Frost and drought: effects of extreme weather events on stem carbon dynamics in a Mediterranean beech forest

The effects of short-term extreme events on tree functioning and physiology are still ratherelusive. European beech is one of the most sensitive species to late frost and water shortage.We investigated the intra-annual C dynamics in stems under such conditions.Wood formation and stem CO 2 efflux were monitored in a Mediterranean beech forest forthree years (2015-2017), including a late frost (2016) and a summer drought (2017).The late frost reduced radial growth and, consequently, the amount of carbon fixed in thestem biomass by 80%. Stem carbon efflux in 2016 was reduced by 25%, which can beattributed to the reduction of effluxes due to growth respiration. Counter to our expectations,we found no effects of the 2017 summer drought on radial growth and stem carbon efflux.The studied extreme weather events had various effects on tree growth. Even though latespring frost had a devastating impact on beech radial growth in the current year, trees fullyrecovered in the following growing season, indicating high resilience of beech to thisstressful event.