Complex environmental control of growth in a dominant Mediterranean‐alpine shrub species

Abstract Mediterranean‐alpine plants are exposed to harsh conditions, forcing them to perform with well‐adapted physiological strategies to withstand the dual stressors that arise from winter cold and summer drought. Such growth strategies are not yet fully understood, although they gain importance with regard to the resilience of species in the face of ongoing climate variability. Here, we aimed at understanding shrub growth in a widespread Mediterranean‐alpine species, Cytisus galianoi Talavera & Gibbs. Using long‐term time series of stem diameter change obtained from dendrometer measurements across the species´ range, we were able to characterise its spatiotemporal growth plasticity. Furthermore, separating water‐related fluctuations in stem diameter from irreversible stem increment allowed us to disentangle the species´ seasonal growth patterns. Using fine‐scale measurements of on‐site environmental conditions, we were then able to identify micro‐ecological drivers controlling the species´ growth processes by applying correlation analysis and partial least squares regressions. We show the species´ adaptation to the spatial heterogeneity across its range for the first time. Our findings highlight that the combination of bimodality and overall high growth plasticity likely allows the species to cover a wide geographical range across alpine areas and over a wide range of weather conditions. We show the environmental control of bimodal growth in C. galianoi, and the importance of pre‐growth environmental control, leading to pronounced carry‐over effects. These lead to a major advantage in resisting adverse growth conditions and adapting to changing conditions. Synthesis: Overall, our findings improve the understanding of the species´ ecological niche and show that preceding photosynthetic activity helps C. galianoi to perform even under unfavourable conditions in winter and during the active growth phase, challenging the general assumption on the coupling of growth to specific seasons and suggesting that the species is capable of adapting to future climate variability.