Search

A fundamental assumption in trait-based ecology is that relationships between traits and environmental conditions are globally consistent. We use field-quantified microclimate and soil data to explore if trait–environment relationships are generalizable across plant communities and spatial scales. We collected data from 6,720 plots and 217 species across four distinct tundra regions from both hemispheres. We combined these data with over 76,000 database trait records to relate local plant community trait composition to broad gradients of key environmental drivers: soil moisture, soil temperature, soil pH and potential solar radiation. Results revealed strong, consistent trait–environment relationships across Arctic and Antarctic regions. This indicates that the detected relationships are transferable between tundra plant communities also when fine-scale environmental heterogeneity is accounted for, and that variation in local conditions heavily influences both structural and leaf economic traits. Our results strengthen the biological and mechanistic basis for climate change impact predictions of vulnerable high-latitude ecosystems. acceptedVersion

In the tundra, woody plants are dispersing towards higher latitudes and altitudes due to increasingly favourable climatic conditions. The coverage and height of woody plants are increasing, which may influence the soils of the tundra ecosystem. Here, we use structural equation modelling to analyse 171 study plots and to examine if the coverage and height of woody plants affect the growing-season topsoil moisture and temperature (

[Background]: Understanding the large-scale patterns of microbial functional diversity is essential for anticipating climate change impacts on ecosystems worldwide. However, studies of functional biogeography remain scarce for microorganisms, especially in freshwater ecosystems. Here we study 15,289 functional genes of stream biofilm microbes along three elevational gradients in Norway, Spain and China., [Results]: We find that alpha diversity declines towards high elevations and assemblage composition shows increasing turnover with greater elevational distances. These elevational patterns are highly consistent across mountains, kingdoms and functional categories and exhibit the strongest trends in China due to its largest environmental gradients. Across mountains, functional gene assemblages differ in alpha diversity and composition between the mountains in Europe and Asia. Climate, such as mean temperature of the warmest quarter or mean precipitation of the coldest quarter, is the best predictor of alpha diversity and assemblage composition at both mountain and continental scales, with local non-climatic predictors gaining more importance at mountain scale. Under future climate, we project substantial variations in alpha diversity and assemblage composition across the Eurasian river network, primarily occurring in northern and central regions, respectively., [Conclusions]: We conclude that climate controls microbial functional gene diversity in streams at large spatial scales; therefore, the underlying ecosystem processes are highly sensitive to climate variations, especially at high latitudes. This biogeographical framework for microbial functional diversity serves as a baseline to anticipate ecosystem responses and biogeochemical feedback to ongoing climate change., The study was supported by National Natural Science Foundation of China (91851117), the Program of Global Change and Mitigation (2017YFA0605200), CAS Key Research Program of Frontier Sciences (QYZDB-SSW-DQC043), CAS Strategic Pilot Science and Technology (XDA20050101), and National Natural Science Foundation of China (41571058, 41871048). AV was supported by the Chinese Academy of Sciences President’s International Fellowship Initiative (2018PS0007). EOC was supported by grant BRIDGES CGL2015-69043-P (Spanish Office for Science-MINECO-ERDF).

Forest canopies buffer macroclimatic temperature fluctuations. However, we do not know if and how the capacity of canopies to buffer understorey temperature will change with accelerating climate change. Here we map the difference (offset) between temperatures inside and outside forests in the recent past and project these into the future in boreal, temperate and tropical forests. Using linear mixed-effect models, we combined a global database of 714 paired time series of temperatures (mean, minimum and maximum) measured inside forests vs. in nearby open habitats with maps of macroclimate, topography and forest cover to hindcast past (1970–2000) and to project future (2060–2080) temperature differences between free-air temperatures and sub-canopy microclimates. For all tested future climate scenarios, we project that the difference between maximum temperatures inside and outside forests across the globe will increase (i.e. result in stronger cooling in forests), on average during 2060–2080, by 0.27 ± 0.16 °C (RCP2.6) and 0.60 ± 0.14 °C (RCP8.5) due to macroclimate changes. This suggests that extremely hot temperatures under forest canopies will, on average, warm less than outside forests as macroclimate warms. This knowledge is of utmost importance as it suggests that forest microclimates will warm at a slower rate than non-forested areas, assuming that forest cover is maintained. Species adapted to colder growing conditions may thus find shelter and survive longer than anticipated at a given forest site. This highlights the potential role of forests as a whole as microrefugia for biodiversity under future climate change.

