A quantitative analysis of the interactions between climatic response and intraspecific competition in European beech

In dendroclimatology, trees growing at low competition level are often sampled, to avoid the effects of competition on tree growth. But trees generally live in dense stands, and the analysis of the climatic response should take into consideration the intraspecific relations, because competition could affect resource availability and climate sensitivity. To analyze the climate-competition interactions, 74 trees were cored in a pure even-aged beech (Fagus sylvatica L.) forest. A distance-dependent growth model was used to quantify competition as the source of growth variability in ring-width series, providing a statistical interpretation of growth trend and competition signal, while residuals were considered as climatic perturbation. The ratio between observed and predicted basal area increment (BAI) for the period 1974-1993 was utilized as a growth index. Correlation functions computed between growth indices and monthly climatic variables show that BAI responses to climate vary with competition. Correlation coefficients between temperature and growth indices change from positive to negative as competition increases, whereas precipitation shows an opposite trend. Similarly, correlation with yearly water deficits shows a negative trend, while correlation with water surplus increases. The quantitative analysis of the climate-competition interactions may establish a link between forest management and tree response to climate change.