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Black Spruce

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

Description

Range of black spruce

Black spruce commonly grows in pure stands on organic soils and in mixed stands on mineral soils. Mixed stands often include northern white-cedar, white spruce, balsam fir, and tamarack. It is found throughout the northern Lake States, but especially northern Minnesota (Figure 6-5).

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Products and Uses

Black spruce is grown almost exclusively for pulpwood. The spruce grouse depends on this forest type for most of its food and cover. Several songbirds use this forest type in summer.

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Site Conditions

Black spruce on wet organic soilBlack spruce usually grows on wet organic soils, but productive stands are found on a variety of soil types from deep humus through clays, loams, sands, coarse till, boulder pavements, and shallow soil over bedrock. The most productive black spruce stands are on dark brown to blackish peats, which usually have a considerable amount of decayed woody material. The best sites occur where the soil water is part of the regional groundwater system and is enriched by nutrients flowing from mineral soil areas. The poorest sites occur where the soil water is separated from the groundwater system, and where there is two feet or more of poorly decomposed, yellowish-brown sphagnum moss. When found on mineral soil, black spruce grows best where the slope is gentle and moisture is plentiful, either from a shallow water table or seepage along bedrock. Site index curves for black spruce are in Appendix B-3.

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Regeneration

Rotation lengths for black spruce range from 60 to 140 years, but usually should not exceed 100 years on organic soils or 70 years on mineral soils because of butt rot and subsequent wind damage. Black spruce stands 40 years or older have a nearly continuous seed supply. Good seed crops occur every two to six years, but partially closed cones remain on trees and disperse seed over several years. Under natural conditions, most seed is dispersed after a fire. Black spruceReproduction by layering (root development from low-hanging branches) is common in swamps and bogs.

A good seedbed is moist, but not saturated, and free from competing vegetation. Moist mineral soil usually provides a good seedbed, but exposed mineral soil may be too waterlogged or subject to frost heaving in low-lying areas. Living sphagnum moss makes a good seedbed, but some moss species may outgrow and smother spruce seedlings. Other mosses, especially feather mosses, tend to dry out after clearcutting and make poor seedbeds. Moss seedbeds should be removed by fire or machine or compacted by machine.

Clearcutting blocks or strips is the best method for harvesting and reproducing black spruce. The best growing sites on organic soil usually are brushy and require broadcast burning of slash to reduce shrub competition. To avoid heavy slash that covers desirable residual trees or good sphagnum moss seedbeds, use whole-tree harvesting or burn the slash. Fires that completely remove the surface organic layer usually provide good seedbeds. Seedbed scarification also increases the number of surviving black ash seedlings. Natural seeding can be effective with large, wind-firm stands. Cut progressive strips perpendicular to the prevailing wind to maximize seed dispersal and minimize wind damage. Cut these strips into the wind, up to six chains wide where natural seeding occurs from both sides, or four chains wide where natural seeding occurs only from the windward side.

Rely on natural seeding along the outer portion of large stands while considering direct seeding of interior areas. On well-prepared sites, sow two to three ounces of seed an acre between March and mid-May of the first year following burning or other site preparation. Treat seed with bird repellent and fungicide.

Natural seeding, especially on nonbrushy sites, often results in stands that are too dense for optimum pulpwood growth. To avoid overstocking, count the trees three years after site preparation. If there are at least 600 healthy, well-spaced black spruce seedlings an acre that are at least 6 inches tall, clearcut the adjacent area of mature spruce to eliminate further seeding into the new stand. Planting seedlings is more reliable than seeding, but also more expensive. Black spruce can be planted successfully using 3-0 or container-grown seedlings. Transplants (2-2) are expensive but useful where serious weed competition is expected.

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Intermediate Treatments

Thinning overstocked sapling and poletimber stands is generally not economical and may lead to increased wind damage. Although black spruce is shade tolerant, on good sites a dense overstory of undesirable shrubs or hardwoods may severely suppress seedling growth. In these situations control brush with herbicide to release the spruce.

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Pests and Diseases

Eastern dwarf-mistletoe is the most serious disease affecting black spruce. It causes branch deformations (witches' brooms, or dense clusters of abnormal small branches), reduces growth, and eventually kills trees. Mistletoe survives only on living trees and spreads slowly. To kill mistletoe, cut all trees in infected areas plus a border strip one to two chains wide; then burn the site with a hot fire. To prevent mistletoe infections, clearcut and burn all mature stands where feasible to eliminate undetected mistletoe sources.

Wind may cause substantial breakage and uprooting in older black spruce stands, especially where butt rot is present and where stands have been opened up by partial cutting. Minimize wind damage by using the rotations recommended above and clearcutting narrow strips that progress over time toward prevailing winds.

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