Traditional Removal Strategies Mitigate Shrub Encroachment Driven by Canopy Competition on the Tibetan Plateau

Alpine grasslands of the Tibetan Plateau rank among Earth's ecologically critical yet vulnerable ecosystems. These ecosystems sustain pastoral livelihoods and preserve nomadic cultural traditions. However, climate warming combined with intensified anthropogenic pressures is accelerating shrub encroachment in these ecosystems. For centuries, Tibetan pastoralists have counteracted this process through targeted interventions: manual uprooting of dominant shrubs, controlled patch burning during dormant seasons, and rotational grazing systems coupled with strategic herbivore deployment to suppress woody seedlings. Despite their shrub management efficacy, the scientific rationale underlying Tibetan traditional ecological knowledge-the role of shrub-herbaceous interaction variability in driving encroachment dynamics-remains understudied. We quantified shrub encroachment patterns across alpine meadows of the Zoige Plateau. Shrub encroachment dynamics were monitored across the elevation gradient (3400-3900 m), spanning the core elevational range of shrub encroachment. To identify shrub-herbaceous interactions in driving encroachment dynamics, we conducted a manipulative experiment with four shrub treatments: shrub removal, canopy restriction, root exclusion, and ambient control. Our analysis identified that elevation imposed a strong linear constraint on short-term encroachment rates (RSEI_Three = -0.06E + 0.28, R ² = 0.83, p < 0.001; E (elevation, km)). No significant elevational effect was observed on long-term encroachment rates (RSEI_Outset; p > 0.05). Canopy competition (RII_Canopy = 0.06E - 0.41, R ² = 0.81, p < 0.001) mainly explained 60.6% of the variation in encroachment dynamics, while root competition (RII_Root = -0.05E + 0.05, R ² = 0.76, p < 0.001) accounted for 2.8%. Our findings highlight that canopy-mediated suppression of herbaceous plants is the primary pathway driving encroachment, while root-driven processes act as secondary mechanisms dependent on canopy architecture. Tibetan traditional methods directly disrupt key ecological drivers of shrub encroachment. By targeting shrub canopy removal, reducing herbaceous communities' light limitation, and weakening shrub competitive advantages that drive shrub encroachment, we promote the recovery of understory herbaceous communities.