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Hemlock - Yellow Birch

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


Range of eastern hemlock This type occurs mainly in northern Wisconsin, Michigan's Upper Peninsula, and the northern portion of lower Michigan (Figure 6-10). Eastern hemlock and yellow birch are the principal species, with hemlock usually dominating. Common associates include red maple, sugar maple, and American basswood.

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Products and Uses

Hemlock is used for paper and lumber. Yellow birch lumber and veneer are used in making furniture, paneling, plywood, cabinets, boxes, woodenware, handles, and interior doors. It is one of the principal hardwoods used in the distillation of wood alcohol, acetate of lime, charcoal, tar, and oils. Yellow birch is good browse for deer and moose. Other wildlife feed on the buds and seeds.

Hemlock stands are essential for shelter and bedding of white-tailed deer during winter. The type also provides important cover for ruffed grouse, turkeys, and many other animals.

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A stand of hemlockSite Conditions

Hemlock and yellow birch grow best on moist, well-drained sandy loam, loamy sand, and silt loam soils. Older stands typically occur on soils with a high water table and varying texture that develop a thick humus layer under a relatively low, dense overstory. As the site becomes drier, the type merges with sugar maple, sugar maple-beech-yellow birch, or beech-sugar maple. On wetter sites, hemlock-yellow birch frequently merges into the hemlock and white pine-hemlock types and on the wettest sites with the black ash-American elm-red maple type.

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Eastern hemlock is a slow-growing, long-lived tree that grows well in shade. It may take 250 years to reach maturity and may live over 800 years. Hemlock begins producing seed at age 15 and good seed crops occur every other year. Seeds fall from mid-October through early winter, but are dispersed only about one tree height in distance. Hemlock requires a warm, moist site for stand establishment, but successful regeneration is difficult to achieve. Seed viability is low. Seeds require temperatures of about 44° to 64° F for 45 to 60 days to germinate (longer than most tree species require). Seeds are severely damaged after only two hours of drying, and seedlings are subject to damping-off and root rot fungi.

Yellow birchYellow birch begins producing good seed crops at age 40 in dense stands, and good crops occur every two to three years. Seeds are dispersed by wind primarily in October. Good seed fall occurs at least 330 feet from seed-bearing trees and seed can disperse much farther when blown across crusted snow. Yellow birch seedlings and small saplings reproduce from sprouts when cut, but sprouting from larger stems is very poor.

Regeneration of this type is most successful on moist flats or sites providing some protection from extended periods of sunlight. Use a shelterwood system that leaves 70 to 80 percent crown cover for optimum hemlock regeneration or 45 to 50 percent crown cover for optimum yellow birch regeneration. Kill advance regeneration and remove litter with a spring fire or scarify the site, mixing organic and mineral soil over 50 to 75 percent of the area. Plan treatments to coincide with good seed crops because the effects of scarification last only two or three growing seasons.

Without these conditions most eastern hemlock and yellow birch regeneration occurs on rotten logs, stumps, and mounds that normally have warmer surfaces and better moisture retention than the forest floor.

Seedlings develop slowly even under ideal growing conditions, with stable moisture in the upper soil horizon throughout the growing season. Once the root system has reached a soil depth not radically affected by surface drying, usually after the second year, seedlings grow more rapidly without interference from overhead shade. Supplemental seeding would enhance natural seeding under most conditions. Seedlings are fully established when they are 3 to 5 feet tall, and then can be released completely from overhead competition.

Survival and height growth of planted hemlock (3-0 stock) and yellow birch (2-0 stock) usually is good in small openings or under a partial overstory. To artificially seed birch, stratify seed for 4 to 8 weeks at 41° F in moist peat or sand. Spread 0.5 lb an acre of birch seed about a week after site preparation in May, or sow unstratified seed before January.

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Intermediate Treatments

Both hemlock and yellow birch are very slow growing species, but hemlock is longer lived, commonly surviving to 400 years of age. Eastern hemlock is the most shade tolerant of all tree species and can withstand suppression for 400 years. Yellow birch is intermediate in shade tolerance. Within five years of regeneration, yellow birch seedlings may require release from faster growing species. In the sapling stage, thin stands to provide 6 to 8 feet of open space around the best dominant and codominant trees. Continue periodically releasing dominant and codominant trees through the small sawlog stage. However, excessive release of hemlock may reduce growth, increase mortality, and contribute to windthrow. Heavy release of yellow birch results in epicormic branches that degrade the stem.

In mixed stands of hardwoods and hemlock, where the proportion of hemlock is 15 percent or more, it is feasible to manage for hemlock at various residual stocking levels. Hemlock does not require as much growing space as hardwoods, so residual stocking is greater in stands where hemlock predominates. Stands with less than 15 percent hemlock should be managed for hardwoods.

When thinning stands exceeding 200 square feet an acre of basal area, remove no more than one-third of the total basal area at one time. Excessive cutting results in reduced growth and increased mortality and contributes to windthrow. In addition, hardwood encroachment interferes with the successful establishment of hemlock. Fully stocked stands with basal areas of less than 200 square feet an acre can be thinned to a minimum of 120 square feet an acre. Yellow birch prunes itself well so long as its crown is allowed to close within five or six years after release. It can, however, be pruned to 50 percent of its height without reducing growth. Prune small, fast-growing trees with small knotty cores to limit discoloration and decay.

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Pests and Diseases

Young hemlock seedlings are often damaged by desiccation, damping-off fungi and root rot. In the Eastern United States, the hemlock woolly adelgid is a serious insect pest that feeds on needles. It is expected to reach the Lake States sometime in the future. Young hemlock and birch are susceptible to fire damage. The bronze birch borer is the most serious insect pest of yellow birch. Mature and over-mature trees left severely exposed after logging and in lightly stocked stands are more subject to attack than are trees in well-stocked stands. Yellow birch is a preferred food of snowshoe hare and white-tailed deer. Overmature birch are subject to canker diseases, root rots, and stem decay. Birch is not a preferred host for leaf-feeding insects, but severe outbreaks that last several years will kill birch.

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