Dwarf Shrub Tundra Research Articles

Высокогорная растительность нагорья Сангилен: кобрезиевники, кустарничковые и кустарниковые тундры

Высокогорная растительность нагорья Сангилен: кобрезиевники, кустарничковые и кустарниковые тундры

Phosphorus Availability Determines the Response of Tundra Ecosystem Carbon Stocks to Nitrogen Enrichment

Northern permafrost soils contain important carbon stocks. Here we report the long-term response of carbon stocks in high Arctic dwarf shrub tundra to short-term, low-level nutrient enrichment. Twenty years after experimental nitrogen addition, carbon stocks in vegetation and organic soil had almost halved. In contrast, where phosphorus was added with nitrogen, carbon storage increased by more than 50%. These responses were explained by changes in the depths of the moss and organic soil layers. Nitrogen apparently stimulated decomposition, reducing carbon stocks, whilst phosphorus and nitrogen co-stimulated moss productivity, increasing organic matter accumulation. The altered structure of moss and soil layers changed soil thermal regimes, which may further influence decomposition of soil carbon. If climate warming increases phosphorus availability, any increases in nitrogen enrichment from soil warming or expanding human activity in the Arctic may result in increased carbon sequestration. Where phosphorus is limiting in tundra areas, however, nitrogen enrichment may result in carbon loss.

Warming, shading and a moth outbreak reduce tundra carbon sink strength dramatically by changing plant cover and soil microbial activity

Future increases in temperature and cloud cover will alter plant growth and decomposition of the large carbon pools stored in Arctic soils. A better understanding of interactions between above- and belowground processes and communities of plants and microorganisms is essential for predicting Arctic ecosystem responses to climate change. We measured ecosystem CO2 fluxes during the growing season for seven years in a dwarf-shrub tundra in West Greenland manipulated with warming and shading and experiencing a natural larvae outbreak. Vegetation composition, soil fungal community composition, microbial activity, and nutrient availability were analyzed after six years of treatment. Warming and shading altered the plant community, reduced plant CO2 uptake, and changed fungal community composition. Ecosystem carbon accumulation decreased during the growing season by 61% in shaded plots and 51% in warmed plots. Also, plant recovery was reduced in both manipulations following the larvae outbreak during the fifth treatment year. The reduced plant recovery in manipulated plots following the larvae outbreak suggests that climate change may increase tundra ecosystem sensitivity to disturbances. Also, plant community changes mediated via reduced light and reduced water availability due to increased temperature can strongly lower the carbon sink strength of tundra ecosystems.

Drivers of tall shrub proliferation adjacent to the Dempster Highway, Northwest Territories, Canada

Arctic ecosystems are undergoing rapid changes as a result of climate warming and more frequent disturbances. Disturbances can have particularly large effects on high-latitude ecosystems when ecosystem structure and function is controlled by strong feedbacks between soil conditions, vegetation, and ground thermal regime. In this study we investigated the impact of road construction and maintenance on vegetation structure and biomass along the Dempster Highway where it crosses the Peel Plateau in the Northwest Territories. To explore drivers of tall shrub proliferation and to quantify shrub proliferation in this region of continuous permafrost, greyscale air photos (1975) and Quickbird satellite imagery (2008) were used to map landcover change within two 0.6 km2 belts next to the road and two 0.6 km2 belts 500 m away from the road. Maps showing areas where: 1) tall shrubs expanded, and 2) dwarf shrub tundra resisted invasion were then used to select field sites where a suite of biophysical variables were measured. Rapid tall shrub proliferation and greater biomass adjacent to the road indicate that disturbance can facilitate vegetation change in tundra environments. Our field data also suggests that increased shrub proliferation adjacent to the road was caused by greater soil moisture. Tall shrub proliferation adjacent to the road occurred at lower elevation sites characterized by wetter soils with thicker organic layers. Areas that resisted tall shrub encroachment were located at higher elevations and had drier soils with thin organic layers. Our observations also support previous work illustrating that tall shrub expansion next to the highway promotes strong positive feedbacks to ongoing shrub growth and proliferation.

