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Understanding and predicting large-scale ecological responses to global environmental change requires comparative studies across geographic scales with coordinated efforts and standardized methodologies. We designed, applied and assessed standardized protocols to measure tundra herbivory at three spatial scales: plot, site (habitat), and study area (landscape). The plot and site-level protocols were tested in the field during summers 2014-2015 at eleven sites, nine of them comprising warming experimental plots included in the International Tundra Experiment (ITEX). The study area protocols were assessed during 2014-2018 at 24 study areas across the Arctic. Our protocols provide comparable and easy-to-implement methods for assessing the intensity of invertebrate herbivory within ITEX plots and for characterizing vertebrate herbivore communities at larger spatial scales. We discuss methodological constraints and make recommendations for how these protocols can be used and how sampling effort can be optimized to obtain comparable estimates of herbivory, both at ITEX sites and at large landscape scales. The application of these protocols across the tundra biome will allow characterizing and comparing herbivore communities across tundra sites and at ecologically relevant spatial scales, providing an important step towards a better understanding of tundra ecosystem responses to large-scale environmental change. CGB was funded by the Estonian Research Council (grant IUT 20-28), and the European Regional Development Fund (Centre of Excellence EcolChange). JDMS was supported by the Research Council of Norway (262064). OG and LB were supported by the French Polar Institute (program “1036 Interactions”) and PRC CNRS Russie 396 (program “ICCVAT”). DSH, NL, MAG, JB and JDR were supported by the Natural Sciences and Engineering Research Council (Canada). NL, MAG, JB and JDR were supported by the Polar Continental Shelf Program. NL was supported by the Canada Research Chair program and the Canada Foundation for Innovation. NL and JB were supported by Environment Canada and Polar Knowledge Canada. NL and MAG were supported by the Government of Nunavut, the Igloolik Community, and Université de Moncton. NL, MAG and JB were supported by the Northern Scientific Training Program. JMA was funded by Carl Tryggers stiftelse för vetenskaplig forskning and Qatar Petroleum (QUEX-CAS-QP-RD-18_19). IHM-S was funded by the UK Natural Environmental Research Council Shrub Tundra (NE/M016323/1) grant. ISJ was funded by the University of Iceland Research Fund. Fieldwork in Yamal peninsula (Erkuta, Sabetta and Belyi) for DE, NS and AS was supported by the Russian Foundation for Basic Research (No: 18-05-60261 and No: 18-54-15013), Fram Centre project YaES (No: 362259), the Russian Center of Development of the Arctic, and the “Yamal-LNG” company. Fieldwork in Utqiaġvik was supported by the U.S. Fish and Wildlife Service. Fieldwork in Svalbard was supported by the Norwegian Research Council (AFG No: 246080/E10), the Norwegian Polar Institute, Climate-ecological Observatory for Arctic Tundra – COAT, the Svalbard Environmental protection fund (project number 15/20), and the University Centre in Svalbard (UNIS) and the AB-338/AB-838 students of 2018. Sampling at Billefjorden was supported by GACR 17- 20839S.

Rangeland ecosystems are changing worldwide with the abandonment of extensive pastoralism practices and greater interest for species coexistence. However, the lack of compiled data on current changes in the abundance and distribution of herbivores challenges rangeland management decisions. Here we gathered and made available for the first time the most extensive set of occurrence data for rangeland herbivores in Iceland in an Open Access framework for transparent and repeatable science-based decisions. We mapped fine scale species distribution overlap to identify areas at risk for wildlife-livestock conflict and overgrazing. Nationwide and long term (1861-2021) occurrence data from 8 independent datasets were used alongside 11 predictor raster layers ("Big Data") to data mine and map the distribution of the domestic sheep (Ovis aries), feral reindeer (Rangifer tarandus tarandus), pink-footed geese (Anser brachyrhynchus), and rock ptarmigan (Lagopus muta islandorum) over the country during the summer. Using algorithms of Maxent in R, RandomForest, TreeNet (stochastic gradient boosting) and MARS (Splines) in Minitab-SPM 8.3, we computed 1 km pixel predictions from machine learning-based ensemble models. Our high-resolution models were tested with alternative datasets, and Area Under the Curve (AUC) values that indicated good (reindeer: 0.8817 and rock ptarmigan: 0.8844) to high model accuracy (sheep: 0.9708 and pink-footed goose: 0.9143). Whenever possible, source data and models are made available online and described with ISO-compliant metadata. Our results illustrate that sheep and pink-footed geese have the greatest overlap in distribution with potential implication for wildlife-livestock conflicts and continued ecosystem degradation even under diminishing livestock abundance at higher elevation. These nationwide models and data are a global asset and a first step in making available the best data for science-based sustainable decision-making about national herbivores affecting species coexistence and environmental management.

