Influence of climate drivers and the North Atlantic Oscillation on beech growth at marginal sites across the Mediterranean

Abstract

European beech Fagus sylvatica L. represents one of the most commercially and ecologically important forest tree species in Europe. The study of climate-growth relationships may provide relevant information to assist projections of future species' distribution as well as forest management strategies. In this study, 9 European beech stands were selected at the rear edges of the species' distribution across an east-west gradient in the Mediterranean Basin (MB).Most of the tree-ring chronologies reached back more than a century; however we investigated the common period 1950-2012 in order to avoid past intensive management activities at some sites. The influences of temperature and precipitation on tree growth as well as their geographical patterns were investigated. Furthermore, the influence of the dominant atmospheric circulation pattern, the North AtlanticOscillation (NAO), was also assessed. The results reveal that tree growth in stands located in the western MB are limited by the combined influences of summer temperature and precipitation while stands located in central and eastern MB are mainly limited by summer temperature and show consistent lag effects on growth. The dry conditions prevailing during positive phases of the winter NAO have exerted a significant negative influence at sites located in western and central MB for the last 6 decades. However, the significance of NAO influence has generally decreased from western to eastern MB during recent decades. The results also provide evidence for the existence of carry-over effects that may be essential for the persistence and survival of some of these marginal populations.