Tundra ecosystems have experienced changes in vegetation composition, distribution, and productivity over the past century due to climate warming. However, the increase in above-ground biomass may be constrained by cryogenic land surface processes that cause topsoil disturbance and variable microsite conditions. These effects have remained unaccounted for in tundra biomass models, although they can impact multiple opposing feedbacks between the biosphere and atmosphere, ecosystem functioning and biodiversity. Here, by using field-quantified data from northern Europe, remote sensing, and machine learning, we show that cryogenic land surface processes substantially constrain above-ground biomass in tundra. The three surveyed processes (cryoturbation, solifluction, and nivation) collectively reduced biomass by an average of 123.0 g m(-2) (-30.0%). This effect was significant over landscape positions and was especially pronounced in snowbed environments, where the mean reduction in biomass was 57.3%. Our results imply that cryogenic land surface processes are pivotal in shaping future patterns of tundra biomass, as long as cryogenic ground activity is retained by climate warming. Vegetation in tundra ecosystems is constrained by cryogenic land surface processes, despite the fact that models of future biomass changes rarely take these into account, according to field and remote sensing data from northern Europe.

Ecological research heavily relies on coarse-gridded climate data based on standardized temperature measurements recorded at 2 m height in open landscapes. However, many organisms experience environmental conditions that differ substantially from those captured by these macroclimatic (i.e. free air) temperature grids. In forests, the tree canopy functions as a thermal insulator and buffers sub-canopy microclimatic conditions, thereby affecting biological and ecological processes. To improve the assessment of climatic conditions and climate-change-related impacts on forest-floor biodiversity and functioning, high-resolution temperature grids reflecting forest microclimates are thus urgently needed. Combining more than 1200 time series of in situ near-surface forest temperature with topographical, biological and macroclimatic variables in a machine learning model, we predicted the mean monthly offset between sub-canopy temperature at 15 cm above the surface and free-air temperature over the period 2000-2020 at a spatial resolution of 25 m across Europe. This offset was used to evaluate the difference between microclimate and macroclimate across space and seasons and finally enabled us to calculate mean annual and monthly temperatures for European forest understories. We found that sub-canopy air temperatures differ substantially from free-air temperatures, being on average 2.1°C (standard deviation ± 1.6°C) lower in summer and 2.0°C higher (±0.7°C) in winter across Europe. Additionally, our high-resolution maps expose considerable microclimatic variation within landscapes, not captured by the gridded macroclimatic products. The provided forest sub-canopy temperature maps will enable future research to model below-canopy biological processes and patterns, as well as species distributions more accurately. ispartof: GLOBAL CHANGE BIOLOGY vol:27 issue:23 pages:6307-6319 ispartof: location:England status: published

The functional composition of plant communities is a critical modulator of climate change impacts on ecosystems, but it is not a simple function of regional climate. In the Arctic tundra, where climate change is proceeding the most rapidly, communities have not shifted their trait composition as predicted by spatial temperature–trait relationships. Important causal pathways are thus missing from models of trait composition change. Here, we study causes of plant community functional variation in an oroarctic tundra landscape in Kilpisjärvi, Finland. We consider the community-weighted means of plant vegetative height, as well as two traits related to the leaf economic spectrum. Specifically, we model their responses to locally measured summer air temperature, snow conditions, and soil resource levels. For each of the traits, we also quantify the importance of intraspecific trait variation (ITV) for between-community functional differences and trait–environment matching. Our study shows that in a tundra landscape (1) snow is the most influential abiotic variable affecting functional composition, (2) vegetation height is under weak local environmental control, whereas leaf economics is under strong local environmental control, (3) the relative magnitude of ITV differs between traits, and (4) ITV is not very consequential for community-level trait–environment relationships. Our analyses highlight the importance of winter conditions for community functional composition in seasonal areas. We show that winter climate change can either amplify or counter the effects summer warming, depending on the trait. Electronic supplementary material The online version of this article (10.1007/s00442-019-04508-8) contains supplementary material, which is available to authorized users.

