Summary: Climate change in northern high latitudes is predicted to be greater in winter rather than summer, yet little is known about the effects of winter climate change on northern ecosystems. Among the unknowns are the effects of an increasing frequency of acute, short-lasting winter warming events. Such events can damage higher plants exposed to warm, then returning cold, temperatures after snow melt, and it is not known how bryophytes and lichens, which are of considerable ecological importance in high-latitude ecosystems, are affected by such warming events. However, even physiological adaptations of these cryptogams to winter environments in general are poorly understood. Here we describe findings from a novel field experiment that uses heating from infrared lamps and soil warming cables to simulate acute mid-winter warming events in a sub-Arctic heath. In particular, we report the growing season responses of the dominant lichen, Peltigera aphthosa, and bryophyte, Hylocomium splendens, to warming events in three consecutive winters. While summertime photosynthetic performance of P. aphthosa was unaffected by the winter warming treatments, H. splendens showed significant reductions in net photosynthetic rates and growth rates (of up to 48% and 52%, respectively). Negative effects were evident already during the summer following the first winter warming event. While the lichen develops without going through critical phenological stages during which vulnerable organs are produced, the moss has a seasonal rhythm, which includes initiation of growth of young, freeze-susceptible shoot apices in the early growing season; these might be damaged by breaking of dormancy during warm winter events. Synthesis. Different sensitivities of the bryophyte and lichen species were unexpected, and illustrate that very little is known about the winter ecology of bryophytes and lichens from cold biomes in general. In sharp contrast to summer warming experiments that show increased vascular plant biomass and reduced lichen biomass, these results demonstrate that acute climate events in mid-winter may be readily tolerated by lichens, in contrast to previously observed sensitivity of co-occurring dwarf shrubs, suggesting winter climate change may compensate for (or even reverse) predicted lichen declines resulting from summer warming.
Contrasting sensitivity to extreme winter warming events of dominant sub‐Arctic heathland bryophyte and lichen species
Rain-on-snow (ROS) events can greatly affect the snow process and cause severe snowmelt-related hazards. It is important to monitor the spatiotemporal distribution of ROS events over the ungauged High Mountain Asia (HMA). This study investigated the spatiotemporal variability of ROS events over the HMA and its potential influencing factors from 1981 to 2020 based on stand-alone Noah-MP land surface model simulations forced by hourly HARv2 reanalysis dataset. The results demonstrated that ROS activity occurred more frequently in the higher-elevation (2500–4000 m and 5500–6000 m a.s.l) regions of the Tianshan Mountains, Pamir, eastern Hindu Kush, Himalayas, and the western Hengduan Shan, with an annual maximum ROS frequency exceeding 15 days and a maximum intensity reaching 40 mm concentrated in spring and summer. ROS frequency experienced a significant decrease in the high-elevation (3000–4500 m a.s.l) regions of the eastern Hindu Kush, West Himalaya, and western Hengduan Shan with a rate exceeding −1.5 days/decade. The decrease in ROS frequency could be explained by a shifting of precipitation type from snowfall to rain driven by dramatic warming and resulting in a decline in snowfall and shortened snow cover persistence, particularly in spring and summer. On the contrary, significantly increasing trend mainly prevailed in the high-elevation (5000–6000 m a.s.l) regions of Transhimalaya and East Himalaya, exceeding 0.9 days/decade.
Trends and spatial variations of rain-on-snow events over the high Mountain Asia
ABSTRACT The origin of lichen-free areas in the High Arctic has been attributed to lichen-kill under permanent snowfields developed 300 yr ago during the Little Ice Age. There are inconsistencies in this hypothesis, particularly in regard to the manner of lichen-kill, the mechanism of dead lichen removal once the previously ice-covered ground is exposed again, the period when the lichen-kill occured, and the form of lichen trimlines. An alternative hypothesis is suggested whereby lichen-free areas occur where seasonal snowfields persist for a much greater part of the summer than elsewhere. As a result the lichen growth season there is very short.
The Problem of Lichen-Free Zones in Arctic Canada
Using FAIR and Open Science practices to better understand vegetation browning in Troms and Finnmark (Norway)
Abstract. Rain-on-snow (ROS) events in mountainous catchments can cause enhanced snowmelt, leading to an increased risk of destructive winter floods. However, due to differences in topography and forest cover, the generation of snowpack outflow volumes and their contribution to streamflow are spatially and temporally variable during ROS events. In order to adequately predict such flood events with hydrological models, an enhanced process understanding of the contribution of rainwater and snowmelt to stream water is needed.
