Ten-year Growth Response of Black Spruce to Thinning and Fertilization Treatments
A 65-year-old upland black spruce (Piceamariana Mill. B.S.P.) stand near Baie Comeau, Quebec, was thinned and fertilized with urea; each treatment was at 2 levels in a split plot factorial design. The trees responded to the nitrogen addition after 1 year and to thinning after 7 years. The trees were still growing faster in response to most treatments after 10 years. Trees of all size classes responded to the treatments. The periodic increment was not increased by 25% thinning, but was increased by 50% thinning and was always increased by nitrogen additions. Absolute increases over control values ranged from 130 to 290 ft3 (11 to 24.6 m3) for an application of 100 lb N per acre (112 kg N per hectare) and 238 to 297 ft3 (20 to 25.2 m3) for 400 lb N per acre (444 kg N per hectare) (1 ha = 104 m2). Some synergistic effect of combined thinning and fertilizer treatments is indicated.Mortality losses in the 10-year period were appreciable because of excessive stand density. The roles of thinning and fertilizer treatments in black spruce management are discussed.