## 4 Results
### Remote Sensing-Derived Forest Carbon Sinks Estimates in the Qinba Mountain Region
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Forest Age Grouping** & **Number of Grids** & **Percentage of Total Grids** \\ \hline
1–10 & 4 & 0.12\% \\
10–20 & 86 & 2.51\% \\
20–30 & 298 & 8.70\% \\
30–40 & 364 & 10.63\% \\
40–50 & 414 & 12.09\% \\
50–60 & 499 & 14.57\% \\
60–70 & 454 & 13.26\% \\
70–80 & 411 & 12.00\% \\
80–90 & 348 & 10.16\% \\
90–100 & 180 & 5.26\% \\
100–110 & 145 & 4.23\% \\
110–120 & 197 & 5.75\% \\
120–130 & 22 & 0.64\% \\
130–140 & 1 & 0.03\% \\ \hline \hline \end{tabular} Note: Number of Grids represents the quantity of grids in that forest age group, while Percentage of Total Grids represents the proportion of grids in that forest age group relative to the total number of grids.  
\end{table} 
Table 6: Classification of forest ages in the Qinba Mountain area and grid count distribution. Figure 9: Distribution of forest ages in the Qinba Mountain area. Note: The greener the color, the older the forest age; the browner the color, the younger the forest age. In the Qinba Mountain area, there are 2664 natural forest grids and 437 plantation forest grids. The ratio of plantation forests to natural forests is 16.4%, which serves as the typical proportion (P) for plantation forests relative to natural forests in the region. By combining the forest age and type data, we can calculate the carbon source/sink ratio for each forest age group. Upon analyzing the data presented in Table 8, the following conclusions can be drawn:  
For forests aged between 10 and 70 years, 91.67% of the carbon source/sink ratios exceed 16.4%, indicating that plantation forests in this age group generally have stronger carbon source and sink capabilities than natural forests. These plantation forests account for 10.64% of the total grid area. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Number of Grids** & **Percentage of Grids** \\ \hline Natural Forest & 2770 & 85.07\% \\ Plantation Forest & 486 & 14.93\% \\ \hline \hline \end{tabular} Note: The horizontal title reflects the number of grids for different forest types and the proportion of these grids relative to the total number of grids, while the vertical title reflects the different forest types.  
\end{table} 
Table 7: Proportion of different forest types in the Qinba Mountain area. Figure 10: Spatial distribution of natural and plantation forests in the Qinba Mountain area. Note: Light green represents natural forests, and dark green represents plantation forests. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Forest Age Grouping** & **Carbon Source Ratio** & **Carbon Sink Ratio** \\ \hline
1–10 & 0.00\% & 0.00\% \\
10–20 & 33.33\% & 31.91\% \\
20–30 & 51.52\% & 23.03\% \\
30–40 & 18.37\% & 19.31\% \\
40–50 & 28.99\% & 19.03\%  
Specifically, for forests aged between 10 and 30 years, the carbon source and sink ratios reach their highest values, indicating that plantation forests in this age range possess the strongest carbon source and sink capabilities. These forests represent 2.29% of the total grid area. In contrast, for forests aged between 70 and 130 years, 90.91% of the carbon source/sink ratios are below 16.4%, suggesting that natural forests in this age group exhibit stronger carbon source and sink capabilities than plantation forests. These natural forests account for 35.05% of the total grid area. Within the 70 to 90-year age group, both the carbon source and sink ratios are at their lowest, highlighting that natural forests in this range have the most significant carbon source and sink capabilities. These forests make up 21.64% of the total grid area. In summary, plantation forests show stronger carbon source and sink capabilities when aged between 10 and 70 years, while natural forests exhibit superior carbon source and sink capabilities when aged between 70 and 130 years. Plantation forests have the strongest carbon source and sink capabilities at ages between 10 and 30 years, while natural forests excel in this regard between the ages of 70 and 90 years.