Adaptation strategies for spruce forests—economic potential of bark beetle management and Douglas fir cultivation in future tree species portfolios

Abstract

Abstract Productive Norway spruce forests in mountainous growing areas are expected to be affected by increasing climate-driven disturbances, which will most likely result in a reduction of their economic performance. This study seeks to compare the potential of currently discussed management options aiming to maintain the economic performance on typical sites of spruce under a changing climate. For this purpose, we used a combined approach of tree mortality simulation and portfolio optimization to assess the management options: (1) including a deciduous species, (2) establishing mixed stands, (3) shortening the rotation periods, (4) forest protection measures focusing on bark beetles and (5) introducing another highly productive species. As a novel feature, we also compared the effect of combined management strategies on the return and risk of stand management. In our simulation and optimization approach, the inclusion of an alternative, highly productive tree species, such as Douglas fir, into the tree species portfolio outcompeted the forest protection measure of intensive bark beetle monitoring with timely sanitation fellings in terms of balancing risks and returns. The adaptation gain of introducing Douglas fir was further enhanced when combined with additional management options such as adapted rotation periods. The resulting synergies were able to overcompensate for the adverse economic effects of climate change. On the contrary, including beech did not only reduce the risks but also the return in a magnitude which was clearly outcompeted by Douglas fir, even with the assumption of high mortality risks for Douglas fir. These results prove the importance of a proactive tree species selection in relation to more reactive forest protection measures for climate change adaptation. They also advise a careful consideration of expected market demands when selecting an additional species for the portfolio.