Do tree-ring data reflect contrasting climate sensitivity in the Himalayan treeline ecotone? A comparison of Abies spectabilis (D. Don) Mirb. and Rhododendron campanulatum D. Don

High mountain ecosystems are especially sensitive to climate change. The treeline is expected to shift to higher elevations due to rising temperatures. However, temperature and precipitation sensitivities of tree species within treeline ecotones may differ. Using a dendroclimatological approach, we compared the tree growth-climate relationships of Abies spectabilis and Rhododendron campanulatum , two of the dominant treeline-forming species in Central Himalayan treeline ecotones. We correlated tree ring widths with monthly and seasonal climate data, including the Standardized Precipitation-Evapotranspiration Index (SPEI). We found contrasting climate sensitivities between these species. Moving and evolving correlation analyses revealed that Abies spectabilis showed a strong negative response to spring temperatures (March-May) in recent decades. In past decades, spring growth-climate relationships were inconsistent. Responses to precipitation and SPEI suggest that the shifts to stable negative spring temperature responses are linked to rising drought stress. In contrast, the growth-climate relationships of Rhododendron campanulatum remained more stable over time, with weaker signs of drought stress, indicating greater resilience to climate variability than Abies spectabilis . Moreover, Rhododendron campanulatum showed a positive response to winter temperatures (December-February). Abies spectabilis appears to be more vulnerable to the currently changing climatic conditions, indicating shifting competitive relationships of Himalayan treeline species that need to be considered to understand and predict the effects of climate change on treeline dynamics.