Forest Carbon Certification in Freiburg Shows Delayed Payoffs Under Climate and Mortality Uncertainty

A modelling study of spruce-dominated forest plots in Freiburg, Germany, has found that no single management scenario wins across both ecological and economic measures, and that the carbon benefits of transformative forest management arrive late and depend heavily on starting conditions. The research, published in Carbon Balance and Management, simulated forest development from 2020 to 2080 and compared four options: no management, business-as-usual management, a conventional certification scenario, and a transformative certification scenario.

The team, led by Rocio Belen Lopez Scribante, Marc Djahangard and Rasoul Yousefpour, ran 480 stand-level simulations across five spruce-dominated plots. They combined three climate models, two emissions pathways and four mortality assumptions, using the 3-PG-Hydro model to project growth. Timber-based net present value was calculated at discount rates of 1, 2 and 4 percent, and an indicative carbon-credit potential was estimated relative to the business-as-usual baseline.

A central finding concerns what drives outcomes. Management choices, mortality severity and initial stand structure generally had larger effects on biomass than differences among climate models or emissions pathways. In other words, decisions made by forest managers and the condition of the stand at the outset mattered more than which climate projection was used.

Under no and low mortality, leaving forests unmanaged retained the highest biomass, but that advantage shrank as mortality assumptions strengthened. Business as usual produced the greatest harvest volumes and pronounced harvest-related swings in biomass. The transformative scenario generally achieved among the highest net primary production values in Plots 1 through 4, while deep-percolation responses were modest and varied by plot.

Economics proved highly sensitive to how future revenues are discounted. Lower discount rates favoured terminal standing stock, meaning trees left standing at the end of the planning horizon, 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 only later in the simulation period.

The timing of the carbon advantage was a key concern. Sustained biomass breakeven between the transformative scenario and business as usual occurred between approximately 2045 and 2075 in four of the five plots, and was not robust in the youngest plot. This means that in a young stand, the transformative approach may never reliably demonstrate a sustained biomass advantage over continued conventional management within the simulated window.

The authors conclude that transformation-oriented management imposes an initial cost in both biomass and timber revenue, while its potential carbon advantage is delayed and strongly dependent on initial stand structure and the timing of baseline harvests.

According to the study, the results show why stand-specific planning, dynamic baselines and explicit treatment of harvest cycles are essential when evaluating forest-carbon additionality. Carbon finance may support the transformation of climate-sensitive stands, but financing mechanisms are needed to bridge the period before sustained additionality can be demonstrated. The work is presented as an early-access, peer-reviewed accepted article, subject to further edits before the final version of record.

Subject of Research: Modelling the ecological and economic trade-offs of forest carbon certification scenarios under climate and mortality uncertainty in Freiburg, Germany.

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

Article References: Lopez Scribante, R. B., Djahangard, M., & Yousefpour, R. (2026). Forest carbon certification under climate and mortality uncertainty: ecological and economic trade-offs of management scenarios in Freiburg, Germany. Carbon Balance and Management. https://doi.org/10.1186/s13021-026-00518-1

Image Credits: AI Generated

DOI: 10.1186/s13021-026-00518-1

Keywords: forest carbon certification, carbon credits, Freiburg, spruce forests, 3-PG-Hydro, net present value, mortality uncertainty, climate models, forest management, additionality, biomass, net primary production