Identifying drivers of non-stationary climate-growth relationships of European beech

The future performance of the widely abundant European beech (Fagus sylvatica L.) across its ecological amplitude is uncertain. Although beech is considered drought-sensitive and thus negatively affected by drought events, scientific evidence indicating increasing drought vulnerability under climate change on a cross-regional scale remains elusive. While evaluating changes in climate sensitivity of secondary growth offers a promising avenue, studies from productive, closed-canopy forests suffer from knowledge gaps, especially regarding the natural variability of climate sensitivity and how it relates to radial growth as an indicator of tree vitality. Since beech is sensitive to drought, we in this study use a drought index as a climate variable to account for the combined effects of temperature and water availability and explore how the drought sensitivity of secondary growth varies temporally in dependence on growth variability, growth trends, and climatic water availability across the species’ ecological amplitude. Our results show that drought sensitivity is highly variable and non-stationary, though consis- tently higher at dry sites compared to moist sites. Increasing drought sensitivity can largely be explained by increasing climatic aridity, especially as it is exacerbated by climate change and trees’ rank progression within forest communities, as (co-)dominant trees are more sensitive to extra-canopy climatic conditions than trees embedded in understories. However, during the driest periods of the 20th century, growth showed clear signs of being decoupled from climate. This may indicate fundamental changes in system behavior and be early-warning signals of decreasing drought tolerance. The multiple significant interaction terms in our model elucidate the complexity of European beech’s drought sensitivity, which needs to be taken into consideration when assessing this species’ response to climate change.

Additional authors: Isabel Dorado-Liñán, Choimaa Dulamsuren, Balázs Garamszegi, Michael Grabner, Andrew Hacket-Pain, Jon Kehlet Hansen s, Claudia Hartl, Weiwei Huang, Pavel Janda, Marko Kazimirović, Florian Knutzen, Jürgen Kreyling, Alexander Land, Nicolas Latte, François Lebourgeois, Christoph Leuschner, Luis A. Longares, Edurne Martinez del Castillo, Annette Menzel, Renzo Motta, Lena Muffler-Weigel, Paola Nola, Momchil Panayatov, Any Mary Petritan, Ion Catalin Petritan, Ionel Popa, Cǎtǎlin-Constantin Roibu , Álvaro Rubio-Cuadrado, Miloš Rydval, Tobias Scharnweber, J. Julio Camarero, Miroslav Svoboda, Elvin Toromani, Volodymyr Trotsiuk, Marieke van der Maaten-Theunissen, Ernst van der Maaten, Robert Weigel, Martin Wilmking, Tzvetan Zlatanov, Anja Rammig, Christian S. Zang