Characteristics of bark and wood of Norway spruce infested by spruce bark beetle and blue-stain fungi : relevance for biomass utilization

Abstract

Recent droughts have accentuated problems with attacks of the European spruce bark beetle (SBB) (Ips typographus) on Norway spruce (Picea abies), one of the most important tree species in European forestry. SBB attacks are typically accompanied by infestation with Ophiostomatoid fungi causing blue stain. The chemical composition of sapwood and bark from spruce trees infested by SBB, or by both SBB and blue-stain fungi (BSF), was investigated and compared to corresponding fractions from non-infested reference (REF) trees. While sapwood from infested trees showed higher carbohydrate:lignin (C:L) ratios (SBB, 2.21; BSF, 2.47) than sapwood from non-infested trees (REF, 2.17), BSF bark showed lower C:L ratio (0.81) than REF bark (1.23). For BSF sapwood and bark, and SBB bark, the fractions of extractives were half or less than half of that of the corresponding REF materials. Group analysis using GC-FID showed significantly (p ≤ 0.01) lower levels of resin acids, fatty acids, steryl esters, and triglycerides in BSF materials than in REF materials, a phenomenon that was, however, not observed for sterols. Analysis of subgroups and individual fatty acids, resin acids, and sterols identified using GC-MS revealed complex patterns, in which many, but not all, substances exhibited lower values in BSF and SBB materials than in REF materials. Overall, the results point towards the possibility to utilize a larger portion of wood logs from trees infested by beetles and fungi for value-added applications, such as pulping, rather than as fuel wood