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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.

Abstract Aims: An Arctic Vegetation Classification (AVC) is needed to address issues related to rapid Arctic-wide changes to climate, land-use, and biodiversity. Location: The 7.1 million km2 Arctic tundra biome. Approach and conclusions: The purpose, scope and conceptual framework for an Arctic Vegetation Archive (AVA) and Classification (AVC) were developed during numerous workshops starting in 1992. The AVA and AVC are modeled after the European vegetation archive (EVA) and classification (EVC). The AVA will use Turboveg for data management. The AVC will use a Braun-Blanquet (Br.-Bl.) classification approach. There are approximately 31,000 Arctic plots that could be included in the AVA. An Alaska AVA (AVA-AK, 24 datasets, 3026 plots) is a prototype for archives in other parts of the Arctic. The plan is to eventually merge data from other regions of the Arctic into a single Turboveg v3 database. We present the pros and cons of using the Br.-Bl. classification approach compared to the EcoVeg (US) and Biogeoclimatic Ecological Classification (Canada) approaches. The main advantages are that the Br.-Bl. approach already has been widely used in all regions of the Arctic, and many described, well-accepted vegetation classes have a pan-Arctic distribution. A crosswalk comparison of Dryas octopetala communities described according to the EcoVeg and the Braun-Blanquet approaches indicates that the non-parallel hierarchies of the two approaches make crosswalks difficult above the plant-community level. A preliminary Arctic prodromus contains a list of typical Arctic habitat types with associated described syntaxa from Europe, Greenland, western North America, and Alaska. Numerical clustering methods are used to provide an overview of the variability of habitat types across the range of datasets and to determine their relationship to previously described Braun-Blanquet syntaxa. We emphasize the need for continued maintenance of the Pan-Arctic Species List, and additional plot data to fully sample the variability across bioclimatic subzones, phytogeographic regions, and habitats in the Arctic. This will require standardized methods of plot-data collection, inclusion of physiogonomic information in the numeric analysis approaches to create formal definitions for vegetation units, and new methods of data sharing between the AVA and national vegetation-plot databases.? Abbreviation:? AVA = Arctic Vegetation Archive; AVC = Arctic Vegetation Classification; BEC = Biogeoclimatic Ecological Classification; Br.-Bl. = Braun-Blanquet; CAFF = Conservation of Arctic Flora and Fauna; CAVM = Circumpolar Arctic Vegetation Map; CNVC = Canadian National Vegetation Classification; EUNIS = European Nature Information System; EVC = European Vegetation Classification; GIVD = Global Index of Vegetation-plot Databases; IASC = International Arctic Science Committee; ICPN = International Code of Phytosociological Nomenclature; PAF = Pan-Arctic Flora (for nomenclature of vascular plants); PASL = Pan-Arctic Species List (includes circumpolar checklist of vascular plants, mosses, liverworts, and lichens); USNVC = United States National Vegetation Classification. Submitted: 30 January 2017; first decision: 26 March 2017; accepted: 24 July 2017

AbstractWe investigated dietary variation during three winters in female Svalbard reindeer (Rangifer tarandus platyrhynchus) on the basis of rumen samples from animals culled in early and late winter during 2000–2002. The winter diet was compared to a late summer diet on the basis of samples from 1999, with variations in dietary composition in early and late winter among years also investigated. We conducted our assessment by identifying plant fragments in rumen samples using a point identification method. The effects of season and year on dietary composition of females were tested using non-parametric multifactorial MANOVA. During early winter, the diet seemed to be a function of both plant availability and plant quality, with the latter also highly important for the summer diet. During late winter, restricted forage availability due to snow cover seemed to have influenced dietary composition. We also found dietary variation among years both in early and late winter. We hypothesize that climatic effects previously found on the growth rate of Svalbard reindeer populations may be mediated through interannual variation in their diet where increased summer precipitation and winter rain may affect the dietary composition through decreased availability of forage biomass.

Climate change may have large effects on plants, especially in the Arctic. At two different sites, we studied the effects of enhanced temperature by using open‐top chambers (OTCs) on the clonal sedge Carex bigelowii, a common plant in arctic and alpine tundra. At the subarctic‐alpine site Latnjajaure, northern Sweden, overall flowering phenology was accelerated by open‐top chambers (OTCs) during the five years of treatment. For this protogynous population, male flower phenology accelerated more than female flower phenology, which resulted in an increased gender phase overlap. Sexual reproductive effort at the ramet‐level increased, both in male and female functions. Smut fungus incidence was not different among treatments, but a Dipteran seed predator attacked more ramets in the OTCs in one of five years. However, neither the fungus nor the seed predators affected plant growth or seed set measurably. Ramet‐level growth increased in the OTCs at Latnjajaure, but decreased in the OTCs at the maritime subarctic site Thingvellir, Iceland after three years of treatment. At Latnjajaure, the initial ramet‐ level responses were still evident after five years, while responses at the ramet population level disappeared: there was no difference in flowering frequency of ramets in the fifth year of the warming treatment. This is interpreted as either meristem limitation or internal resource depletion. At Thingvellir flowering frequency was unaffected by warming treatment, while ramet production decreased. Ramet production was unaffected by the treatment at Latnjajaure. These site differences in responses could be the consequences of differences in climate or site specific conditions. The trade‐off (negative correlation) between the number and size of vegetative offspring at Latnjajaure disappeared under enhanced temperatures (within the OTCs). This trade‐off was not apparent under the warmer conditions at Thingvellir.

The aim of this study was to investigate whether resource availability affects the degree of physiological integration and the growth pattern of interconnected ramets in the clonal plantMaianthemum bifolium(L.)F.W. Schmidt(Liliaceae), a rhizomatous herb of European forests, by studying it at two contrasting South Swedish beech forest sites termed “poor” and “rich”. The degree of physiological integration was studied by tracing the pattern of14C translocation and in a cutting experiment involving rhizome severing and defoliation treatments. The size of the plants, growth of new rhizomes, branching frequency, distance between shoots and the internode length were compared.