International audience; Forest microclimates contrast strongly with the climate outside forests. To fully understand and better predict how forests' biodiversity and functions relate to climate and climate change, microclimates need to be integrated into ecological research. Despite the potentially broad impact of microclimates on the response of forest ecosystems to global change, our understanding of how microclimates within and below tree canopies modulate biotic responses to global change at the species, community and ecosystem level is still limited. Here, we review how spatial and temporal variation in forest microclimates result from an interplay of forest features, local water balance, topography and landscape composition. We first stress and exemplify the importance of considering forest microclimates to understand variation in biodiversity and ecosystem functions across forest landscapes. Next, we explain how macroclimate warming (of the free atmosphere) can affect microclimates, and vice versa, via interactions with land-use changes across different biomes. Finally, we perform a priority ranking of future research avenues at the interface of microclimate ecology and global change biology, with a specific focus on three key themes: (1) disentangling the abiotic and biotic drivers and feedbacks of forest microclimates; (2) global and regional mapping and predictions of forest microclimates; and (3) the impacts of microclimate on forest biodiversity and ecosystem functioning in the face of climate change. The availability of microclimatic data will significantly increase in the coming decades, characterizing climate variability at unprecedented spatial and temporal scales relevant to biological processes in forests. This will revolutionize our understanding of the dynamics, drivers and implications of forest microclimates on biodiversity and ecological functions, and the impacts of global changes. In order to support the sustainable use of forests and to secure their biodiversity and ecosystem services for future generations, microclimates cannot be ignored.

Highlights • Climate change-induced risks to EU Habitats Directive species are poorly known. • Adverse land use for species often coincides with high climate change velocity. • Climate change and land use threats vary notably both between and within species. • Mapping risks across species occurrences is central to climate-wise conservation. • Climate change land-use risks hinder Habitats Directive species from reaching a favourable status. The Habitats Directive of the European Union is a key legislative instrument in Europe, supporting the conservation of rare, threatened or endemic species. It aims at ensuring that the species listed in the Annexes of the Habitats Directive show a favourable conservation status, i.e., that they are able to maintain viable populations and that their natural range is sufficient and not decreasing currently, nor will in the future. However, climate change may hamper Habitats Directive species in achieving (or maintaining) a favourable conservation status, particularly when these impacts are amplified by adverse land use. Here, we studied Habitats Directive species in Finland for which ≥70% of the occurrences were recorded with the resolution of ≤100 m. The number of occurrence sites for the 52 species studied ranged from one site to 13,653 sites, summing up to 19,367 sites. For all these sites and their surroundings, we assessed the vulnerabilities caused by climate change and land use. The climate exposure of occurrence sites was measured based on the rapidity of climatic changes (i.e. climate velocity) in three climate variables (growing degree days, mean January air temperature, water balance) at each site. Risks caused by land use were assessed using two negative and four positive variables that respectively described the quantity of land cover and habitats that is either harmful (e.g. clear-cut forest and drained peatlands) or supportive (protected areas and suitable habitats) to species occurrences. To complement climate and land-use variables, three additional variables describing protection status of the sites and the number of occurrences of the same species in the landscape were examined. Comparison of the mean vulnerability values for each species showed that some of the species inhabit, on average, areas with high climate exposure. Moreover, in certain species climate change-induced vulnerabilities consistently coincide with negative land use. However, in many of the 52 species there was large variation in the vulnerability levels between individual occurrence sites, concerning both climate exposure and land-use variables. Considering the vulnerabilities due to climate change separately, 40–60% of the species occurrence sites are expected to face high exposure caused by rapid changes in summer or winter temperatures, which presents challenges in maintaining a favourable conservation status. Our results also revealed numerous species occurrences where high climate velocity coincided with a large amount of negative land use and low amount of suitable habitat, for which climate-wise conservation planning could be targeted.

