The Mediterranean forests are rapidly changing; how trees will respond and adapt to these changes is largely unknown. It is necessary to increase the basic knowledge on the mechanisms controlling the development of native forest species, their interrelations, as well as their responses to environmental stresses. The cork oak (Quercus suber L.) is an evergreen tree, mostly associated with a savanna-like ecosystem called the montado, which covers around 700 000 ha of the portuguese territory, subjected to annual rainfall amounts ranging between 500 and 1300 mm. In order to investigate the intra-specific variation in Q. suber, at the tree and leaf level, along an 800mm rainfall gradient, we have measured tree and leaf morphological attributes, as well as leaf carbon isotope content. The values of specific leaf area of Q. suber were strongly positive correlated with rainfall, decreasing as rainfall decreased. This reduction was mainly driven by leaf thickness, which was tightly correlated with SLA (R=-0.80, P < 0.001) and steadily increased with declining rainfall. The significant increase in carbon isotope discrimination towards the wetter end of the gradient, with a difference in Δ between the two extremes of 4.2‰, suggests a strong adjustment of leaf gas exchange to water availability. Leaf changes associated with precipitation in Q. suber seem thus to influence water economy, since reduction of SLA, with the increase of LT with aridity may improve water use efficiency. These data suggest that this evergreen tree species relies on its foliage plasticity and physiology to overcome water shortage.
