Shrubification (i.e., increasing shrub abundance) and thermophilisation (i.e., increasing dominance of warmth-demanding species) are among the most widely documented imprints of climate change on mountain ecosystems. Still, it remains insufficiently quantified how increasing shrub cover alters the near-ground microclimate and snow duration, and in turn, how this interacts with the climate-change responses of alpine plant communities. To this end, we leveraged 21 years of vegetation resampling data and soil temperature time-series from 576 permanent plots positioned on European mountaintops and covering the treeline ecotone up to the middle alpine belt. Snow duration decreased faster in plots with stronger macroclimate warming, which in turn led to a rise in minimum soil temperatures of 0.28°C per decade across all plots. Overall thermophilisation rates were higher in sheltered habitats with snow accumulation, while habitats with higher shrub cover showed faster loss of cold-adapted species. Further research is needed to disentangle the joint effects of shrubs, snow and microclimates, yielding more accurate projections of climate-induced plant community reshuffling in alpine habitats.

Climate change increases plant species richness in alpine ecosystems. However, to what extent this diversity enrichment masks extinction dynamics of resident species remains elusive. In this study, we used floristic resurvey data from 896 permanent vegetation plots across 62 European mountain summits to show that local extinctions have increased over the past 21 years. Extinction rates rose with the magnitude of warming, and species were more likely to go extinct toward their low-elevation range margins and in communities undergoing stronger thermophilization. Moreover, local extinctions were significantly related to preceding abundance declines, which can serve as an early warning signal. These findings suggest that despite increasing plant species richness, plant assemblages above the treeline face an accelerating but so far neglected loss of their most characteristic species.

ABSTRACT Understanding the factors behind species' range limits is a fundamental objective in ecology. Recent research in alpine plant ecology has moved beyond the classical view that distributions are chiefly shaped by climate and competition. Specifically, broader sets of factors have been taken into account, comprising both biotic factors such as facilitation and herbivory as well as additional abiotic factors such as soil properties. However, an overview of the factors that have been identified and studied as important for elevational range limits of alpine plant species is lacking. In this systematic literature review, we synthesize evidence derived from 107 empirical studies on 226 vascular plant species occurring beyond elevational and latitudinal treelines. We find a persistent research focus on the upper elevational range limit (73% of the studies) and on the role of abiotic factors (54% of the studies), particularly temperature (36% of the studies), whereas research on inter‐ and intraspecific factors (40% and 25%, respectively), such as herbivory or phenology, remained comparatively rare. While temperature was clearly identified as a major factor influencing the upper range limit (29% of the studies), water availability (15% of the studies) was most commonly studied at the lower range limit. Even though a broad set of factors has been investigated, many potentially important factors remain poorly researched, such as the influence of gene flow and connectivity between populations, phenology and light (each only one or two studies). Our findings highlight the need to move beyond temperature and plant–plant interactions as factors influencing the elevational range limits of alpine plants and to integrate intraspecific (such as gene flow and adaptations) and edaphic factors more fully into future research. Improved methodological standardization and transparency and increased attention on lower range limits will be essential for explaining and predicting alpine plant responses under accelerating environmental change.

Climate warming is shifting biological communities, with warmth-demanding species being favoured at the expense of cold-adapted species in a process referred to as thermophilization1-4. Because biodiversity responses often lag behind climate warming, climatic debts are accumulating in many ecosystems across the world5-7. Although we might expect that thermophilization and climatic debts will vary among habitats, standardized quantification across ecosystems is lacking. Here we analysed multidecadal data from 6,067 resurveyed vegetation plots over 12-78 years in forests, grasslands and on alpine summits across Europe. We demonstrate that forest understory and grassland plant communities experienced positive thermophilization, although not significantly different from zero. By contrast, alpine summit vegetation showed much stronger (up to five times) and significant thermophilization. Thermophilization was driven largely by increases in warmth-demanding species in grasslands, by declines in cold-adapted species on alpine summits and by both processes in forests. Significant climatic debts have accumulated in forests and alpine summits, but less so in grasslands, with debts positively correlated with macroclimate temperature changes. Our findings uncover divergent thermophilization trajectories and increasing climatic debts across ecosystems. Moreover, we highlight the mechanisms that enable some communities to track climate change more closely than others and provide a basis for projecting future shifts in plant communities under accelerating climate warming.

