The Effects of Soil Parent Material and Nitrogen Fertilization on Tree Growth and Wood Quality of Douglas-fir in the Pacific Northwest

The influence of four soil parent material types (SPMs) and nitrogen fertilization treatment (224 kg N/ha) on Douglas-fir (Pseudotsuga menziesii (Mirb.) plantation growth and wood quality was studied on seven sites across western Washington and Oregon. Six aspects regarding wood quality were assessed and analyzed, (1) tree sonic acoustic velocity (TSAV), (2) log resonance acoustic velocity (LRAV), (3) dynamic modulus of elasticity (MOEd), (4) specific gravity (SG), (5) latewood percentage (LWP), and (6) rings per inch (RPI). Analysis of tree growth suggests the Mixed SPM type (Sedimentary and Igneous) is the most productive type in terms of timber volume increment. Fertilization has significantly enhanced Douglas-fir lateral growth and volume gain, but a variety of effects upon wood quality attributes were detected. In general, growth increment was negatively associated with quality observed in the breast height region. From the perspective of a whole tree, higher quality wood can be found in the segment from stump height to the live crown base. A strong correlation (R2 = 0.92) between TSAV and LRAV was observed, and TSAV was 8% higher than LRAV.