High mountain ecosystems and their biota are governed by low-temperature conditions and thus can be used as indicators for climate warming impacts on natural ecosystems, provided that long-term data ...exist.
We used data from the largest alpine to nival permanent plot site in the Alps, established in the frame of the Global Observation Research Initiative in Alpine Environments (GLORIA) on Schrankogel in the Tyrolean Alps, Austria, in 1994, and resurveyed in 2004 and 2014.
Vascular plant species richness per plot increased over the entire period, albeit to a lesser extent in the second decade, because disappearance events increased markedly in the latter period. Although presence/absence data could only marginally explain range shift dynamics, changes in species cover and plant community composition indicate an accelerating transformation towards a more warmth-demanding and more drought-adapted vegetation, which is strongest at the lowest, least rugged subsite.
Divergent responses of vertical distribution groups of species suggest that direct warming effects, rather than competitive displacement, are the primary causes of the observed patterns. The continued decrease in cryophilic species could imply that trailing edge dynamics proceed more rapidly than successful colonisation, which would favour a period of accelerated species declines.
Nitrogen (N) mineralization, nutrient availability, and plant growth in the Arctic are often restricted by low temperatures. Predicted increases of cold-season temperatures may be important for plant ...nutrient availability and growth, given that N mineralization is also taking place during the cold season. Changing nutrient availability may be reflected in plant N and chlorophyll content and lead to increased photosynthetic capacity, plant growth, and ultimately carbon (C) assimilation by plants. In this study, we increased snow depth and thereby cold-season soil temperatures in high Arctic Svalbard in two vegetation types spanning three moisture regimes. We measured growing-season availability of ammonium (NH₄⁺), nitrate (NO₃⁻), total dissolved organic carbon (DOC) and nitrogen (TON) in soil; C, N, δ¹⁵N and chlorophyll content in Salix polaris leaves; and leaf sizes of Salix, Bistorta vivipara, and Luzula arcuata at peak season. Nutrient availability was significantly higher with increased snow depth in the two mesic meadow vegetation types, but not in the drier heath vegetation. Nitrogen concentrations and δ¹⁵N values of Salix leaves were significantly higher in all vegetation types, but the leaf sizes were unchanged. Leaves of Bistorta and Luzula were significantly larger but only significantly so in one moist vegetation type. Increased N and chlorophyll concentrations in leaves indicate a potential for increased growth (C uptake), supported by large leaf sizes for some species. Responses to cold-season soil warming are vegetation type- and species-specific, with potentially stronger responses in moister vegetation types. This study therefore highlights the contrasting effect of snow in a tundra landscape and has important implications for projections of whole tundra responses to climate change.
Land-use has transformed ecosystems over three quarters of the terrestrial surface, with massive repercussions on biodiversity. Land-use intensity is known to contribute to the effects of land-use on ...biodiversity, but the magnitude of this contribution remains uncertain. Here, we use a modified countryside species-area model to compute a global account of the impending biodiversity loss caused by current land-use patterns, explicitly addressing the role of land-use intensity based on two sets of intensity indicators. We find that land-use entails the loss of ~15% of terrestrial vertebrate species from the average 5 × 5 arcmin-landscape outside remaining wilderness areas and ~14% of their average native area-of-habitat, with a risk of global extinction for 556 individual species. Given the large fraction of global land currently used under low land-use intensity, we find its contribution to biodiversity loss to be substantial (~25%). While both sets of intensity indicators yield similar global average results, we find regional differences between them and discuss data gaps. Our results support calls for improved sustainable intensification strategies and demand-side actions to reduce trade-offs between food security and biodiversity conservation.
The duration of specific periods within a plant's life cycle are critical for plant growth and performance. In the High Arctic, the start of many of these phenological periods is determined by ...snowmelt date, which may change in a changing climate. It has been suggested that the end of these periods during late-season are triggered by external cues, such as day length, light quality or temperature, leading to the hypothesis that earlier or later snowmelt dates will lengthen or shorten the duration of these periods, respectively, and thereby affect plant performance. We tested whether snowmelt date controls phenology and phenological period duration in High Arctic Svalbard using a melt timing gradient from natural and experimentally altered snow depths. We investigated the response of early- and late-season phenophases from both vegetative and reproductive phenological periods of eight common species. We found that all phenophases follow snowmelt patterns, irrespective of timing of occurrence, vegetative or reproductive nature. Three of four phenological period durations based on these phenophases were fixed for most species, defining the studied species as periodic. Periodicity can thus be considered an evolutionary trait leading to disadvantages compared with aperiodic species and we conclude that the mesic and heath vegetation types in Svalbard are at risk of being outcompeted by invading, aperiodic species from milder biomes.