Recent changes in alpine vegetation are often attributed to climate warming, particularly community composition shifts towards more warmth-associated species, or thermophilization. Here we assess the link between thermophilization and warming across 53 European mountain summits. We combine long-term macroclimatic and microclimatic temperature time series with vegetation surveys in 724 permanent plots, monitored over 21 years, to evaluate a possible thermophilization signal and relate it to rates of change in 10 temperature metrics. We find evidence of both thermophilization of alpine plant communities and an increase in temperatures. However, although these two trends are related when averaged across mountain regions, their relationship is weak at the individual plot scale, especially when considering microclimatic temperature metrics. Instead, substrate conditions and particularly the availability of thermophilic colonizers in the surrounding vegetation have a major influence on plot-level thermophilization rates. We conclude that the response of plant communities to climate change strongly depends on the abiotic and biotic context, and intensified monitoring efforts are needed to reduce the resulting uncertainties.

Shrubs are expanding across the cold ecosystems of our planet with potentially profound consequences for their biodiversity and functioning. However, evidence is still strongly biased towards the Arctic tundra, while a large-scale assessment of shrub expansion in alpine areas above the elevational treeline is missing so far. Here we quantified shrub cover changes over the past two decades in 576 permanent plots of 1 m2 spread across the alpine vegetation belt of Europe's major mountain chains. Total shrub cover clearly increased in the plots with an average rate of about 2.6% per m2 per decade (95% CI = 1.9%-3.4%), and this expansion was more pronounced for evergreen (2.0% per m2 per decade, CI = 1.3%-2.7%) than for deciduous species (1.7% per m2 per decade, CI = 0.9%-2.4%). The magnitude of individual species' cover shifts was positively associated with their plant height, but negatively with their leaf nitrogen content and light affinity. In sum, we show that shrub expansion is a widespread phenomenon also in the alpine zone of European mountains, with potentially far-reaching consequences for alpine plant dynamics, soil microclimates, snow patterns, carbon cycling, food chains and livelihoods.

Aim The role of microclimate in influencing range limits and vegetation shifts, especially in topographically heterogeneous mountain ecosystems, has gained attention in recent years. However, disturbance by large animals and snow pressure complicate reliable year-round time series of microclimatic measurements near the soil surface, calling for more robust logger setups.Location Swiss Alps.Methods We presented a novel, low-cost, and effective method to monitor above- and belowground microclimate in mountain environments year-round that withstands large animals and snow pressure and is suitable for remote areas. Specifically, we customized the widely used TOMST TMS-4 data loggers and tested their functionality and reliability in a factorial field experiment as well as in a regional-scale field study in heterogeneous mountain terrain.Results We found that standard TMS-4 loggers were frequently destroyed by snow creep or snow pressure over winter, but customized loggers remained intact. In addition, camera-trap footage demonstrated that only customized loggers were efficiently protected against large mammals, such as wolves, foxes, red deer, and chamois. The customization of loggers had ecologically negligible effects on the recorded above- and belowground microclimate.Conclusions With this method, we enable combined monitoring of air, surface, and soil temperatures as well as soil moisture in alpine environments throughout the year, and thus the collection of crucial microclimatic variables for research in mountain ecosystems.

High mountains are hotspots of climate and global environmental change. Mountain biodiversity is threatened by quickly rising temperatures which cause vegetation shifts, such as upslope migration. At the same time, natural hazards develop as mountain slopes become increasingly unstable due to permafrost degradation and changes in rain and snowfall regimes. Resulting slope movements, such as rockfalls and debris flows, can limit colonization by plants. However, plants that manage to colonize mountain slopes can stabilize them through their roots and above ground biomass.Therefore, we believe that an interdisciplinary approach linking ecology and geomorphology is needed as a next step to better understand how climate change affects high mountain landscapes and ecosystems. Combining results from previous geomorphic, ecological and palaeoecological studies, we show that the response of high mountain environments to climate change can depend on the balance between slope movement intensity and the trait-dependent ability of plants to colonize and stabilize moving slopes. For this ‘biogeomorphic balance’ we envisage three possible scenarios: (1) Intensifying slope movements impede vegetation shifts, amplifying instability. (2) Ecosystem engineer species, adapted to moving slopes, stabilize slopes and facilitate shifts for less movement-adapted species. (3) Competitive trees and tall shrubs, shifting on stable slopes, reduce instability but potentially diminish biodiversity. Given the disparate rates of ecological and geomorphic responses to climate change, coupled with high environmental heterogeneity and elevational gradients in in mountains, we anticipate that future biogeomorphic balances will be variable and heterogeneous in both space and time.To unravel these intricate biogeomorphic balances, we advocate for collaborative research between mountain geomorphologists and ecologists and propose three distinct future directions that combine advancing field measurement, remote sensing techniques and modeling approaches. We believe that by recognizing high mountains as 'biogeomorphic ecosystems', shaped by the interplay of geomorphic and ecological processes, we can improve our ability to safeguard people, infrastructure and ecosystems in mountain environments around the world. References:Eichel J, Stoffel M, Wipf S. 2023. Go or grow? Feedbacks between moving slopes and shifting plants in high mountain environments. Progress in Physical Geography: Earth and Environment 47 : 967–985. DOI: 10.1177/03091333231193844

