Correlation coefficients1 of soil carbon concentrations and relative soil carbon stock differences2 with explanatory variables at three depths.

1Spearman rank correlation test, marginally significant at †P≤0.1, and significant at *P≤0.05, and **P≤0.01.2Relative soil carbon stock differences were calculated as carbon stock in rubber plantation minus carbon stock of the reference secondary forest divided by carbon stock of the reference secondary forest multiplied by 100. Relative soil carbon stock differences were correlated with explanatory variables of the rubber plantations.