Minnesota’s black spruce forest type

April 20, 2007 at 5:47 pm Leave a comment

Products and Uses

Black spruce is grown almost exclusively for pulpwood. In the past, Christmas trees were cut from the top 3 feet of old trees that were 20 to 35 feet tall and growing on poor sites. The spruce grouse depends on the black spruce type for most of its habitat needs.

Growing Conditions

Classic northern MN black spruce stand. Click for a better view.Black spruce grows mainly in pure stands, but also may be mixed with tamarack, northern white-cedar, and balsam fir on organic soil and with other conifers, especially jack pine, and various hardwoods, including black ash, red maple, and paper birch, on better drained, mineral soil.

The black spruce forest type is found mainly on organic soil in the Lake States, but black spruce trees also commonly occur on upland mineral soil in mixture with other species. The best black spruce sites on organic soils occur where the soil water is part of the regional groundwater system and is enriched by nutrients flowing from mineral soil areas. They have moderately well-decomposed organic soil that contains much partially decayed wood and is dark brown to black. However, the upper 6 inches may be poorly decomposed sphagnum or other mosses, especially in old stands. The poorest sites occur where the soil water is separated from the groundwater system, and where there is 2 feet or more of poorly decomposed, yellowish-brown sphagnum moss.

Black spruce is common on mineral soil only on the Laurentian Shield in northeastern Minnesota and in a few areas of Upper Michigan. Growth is best where the slope is gentle and moisture is plentiful either from a shallow water table or seepage along bedrock.

map showing range of black spruce
Range of black spruce.

Regeneration

Rotation lengths for black spruce range from 60 to 140 years, but where dwarf-mistletoe is a problem, rotations usually should not exceed 100 years on organic soils or 70 years on mineral soils.

Black spruce stands 40 years or older have a nearly continuous seed supply because cones remain on the trees and shed their seed over several years. In addition, seed crops seldom fail. Reproduction by layering is common, particularly in swamps and bogs.

Clearcutting blocks or strips is the best method for harvesting and reproducing black spruce. Seedling establishment requires a seedbed that is moist but not saturated and free from competing vegetation. Establishment is generally successful if the surface layer of the soil is:

  1. Removed by fire or machine;
  2. Compacted, as in a skid road; or
  3. Composed of living sphagnum moss.

Feather mosses make poor seedbeds because they dry up and die after clearcutting. Broadcast burn heavy slash if it covers desirable residual trees or good sphagnum moss seedbeds. Skidding whole trees from the site may eliminate the need for slash disposal. If your site requires broadcast burning, you can reduce the cost per acre by clearcutting and direct seeding large blocks (40 acres or more).

Sow seed between March and mid-May of the first year following burning. On well-prepared sites, 2 to 3 ounces of seed per acre should be adequate. Seed should be treated with bird repellent and fungicide.

Natural seeding can be effective with large, wind-firm stands. These sites may not require broadcast burning. Cut progressive strips perpendicular to the prevailing wind to maximize seed dispersal and minimize wind damage. Successive strips should be cut into the wind. A strip perpendicular to the prevailing wind can be up to 6 chains wide (1 chain = 66 feet) if natural seeding can occur from both sides or 4 chains wide if natural seeding can occur only from the windward side. The outer portion of large stands can be reproduced by natural seeding, thus significantly reducing the area requiring direct seeding.

Natural seeding of black spruce, especially on non brushy sites, often results in stands that are too dense for optimum pulpwood growth. To avoid overstocking, count the trees about three years after site preparation. If there are at least six hundred healthy, well-spaced black spruce seedlings per 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 are expensive but useful where serious weed competition is expected.

Intermediate Treatments

Thinning of 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 to release the spruce.

Pests

Eastern dwarf-mistletoe is the most serious disease affecting black spruce. It causes branch deformations (witches’ brooms), reduces growth, and eventually kills trees. To avoid mistletoe infections, clearcut and burn all mature stands where feasible to eliminate undetected mistletoe sources.

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

Spruce budworm is not a common problem on black spruce because of the spruce’s late budbreak.

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Minnesota’s northern white-cedar forest type Minnesota’s jack pine forest type

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News and information of interest to Minnesota woodland owners. Sister site to MyMinnesotaWoods.org.

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