## 1 Introduction  
Forest and grassland ecosystems represent some of the most intricate and biodiverse terrestrial systems, providing a wide range of ecosystem services, including water regulation, carbon storage, soil fertility enhancement, and pollination support [1]. Forests, which occupy approximately 31% of the global land area, serve as habitats for numerous wildlife species while offering vital ecological functions such as water conservation, soil stabilization, carbon sequestration, and oxygen production [2, 3, 4]. grasslands, covering nearly 40% of Earth's terrestrial surface, similarly play critical roles in biodiversity conservation, climate regulation, and soil stabilization [5, 6]. However, the combined pressures of climate change and anthropogenic activities have led to significant transformations in these ecosystems, intensifying habitat degradation and biodiversity loss globally [7, 8, 9, 10]. Recent studies indicate that only 40% of the world's forests retain high ecosystem integrity, defined by minimal human disturbance, intact species composition, and well-functioning ecological processes [11], while nearly half of all grasslands have experienced substantial degradation [12; 13]. As a result, numerous scholars have underscored the urgent need for enhanced conservation efforts to protect these ecosystems [14; 15; 16; 17; 18; 19; 20]. Despite the Altai Mountains' ecological significance and their designation as one of the 49 candidate regions for the establishment of a national park under China's General Plan for the Establishment of a National Park System [21; 22], critical knowledge gaps remain regarding the drivers and mechanisms behind the spatial and temporal changes in forest and grassland ecosystems in this region. Previous studies have largely focused on either forest or grassland dynamics in isolation, or have emphasized global and regional patterns without systematically linking these findings to the unique conditions of the Altai Mountains [23; 24; 25; 26]. Moreover, limited research has examined the response of forest and grassland ecosystems--key conservation targets--to climatic variability and anthropogenic pressures, particularly in light of the Altai Mountains' role as an ecological corridor linking China, Mongolia, Russia, and Kazakhstan [27; 28]. Therefore, there is an urgent need to investigate the spatial patterns, temporal dynamics, and underlying drivers of forest and grassland ecosystems in the Altai Mountains National Park Candidate Area. Land cover change, recognized as a key indicator within the United Nations Convention to Combat Desertification framework [29], serves as an effective metric for evaluating changes in forest and grassland coverage [30]. To objectively analyze long-term trends in these changes, the Sen and Mann-Kendall trend detection methods are particularly robust against outliers and non-normally distributed data, making them well suited for detecting subtle, long-term trends in complex mountainous regions [31]. [PERSON] et al. [32] observed that global grassland degradation is predominantly concentrated in tropical savanna regions, whereas positive trends are more commonly noted in the Eurasian steppes. Concurrently, increasing attention has been directed toward understanding the interactions between forest and grassland dynamics and both environmental and anthropogenic drivers. Natural factors influencing these dynamics include slope, temperature, precipitation, solar radiation, and soil texture [33; 34; 35], while anthropogenic influences encompass population growth, agricultural intensification, grazing, deforestation, and ecological restoration efforts [36; 37; 38; 39]. The effects of these drivers are often nonlinear and interactive, necessitating analytical tools capable of capturing such complexities. The Geodetector tool, for instance, facilitates the quantification of spatial stratified heterogeneity and assesses the coupling relationships among multiple variables [40].