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

Jet stream position explains regional anomalies in European beech forest productivity and tree growth.

The mechanistic pathways connecting ocean-atmosphere variability and terrestrial productivity are well-established theoretically, but remain challenging to quantify empirically. Such quantification will greatly improve the assessment and prediction of changes in terrestrial carbon sequestration in response to dynamically induced climatic extremes. The jet stream latitude (JSL) over the North Atlantic-European domain provides a synthetic and robust physical framework that integrates climate variability not accounted for by atmospheric circulation patterns alone. Surface climate impacts of north-south summer JSL displacements are not uniform across Europe, but rather create a northwestern-southeastern dipole in forest productivity and radial-growth anomalies. Summer JSL variability over the eastern North Atlantic-European domain (5-40E) exerts the strongest impact on European beech, inducing anomalies of up to 30% in modelled gross primary productivity and 50% in radial tree growth. The net effects of JSL movements on terrestrial carbon fluxes depend on forest density, carbon stocks, and productivity imbalances across biogeographic regions

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world\u27s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all the world’s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

The handbook for standardized field and laboratory measurements in terrestrial climate change experiments and observational studies (ClimEx)

1. Climate change is a world‐wide threat to biodiversity and ecosystem structure, functioning and services. To understand the underlying drivers and mechanisms, and to predict the consequences for nature and people, we urgently need better understanding of the direction and magnitude of climate change impacts across the soil–plant–atmosphere continuum. An increasing number of climate change studies are creating new opportunities for meaningful and high‐quality generalizations and improved process understanding. However, significant challenges exist related to data availability and/or compatibility across studies, compromising opportunities for data re‐use, synthesis and upscaling. Many of these challenges relate to a lack of an established ‘best practice’ for measuring key impacts and responses. This restrains our current understanding of complex processes and mechanisms in terrestrial ecosystems related to climate change. 2. To overcome these challenges, we collected best‐practice methods emerging from major ecological research networks and experiments, as synthesized by 115 experts from across a wide range of scientific disciplines. Our handbook contains guidance on the selection of response variables for different purposes, protocols for standardized measurements of 66 such response variables and advice on data management. Specifically, we recommend a minimum subset of variables that should be collected in all climate change studies to allow data re‐use and synthesis, and give guidance on additional variables critical for different types of synthesis and upscaling. The goal of this community effort is to facilitate awareness of the importance and broader application of standardized methods to promote data re‐use, availability, compatibility and transparency. We envision improved research practices that will increase returns on investments in individual research projects, facilitate second‐order research outputs and create opportunities for collaboration across scientific communities. Ultimately, this should significantly improve the quality and impact of the science, which is required to fulfil society's needs in a changing world

Global maps of soil temperature.

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Phenotypic plasticity and genetic adaptation in European beech: Insights into natural regeneration patterns and adult growth performance across the distribution range

