Impact of spacing and pruning on quantity, quality and economics of Douglas-fir sawn timber: scenario and sensitivity analysis

• Published in: European journal of forest research 2020-10, Vol.139 (5), p.747-758
• Main Authors: Rais, Andreas, Poschenrieder, Werner, van de Kuilen, Jan-Willem G., Pretzsch, Hans
• Format: Article
• Language: English
• Subjects: Biomedical and Life Sciences; Forestry; Life Sciences; Original Paper; Plant Ecology; Plant Sciences
• ISSN: 1612-4669; 1612-4677
• DOI: 10.1007/s10342-020-01282-8

Controlling the long-term effect of management on the quantity and properties of individual boards is a fundamental challenge for silviculture. Within this basic study on Douglas-fir, we have investigated the sensitivity of the net present value (NPV) to three most common planting densities and a prominent pruning strategy. We therefore have applied an individual tree growth model, which represents intrinsic stem structure as a result of crown competition. The model extrapolated board strength development to the rotational age of 70 years, starting from real and comprehensive data recorded from experimental Douglas-fir plots at the age of 20 years. Total volume production increased from about 1600 m 3 ha −1 for 1000 and 2000 trees ha −1 to 1800 m 3  ha −1 for 4000 trees ha −1 . The economic superiority of the lowest density stands increased considering the NPV at inflation-adjusted interest rates of 0%, 2% and 4%: Given an interest rate of 2% and no pruning, the NPV at 2000 was at about 50% of the one at 1000 trees ha −1 . The NPV at 4000 trees ha −1 was even negative. Generally, artificial pruning was not effective. The revealed financial trade-off between growth and timber quality in young stands underlines the importance of silvicultural guidelines, which quantify the effect of management on yield per strength class and financial outcome.