No abstract

• Key message Root and rot (RBR) caused byHeterobasidion parviporumNiemelä & Korhonen andHeterobasidion annosum(Fr.) Bref. damages Fennoscandian spruce stands. In case the rot infection and its severity are unknown, the mere risk of infection should seldom affect the harvest timing. When it does, the gains by harvesting earlier are minimal. • Context It has been suggested that stands infected by RBR should be harvested earlier than the healthy ones. Yet, we must decide on harvest timing decisions without reliable information on the infection. • Aims We studied if harvesting earlier pays off under RBR uncertainty. • Methods We structured the uncertainty with a decision tree and calculated the optimal rotations based on expected net present values. We compared rotation lengths to those of healthy stands and calculated gains from earlier harvesting. • Results The inclusion of RBR-related uncertainty in the model changed the rotation length of only 14–23% of the stands. The average reduction was 1.3–4.7 years. Yet, the gain from harvesting earlier was too low to be considered. • Conclusion In the absence of information on the extent and severity of RBR, it seldom pays off to advance harvests. The value growth in healthy trees tends to compensate for the value reduction due to rot.

Highlights• We present the best species to plant on previously spruce-dominated sites with different site indexes and rot levels. • We recommend planting Norway spruce on low-rot sites, Scots pine on higher-rot sites, and allowing natural regeneration on low site indexes. • We demonstrate the Precision forestry method for determining the optimal tree species in heterogenous stands. • In the case study, the method increased net present value by approximately 6% on average.

Because the two common tree species in Norway, Picea abies L. Karst (Norway spruce) and Pinus sylvestris L. (Scots pine), differ in their susceptibility to the fungus Heterobasidion spp., converting at least parts of the rot-infested spruce stands to pine pays-off economically in some cases. Pixel-level information on rot levels and site indexes (SI) across the stand are required to identify these cases to make decisions that increase the expected economic return of the stand. Applying the Value of Information (VoI) concept, we assessed the value of such information when choosing between planting spruce and pine on a clear-cut spruce stand. The VoIs were highest for the stands of medium–low dominant SI. There, the shift from spruce to pine in some pixels instead of planting spruce across the whole stand has the best-expected impact on the stand’s net present value. Additionally, planting densities are more often adjusted to the pixel SI in these dominant SIs. Given that the stand’s dominant SI is known, information on rot levels alone is more valuable than information on SI alone. The lower the interest rate in decision-making, the more the forest owner is willing to invest in information supporting forest management.

Harvested wood products (HWP) contribute to climate change mitigation via two main mechanisms: carbon storage and substitution. The authors examined the data on carbon storage and substitution factors of HWPs that are relevant in evaluating the climate change mitigation potential in the context of the Norwegian forest sector. While there seem to be many uncertainties in these parameters, the data suggest that several uses of wood for industrial products come with clear carbon substitution benefits and, in some cases, provide long-term carbon storage. Such wood products could play an important role in climate-friendly bioeconomic transformation. In particular, the authors considered wood- based construction materials, textile fibres, and insulation materials as examples of such products with potential in future bioeconomy. The decay of the carbon stored in HWP pools over time is often modelled using the product half-lives that correspond to the number of years it takes for the carbon in a pool to be reduced to half of its initial value. Using the default half-life values of greenhouse gases reported to the United Nations Framework Convention on Climate Change, the average half-life of carbon in HWPs produced by the forest industry in Norway of today is approximately 21 years. Shifting some of the use of pulpwood and sawn wood chips from producing paper and pellets to produce insulation materials or panels for construction would increase the time carbon is stored in the HWP pool. Accounting for the large uncertainty in the carbon substitution parameters of HWPs found in this study, a cautious estimate of the substitution benefits of HWPs produced in Norway can be considered to amount to at least 5 Mt CO2. Redirecting some pulpwood use from paper production to the production of textile fibres and the above-mentioned construction materials would increase the substitution benefits.