A portfolio effect of shrub canopy height on species richness in both stressful and competitive environments

Summary Facilitating effects of benefactor plants on plant species richness have been commonly tested in stressful habitats because competitive effects are assumed to predominate in more productive habitats. Here, we examine this assumption by testing whether benefactor plants can nonetheless be facilitating in competitive environments. We provide a conceptual framework describing how a trait of benefactor plants, canopy height of shrubs, can have a portfolio of facilitative effects on species richness in more competitive environments, and we provide an empirical assessment of this portfolio effect in tundra plant communities. Across tundra plant communities representing an extensive gradient in aboveground live biomass ranging from 11 to above 800 grams per m2, we found that species richness exhibited a humped‐back relationship. Increasing canopy height of shrubs to a maximum height of what defines the dwarf shrub tundra, that is 40 cm, consistently and significantly increased species richness along the entire biomass gradient tested. The positive effect of shrub canopy height was not confounded with herbivore intensity, competitive interference or abiotic factors such as bedrock‐weathered mineral availability, moisture availability or temperature. However, we cannot rule out that the general presence of large mammalian herbivory may have been central to the positive effect of shrub canopy height in reducing herbivore impacts on species richness. In this study, conceptual and empirical evidence support that increasing canopy height of shrubs facilitates species richness regardless of relative abiotic stress levels within tundra ecosystems. We propose that positive interactions can play an important ecological role in systems where competitive effects are observed or assumed. For tundra plant communities where climate change is currently causing encroachment of shrub species, the effects of increasing canopy height may have unprecedented effects on plant species richness.

NDVI as a predictor of canopy arthropod biomass in the Alaskan arctic tundra.

The physical and biological responses to rapid arctic warming are proving acute, and as such, there is a need to monitor, understand, and predict ecological responses over large spatial and temporal scales. The use of the normalized difference vegetation index (NDVI) acquired from airborne and satellite sensors addresses this need, as it is widely used as a tool for detecting and quantifying spatial and temporal dynamics of tundra vegetation cover, productivity, and phenology. Such extensive use of the NDVI to quantify vegetation characteristics suggests that it may be similarly applied to characterizing primary and secondary consumer communities. Here, we develop empirical models to predict canopy arthropod biomass with canopy-level measurements of the NDVI both across and within distinct tundra vegetation communities over four growing seasons in the Arctic Foothills region of the Brooks Range, Alaska, USA. When canopy arthropod biomass is predicted with the NDVI across all four growing seasons, our overall model that includes all four vegetation communities explains 63% of the variance in canopy arthropod biomass, whereas our models specific to each of the four vegetation communities explain 74% (moist tussock tundra), 82% (erect shrub tundra), 84% (riparian shrub tundra), and 87% (dwarf shrub tundra) of the observed variation in canopy arthropod biomass. Our field-based study suggests that measurements of the NDVI made from air- and spaceborne sensors may be able to quantify spatial and temporal variation in canopy arthropod biomass at landscape to regional scales.

‘Warm’ Tundra: Atmospheric and Near‐Surface Ground Temperature Inversions Across an Alpine Treeline in Continuous Permafrost, Western Arctic, Canada

AbstractPermafrost conditions were examined between 2010 and 2014 at four sites across an alpine treeline on Peel Plateau, Northwest Territories, Canada. Ground and air temperature sensors were installed in forest and tundra between 30 and 500 m asl. Annual mean air temperatures increased and the number of freezing degree days declined with elevation, due to persistent winter air temperature inversions. The annual mean temperature at the permafrost surface (Tps) in mineral soils increased with elevation from about −2.5 °C in lowland forest to about −1.5 °C in dwarf shrub tundra. The increase in Tps coincided with higher air temperatures and earlier snow accumulation at tundra sites. The higher Tps in alpine tundra compared to lowland forest in Peel Plain contrasts with the northward decrease in Tps across latitudinal treeline elsewhere in the western Arctic. An increase in Tps with elevation may be common in Arctic mountain environments due to the prevalence of atmospheric temperature inversions in winter. In such contexts, although vegetation characteristics are governed by summer climate, permafrost conditions are critically influenced by the winter regime. The tundra permafrost on Peel Plateau is considerably warmer and, hence, more sensitive to disturbance than perennially frozen ground north of treeline in other parts of the western Arctic. Copyright © 2015 John Wiley & Sons, Ltd.

