Multidimensional evidence of the positive effects of land use on plant biodiversity in the Hengduan Mountains

Land-use change is generally considered a major threat to biodiversity, yet the ecological effects of traditional land use in heterogeneous mountain regions remain poorly understood. To address this gap, we conducted vegetation surveys across 210 plots along a steep elevational gradient (955-4160 m) in the Hengduan Mountains, comparing human-modified habitats with natural ecosystems. We assessed plant diversity across taxonomic, phylogenetic, and functional dimensions, integrating them into a multidimensional composite index (μ-diversity) to evaluate land-use impacts. Our results reveal that traditional land use triggers divergent and compensatory responses: while taxonomic richness consistently declined under human modification by 12.49%, phylogenetic and functional diversity significantly increased by 18.71% and 14.54%, respectively, leading to a substantial net increase of 38.55% in overall μ-diversity. Crucially, these effects were highly elevation-dependent. Moderate land use exerted positive, heterogeneity-driven effects on multidimensional diversity at low-to-mid elevations, but these benefits reversed at high elevations (>3000 m), where severe climatic constraints magnified the negative impacts of disturbance. Furthermore, all diversity dimensions exhibited unimodal relationships with land-use intensity, peaking at a moderate intensity level (LUI ≈ 0.35-0.40). An integrated multi-model framework identified a climate-soil-land use triad shaping mountain biodiversity, with land-use intensity emerging as the strongest and most actionable predictor. These findings challenge the assumption that human activity uniformly degrades mountain biodiversity. Instead, they advocate for moving beyond single-dimension assessments and implementing elevation-stratified conservation strategies: accommodating moderate traditional land use to maintain landscape heterogeneity at lower elevations, while enforcing strict protection in high-alpine zones to safeguard disturbance-sensitive habitats.