The regional variability in tundra and boreal carbon dioxide (CO2) fluxes can be high, complicating efforts to quantify sink-source patterns across the entire region. Statistical models are increasingly used to predict (i.e., upscale) CO2 fluxes across large spatial domains, but the reliability of different modeling techniques, each with different specifications and assumptions, has not been assessed in detail. Here, we compile eddy covariance and chamber measurements of annual and growing season CO2 fluxes of gross primary productivity (GPP), ecosystem respiration (ER), and net ecosystem exchange (NEE) during 1990–2015 from 148 terrestrial high-latitude (i.e., tundra and boreal) sites to analyze the spatial patterns and drivers of CO2 fluxes and test the accuracy and uncertainty of different statistical models. CO2 fluxes were upscaled at relatively high spatial resolution (1 km2) across the high-latitude region using five commonly used statistical models and their ensemble, that is, the median of all five models, using climatic, vegetation, and soil predictors. We found the performance of machine learning and ensemble predictions to outperform traditional regression methods. We also found the predictive performance of NEE-focused models to be low, relative to models predicting GPP and ER. Our data compilation and ensemble predictions showed that CO2 sink strength was larger in the boreal biome (observed and predicted average annual NEE −46 and −29 g C m−2 yr−1, respectively) compared to tundra (average annual NEE +10 and −2 g C m−2 yr−1). This pattern was associated with large spatial variability, reflecting local heterogeneity in soil organic carbon stocks, climate, and vegetation productivity. The terrestrial ecosystem CO2 budget, estimated using the annual NEE ensemble prediction, suggests the high-latitude region was on average an annual CO2 sink during 1990–2015, although uncertainty remains high.

Current analyses and predictions of spatially explicit patterns and processes in ecology most often rely on climate data interpolated from standardized weather stations. This interpolated climate data represents long-term average thermal conditions at coarse spatial resolutions only. Hence, many climate-forcing factors that operate at fine spatiotemporal resolutions are overlooked. This is particularly important in relation to effects of observation height (e.g. vegetation, snow and soil characteristics) and in habitats varying in their exposure to radiation, moisture and wind (e.g. topography, radiative forcing or cold-air pooling). Since organisms living close to the ground relate more strongly to these microclimatic conditions than to free-air temperatures, microclimatic ground and near-surface data are needed to provide realistic forecasts of the fate of such organisms under anthropogenic climate change, as well as of the functioning of the ecosystems they live in. To fill this critical gap, we highlight a call for temperature time series submissions to SoilTemp, a geospatial database initiative compiling soil and near-surface temperature data from all over the world. Currently, this database contains time series from 7,538 temperature sensors from 51 countries across all key biomes. The database will pave the way toward an improved global understanding of microclimate and bridge the gap between the available climate data and the climate at fine spatiotemporal resolutions relevant to most organisms and ecosystem processes. ispartof: GLOBAL CHANGE BIOLOGY vol:26 issue:11 pages:6616-6629 ispartof: location:England status: published

Climate change velocity is an increasingly used metric to assess the broad-scale climatic exposure and climate change induced risks to terrestrial and marine ecosystems. However, the utility of this metric in conservation planning can be enhanced by determining the velocities of multiple climatic drivers in real protected area (PA) networks on ecologically relevant scales. Here we investigate the velocities of three key bioclimatic variables across a nation-wide reserve network, and the consequences of including fine-grained topoclimatic data in velocity assessments. Using 50-m resolution data describing present-day and future topoclimates, we assessed the velocities of growing degree days, the mean January temperature and climatic water balance in the Natura 2000 PA network in Finland. The high-velocity areas for the three climate variables differed drastically, indicating contrasting exposure risks in different PAs. The 50-m resolution climate data revealed more realistic estimates of climate velocities and more overlap between the present-day and future climate spaces in the PAs than the 1-km resolution data. Even so, the current temperature conditions were projected to disappear from almost all the studied PAs by the end of this century. Thus, in PA networks with only moderate topographic variation, far-reaching climate change induced ecological changes may be inevitable.

