Pinus radiata (D. Don) intensively managed plantations, that dominate Chilean forest landscape, have been challenged on their potential for carbon sequestration. Therefore, under this scenario, our study considered to account for potential under recognized carbon (C) sequestration pools and the following objectives: : i) above and belowground biomass (TBC), forest floor (FFC), mineral soil (SOC) and total C stocks (TCS) of adult stands at sandy and volcanic ash soils sites; ii) model the effect of stand productivity and soil type on C stock; and iii) model the C stock with respect to environmental, soil and site variables. Ten Pinus radiata stands were selected across a productivity gradient in sandy and volcanic ash soil sites. At each site, three 1000 m² plots were established. TBC was determined using allometric equations, while SOC was sampled to a depth of 1 meter. Litter and woody debris were sampled to assess FFC. Results showed that recent ash soil sites presented a slightly higher TBC than sandy soil sites (178.5 Mg ha^-1 vs 172.4 Mg ha^-1 respectively), and significantly higher SOC for recent ash soil sites (281.4 Mg ha^-1) than sandy soil sites (139.9 Mg ha^-1). In both soil types, FFC represented the lowest carbon stock of stands, with 2.9 % for recent ash and 5.8 % for sandy soil sites. There was a strong relationship between productivity with SOC and TCS (r²= 0.91, p < 0.001) when considering soil type. The variables related to better nutritional and soil water conditions had a positive effect on the total C stock, and there was a negative effect on the variables related to water stress. Differences in C stocks according to soil type and climate showed the value of developing site-specific models to adequately estimate C stocks.