Ecological recovery in an Arctic delta following widespread saline incursion.

Arctic ecosystems are vulnerable to the combined effects of climate change and a range of other anthropogenic perturbations. Predicting the cumulative impact of these stressors requires an improved understanding of the factors affecting ecological resilience. In September of 1999, a severe storm surge in the Mackenzie Delta flooded alluvial surfaces up to 30 km inland from the coast with saline waters, driving environmental impacts unprecedented in the last millennium. In this study we combined field monitoring of permanent sampling plots with an analysis of the Landsat archive (1986-2011) to explore the factors affecting the recovery of ecosystems to this disturbance. Soil salinization following the 1999 storm caused the abrupt dieback of more than 30,000 ha of tundra vegetation. Vegetation cover and soil chemistry show that recovery is occurring, but the rate and spatial extent are strongly dependent on vegetation type, with graminoid- and upright shrub-dominated areas showing recovery after a decade, but dwarf shrub tundra exhibiting little to no recovery over this period. Our analyses suggest that recovery from salinization has been strongly influenced by vegetation type and the frequency of freshwater flooding following the storm. With increased ocean storm activity, rising sea levels, and reduced sea ice cover, Arctic coastal ecosystems will be more likely to experience similar disturbances in the future, highlighting the importance of combining field sampling with regional-scale remote sensing in efforts to detect, understand, and anticipate environmental change.

Cumulative Impacts and Feedbacks of a Gravel Road on Shrub Tundra Ecosystems in the Peel Plateau, Northwest Territories, Canada

Gravel highways in the continuous permafrost zone provide critical transportation links that are increasingly vulnerable to the impacts of climate warming and permafrost thaw. To examine if the physical effects associated with the construction, maintenance, and use of gravel roads alter vegetation and permafrost conditions, we measured vegetation, soils, and near-surface ground temperatures at tall and dwarf shrub tundra sites adjacent to and distant from the Dempster Highway in the Northwest Territories of Canada. We found that alder growth and recruitment were significantly enhanced adjacent to the highway. Where alder shrubs had formed closed canopies, we observed dramatic alterations to plant community composition, soil properties, and ground temperatures. Tall shrub sites adjacent to the road exhibited less understory vegetation, greater litter and organic layer thickness, higher nutrient availability, and thicker snowpack than all other site types. Our results show that in shrub tundra ecosystems the conditions generated by the maintenance and use of a gravel road can drive ecological feedbacks that magnify changes to vegetation communities and soils. We found that where the road facilitated shrub dominance, feedbacks were initiated that enhanced snow accumulation and altered ground temperatures and soil chemistry. In turn, these changes likely promoted enhanced shrub recruitment and growth. Shrub proliferation adjacent to highways is an important consideration for the planning and maintenance of this form of infrastructure. To improve our understanding of the spatial heterogeneity of shrub proliferation, research exploring the relationships between biophysical landscape features and shrub development is also needed.

Small rodents in the shrub tundra of Yamal (Russia): Density dependence in habitat use?

Northern small rodents are well known for their population cycles which represent a key process for the functioning of arctic and boreal ecosystems. Habitat use often changes in the course of the cycle. Higher densities can either lead to spill-over into secondary habitats or to increased habitat specificity because of interspecific competition. Here we investigate whether voles in the shrub tundra of southern Yamal exhibit density dependent habitat use. Voles were trapped at the Erkuta Tundra Monitoring Site (N 68.2°, E 69.2°) in three characteristic habitats over five years covering all phases of the population cycle. Our analyses focused on the two most numerous species Microtus gregalis (52% of individuals caught) and M. middendorffii (36%). A small-scale spill-over effect was observed for M. gregalis, which increasingly used the open habitat adjacent to their preferred willow thickets at high abundance. At a larger scale no such effect was observed for the two Microtus species – a result which is explained by the overall moderate densities of voles and the large spatial extent of the primary habitat of M. middendorffii: moist moss dwarf shrub tundra.

