Impact of coppice conversion to high forest as a carbon farming practice: a case study from broadleaved forests in central Italy

The conversion of abandoned coppice forests into high forests is promoted in Europe as a sustainable forest management strategy and as a potential carbon farming intervention under the EU Carbon Removal Certification Framework (CRCF, European Union, 2024), replacing low-input, low-output systems with practices aligned to long-term carbon sequestration goals. While the expected increase in aboveground biomass (AGB) carbon stock is supported by prior research, the effect of this transition on soil organic carbon (SOC) remains insufficiently quantified (Chiti et al., 2026). This study evaluates carbon stock variations across five ecosystem pools, AGB, belowground biomass (BGB), litter, deadwood, and SOC, in two broadleaved forest types, beech and mixed broadleaves, in central Italy. For each forest type, three abandoned coppice stands and three coppices converted to high forest were selected. Conversion occurred 5 years prior in mixed broadleaved forests and 18 years prior in beech stands. Biomass was measured using forest inventory protocols and species-specific allometric equations, while SOC was quantified across the 0–30 cm mineral soil layer by dry combustion (CHN) following carbonate removal.

In beech forests, AGB carbon stock increased from 59.00 Mg C ha⁻¹ (control) to 77.88 Mg C ha⁻¹ in the converted sites, with statistically significant differences (p = 0.001). In mixed broadleaved stands, no statistically significant differences were observed five years after conversion (46.47 vs. 49.70 Mg C ha⁻¹, p = 0.8147).

SOC stocks across the 0–30 cm profile decreased in both forest types following conversion. In mixed broadleaves, total SOC declined from 59.44 Mg C ha⁻¹ to 43.08 Mg C ha⁻¹, in beech, from 89.83 to 78.47 Mg C ha⁻¹. While no significant differences were observed at individual depth layers (0–5, 5–15, and 15–30 cm), total SOC over the 0–30 cm profile was significantly reduced following coppice conversion.

Litter carbon stocks increased significantly in mixed broadleaved forests (from 1.54×10³ to 2.92×10³ kg C ha⁻¹, p = 0.0022), while a non-significant decrease was observed in beech stands. Deadwood carbon stocks remained stable in mixed broadleaves and showed slight reductions in beech.

The results demonstrate that conversion to high forest enhances carbon storage in aboveground biomass, particularly in older stands, while SOC exhibits early-phase declines that may persist in the short to medium term. This highlights the importance of pool-specific and time-sensitive assessment frameworks when evaluating the climate mitigation potential of forest management practices. The inclusion of coppice-to-high forest transitions in CRCF-aligned carbon farming schemes is supported, provided that monitoring protocols capture dynamics across all major carbon pools.

- Chiti, T., Rey, A., Abildtrup, J., et al. (2026). A review of forest management practices potentially suitable for carbon farming in European forests. Journal of Environmental Management, 398, 128391. https://doi.org/10.1016/j.jenvman.2025.128391

- European Union. Regulation (EU) 2024/3012 of the European Parliament and of the Council of 27 November 2024 establishing a Union certification framework for permanent carbon removals, carbon farming and carbon storage in products (Regulation 2024/3012) https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=OJ:L_202403012