Aboveground carbon dynamics following plantation thinning to establish a silvopastoral system in subtropical Australia

Abstract Understanding the impact of plantation thinning for silvopastoral systems (SPS) on carbon storage is crucial for the development of grazing systems to integrate production and carbon goals. This study compared aboveground carbon (AGC) among a SPS established through thinning the Corymbia hybrid plantation in 2021, an open pasture (OP), a timber plantation (TP), and an unthinned plantation (UP) in subtropical Australia. Thinning had a positive effect on tree diameter and AGC. Over 3.2 years following thinning, SPS had the highest diameter (26.5 ± 0.9 cm), which was 21.0% higher than TP and 29.3% larger than UP. Correspondingly, SPS increased annual diameter increment by 87% and 216% compared to TP and UP, respectively. By 2025, SPS had 77% higher tree-level AGC than UP, although its stand-level AGC (24.63 Mg C ha −1 ) remained 56% lower than UP (55.66 Mg C ha −1 ). Annual tree-level AGC increment in SPS was 138% higher than in TP and 280% higher than in UP, whereas annual stand-level AGC increment did not differ significantly among these treatments. SPS exhibited the highest ground vegetation carbon (1.22–1.61 Mg C ha −1 ) but the lowest tree litter carbon (1.37–1.45 Mg C ha −1 ) among tree-based treatments, while supporting a ground vegetation carbon level comparable to OP. These findings indicate that SPS can enhance AGC relative to OP, while promoting tree growth and increasing tree-level AGC and ground vegetation carbon compared to TP and UP. Thinning plantations for SPS therefore might provide a promising strategy to enhance AGC storage in subtropical Australia.