Increased attention is being paid to the ecological drivers and conservation measures which could mitigate climate change-induced pressures for species survival, potentially helping populations to remain in their present-day locations longer. One important buffering mechanism against climate change may be provided by the heterogeneity in topography and consequent local climate conditions. However, the buffering capacity of this topoclimate has so far been insufficiently studied based on empirical survey data across multiple sites and species. Here, we studied whether the fine-grained air temperature variation of protected areas (PAs) affects the population changes of declining northern forest bird species. Importantly to our study, in PAs harmful land use, such as logging, is not allowed, enabling the detection of the effects of temperature buffering, even at relatively moderate levels of topographic variation. Our survey data from 129 PAs located in the boreal zone in Finland show that the density of northern forest species was higher in topographically heterogeneous PAs than in topographically more homogeneous PAs. Moreover, local temperature variation had a significant effect on the density change of northern forest birds from 1981&ndash, 1999 to 2000&ndash, 2017, indicating that change in bird density was generally smaller in PAs with higher topographic variation. Thus, we found a clear buffering effect stemming from the local temperature variation of PAs in the population trends of northern forest birds.

Climate is a crucial driver of the distributions and activity of multiple biotic and abiotic processes, and thus high-quality and high-resolution climate data are often prerequisite in various envi ...

International audience; Aim. Although species distribution models (SDMs) traditionally link species occurrences to free‐air temperature data at coarse spatio‐temporal resolution, the distribution of organisms might instead be driven by temperatures more proximal to their habitats. Several solutions are currently available, such as downscaled or interpolated coarse‐grained free‐air temperatures, satellite‐measured land surface temperatures (LST) or in‐situ‐measured soil temperatures. A comprehensive comparison of temperature data sources and their performance in SDMs is, however, currently lacking. Location. Northern Scandinavia. Time period. 1970–2017. Major taxa studied. Higher plants. Methods. We evaluated different sources of temperature data (WorldClim, CHELSA, MODIS, E‐OBS, topoclimate and soil temperature from miniature data loggers), differing in spatial resolution (from 1″ to 0.1°), measurement focus (free‐air, ground‐surface or soil temperature) and temporal extent (year‐long versus long‐term averages), and used them to fit SDMs for 50 plant species with different growth forms in a high‐latitudinal mountain region. Results. Differences between these temperature data sources originating from measurement focus and temporal extent overshadow the effects of temporal climatic differences and spatio‐temporal resolution, with elevational lapse rates ranging from −0.6°C per 100 m for long‐term free‐air temperature data to −0.2°C per 100 m for in‐situ soil temperatures. Most importantly, we found that the performance of the temperature data in SDMs depended on the growth forms of species. The use of in‐situ soil temperatures improved the explanatory power of our SDMs (R2 on average +16%), especially for forbs and graminoids (R2 +24 and +21% on average, respectively) compared with the other data sources. Main conclusions. We suggest that future studies using SDMs should use the temperature dataset that best reflects the ecology of the species, rather than automatically using coarse‐grained data from WorldClim or CHELSA.

