Climate change and oak growth decline: Dendroecology and stand productivity of a Turkey oak (Quercus cerris L.) old stored coppice in Central Italy

We combined stem volume increment analysis with dendroecological tools to address two unresolved issues concerning oak dieback in Mediterranean areas: early detection of changes in stand growth, and identification of mechanisms for observed growth declines. We reconstructed productivity of a stored coppice formed by Turkey oak (Quercus cerris) to test if its growth decline was linked to climatic variability, while also accounting for age-related and sociological factors. Drought in May-June and in prior-year late summer-autumn was negatively correlated with current growth during 1974-2006. Previous November water balance was the strongest signal. Moving Correlation Functions (11 y windows) indicated that the May June signal remained dominant until 1996, thereafter falling to non-significant values in parallel with the May June water balance drying trend; at the same time the previous autumn correlations reached significant values. Since 1994 there was a two-year lagged response to June water balance, suggesting that, when growth declined, loss of current-year climate signals was accompanied by the emergence of previous-year ones. Growth and productivity of deciduous oaks in Mediterranean environments is linked to late spring-early summer hydrologic balance; at both annual and decadal timescales, oak growth decline was associated with a delayed response to climate.