Traditional food is central to Inuit culture and sense of identity. Recent changes in lifestyle, climate, and animal populations have influenced how people practice and experience activities on the land. We summarize the findings of 191 new and archived interviews addressing the continued relationships of Inuit to berries in the Canadian territories of Nunavut, Nunavik, and Nunatsiavut. Berry plants have been and remain widely used throughout the study area. Berry picking is an important cultural activity that contributes to spiritual, personal, and community wellbeing. In some regions, the availability of berries and accessibility to berry patches are threatened by climate change, recent increases in goose populations, as well as community development. Study outcomes suggest that berry picking should be considered in land-use planning since, alongside hunting and fishing, it is an activity that contributes to physical and mental health while being an important cultural practice across Inuit territories.

Significance Two defining features of climate change in the Arctic are the rapid decline of sea ice and “shrubification” of the tundra. While previous studies have inferred warming-related linkages between the two, these have been limited to a few locations. Our Pan-Arctic analysis of shrub growth chronologies reveals two important insights. Tundra shrub growth dynamics are associated with sea ice decline throughout the Arctic; however, while shrubs from most locations increased their growth, more than one-third showed evidence of declining growth in response to warming and drying associated with sea ice loss. These results highlight pronounced growth response heterogeneity across the tundra biome that will have important implications for tundra productivity and vegetation–climate feedback., Arctic sea ice extent (SIE) is declining at an accelerating rate with a wide range of ecological consequences. However, determining sea ice effects on tundra vegetation remains a challenge. In this study, we examined the universality or lack thereof in tundra shrub growth responses to changes in SIE and summer climate across the Pan-Arctic, taking advantage of 23 tundra shrub-ring chronologies from 19 widely distributed sites (56°N to 83°N). We show a clear divergence in shrub growth responses to SIE that began in the mid-1990s, with 39% of the chronologies showing declines and 57% showing increases in radial growth (decreasers and increasers, respectively). Structural equation models revealed that declining SIE was associated with rising air temperature and precipitation for increasers and with increasingly dry conditions for decreasers. Decreasers tended to be from areas of the Arctic with lower summer precipitation and their growth decline was related to decreases in the standardized precipitation evapotranspiration index. Our findings suggest that moisture limitation, associated with declining SIE, might inhibit the positive effects of warming on shrub growth over a considerable part of the terrestrial Arctic, thereby complicating predictions of vegetation change and future tundra productivity.

Arctic terrestrial ecosystems are heterogeneous because of the strong influences of microtopography, soil moisture and snow accumulation on vegetation distribution. The interaction between local biotic and abiotic factors and global climate patterns will influence species responses to climate change. Salix arctica (Arctic willow) is a structuring species, ubiquitous and widespread, and as such is one of the most important shrub species in the High Arctic. In this study, we measured S. arctica reproductive effort, early establishment, survival and growth in the Zackenberg valley, north-east Greenland. We sampled four plant communities that varied with respect to snow conditions, soil moisture, nutrient content and plant composition. We found large variability in reproductive effort and success with total catkin density ranging from 0.6 to 66 catkins/m 2 and seedling density from

Compilation of the species richness data was made possible through the TFI Networks grant to CD, “Effect Studies and Adaptation to Climate Change,” under the Norforsk initiative (2011 – 2014) which supported two CBIONET-AVA workshops held in Denmark during 2013. The genetic studies were funded by the Research Council of Norway (grant nos. 150322/720 and 170952/V40 to CB).