The Arctic is one of the ecosystems most affected by climate change; in particular, winter temperatures and precipitation are predicted to increase with consequent changes to snow cover depth and ...duration. Whether the snow-free period will be shortened or prolonged depends on the extent and temporal patterns of the temperature and precipitation rise; resulting changes will likely affect plant growth with cascading effects throughout the ecosystem. We experimentally manipulated snow regimes using snow fences and shoveling and assessed aboveground size of eight common high arctic plant species weekly throughout the summer. We demonstrated that plant growth responded to snow regime, and that air temperature sum during the snow free period was the best predictor for plant size. The majority of our studied species showed periodic growth; increases in plant size stopped after certain cumulative temperatures were obtained. Plants in early snow-free treatments without additional spring warming were smaller than controls. Response to deeper snow with later melt-out varied between species and categorizing responses by growth forms or habitat associations did not reveal generic trends. We therefore stress the importance of examining responses at the species level, since generalized predictions of aboveground growth responses to changing snow regimes cannot be made.
Thicker snow cover in permafrost areas causes deeper active layers and thaw subsidence, which alter local hydrology and may amplify the loss of soil carbon. However, the potential for changes in snow ...cover and surface runoff to mobilize permafrost carbon remains poorly quantified. In this study, we show that a snow fence experiment on High‐Arctic Svalbard inadvertently led to surface subsidence through warming, and extensive downstream erosion due to increased surface runoff. Within a decade of artificially raised snow depths, several ice wedges collapsed, forming a 50 m long and 1.5 m deep thermo‐erosion gully in the landscape. We estimate that 1.1–3.3 tons C may have eroded, and that the gully is a hotspot for processing of mobilized aquatic carbon. Our results show that interactions among snow, runoff and permafrost thaw form an important driver of soil carbon loss, highlighting the need for improved model representation.
Plain Language Summary
Snow cover is steadily disappearing as a result of climate change, but in areas that remain below 0°C we can still expect an increase in snow depth in the middle of winter. Since snow acts akin to a blanket, this warms the soil and accelerates the thaw of permafrost—thereby potentially contributing to carbon release from these frozen soils. Ice wedges, which are typical for permafrost landscapes, are particularly vulnerable to thaw because they hold a large amount of ice. When this ice melts, the surface sinks down, and soil carbon may be lost. In this study, we show how experimentally raised snow cover triggered the collapse of several ice wedges, not only through a warming effect of the snow but also due to an increase in the flow of water through the ice wedge network. As a result, we estimate that 1.1–3.3 tons of carbon were removed from this location, of which a portion could have entered the atmosphere as CO2. We emphasize the importance of studying the interactions among snow, runoff, and permafrost thaw to better understand how this may affect the release of greenhouse gases to the atmosphere.
Key Points
A decade of raised snow depths led to strong local thaw subsidence, while increased runoff triggered the downstream collapse of ice wedges
The abrupt thaw process mobilized about 1.1–3.3 tons of soil organic carbon in total, and dissolved organic carbon was degraded in the thermo‐erosion gully
Feedbacks linking changes in snow cover, surface drainage, and permafrost thaw are important drivers of thermokarst and soil carbon loss
Arctic tundra active-layer soils are at risk of soil organic carbon (SOC) depletion and degradation upon global climate warming because they are in a stage of relatively early decomposition. ...Non-growing season (NGS) warming is particularly pronounced, and observed increases of CO2 emissions during experimentally warmed NGSs give concern for great SOC losses to the atmosphere. Here, we used snow fences in Arctic Spitsbergen dwarf shrub tundra to simulate 1.86 °C NGS warming for 9 consecutive years, while growing season temperatures remained unchanged. In the snow fence treatment, the 4-11 cm thick A-horizon had a 2% lower SOC concentration and a 0.48 kg C m−2 smaller pool size than the controls, indicating SOC pool depletion. The snow fence treatment's A-horizon's alkyl/O-alkyl ratio was also significantly increased, indicating an advance of SOC degradation. The underlying 5 cm of B/C-horizon did not show these effects. Our results support the hypothesis that SOC depletion and degradation are connected to the long-term transience of observed ecosystem respiration (ER) increases upon soil warming. We suggest that the bulk of warming induced ER increases may originate from surface and not deep active layer or permafrost horizons. The observed losses of SOC might be significant for the ecosystem in question, but are in magnitude comparatively small relative to anthropogenic greenhouse gas enrichment of the atmosphere. We conclude that a positive feedback of carbon losses from surface soils of Arctic dwarf shrub tundra to anthropogenic forcing will be minor, but not negligible.
