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University of Padova (2017)

Dendroanatomy : a new approach to sharpen the focus on the climatic drivers of tree growth in the Mediterranean

Pacheco Solana, Arturo

Titre : Dendroanatomy : a new approach to sharpen the focus on the climatic drivers of tree growth in the Mediterranean

Auteur : Pacheco Solana, Arturo

Université de soutenance : University of Padova

Grade : Doctoral Thesis 2017

Climate change is the biggest challenge of our time and the Mediterranean basin one of the hot spots where its effects are already tangible. For this region most climate models predict higher temperatures and diminishing rainfall with likely longer and more frequent drought events which represent the principal threat for tree species, affecting growth, mortality and composition of future forest. Using cutting edge techniques for sample preparation and microscopic image analysis, this dissertation assessed the growth responses of xylem anatomy to climatic constraints. This dendroanatomical approach permits the long-term retrospective analysis of intra-annual growth information permanently fixed and archived in secondary xylem tissue. Wood anatomical results were contrasted and complemented by the use of many other methodologies like xylogenesis, dendrometers and non-structural carbohydrate analysis. The main species targeted was Aleppo pine (Pinus halepensis). Its growth pattern was firstly compared with another coexisting conifer (Juniperus thurifera) and their correlations with climate variables evaluated. Afterwards, the bimodal growth pattern shown by this species was assessed in two distinct climatic zones (continental vs. oceanic). Finally, three groups of trees under different irrigation treatments were compared. The dendroanatomical analysis of all three stages comprised always a time span of about 40 years, while the complementary methodologies varied according to the different experimental settings. Applying this dendroanatomical approach it was possible to link xylogenesis with wood anatomy on a decadal-long time scale and explain the climatic correlations that drive the bimodal growth patterns commonly reported in Mediterranean species. In addition, it was possible to disentangle the climatic cues influencing the growth plasticity of Aleppo pines under different conditions : where climate is milder the bimodality in growth is stronger. At the end, the irrigation trial highlighted that growth performances and xylem anatomy can be significantly affected by water availability and that trees tend to maintain a fairly good coordination between C supply and demand even during prolonged drought. This dissertation improves the general understanding of how higher temperatures and drier conditions will impact and influence the growth and distribution of the Aleppo pine. As one of the most common tree species of the Mediterranean region, the results of these studies can help to understand and predict the future forest dynamics under an uncertain climatic future.

Mots Clés  : wood anatomy, dendroanatomy, dendrochronology, IADF, pinus halepensis


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