Boundary-resolved dynamic assessment of mitigation in forest–wood product systems

Forest–wood systems are increasingly positioned as climate mitigation instruments, yet reported carbon payback times range from near-instantaneous benefit to multi-decade debt. This divergence shapes carbon markets, offset protocols and investment decisions, but it remains unresolved whether it reflects differences in system physics or differences in accounting design. Here we show that reported mitigation outcomes are boundary-conditioned properties of attribution rather than intrinsic properties of forest–product systems. We develop a Boundary-Resolved Dynamic Ledger (BRDL) that applies alternative reporting operators to a single conserved carbon ledger, enabling direct comparison of full-ledger and disturbance-rebased framings without altering underlying biophysical fluxes. In a mill-scale case study with total anthropogenic emissions of 676.09 kg CO 2 eq m −3 , apparent “instant” payback emerges only when inherited forest stock accumulation is commingled with post-disturbance change; rebasing to the disturbance year yields a carbon payback of 6 years under identical carbon dynamics. Residue routing modifies early atmospheric trajectories but does not overturn the regrowth-dominated control of long-horizon magnitude. When mitigation is temporally distributed but costs are front-loaded, discounting structurally amplifies economic thresholds, revealing that feasibility is governed by the geometry of credited abatement rather than by physical removal alone. By separating carbon conservation from claim construction, BRDL reframes forest-based mitigation as a problem of attribution architecture, providing a transparent basis for evaluating what counts, when it counts, and under what liability.