Impact of late Quaternary environmental changes on deep-sea benthic foraminiferal faunas of the Red Sea

Fluctuations in abundance, diversity and species composition of benthic foraminifera from two sites of the northern and southern Red Sea indicate strong variability of deep-sea ecosystems during the last four glacial to interglacial cycles. In total, five and four different benthic foraminiferal assemblages have been identified in the northern core and southern core, respectively. Comparison with recent faunas from the Red Sea and adjacent oceans allowed the reconstruction of temporal changes in deep-water ventilation, salinity and food availability at the seafloor. Generally, the abundance of infaunal and miliolid taxa increase during glacial intervals indicating increased organic matter fluxes, oxygen decrease and salinity increase in deep waters during these times. These fluctuations are attributed to enhanced oxygen consumption rates and temporarily reduced deep-water formation in the northern Red Sea during glacial intervals. The recorded environmental changes are a reflection of both high- and low-latitude climate changes. The northern Red Sea is mainly influenced by glacio-eustatic sea level fluctuations that control deep-water formation rates and by mid-latitude climate changes of the Mediterranean region that control surface productivity. In contrast, deep-sea ecosystem variability of the southern Red Sea is additionally influenced by low-latitude climate changes attributed to the NE monsoon intensity that drives the inflow of nutrient-rich surface waters from the Gulf of Aden. These results demonstrate the high sensitivity of deep-sea ecosystems of the Red Sea to both global and regional climate changes.     

Paläoklima: Knochen weisen den Weg

Climate change at the end of the Last Glacial and its consequences on biodiversity The Weichselian Glacial and also the Holocene, our current interglacial, were characterized by numerous sudden changes of climate. The recent pattern of biological diversity in the northern European Lowlands carries a clear signature of the past. Using interdisciplinary scientific methods of both bio‐ and geosciences, it is possible to decipher and understand the interplay of processes like climate change, colonization and extinction processes of species, changing ecosystems and the influence and distribution of humans in the Stone Age. The spatio‐temporal pattern of subfossil bone records, ancient DNA and stable isotopes are helpful tools to explore those past processes. Palaeoecology offers a scientific perspective how the past shaped the present diversity and what may happen in future.     

Holocene Carbon Accumulation of Fen Peatlands in Boreal Western Canada: A Complex Ecosystem Response to Climate Variation and Disturbance

Understanding the long-term ecological dynamics of northern peatlands is essential for assessment of the possible responses and feedbacks of these carbon-rich ecosystems to climate change and natural disturbance. I used high-resolution macrofossil and lithological analyses of a fen peatland in western Canada to infer the Holocene developmental history of the peatland, to document the temporal pattern of long-term peat accumulation, and to investigate ecosystems responses to climate changes in terms of species composition and carbon accumulation. The peatland has been dominated by sedges and brown mosses during its 10,000-year history, despite interruption by tephra deposition. Peat accumulation rates vary by more than an order of magnitude and decline from 5500 to 1300 cal BP, resulting in a convex depth–age curve, which contrasts with the carbon accumulation patterns documented for oceanic peatlands. The synthesis of regional data from continental western Canada indicates that fens tend to accumulate more carbon than bogs of the same ages. These data suggest that the carbon sink potential of northern peatlands has varied dramatically in the past, so estimates of the present and projected carbon sink strengths of these peatlands need to take this temporal variation into consideration. Widespread slowdown of peat accumulation over the last 4000 years may have resulted from climate cooling in northern latitudes after the Holocene insolation maximum. The findings indicate that long-term peatland dynamics are modified by many local and regional factors and that gradual environmental change may be capable of triggering abrupt shifts and jumps in ecosystem states.     

