Contrasting responses of radial growth and wood anatomy to climate in a Mediterranean ring-porous oak: implications for its future persistence or why the variance matters more than the mean

The plasticity of radial growth and earlywood anatomy to climate has not been properly assessed. To solve this, we evaluated how growth and earlywood anatomy changed in a Mediterranean ring-porous oak (Quercus faginea) across a climatic gradient. We hypothesized that the anatomical variables will be the most sensitive to climatic stress, particularly to water deficit in late winter and early spring when earlywood is formed. Testing these hypotheses allows evaluating whether such plasticity in growth and earlywood anatomy affects the projected responses of trees to climate forecasts. The gradient included high- (H), mid- (M), and low-elevation (L) sites and a xeric site (X). We used dendrochronology to quantify changes in growth and anatomy and to relate them to recent and twenty-first-century forecasted climatic data. The highest interannual variance was observed for the latewood width in the xeric site, where the earlywood vessel area reached the lowest values. Tree-ring width correlated positively with spring precipitation, whereas the earlywood vessel area correlated negatively with winter temperature. The predicted drier and warmer climate caused a 10 % reduction in tree-ring width and earlywood vessel area. Earlywood anatomical traits were less sensitive to climatic variability than radial-growth ones since the percentage of their variance explained by climate varied from 12 to 49 % in the former variables and from 15 to 57 % in the latter ones. The plastic xylem responses to climatic variability across time, mainly in the xeric site, indicate that this plasticity must be explicitly considered when forecasting changes in growth and persistence of trees.