Instability of climate signal in tree-ring width in Mediterranean mountains: a multi-species analysis

Temporal instability of climate signal in tree-ring width of the five dominant species (Pinus nigra, P. sylvestris, P. uncinata, Abies alba, Fagus sylvatica) growing under Mediterranean mountainous climate was studied over the last century (1910-2004). To disentangle the tree-climate-site complex, the effects of both soil water availability (SWA) (dry, mesic and humid sites) and altitude (from 430 to 1,690 m) were investigated on the response patterns. Responses to climate were analysed using bootstrapped correlation coefficients from 17 ring-width chronologies built from 293 trees sampled in 64 stands in South-Eastern France. Temporal analyses were performed considering forty-six 50-years intervals (from 1910-1959 to 1955-2004). May-June drought was the primary limiting factor. For P. sylvestris, summer precipitation also played a key role. F. sylvatica was the less responding species with no clear common pattern. Low SWA led to an increasing correlation with precipitation in May for P. nigra and A. alba. Precipitation from May to August prevailed on the driest conditions for P. sylvestris. Correlation analyses suggested that warm autumn or winter enhanced growth, except for F. sylvatica. For P. nigra, the importance of April temperature increased with increasing altitude. Temporal analyses revealed a stability of sensitivity for the highest contexts (P. uncinata and F. sylvatica). At lower altitudes, the correlation with minimum temperature in April increased while temperature more often exceeded the threshold of 0A degrees C over the last decades. For precipitation, a decrease in the strength of correlation was observed without close relationships with local xericity.