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. Zan

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 consistently 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

The Future of European Beech in Northern Germany—Climate Change Vulnerability and Adaptation Potential

Open-Access-Publikationsfonds 202

Effects of forest fragmentation on organic carbon pool densities in the Mongolian forest-steppe

The hypothesis was tested that the size and the degree of isolation of Larix sibirica forests in the forest-steppe ecotone of Mongolia affects aboveground and belowground carbon pool densities. The research question was based on the fact that both microclimate and the drought sensitivity of stemwood production were earlier shown to differ with stand size and isolation in this ecotone. Contrary to our hypothesis, we did not find significant differences in the organic carbon stock densities of the tree biomass and the mineral soil. The depth, carbon content and carbon stock density of the organic layer increased with stand size, but was not a major determinant of total ecosystem carbon stock density. Nevertheless, the increasing depth and the increasing humus content of the organic layer with stand size could be significant by improving moisture availability and, thus, promoting forest regeneration. Furthermore, reduced organic layer thickness and humus content and thus water storage capacity could be one out of several causes of the previously observed higher drought vulnerability of stemwood formation in small forest stands of the Mongolian forest-steppe. A mean carbon stock density of 237 Mg C ha⁻¹ for total ecosystem organic carbon stock density matches with earlier estimates for Mongolia's boreal forest corroborating the view that the ecosystem carbon pool density at the southern edge of the boreal forest is lower compared to forests at higher latitudes with even colder climate and deeper and more widespread permafrost

Soil water availability and branch age explain variability in xylem safety of European beech in Central Europe

Xylem embolism resistance has been identified as a key trait with a causal relation to drought-induced tree mortality, but not much is known about its intra-specific trait variability (ITV) in dependence on environmental variation. We measured xylem safety and efficiency in 300 European beech (Fagus sylvatica L.) trees across 30 sites in Central Europe, covering a precipitation reduction from 886 to 522 mm year−1. A broad range of variables that might affect embolism resistance in mature trees, including climatic and soil water availability, competition, and branch age, were examined. The average P50 value varied by up to 1 MPa between sites. Neither climatic aridity nor structural variables had a significant influence on P50. However, P50 was less negative for trees with a higher soil water storage capacity, and positively related to branch age, while specific conductivity (Ks) was not significantly associated with either of these variables. The greatest part of the ITV for xylem safety and efficiency was attributed to random variability within populations. We conclude that the influence of site water availability on P50 and Ks is low in European beech, and that the high degree of within-population variability for P50, partly due to variation in branch age, hampers the identification of a clear environmental signal

A genome-wide genetic association study reveals SNPs significantly associated with environmental variables and specific leaf area in European beech

European beech is negatively affected by climate change and a further growth decline is predicted for large parts of its distribution range. Despite the importance of this species, little is known about its genetic adaptation and especially the genetic basis of its physiological traits. Here, we used genotyping by sequencing to identify SNPs in 43 German European beech populations growing under different environmental conditions. In total, 28 of these populations were located along a precipitation and temperature gradient in northern Germany, and single tree-based hydraulic and morphological traits were available. We obtained a set of 13,493 high-quality SNPs that were used for environmental and SNP-trait association analysis. In total, 22 SNPs were identified that were significantly associated with environmental variables or specific leaf area (SLA). Several SNPs were located in genes related to stress response. The majority of the significant SNPs were located in non-coding (intergenic and intronic) regions. These may be in linkage disequilibrium with the causative coding or regulatory regions. Our study gives insights into the genetic basis of abiotic adaptation in European beech, and provides genetic resources that can be used in future studies on this species. Besides clear patterns of local adaptation to environmental conditions of the investigated populations, the analyzed morphological and hydraulic traits explained most of the explainable genetic variation. Thus, they could successfully be altered in tree breeding programs, which may help to increase the adaptation of European beech to changing environmental conditions in the future

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

Climate-change-driven growth decline of European beech forests

The growth of past, present, and future forests was, is and will be affected by climate variability. This multifaceted relationship has been assessed in several regional studies, but spatially resolved, large-scale analyses are largely missing so far. Here we estimate recent changes in growth of 5800 beech trees (Fagus sylvatica L.) from 324 sites, representing the full geographic and climatic range of species. Future growth trends were predicted considering state-of-the-art climate scenarios. The validated models indicate growth declines across large region of the distribution in recent decades, and project severe future growth declines ranging from −20% to more than −50% by 2090, depending on the region and climate change scenario (i.e. CMIP6 SSP1-2.6 and SSP5-8.5). Forecasted forest productivity losses are most striking towards the southern distribution limit of Fagus sylvatica, in regions where persisting atmospheric high-pressure systems are expected to increase drought severity. The projected 21(st) century growth changes across Europe indicate serious ecological and economic consequences that require immediate forest adaptation