## 3 Results
### Cross-Sectional Area Increments of Cork and Stem Diameter  
In the time window of a cork production cycle, the increments of cork (cork-ring width, C\({}_{\text{rw}}\)) and stem diameter at breast height (D\({}_{\text{bh}}\)) (Figure 2) extrapolated to cork-ring area increments (Crai) and to the basal area increments (BAi), respectively, showed average values of C\({}_{\text{rw}}\) ranging between 3 and 4 mm, and of D\({}_{\text{bh}}\), ranging between 7 and 10 mm. This radial growth represented higher proportional cross-sectional areas that were highly correlated (r = 0.71, \(p\)-value \(<\) 0.01) and more than 2.5 times higher in the largest trees (D\({}_{\text{bh}\_4}\)) than in the smallest ones (D\({}_{\text{bh}\_1}\)) (Figure 5). Moreover, tree size-related curves for these cross-sectional area increments clearly showed that the lowest values of Crai and BAi of the smaller trees reached more than 30% and 60% of stem basal area, respectively. Thus, in smaller trees (e.g., D\({}_{\text{bh}\_1}\)), low values of cross-sectional stem diameter area increments (i.e., values below the normalized stem basal area increments of 0.5) represented more than half of their stem basal area. In contrast, larger trees (e.g., D\({}_{\text{bh}\_4}\)) presented high values of cross-sectional area increments (i.e., values above the normalized stem basal area increments of 1.5), less than half of their stem basal area (40%) (Figure 5b).  
Figure 4: Representation of the selected mixed-effects model fitting with stem diameter growth index (ID\({}_{\text{bh}}\)) as the response function: M0 (upper plots) and M4 (lower plots), for summer precipitation (June–July) and summer temperature (June) (fixed effects) only, with random intercept (on the left), and with random slope and random intercept (on the right). Random effects are related to tree size stem diameter (D\({}_{\text{bh}}\)). The four D\({}_{\text{bh}}\) classes are represented: D\({}_{\text{bh}\_1}\), D\({}_{\text{bh}}\)\(\leq\) 35 cm; D\({}_{\text{bh}\_2}\), 35 cm \(<\) D\({}_{\text{bh}\_3}\), 55 cm \(<\) D\({}_{\text{bh}\_4}\) \(<\) 70 cm and; D\({}_{\text{bh}\_4}\), D\({}_{\text{bh}}\)\(\geq\) 70 cm.  
Figure 5: Variation of normalized cork-ring width areas (**a**) and basal area increments (**b**) with the percentage of stem basal area, along the cork production cycle (11 years) for all the sampled trees, clustered by D\({}_{\text{bh}}\) classes: D\({}_{\text{bh}\,1}\) (smallest trees; white circles); D\({}_{\text{bh}\,2}\) (black triangles); D\({}_{\text{bh}\,3}\) (white squares); and D\({}_{\text{bh}\,4}\) (largest trees; black squares).  
Results also showed clear inter-annual variations and, specifically, a reduction of the cross-sectional area increments related with climate, namely under the influence of drought years (e.g., 2005 or 2009) (Figure 5). Trees' BAi showed a clear deceleration of growth in those years, and the BAi of larger trees (D\({}_{\text{bh\_4}}\)) was greatly reduced when compared to smaller trees. These higher decreases of the cross-sectional area increment in the larger trees, however, corresponded to relatively lower percentages of the stem basal area affected when compared to smaller trees.