Tree taxa immigration to the eastern Baltic region, southeastern sector of Scandinavian glaciation during the Late-glacial period (14,500–11,700 cal. b.p.)

The eastern Baltic region is situated in the southeastern part of the area which was covered by the last Scandinavian glaciation. Four well-dated sediment profiles from sites distributed along a ~330-km north–south transect were analysed for their macrofossil contents. The immigration of tree taxa during the Late-glacial (LG) period, which was the time of environmental change from tundra to woodland in previously glaciated areas, can be determined from these data. The pioneer vegetation in the study area was treeless dwarf shrub tundra with various dominant taxa. The so-called Allerod hemispheric warming permitted the Post-glacial immigration of trees into the southern part of the eastern Baltic region; however, these most probably disappeared during the following cold period, the Younger Dryas/GS-1. The local presence of Betula sect. Albae, Pinus sylvestris, Populus tremula and Picea abies during the LG period in the southern part of the region was confirmed. The northern part of the area presumably remained treeless for the entire LG period. Therefore, until the beginning of the Holocene, the tree line in the eastern Baltic region did not reach beyond 58°N.

К синтаксономии мелкобугристых болотных комплексов в лесотундре и тундре на севере Кольского полуострова

Mires of the Kola Peninsula were investigated mainly in its southern part (Botch, 1989; Payanskaya-Gvozdeva, 1990; Smagin, 1999а, 1999b). The published relevés of tundra mires of the Peninsula are poor (Kalliola, 1939; Koroleva, 2001, 2006), and this paper surveys pounikkos mire complexes in its northern part, represents their classification according to the Braun-Blanquet approach accompanied by syntaxonomical tables. The investigated area is situated in the north of the Kola Peninsula within the forest tundra and in southern arctic tundra, with the mean annual air temperature between –0.5 °C and –2.0 °C and annual precipitation 600–700 mm. The geological basis is Archean and Proterozoic crystalline rocks, covered by coarse gravelly moraine and sandy fluvial-glacial deposits, and peat deposits in wetlands. Plant cover represents the combination of subarctic birch forests, tundra and mires. The mire complexes occur in river valleys, in lake and between moraine hill depressions, alternating with shrub and dwarf-shrub lichen tundra and forest-tundra on hill tops and slopes. Peat hummock (pounikkos) height is 0.3–0.5 (up to 1.0) м, their diameter is 0.3–0.7 (up to 1.5) м. In July the ice core is kept at 20–30 cm below the surface. Water-logged narrow ditches separate hummocks from each other. Inundated sedges- and water-cotton-dominated lawns, willow thickets along the water currents and small lakes are common within the mire complex. In the 2012 field season mounds and hummocks were densely inhabited by rodents, in particular by Lemmus lemmus. Oligotrophic and ombrogenous mosses lichens dwarf-shrub dominated communities of mounds, small turf hummocks (pounus, pounikkos) and on the margin of mire massifs belong to the alliance Oxycocco−Empetrion hermaphroditi Nordh. 1936 ex Neuhäusl 1969 (diagnostic taxa (DT): Eriophorum vaginatum, Oxycoccus microcarpus, Rubus chamaemorus, Mylia anomala, Sphagnum fuscum) with the ass. Empetro−Sphagnetum fusci subass. typicum Dierssen (1982) 1996 (DT Ledum palustre and Orthocaulis kunzeanus) and Empetro−Sphagnetum fusci subass. dicranetosum elongati (Regel 1923) stat. nov. (DT Dicranum elongatum). Species poor sedges- and cottongrass dominated oligo-, oligomesotrophic fens of flark and lawns belong to the alliance Caricion rotundatae (Kalliola 1939) stat. nov. (DT Carex concolor, C. rariflora, C. rotundata, Baeothryon cespitosum, Eriophorum polystachion, Sphagnum lindbergii, S. compactum, Warnstorfia exannulata, Sarmentypnum sarmentosum, Calliergon stramineum) with three associations: ass. Gymnocoleo inflatae−Caricetum rariflorae ass. nov. (DT Nardus stricta, Sphagnum compactum, Gymnocolea inflata, Anthelia juratzkana), ass. Warnstorfio sarmentosi−Caricetum concoloris ass. nov. (DT the same as for the alliance), ass. Eriophoro polystachii−Sphagnetum lindbergii (Kalliola 1939) stat. nov. (DT Sphagnum lindbergii). Low willows and sedges dominated communities along mire springs or in percolated areas are described as ass. Salici lapponi−Caricetum concoloris ass. nov. (DT Betula nana, Salix lapponum, S. phylicifolia, Calamagrostis strictа, Carex rostrata, Comarum palustre, Molinia caerulea, Viola palustris, Lophozia longiflora) with no affiliation to any alliance. Proposed new alliance Caricion rotundatae occurs in tundra and forest-tundra zone to the north of main areal of alliances Rhynchosporion albae Koch 1926 and Caricion lasiocarpae Vanden Berghen ap. Lebrun et al. 1949, which comprise oligotrophic and mesotrophic flark communities of boreal mires. Among diagnostic taxa of Caricion rotundatae are low sedges and brown mosses and in opposite to the alliance Rhynchosporion albae it doesn’t include the character species of Rhynchosporion albae (Carex livida, Scheuchzeria palustris, Rhynchospora alba). The studied mire complexes are very characteristic for the entire subarctic Fennoscandia, being located in the north of the Kola Peninsula close to the east-northern border of their European distribution area. They are considered to include more fast-growing permafrost hummocks comparing with palsa mires (Grab, 2003). Based upon their high alpha diversity and important ecological and scientific role, the discussed pounus mire massifs are perspective to be examined as possible value natural habitats.

