## 3 Results and Analysis
### Spatiotemporal Evolution of Carbon Sink and SDE Analysis
#### 3.1.3 Analysis of Spatial Changes in the Carbon Sink Value  
To investigate the spatial changes in the carbon sink value during the study period, this paper used the spatial distribution maps of the carbon sink (500 m) in the SOFRs in 2001 and 2019. Combined with the function of map algebra in ArcGIS 10.7, the growth rate of the carbon sink at the grid scale was calculated. Then, based on the clustering of the results, the spatial regional carbon sink growth was classified, and the spatial change trend map of the carbon sink in the studied region from 2001 to 2019 was drawn (Figure 4). ArcGIS 10.7 then reclassified the results and calculated the area and corresponding proportions of the five changing trends.  
From the perspective of the growth rate of the spatial carbon sink in the 40 key SOFRs in Heilongjiang Province, the carbon sink of the SOFRs from 2001 to 2019 showed an \"overall increase and small-scale reduction\" phenomenon (Figure 4). Among them, the area where the growth rate of the carbon sink was between 0.151 and 0.300 was the largest, accounting for 36.15%; the second largest growth rate of the carbon sink was between 0.001 to 0.150 and 0.301 to 1.353, accounting for 29.90% and 27.05%, respectively. From 2001 to 2019, the total proportion of positive growth in the carbon sink value in the SOFRs in Heilongjiang Province reached 93.10%. The areas with negative growth rates were divided into two levels, namely, \(-\)0.908\(--\)0.086 and \(-\)0.087\(-\)0.000, and the corresponding area proportions were 2.06% and 4.84%, respectively. Areas with a growth rate of 0.151 or more accounted for 63.20%, indicating that the carbon sink in most regions increased significantly during the study period. Corresponding to the analysis in Figure 3, the carbon sinks of the regions with higher growth rates were lower, which proved that the initial value was lower and the growth potential was greater. However, the regions with growth rates of 0.001 to 0.150 and negative growth rates were mostly located in regions with high carbon sinks, and their growth space was small.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & **Shape** & **Shape** & \multirow{2}{*}{**CenterX/m**} & \multirow{2}{*}{**CenterY/m**} & \multirow{2}{*}{**XStdDist/m**} & \multirow{2}{*}{**YStdDist/m**} & \multirow{2}{*}{**Rotation/\({}^{\circ}\)**} \\  & **Length/m** & & & & & & \\ \hline
2001 & 1,328,061 & 130,954.8 & 1,871,536 & 5,231,694 & 164,395.2 & 253,577.7 & 155.3266 \\
2003 & 1,302,777 & 125,081.2 & 1,864,519 & 5,235,355 & 158,822.  
The possible reasons for the negative growth of the carbon sink in some regions are as follows. First, the DongFanghong Forest Region has a large scale of forest management and high timber output, which makes forest management and protection more difficult. Second, after 1998, forest management and protection were strengthened, resulting in a decrease in logging, but the geographical distribution was wider. Therefore, there is illegal carbon burning in forest areas with inconvenient transportation and low population density. In addition, it takes a certain period for the area of unforested land to increase as a result of forest tending and other methods to transform into forest land. Therefore, there may be a decrease in the carbon sink value during the study period.