Phylogeography and demographic history of Shaw's Jird (Meriones shawii complex) in North Africa

Palaeoenvironmental data and climatic reconstructions show that the Mediterranean ecoregion of North Africa underwent drastic ecological changes during the Pleistocene. Given its rich palaeontological record, North Africa is a pertinent region for documenting the role of climate change and human mediated‐habitat changes on the demography and genetic structure of faunal species. In the present study, we collected data from this species in Morocco, Algeria, and Tunisia, and we combined molecular (mitochondrial and nuclear DNA sequences, microsatellites), fossil, palaeoenvironmental, and human context data to propose an explanation for the fluctuations of populations belonging to the Meriones shawii complex in the past. Genetic and fossil data both indicate a strong bottleneck in Moroccan populations at the Middle Holocene (last interglacial optimum) compared to the Late Pleistocene. Our mitochondrial DNA data suggest a diversification event within Morocco corresponding to the 130–125 kya interglacial optimum. Given that (1) major demographic changes in the M. shawii complex coincide with the interglacial optimums, and (2) the impact of human activities on the landscape and faunal communities was moderate during the Middle Holocene (beginnings of the Neolithic culture), our results demonstrate that climate, rather than anthropogenic influences, likely explains the M. shawii complex population decline in the Holocene.     

The Impact of 850,000 Years of Climate Changes on the Structure and Dynamics of Mammal Food Webs

Most evidence of climate change impacts on food webs comes from modern studies and little is known about how ancient food webs have responded to climate changes in the past. Here, we integrate fossil evidence from 71 fossil sites, body-size relationships and actualism to reconstruct food webs for six large mammal communities that inhabited the Iberian Peninsula at different times during the Quaternary. We quantify the long-term dynamics of these food webs and study how their structure changed across the Quaternary, a period for which fossil data and climate changes are well known. Extinction, immigration and turnover rates were correlated with climate changes in the last 850 kyr. Yet, we find differences in the dynamics and structural properties of Pleistocene versus Holocene mammal communities that are not associated with glacial-interglacial cycles. Although all Quaternary mammal food webs were highly nested and robust to secondary extinctions, general food web properties changed in the Holocene. These results highlight the ability of communities to re-organize with the arrival of phylogenetically similar species without major structural changes, and the impact of climate change and super-generalist species (humans) on Iberian Holocene mammal communities.     

Impacts of co-occurring environmental changes on Alaskan stream fishes

1. Freshwater fishes are now facing unprecedented environmental changes across their northern ranges, especially due to rapid warming occurring at higher latitudes. However, empirical research that examines co-occurring environmental effects on northern fish communities remains limited.
2. We used fish community data from 1587 Alaskan stream sites to examine the potential combined and interacting effects of climate change, current weather, habitat, land use, and fire on two community-level metrics (species richness, relative abundance), and on the distributions of three Alaskan fish species.
3. Our models were 71–76% accurate in predicting the distribution of Alaskan stream fishes using a combination of climate and habitat variables. In contrast to other freshwater ecosystems that are most threatened by land use pressures, we did not detect any evidence for the potential stress of anthropogenic land use or fire on stream fishes.
4. Warming temperatures increased overall community richness and abundance but produced differing responses at the species level. Juvenile salmon presence was positively associated with several climate variables including warmer spring and autumn temperatures and wetter summers. In comparison, warmer seasonal temperatures contributed to declines for northern-adapted species such as Arctic grayling and Dolly Varden.
5. This study highlights the overarching role of current and changing climate in regulating northern stream fish biodiversity. Although many fish species may benefit from climate change across their northern ranges, localised declines are likely to occur and may prove detrimental for communities with limited fishing portfolios. Climate change adaptation and mitigation strategies customised for rapidly changing northern ecosystems will play an essential role in preserving ecologically unique northern species.

