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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.

MotivationThe BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene.Main types of variables includedThe database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record.Spatial location and grainBioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2).Time period and grainBioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year.Major taxa and level of measurementBioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.Software format.csv and .SQL.

To better understand climatic origins of annual tree-growth anomalies in boreal forests, we analysed 895 black spruce (Picea mariana (Mill.) B.S.P.) tree-growth series from 46 xeric sites situated along three latitudinal transects in Eastern Canada. We identified interannual (based on comparison with previous year growth) and multidecadal (based on the entire tree-ring width distribution) growth anomalies between 1901 and 2001 at site and transect levels. Growth anomalies occurred mainly at site level and seldom at larger spatial scales. Both positive interannual and multidecadal growth anomalies were strongly associated with below-average temperatures and above-average precipitation during the previous growing season ([June.sub.t-1] - [August.sub.t-1]). The climatic signature of negative interannual and multidecadal growth anomalies was more complex and mainly associated with current-year climatic anomalies. Between the early and late 20th century, only negative multidecadal anomalies became more frequent. Our results highlight the role of previous growing season climate in controlling tree growth processes and suggest a positive association between climate warming and increases in the frequency of negative multidecadal growth anomalies. Projected climate change may further favour the occurrence of tree-growth anomalies and enhance the role of site conditions as modifiers of tree response to regional climate change. Key words: ecological resilience, climate change, growth sensitivity, adaptive capacity, forest productivity. Nous avons etudie l'origine climatique des anomalies de croissance des forets boreales en analysant 895 series de croissance d'epinette noire (Picea mariana (Mill.) B.S.P.) provenant de 46 sites xeriques repartis le long de trois transects latitudinauxdans l'Est Canadien. Nous avons identifie les anomalies de croissance interannuelles (comparaison al'annee precedente) et multi-decennales (comparaison a toutes les annees) pour chaque site et transect de 1901 a 2001. Les anomalies de croissance apparaissent principalement a l'echelle du site mais rarement a de plus larges echelles geographiques. Les anomalies positives (interannuelles et multi-decennales) sont fortement associees a des temperatures basses et des precipitations fortes pendant la saison de croissance de l'annee precedente. L'origine climatique des anomalies negatives (interannuelles et multi-decennales) est plus complexe et generalement associee a des anomalies climatiques de l'annee en cours. Entre le debut et la fin du XXe siecle, seules les anomalies multi-decennales negatives sont devenues plus frequentes. Nos resultats revelent l'importance du climat de la saison de croissance precedente dans l'apparition d'anomalies de croissance et suggerent un lien positif entre le rechauffement climatique et l'augmentation de la frequence des anomalies multi-decennales negatives. L'augmentation prevue des temperatures dans les prochaines decennies pourrait davantage accroitre la frequence des anomalies. Mots-cles: resilience ecologique, changement climatique, sensitivite de croissance, capacite d'adaptation, production forestiere., Introduction Recent climate dynamics indicate an increase in global mean temperature and in the frequency and intensity of climate extremes (Intergovernmental Panel on Climate Change (IPCC) 2014). Trees have shown [...]

Tree growth at the treeline ecotone is known to be sensitive to climate variability and is thus considered to be a worldwide biomonitor of climate change. However, our understanding of within-region variation in growth responses through space and time is limited. A dry south-facing slope dominated by Pinus wallichiana A.B. Jacks. and a wet north-facing slope dominated by Abies spectabilis (D. Don) Spach in Nepal, central Himalaya, were used to analyze the intersite (i.e., dry vs. wet sites) and intrasite (i.e., treeline vs. forest line elevations) tree-growth relationships, as well as response to monthly and seasonal temperature and precipitation at annual and bidecadal time scales. At both study sites and at two elevations within each site, growth can be strongly affected by growing-season and nongrowing-season factors; however, there are inconsistencies in terms of the climate-growth relationship across space and over time. At the dry site, only a weak positive growth response to summer temperature is observed. At both sites, there is a negative growth response to winter precipitation at both high and low elevations, and this response is markedly independent of the summer and winter temperature trends of the respective site. At the wet site, growth at the higher elevation is negatively correlated to the early summer temperature, whereas a positive growth response to spring precipitation is observed at the lower elevation, indicating a possible drought effect. The results illustrate how different climatic drivers may govern tree-growth responses both between sites with contrasting climates within a region and along elevational gradients within the treeline ecotone. This underlines the need for multiscale studies and a focus on multiple climate variables when analyzing treeline ecotone responses to climate change. Key words: Abies spectabilis, climate-growth relations, forest line, Pinus wallichiana, treeline, tree rings. On sait que la croissance des arbres dans l'ecotone de la limite des arbres est sensible aux variations du climat et qu'elle est par consequent consideree comme un indicateur biologique du changement climatique global. Cependant, notre comprehension de la variation intraregionale des reactions de la croissance dans l'espace et le temps est limitee. Une pente seche exposee au sud dominee par Pinus wallichiana A.B. Jacks. et une pente humide exposee au nord dominee par Abies spectabilis (D. Don) Spach au Nepal, dans l'Himalaya central, ont ete utilisees pour analyser le comportement de la croissance des arbres entre les sites (c.-a-d. sec vs. humide) et dans les sites (c.-a-d. altitude de la limite des arbres vs. celle de la limite de la foret commerciale) ainsi que sa reaction a la temperature et a la precipitation mensuelles et saisonnieres a des echelles temporelles annuelle et bi-decennale. Dans les deux sites a l'etude, et aux deux altitudes dans chacun des sites, la croissance peut etre fortement influencee par des facteurs associes ou non a la saison de croissance. Cependant, la relation entre le climat et la croissance n'est pas coherente dans l'espace ni dans le temps. Dans le site sec, seulement une faible reponse positive de la croissance a la temperature estivale a ete observee. Dans les deux sites, la croissance reagit negativement aux precipitations hivernales, aux altitudes elevee et faible, et cette reaction est manifestement independante des tendances des temperatures estivales et hivernales dans chacun des sites. Dans le site humide, la croissance a l'altitude la plus elevee est negativement correlee a la temperature en debut d'ete tandis qu'on observe une reponse positive de la croissance aux precipitations printanieres a l'altitude plus basse, l'indication d'un effet de secheresse potentiel. Les resultats illustrent de quelle facon differents facteurs climatiques peuvent controler les reponses en croissance des arbres tant entre les sites dont le climat differe a l'interieur d'une region que le long de gradients altitudinaux dans l'ecotone de la limite des arbres. Cela met en evidence la necessite d'etudes a differentes echelles, avec un accent sur de multiples variables climatiques lorsqu'on analyse les reponses de l'ecotone de la limite des arbres au changement climatique. [Traduit par la Redaction] Mots-cles: Abies spectabilis, relations entre la croissance et le climat, limite de la foret commerciale, Pinus wallichiana, limite des arbres, cernes annuels., Introduction The treeline ecotone, which marks the transition from closed forest to the treeless alpine or arctic tundra, is highly responsive to climate (Germino et al. 2002; Dullinger et al. [...]