Greenhouse gas soil production and surface fluxes at a high arctic polar oasis

Arctic vegetation and soil biological communities interact with a range of biotic and abiotic factors to produce or consume the greenhouse gases (GHG) carbon dioxide, methane, and nitrous oxide. In Arctic environments the parameters controlling these processes are not well understood. We measured soil GHG concentrations and surface fluxes from six vegetation communities at a High Arctic polar oasis and adjacent polar deserts in order to identify regions within the soil profile of production and consumption of CO2, CH4, and N2O. Examined communities included two polar deserts differing in parent material and soil pH, and four lowland tundra communities: prostrate dwarf-shrub, herb tundra, prostrate/hemiprostrate dwarf-shrub tundra, nontussock sedge, dwarf-shrub, moss tundra and a sedge/grass, moss wetland, representative of large areas at lower Arctic latitudes. Polar desert soils were net producers of greenhouse gases during the brief High Arctic growing season, including at depths close to the permafrost layer, and effluxes from the surface were of a similar magnitude to nearby mesic and hydric tundra soils including for CO2, indicative of soil respiration in desert soils with few roots. Differences in water content, rather than calculated diffusivity, appear to drive gas transport in at least some soils, with all three GHG appearing to move rapidly through, for example, the soil at 10 cm above permafrost in the Prostrate (dominated by Dryas integrifolia) plant community. Such physical processes may obscure or falsely suggest biological processes in soil ecosystems.

Simulating Biome Distribution on the Tibetan Plateau Using a Modified Global Vegetation Model

