Elevation gradient modulates the effects of herbaceous encroachment on the long-term growth trends and climate sensitivity of <i>Rhododendron aureum</i> in alpine tundra

Abstract As global warming drives plant upward migration, the alpine tundra of Changbai Mountain is experiencing encroachment by Deyeuxia angustifolia (Komarov) Y. L. Chang, a low-elevation herb. However, its impact on native shrubs such as Rhododendron aureum Georgi remains unclear. Here, we analyzed the radial growth trends and climate sensitivity of R. aureum across elevations and encroachment gradients using linear and mixed-effects model methods, and explored the mediating roles of soil properties and plant traits. Our study revealed that R. aureum exhibited stronger positive long-term growth trend at higher elevations compared to lower elevations. Mild and moderate encroachment of D. angustifolia enhanced the positive growth trend of R. aureum, especially at the low elevations. Moreover, R. aureum showed weak climate sensitivity at mid-elevation but stronger responses to winter temperatures at low elevation and to spring–summer temperatures and precipitation at high elevation. D. angustifolia encroachment further intensified this sensitivity, characterized by stronger negative responses to spring, autumn and winter temperatures but positive responses to summer temperatures and autumn precipitation. Overall, elevation primarily influenced R. aureum growth and its sensitivity to precipitation through soil conditions and plant size traits, while soil conditions and leaf economic traits influence temperature sensitivity. These findings advance understanding of alpine vegetation dynamics and contribute to ecosystem conservation under climate change.