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

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

A group of trees is called a forest : a holistic approach to study the anatomy and growth of Picea glauca

Forest ecosystems around the world and especially boreal forests, are facing drastically changing climatic conditions. It is known that these changes could challenge their functionality and vitality. Still, the exact impact is not fully understood, as tree growth is a complex process and depends on countless environmental and genetic factors. To estimate the effects of climate change on tree growth and forest development precisely, we must learn more about tree growth itself. A comprehensive approach is needed where trees and forests are investigated on different scales and levels of detail, ranging from global studies to studies on single individuals. In this dissertation, I follow such a comprehensive approach, using the North American conifer white spruce as an example. I present three papers in the form of three chapters in which my co-authors and I studied the growth and anatomy of white spruce (Picea glauca [Moench] Voss) and how it is influenced by environmental, climatic, and genetic factors. We used diverse approaches and methods on different spatial scales, ranging from investigations on the landscape to the local scale. We established three paired plots with forest and treeline sites (two cold-limited and one drought-limited). as well as one additional forest site. In the first chapter, we concentrated on the genetic diversity of white spruce within and between populations at all study sites throughout Alaska. The genetic investigations were combined with analyses on the individual growth response of trees to climatic conditions to find whether genetic similarities or spatial proximity caused similarities in growth and climatic sensitivity. In the second chapter, we studied the direct and indirect effects of environmental conditions on the xylem tissue of white spruce. We analyzed the impact of precipitation, temperature, and tree height on four xylem anatomical traits in trees growing at the three treelines. The investigated traits represented the main functions of xylem tissue (i.e., water transport and structural support). In the third chapter, we investigated similar xylem anatomical traits at one cold-limited treeline. We compared xylem anatomy and annual increment between genetic groups and individuals and between spatial groups to investigate whether spatial or genetic grouping influenced the anatomy and growth of white spruce. We found an overall high gene flow and high genetic diversity in white spruce. However, the sensitivity of the growth and anatomical traits of white spruce was driven mainly by spatial rather than genetic effects and differed between study sites. Trees from the drought-limited site were more sensitive towards precipitation and a moisture index, while trees from the cold-limited sites were more sensitive towards temperature. A strong direct effect of tem- perature was primarily found in latewood traits related to the structural sup- port of the tree. Earlywood traits related to water transport, however, were influenced mainly by tree height. Tree height itself was potentially affected by diverse abiotic and biotic factors (e.g., (micro)climate, soil conditions, and competition). Thus, traits related to water transport were indirectly influenced by environmental conditions. Genetic effects in xylem anatomical traits were found in the earlywood hydraulic diameter and latewood den- sity, whereas in general, primarily spatial rather than genetic grouping was influencing the anatomy of white spruce. Overall, white spruce showed to be a genetically diverse species with a high gene flow. The effects of spatial proximity and spatial grouping on the sensitivity and anatomy of white spruce indicate high phenotypic plastic- ity. This high phenotypic plasticity combined with the vast genetic diversity translates into an immense potential for the species to adjust (phenotypically) and possibly adapt (genetically) to changing conditions. Thus, in terms of climate change, white spruce may be a rather persistent species that manages to cope with the drastic changes. Though additional work might be needed to draw a more solid conclusion, the presented work shows how a comprehensive study approach can help to interpret and understand the growth and ecology of a tree species. It may be an inspiration for future studies to broaden their approaches and to use comprehensive methods on different levels of detail to not only observe trees but to explore and understand them.Waldökosysteme auf der ganzen Welt, insbesondere boreale Wälder sind mit drastischen klimatischen Veränderungen konfrontiert. Es ist bekannt, dass diese Veränderungen die Funktionalität und Vitalität der Wälder vor eine Herausforderung stellen. Die genauen Auswirkungen sind jedoch