More than carbon: SOC and CEC as integrative indicators of chemical recovery in tropical montane Atlantic forest soils – a case study from the Serra do Mar, Brazil

Purpose Tropical montane Atlantic Forests are increasingly being converted into pastures and silvicultural systems, altering soil functioning and compromising long-term ecosystem resilience. However, soil indicators capable of diagnosing functional recovery across restoration pathways remain poorly defined, particularly in highly weathered tropical mountain environments. Methods This study evaluated whether soil chemical properties can discriminate among alternative recovery trajectories in a tropical montane Atlantic Forest landscape in the Serra do Mar, southeastern Brazil. Within a single experimental site, four adjacent land-cover types were assessed along a 0–60 cm soil profile: interior secondary forest (ISF), edge secondary forest (ESF), eucalyptus plantation, and pasture. Soil samples ( n = 10 per land-cover type) were collected and analyzed for soil organic carbon (SOC), total nitrogen (N), pH, exchangeable nutrients, and cation exchange capacity (CEC). Results Forest restoration promoted substantial increases in SOC (+ 28%) and CEC (+ 28–44%) relative to anthropogenic land uses, with the highest values occurring in secondary forests. In contrast, pH and conventional fertility attributes showed limited capacity to distinguish restoration trajectories. Across the entire soil profile, SOC was strongly associated with CEC ( r = 0.97, p < 0.05), indicating that organic matter accumulation directly enhanced nutrient-retention capacity and soil chemical functioning. Notably, restored forests exhibited greater SOC, N, and CEC despite maintaining acidic conditions and elevated exchangeable Al concentrations. Conclusion Contrasting land uses revealed distinct patterns of soil chemical recovery, with forest systems sustaining higher SOC, N, and CEC despite persistent acidity and exchangeable Al. The strong SOC–CEC coupling highlights organic matter-mediated nutrient retention as a component of chemical resilience. Overall, these findings emphasize integrating nutrient-retention processes and vertical soil variability when assessing chemical recovery, while validation across replicated landscapes and restoration pathways is needed to establish SOC and CEC as robust monitoring indicators.