Growth sensitivity to water availability as potential indicator of drought-induced tree mortality in Mediterranean Pinus sylvestris forests

Drought-associated tree mortality has worldwide increased in the last decades, impacting structure and functioning of forest ecosystems, with implications for energy, carbon and water fluxes. However, the understanding of the factors underlying this mortality are still limited, especially at stand scale. We aim to identify the factors that triggered the mortality of the widely distributed Pinus sylvestris in an extensive forest area in central Spain. We compared radial growth patterns in pairs of live and recently dead individuals that co-occur in close proximity and present similar age and size, thereby isolating the effects of size and environment from the mortality process. Temporal dynamics of growth, growth synchrony, and growth sensitivity to water availability (P-PET) were compared between live and recently dead trees. Over the last 50 years, we observed an increase in the growth synchrony and sensitivity to water availability as drought conditions intensified consistent to prior research. However, no differences were found in radial growth between live and dead individuals 15 years before mortality, and dead individuals showed lower growth synchrony and sensitivity to water availability than live ones for much of the period studied. This suggests a decoupling between tree’s growth responses and climatic conditions, which could increase vulnerability to hydraulic failure and/or carbon starvation. Overall, our results point to an important role of growth sensitivity to water availability in tree mortality for P. sylvestris at its southern distribution limit.

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