Elevation-dependent drivers of plant diversity across spatial scales on the Qinghai-Tibet Plateau

Introduction In mountain ecosystems, plant diversity often exhibits regular patterns along elevational gradients. Yet, it remains poorly understood how multiple factors jointly shape these patterns. Methods To fill this gap, we used a dataset of 758 vegetation plots sampled across the Qinghai-Tibet Plateau to explore how climatic, topographic and anthropogenic variables drive alpha, beta and gamma diversity across different elevations. In particular, we explored how the effects on gamma diversity are mediated through alpha and beta diversity, and whether these effects are elevation-dependent, thereby explaining the peaked diversity at medium elevations. Results Overall, annual mean temperature and precipitation seasonality influenced gamma diversity primarily through positive effects on alpha diversity. Aridity index was the strongest positive driver, increasing gamma diversity by enhancing both alpha and beta diversity. Slope aspect (as heat load index) enhanced gamma diversity by positively affecting beta diversity, whereas slope inclination increased gamma diversity by positively affecting alpha diversity. Grazing exhibited nonlinear effects, first decreasing and then increasing gamma diversity, primarily by affecting beta diversity. Moreover, the variables’ effects shifted with elevation: at low elevations (<3000 m), precipitation seasonality and slope inclination influenced gamma primarily through alpha diversity, and grazing increased gamma diversity via both alpha and beta diversity; at high elevations (>4500 m), climatic effects dominated through both pathways. At medium elevations (3000–4500 m), climatic variables and slope inclination increased gamma diversity via alpha and/or beta diversity, underpinning the peaked diversities. Conclusion These findings highlight elevation-explicit approaches to conserving biodiversity in mountain areas.