3.1 Ecological type improvement
Based on the remote sensing monitoring data of the area evolution of forest land, grassland, cultivated land, wetland and other ecosystems within the scope of the implementation of the Ruoergai Mountain water Project, a single monitoring and evaluation model was introduced to estimate the area growth efficiency assessment results of important ecosystems (Fig. 5a).
3.2 Landscape pattern optimization
The optimization, monitoring and evaluation of landscape pattern of ecological restoration projects (Wu, 2000) was carried out with reference to the Technical Guide for Assessment of Ecological Protection and Restoration Effectiveness.
3.2.1 Landscape connectivity
The landscape pattern reflects the extent of human influence on the landscape to a certain degree (Wan et al., 2015). Using multi-source remote sensing identification information and referring to monitoring and evaluation data from ecological environment departments, natural resources departments, implementing units, or evaluation units, Conefor software was employed for calculation. Scores were assigned based on the improvement in the overall connectivity degree of the ecosystem within the evaluation range. The evaluation results are illustrated in Fig. 5b.
3.2.2 Landscape fragmentation
It represents the fragmentation degree of landscape segmentation and reflects the degree of human disturbance to the landscape to a certain extent (Wang, 2011). Scores are assigned based on the improvement in the overall fragmentation degree of the ecosystem within the assessment range, and the assessment results are shown in Fig. 6a.
3.2.3 Landscape diversity
The Simpson's landscape diversity index (SHDI) can effectively reflect landscape heterogeneity and is particularly sensitive to the unbalanced distribution of various patch types within the landscape. Furthermore, in a landscape system, the greater the diversity of land use, the higher the degree of fragmentation, and consequently, the higher the SHDI value (Zhang et al., 2020). The evaluation results are illustrated in Fig. 6b.
3.3 Ecological function enhancement
Based on the natural ecological background and the goals and tasks of the Zoige Mountain Water Project, and with reference to the existing monitoring and evaluation system, key ecological function improvement indicators were identified. These include vegetation coverage, biological abundance, water network density, water source conservation, soil conservation, wind prevention and sand fixation, ecological carbon sequestration, and net primary productivity.The monitoring and evaluation of these indicators are conducted in accordance with the "Technical Specifications for National Ecological Status Investigation and Evaluation" and "Technical Specifications for Ecological Environment Status Evaluation".
3.3.1 Vegetation coverage and biological abundance increased
Improvement in Vegetation Coverage: The evaluation assessed the degree of improvement in vegetation coverage within the region resulting from the implementation of the restoration project (Zhang et al., 2024(a)). This was quantified using the estimated change value of the Normalized Difference Vegetation Index (NDVI) per unit area in the evaluation area. The evaluation results are presented in Fig. 7a.。
Increase in Biological Abundance: The evaluation assessed the degree of increase in biological abundance and diversity in the restoration project area, expressed using the Biodiversity Change Index (Zhang, 2023). The evaluation results are presented in Fig. 7b.
3.3.2 The density of water network and water source conservation are improved
Water Network Density Improvement: The evaluation utilized current status and change data regarding water area range, length, and water resource volume per unit area (Liu et al., 2010) to analyze and estimate the regional improvement in water network density. The evaluation results are depicted in Fig. 8a.
Water Conservation Improvement: Focusing on the critical goal of enhancing water conservation in the upper reaches of the Yellow River, this study comprehensively estimated ecosystem area, quality, water resources, and climate (Lin et al., 2020). This analysis aimed to determine the increase in available water resources within the restoration and treatment project area. The assessment results are presented in Fig. 8b.
3.3.3 Soil conservation, windbreak and sand fixation capacity improved
Improvement in Soil Conservation Ability: The enhancement of soil conservation ability, including the reduction of rainwater erosion and soil loss, as well as the prevention of sediment accumulation through ecosystem protection and treatment measures, was calculated using the modified Revised Universal Soil Loss Equation (RUSLE) (Yue et al., 2023). The evaluation results are presented in Fig. 9a.
Improvement in Windproof and Sand-fixing Ability: The restoration and treatment projects aimed to increase the soil's resistance to wind and reduce wind erosion and sand damage. The Revised Wind Erosion Equation (RWEQ) model (Huang et al., 2022) was utilized for budget prediction. The evaluation results are shown in Fig. 9b.
3.3.4 Net primary productivity and ecological carbon sequestration were improved
Increase in Net Primary Productivity: This refers to the amount of organic matter accumulated per unit area per unit time by green vegetation after deducting its own respiratory consumption. The classical Carnegie-Ames-Stanford Approach (CASA) model (Yuan et al., 2022) was adopted for prediction and estimation based on remote sensing monitoring and collected data. The evaluation results are presented in Fig. 10a.
Improvement in Ecological Carbon Sequestration: Carbon sequestration serves as an evaluation index of ecosystem carbon sequestration function, obtained by subtracting soil respiration (RS) consumption from net primary productivity (NPP). The evaluation results are depicted in Fig. 10b.。
3.4 Evaluation results and analysis
Based on the estimated monitoring index values of the Zoige Mountain Water Project and utilizing the comprehensive assessment method model calculations, the evaluation results of ecological restoration effectiveness were derived, as illustrated in Fig. 11. By 2023, the area demonstrating a significant ecological restoration effect will constitute 1.21% of the total study area. These areas are predominantly located in the grassland and wetland ecological protection and restoration unit of the Heihe River Basin in Ruoergai County, as well as the land comprehensive regulation and forest ecological protection and restoration unit of the Bailong River basin. These areas are mainly within the management scope of sub-projects such as water conservation improvement comprehensive management, wetland protection improvement, desertification land management, and rat wasteland comprehensive management. These efforts have notably enhanced regional water conservation and vegetation coverage while reducing ecological and environmental issues such as land desertification and soil erosion.Areas exhibiting a good ecological restoration effect account for 7.79% of the total study area. These areas are mainly distributed in the water conservation and grassland ecological protection and restoration unit of the Baihe River basin in Hongyuan County and the Dadu River basin in Aba County. They are mostly within the management scope of sub-projects such as grassland ecological protection, historical mine ecological restoration, small watershed comprehensive management, and grassland ecological carbon sink. These efforts have significantly improved vegetation coverage rates and mitigated trends of soil erosion and grassland degradation.The general ecological restoration effect area encompasses 36.82% of the total study area. These areas are primarily distributed in the forest grassland and water ecological protection and restoration unit of the Minjiang River basin in Songpan County and the water source conservation and grassland ecological protection and restoration unit of the Baihe River basin. They are mostly within the management scope of sub-projects such as forest protection and protection, grassland sealing and protection, and ecological river embankment construction. However, the restoration methods of forest protection and grassland sealing and protection sub-projects are relatively straightforward, and the restoration effects have not been significant. Regarding the subproject of ecological embankment construction, conventional embankment engineering measures are primarily adopted. Although this approach eliminates the problem of embankment erosion, the overall ecological improvement effect is moderate.The area with weak ecological restoration effect encompasses 54.17% of the total study area. These areas are mainly located outside the scope of the ecological restoration and governance sub-project area and have not directly produced ecological environment improvement effects at present.