Water is crucial for plant productivity and survival as a fundamental resource, but water conditions can also cause physiological stress and mechanical disturbance to vegetation. However, these different influences of water on vegetation patterns have not been evaluated simultaneously. Here, we demonstrate the importance of three water aspects (spatial and temporal variation of soil moisture and fluvial disturbance) for three ecologically and evolutionary distinct taxonomical groups (vascular plants, mosses, and lichens) in Fennoscandian mountain tundra. Fine‐scale plant occurrence data for 271 species were collected from 378 x 1 m2 plots sampled over broad environmental gradients (water, temperature, radiation, soil pH, cryogenic processes, and the dominant allelopathic plant species). While controlling all other key environmental variables, water in its different aspects proved to be a crucial environmental driver, acting on individual species and on community characteristics. The inclusion of the water variables significantly improved our models. In this high‐latitude system, the importance of spatial variability of water exceeds the importance of temperature for the fine‐scale distribution of species from the three taxonomical groups. We found differing responses to the three water variables between and within the taxonomical groups. Water as a resource was the most important water‐related variable in species distribution models across all taxonomical groups. Both water resource and disturbance were strongly related to vascular plant species richness, whereas for moss species richness, water resources had the highest influence. For lichen species richness, water disturbance was the most influential water‐related variable. These findings demonstrate that water variables are not only independent properties of tundra hydrology, but also that water is truly a multifaceted driver of vegetation patterns at high‐latitudes. Water is crucial for plant productivity and survival as a fundamental resource, but water conditions can also cause physiological stress and mechanical disturbance to vegetation. However, these different influences of water on vegetation patterns have not been evaluated simultaneously. Here, we demonstrate the importance of three water aspects (spatial and temporal variation of soil moisture and fluvial disturbance) for three ecologically and evolutionary distinct taxonomical groups (vascular plants, mosses and lichens) in Fennoscandian mountain tundra. Fine‐scale plant occurrence data for 271 species were collected from 378 × 1 m2 plots sampled over broad environmental gradients (water, temperature, radiation, soil pH, cryogenic processes and the dominant allelopathic plant species). While controlling all other key environmental variables, water in its different aspects proved to be a crucial environmental driver, acting on individual species and on community characteristics. The inclusion of the water variables significantly improved our models. In this high‐latitude system, the importance of spatial variability of water exceeds the importance of temperature for the fine‐scale distribution of species from the three taxonomical groups. We found differing responses to the three water variables between and within the taxonomical groups. Water as a resource was the most important water‐related variable in species distribution models across all taxonomical groups. Both water resource and disturbance were strongly related to vascular plant species richness, whereas for moss species richness, water resources had the highest influence. For lichen species richness, water disturbance was the most influential water‐related variable. These findings demonstrate that water variables are not only independent properties of tundra hydrology, but also that water is truly a multifaceted driver of vegetation patterns at high‐latitudes.

Aim: Species' biogeographical patterns are already being altered by climate change. Here, we provide predictions of the impacts of a changing climate on species' geographical ranges within high-latitude mountain flora on a sub-continental scale. We then examined the forecasted changes in relation to species' biogeographic histories. Location: Fennoscandia, Northern Europe (55-72 degrees N). Methods: We examined the sensitivity of 164 high-latitude mountain species to changing climate by modelling their distributions in regard to climate, local topography and geology at a 1 km(2) resolution. Using an ensemble of six statistical modelling techniques and data on current (1981-2010) and future (2070-2099) climate based on three Representative Concentration Pathways (RCPs 2.6, 4.5, 8.5), we developed projections of current and future ranges. Results: The average species richness of the mountain flora is predicted to decrease by 15%-47% per 1 km(2) cell, depending on the climate scenario considered. Arctic flora is projected to undergo severe range loss along with non-poleward range contractions, while alpine flora is forecasted to find suitable habitat in a warmer North. A substantial majority (71%-92%) of the studied species are projected to lose more than half of their present range by the year 2100. Species predicted to lose all suitable habitat had ranges centred in the northernmost (>68 degrees N) part of continental Europe. Main conclusions: Climate change is predicted to substantially diminish the extent and richness of Europe's high-latitude mountain flora. Interestingly, species' biogeographic histories affect their vulnerability to climate change. The vulnerability of true Arctic and endemic species marks them as highly important for conservation decisions.

The functional composition of plant communities is a critical modulator of climate change impacts on ecosystems, but it is not a simple function of regional climate. In the Arctic tundra, where climate change is proceeding the most rapidly, communities have not shifted their trait composition as predicted by spatial temperature-trait relationships. Important causal pathways are thus missing from models of trait composition change. Here, we study causes of plant community functional variation in a tundra landscape. We consider the community weighted means of plant vegetative height, as well as two traits related to the leaf economic spectrum. Specifically, we model their responses to locally measured summer air temperature, snow conditions, and soil resource levels. For each of the traits we also quantify the importance of intraspecific trait variation (ITV) for between-community functional differences and trait-environment matching. Our study shows that in a tundra landscape 1) snow is the most influential abiotic variable affecting functional composition, 2) vegetation height is under weak local environmental control, whereas leaf economics is under strong local environmental control, 3) the relative magnitude of ITV differs between traits, and 4) ITV is not very consequential for community-level trait-environment relationships.