     

Biome changes and their inferred climatic drivers in northern and eastern continental Asia at selected times since 40 cal ka <Emphasis Type="SmallCaps">bp</Emphasis>

Recent global warming is pronounced in high-latitude regions (e.g. northern Asia), and will cause the vegetation to change. Future vegetation trends (e.g. the “arctic greening”) will feed back into atmospheric circulation and the global climate system. Understanding the nature and causes of past vegetation changes is important for predicting the composition and distribution of future vegetation communities. Fossil pollen records from 468 sites in northern and eastern Asia were biomised at selected times between 40 cal ka bp and today. Biomes were also simulated using a climate-driven biome model and results from the two approaches compared in order to help understand the mechanisms behind the observed vegetation changes. The consistent biome results inferred by both approaches reveal that long-term and broad-scale vegetation patterns reflect global- to hemispheric-scale climate changes. Forest biomes increase around the beginning of the late deglaciation, become more widespread during the early and middle Holocene, and decrease in the late Holocene in fringe areas of the Asian Summer Monsoon. At the southern and southwestern margins of the taiga, forest increases in the early Holocene and shows notable species succession, which may have been caused by winter warming at ca. 7 cal ka bp. At the northeastern taiga margin (central Yakutia and northeastern Siberia), shrub expansion during the last deglaciation appears to prevent the permafrost from thawing and hinders the northward expansion of evergreen needle-leaved species until ca. 7 cal ka bp. The vegetation-climate disequilibrium during the early Holocene in the taiga-tundra transition zone suggests that projected climate warming will not cause a northward expansion of evergreen needle-leaved species.     

Refugial ecosystems in central Asia as indicators of biodiversity change during the Pleistocene–Holocene transition

Site-scale species richness (alpha diversity) patterns are well described for many present-day ecosystems, but they are difficult to reconstruct from the fossil record. Very little is thus known about these patterns in Pleistocene full-glacial landscapes and their changes following Holocene climatic amelioration. However, present-day central Asian ecosystems with climatic features and biota similar to those of the full-glacial periods may serve as proxies of alpha diversity variation through both space and time during these periods. We measured alpha diversity of vascular plants, bryophytes, macrolichens and land snails, as well as environmental variables, in 100-m² plots located in forests and open habitats in the Russian Altai Mountains and their northern foothills. This region contains adjacent areas that possess climatic and biotic features similar to mid-latitude Europe for both the Last Glacial Maximum and contemporaneous Holocene ecosystems. We related alpha diversity to environmental variables using generalized linear models and mapped it from the best-fit models. Climate was identified as the strongest predictor of alpha diversity across all taxa, with temperature being positively correlated to number of species of vascular plants and land snails and negatively correlated to that of bryophytes and macrolichens. Factors important for only some taxa included precipitation, soil pH, percentage cover of tree layer and proportion of grassland areas in the landscape around plots. These results, combined with the high degree of similarity between the current Altai biota and dry-cold Pleistocene ecosystems of Europe and northern Asia, suggest that vascular plant and land snail alpha diversity was low during cold phases of the Pleistocene with a general increase following the Holocene climatic amelioration. The opposite trend probably existed for terricolous bryophytes and macrolichens.     

Quaternary and pre‐Quaternary historical legacies in the global distribution of a major tropical plant lineage

Aim The relative importance of current climate and past historical legacies is hotly debated. Here, we assess their role in determining the global distribution and diversity patterns of palms (Arecaceae), a widespread, species‐rich group of keystone ecological importance in tropical ecosystems. Location Global. Methods We assembled country‐level species lists world‐wide and compiled associated data on potential contemporary environmental drivers (current climate, habitat heterogeneity, area, and insularity), Quaternary glacial–interglacial climate change and major biogeographic regions to evaluate to what extent the global distribution and species richness patterns in palms reflect Quaternary climatic oscillations or regional effects reflecting pre‐Quaternary legacies. We also assessed for the first time if historical legacies differ between continents and islands, providing novel insights into determinants of insular species richness. Results Palm species richness was significantly affected by Quaternary climate changes and further differed between biogeographic regions even when both current environmental conditions and Quaternary climate changes were accounted for. In contrast, global limits to the distribution of the palm family were best explained by current temperature while biogeographic regional differences were unimportant and Quaternary climate change caused only a small constraint. Historical legacies were weak on islands, with only a small regional effect and no effect of Quaternary climate changes. Main conclusions Strong historical legacies supplement current environment as determinants of palm species richness. These primarily comprise pre‐Quaternary historical effects, reflected in low African species richness (possibly linked to pre‐Quaternary extinctions) and outstandingly high Neotropical and Indomalayan palm species richness (possibly linked to these regions' long‐term climatic suitability for palms). In contrast to species richness, the global distribution of the family range is largely in equilibrium with current climate. The small historical effects on islands are consistent with climatic buffering from their oceanic environment.     

