Influence of initial plant density on sawn timber properties for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)

Overview & Synopsis

& Context Mechanical wood properties are increasingly rele-vant for structural applications and are influenced by growing space availability. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) has an increasing market share in Europe and is mainly processed to sawn timber. & Aim A sample of 164 thinning trees was taken from two Douglas-fir long-term forestry research plots in Germany. The end-use quality of about 2,000 side and center boards was analyzed as a function of initial plant density (1,000, 2,000, and 4,000 trees per hectare) and log position within the stem. & Methods Sawn timber quality was described by knottiness, density, modulus of elasticity, and strength. Explanatory pa-rameters were radial position, longitudinal position, and initial plant density. All boards were strength graded visually and by the grading machine GoldenEye-706 using both X-rays for detecting densities and size as well as position of knots and laser interferometry for detecting eigenfrequency (DIN 4074, DIN 2012; EN 14081-2, CEN 2010). & Results High plant density led to better mechanical sawn timber quality. Significant differences were especially ob-served between 1,000 and 2,000 trees per hectare. The yield of machine strength-graded center boards of strength class C24 increased from 50 to 89 % at low and high initial plant density, respectively. & Conclusion Foresters are able to improve end-product qual-ity by controlling planting density in particular. The round-wood price that foresters get should be based on the propor-tion of higher strength classes within logs to give incentives for a more quality-oriented forest management.