Considerable uncertainty exists regarding the strength, direction and relative importance of the drivers of decomposition in the tundra biome, partly due to a lack of coordinated decomposition field studies in this remote environment. Here, we analysed 3717 incubations of two uniform litter types, green and rooibos tea, buried at 330 circum-Arctic and alpine sites to quantify the effects of temperature, moisture and litter quality on decomposition. We found a surprisingly linear positive relationship between decomposition and soil temperature across all sites, counter to theory and previous model estimates. Litter mass loss was greater at wetter sites, even where soils reached almost full water saturation. However, litter quality was the strongest driver of litter mass loss across the tundra biome, explaining six times more variation in summer decomposition than soil temperature. Our results indicate that climate warming will directly increase decomposition across tundra environments. However, the indirect effects of climate change on vegetation communities, and thus plant litter inputs and quality, could have a more profound impact than direct effects on the balance of this globally important carbon store.

MotivationHere, we make available a second version of the BioTIME database, which compiles records of abundance estimates for species in sample events of ecological assemblages through time. The updated version expands version 1.0 of the database by doubling the number of studies and includes substantial additional curation to the taxonomic accuracy of the records, as well as the metadata. Moreover, we now provide an R package (BioTIMEr) to facilitate use of the database.Main Types of Variables IncludedThe database is composed of one main data table containing the abundance records and 11 metadata tables. The data are organised in a hierarchy of scales where 11,989,233 records are nested in 1,603,067 sample events, from 553,253 sampling locations, which are nested in 708 studies. A study is defined as a sampling methodology applied to an assemblage for a minimum of 2 years.Spatial Location and GrainSampling locations in BioTIME are distributed across the planet, including marine, terrestrial and freshwater realms. Spatial grain size and extent vary across studies depending on sampling methodology. We recommend gridding of sampling locations into areas of consistent size.Time Period and GrainThe earliest time series in BioTIME start in 1874, and the most recent records are from 2023. Temporal grain and duration vary across studies. We recommend doing sample-level rarefaction to ensure consistent sampling effort through time before calculating any diversity metric.Major Taxa and Level of MeasurementThe database includes any eukaryotic taxa, with a combined total of 56,400 taxa.Software Formatcsv and. SQL.

Responses of ecological communities to perturbations are inherently variable because responses of their constituent populations also vary. Species within a single community may show combinations of no response, positive responses, and negative responses to any given perturbation often canceling each other out resulting in small or no signal that the community level. Here we explore the impacts of warming and loss of the dominant species on alpine ecosystems in a global study. We investigate warming and species-loss treatments on population- and community-level dynamics across alpine-plant communities at two elevations in five globally-distributed mountain locations. Communities showed varied responses to treatments; no community showed strong responses to a single treatment. Rather, most sites were influenced by both perturbations. Populations within these communities responded idiosyncratically, suggesting that constituent species are not all equally robust to perturbations even when community-level effects appear weak. Our results highlight the challenge of making general predictions about population- and community-level responses of alpine ecosystems in the face of present and future perturbations. ### Competing Interest Statement The authors have declared no competing interest.

Mountain regions harbor unique and rich biodiversity, forming an important part of our global life support system. This rich biodiversity underpins the ecological intactness and functioning of mountain ecosystems, which are imperative for the provision of key ecosystem services. A considerable amount of data are required to assess ecological intactness and ecosystem functioning and, given the profound anthropogenic pressures many mountain regions are being subjected to, are urgently needed. However, data on mountain biodiversity remain lacking. The essential biodiversity variables (EBVs) framework can help focus efforts related to detecting, investigating, predicting, and managing global biodiversity change, but has not yet been considered in the context of mountains. Here, we review key biological processes and physical phenomena that strongly influence mountain biodiversity and ecosystems and elucidate their associations with potential mountain EBVs. We identify seven EBVs of highest relevance for tracking and understanding the most critical drivers and responses of mountain biodiversity change. If they are implemented, the selected EBVs will contribute useful information to inform management and policy interventions seeking to halt mountain biodiversity loss and maintain functional mountain ecosystems.