Paleoenvironmental interpretation of the mid‐late Holocene of Corrientes province,Argentina

The objective of the present paper is to recognize and reconstruct, from the analysis of pollen recovered from sedimentary cores, the predominant plant communities and their variations during the Holocene in Corrientes Argentina, in order to infer changes in climatic conditions, vegetation and paleoenvironmental evolution in the northeast of Argentina. For this study, lakes located in the central region of Corrientes province were selected, comprising part of the western margin of the Iberá Wetland. The palynological analysis of the paleocommunities shows, in a first stage of the mid Holocene, the predominance of marsh grasslands and hygrophilous communities that indicates humid to sub‐humid environmental conditions. In a later stage of the mid Holocene, the paleocommunities show a characteristic association of wetlands, which together with the presence of Typha sp., would indicate sub‐humid to humid conditions and waterlogged or flooded soils with slow‐moving water. For the late Holocene, the paleocommunities show, initially, the presence of a grass‐dominated herbaceous steppe, indicating environmental disturbances, which in the fossil record could reflect the combination of intense wind action under a dry climate. In a later stage, the frequency and variety of species characteristic of humid environments increase, dominated by marshy‐herbaceous species, in addition to the development of the hygrophilous forest. Consequently, since the mid Holocene, the main climate factors responsible for the observed changes in wetland conditions were the location and intensity of the Atlantic and Pacific anticyclones in addition to changes in sea level. These forces mainly affected the distribution of precipitation, causing significant changes in the vegetation communities.     

A new Late-glacial site with Picea abies in the northern Apennine foothills: an exception to the model of glacial refugia of trees

We describe a new palaeobotanical site at Bubano quarry on the easternmost Po plain, northern Italy. Pollen and macrofossils from river and marsh sediments demonstrate the occurrence of Picea in a Pinus sylvestris forest growing in a radius of some tens of kilometres south of the sedimentation place, at the beginning of the Late-glacial interstadial. The Late-glacial and Holocene history of Picea in the northern Apennines is reconstructed on the basis of the palaeobotanical record. The sharp climatic continentality increase eastwards across the northern Apennines from the Tyrrhenian to the Adriatic coast is considered significant for the survival of Picea during the Late-glacial. The most critical phase of survival is related to the moisture changes and consequent Abies competition associated with the last glacial-interglacial transition and the early Holocene. The residual spruce populations expanded during the middle Holocene. The history of Picea in the northern Apennines is a case of ineffective interglacial spread of tree populations from pre-existing stands of LGM (Last Glacial Maximum) and Late-glacial age.     

Glacial and interglacial refugia within a long-term rainforest refugium: The Wet Tropics Bioregion of NE Queensland, Australia

