Rising CO2 atmospheric concentration ([CO2]) as a consequence of anthropogenic emissions is driving an increase in the average temperature of the planet. The Mediterranean basin is particularly sensitive to more intense disturbances due to aridification and land-use legacies that have strongly shaped the current landscapes in the Region. In this context of global change, we studied the decline and regeneration dynamics of three co-occurring Mediterranean coniferous species of different drought tolerance: Pinus pinaster < Pinus pinea < Juniperus oxycedrus (Chapter 2). We compared the growth patterns and climatic response of trees with different health status: healthy (for the three species), declining (only P. pinaster) and dead (P. pinaster and P. pinea). The currently dominant species, P. pinaster, shows extensive signs of decline -assessed by high canopy defoliation and mistletoe infection-and mortality. In addition, the species presents scarce regeneration, whereas it is being replaced by Quercus ilex, P. pinea and J. oxycedrus, with more abundant regeneration and abundance in juvenile stages. Since the 1980s, more frequent and severe drought events have occurred, inciting tree growth decline in dead and non-healthy pine trees, but with differences between species. Nonhealthy individuals of P. pinaster exhibited negative growth trends since 1995. In dead P. pinea trees, the growth decline started later since 2005. P. pinaster survival in the study area was linked to a higher sensitivity to spring precipitation and was concentrated in sites with higher moisture availability, while P. pinea survival was higher in trees with larger diameters. In Chapter 3, we selected 5 individuals from each status and species and studied the xylem anatomical traits and carbon isotopic discrimination ( 13 C) in annual tree-rings. Pine trees exhibited larger tracheids and higher xylem plasticity to climate variability than J. oxycedrus. Xylem traits differed between different health status in Pinus pinaster and Pinus pinea. Healthy pine trees had bigger lumen sizes in the earlywood and thicker cell walls in the latewood than non-healthy trees, along with expressing a higher xylem plasticity to climate. This xylem plasticity allowed P. pinea to adjust their xylem characteristics to increase cell safety during drought events. The ability to maintain a competitive yet plastic xylem structure is crucial to sustain productivity rates under more xeric, climate change scenarios. Our study revealed that non-healthy pines (i.e. declining and dead pine trees) and healthy trees exhibited similar 13 C, which suggests that non-healthy pine trees had low stomatal control to maximize photosynthesis and increase water transport to the crown to compensate for the excessive water loss.