Abstract: Land use is widely regarded as a major driver of biodiversity loss, yet its effects on mountain ecosystems remain unclear and may be inconsistent across spatial scales due to pronounced environmental heterogeneity. However, few studies have simultaneously quantified multi-scale (α, β and γ) diversity responses to land use along mountain gradients. We hypothesized that under certain levels of disturbance, traditional land use (e.g. agriculture, planted forestry, and secondary forestry) can enhance environmental and landscape heterogeneity, thereby sustaining or even increasing diversity at specific spatial scales rather than uniformly reducing it. In the Hengduan Mountains, a global biodiversity hotspot with complex topography and long-standing traditional land use, We quantified plant α (species richness), β (species turnover), and γ diversity (regional species pool) across different vegetation belts under varying land use intensity (LUI). We found that land use significantly reduced α by 21.7% (P < 0.001) but increased β by 5.9% (P < 0.05) and γ by 16.3% (P < 0.05) relative to natural forests. These effects varied with elevation: α diversity increased at low elevations by 32.8% (P < 0.05) but declined at mid- and high elevations. Both β and γ diversity showed unimodal response to LUI, peaking at moderate intensity (0.2–0.4). Precipitation mediated α and γ responses, whereas altitude governed β diversity responses, indicating biodiversity responses to land use are mediated by distinct ecological processes operating across spatial scales. PLS-SEM further showed that γ diversity was driven mainly by β diversity rather than α diversity. These findings challenge conventional wisdom that land use impacts are uniformly negative and highlight the importance of maintaining moderate land use intensity and landscape heterogeneity to conserve regional biodiversity in mountainous landscapes.

Key words: Land use, Plant diversity, Mountain ecosystems, α, β, γ, Spatial scales