Species have to cope with climate change either by migration or by adaptation and acclimatisation. Especially for long-living tree species with a low seed dispersal capacity (e.g. European beech, hereafter called beech), the in situ responses through genetic adaptation and phenotypic plasticity play an important role for their persistence. Beech, the dominant climax tree species in Central Europe, shows a high drought sensitivity and its distribution range is expected to shift northwards. On the other hand, projected northward shifts need to be taken with caution, as some studies suggest a sensitivity of beech to frost events in winter and spring. However, studies on the growth performance of cold-marginal beech populations are still rare. Previous studies on beech populations found local adaptation to drought and phenotypic plasticity in fitness-related traits as well as phenological traits. However, studies on the regeneration of beech under natural conditions are yet missing, although germination and establishment of young trees are a very first selective bottleneck and are crucial for tree population persistence and for successful range shifts. This PhD-thesis aimed to identify the potential of plasticity and local adaptation in the important early life-history traits germination, establishment after the 1st year, and survival after the 2nd year in a reciprocal transplantation experiment at 11 sites across and even beyond the distribution range of beech (Manuscript 1). Moreover, this thesis investigated the climate sensitivity and the adaptation potential of beech populations by conducting dendroecological studies along a large climatic gradient across the distribution range (Manuscript 2) and along a strong winter temperature gradient towards the cold distribution margin in Poland (Manuscript 3). In addition, the impact of local climatic singularities was studied in a local study at the southern margin (Manuscript 4). Warm and dry conditions limited natural regeneration, which was indicated by very low survival of young trees, even though germination rates increased with increasing temperature (Manuscript 1). This was also the case in parts of the distribution centre due to the hot and dry conditions in 2018. Although the transplantation experiment revealed high plasticity in the early life-history traits, this plasticity might thus not buffer against climate change under dry conditions. Local adaptation was not detected for any of these traits along the climatic gradient. In contrast, the results of the dendroecological study across the gradient (Manuscript 2) hint towards an adaptation potential of adult trees to drought at the southern margin. Thus, adult trees seemed to be adapted to drought at the southern margin, whereas tree growth in the distribution centre was sensitive to drought. These results indicate that parts of the centre may become ecologically marginal with increasing drought frequency in times of climate change. Interestingly, Manuscript 4 shows that beech growth was positively influenced by frequent fog immersion at the southern distribution margin in north-eastern Spain. This study underlines the importance of local climatic singularities, as they may allow marginal populations to grow in climate refugia in an otherwise unfavourable climate. At the cold distribution margin, the study in Manuscript 1 found a remarkably higher survival of young trees in Sweden than in Poland. Moreover, the dendroecological studies revealed that beech was hampered by both drought at the cold-dry margin (Manuscript 2) and by winter cold at the cold-wet margin in Poland (Manuscript 3). All these results highlight the importance to study climate sensitivity of adult trees and the response of early life-history traits at the cold margin with a more differentiated view comparing cold-dry against the cold-wet populations and growing conditions. However, the high plasticity of the early life-history traits may allow for an increasing germination rate with climate warming at the northern margin and may thus facilitate natural regeneration there. In contrast, the dendroecological studies suggest that adult trees at the cold distribution margin may suffer either from drought or from winter cold and that the risk for spring frost may increase. Thus, the often-predicted compensation of dry-marginal population decline by a northward range expansion should be discussed more critically. In conclusion, my PhD thesis provides new knowledge about the potential of natural regeneration and about climate sensitivity of adult trees across the distribution range of beech. Moreover, it underlines the importance to study both the young tree stages as well as adult trees to assess the performance and vulnerability of tree species under climate change, as both showed differences in their response to changing environmental conditions.Arten können den Klimawandel entweder durch Migration oder durch Anpassung und Akklimatisierung bewältigen. Insbesondere für langlebige Baumarten mit einer geringen Samenverbreitungskapazität (z.B. Rotbuchte) spielen die In-situ-Reaktionen der genetischen Anpassung und der phänotypischen