Biomass Carbon Stocks and Soil Organic Carbon of Selected Native Tree Species Across Developmental Stages in Semi-Arid Mediterranean Environments

Forest ecosystems play an important role in climate change mitigation through carbon storage in biomass and soils. However, information on species-specific carbon sequestration in Mediterranean forests is still limited. This study evaluated biomass accumulation and carbon sequestration capacity of three native Mediterranean tree species (Quercus coccifera, Pinus halepensis, and Ceratonia siliqua) across different developmental stages, including young seedlings (1–3 years) and mature stands (20–80 years), in northern Jordan. Young seedlings were assessed using destructive biomass sampling, while mature stands were evaluated using species-specific allometric equations based on diameter measurements and soil carbon analyses. In addition, seedling and mature-tree evaluations were conducted under different environmental conditions. Carbon concentration varied significantly among plant organs, with generally higher values in leaves than in stems and roots. During early growth stages, young seedlings of C. siliqua exhibited greater annual carbon sequestration (0.55 kg tree−1year−1) than Q.coccifera and P.halepensis (0.1–0.2 kg tree−1 year−1). In mature stands, P.halepensis showed the greatest aboveground carbon storage, reaching approximately 588 kg C tree−1. Soil organic carbon stocks across the 0–60 cm soil profile varied among species, ranging from 17.9 kg m−2 under Q.coccifera to 24.1 kg m−2 under C.siliqua. Annual carbon sequestration rates derived from short-term field observations and allometric biomass estimations (including both above- and belowground components) differed markedly among species. P.halepensis showed the highest sequestration rate (>65 kg tree−1 yr−1), followed by Q.coccifera (∼23–24 kg tree−1 yr−1), whereas C.siliqua exhibited substantially lower rates (<5 kg tree−1 yr−1). These findings suggest that carbon sequestration capacity in Mediterranean forests varies with species, growth stage, and environmental conditions. This variability highlights the need to consider both species selection and site characteristics when designing restoration and afforestation programs aimed at maximizing long-term carbon storage and climate change mitigation in dryland ecosystems.