Transformation of plantation forests — expected wood properties of Norway spruce ( Picea abies (L.) Karst.) within the period of stand stabilisation

In Germany transformation of even-aged pure Norway spruce stands is a much discussed topic. The sawmilling industry, as the most important buyer of the softwoods, is very critical of the new silvicultural strategies and has fears about the wood quality. The investigation concentrates on the first step of the transformation — the period of stand stabilisation — which will probably be characterised by wider spaced growing conditions for the trees of Norway spruce. The aim of this investigation is to estimate within this period of stabilisation the consequences for the roundwood quality as well as for sawn timber properties. The solid wood processing chain in the sawmilling industry is totally included — starting at the fresh sawn timber up to stress grading of the dried sawn timber. The material of this investigation was harvested in silvicultural thinning trials that were started 23 years ago in a previously unthinned pure Norway spruce stand at the age of 27 years. The results show a tendency with increasing spacing towards lower roundwood quality caused by wider annual year rings, higher taper, higher branch stub diameters and a higher percentage of compression wood. Considering the sawn timber properties — drying behaviour, bending strength and static E-modulus — it becomes obvious that mainly the drying behaviour of the sawn timber gets worse from stands with wider spacing. The effect on the output of straight, dry timber will be analysed in further steps of the investigation.