The extensive afforestation efforts on the Loess Plateau, incurring hundreds of billions of CNY, trigger heightened vegetation cover, depleting soil water, and imperiling ecosystem sustainability. Widespread debate persists over the feasibility and optimal locations for afforestation. However, what has been overlooked is the potential presence of alternative stable states within ecosystems, a captivating system equilibrium behavior. This study integrates remote sensing, minimal model, and environmental data to investigate the equilibrium behavior (quantified by tree cover) of forest ecosystems on the Loess Plateau and its implications. The findings suggest a threshold relationship between tree cover and annual precipitation, with a significant increase observed up to 400 mm. Beyond this threshold, alternative stable states emerge, characterized by high tree cover (forest, >35%) and medium tree cover (open woodland, 7%~35%). The equilibrium behavior of the forest ecosystem combines thresholds and alternative stable states. Increasing spatial heterogeneity, especially the positive feedback between vegetation and precipitation, results in advancing transition thresholds with higher annual precipitation. Regime shifts from forest to open woodland increase carbon stock but decrease water yield, revealing a trade-off between carbon sequestration and water resources. This nuanced understanding of equilibrium enhances both theoretical comprehension and practical planning for afforestation on the Loess Plateau, promoting the functions and services of the forest ecosystem.