Climate signals in width, density, δ 13 C and δ 18 O tree-ring series at two Iberian sites.

Tree-rings proxy based climate reconstructions have largely proven to be an accurate assessment of past climate variations at local, regional and hemispheric scales. For this purpose, the characterization of the influence of climate on tree growth is a necessary and crucial step. Sensitive trees would record the climate variable and period that limit their annual growth and this information is then used to reconstruct climate based on tree-ring proxies (Fritts 1976). The existing reconstructions based on tree rings are dominated by temperature signals. The reason is because dendroclimatological studies are usually conducted in high altitudes or high latitudes, where long-lived individuals can be found more easily because of the lower anthropogenic pressure and where harsh conditions shape very sensitive trees. Existent literature reports that, in general terms, species growing under temperate climate response positively to summer warmth (Etien et al. 2008; Buntgen et al. 2006, 2008) since precipitation is generally not a limitation whereas cold temperatures stops cell division and development in the trunk (Rossi et al. 2003). On the other hand, species living under Mediterranean climate are usually described to depend on moisture availability (Touchan et al. 2005, 2007, 2008a). This often leads in combination with temperature effects to a drought sensitivity signal (Esper et al. 2007, Nicault et al. 2008; Touchan et al. 2008b, 2010). The Iberian Peninsula has a predominant Mediterranean climate which is characterized by cool temperatures in winter and dry and hot summers. In addition, there is high spatial and temporal variability in precipitation (Rodriguez-Puebla et al. 1998) and ecosystems dynamics are basically controlled by moisture availability (Pinol et al. 1998). Previous work on the climate-growth relationship at high altitudes in this area reports a sensitivity mainly to temperature in the northern part (Pyrenees, Tardiff et al. 2003, Andreu et al. 2007, Buntgen et al. 2007) which loses its positive influence on tree growth towards the south but, in turn, no clear influence of precipitation is found (Parque Natural de Sierra de Cazorla, Martin Benito et al. 2008). Except for the Pyrenees area, tree-ring climate relationships in the Iberian Peninsula are still rather unclear and dendroclimatological investigations in old forests to assess their potential for climate reconstructions are scarce. Moreover, the usefulness of proxies such as tree-ring stable isotopes has barely been explored. With the aim of assessing the strength of the climatic signal in each tree-ring record and thus, their potential for climatic reconstructions, we analyze the climatic significance of several tree-ring series from two pine-species stands growing at high elevations in the Iberian Peninsula: Pyrenees and South of Spain. Six tree-ring variables were used: tree-ring width (TRW), earlywood width (EWw) and latewood width (LWw), maximum latewood density (MXD), stable carbon (δC) and oxygen (δO) isotopes.