Plastizität eine wichtige Rolle für ihr Bestehen. Die Rotbuche, die dominierende Klimaxbaumart in Zentraleuropa, weist eine hohe Sensitivität gegenüber Trockenheit auf und ihr Verbreitungsgebiet wird sich aufgrund des Klimawandels in Zukunft voraussichtlich in Richtung Norden verschieben. Allerdings müssen projizierte Verschiebungen des Verbreitungsgebietes nach Norden mit Vorsicht betrachtet werden, da einige Studien eine Sensitivität der Buche gegenüber Frostereignissen im Winter und im Frühling zeigen. Studien zur Klimasensitivität von Buchenpopulationen am nördlichen Verbreitungsrand sind jedoch kaum vorhanden. Bisherige Studien zu Buchenpopulationen haben eine lokale Anpassung an Dürre und phänotypische Plastizität in fitnessbezogenen und phänologischen Merkmalen gefunden. Studien zur Verjüngung der Buche unter natürlichen Bedingungen fehlen allerdings noch, obwohl die Keimung und Etablierung juveniler Bäume ein erster selektiver Flaschenhals sind. Eine erfolgreiche Verjüngung ist entscheidend für das Bestehen einer Population und für eine erfolgreiche Ausbreitung von Verbreitungsgebieten. Ziel dieser Dissertation war es das Potential von Plastizität und lokaler Anpassung in den wichtigen pflanzenökologischen Merkmalen des juvenilen Pflanzenstadiums, Keimung, Etablierung im ersten Jahr und Überleben im zweiten Jahr, in einem reziproken Transplantationsexperiment an 11 Standorten über und sogar über das Verbreitungsgebiet hinaus zu identifizieren (Manuskript 1). Darüber hinaus untersuchte diese Arbeit die Klimasensitivität und das Anpassungspotential von Buchenpopulationen mithilfe von dendroökologischen Studien entlang eines großen Klimagradienten über das Verbreitungsgebiet (Manuskript 2) und entlang eines starken Wintertemperaturgradienten in Richtung der Kältegrenze in Polen (Manuskript 3). Zusätzlich wurde der Einfluss lokaler klimatischer Besonderheiten in einer lokalen Studie am südlichen Verbreitungsrand der Buche untersucht (Manuskript 4). Warme und trockene Bedingungen schränkten die natürliche Verjüngung ein, was sich durch das geringe Überleben juveniler Bäume zeigte, obwohl die Keimrate mit ansteigender Temperatur zunahm (Manuskript 1). Eine eingeschränkte Verjüngung wurde auch in Teilen des Verbreitungszentrums aufgrund der heißen und trockenen Bedingungen im Jahr 2018 gefunden. Obwohl die Jungpflanzen sehr plastisch reagierten, scheint es eher, dass diese Plastizität unter trockenen Bedingungen den Klimawandel dennoch nicht abpuffern kann. Lokale Anpassung konnte entlang des Klimagradienten nicht festgellt werden. Im Gegensatz dazu deuten die Ergebnisse der dendroökologischen Gradientstudie (Manuskript 2) auf ein Anpassungspotential adulter Bäume an Dürre am südlichen Verbreitungsrand hin. Adulte Bäume schienen an Dürre am südlichen Verbreitungsrand angepasst zu sein, während zentrale Populationen sehr sensitiv auf Dürre reagierten. Diese Ergebnisse deuten darauf hin, dass Teile des Verbreitungszentrums in Zeiten des Klimawandels einhergehend mit einer zunehmenden Häufigkeit von Dürreereignissen ökologisch marginal werden könnten. Interessanterweise zeigt Manuskript 4, dass das Buchenwachstum durch die häufige Nebelbildung am südlichen Verbreitungsrand im Nordosten Spaniens positiv beeinflusst wird. Diese Studie unterstreicht die Bedeutung von lokalen klimatischen Singularitäten wie Nebelbildung, da diese südlichen Populationen ermöglichen können in Klimarefugien unter ansonsten ungünstigen Klimabedingungen zu wachsen. Am kalten Verbreitungsrand ergab die Studie in Manuskript 1 ein bemerkenswert höheres Überleben juveniler Bäume in Schweden als in Polen. Darüber hinaus zeigten die dendroökologischen Studien, dass das Buchenwachstum sowohl durch Trockenheit am kalt-trockenen Verbreitungsrand (Manuskript 2) als auch durch Winterkälte am kalt-feuchten Verbreitungsrand in Polen beeinträchtig war. Ein differenzierter Blick auf Unterschiede in der Klimasensitivität zwischen kalt-trockenen und kalt-feuchten Populationen ist daher wichtig. Die hohe Plastizität der Merkmale des juvenilen Pflanzenstadiums könnte jedoch eine zunehmende Keimrate am nördlichen Verbreitungsrand durch die Klimaerwärmung ermöglichen und somit eine natürliche Verjüngung dort erleichtern. Im Gegensatz dazu legen die dendroökologischen Studien nahe, dass adulte Bäume am kalten Verbreitungsrand entweder unter Trockenheit oder Winterkälte leiden könnten und dass das Risiko für Frostschäden im späten Frühjahr zunehmen könnte. Daher sollte die häufig projizierte Kompensation eines Rückzuges des Verbreitungsgebietes der Buche im Süden durch eine Expansion des Verbreitungsgebietes nach Norden kritischer diskutiert werden. Zusammenfassend liefert diese Dissertation neue Erkenntnisse über das Potenzial der natürlichen Verjüngung und über die Klimasensitivität von Buchenpopulationen über das Verbreitungsgebiet. Darüber hinaus ist zu betonen, wie wichtig es ist, sowohl juvenile als auch adulte Bäume zu untersuchen, wenn man das Wachstumspotential und die Vulnerabilität von Baumarten in Zeiten des Klimawandels bewerten möchte, da beide Stadien unterschiedliche Reaktionen auf sich ändernde Umweltbedingungen zeigen

