David M. Morris, Government of Ontario, Thunder Bay, ON, CANADA and Martin Kwiaton, Centre for Northern Forest Ecosystem Research, Ontario Ministry of Natural Resources and Forestry, Thunder Bay, ON, Canada
Study objectives were: 1) to document changes occurring to soil chemical and biological properties resulting from different biomass harvest intensities conducted in black spruce-dominated soil types (outwash sands, loamy tills, peaty-phase wet mineral, and peatlands) and 2) to determine if any of the detected changes in soil indices are correlated to patterns in planted seedling growth or foliar nutrition. Experimental harvests were conducted on 9 mature, black spruce stands consisting of 5 replicated treatments: uncut reference state condition, stem only - coarse and fine slash left on the plots, chipped - all chipper debris returned to the plot, full-tree - fine slash removed to roadside, and a full-tree + blading - complete removal of logging debris and upper organic soil layer. Ten years after the harvest treatments were established, soil chemical and biological properties of the O horizon and upper B horizon were compared across soil type and treatment combinations, as well as the growth and foliar nutrition of planted black spruce seedlings. For almost all soil chemical parameters evaluated, significantly lower values occurred following harvesting, with a consistent downward trend in most soil parameters corresponding to increased biomass removal. The operational stem-only and full-tree treatments, however, were comparable to each other. Mineralizable N (a 14-day anaerobic lab incubation) had the highest correlation to the foliar N measurements. This is an easily applied, rapid technique that should be considered as part of a soil quality monitoring protocol when evaluating the sustainability of new biomass harvesting alternatives.