## 1 Introduction  
Climate changes are expected to cause more extreme drought conditions in southern Europe [1]. The evergreen woodlands of cork oak (_Quercus suber_ L.) of southwestern Iberia (in Portugal and Spain) are climatically sensitive and are among the most vulnerable forest ecosystems [2]. Despite its strategies to tolerate drought [3,4], the species risks failing to cope with increasing temperatures and longer and more frequent summer droughts in the near future that will most likely aggravate water stress conditions and will eventually influence cork oak growth rates and patterns [5].  
Climate change effects on cork oak growth, at tree or stand level, have been exclusively and extensively addressed--though not fully explored--in numerous dendroecological studies on the relationship between interannual fluctuations of cork-ring widths and climate parameters and their impact on the cork growth rates and yield [5; 6; 7]. The widely held assumption of these studies is that cork-ring width (or cork growth) at breast height is a reliable predictor of tree stem diameter (and basal area) growth, since cork represents a large part of cork oak's radial increment [8], and the contribution of a \"non-cork\" (wood) growth to that increment is ignored. On one hand, such a consensus derives from the difficulty and scarcity of measurements of wood growth, which is slow and results in narrow and undefined tree rings [9], while cork growth shows wide and clearly defined rings; on the other hand, few studies have addressed stem radial growth sensitivity to climate [8; 10; 11].  
In harvested cork oak's, stem diameter growth has two main components--wood growth and cork (bark) growth--resulting from the independent activities of two merristems, the cambium, producing xylem cells inward, and the phellogen, producing cork cell outward, respectively. In response to cork harvesting, cork growth rates are increased by 400% on the first 2 years, in relation to rates at the end of cork production cycles of 9-12 years, while wood growth rates decrease by more than 50% [6; 8; 12; 13]. It has been reported that cork growth is artificially enhanced at the expense of wood growth [12; 13], eventually affecting stem diameter growth, but so far, the stem diameter growth in harvested cork oak's has been poorly addressed [8; 10]. Moreover, climatic influence on cork-ring width is relatively poorly expressed [5; 6; 7]--only strongly linked to the previous autumn-winter rainfall. Thus, cork growth variations may be insufficient for an adequate interpretation of climate change effects on stem diameter growth, considering that the activity of the phellogen is less sensitive to climatic influences than that of the cambium [8] and particularly unsuitable because cork-ring area growth responses are possibly biased by the size-related stem radial growth dynamics [11].  
In the present study, we measured the annual stem radial growth and cork-ring width (cork growth) of 47 mature cork oak's over a 12-year production cycle. By de-trending the growth curves, we focused on the independent inter-annual fluctuations of stem diameter growth and cork growth indices, assessing their high-frequency sensitivity to climate. Furthermore, tree size-related variations in sensitivity to climate of both radial growths were addressed. The extrapolation to cork-ring area increments and to stem basal area increments was examined, and we hypothesize that _Quercus super_'s cork growth is a proxy for stem diameter growth, which, in turn, responds to climate and to tree size (age) as physiological changes in the aging cambium affect stem diameter growth patterns. This approach was expected to add valuable information to stem growth and biomass modeling aiming at a sustainable production of cork (bark) throughout the tree's life.