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Temporal instability of forest climategrowth relationships has been evidenced at high elevations and latitudes, and in Mediterranean contexts. Investigations under temperate conditions, where growth is under the control of both winter frost and summer water stress, are scarce and could provide valuable information about the ability of forest to cope with climate change. To highlight the main climatic factors driving the radial growth of Quercus petraea forests and to detect their possible evolutions over the last century, dendroecological analyses were performed along a longitudinal gradient of both decreasing summer water stress and increasing winter frost in northern France (from oceanic to semi-continental conditions). The climategrowth relationships were evaluated from 31 tree-ring chronologies (720 trees) through the calculation of moving correlation functions. Q. petraea displayed a rather low sensitivity to climate. High temperature in March and water stress from May to July appeared to be the main growth limiting factors. The sensitivity to winter precipitation and summer water stress decreased from oceanic to semi-continental conditions, whilst the correlation to winter frost tended to increase. Moving correlations revealed a general instability of climate-growth relationships, with a moderate synchronicity with climatic fluctuations. The main changes occurred during previous autumn for both temperature and precipitation whilst climatic trends were rather low or non-significant. The most coherent trends were pointed out (i) in April with a cooling (-0.9°C) leading to positive correlation to temperature at the end of the century, and (ii) in July with a decreasing inter-annual variability of precipitation resulting in a loss of correlation. On the contrary, the decreasing temperature and increasing precipitation in May and June led to few significant changes climate-growth relationships.

Temporal instability of climate signal in treering 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 . 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-

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