Ecological succession influences vegetation structure, ecosystem functioning, and soil properties. This study evaluated soil changes along a Mediterranean successional gradient, from open gaps (G) to low maquis (LM) and mature high maquis (HM), in the Castel Volturno Nature Reserve (CE, Italy). Soil samples (0–10 cm) were collected over two consecutive years in early spring and early summer. Physicochemical parameters (soil organic matter-SOM, total C and N, pH) and biological indicators (soil respiration-Resp, microbial biomass-Cmic, metabolic quotient-qCO₂, mineralization rate-qM, and functional diversity) were analyzed to assess the effects of succession on soil quality.

The results revealed progressive changes in soil functions along the vegetation successional gradient, with increasing vegetation complexity. SOM and C/N increased progressively along the successional gradient, and a significant decline was observed during summer in both LM and HM. Soil pH also increased significantly along the successional sequence. In contrast, N decreased from G to HM and showed significant seasonal variation only in LM soils, with lower values recorded during the summer sampling period. The quantity and quality of soil organic matter strongly influenced the microbial component, affecting both Cmic and functional diversity. Both variables increased along the successional gradient, reaching their highest values in HM soils, particularly during the summer sampling period. In contrast, Resp did not exhibit a clear trend associated with the successional gradient. Both the qCO₂  and qM were highest in LM soils.

These findings demonstrate that ecological succession promotes the simultaneous recovery of soil functions and plant functional diversity in Mediterranean shrublands. The increasing complexity of vegetation communities contributes to improved soil fertility, C storage, and ecosystem resilience, highlighting the importance of conserving mature maquis and facilitating natural successional processes in restoration strategies aimed at mitigating the impacts of land-use change and climate change in Mediterranean environments.