Influence of purchased forage on grassland sustainability and livelihoods in the Qilian Mountains: Evidence from Tianzhu County

This study evaluated the impacts of purchased forage on the grass-livestock balance and ecological livelihoods in Tianzhu County, located in the Qilian Mountain region of western China. We employed grassland carrying capacity estimation, Theil-Sen slope and Mann-Kendall trend analyses, a grass-livestock balance assessment with and without purchased forage adjustment, and an ecosystem service valuation of forage substitution. These methods were used to examine the spatiotemporal dynamics of grassland carrying capacity from 2001 to 2023 and the substitution effects of purchased forage in 2023. The results show that grassland carrying capacity increased significantly over the study period, with an average annual rise of 0.0113 sheep units (SU) ha^-1. A clear turning point occurred in 2011, after which the upward trend intensified. When accounting for the widespread use of purchased forage, livestock overloading rates were adjusted to reflect its substitution effect, reducing the county-level average overloading rate from 88.3% to 49.0%. This reduction was particularly pronounced in central and eastern townships, where dependence on purchased forage exceeded 30%. In 2023, purchased forage contributed an ecosystem service value of 1.09 billion CNY and net economic benefits of 0.84 billion CNY, indicating substantial ecological and economic gains. Overall, the findings suggest that purchased forage enhances grass-livestock interactions through spatial substitution effects and plays a crucial role in promoting ecological restoration and improving pastoral livelihoods in mountain pastoral systems.