing from a single stump to one or two dominantsprouts that have good form and are connected to the stump below or near the ground. Thin when sprouts are about 10 years old (2 to 3 inches in diameter). Oak stands managed for timber should be kept fairly dense until the bottom 20 to 25 feet of the stems are essentially free of live branches. This generally will occur when trees are 40 to 50 feet tall (30 to 45 years). At this stage thin stands to stimulate diameter growth of crop trees. Release no more than 100 crop trees per acre. As an alternative to the crop-tree release guidelines you can follow the stocking charts for upland central hardwoods.
Pruning will improve wood quality and may be needed if stand density is not sufficient to cause natural pruning.
The red humped oakworm, two-lined chestnut borer, oak wilt, and shoestring root rot are significant pests on oaks.
Minimize chestnut borer damage by maintaining vigorous stands. Specifically, in upland stands with a site index less than 65, maintain basal areas at less than 120 square feet per acre in stands with trees averaging 7 to 15 inches DBH, and at less than 100 square feet per acre in stands averaging more than 15 inches DBH. Avoid thinning for five years after a serious drought or defoliation.
To minimize oak wilt infections, do not thin or prune oaks from mid-April through mid-July, when fungal spores are present and can be transported by picnic beetles to fresh wounds. Dormant season operations are best because spores are not present and the trees are not susceptible to infection. Since oak wilt commonly spreads through root grafts between neighboring oaks, surround valuable oak stands in areas with a high oak wilt hazard with a 100-foot buffer of an alternate species. If trees become infected, harvest them before the following spring. Use a trenching machine or vibratory plow to break the root grafts through which the disease spreads. Trench placement and depth are critical. Consult a forester for advice before trenching. Left untreated, oak wilt will spread through the stand until it kills all red oaks. White and bur oaks are not commonly affected by oak wilt.
The red humped oakworm defoliates late in the year. It causes little growth loss, but weakens the trees and makes them more prone to shoestring root rot and two-lined chestnut borer. High value stands can be sprayed. No cultural control is available for oakworm, but maintaining stand vigor should help minimize damage.
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