## 1 Introduction  
The Loess Plateau is one of the regions most severely affected by soil erosion in China and the world and is globally recognized as an ecologically fragile zone. Due to its unique geological structure and climatic conditions, the region exhibits significant ecological sensitivity, where any external disturbance can have profound impacts on its ecosystem [1,2]. The intensive extraction of open-pit coal--as a form of high-intensity surface disturbance--has contributed to regional economic development while severely damaging the local ecological environment. The large-scale land degradation caused by coal mining not only manifests as vegetation loss and soil fertility decline but also includes biodiversity reduction, changes in hydrological processes, aggravated soil erosion, and the presence of toxic chemical elements in excessive concentrations [3; 4]. Therefore, effectively achieving land reclamation and ecological restoration after open-pit coal mining has become a major research focus in the fields of ecology and environmental science. In land reclamation practices, the establishment of mixed forests has emerged as an important vegetation restoration model in coal mine reclamation areas due to its diverse ecological functions and strong resistance to disturbances [5; 6]. Mixed forests can effectively improve soil structure and water retention capacity in reclamation areas while promoting long-term ecosystem stability through enhanced biodiversity. However, the sustainability of mixed forest ecosystems in reclamation areas still faces numerous challenges, among which the lack of natural regeneration capacity is considered one of the core constraints on ecological restoration. Natural regeneration refers to the ecological process by which plant communities achieve population renewal through seed dispersal, germination, seedling survival, and growth [7; 8]. This process serves as both a natural driving mechanism of vegetation restoration and a critical indicator for assessing the self-regulation capacity of ecosystems. In the open-pit coal mine reclamation areas of the Loess Plateau, natural regeneration is often restricted by various limiting factors, including insufficient seed sources, soil degradation, and human disturbances [9; 10; 11]. Although extensive research has been conducted on vegetation restoration, systematic studies on the specific processes and driving factors of natural regeneration in mixed forests within reclamation areas remain limited. Recent studies on natural regeneration in mixed forests in the Loess Plateau reclamation areas have made some progress, mainly focusing on three aspects: (1) the spatiotemporal patterns of seed dispersal and the mechanisms of dispersal agents [12; 13]; (2) the influence of soil physicochemical properties and microbial communities on seed germination and seedling growth [14; 15]; and (3) the combined effects of climatic conditions, topography, and human disturbances on natural regeneration patterns [16; 17]. These studies provide an essential foundation for understanding the natural regeneration process and its driving factors in reclamation areas. However, the applicability and generalization of the research findings remain limited by regional differences and ecological complexities. The large-scale mining operations at the Antaibao open-pit coal mine have not only degraded land resources but also posed ecological security risks. Vegetation restoration is fundamental and crucial for the ecological rehabilitation of degraded lands [18; 19]. Artificially constructed plant communities based on self-regulation theory must achieve self-renewal during vegetation succession to maintain dynamic equilibrium with the local environment [20]. In the tree life cycle, the transition from seedling to sapling is a critical developmental bottleneck and is considered the stage most sensitive to environmental changes.