TiMBA - Timber market Model for policy-Based Analysis: Validation of a partial equilibrium model

TiMBA (Timber market Model for policy-Based Analysis) is a partial economic equilibrium model that simulates the global forestry sector, capturing economic interactions from raw material extraction to the processing of intermediate and end products (TI-FSM et al. 2025). The model underwent an intercomparison to ensure its quality and functionality. Information about the validation process and results is published in this working paper. Model validation, as emphasized by Buchholz (2023), is a central, iterative component of model development that confirms the plausibility and reliability of model outputs. Distinct from verification (testing inputs, assumptions, and code) and calibration (adjusting parameters to improve fit), validation assesses the realism and accuracy of model outcomes through systematic comparison with empirical data or alternative models. The validation of TiMBA was conducted using a model intercomparison approach, comparing its results with other established partial equilibrium models. On the supply side, validation draws on the intercomparison study by Daigneault et al. (2022) within the Forest Sector Model Intercomparison Project (ForMIP), which includes the Global Timber Model (GTM), the Global Biosphere Management Model (GLOBIOM), and the Global Forest Products Model (GFPM). On the demand side, comparisons are made against GFPM results from Morland and Schier (2020). Both studies are based on Shared Socioeconomic Pathways, providing a standardized scenario framework for assessing long-term developments in the global forest sector between. Graphical analyses compare TiMBA's projections across regions and scenarios, focusing on key indicators such as forest area, industrial roundwood harvest, and wood product demand. Despite differences in baseline years and structural assumptions among models-such as in technological change, forest dynamics, and market elasticities-TiMBA shows a high degree of internal consistency and external plausibility. Globally, TiMBA's industrial roundwood harvest projections are in the middle of the multi-model range by 2100, while its forest area projections position it in the upper third of the scenario range, closely aligned with GFPM results. On the demand side, trends projected with TiMBA align closely with GFPM in the sawnwood sector, display mixed results for wood-based panels, and diverge somewhat in the paper sector. The differences are largely attributable to contrasting model structures and assumptions. Overall, TiMBA demonstrates strong credibility as a policy- analysis tool, with robust, plausible, and comparable results across global and regional levels. Its validation confirms that TiMBA provides a balanced and competitive representation of future developments in the forest sector, supporting informed decision-making in forestry policy and management. [...]