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•Soil was warmed in situ for nine consecutive non-growing seasons (NGS) in Svalbard.•NGS warming depleted soil organic carbon (SOC) pool of the soil's shallow A-horizon.•NGS warming transitioned the A-horizon SOC to an advanced state of decomposition.•The underlying B/C-horizon's SOC pool and state was not affected.•NGS warming mineralizes more C in shallow than in deep soil.
Climate models predict extended periods with sea-ice free Arctic waters during the next decade, which will allow more shipping activity and easier access to petroleum resources. Increased industrial ...activities raise concerns about the biological effects of accidental petroleum release on key species of the Arctic marine ecosystem, such as the polar cod (Boreogadus saida). This study examines effects on physiological traits related to the fitness of adult polar cod, such as growth, survival, and lipid parameters. Fish were exposed to environmentally-relevant crude oil doses through their diet over an 8-month period, concurrent with reproductive development. In liver tissue, lipid class composition differed between treatments while in gonad tissue, lipid class composition varied between sexes, but not treatments. Crude oil did not affect growth and survival, which indicated that polar cod were relatively robust to dietary crude oil exposure at doses tested (0.11–1.14 μg crude oil/g fish/day) in this study.
•Experiment to investigate the effects of chronic crude oil exposure on polar cod.•Polar cod were exposed to low dietary doses during their gonadal development.•The exposure did not affect polar cod growth and survival.•The exposure caused sublethal effects on the lipid composition of liver tissue.
The High Arctic winter is expected to be altered through ongoing and future climate change. Winter precipitation and snow depth are projected to increase and melt out dates change accordingly. Also, ...snow cover and depth will play an important role in protecting plant canopy from increasingly more frequent extreme winter warming events. Flower production of many Arctic plants is dependent on melt out timing, since season length determines resource availability for flower preformation. We erected snow fences to increase snow depth and shorten growing season, and counted flowers of six species over 5 years, during which we experienced two extreme winter warming events. Most species were resistant to snow cover increase, but two species reduced flower abundance due to shortened growing seasons. Cassiope tetragona responded strongly with fewer flowers in deep snow regimes during years without extreme events, while Stellaria crassipes responded partly. Snow pack thickness determined whether winter warming events had an effect on flower abundance of some species. Warming events clearly reduced flower abundance in shallow but not in deep snow regimes of Cassiope tetragona, but only marginally for Dryas octopetala. However, the affected species were resilient and individuals did not experience any long term effects. In the case of short or cold summers, a subset of species suffered reduced reproductive success, which may affect future plant composition through possible cascading competition effects. Extreme winter warming events were shown to expose the canopy to cold winter air. The following summer most of the overwintering flower buds could not produce flowers. Thus reproductive success is reduced if this occurs in subsequent years. We conclude that snow depth influences flower abundance by altering season length and by protecting or exposing flower buds to cold winter air, but most species studied are resistant to changes.
Winter warming events, often occurring together with rain, can substantially remove snow cover and thereby expose plants to cold winter air. Depending on morphology, different parts of the plant can be directly exposed. On this picture, we see Dryas octopetala seed heads from the previous growing season protrude through the remaining ice layer after a warming event in early 2010. The rest of the plant, including meristems and flower primordia, are still somewhat protected by the ice. In the background we can see a patch of Cassiope tetragona protruding through the ice; in this case, the whole plant including flower primordia is exposed, which might be one reason why this species experienced a loss of flowers the following season. Photograph by Philipp Semenchuk.
While the regional distribution of non-native species is increasingly well documented for some taxa, global analyses of non-native species in local assemblages are still missing. Here, we use a ...worldwide collection of assemblages from five taxa - ants, birds, mammals, spiders and vascular plants - to assess whether the incidence, frequency and proportions of naturalised non-native species depend on type and intensity of land use. In plants, assemblages of primary vegetation are least invaded. In the other taxa, primary vegetation is among the least invaded land-use types, but one or several other types have equally low levels of occurrence, frequency and proportions of non-native species. High land use intensity is associated with higher non-native incidence and frequency in primary vegetation, while intensity effects are inconsistent for other land-use types. These findings highlight the potential dual role of unused primary vegetation in preserving native biodiversity and in conferring resistance against biological invasions.
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