Climatic signals in earlywood, latewood and total ring width of Corsican pine from western France

The influence of climatic factors on the growth of Corsican pine, growing a t low elevation on acidic well-drained soils in western France, was evaluat ed by comparing annual earlywood, latewood and total ring indices with mont hly temperature and precipitation data collected at Angers over the period 1922-1991. Latewood formation appeared to be more sensitive to climate than earlywood formation. Pointer years analysis and climatic models showed tha t summer drought was a major limiting-growth factor in the studied area. Ex treme growth reductions specially highlighted the effects of low precipitat ion whereas response functions clearly underlined the importance of tempera ture. The climatic models accounted for 46%, 37% and 42% of the variability of total ring, earlywood and latewood indices, and suggested that the peri od of earlywood formation occurred mainly in early spring (May) whereas the growth of the latewood band was maximum in summer (July). Winter photosynt hesis and the advance in the timing of the resumption of cambial activity w ere possible causes of the positive winter temperature correlation with ear lywood. A cool and wet spring was also beneficial to growth as it affected the water balance of the toes at the beginning of the growing season. Prior October weather conditions also influenced growth, suggesting a preconditi oning of the current year's growth by climate during the previous year. The regional climatic data revealed: no change in precipitation and thermal am plitude between 1950-1997; a significant (alpha = 0.01) increase in mean an nual temperature of 1.1 degrees C, mean annual minimum temperature (1.5 deg rees C), mean summer (July-August) tem perature (2.2 degrees C) and minimum summer temperature (2.3 degrees C). By increasing summer water stress, a s teady rise may induce growth decrease and probably forest decline in the ne xt years. These results should be taken into account when predicting possib le responses of Corsican pine plantations to global change.