Hemiboreal Stand Development and Living Biomass Carbon Stocks: An Ontogenetic and Typology-Based Assessment Using...

Carbon stocks in hemiboreal forests are frequently assessed using dominant-species or growing stock metrics, which may obscure ontogenetic and demographic processes governing biomass turnover. This study applied a process-based framework integrating succession theory, forest typology, and ontogenetic strategies to Lithuanian National Forest Inventory data reorganized by forest type-series. Three research expectations were evaluated: whether typology-based classification reveals patterns not visible under dominant-species reporting (H0), whether stand composition converges toward phase-typical configurations (H1), and whether fertile four-phase forests exhibit higher productivity and earlier CO₂ flux reversals than three-phase forests (H2). H0 was rejected: forest type-series reorganization revealed contrasts in species assembly, stand structure, and carbon dynamics not detectable under dominant-species classification. H1 was supported: three-phase forests converged toward colonizer-dominated assemblies, while four-phase forests sustained multi-species, multi-cohort canopies with persistent broadleaved contributions. H2 was supported: four-phase forests exhibited higher gross volume increment and transitioned to negative CO₂ accumulation 40 years earlier (61-80 years) than three-phase forests (101-120 years). Across both pathways, growing stock volume increased while CO₂ accumulation turned negative in older stands, demonstrating divergence between cumulative biomass stock and net annual carbon flux. Forest Inventory data reorganized by forest type-series functioned as a process-based diagnostic tool supporting climate- and biodiversity-oriented management.