On 2 June 2023, the first Research Symposium SNP+ took place in Zernez, Switzer-land, at the headquarters of the Swiss National Park (SNP). The symposium aimed to bring together active researchers from various scientific fields relevant to the work of the Swiss National Park, the Regional Nature Park Biosfera Val Mustair (BVM), and the overarching UNESCO Biosphere Reserve Engiadina Val Mustair (UBEVM) - all represented here by SNP+. Addressing subjects bridging the gap between strict nature preservation and cultivated landscape areas, the importance of ongoing monitoring over extended periods, and the influence of climate change on eco-systems and natural processes, the day unfolded as a profoundly captivating and interdisciplinary experience. This text aims to summarize the key messages of the symposium and provides a preview of upcoming events.

Aims: We introduce ReSurveyEurope - a new data source of resurveyed vegetation plots in Europe, compiled by a collaborative network of vegetation scientists. We describe the scope of this initiative, provide an overview of currently available data, governance, data contribution rules, and accessibility. In addition, we outline further steps, including potential research questions. Results: ReSurveyEurope includes resurveyed vegetation plots from all habitats. Version 1.0 of ReSurveyEurope contains 283,135 observations (i.e., individual surveys of each plot) from 79,190 plots sampled in 449 independent resurvey projects. Of these, 62,139 (78%) are permanent plots, that is, marked in situ, or located with GPS, which allow for high spatial accuracy in resurvey. The remaining 17,051 (22%) plots are from studies in which plots from the initial survey could not be exactly relocated. Four data sets, which together account for 28,470 (36%) plots, provide only presence/absence information on plant species, while the remaining 50,720 (64%) plots contain abundance information (e.g., percentage cover or cover-abundance classes such as variants of the Braun-Blanquet scale). The oldest plots were sampled in 1911 in the Swiss Alps, while most plots were sampled between 1950 and 2020. Conclusions: ReSurveyEurope is a new resource to address a wide range of research questions on fine-scale changes in European vegetation. The initiative is devoted to an inclusive and transparent governance and data usage approach, based on slightly adapted rules of the well-established European Vegetation Archive (EVA). ReSurvey:Europe data are ready for use, and proposals for analyses of the data set can be submitted at any time to the coordinators. Still, further data contributions are highly welcome.

Improving species distribution models (SDMs) and species abundance models (SAMs) of woody shrubs is critical for predicting biodiversity changes in the Arctic, which is experiencing especially high warming rates. Yet, it remains relatively unexplored if SDMs and SAMs can explain local scale patterns. We aim to identify predictor differences for the distribution versus abundance of two widespread Arctic shrub species with high resolution models and to compare validation approaches to assess the models’ predictive abilities.

The browsing of wild ungulates can have profound effects on the structure and composition of forests. In the Swiss National Park, the density of wild ungulates, including red deer (Cervus elaphus), ibex (Capra ibex), and chamois (Rupicapra rupicapra), is exceptionally high due to strict protection and the absence of large predators. We examined count data of larch (Larix decidua), cembra pine (Pinus cembra), spruce (Picea abies), upright mountain pine (Pinus mugo subsp. uncinata), and mountain ash (Sorbus aucuparia) of four sampling years between 1991 and 2021, and modelled how topographic and location factors affected the probability of browsing on saplings of larch, cembra pine, and spruce. Despite the high density of wild ungulates, the number of saplings and young trees has increased over the past 30 years. The probability of browsing on saplings was highest for larch at a height of 10–40 cm and increased with increasing elevation. In our study area, open grasslands are mainly located above the tree line, which might explain the positive correlation between elevation and the probability of browsing. Further, the probability of browsing was related to exposition and slope, diversity of tree species, and disturbance by humans. It appears that in the investigated part of the Swiss National Park, the potential of the forest to regenerate has increased despite the high densities of wild ungulates.

