## 4 Results
### Ecological Source Identification Model Performance Analysis  
As mentioned in the methodology, ESs within the TRHR from 2000 to 2020 were determined by applying a zoning model built upon the CAZ and ABF selection criteria, considering the overlapping results of both methodologies. As shown in Figure 6, ES identification results are diverse between different ecological priority rules. The CAZ method extracted source sites that are ecologically preferred. However, the resulting patches were smaller and exhibited a more random distribution. In contrast, the ABF method produced more continuous results but overlooked the significance of water bodies as crucial ecological source providers. So, it is necessary to combine the two extraction methods.  
Based on Table 2, the temporal changes reveal a sustained presence of potential areas for 20 years. The conversion of areas into ES sites shows an increasing trend over time, with 20% of the total TRHR being recognized as ecological source areas. These identified ESs provide a high ESV and carbon sinks. From 2000 to 2020, the ecological patches fluctuated insignificantly and primarily had an interconversion of the top 20% and 30% of areas. Meanwhile, the top 10% of total source areas remain relatively stable, showing minimal and non-significant changes.  
Regarding spatial distribution depicted in Figures 7 and 8, ES exhibits distinct characteristics. In the northwest, there is a discrete and sparse arrangement, while a more consolidated, block- and surface-like distribution is evident in the southeast. From 2000 to 2010, the spatial distribution of ES was stable. The top 10% of areas are mainly distributed in Henan Mongol Autonomous Prefecture and Jigzhi County, which are sporadically distributed in the central regions. The top 20% of ESs are spread in a ring around the top 10% of ES areas.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Year**} & **Potential Area** & **Top 30\% Area** & **Top 20\% Area** & **Top 10\% Area** \\  & **(km2)** & **(km2)** & **(km2)** & **(km2)** \\ \hline
2000 & 319,917 & 32,061 & 29,836 & 29,775 \\
2005 & 318,850 & 33,349 & 30,081 &  
Since 2010, Zhalin lakes and others in the northwest have transitioned gradually from potential areas to the top 30% of areas, while the top 10% of ES patches have decreased in the central region. The establishment of the Sanjiangyuan National Park in 2012 has played a positive role in maintaining and cultivating ecological sources. A discernible trend in some southeastern areas indicates an initial increase followed by a subsequent decrease from 2000 to 2020. Notably, in 2020, certain areas classified initially as the top 10% have been downgraded to the top 20%, but other areas are still showing an improving trend.  
As depicted by [PERSON] et al. [78], the grassland coverage and productivity increased while grassland degradation was controlled and desertification was prevented after the first phase of the Ecological Project (2005-2012) in the TRHR. It is also reflected in our results. Although the potential area still covers huge areas in the TRHR, some of potential areas, which mainly consist of grassland, were gradually transferred to the top 30% of areas gradually. According to [PERSON] et al. [79], the restoration area greatly increased during the implementation of the second phase of the Ecological Project. Thus, it is not hard to understand that the potential of ESs will change into the top 30% of ESs. However, the degraded top 10% of ESs are distributed in the eastern part of the TRHR. These degraded  
Figure 8: ES composition and the temporal changes in the TRHR.  
Figure 7: Spatio-temporal patterns of priority areas of the TRHR from 2000 to 2020.  
areas are mainly dominated by human activities, which will offset the temporary ecological restoration, causing ES degradation.