Climatically driven Earth surface processes (ESPs) govern landscape and ecosystem dynamics in high-latitude regions. However, climate change is expected to alter ESP activity at yet uncertain rate and amplitude. We examined the sensitivity of key ESPs (cryoturbation, solifluction, nivation, and palsa mires) to changing climate by modeling their distribution in regard to climate, local topography, and soil variables in northern Fennoscandia. The distributions of ESPs were then forecasted under two future time periods, 2040–2069 and 2070–2099, using ensemble modeling and three emission scenarios. Increase of 2°C in current temperature conditions caused an almost complete loss of ESPs, highlighting the extreme climatic sensitivity of high-latitude geomorphic processes. Forecasts based on three scenarios suggest a disappearance of suitable climate for studied ESPs by the end of this century. This could initiate multiple opposing feedback between land surface and atmosphere through changes in albedo, heat fluxes, and biogeochemical cycles.

Soil temperature and moisture are key determinants of abiotic and biotic processes in arctic-alpine regions. They are important links to understanding complex ecosystem dynamics under changing climate. The aims of this study were to (1) quantify fine-scale soil temperature and soil moisture variation, and (2) assess the influence of vegetation on soil temperature and moisture patterns in a northern European arctic-alpine environment. Inclusion of vegetation variables significantly improved models of soil temperature and moisture, despite abiotic variables (local topography and soil properties) being the most influential predictors. Temperature varied by ≥5 °C and moisture by ≥50% (volumetric water content) over very short distances (≥ 1 m), reflecting the extreme spatial heterogeneity of thermal and hydrological conditions in these systems. These results thus highlight the biotic mediation of changes in abiotic conditions, showing how vegetation can strongly affect local habitat conditions at fin...

Shifts in precipitation regimes are an inherent component of climate change, but in low-energy systems are often assumed to be less important than changes in temperature. Because soil moisture is the hydrological variable most proximally linked to plant performance during the growing season in arctic-alpine habitats, it may offer the most useful perspective on the influence of changes in precipitation on vegetation. Here we quantify the influence of soil moisture for multiple vegetation properties at fine spatial scales, to determine the potential importance of soil moisture under changing climatic conditions. A fine-scale data set, comprising vascular species cover and field-quantified ecologically relevant environmental parameters, was analysed to determine the influence of soil moisture relative to other key abiotic predictors. Soil moisture was strongly related to community composition, species richness and the occurrence patterns of individual species, having a similar or greater influence than soil temperature, pH and solar radiation. Soil moisture varied considerably over short distances, and this fine-scale heterogeneity may contribute to offsetting the ecological impacts of changes in precipitation for species not limited to extreme soil moisture conditions. In conclusion, soil moisture is a key driver of vegetation properties, both at the species and community level, even in this low-energy system. Soil moisture conditions represent an important mechanism through which changing climatic conditions impact vegetation, and advancing our predictive capability will therefore require a better understanding of how soil moisture mediates the effects of climate change on biota.

International audience; Soil temperature (ST) has a key role in Arctic ecosystem functioning and global environmental change. However, soil thermal conditions do not necessarily follow synoptic temperature variations. This is because local biogeophysical processes can lead to a pronounced soil-atmosphere thermal offset (∆T) while altering the coupling (βT) between ST and ambient air temperature (AAT). Here, we aim to uncover the spatiotemporal variation in these parameters and identify their main environmental drivers. By deploying a unique network of 322 temperature loggers and surveying biogeophysical processes across an Arctic landscape, we found that the spatial variation in ∆T during the AAT≤0 period (mean ∆T = 6.0 °C, standard deviation ± 1.2 °C) was directly and indirectly constrained by local topography controlling snow depth. By contrast, during the AAT>0 period, ∆T was controlled by soil characteristics, vegetation and solar radiation (∆T = −0.6 °C ± 1.0 °C). Importantly, ∆T was not constant throughout the seasons reflecting the influence of βT on the rate of local soil warming being stronger after (mean βT = 0.8 ± 0.1) than before (βT = 0.2 ± 0.2) snowmelt. Our results highlight the need for continuous microclimatic and local environmental monitoring, and suggest a potential for large buffering and non-uniform warming of snow-dominated Arctic ecosystems under projected temperature increase.