Shift from acquisitive to conservative plant strategies with increasing drought and temperature extremes in an alpine shrub.

Background and aims: Trait-based approaches have advanced our understanding of plant strategies, yet they often focus on leaf-level traits, overlooking the functional roles of stem anatomy and twig characteristics. We investigated intraspecific trait variation in Salix flabellaris, an alpine dwarf shrub, along climatic gradients in the Himalayas. Our goal was to identify distinct axes of trait variation related to stem, twig, and leaf traits, assess their environmental drivers, and evaluate population-specific growth responses to recent climate change.

Methods: We measured anatomical and morphological traits in stem, twig, and leaves across central and marginal populations along three Himalayan transects. Environmental gradients included variation in growing season temperature and soil moisture. Basal area increment from 2000 to 2021 was analyzed to assess long-term growth trends in different areas.

Results: Trait dimensions were largely independent, reflecting distinct ecological strategies: (1) stem anatomical trade-off between hydraulic safety and conductivity; (2) twig dimension balancing construction costs and mechanical strength; and (3) leaf dimension along the exploitative-conservative axis. Higher temperatures enhanced performance manifested as larger twigs and reduced tissue construction costs but only under sufficient soil moisture conditions. Central populations at mid-elevations displayed the favorable trait combinations and highest growth rates. In contrast, marginal populations (higher and lower elevations) showed traits indicating structural reinforcement and conservative resource use. Climate warming over recent decades enhanced stem growth primarily in high-elevation populations, where low-temperature constraints were relaxed.

Conclusions: This study demonstrates that stem, twig, and leaf traits represent distinct yet complementary strategies, with environmental filtering shaping their expression along climate gradients. Central populations exhibit highest growth under current conditions, while climate change is shifting growth advantages toward higher elevations. These findings highlight the need for integrated, multi-organ trait assessments to predict species performance, persistence, and potential range shifts under future climatic scenarios.