Reaction to Competition
Aerial spraying of selective herbicides such as 2, 4-D usually results in effective release of black spruce in brushy stands (26,50). Released trees, however, apparently do not increase growth for about 2 years, and complete release can result in winter drying. Applying pellets of the nonselective herbicide picloram to speckled alder clumps seems to control regrowth longer than 2,4-D but can damage associated black spruce even on well-drained soils (40). Although quite expensive, recently introduced selective herbicides such as glyphosate and hexazinone are also registered for release of spruce. Directions on all herbicide labels should be followed carefully and pertinent precautions heeded.
In spruce-fir stands, mature black spruce apparently responds better to release than white spruce and subalpine fir (Abies lasiocarpa); its diameter increment increases by several times (9). Many intermediate and suppressed black spruce in swamp stands, however, die after heavy cutting (21).
Black spruce has less ability than white spruce to overcome stagnation in even-aged stands because it develops a smaller range of crown classes. Heavy thinning in dense, middle-aged stands increases diameter increment but often decreases volume increment, probably because the site is not fully utilized (47).
Black spruce is often a postfire pioneer on both uplands and peatlands, and fire usually results in the immediate reestablishment of black spruce as long as a seed source is available. Black spruce often dominates fire-prone areas, such as upland ridges, because it produces seed at an early age (20). It also becomes dominant on poor peatland (bog) sites where it has little competition. Tamarack and black spruce are the first trees to invade the sedge mat in filled-lake bogs.
Postfire stands of black spruce are generally even aged. Uneven- to all-aged stands are almost absent in virgin forests because wildfires have been frequent and extensive enough to prevent their development on most sites. Such stands are common on bogs and muskegs, however, where the average interval between fires is probably longer than on uplands. Closed stands that escape fire for more than 100 years usually become uneven aged when black spruce layerings fill the gaps created by deterioration of the overstory (17).
Black spruce grows more slowly than many of the trees and shrubs with which it is associated. Thus, it encounters substantial competition where these species are abundant, particularly when they reproduce from sprouts or suckers rather than from seed. Black spruce is fairly common as an understory tree in jack pine and lodgepole pine stands on dry sites, and succeeds the pines in the absence of fire or harvesting (12). Various mixtures of black spruce, white spruce, and balsam fir-plus northern white-cedar south of the boreal forest-eventually form the main stand on most well-drained sites supporting quaking aspen, paper birch, or balsam poplar. On the better peatland sites, black spruce is often overtopped by quaking aspen, paper birch, tamarack, black ash, or red maple for many years before it becomes dominant. Over much of its range, it is eventually succeeded by balsam fir and, to a lesser extent, northern white-cedar if undisturbed by fire (17).
Black spruce does not compete successfully with balsam fir, northern white-cedar, red maple, balsam poplar, and black ash after cutting in mixed stands on good peatland sites (12). Similarly, harvesting or other disturbances on well-drained sites often lead to high proportions of balsam fir, paper birch, quaking aspen, and balsam poplar, or shrubs (50). Speckled alder is a strong competitor following harvesting on good peatland sites. The spruce, however, is generally able to grow through the alder canopy after several years (50). In Newfoundland and parts of Quebec, there has been extensive conversion of black spruce stands to heathland, dominated by lambkill and Labrador-tea, following repeated fires.
Clearcutting in strips or patches is generally considered to be the best silvicultural system for managing black spruce (21,26,50). Satisfactory reestablishment of black spruce after clearcutting, however, requires an adequate source of reproduction and often some kind of site preparation, such as slash disposal. Uneven- or all-aged management is best applied on poor sites where stands are windfirm. and have abundant layering (27).
- Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp. http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm
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