Deforestation impacts soil organic carbon and nitrogen pools and carbon lability under Mediterranean climates

Purpose Deforestation is one of the ecosystem disservices associated with accelerated loss of soil organic carbon (SOC) and nitrogen (TN). The objective of our study was to evaluate the impact of deforestation on the partition of SOC pools, TN content, and the SOC lability when compared with the well-stocked Red Pine (Pinus brutia Ten.) and Oak (Quercus coccifera) forests. Methods Geo-referenced replicated soils under Red Pine and Oak and their adjacent deforested shrubby sites (control) were sampled at 0 to 15 am and 15 to 30 cm depths from the Goksu catchment in Mediterranean region of Turkey. Soils were analyzed for SOC, active C (AC), passive C (PC), and TN contents. Results SOC content under both forests was higher compared to deforested shrubby sites; however, SOC under Red Pine was 22% higher than under Oak. A similar pattern in AC, PC, and TN pools was observed with a higher partition of PC:AC under both forests than under shrubby sites. The equivalent mass SOC, AC, PC, and TN stocks linearly and positively accounted for > 95% of the variability (R-2) in their stocks based on equivalent depth. However, the equivalent depth overestimated 5.6 +/- 0.71 Mg/ha to predict SOC storage based on equivalent mass. While the C and N pool indices (CPI and NPI) were higher under both forests compared to shrubby sites, SOC lability did not vary consistently among themselves. The CPI non-linearly and inversely accounted for 57% of the variability (R-2) in SOC lability, suggesting increasing SOC accumulation significantly decreased its lability. In contrast, the CPI accounted for 42% of the variability (R-2) in the NPI with a slope of only 0.57; suggesting both SOC and TN are disproportionately coupled in soil organic matter (SOM) under existing forest ecosystems. Conclusion Deforestation affected both SOC and TN stocks. However, increasing SOC sequestration under well-stocked forests is responsible for decreasing SOC lability (higher PC:AC) and partially decoupled C:N stoichiometry in SOM. Future research is needed to evaluate the impact of forest management practices on SOC and TN stocks and their lability across geographic landscape-scale under Mediterranean climates.