We used a regionally modified global vegetation model (BIOME4-Tibet) to simulate biome distribution on the Tibetan Plateau under current climate conditions derived from regional meteorological observations. The bioclimatic limits (mean temperatures of the coldest and warmest months, minimum temperature, growing degree-days on 5 °C and 0 °C bases) for some key alpine plant functional types (temperate deciduous and conifer trees, boreal deciduous and conifer trees, desert woody plants, tundra shrubs, cold herbaceous plants, and lichens/forbs) were redefined based on regional vegetation-climate relationships. Modern vegetation maps confirmed that the BIOME4-Tibet model does a better job of simulating biome patterns on the plateau (gridcell agreement 52%) than the original BIOME4 model (35%). This improved model enhanced our ability to simulate temperate conifer forest, cool conifer and mixed forest, evergreen taiga, temperate xerophytic shrubland, temperate grassland and desert, and steppe and shrub tundra biomes, but made a negligible or reduced difference to the prediction of temperate deciduous forest, warm-temperate mixed forest, and three tundra biomes (erect dwarf-shrub tundra, prostrate dwarf-shrub tundra, and cushion forb, lichen, and moss tundra). Future modification of the vegetation model, by increasing the number of shrub and herb plant functional types, re-parameterization of more precise bioclimatic constraints, and improved representation of soil, permafrost, and snow processes, will be needed to better characterize the distribution of alpine vegetation on the Tibetan Plateau.

The Lateglacial and early Holocene vegetation and environment in the Dovre mountains, central Norway, as signalled in two Lateglacial nunatak lakes

By using heavy coring equipment in two high-altitudinal lakes (1253 and 1316 m a.s.l.) at Dovre, Central Norway, 1–1.5 m of unsorted coarsely minerogenic sediments were retrieved below the Holocene organic sediments. The minerogenic sequence contained well-preserved pollen and chironomid remains, revealing new and detailed palaeoenvironmental knowledge of the mountains in Central Norway during the last 5–6000 years of the Lateglacial (LG) period. However, the LG chronology is based on biostratigraphical correlations and not on 14C-dates, due to low organic content in the minerogenic sediments. The emerging LG nunataks, probably indicating a thin and multi-domed Scandinavian ice-sheet, was rapidly inhabited by immigrating species which could explain the present centric distributions of certain arctic-alpine plants. The LG vegetation development included a pre-interstadial dominated by mineral-soil pioneers, an interstadial dominated by shrubs and dwarf-shrubs, and the Younger Dryas cold period with recurring dominance of pioneers. Pollen and stomata of Pinus and Picea indicate their local LG presence at Dovre. LG climate oscillations are indicated by pollen stratigraphy and for the later part of LG also by chironomids. These oscillations could correspond to Heinrich event 1, GI-1d, GI-1b, and the Younger Dryas cold events. The LG interstadial reached July mean temperatures of more than 7–8 °C, similar to the present. Chironomids colonized the lake already during the onset of the interstadial, albeit at very low richness and abundances. Starting from YD, there are sufficient chironomid head capsules to perform a temperature reconstruction. The Holocene warming of about 2 °C initiated a vegetation closure from snow beds and dwarf-shrub tundra to shrubs and forests. Birch-forests established about 10 ka cal BP, slightly earlier than pine forests. Alnus expanded ca 9.2 ka cal BP and a thinning of the local forests occurred from ca 7 ka cal BP. Two short-lasting climate deteriorations found in the pollen record and the chironomid record may represent the Preboreal Oscillation and the 8.2 event. The Holocene Thermal Maximum is indicated around ca 7.8–7.3 ka cal BP showing a chironomid-inferred July mean of at least 11 °C. This is ca 3 °C warmer than today.

Holocene and Last Interglacial cloudiness in eastern Baffin Island, Arctic CanadaThis article is one of a series of papers published in this Special Issue on the themePolar Climate Stability Network.GEOTOP Publication 2008-0027.

