Stem Diameter and Height as Traits Linked to Cork Quality (Thickness and Porosity) in Cork Oak (Quercus suber L.)

Thickness and porosity are properties of raw (natural) cork planks that have strong influence on the end-product quality, particularly on natural cork stoppers or discs, both highly valued natural cork products. In cork oak (Quercus suber L.), the between-trees variability of cork quality (thickness and porosity) is relatively well known and has been extensively studied. However, the within-tree variability of these properties has been scarcely addressed in the literature. In this study, we have focused on the within-tree variability of cork quality. Our major working hypothesis is that the within-tree variability of cork quality is related with trees specific growth patterns. We assessed, at tree individual level, the stem height-cork thickness and the stem height-cork porosity relationships that, so far, were not clear. Eventually, the patterns of radial growth, along the stem upwards may have a strong physiological basis. Our results showed: i) a stem height-cork thickness relationship, with trees showing a decrease of the cork thickness with the stem height and; (ii) a stem height-cork porosity relationship, with trees showing a decrease in the cork porosity with the stem height. Forest managers and cork processors require more quantitative information on the inter- and intra-stem variation of cork-thickness and cork-porosity in order to understand the effects of forest management decisions at cork oak woodlands level. This way, the modeled stem profiles of cork quality (thickness and porosity) allow the optimization of high quality raw cork (planks) and determine the economic feasibility of cork harvesting practices.