An artificial neural network is used to classify environments, including climate, terrain and soil variables, according to their suitability for fifteen structural/environmental forest classes in the Wet Tropics Bioregion of north-east Queensland. We map the environments characteristic of these forest classes in four climate regimes (the present and three past climate scenarios), quantify the changes in area of these environments in response to past regional changes in climate and identify areas that would have been environmentally suitable for rainforests at last glacial maximum (glacial refugia). We also identify areas that would have been suitable for upland and highland rainforest classes during the warmest parts of the interglacial (interglacial refugia) and map locations that consistently remain favourable to specific forest classes despite large changes in climate.In the climate of the last glacial maximum (LGM), rainforest environments are predicted in three relatively distinct refugia in the northern, central and southern Wet Tropics. Only three percent of the total area contains lowland, Mesophyll Vine Forest and the majority of the area of the rainforest refugia supports upland rainforest classes. In the cool, wet climate of the Pleistocene/Holocene transition (PHT), rainforest environments expand to form a more or less continuous block from the northern limits of the region to the Walter Hill Range, except for discontinuous patches extending through the Seaview and Paluma Ranges in the south. During the Holocene climatic optimum (HCO), rainforest environments become more fragmented, especially in the south. Lowland rainforest environments are very extensive in this climate while upland rainforest classes are restricted to what we term “interglacial refugia”.Estimated distributions and stable locations (consistently predicted in all four climate scenarios) for the various rainforest environment classes are our main, novel contribution. Each forest environment responds individualistically to climate change. Our results confirm the highly dynamic nature of the Wet Tropics landscape and present a much more detailed picture of landscape change since the late Pleistocene than previously has been available. This mapping exercise should be useful in the future for analyses of present-day biogeographic patterns. We argue that empirical modelling approaches have an important role in palaeoecology and global change research that is complementary to the developing mechanistic methods.     

Long-term warming affects ecosystem functioning through species turnover and intraspecific trait variation

Effects of climate change on natural ecosystems can be mediated by ecological processes, but also by rapid evolutionary adaptations and/or non-heritable trait changes in organisms. So far, most studies testing the importance of inter- versus intraspecific changes for how communities and their functioning responds to climate change are either short-term laboratory experiments in highly controlled (artificial) environments, or long-term field surveys suffering from lack of experimental manipulation. Here, we quantified how community composition and functioning has changed in response to long-term warming, including the potential direct and indirect effects via immediate and delayed physiological, non-heritable plastic, ecological, evolutionary and eco-evolutionary responses. We used a site-for-time approach, sampling sites in an artificially heated basin and a nearby area to quantify how >30 years of experimental warming in situ affects benthic grazer communities and traits of grazer taxa, as well as their contribution to a key ecosystem function: grazing on filamentous algae. The community composition shifted with warming, because a non-native species was highly common, and taxa with higher mobility, became more common in the heated areas compared to the control sites. Warming altered community functioning but the underlying mechanisms varied between traits: increased metabolism was caused by intraspecific trait change, while increased grazing rate was mainly driven by species turnover. Our results suggest that both population- and community-level processes mediate the responses of natural communities to long-term environmental change, and that the ongoing warming of coastal waters is likely to alter the functioning of key marine ecosystems.     

Contemporary genetic structure and postglacial demographic history of the black scorpionfish,Scorpaena porcus,in the Mediterranean and the Black Seas

Understanding the distribution of genetic diversity in the light of past demographic events linked with climatic shifts will help to forecast evolutionary trajectories of ecosystems within the current context of climate change. In this study, mitochondrial sequences and microsatellite loci were analysed using traditional population genetic approaches together with Bayesian dating and the more recent approximate Bayesian computation scenario testing. The genetic structure and demographic history of a commercial fish, the black scorpionfish, Scorpaena porcus, was investigated throughout the Mediterranean and Black Seas. The results suggest that the species recently underwent population expansions, in both seas, likely concomitant with the warming period following the Last Glacial Maximum, 20 000 years ago. A weak contemporaneous genetic differentiation was identified between the Black Sea and the Mediterranean Sea. However, the genetic diversity was similar for populations of the two seas, suggesting a high number of colonizers entered the Black Sea during the interglacial period and/or the presence of a refugial population in the Black Sea during the glacial period. Finally, within seas, an east/west genetic differentiation in the Adriatic seems to prevail, whereas the Black Sea does not show any structured spatial genetic pattern of its population. Overall, these results suggest that the Black Sea is not that isolated from the Mediterranean, and both seas revealed similar evolutionary patterns related to climate change and changes in sea level.     