noch nicht vollständig bekannt, da das Wachstum von Bäumen ein komplexer Prozess ist, der von unzähligen Umwelt- und genetischen Faktoren abhängt. Um die Auswirkungen des Klimawandels auf das Wachstum der Bäume und die Entwicklung der Wälder besser abschätzen zu können, müssen wir mehr über das Wachstum der Bäume selbst erfahren. Es ist ein umfassender Ansatz erforderlich, bei dem Bäume und Wälder in verschiedenen Maßstäben und Detailtiefen untersucht werden, von globalen Studien bis hin zu Studien über einzelne Individuen. In dieser Dissertation verfolge ich einen solchen umfassenden Ansatz am Beispiel der nordamerikanischen Weißfichte. Ich präsentiere drei Arbeiten in Form von drei Kapiteln, in denen meine Mitautoren und ich das Wachstum und die Anatomie der Weißfichte (Picea glauca [Moench] Voss) und deren Beeinflussung durch Umwelt-, Klima- und genetische Faktoren untersucht haben. Wir verwendeten verschiedene Ansätze und Methoden auf unterschiedlichen räumlichen Skalen, von Untersuchungen auf der Landschaftsebene bis hin zur lokalen Ebene. Wir haben drei paarweise Parzellen mit Wald- und Baumstandorten (zwei kältebegrenzte und ein trockenheitsbegrenzter) sowie einen zusätzlichen Waldstandort untersucht. Im ersten Kapitel konzentrierten wir uns auf die genetische Vielfalt der Weißfichte innerhalb und zwischen Populationen an allen Untersuchungsstandorten in Alaska. Die genetischen Untersuchungen wurden mit Analysen der individuellen Wachstumsreaktion von Bäumen auf klimatische Bedingungen kombiniert, um herauszufinden, ob genetische Verwandtschaft oder räumliche Nähe Ähnlichkeiten im Wachstum und in der Klimaempfindlichkeit verursachten. Im zweiten Kapitel untersuchten wir die direkten und indirekten Auswirkungen der Umweltbedingungen auf das Xylem der Weißfichte. Wir analysierten die Auswirkungen von Niederschlag, Temperatur und Baumhöhe auf vier xylem-anatomische Merkmale von Bäumen, die an den drei Baumgrenzen wuchsen. Die untersuchten Merkmale repräsentieren die Hauptfunktionen des Xylems (Wassertransport und strukturelle Unterstützung). Im dritten Kapitel untersuchten wir ähnliche xylem-anatomische Merkmale an einer kältebegrenzten Baumgrenze. Wir verglichen die Xylem-Anatomie und den jährlichen Zuwachs zwischen genetischen Gruppen und Individuen sowie zwischen räumlichen Gruppen, um zu untersuchen, ob die räumliche oder genetische Gruppierung die Anatomie und das Wachstum der Weißfichte beeinflusst. Wir fanden einen insgesamt hohen Genfluss und eine hohe genetische Vielfalt bei der Weißfichte. Die Empfindlichkeit von Wachstum und anatomischen Merkmalen der Weißfichte wurde jedoch hauptsächlich durch räumliche und nicht durch genetische Effekte bestimmt und unterschied sich zwischen den Untersuchungsstandorten. Die Bäume an den trockenheitsbegrenzten Standorten reagierten empfindlicher auf Niederschlag und einen Feuchtigkeitsindex, während die Bäume an den kältebegrenzten Standorten empfindlicher auf die Temperatur reagierten. Eine starke direkte Auswirkung der Temperatur wurde vor allem bei den Merkmalen des Spätholzes festgestellt, die mit der strukturellen Unterstützung des Baumes zusammenhängen. Die Merkmale des Frühholzes, die mit dem Wassertransport zusammenhängen, wurden dagegen hauptsächlich von der Baumhöhe beeinflusst. Die Baumhöhe selbst wurde potenziell durch verschiedene abiotische und biotische Faktoren (z. B. (Mikro-)Klima, Bodenbedingungen und Konkurrenz) beeinflusst. Somit wurden Merkmale, die mit dem Wassertransport zusammenhängen, indirekt durch Umweltbedingungen beeinflusst. Genetische Auswirkungen auf xylem-anatomische Merkmale wurden beim hydraulischen Durchmesser des Frühholzes und bei der Dichte des Spätholzes festgestellt, während jedoch im Allgemeinen eher die räumliche als die genetische Gruppierung die Anatomie der Weißfichte beeinflusste. Insgesamt erwies sich die Weißfichte als eine genetisch vielfältige Art mit einem hohen Genfluss. Die Auswirkungen der räumlichen Nähe und der räumlichen Gruppierung auf die Empfindlichkeit und Anatomie der Weißfichte deuten auf eine hohe phänotypische Plastizität hin. Diese hohe phänotypische Plastizität in Verbindung mit der enormen genetischen Vielfalt bedeutet ein immenses Potenzial für die Art, sich phänotypisch und genetisch an veränderte Bedingungen anzupassen. Im Hinblick auf den Klimawandel könnte die Weißfichte also eine ziemlich ausdauernde Art sein, der es gelingt, mit den drastischen Veränderungen fertig zu werden. Obwohl weitere Untersuchungen erforderlich sind, um eine solidere Schlussfolgerung zu ziehen, zeigt die vorgestellte Arbeit, wie ein umfassender Studienansatz helfen kann, das Wachstum und die Ökologie einer Baumart zu interpretieren und zu verstehen. Diese Arbeit kann eine Inspiration für künftige Studien sein, ihre Ansätze zu erweitern und umfassende Methoden auf verschiedenen Detailebenen anzuwenden, um Bäume nicht nur zu beobachten, sondern auch zu erforschen und zu verstehen

