Evaluating the effects of biomass harvesting on soil nutrient availability, foliar nutrition, and seedling growth in third-growth black spruce plantations in northwestern Ontario

Abstract

Residual forest biomass is a viable feedstock that can be used in the bioenergy stream. There remains, however, a concern that excessive removal of forest biomass may have negative impacts on forest biodiversity, stand regeneration, tree growth, soil nutrient availability, and foliar nutrition. This study examines the effects of different amounts of biomass removed from clear-cut harvested, 2nd growth black spruce (Picea mariana) plantations. The specific questions addressed in this study were: 1. How does the level of biomass retention influence seedling growth? 2. Are there measurable differences in soil N availability across a gradient of biomass removals? 3. Are any of the differences in soil N availability reflected in seedling foliar N concentrations or content? The study was conducted on two black spruce plantations that were planted in 1962, and clearcut harvested in 2007. The sites represented contrasting soil types (i.e., clay versus loam). Six biomass retention treatments were applied in 15 x 15m treatments across 3 blocks at each site that represented a gradient of C (0 – 22 Mg ha-1 ) and N (0 – 325 kg ha-1 ) retention levels. PGPs (100 m2 ) were established in each treatment plot, with tree measurements, foliar, and soil sampling done every 5 years up to year 15. The results showed that biomass removal had little effect on the stand and soil condition in both sites out to 15 years since establishment. The most significant results were the differential responses across soil types, with the clay site having better growth, soil N availability, and foliar N concentrations. These results suggest that proper management and timing of the additional removal of biomass as bioenergy feedstock are unlikely to have significant negative effects on stand development and early growth.