Data overview: These data correspond to the analyses conducted for the article "Resampling alpine herbarium records reveals changes in plant traits over space and time" by Francesca Jaroszynska, Christian Rixen, Sarah Woodin, Jonathan Lenoir and Sonja Wipf, in Journal of Ecology Metadata for jaroszynska_herbarium_traits_data.csv: date = date; date of collection time = factor; time of collection (historical or recent) elevation = numerical; elevation in metres above sea level of the sample collection site selevation = numerical; scaled elevation selevation2 = numerical; elevation in metres above sea level of sample collection site (elevation/1000). sSlope = numerical; scaled slope (slope/10) slope = numerical; computed slope based on elevation trait = string; name of the measured trait crFlowerN = numerical; Cardamine resedifolia; number of flowers crHeight = numerical; Cardamine resedifolia; plant height crLeafL = numerical; Cardamine resedifolia; length of longest leaf crRosetteLeafN = numerical; Cardamine resedifolia; number of leaves in rosette paBasalLeafL = numerical; Poa alpina; basal leaf length paInflorescenceL = numerical; Poa alpina; inflorescence length paHeight = numerical; Poa alpina; plant height pvInfL = numerical; Polygonum viviparum; length of inflorescence pvLA = numerical; Polygonum viviparum; leaf area (length x width) pvLeafL = numerical; Polygonum viviparum; leaf length pvRepH= numerical; Polygonum viviparum; plant height rgFlowerStemL = numerical; Ranunculus glacialis; flowering stem length rgLeafStemL = numerical; Ranunculus glacialis; petiole length rgLeafW = numerical; Ranunculus glacialis; leaf width rgFlowerN = integer; Ranunculus glacialis; number of flowers traitGroup = factor; the group to which each trait belongs (VegHeight = vegetative height, ReprHeight = reproductive height, ReprOut = reproductive output, PhotoCap = photosynthetic capacity) value = numerical; value of the trait measured species = factor; species code (car_res = Cardamine resedifolia, ran_glac = Ranunculus glacialis, pol_viv = Polygonum viviparum, poa_alp = Poa alpina) transect = string; transect along which the herbarium sample was taken confidence = factor; reliability of the metadata associated with the herbarium sample, assigned by the authors Jaroszynska and Wipf (low, medium, high) northness = numerical; northness eastness = numerical; eastness observer = string; botanist who conducted the collection sheet = string; unique identifier for the collection sheet Metadata for jaroszynska_climate_traits_data.csv: year = year; year of sample collection Month = integer; month of sample colection Temperature = numerical; monthly average temperature (ºC) Precipitation = numerical; monthly total precipitation (mm) yearMonth = string; year.month season = factor; season associated to the corresponding month (spring, summer, autumn, winter) timePeriod = factor; climate period referring to the time before, after, or during the baseline reference period (see article for further details) meanAnnTemp = numerical; mean annual temperature (ºC) sumAnnPrecip = numerical; total annual precipitation (mm) meanSeaTemp = numerical; mean seasonal temperature (ªC) sumSeaPrecip = numerical; total seasonal precipitation (mm) meanRefTemp = numerical; mean seasonal temperature for reference period (ªC) temp_anomaly = numerical; temerature anomaly from the reference period (ªC) lagMonths = string; used in seasonal calculation seasonal_precip = numerical; seasonal precipitation (mm) precip_anomaly = numerical; seasonal precipitation anomaly (mm)

High mountains are climate change hotspots. Quickly rising temperatures trigger vegetation shifts such as upslope migration, possibly threatening mountain biodiversity. At the same time, mountain slopes are becoming increasingly unstable due to degrading permafrost and changing rain and snowfall regimes, which favour slope movements such as rockfall and debris flows. Slope movements can limit plant colonization, while, at the same time, plant colonization can stabilize moving slopes. Thus, we here propose that response of high mountain environments to climate change depends on a 'biogeomorphic balance' between slope movement intensity and the trait-dependent ability of mountain plants to survive and stabilize slopes. We envision three possible scenarios of biogeomorphic balance: (1) Intensifying slope movements limit vegetation shifts and thus amplify instability. (2) Shifting ecosystem engineer species reduce slope movement and facilitate shifts for less movement-adapted species. (3) Trees and tall shrubs shifting on stable slopes limit slope instability but decrease biodiversity. Previous geomorphic, ecological and palaeoecological studies support all three scenarios. Given differences in ecologic and geomorphic response rates to climate change, as well as high environmental heterogeneity and elevational gradients in mountain environments, we posit that future biogeomorphic balances will be variable and heterogeneous in time and space. To further unravel future biogeomorphic balances, we propose three new research directions for joint research of mountain geomorphologists and ecologists, using advancing field measurement, remote sensing and modelling techniques. Recognizing high mountains as 'biogeomorphic ecosystems' will help to better safeguard mountain infrastructure, lives and livelihoods of millions of people around the world.