Altres ajuts europeus: P.A.W. was additionally supported by the European Union Fourth Environment and Climate Framework Programme (Project Number ENV4-CT970586)P.A.W. was additionally supported by the European Union Fourth Environment and Climate Framework Programme (Project Number ENV4-CT970586). The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature-trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming.

Annual fluctuations in the abundance of wild berries have repercussions on animals and humans who depend on this important resource. Although studies have tried to disentangle the effect of climate and herbivores on inter-annual berry yield, there are still many uncertainties as to which factors are driving productivity. In this research, we evaluated the effect of climate and predation by rodents and moths on the abundance of bilberry (Vaccinium myrtillus) flowers and berries at the Kilpisjarvi Biological Station in northwest Finnish Lapland. The data were collected from 1973 to 2014 in a forest and an alpine site, both undisturbed by human activities. This dataset is unique due to the length of the sampling period, the availability of flower, berry, and rodent abundance data as well as the undisturbed nature of the habitat. Previous summer temperatures, the abundance of rodents, and the presence of a moth outbreak were complementary factors explaining the abundance of flowers. Herbivores had a larger impact on flower production than climate, but both variables were important to understand reproductive effort. Contrary to results from experimental studies, warmer winters did not significantly influence reproductive success. The abundance of fruits was strongly correlated with pollinator activity; the forest site, with a larger pollinator network, had a higher reproductive success and spring conditions were linked to inter-annual variability in fruit production. Our results illustrate the importance of the location of the population within the species distribution range to understand plant sensitivity to climatic fluctuations with fruit production only influenced by current year summer temperatures at the alpine site. Finally, we observed a general increase in flower and fruit production at the alpine site, which was driven by large yields since the early 1990s. Fruit production at the forest site was comparatively stable throughout the study period.

Aim Alterations to the abundance and distribution of plants, especially shrubs, have been predicted by warming experiments and confirmed by remote-sensing analyses and land-based observations in the Low Arctic. In the High Arctic, analyses of satellite images suggest a recent increase in the normalized difference vegetation index (NDVI) and warming experiments have shown a positive correlation between temperature and shrub cover, but little is known about the responses of natural systems. In this context, we investigated populations of Arctic willow (Salix arctica Pall.) to assess the potential contribution of this structuring species to High Arctic shrubification. Location Seven polar semidesert sites, including two glacier forelands, in High Arctic Canada and Greenland. Methods We evaluated the size distribution and establishment age of Arctic willow populations through field measurements and dendrochronological analysis. We also assessed the cover of Arctic willow at each site and compared current data with historical records. Results Age determination of over 200 large individuals established by seed suggests that colonization events were associated with the melting of permanent snow and glacial ice. Size distributions showed that recent recruitment was more frequent on glacier forelands, even though seedling establishment was common in other sites. Comparing our measurements with previous studies at the same sites revealed that significant increases in cover over the past few decades occurred only on glacier forelands. Main conclusions Our results suggest that the population structure and dynamics of Arctic willow in the High Arctic are influenced by site-specific factors. Rapid glacier retreat is increasing the extent of the glacier forelands, which are currently experiencing relatively rapid plant colonization. Some sheltered sites with greater snow accumulation will probably experience increased shrub colonization under current and predicted climate change. It appears, however, that shrub recruitment and growth are still strongly limited by water availability, and the reduction in permanent snow cover may exacerbate this stress.

