Differential response of oak and beech to late frost damage: an integrated analysis from organ to forest

Abstract

Intense spring freezing events can kill the recently produced cohort of leaves, forcing trees to expend additional carbon and nutrient stocks to produce a second cohort of leaves. The future trends in the frequency of late spring frosts will affect the adaptation of some tree species to their current habitats. Here we studied the effect of a late frost which occurred in 2017 on a mixed beech (Fagus sylvatica)-oak (Quercus petraea) forest located in central Spain, where these species reach their southernmost distribution limits. We followed a multi-scale approach from organ to forest levels. At the organ level, leaf and stem morphological and biochemical traits were compared between frost-damaged and non-damaged trees. At the tree level, we compared the 2017 radial growth between damaged and non-damaged trees. At the stand level, the 2017 Leaf Area Index (LAI) and daily variations of NDVI during 2017 were compared with those of average years in areas dominated by beech and oak. Finally, at the forest scale, daily NDVI dynamics during 2017 were compared with those of the three previous years. According to our results, beech trees damaged by late frost kept non-structural carbohydrate (NSC) concentrations stable by drastically reducing wood production. This growth reduction could compensate for the drop in carbon inputs due to the death of the first leaf cohort, the need to form a second leaf cohort, the one-month delay between both leaf flushes and the smaller photosynthetic surface of the second leaf cohort. In contrast, although the frost-damaged oaks lost the first cohort of leaves and formed a second one, no differences in leaf individual area and phenology, nor stem NSC concentrations and radial growth were found when comparing damaged and non-damaged oaks. The differential response between both tree species seems to provide oak with a competitive advantage over beech.