Land use legacies drive higher growth, lower wood density and enhanced climatic sensitivity in recently established forests

Europe is undergoing significant forest expansion due to the abandonment of rural areas driven by economic and demographic changes. Recently established forests provide key ecosystem services such as habitat provision and increased carbon stocks. However, we lack understanding of whether past land use might alter their resilience to climate change compared with long-established forests. Forests established in former agricultural areas may benefit from land use legacies resulting in higher fertility, yet such a benefit might turn into a disadvantage if it involves changes in functional attributes that lower their ability to cope with negative climatic events (e.g. droughts). Here we examined whether recently (post 1956) and long-established (pre 1956) beech forests in Catalonia (NE Spain) differ in their growth patterns, wood density, sensitivity to climate and response to extreme climatic events. Our results indicate higher growth (32%) and lower wood density (3%) in trees from recently established forests, even when controlling for tree age and competition. In addition, recently established forests showed a higher sensitivity to Standardised Precipitation-Evapotranspiration Index (SPEI), precipitation and temperature and to extreme negative and positive climatic events. In particularly wet years, recently established forests show twice the number of positive pointer years than long-established forests. Compensatory growth during positive years in recently established forests, may be driving the similar or even higher recovery and resilience detected after drought episodes. Nevertheless, the higher climatic sensitivity of the recently established forests, together with their greater growth and lower wood density indicates that they may be particularly vulnerable to future droughts. Such enhanced vulnerability might question their ability to contribute to carbon sequestration in the long term and emphasises the need to account for land use legacies to better predict future forest function as climate changes.