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Silver Maple - American Elm

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


Range of silver maple The silver maple-American elm forest type is common in the southern Lake States (Figure 6-15) on well-drained moist sites along river bottoms, floodplains, and lake shores. It often replaces stands that originally held cottonwood, willow, and red-osier dogwood. Other associates may include pin oak, green ash, red maple, basswood, black walnut, black cherry, hackberry, and box elder. American elm is no longer a major component of mature stands because of Dutch elm disease.

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Silver maple sawlogsProducts and Uses

Silver maple, cottonwood, green ash, and associated hardwoods are used primarily for lumber, veneer, and firewood. In some areas cottonwood is used for pulpwood. Green ash is used in specialty items such as tool handles and baseball bats. A high number of wildlife species, especially birds, can be found in a mature bottomland hardwood forest. Mature and overmature stands provide cavities that are essential to many wildlife species, including woodpeckers, wood ducks, barred owls, and raccoons. Whitetailed deer, beaver, and other fur-bearers also can be found in this forest type. Silver maple buds are a staple food for squirrels in the spring. Beavers feed on silver maple and cottonwood bark.

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Site Conditions

Silver maple commonly is found on the alluvial flood plains of major rivers where there are moist, fine-textured silt and clay soils that are imperfectly drained. Its best growth is in better drained, moist areas. Silver maple can tolerate annual flooding in the springSoil pH should be above 4.0. Silver maple seedlings are intermediate in tolerance to water-saturated soils but can tolerate prolonged periods of inundation.

Green ash grows naturally on a range of sites from clay soils subject to frequent flooding and overflow to sandy or silty soils where the amount of available moisture may be limited. It grows best on fertile, moist, well-drained soils. Green ash commonly is found on alluvial soils along rivers and streams and less frequently in swamps. It can remain healthy when flooded for as long as 40 percent of the time during a growing season. Young green ash can withstand flooding for several months during the dormant and early growing season. It prefers a pH of between 7.5 and 8.0.

Cottonwood survives on deep, infertile sands and clays but makes its best growth on moist, well-drained, fine sandy or silt loams close to streams. Stands with site indexes below 70 for green ash (see Appendix B-5), eastern cottonwood (see Appendix B-6), or silver maple should be managed for wildlife, aesthetics, or other nontimber uses.

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Silver maples begin producing seed at about age 11. Seeds ripen from April through June. Dissemination is mainly by wind and occasionally by water. Natural regeneration is most successful on a seedbed of moist mineral soil with considerable organic matter. Initial seedling growth may be rapid, but because silver maples cannot compete with overtopping vegetation, first-year mortality is high if they are not released. . Silver maple stand on a bottomlandThe preferred size of seedlings for plantations is 12 inches in height and 0.25 inches in root-collar diameter. Sprouts appear readily from stumps that are 12 inches or less in diameter.

Green ash starts producing seed when trees are 3 to 4 inches DBH. Seeds drop from late September into the winter. Most seeds are dispersed by wind within short distances of the parent tree. Some dispersal by water also may occur. The best seedbed is in partial shade on moist litter or mineral soil. Stumps of sapling and pole-size green ash sprout readily. Cuttings made from 1-0 seedlings or 1-year-old sprouts root easily under greenhouse and field conditions. Cuttings may be planted horizontally under the soil or vertically with good results.

Cottonwood seed production starts when trees are 5 to 10 years old and good crops occur annually. Seeds disperse from June through mid-July via wind and water. Abundant deposits of seed occur along water courses as spring floodwaters recede. Cottonwood seedlings require very moist, exposed mineral soil, such as fresh silt deposits, and full sunlight for establishment. Artificial propagation normally involves use of cuttings from 1-year stem growth from nursery trees. These may or may not be rooted before outplanting.

To stimulate natural regeneration, clearcut all trees greater than 2 inches DBH. Tree seedlings present in the understory before harvest usually are not abundant, and if present, will probably include elm, maple, and possibly ash. A dormant season harvest encourages more stump sprouts, but should be planned to scarify the soil surface, providing exposed mineral soil for seed germination.

Consider planting within two years after harvest if natural regeneration is not adequate. Since planting is expensive, confine planting to the best sites and avoid locations that frequently flood. Prepare sites as follows:

  1. Shear all residual woody vegetation near ground level.
  2. Pile debris in windrows and burn it.
  3. Rake the entire surface to collect any remaining vegetation.
  4. Deeply disk and till the planting bed.

Silver maple and ash generally are established from seedlings. Cottonwood generally is established from cuttings. Plant at a 12-foot by 12-foot spacing as early as possible in the spring using genetically improved stock, if available. Planting with an auger will create better odds for survival than using a planting bar. Mechanical weeding will be necessary for the first two or three years.

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Intermediate Treatments

Follow the guidelines below based on the dominant species in your stand.

The shade tolerance of silver maple ranges from tolerant on good sites to very intolerant on poor sites. Silver maple leaf. On upland soils, silver maple grows well but is highly intolerant of competing vegetation. In very dense stands a precommercial thinning and weeding of undesirable trees is recommended to encourage the growth of the most desirable trees. The first commercial thinning should occur when codominant trees average 8 to 10 inches DBH. Two or three more thinnings will be required every 7 to 15 years to sustain fast growth. Remove diseased trees and those of low vigor or poor form. Follow the crop-tree release method described in Chapter 5: Woodland Improvement Practices or the stocking chart for elm-ash-cottonwood in Appendix C-2 on page 208 to determine when and how much to thin. At final harvest most stands should have 120 to 130 square feet of basal area (roughly 50 high-quality trees) an acre of commercial species.

High quality green ash treeGreen ash varies from intolerant to moderately tolerant of shade. Natural stands may have enough volume to allow commercial thinnings at 25 to 30 years. To ensure reasonable volume production and reduce epicormic branching in the remaining trees in the stand, do not reduce the basal area below 100 to 120 square feet an acre.

Cottonwood is very intolerant of shade. In natural stands, uneven spacing and size permit some trees to become dominant and natural thinning allows production of large trees. Under plantation conditions, and particularly when only clones with similar growth rates are used and all trees get off to a good start, stagnation can occur quickly. Spacing and the timing of thinning become critical under these conditions. Optimum growth of individual trees requires very wide, seemingly wasteful, spacing.

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Pests and Diseases

Major insect pests in this type of forest are the emerald ash borer, forest tent caterpillar and cankerworms. The emerald ash borer continues to move westward across the Lake States. Follow state department of agriculture recommendations about handling stands that are infested with emerald ash borer and about moving ash wood. If there is an emerald ash borer infestation within 10 miles of your stand, harvest your ash trees as soon as possible to salvage their value and remove possible host trees.

Chemical or microbial insecticides may be required to control defoliators. Major diseases include Dutch elm disease, ash yellows, and cytospora canker. Harvest commercial-size elms whenever possible to salvage their value before Dutch elm disease kills them. Retain elms during thinning only when no other desirable tree is available. Reduce canker damage by thinning to promote tree vigor, but be very careful to avoid damaging remaining trees.

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