Ecological requirements of Abies alba in the French Alps derived from dendro-ecological analysis

We used dendro-ecological techniques to investigate fundamental relationshi ps between climate and growth of Abies alba (silver fir) in eastern France. Seven Abies forests in the Trieves region of the French Alps were chosen t o represent a wide range of ecological conditions based on the results of p revious forest vegetation surveys. In each forest, four trees were sampled in each of five different stands with two cores per tree. These 280 cores w ere studied using two separate dendro-ecological methods: the pointer years method (based on extreme growth events), and correlation functions between tree ring-widths and monthly climatic data. Data from 11 meteorological st ations were combined to provide a regional analysis of precipitation and mi nimum and maximum temperatures. The two dendro-ecological methods appear to be complementary, as the first technique emphasizes common and low intensi ty linear correlations between ring-widths and climatic variations, and the second method emphasizes extreme and unusual climatic events such as excep tionally cold or dry years. Across all sites, drought in the previous year was consistently correlated with a low growth rate; however, other climatic variables varied substantia lly among sites. For example, drought in the current year reduced growth mo re in the low elevation sites than in the high elevation sites and severe w inter frost reduced growth the most in the high altitude sites and the drie st site. Moreover, certain growth responses are better correlated with the age of the stands, the canopy closure and the floristic composition of the community than the abiotic factors, emphasizing the value of dendro-ecologi cal sampling based on phytosociological units.