Competition overrides climate as trigger of growth decline in a mixed Fagaceae Mediterranean rear-edge forest

International audienceAbstractKey messageIn recent decades, there has been a decline in growth in a rear-edge broadleaf forest ofFagus sylvatica,Quercus petraea, and Quercus pyrenaica. Although temperatures have been rising due to climate change, the observed decline in growth was mainly attributed to increased density and competition between trees since the cessation of traditional uses such as logging in the 1960s.ContextIn recent decades, two major factors have influenced tree growth in many forests: climate warming, which is associated with aridification and negative growth trends in many Mediterranean forests, and abandonment of forest management, resulting from forest policy in conjunction with rural depopulation in Europe, often leading to an increase in competition and a decrease in growth.AimsHere, we study the growth trends in a mixed forest of Fagus sylvatica, Quercus petraea, and Quercus pyrenaica, where the abandonment of traditional uses in the 1960s has been followed by an increase in tree density. In this forest, both F. sylvatica and Q. petraea reach their south-westernmost limits of distribution.MethodsUsing dendrochronological methods and growth modeling, we assess the importance of climate warming on the shifts in competitive growth advantage of these three coexisting tree species and the relative importance of climate and competition on growth trends.ResultsQ. petraea and especially F. sylvatica showed a favorable evolution of their competitive capacity, despite the increase in temperatures that has occurred in the area in recent decades. F. sylvatica presented the lowest sensitivity to climate.ConclusionUnder the current climate and forest structure conditions, competition is the most limiting factor on tree growth for the two oak species