3.3 SOC and TN storage calculated using the FD and ESM methods
In recent years, uncertainties from the methods estimating SOC/TN caused by BD change have attracted more attention (Lee et al., 2009; Toledo et al., 2013). This study compared SOC and TN storage between two estimation methods (i.e., FD, Fig. 2a; ESM, Fig. 2b).
Not surprisingly, the lnRR of SOC after deforestation was -0.43 (95%CI : [-0.48, -0.38], P < 0.05) based on the FD and -0.66 (95%CI : [-0.74, -0.58], P< 0.05) based on the ESM. This means that deforestation calculated by the FD caused 34.8% carbon loss, while the ESM results showed that the SOC loss was as high as 48.2%. Similarly, thelnRR of TN storage estimated by the FD and ESM were -0.29 (95%CI : [-0.38, -0.21], P < 0.05) and -0.62 (95%CI : [-0.78, -0.46], P < 0.05), respectively. The loss efficiency of TN storage was 25.4% and 46.0%. Obviously, there were notable variations in the estimation of SOC and TN storage if using alternative methods (Fig. 2a, paired t-test: P< 0.01). On the other hand, the FD and ESM calculations showed that land restoration could significantly increase SOC and TN storage (Fig. 2b). The lnRR of SOC and TN storage calculated by the FD and ESM were 0.23 (95%CI: [0.17, 0.28], P < 0.05), 0.25 (95%CI : [0.17, 0.32], P < 0.05), 0.16 (95%CI : [0.10, 0.21], P < 0.05), and 0.23 (95%CI : [0.14, 0.31], P < 0.05), respectively. The FD and ESM evidently provided different estimations (Fig. 2b, paired t-test:P < 0.01), which led to uncertainties in estimating SOC and TN storage. Thus, we should carefully select the estimation method when calculating the SOC and/ or TN storages.