Biocomplexity in Populations of European Anchovy in the Adriatic Sea

The sustained exploitation of marine populations requires an understanding of a species'' adaptive seascape so that populations can track environmental changes from short- and long-term climate cycles and from human development. The analysis of the distributions of genetic markers among populations, together with correlates of life-history and environmental variability, can provide insights into the extent of adaptive variation. Here, we examined genetic variability among populations of mature European anchovies (n = 531) in the Adriatic (13 samples) and Tyrrhenian seas (2 samples) with neutral and putative non-neutral microsatellite loci. These genetic markers failed to confirm the occurrence of two anchovy species in the Adriatic Sea, as previously postulated. However, we found fine-scale population structure in the Adriatic, especially in northern areas, that was associated with four of the 13 environmental variables tested. Geographic gradients in sea temperature, salinity and dissolved oxygen appear to drive adaptive differences in spawning time and early larval development among populations. Resolving adaptive seascapes in Adriatic anchovies provides a means to understand mechanisms underpinning local adaptation and a basis for optimizing exploitation strategies for sustainable harvests.     

Antarctic nematode communities: observed and predicted responses to climate change

The rapidly changing climate in Antarctica is impacting the ecosystems. Since records began, climate changes have varied considerably throughout Antarctica with both positive and negative trends in temperatures and precipitation observed locally. However, over the course of this century a more directional increase in both temperature and precipitation is expected to occur throughout Antarctica. The soil communities of Antarctica are considered simple with most organisms existing at the edge of their physiological capabilities. Therefore, Antarctic soil communities are expected to be particularly sensitive to climate changes. However, a review of the current literature reveals that studies investigating the impact of climate change on soil communities, and in particular nematode communities, in Antarctica are very limited. Of the few studies focusing on Antarctic nematode communities, long-term monitoring has shown that nematode communities respond to changes in local climate trends as well as extreme (or pulse) events. These results are supported by in situ experiments, which show that nematode communities respond to both temperature and soil moisture manipulations. We conclude that the predicted climate changes are likely to exert a strong influence on nematode communities throughout Antarctica and will generally lead to increasing abundance, species richness, and food web complexity, although the opposite may occur locally. The degree to which local communities respond will depend on current conditions, i.e., average temperatures, soil moisture availability, vegetation or more importantly the lack thereof, and the local species pool in combination with the potential for new species to colonize.     

Marine biological shifts and climate

Phenological, biogeographic and community shifts are among the reported responses of marine ecosystems and their species to climate change. However, despite both the profound consequences for ecosystem functioning and services, our understanding of the root causes underlying these biological changes remains rudimentary. Here, we show that a significant proportion of the responses of species and communities to climate change are deterministic at some emergent spatio-temporal scales, enabling testable predictions and more accurate projections of future changes. We propose a theory based on the concept of the ecological niche to connect phenological, biogeographic and long-term community shifts. The theory explains approximately 70% of the phenological and biogeographic shifts of a key zooplankton Calanus finmarchicus in the North Atlantic and approximately 56% of the long-term shifts in copepods observed in the North Sea during the period 1958–2009.     

Diversity and occurrence of herbaceous communities in West African savannas in relation to climate,land use and habitat

In the face of the current changes in land use and climate as well as habitat destruction, it is important to study herbaceous vegetation as an indicator of changes occurring in savanna ecosystems. We investigated the effects of climate, land use and habitat, both alone and in combination, on the diversity and occurrence of West African savanna herbaceous plant communities. Floristic data and environmental variables were sampled in Burkina Faso and subjected to ordination and indicator species analysis to explore the variation in nine vegetation types. Regression analyses showed that climate, land use, humidity gradient, soil fraction and vegetation structure discriminate herbaceous plant communities. Climate, habitat and their interaction had the greatest effect on the occurrence of these communities. Changes in species richness of the studied communities were mainly due to climate, land use and their interaction, which were more important for increasing rather than decreasing diversity. In all cases, climate conditions remained the most important environmental factor driving vegetation variation in West African savannas. Beside this, the effects of habitat degradation in interaction with land use and climatic conditions indicate land use to be a threat for the diversity of the herbaceous vegetation.     

