To mix or not to mix—efficient adaptation to windthrow risk

Abstract Disturbance to spruce forests from wind and bark beetles is projected to worsen. It has been suggested that mixed-species forests could provide a more disturbance-resilient option than spruce monocultures. We used dynamic optimization to study how profitable mixed forests are compared to pure spruce forests by examining two similar neighboring stands facing a windthrow risk. We found that under high current windthrow risk levels in northeastern Finland, Norway spruce ( Picea abies )-only forests are more profitable than mixed forests consisting of spruce and silver birch ( Betula pendula ). However, if the windthrow risk to spruce trees increases by 35% compared to its current level, and the risk level of birch remains at its current level, mixed forests become more profitable. When carbon is priced at €50 per ton of CO 2 , the additional income from carbon storage in mixed forests outweighs the economic advantage of spruce timber, making mixed forests more profitable—even if the risk to spruce increases by only 25%. Hence, mixed-species forests become increasingly profitable as carbon prices rise. Therefore, mixed-species forestry represents a cost-efficient strategy for adapting to increasing environmental risks and mitigating climate change.