Growth and Yield
Volumes of 196 m³/ha (2,800 ft³/acre) are common in 80- to 100-year-old stands on the best peatlands and good upland sites in southern Canada and the Lake States (12). One unmanaged stand had a total volume of 492 m³/ha (7,024 ft³/acre) and a basal area of 53.5 m²/ha (233 ft²/acre) when it was slightly more than 100 years old.
Regional differences in the site index of black spruce are apparently related to climatic factors, whereas differences within regions are associated with soil moisture and nutrients. The moisture-aeration regime influences growth more than the nutrient regime (22). Within peatlands, water chemistry-as determined by water sources and movement-seems to be the principal factor influencing site quality (19).
Black spruce site index curves differ among regions and substrates. For example, the curves are lower at older ages in Newfoundland than in continental Ontario and Quebec. In Ontario, the height-growth patterns of black spruce are different for peatland and upland stands, particularly for site indexes less than 8 m (26 ft) at 50 years and stands older than 80 years (38).
Variable-density yield tables-for stands of various stocking levels-provide better estimates of black spruce growth than normal and empirical yield tables in Ontario (10). They show that both site and stocking influence tree size and volume production. Good sites can grow larger trees than poor sites, whereas stocking has an adverse effect on average d.b.h. and no effect on average height. Merchantable volume, however, increases with stocking except on poor sites (table 1). Variable-density yield tables are also available for black spruce stands in Minnesota (39).
Table 1- Merchantable yields of 120-year-old black spruce stands in Ontario for trees 10 cm (4 in) d.b.h. and larger (adapted from 10) Site index at base age 50 years
Characteristic Stocking¹ at age 30
12.5 m or 41 ft
10.7 m or 35 ft
8.2 m or 27 ft Average height, m Full 17 14 11 Half 17 14 11 Average d.b.h., cm Full 19 13 11 Half 20 15 12 Trees per hectare Full 1,520 2,480 1,490 Half 1,110 1,880 1,780 Basal area, m²/ha Full 42 35 15 Half 36 33 19 Volume, m³/ha Full 298 212 74 Half 260 202 94 Average height, ft Full 57 47 37 Half 57 47 37 Average d.b.h., in Full 7.4 5.3 4.4 Half 8.0 5.9 4.6 Trees per acre Full 615 1,005 605 Half 450 760 720 Basal area, ft²/acre Full 181 152 65 Half 158 145 83 Volume, ft³/acre Full 4,260 3,030 1,050 Half 3,710 2,880 1,350 ¹"Full" refers to a basal area- for trees 2.5 cm (1 in) in d.b.h. and larger- of 18.4 m²/ha (80 ft²/acre) on site index 12.5 m (41 ft) good site/medium site; 13.8 m²/ha (60 ft²/acre) on site index 10.7 m (35 ft); and 4.6 m²/ha (20 ft²/acre) on site index 8.2 m (27 ft) poor site. "Half" refers to one-half of the respective basal areas used for full stocking. Normal yield tables show that rotation age increases as site quality decreases. They also show that the corresponding merchantable volume and mean annual increment decrease greatly from good to poor sites. Averages for black spruce stands of three site classes in the boreal forest of Canada (5, p. 50,91,155,186) are as follows:
Good Medium Poor Rotation age, yr 95 113 132 Merchantable volume, m³/ha 218 160 101 Mean annual increment, m³/ha 2.3 1.4 0.8 Merchantable volume, ft³/acre 3,110 2,285 1,440 Mean annual increment, ft³/acre 33 20 11 Rotation age is the age at which the mean annual increment of merchantable volume culminates and hence yields the most material per unit area per annum.
Little is known about the growth and yield of uneven-aged stands, but they apparently grow more slowly and have lower volumes than even-aged stands (17).
Black spruce plantations reach heights of 1.5 to 4.0 m (5 to 13 ft) 10 years after planting (2,34). A 40-year-old plantation in Minnesota, planted at a 1.2- by 1.2-m (4- by 4-ft) spacing, was 13.3 m (43.6 ft) tall and had a basal area of 32.8 m²/ha (143 ft²/acre) (43). On rich sites in New Brunswick, extensive fast-growing plantations of black spruce have been established for 45-year rotations because the species has good potential height growth and is resistant to spruce budworm.
In experimental studies, fertilization with nitrogen and phosphorus generally results in increased growth in 60- to 90-year-old stands on upland boreal sites (48). The best response to fertilization apparently occurs in stands of low vigor (33,53). For example, fertilization (with nitrogen and phosphorus combined) may convert some marginally nonproductive muskeg stands of black spruce into commercial forest stands (1). Benefits from fertilization will probably be greatest in thinned stands (51).
Drainage may increase the growth and yield of black spruce, but maximum response on peatlands and other wet sites will probably also require fertilization and (in dense stands) thinning. Full-tree harvesting will probably not reduce future productivity, except on sites of marginal fertility (52).
- 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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