Canadian Forest Service Publications
Black spruce: 15-years growth and microbiological responses to thinning and fertilization. 1980. Weetman, G.F.; Roberge, M.R.; Meng, C.H. Can. J. For. Res. 10: 502-509.
Issued by: Laurentian Forestry Centre
Catalog ID: 14406
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A 65-year-old upland black spruce stand was thinned and fertilized with urea in 1961. The 15-year total volume increases ranged from 3 to 9 m3 for an application of 112 kg N/ha and from 11.5 to 12.5 m3 for 448 kg N/ha. Most of the volume increases due to treatment took place in the first 10 years. Heavy thinning and fertilization had almost additive effects to produce an 86% increase in periodic gross increment. Neither periodic tree mortality nor distribution of response by tree size appeared to have been affected by treatment. Humus analyses of control plots and of plots treated with 448 kg N/ha, conducted in 1961, 1966, 1971, and 1976, indicated that after 15 years pH values were still higher, NH4-N levels approached equilibrium values twice as high as controls after 10 years, leaching and volatilization losses of N were negligible, the C/N ratios were lower, and the potential for N mineralization and total biological activity were higher on the N-treated plots. Significant black spruce stand responses to N fertilization have been shown in this stand but responses have been variable in other trials with this species. Further work is needed to explain these results.