Balancing Decisions for Adaptive and Multipurpose Conversion of Norway Spruce (Picea abies L. Karst) Monocultures in the Black Forest Area of Germany

This study presents a combined simulation-optimization approach for the multipurpose conversion of Norway spruce (Picea abies L. Karst) forests in the Black Forest area of Germany. Conversion strategies were modeled as a means of adapting existing spruce forests to an expected climate change by admixing beech (Fagus sylvatica L.), a native species in large areas of the low mountain ranges of Central Europe. The evolution of the forest state over time was simulated by adopting a single-tree growth tool, TreeGrOSS, and using national forest inventory data. The stochastic genetic algorithm was used to solve the optimization problem, incorporating the values of timber, carbon, and species diversity. Analysis of the tradeoffs between objectives was conducted to determine a balanced decision with species enrichment and carbon storage in the growing stock to adapt to future climate changes. An average overall net present value of 12,158(sic)/ha was obtained for satisfying a moderate enhancement in species diversity by establishing beech regeneration in 46% of forest area and storing 39.5 kg/ha carbon in forest biomass. Diversification of silvicultural pathways is needed because of the integration of multiple objectives in the decisionmaking process and dependence on the structural properties of forest stands, e.g., age class.