Decline of Quercus robur forests in northwestern Italy: current situation and tentative aetiology

Quercus robur decline is a widespread phenomenon in northwestern Italy. In order to determine the incidence, the severity and the evolution of the decline, Q. robur crown transparency was assessed starting from 2007 in 11 study sites. In 2007, the mean crown transparency ranged from 35% to 74% depending on sites. No significant variation was observed among crown transparency levels in the 3 sampling periods (2007-2008-2009) at any sites. Soil and climate conditions of study sites were investigated in order to find possible correlations with crown transparency. Drought in spring may be the main factor triggering off oak decline in northwestern Italy. Ongoing experiments indicate that the availability of water and light may have effect only in the medium and long time period.