Temporal Changes in Soil C and N Reserves Resulting From Various Levels of Biomass Removal, and Their Impact On Black Spruce Foliar Nutrition and Growth.

With a fast growing interest in using forest biomass for energy production, concerns regarding impacts to soil quality have also been heightened.  In this context, the objectives of the current study were: 1) to document temporal changes occurring to soil C and N pools resulting from different biomass harvest intensities conducted in upland, black spruce-dominated site types, and 2) to determine if any of the detected soil changes are correlated to patterns in planted seedling growth or foliar nutrition.  Four sites (2 – outwash sand ; 2 – loamy till) were experimentally harvested (replicated stem only, whole-tree, whole-tree+blade) in 1994/5 and measured through year 15 to tract changes in soil C and N stocks, and evaluated planted tree (black spruce) tree performance (survival, growth, and foliar nutrition).

Both soil C and N pools dropped significantly by year 3 across all treatments and site types, but stabilized thereafter.  Tree growth and foliar N levels, however, were only significantly reduced on the WT+B treatment on the infertile, sandy sites. Results to date do suggest that higher biomass utilization levels associated with whole-tree harvesting do not appear to significantly reduce soil C and N stocks compared to stem only harvests or subsequent planted tree performance.