This study presents Last Interglacial and Holocene vegetation and climate changes at Fog Lake (67°11′N, 63°15′W) on eastern Baffin Island, Arctic Canada. The vegetation cover is reported as vegetation structural types (or biomes). July air temperature and sunshine during the growing season (June–July–August–September) were reconstructed from pollen assemblages using the modern analogue technique. The vegetation of the Last Interglacial period evolved from a prostrate dwarf-shrub tundra to a low- and high-shrub tundra vegetation. The succession of four Arctic biomes was distinguished from the Last Interglacial sediments, whereas only one Arctic biome was recorded in the Holocene sediments. From ca. 8300 cal. years BP to present, hemiprostrate dwarf-shrub tundra occupied the soils around Fog Lake. During the Last Interglacial, growing season sunshine was higher than during the Holocene and July air temperature was 4 to 5 °C warmer than present. A principal component analysis helped in assessing relationship between floristic gradients and climate. The major vegetation changes through the Last Interglacial and Holocene were driven by July air temperature variations, whereas the minor, or subtle, vegetation changes seem rather correlated to September sunshine. This study demonstrates that growing season sunshine conditions can be reconstructed from Arctic pollen assemblages, thus providing information on feedbacks associated with cloud cover and summer temperatures, and therefore growing season length.

Initial effects of experimental warming on carbon exchange rates, plant growth and microbial dynamics of a lichen-rich dwarf shrub tundra in Siberia

The aim of this study was to assess initial effects of warming on the CO2 balance of a lichen-rich dwarf shrub tundra, a widespread but little studied ecosystem type in the Arctic. We analyzed whole ecosystem carbon exchange rates as well as nutrient dynamics, microbial and plant community composition and biomass after 2 years of experimental temperature increase. Plant biomass increased significantly with warming, mainly due to the strong response of lichens, the dominant plant group within this ecosystem. Experimental warming also increased soil nitrogen pools and nitrogen turnover rates. Major changes in soil microbial and plant composition, however, were not detected. Although experimental warming increased gross ecosystem productivity, the higher plant biomass did not compensate for the much greater increase in C losses. Ecosystem respiration and net ecosystem CO2 losses were significantly higher in warmed plots compared to control ones. We suggest that this was due to increased soil respiration, since soil carbon pools were lower in warmed soils, at least in the upper horizons. Our study thus supports the general hypothesis that tundra ecosystems turn from a carbon sink to a carbon source when temperatures increase in the short-term. Since lichens, which produce low quality litter, increased their biomass significantly with warming in this specific ecosystem type, CO2 losses may slow down in the long-term.

Climatic and environmental changes in north-western Russia between 15,000 and 8000 cal yr BP: a review

Multi-proxy palaeoenvironmental studies of nine sediment sequences from four areas in north-western Russia reveal significant changes in climate, lake productivity and vegetation during the Lateglacial and early Holocene that show some degree of correlation with changes reconstructed from sites throughout the North Atlantic region. At Lake Nero in the Rostov-Jaroslavl’ area, which is outside the maximum limit of the Scandinavian Ice Sheet, sedimentation recommenced shortly after 15 cal ka BP in response to increases in temperature and humidity during Greenland Interstadial 1 (GI-1; Bølling-Allerød). However, climatic amelioration during GI-1 was slow to increase lake organic productivity or trigger large-scale changes in much of northwestern Russia. In general, this region was characterised by long-lasting lake-ice cover, low lake productivity, soil erosion, and dwarf shrub and herb tundra until the end of Greenland Stadial 1 (GS-1; Younger Dryas). At some sites, distinct increases in lake organic productivity, mean summer temperatures and humidity and the expansion of forest trees coincide with rapid warming at the beginning of the Holocene and the increasing influence of warm air masses from the North Atlantic. At other sites, particularly on the Karelian Isthmus, but also in Russian Karelia, the delayed response of limnic and terrestrial environments to early Holocene warming is likely related to the cold surface waters of the Baltic Ice Lake, the proximity of the Scandinavian Ice Sheet and associated strengthened easterlies, and/or extensive permafrost and stagnant ice. These multi-proxy studies underscore the importance of local conditions in modifying the response of individual lakes and their catchments. While Lateglacial vegetation was dominated by Betula nana and Salix shrubs and various herbs, pollen and plant macrofossils suggest that Betula pubescens trees became established as early as 14–13 cal ka BP in the Rostov-Jaroslavl’ area. In general, our data sets suggest that trees migrated from the southeast to the west and then spread later to the northeast and northwest, paralleling the direction of ice retreat, with Betula pubescens immigrating first, followed by Pinus sylvestris and Picea abies. However, palaeoecological records from Lake Terebenskoye in the Valdai Highlands suggest that the arrival of Picea abies preceded other trees in that area and that it colonised tundra communities as early as 12 cal ka BP. Since Lateglacial vegetation change in north-western Russia was time-transgressive, independent measures of palaeoclimate (e.g., chironomid-based palaeotemperature estimates) are needed for this region.