Direct and Indirect Effects of Environmental Limitations on White Spruce Xylem Anatomy at Treeline

Treeline ecosystems are of great scientific interest to study the effects of limiting environmental conditions on tree growth. However, tree growth is multidimensional, with complex interactions between height and radial growth. In this study, we aimed to disentangle effects of height and climate on xylem anatomy of white spruce [Picea glauca (Moench) Voss] at three treeline sites in Alaska; i.e., one warm and drought-limited, and two cold, temperature-limited. To analyze general growth differences between trees from different sites, we used data on annual ring width, diameter at breast height (DBH), and tree height. A representative subset of the samples was used to investigate xylem anatomical traits. We then used linear mixed-effects models to estimate the effects of height and climatic variables on our study traits. Our study showed that xylem anatomical traits in white spruce can be directly and indirectly controlled by environmental conditions: hydraulic-related traits seem to be mainly influenced by tree height, especially in the earlywood. Thus, they are indirectly driven by environmental conditions, through the environment’s effects on tree height. Traits related to mechanical support show a direct response to environmental conditions, mainly temperature, especially in the latewood. These results highlight the importance of assessing tree growth in a multidimensional way by considering both direct and indirect effects of environmental forcing to better understand the complexity of tree growth responses to the environment

Xylem Anatomical Variability in White Spruce at Treeline Is Largely Driven by Spatial Clustering

The ecological function of boreal forests is challenged by drastically changing climate conditions. Although an increasing number of studies are investigating how climate change is influencing growth and distribution of boreal tree species, there is a lack of studies examining the potential of these species to genetically adapt or phenotypically adjust. Here, we sampled clonally and non-clonally growing white spruce trees (Picea glauca [Moench] Voss) to investigate spatial and genetic effects on tree ring width and on six xylem anatomical traits representing growth, water transport, mechanical support, and wood density. We compared different methods for estimating broad sense heritability (H2) of each trait and we evaluated the effects of spatial grouping and genetic grouping on the xylem anatomical traits with linear models. We found that the three different methods used to estimate H2 were quite robust, showing overall consistent patterns, while our analyses were unsuccessful at fully separating genetic from spatial effects. By evaluating the effect size, we found a significant effect of genetic grouping in latewood density and earlywood hydraulic diameter. However, evaluating model performances showed that spatial grouping was a better predictor than genetic grouping for variance in earlywood density, earlywood hydraulic diameter and growth. For cell wall thickness neither spatial nor genetic grouping was significant. Our findings imply that (1) the variance in the investigated xylem anatomical traits and growth is mainly influenced by spatial clustering (most probably caused by microhabitat conditions), which (2) makes it rather difficult to estimate the heritability of these traits in naturally grown trees in situ. Yet, (3) latewood density and earlywood hydraulic diameter qualified for further analysis on the genetic background of xylem traits and (4) cell wall thickness seems a useful trait to investigate large-scale climatic effects, decoupled from microclimatic, edaphic and genetic influences

Genetic basis of growth reaction to drought stress differs in contrasting high‐latitude treeline ecotones of a widespread conifer

Abstract Climate change is increasing the frequency and intensity of drought events in many boreal forests. Trees are sessile organisms with a long generation time, which makes them vulnerable to fast climate change and hinders fast adaptations. Therefore, it is important to know how forests cope with drought stress and to explore the genetic basis of these reactions. We investigated three natural populations of white spruce (Picea glauca) in Alaska, located at one drought‐limited and two cold‐limited treelines with a paired plot design of one forest and one treeline plot. We obtained individual increment cores from 458 trees and climate data to assess dendrophenotypes, in particular the growth reaction to drought stress. To explore the genetic basis of these dendrophenotypes, we genotyped the individual trees at 3000 single nucleotide polymorphisms in candidate genes and performed genotype–phenotype association analysis using linear mixed models and Bayesian sparse linear mixed models. Growth reaction to drought stress differed in contrasting treeline populations. Therefore, the populations are likely to be unevenly affected by climate change. We identified 40 genes associated with dendrophenotypic traits that differed among the treeline populations. Most genes were identified in the drought‐limited site, indicating comparatively strong selection pressure of drought‐tolerant phenotypes. Contrasting patterns of drought‐associated genes among sampled sites and in comparison to Canadian populations in a previous study suggest that drought adaptation acts on a local scale. Our results highlight genes that are associated with wood traits which in turn are critical for the establishment and persistence of future forests under climate change

Global maps of soil temperature

Abstract 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° degrees C (mean = 3.0 +/‐ 2.1° degrees 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° degrees C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (‐0.7 +/‐ 2.3° degrees 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