Forest carbon certification under climate and mortality uncertainty: ecological and economic trade-offs of management scenarios in Freiburg, Germany

Abstract Background Forest carbon certification could help finance the transformation of climate-sensitive stands, but early interventions may reduce biomass and timber revenue before carbon and ecological benefits emerge. Evidence that jointly evaluates forest growth, hydrological co-benefits, timber economics, carbon accounting, and uncertainty remains limited. We compared no management, business-as-usual management, a conventional certification scenario, and a transformative certification scenario across five spruce-dominated plots in Freiburg, Germany. Forest development was simulated from 2020 to 2080 using 3-PG-Hydro under three climate models, two emissions pathways, and four mortality assumptions, resulting in 480 stand-level simulations. Timber-based net present value was assessed at discount rates of 1%, 2%, and 4%, and indicative carbon-credit potential was estimated relative to business as usual. Results Management, mortality severity, and initial stand structure generally had greater effects on biomass than differences among climate models or emissions pathways. No management retained the highest biomass under no and low mortality, but this advantage declined under stronger mortality assumptions. Business as usual produced the greatest harvest volumes and pronounced harvest-related biomass fluctuations. The transformative scenario generally produced among the highest net primary production values in Plots 1–4, while deep-percolation responses were modest and plot-dependent. Discounting strongly affected economic rankings: lower rates favoured terminal standing stock, whereas higher rates favoured earlier harvest revenues. Under the representative MPI climate model, certification-aligned scenarios generally attained higher timber-based net present value than business as usual later in the simulation. Sustained biomass breakeven between the transformative scenario and business as usual occurred between approximately 2045 and 2075 in four plots and was not robust in the youngest plot. Conclusions No scenario dominated across all ecological and economic indicators. Transformation-oriented management imposed an initial biomass and revenue cost, while its potential carbon advantage was delayed and strongly dependent on initial stand structure and baseline harvest timing. The results demonstrate why stand-specific planning, dynamic baselines, and explicit treatment of harvest cycles are essential when evaluating forest-carbon additionality. Carbon finance may support transformation, but financing mechanisms are needed to bridge the period before sustained additionality can be demonstrated.