Products and Uses
Species composition of bottomland hardwoods varies depending on the site, but may include American elm, green ash, black ash, eastern cottonwood, silver maple, and black willow. Ash, cottonwood, and silver maple are the most commercially desirable species.
Ash is common on alluvial soils along rivers and streams. It is found where good moisture conditions occur in medium- to coarse-textured sands or loams to clays. Black ash can grow on wetter sites than green ash. Ash seedlings become established in partial shade on moist litter or mineral soil.
Range of green ash.
Eastern cottonwood is common on moist alluvial soil ranging from coarse sands to clays but grows best on fine sandy loam near streams. Cottonwood seedlings require moist, exposed mineral soil and full sunlight for establishment.
Silver maple is found on alluvial flood plains of major rivers where there are moist, fine-textured silt and clay soils that are imperfectly drained. Silver maple seedlings require moist litter or mineral soil and full sunlight for establishment.
Bottomland hardwood species can regenerate from their light, wind-disseminated seeds. Some species, especially ash, also may stump sprout. Clearcut all trees greater than 2 inches DBH to promote regeneration. Tree seedlings pre-DBH to promote regeneration. Tree seedlings present in the understory prior to harvest (called advance reproduction) usually are not abundant, and if present, will probably consist of 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.
Range of eastern cottonwood.
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 the site as follows:
- Shear all residual woody vegetation near ground level.
- Pile debris in windrows and burn it.
- Rake the entire surface to collect any remaining vegetation.
- Deeply disk and till the planting bed.
Cottonwood generally is established from cuttings. Ash generally is established from seedlings. Plant at a 12 x 12-foot spacing as early as possible in the spring using genetically improved stock. An auger will give better survival than a planting bar. Mechanical weeding will be necessary for the first two or three years.
In very dense stands a precommercial thinning and weeding of undesirable trees is recommended to concentrate growth on 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 or the stocking chart for elm-ash-cottonwood in Appendix D-1 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) per acre of commercial species.
Major insect pests in bottomland hardwoods are the forest tent caterpillar and cankerworms. Chemical or microbial insecticides may be required to control these 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 residual trees.