White spruce (Picea glauca [Moench] Voss): stagnating boreal old-field plantations unresponsive to fertilization and weed control

Abstract

Two stagnant teenaged but pre-thicket plantations of white spruce (Picea glauca [Moench] Voss) on old-field sites in the Ontario Clay Belt were studied near Cochrane (49°04′N 81°02′W). Three herbicide × four fertilization treatments were applied, with four independently randomized replications at each site. Weed control (heavy, moderate and none) was with glyphosate, pronamide or nothing, respectively. Ammonium nitrate was broadcast in the first year at 0.0, 55.9, 112.0 and 167.9 kg/ha. Plots were 15 m × 15 m, surrounded by 2-m buffer zones. Performance data on individually identified trees were gathered over a 6-year period in the second decade after planting. Mortality of spruce continued throughout the study and was influenced significantly (P = 0.01) by tree size and by treatment. Mortality increased significantly in treatments that included glyphosate. However, treatments did not significantly (P = 0.05) affect any measured growth parameter. No treatment was silviculturally consequential. Stressed spruce were able to respond only sluggishly to weed control and/or fertilization.