Temperature is increasing at unprecedented rates across most of the tundra biome. Remote-sensing data indicate that contemporary climate warming has already resulted in increased productivity over much of the Arctic, but plot-based evidence for vegetation transformation is not widespread. We analysed change in tundra vegetation surveyed between 1980 and 2010 in 158 plant communities spread across 46 locations. We found biome-wide trends of increased height of the plant canopy and maximum observed plant height for most vascular growth forms; increased abundance of litter; increased abundance of evergreen, low-growing and tall shrubs; and decreased abundance of bare ground. Intersite comparisons indicated an association between the degree of summer warming and change in vascular plant abundance, with shrubs, forbs and rushes increasing with warming. However, the association was dependent on the climate zone, the moisture regime and the presence of permafrost. Our data provide plot-scale evidence linking changes in vascular plant abundance to local summer warming in widely dispersed tundra locations across the globe. © 2012 Macmillan Publishers Limited. All rights reserved.

Global circulation models predict that the strongest and most rapid effects of global warming will take place at the highest latitudes of the Northern Hemisphere. Consistent with this prediction, the Ward Hunt Island region at the northern terrestrial limit of Arctic Canada is experiencing the onset of major environmental changes. This article provides a synthesis of research including new observations on the diverse geosystems/ecosystems of this coastal region of northern Ellesmere Island that extends to latitude 83.11° N (Cape Aldrich). The climate is extreme, with an average annual air temperature of -17.2 °C, similar to Antarctic regions such as the McMurdo Dry Valleys. The region is geologically distinct (the Pearya Terrane) and contains steep mountainous terrain intersected by deep fiords and fluvial valleys. Numerous glaciers flow into the valleys, fiords, and bays, and thick multi-year sea ice and ice shelves occur along the coast. These extreme ice features are currently undergoing rapid attrition. The polar desert landscape contains sparse, discontinuous patches of vegetation, including dense stands of the prostrate shrub Salix arctica (Artic willow) at some sites, and 37 species of vascular plants on Ward Hunt Island. Diverse aquatic ecosystems occur throughout the area, including meromictic, epishelf, and perennially ice-covered lakes. Many of these have responded strongly to climate shifts in the past and like other geosystems/ecosystems of the region are now sentinels of ongoing global climate change.

Many studies indicate increases of shrubs in Arctic and alpine regions in recent decades. This often dramatic increase in the abundance and dominance of shrub species is likely due to recent climate warming and has the potential to alter both the structure and function of tundra ecosystems. To better understand recent shrub dynamics and environmental changes in tundra ecosystems, analyses of shrub growth rings offer a vast variety of methods and approaches. However, classical dendrochronological methods, which were developed for tree species, need to be adapted for shrubs, taking into account their complex morphologies and growth eccentricities. Here, we review current and developing methods to measure radial and axial growth, estimate shrub age, and assess shrub growth dynamics in relation to environmental variables. Recent advances in sampling methods, analysis and applications have improved our ability to investigate growth and recruitment dynamics of shrubs in tundra ecosystems. However, future dendroecological work will require new approaches to better address variation in growth within parts of the plant, among individuals within populations and between species to scale up findings to the landscape or biome level.

Rapid climate warming has been linked to increasing shrub dominance in the Arctic tundra. Research now shows that climate–shrub growth relationships vary spatially and according to site characteristics such as soil moisture and shrub height. Rapid climate warming in the tundra biome has been linked to increasing shrub dominance1,2,3,4. Shrub expansion can modify climate by altering surface albedo, energy and water balance, and permafrost2,5,6,7,8, yet the drivers of shrub growth remain poorly understood. Dendroecological data consisting of multi-decadal time series of annual shrub growth provide an underused resource to explore climate–growth relationships. Here, we analyse circumpolar data from 37 Arctic and alpine sites in 9 countries, including 25 species, and ∼42,000 annual growth records from 1,821 individuals. Our analyses demonstrate that the sensitivity of shrub growth to climate was: (1) heterogeneous, with European sites showing greater summer temperature sensitivity than North American sites, and (2) higher at sites with greater soil moisture and for taller shrubs (for example, alders and willows) growing at their northern or upper elevational range edges. Across latitude, climate sensitivity of growth was greatest at the boundary between the Low and High Arctic, where permafrost is thawing4 and most of the global permafrost soil carbon pool is stored9. The observed variation in climate–shrub growth relationships should be incorporated into Earth system models to improve future projections of climate change impacts across the tundra biome.