Links between the quality of Douglas fir sawn timber and selected tree and site characteristics in Germany

The wood quality of Douglas fir sawn timber from Central Europe was examined to facilitate feedback on the quality of mechanical properties of sawn timber achieved by different silvicultural strategies. The visual criteria of the sawn timber have been evaluated and analyzed for their impact in the visual grading of timber to verify the efficiency of the applied standards for Douglas fir sawn timber. Four-point bending tests have been conducted to determine the mechanical properties and categorise the study material into strength classes. An ordinal analysis has indicated, that the negative effect of compression wood on the mechanical performance of boards has been overemphasised and the yield of Douglas fir timber could benefit from specially defined criteria thresholds. Among characteristics at the tree and stand level, knowledge on crown radius, crown base height, tree height and diameter, with reference to the stand age, have proven to be promising predictors for the expected quality yield of sawn timber. A significantly lower quality was detected within sample material from short rotation periods.