Abstract
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 m3 ha−1 for 1000 and 2000 trees ha−1 to 1800 m3 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.
Highlights
The early control of crown dynamics through establishment spacing has been considered as highly relevant for balancing both dimensional growth and timber quality development (Smith and Reukema 1986; Mitchell et al 1989)
Faculty of Civil Engineering and Geosciences, Biobased Structures and Materials, TU Delft, Delft, The Netherlands the one hand, foresters maintain high initial stand densities that result in a rapid lifting of the crown base and an early suppression of branches along the lower and most valuable stem region (Reukema and Smith 1987)
As pruning affected only future crop trees, we focused on the benefits at the time of clear-cutting only and on the Initial planting density
Summary
The early control of crown dynamics through establishment spacing has been considered as highly relevant for balancing both dimensional growth and timber quality development (Smith and Reukema 1986; Mitchell et al 1989). As this study considers Douglasfir in particular, we focused on the wood usage in the field of construction Within this scope, the quality of the final product is most precisely defined by structural sawn timber grading. Strength and stiffness of Douglas-fir boards strongly depend on knottiness and wood density (Whiteside et al 1977). These internal structure characteristics of the stem such as knottiness, wood density, fiber deviation or microfibril angle result from growth, crown dynamics, competition and from stand density (Mitchell 1975; Pretzsch and Rais 2016).
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