Simulation of climate change and thinning effects on Central European beech forests using 3-PGmix

Beech (Fagus sylvatica L.) forests in Central-Eastern Europe play a crucial role in carbon sequestration and biodiversity conservation, yet they are increasingly vulnerable to climate change stressors such as rising temperatures and prolonged droughts. These factors could disrupt established growth dynamics, potentially shifting forests from carbon sequestration to net carbon emissions. Thinning interventions may help counteract these effects by strengthening resilience and supporting their long-term stability. In this study, we use the 3-PGmix model to project forest growth of beech stands in Central Europe and examine thinning under future climate conditions (2020–2070). We calibrated and validated the 3-PGmix model for beech stands at two sites, one in Austria and one in the Czech Republic using Bayesian calibration via the Differential Evolution Markov Chain (DE-MC) algorithm. We adopted machine learning techniques to identify and evaluate the most influential parameters of the process-based model. Finally, we explored the potential impact of different climate change scenarios, CO2 levels, site conditions, and thinning scenarios on forest dynamics in the region. Our simulations reveal a more pronounced climate- induced biomass decline at the Austrian site (11–15% under elevated CO2; 17–19% without CO2 fertilization) compared to the Czech site (≤ 1.5% under elevated CO2; 6–7% without) relative to baseline. Average NPP from 2020 to 2070 at the Austrian site was 5.0, 3.7, and 3.9 ton ha−1 yr−1 on medium soil fertility soils and 8.2, 6.0, and 6.4 ton ha−1 yr−1 on high soil fertility soils under baseline, RCP 4.5, and RCP 8.5 scenarios, respectively at Czech site, corresponding values were 4.1, 4.1, and 4.1 ton ha−1 yr−1 (medium soil fertility) and 6.6, 6.6, and 6.7 ton ha−1 yr−1 (high soil fertility). Thinning improved both diameter and height growth, with diameter showing a stronger response to thinning intensity. Moderate and heavy thinning treatments outperformed light thinning and the control in terms of growth and productivity. In particular, moderate thinning led to a higher carbon stock and CO2 sequestration, especially under high soil fertility conditions and the RCP 8.5 scenario at the Czech site. Overall, the findings suggest that thinning and consideration of site-specific fertility, can play a key role in maintaining the stability, productivity, and carbon storage capacity of beech forests under future climate conditions.