Shrub Removal Practices: Impacts on Herbaceous Plant Diversity and Productivity in Alpine Shrub-encroached Grasslands of the Qinghai-Tibet Plateau

Shrub expansion driven by climate change and grazing significantly impacts the structure and function of grassland ecosystems worldwide. Although shrub removal can effectively restore shrub-encroached grasslands, how to optimize its effectiveness and promote grassland productivity for sustainable management remains unclear on the Qinghai–Tibet Plateau (QTP). To address this gap, we conducted a three-year shrub removal experiment on a representative hillslope on the eastern QTP, applying two mechanical methods: whole-plant removal (canopy and roots) and canopy-only removal, to evaluate how shrub encroachment and its removal influence herbaceous plant biodiversity and productivity in alpine shrub-invaded grasslands. Our results show that shrub encroachment altered species composition, significantly reduced species richness, and decreased both above- and below-ground biomass, primarily by diminishing the contributions of coexisting herbaceous species. Both removal methods enhanced above- and below-ground biomass by restoring the performance of resident species, but their effects on diversity and drought resilience differed. SRM-I rapidly increased herbaceous diversity and richness, whereas SRM-II showed a delayed diversity response. During drought, SRM-II maintained more stable community evenness, while SRM-I sustained higher belowground biomass. Our findings demonstrate that shrub encroachment systematically degrades alpine grassland communities and that removal strategies differentially shape recovery trajectories. Whole-plant removal, despite its higher cost, yields a more substantial recovery of productivity, while canopy retention promotes slow yet stable reassembly of plant communities under stressful conditions. These results emphasize that removal approaches must be tailored to local ecological contexts to achieve long-term, sustainable management of shrub-affected alpine grasslands.