Lowest drought sensitivity and decreasing growth synchrony towards the dry distribution margin of European beech

Abstract Aim Climate limits the potential distribution ranges of species. Establishment and growth of individuals at range margins is assumed to be more limited by extreme events such as drought or frost events than in the centre of their range. We explore whether the growth of beech is more sensitive to drought towards the dry distribution margin and more sensitive to frost towards the cold distribution margin. Furthermore, we aim to gain insight into the adaptive potential of beech towards both the dry and cold distribution margins. Location European gradient from the dry (Spain) to the cold (Poland, Sweden) distribution margin of beech. Taxon European beech (Fagus sylvatica L.). Methods We applied a range‐wide dendroecological study to analyse spatial and temporal trends in climate–growth relationships. We further investigated negative growth anomalies and growth synchrony towards the range margins. Results We found beech to be drought sensitive across its whole range, except at the dry distribution margin. Furthermore, sensitivity to winter temperature was not found in the centre or at the cold distribution margin, but at the southern distribution margin. Growth synchrony was lower at the dry than at the cold distribution margin. Main conclusions Beech seems to be adapted to drought at the dry distribution margin with a high adaptive potential indicated by the lowest growth synchrony along the gradient. At the cold distribution margin, cold events in winter and spring were less important for growth than drought. Still, the importance of spring frost for beech growth appears to increase in recent decades. Considering a projected north‐eastward shift of the distribution range, beech is likely facing drought stress in combination with spring frost risk at the cold margin which could lead to a hampered range expansion

High plasticity in germination and establishment success in the dominant forest tree Fagus sylvatica

Abstract Aim Distribution ranges of temperate tree species are shifting poleward and upslope into cooler environments due to global warming. Successful regeneration is crucial for population persistence and range expansion. Thus, we aimed to identify environmental variables that affect germination and seedling establishment of Europe's dominant forest tree, to compare the importance of plasticity and genetic variation for regeneration, and to evaluate the regeneration potential at and beyond the southern and northern distribution margins. Location Europe. Time period 2016–2018. Major taxa studied European beech (Fagus sylvatica (L.)). Methods We investigated how germination, establishment and juvenile survival change across a reciprocal transplantation experiment using over 9,000 seeds of beech from 7 populations from its southern to its northern distribution range margins. Results Germination and establishment at the seedling stage were highly plastic in response to environmental conditions. Germination success increased with warmer and declined with colder air temperature, whereas establishment and survival were hampered under warmer and drier conditions. Germination differed among populations and was positively influenced by seed weight. However, there was no evidence of local adaptation in any trait. Main conclusions The high plasticity in the early life‐history traits found irrespective of seed origin may allow for short‐term acclimatization. However, our results also indicate that this plasticity might not be sufficient to ensure the regeneration of beech in the future due to the low survival found under dry and hot conditions. The future climatic conditions in parts of the distribution centre and at the rear edge might thus become limiting for natural regeneration, as the likelihood of extreme heat and drought events will increase. By contrast, at the cold distribution margin, the high plasticity in the early life‐history traits may allow for increasing germination success with increasing temperatures and may thus facilitate natural regeneration in the future

High plasticity in germination and establishment success in the dominant forest tree Fagus sylvatica across Europe

Abstract Aim Distribution ranges of temperate tree species are shifting poleward and upslope into cooler environments due to global warming. Successful regeneration is crucial for population persistence and range expansion. Thus, we aimed to identify environmental variables that affect germination and seedling establishment of Europe's dominant forest tree, to compare the importance of plasticity and genetic variation for regeneration, and to evaluate the regeneration potential at and beyond the southern and northern distribution margins. Location Europe. Time period 2016–2018. Major taxa studied European beech (Fagus sylvatica (L.)). Methods We investigated how germination, establishment and juvenile survival change across a reciprocal transplantation experiment using over 9,000 seeds of beech from 7 populations from its southern to its northern distribution range margins. Results Germination and establishment at the seedling stage were highly plastic in response to environmental conditions. Germination success increased with warmer and declined with colder air temperature, whereas establishment and survival were hampered under warmer and drier conditions. Germination differed among populations and was positively influenced by seed weight. However, there was no evidence of local adaptation in any trait. Main conclusions The high plasticity in the early life‐history traits found irrespective of seed origin may allow for short‐term acclimatization. However, our results also indicate that this plasticity might not be sufficient to ensure the regeneration of beech in the future due to the low survival found under dry and hot conditions. The future climatic conditions in parts of the distribution centre and at the rear edge might thus become limiting for natural regeneration, as the likelihood of extreme heat and drought events will increase. By contrast, at the cold distribution margin, the high plasticity in the early life‐history traits may allow for increasing germination success with increasing temperatures and may thus facilitate natural regeneration in the future