Influence of tree density on climate-growth relationships in a Pinus pinaster Ait. forest in the northern mountains of Sardinia (Italy)

In view of the projected increases in the frequency and duration of drought events in the Mediterranean basin, a better understanding on how differences in stand structure affect climate-growth relationships can improve and ehnance the conservation and management strategies for marginal forests in mountain areas. In this study, we examined the intra-annual variability of growth patterns and responses to climate of two maritime pine (Pinus pinaster Ait.) stands growing at contrasting tree densities at low elevation in northern Sardinia (Italy). A dendroclimatic analysis was used to assess the climate-growth relationships on monthly, seasonal and annual scales. Late spring and summer precipitations of the current year appeared to be the crucial climatic driver promoting the radial growth of trees in this mountain stand. However, summer drought was the main climate constraint, triggering negative effects on P. pinaster growth. Summer Palmer's drought severity index showed contrasting influence on latewood growth responses to drought conditions related to stand density, still significant also across the autumn months in the stand with the highest tree density. Our findings indicate that stands growing at high density may experience more prolonged water shortages, especially during the late summer and early autumn months. Additionally, since the early 1980s, as precipitation has decreased, the influence of previous rainy years on radial growth has been highly significant in the stand with the lowest tree density. This result suggests that such trees may explore deeper soil horizons, thus reaching water resources stored in previous rainy years, especially during periods of low precipitation.