Arctic climate change with a 2 ∘C global warming: Timing, climate patterns and vegetation change

The signatories to United Nations Framework Convention on Climate Change are charged with stabilizing the concentrations of greenhouse gases in the atmosphere at a level that prevents dangerous interference with the climate system. A number of nations, organizations and scientists have suggested that global mean temperature should not rise over 2 ∘C above preindustrial levels. However, even a relatively moderate target of 2 ∘C has serious implications for the Arctic, where temperatures are predicted to increase at least 1.5 to 2 times as fast as global temperatures. High latitude vegetation plays a significant role in the lives of humans and animals, and in the global energy balance and carbon budget. These ecosystems are expected to be among the most strongly impacted by climate change over the next century. To investigate the potential impact of stabilization of global temperature at 2 ∘C, we performed a study using data from six Global Climate Models (GCMs) forced by four greenhouse gas emissions scenarios, the BIOME4 biogeochemistry-biogeography model, and remote sensing data. GCM data were used to predict the timing and patterns of Arctic climate change under a global mean warming of 2 ∘C. A unified circumpolar classification recognizing five types of tundra and six forest biomes was used to develop a map of observed Arctic vegetation. BIOME4 was used to simulate the vegetation distributions over the Arctic at the present and for a range of 2 ∘C global warming scenarios. The GCMs simulations indicate that the earth will have warmed by 2 ∘C relative to preindustrial temperatures by between 2026 and 2060, by which stage the area-mean annual temperature over the Arctic (60–90∘N) will have increased by between 3.2 and 6.6 ∘C. Forest extent is predicted by BIOME4 to increase in the Arctic on the order of 3 × 106 km2 or 55% with a corresponding 42% reduction in tundra area. Tundra types generally also shift north with the largest reductions in the prostrate dwarf-shrub tundra, where nearly 60% of habitat is lost. Modeled shifts in the potential northern limit of trees reach up to 400 km from the present tree line, which may be limited by dispersion rates. Simulated physiological effects of the CO2 increase (to ca. 475 ppm) at high latitudes were small compared with the effects of the change in climate. The increase in forest area of the Arctic could sequester 600 Pg of additional carbon, though this effect is unlikely to be realized over next century.

Lateglacial nunataks in central Scandinavia: Biostratigraphical evidence for ice thickness from Lake Flåfattjønn, Tynset, Norway

This study reveals for the first time biostratigraphical evidence of nunataks emerging from the Late Weichselian ice-sheet in central Scandinavia. Almost 1 m of minerogenic basal layers from Lake Flåfattjønn, 1110 m a.s.l., at Tynset, Norway, was deposited in the Lateglacial, possibly as early as 16,000 cal. yr BP. The sediments contain well-preserved remains of plants, diatoms and chironomids and indicate: (1) a mosaic pioneer vegetation of dwarf-shrub tundra, snow bed vegetation and xerophytes on wind-blown ridges, (2) an ice-free lake during summers with clear water at low pH due to little inwash, (3) a continental climate with summers slightly warmer than today (ca 10 °C), and most probably with very cold winters, according to indications of permafrost, and (4) a hiatus/reduced sedimentation during at least the first half of the Younger Dryas when the lake was sealed by a more-or-less permanent ice-cover. The existence of Lateglacial nunataks indicates a thin and multi-domed Lateglacial ice-sheet in Scandinavia. Early migration of arctic-alpine plants to nunataks could explain their centric distribution in S Norway. Furthermore, vegetation establishment on the Flåfatet Lateglacial nunatak indicates that S Norway could have been vegetated by successions along the retreating ice from alpine nunataks and from coastal and southern areas. The upland and lowland vegetation met at the final deglaciation.