## 4 Results
### Remote Sensing-Derived Forest Carbon Sinks Estimates in the Qinba Mountain Region  
3.1 Spatiotemporal Variation Characteristics of Remote Sensing Inversion Results of Forest Carbon Sinks in the Qinba Mountain Area  
Using remote sensing inversion, the forest carbon sinks estimates for the Qinba Mountain region from June to September during the years 2011-2018 were derived, as illustrated in Figure 7. Over the study period, the forests in this region were found to sequester approximately 24.51 TgC annually during the growing season. Figure 6: Scatter plot of estimated ecosystem respiration (R\({}_{\text{eco}}\)) vs. literature-based ecosystem respiration estimates. Note: The black dots represent the scatter plot of estimated R\({}_{\text{eco}}\) versus literature-estimated R\({}_{\text{eco}}\), and the blue line represents the linear regression line between the two. Figure 7: Multi-year average remote sensing inversion of forest carbon sinks in the Qinba Mountain area (June–September, 2011–2018). Note: The red color represents carbon sources, and the green color represents carbon sinks; the deeper the color, the stronger the capacity of the carbon source or sink. \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\alpha\) & \(PC_{max}\) & \(R_{ref}\) & \(E_{0}\) \\ \hline
7.497065851 & 113.3945853 & 8.74436803 & 0.73069437 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Sensitivity analysis of fitted parameters in the ecosystem respiration model for the Huoditang forest area. From a regional perspective, the high-value areas of forest carbon sinks in the Qinba Mountain area from 2011 to 2018 were primarily concentrated in the western and some central forest regions, with an average value of approximately 36.79 g C m\({}^{-2}\) month\({}^{-1}\). In contrast, the low-value areas were mainly located in the southeastern and northern parts of the region, with an average value of about 7.75 g C m\({}^{-2}\) month\({}^{-1}\). As observed from the remote sensing inversion results of forest carbon sinks in the Qinba Mountain area from June to September for each year between 2011 and 2018 (as shown in Figure 8), the western part of the region consistently exhibited high carbon sinks values. In contrast, the southeastern part generally showed low carbon sinks values, except for the years 2012 and 2015. The northern region has consistently maintained low carbon sinks values, while the eastern part displayed notable interannual variability. Figure 8: Annual remote sensing inversion results of forest carbon sinks in the Qinba Mountain area from June to September (2011–2018). Note: The left side represents odd-numbered years, and the right side represents even-numbered years, with the years increasing from top to bottom. 3.2 Relationship Between Forest Carbon Sinks Remote Sensing Inversion Results and Forest Age and Type in the Qinba Mountain Area  
The distribution of forest ages in the Qinba Mountain area (as shown in Figure 9) reveals the following patterns: In the western region, forests aged between 100 and 130 years are concentrated; in the central region, forests predominantly range from 60 to 90 years old; while in the northeastern, southeastern, and northern regions, forests aged between 10 and 50 years are most prevalent. The forest ages in the Qinba Mountain area are categorized into ten-year intervals, resulting in a total of 14 groups (as shown in Table 6). The majority of forests in the Qinba Mountain area are concentrated in the 30-90 year age range, accounting for 72.71% of the total forest area. Within this range, forests aged 50-60 years represent the largest proportion, making up 14.58% of the total forest area in the region. The distribution of forest types in the Qinba Mountain area (as shown in Figure 10 and Table 7) reveals that natural forests dominate the region, comprising 85.07% of the total forest area. In contrast, plantations account for 14.93% of the total forest area.