Impact of climate change on alpine vegetation of mountain summits in Norway

Climate change is affecting the composition and functioning of ecosystems across the globe. Mountain ecosystems are particularly sensitive to climate warming since their biota is generally limited by low temperatures. Cryptogams such as lichens and bryophytes are important for the biodiversity and functioning of these ecosystems, but have not often been incorporated in vegetation resurvey studies. Hence, we lack a good understanding of how vascular plants, lichens and bryophytes respond interactively to climate warming in alpine communities. Here we quantified long-term changes in species richness, cover, composition and thermophilization (i.e. the increasing dominance of warm-adapted species) of vascular plants, lichens and bryophytes on four summits at Dovrefjell, Norway. These summits are situated along an elevational gradient from the low alpine to high alpine zone and were surveyed for all species in 2001, 2008 and 2015. During the 15-year period, a decline in lichen richness and increase in bryophyte richness was detected, whereas no change in vascular plant richness was found. Dwarf-shrub abundance progressively increased at the expense of lichens, and thermophilization was most pronounced for vascular plants, but occurred only on the lowest summits and northern aspects. Lichens showed less thermophilization and, for the bryophytes, no significant thermophilization was found. Although recent climate change may have primarily caused the observed changes in vegetation, combined effects with non-climatic factors (e.g. grazing and trampling) are likely important as well. At a larger scale, alpine vegetation shifts could have a profound impact on biosphere functioning with feedbacks to the global climate.     

Plant Performance in a Warmer World: General Responses of Plants from Cold, Northern Biomes and the Importance of Winter and Spring Events

During the past three decades the Earth has warmed with a rate unprecedented during the past 1000 years. There is already ample evidence that this fast climate warming has affected a broad range of organisms, including plants. Plants from high-latitude and high-altitude sites (‘cold biomes’) are especially sensitive to climate warming. In this paper we (1) review the response in the phenology of plants, changes in their range and distribution, soil nutrient availability, and the effects on the structure and dynamics of plant communities for cold, northern biomes; and (2) we show, by using data from an ongoing snow and temperature manipulation experiment in northern Sweden, that also winter and spring events have a profound influence on plant performance. Both long-term phenological data sets, experimental warming studies (performed in summer or year-round), natural gradient studies and satellite images show that key phenological events are responsive to temperature increases and that recent climate warming does indeed lead to changes in plant phenology. However, data from a warming and snow manipulation study that we are conducting in northern Sweden show that plants respond differently to the various climatic scenarios that we had imposed on these species and that especially winter and spring events have a profound impact. This indicates that it is necessary to include several scenarios of both summer and winter climate change in experimental climate change studies, and that we need detailed projections of future climate at a regional scale to be able to assess their impacts on natural ecosystems. There is also ample evidence that the range shift of herbs and shrubs to more northern regions is for the vast majority of species mainly caused by changes in the climate. This is in line with the observed ‘up-greening’ of northern tundra sites. These rapid northern shifts in distribution of plants as a result of climate warming may have substantial consequences for the structure and dynamics of high-latitude ecosystems. An analysis of warming studies at 9 tundra sites shows that heating during at least 3 years increased net N-mineralization from 0.32±0.31 (SE) g N m⁻² yr⁻¹ in the controls to 0.53±0.31 (SE) g N m⁻² yr⁻¹ in the heated plots (p<0.05), an increase of about 70%. Thus, warming leads to higher N availability in high-latitude northern tundra sites, but the variability is substantial. Higher nutrient availability affects in turn the species composition of high-latitude sites, which has important consequences for the carbon and water balance of these systems.