## 4 Discussion  
### Dynamics of Forest and Grassland Ecosystems  
Between 2000 and 2020, the forest and grassland ecosystems in the Altai Mountains National Park Candidate Area underwent substantial shifts, characterized by a significant decline in grassland cover alongside a notable increase in forested areas [66; 67]. The spatial distribution of forest and grassland frequencies, as well as shifts in their locations, underscores the critical role of key protected areas in maintaining ecosystem stability [51; 68]. In addition to interannual fluctuations, we tracked long-term trends in forest and grassland dynamics. While grassland restoration at the global level exceeds grassland degradation, on a smaller scale, such as within the study area, grassland degradation considerably surpasses restoration [32]. However, the extensive forest expansion observed in China since the 1980s parallels the significant increase in forest cover in the study area [69]. These changes are closely tied to local policies, with the government implementing several forest protection programs, such as the Three-North Shelterbelt Forest Program and the Natural Forest Protection Project. However, the grassland restoration initiative, which involves returning grazing lands to grassland, was introduced later and has yielded limited results. Afforestation activities in the Altai Mountains have been predominantly carried out on grasslands, resulting in a reduction in grassland area by one-fifth and a subsequent 88% increase in forest cover within the Altai Mountains National Park Candidate Area (Figure 4). This change has likely affected critical ecological processes such as groundwater recharge, and may have altered soil bacterial and fungal communities [12; 70; 71; 72]. Furthermore, the Altai Mountains are recognized as part of the \"Global 200\" biodiversity priority areas, functioning as an essential corridor for species dispersal and genetic exchange across China, Mongolia, Russia, and Kazakhstan. This transboundary connectivity significantly strengthens regional biodiversity and enhances ecosystem resilience against environmental  
Figure 10: Area differences in ecosystem loss across different aggregated protected areas from 2000 to 2020: (**a**) forest ecosystem and (**b**) grassland ecosystem. (ATT represents the “average treatment effect on the treated” in protected areas, specifically the estimated average effect of established protected areas in mitigating forest and grassland loss between 2000 and 2020. A significantly negative ATT suggests that the establishment of protected areas effectively reduces ecosystem loss. Kansas: Xinjiang Kanas National Nature Reserve. Baihaba: Baihaba National Forest Park. Keketuohai: Irtysh Keketuohai Wetland Nature Reserve. Habahe: Xinjiang Habahe Birch National Forest Park. Jiadengyu: Jiadengyu National Forest Park. Kanas GeoPark: Xinjiang Burqin Kanas Lake National GeoPark. Akeqi: Xinjiang Habahe Akeqi National Wetland Park. Burqin: Xinjiang Burqin National GeoPark).  
disturbances [73]. The forest-grassland mosaic in the Altai Mountains supports a wide range of endemic species, promotes landscape connectivity, and plays a pivotal role in transboundary conservation efforts. In light of this, we emphasize the importance of adopting integrated management strategies that transcend national and administrative boundaries to effectively protect this ecologically critical region [74; 75].  
We examined land cover type conversions in the study area to assess the patterns of restoration and degradation, recognizing the potential limitations in our choice of indicators. Vegetation indices, such as Net Primary Productivity (NPP) [76] and the Normalized Difference Vegetation Index (NDVI) [77], remain effective tools for monitoring land degradation and desertification processes.