Functional wood traits: xylogenesis, tree rings and intra-annual density fluctuations (IADFs) in Mediterranean species

The occurrence of long and severe summer drought periods, forecasted for the Mediterranean basin (IPCC, 2013), is expected to affect cambial activity and wood formation, thus altering tree growth and vegetation dynamics thus affecting the productivity of forests (Sarris et al., 2007; Martinez del Castillo et al., 2016). In such a context, is important to understand the strategies in water utilisation exploited by different Mediterranean tree and shrub species in response to variation in the climate conditions. Such knowledge would allow to predict the response of Mediterranean ecosystems to climate change and help in decision-making for a focused forest management. The general aim of the thesis is to acquire knowledge on the adaptation strategies operated at the xylem level by Mediterranean species to cope with the intra-annual variation of environmental conditions, and in particular with summer drought. This main aim has been pursued through the study of wood functional traits within tree-ring series, focusing in tree rings presenting Intra-annual density fluctuations (IADFs). The starting hypothesis of this Doctoral Thesis is that the Mediterranean woody species could respond to the seasonal distribution of precipitations and temperature patterns, showing a bimodal model of xylem growth identifiable by main trends in the wood functional traits, attested by the occurrence of IADFs within tree rings.