Monitoring snowpack outflow volumes and their isotopic composition to better understand streamflow generation during rain-on-snow events
Abstract Arctic ecosystems are increasingly exposed to extreme climatic events throughout the year, which can affect species performance. Cryptogams (bryophytes and lichens) provide important ecosystem services in polar ecosystems but may be physiologically affected or killed by extreme events. Through field and laboratory manipulations, we compared physiological responses of seven dominant sub-Arctic cryptogams (three bryophytes, four lichens) to single events and factorial combinations of mid-winter heatwave (6C for 7 days), re-freezing, snow removal and summer nitrogen addition. We aimed to identify which mosses and lichens are vulnerable to these abiotic extremes and if combinations would exacerbate physiological responses. Combinations of extremes resulted in stronger species responses but included idiosyncratic species-specific responses. Species that remained dormant during winter (March), irrespective of extremes, showed little physiological response during summer (August). However, winter physiological activity, and response to winter extremes, was not consistently associated with summer physiological impacts. Winter extremes affect cryptogam physiology, but summer responses appear mild, and lichens affect the photobiont more than the mycobiont. Accounting for Arctic cryptogam response to multiple climatic extremes in ecosystem functioning and modelling will require a better understanding of their winter eco-physiology and repair capabilities.
Sub-arctic mosses and lichens show idiosyncratic responses to combinations of winter heatwaves, freezing and nitrogen deposition
Abstract Extreme climatic events are among the drivers of recent declines in plant biomass and productivity observed across Arctic ecosystems, known as “Arctic browning.” These events can cause landscape-scale vegetation damage and so are likely to have major impacts on ecosystem CO2 balance. However, there is little understanding of the impacts on CO2 fluxes, especially across the growing season. Furthermore, while widespread shoot mortality is commonly observed with browning events, recent observations show that shoot stress responses are also common, and manifest as high levels of persistent anthocyanin pigmentation. Whether or how this response impacts ecosystem CO2 fluxes is not known. To address these research needs, a growing season assessment of browning impacts following frost drought and extreme winter warming (both extreme climatic events) on the key ecosystem CO2 fluxes Net Ecosystem Exchange (NEE), Gross Primary Productivity (GPP), ecosystem respiration (Reco) and soil respiration (Rsoil) was carried out in widespread sub-Arctic dwarf shrub heathland, incorporating both mortality and stress responses. Browning (mortality and stress responses combined) caused considerable site-level reductions in GPP and NEE (of up to 44%), with greatest impacts occurring at early and late season. Furthermore, impacts on CO2 fluxes associated with stress often equalled or exceeded those resulting from vegetation mortality. This demonstrates that extreme events can have major impac
Arctic browning: Impacts of extreme climatic events on heathland ecosystem CO2 fluxes
Jupyter Notebook for training, testing and validating machine learning method to forecast moss and lichen fractional cover mean. This Jupyter Notebook uses Python and Keras.
Forecasting moss & lichen fractional cover mean with machine learning (Jupyter Notebook)
REsearch LIfecycle mAnagemeNt for Earth Science Communities and CopErnicus users in EOSC
In most places on the planet vegetation thrives, this is known as “greening Earth”. However in certain regions, especially in the Arctic, there are areas exhibiting a browning trend. Here we focus on the Troms and Finnmark counties in northern Norway to assess the extend of the phenomenon and any link with local environmental conditions.
Vegetation browning in Troms and Finnmark (Norway)
Iaquinta, Jean, and Anne Fouilloux. "Vegetation browning in Troms and Finnmark (Norway)." ROHub. Oct 12 ,2022. https://w3id.org/ro-id/3ed30e69-fb38-4045-bd34-2fa907d12353.
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A community platform for Big Data geoscience
Vegetation browning in Troms and Finnmark (Norway). In most places on the planet vegetation thrives, this is known as “
However in certain regions, especially in the Arctic, there are areas exhibiting a browning trend.
Here we focus on the Troms and Finnmark counties in northern Norway to assess the extend of the phenomenon and any link with local environmental conditions.
Poster presented at EGU 2023 during the ESSI2.8 "HPC and cloud infrastructures in support of Earth Observation, Earth Modeling and community-driven Geoscience approach PANGEO" Convener: Vasileios Baousis | Co-conveners: Tina Odaka, Umberto Modigliani, Anne Fouilloux, Alejandro Coca-CastroECS
Poster (pdf) Using FAIR and Open Science practices to better understand vegetation browning in Troms and Finnmark (Norway)
This poster shows the work done to estimate the loss in lichens & mosses in the arctic (arctic browning). ERA5 land data from ECMWF have been used to estimate the changes in vegetation. Poster in svg format that has been presented at EGU 2023 at session ESSI2.8 HPC and cloud infrastructures in support of Earth Observation, Earth Modeling and community-driven Geoscience approach PANGEO Convener: Vasileios Baousis | Co-conveners: Tina Odaka, Umberto Modigliani, Anne Fouilloux, Alejandro Coca-Castro
Poster (svg) Using FAIR and Open Science practices to better understand vegetation browning in Troms and Finnmark (Norway)
The State of the Arctic Terrestrial Biodiversity Report (START) is a product of the Circumpolar Biodiversity Monitoring Program (CBMP) Terrestrial Group of the Arctic Council’s Conservation of Arctic Flora and Fauna (CAFF) Working Group. The START assesses the status and trends of terrestrial Focal Ecosystem Components (FECs)—including vegetation, arthropods, birds, and mammals—across the Arctic, identify gaps in monitoring coverage towards implementation of the CBMP’s Arctic Terrestrial Biodiversity Monitoring Plan; and provides key findings and advice for monitoring. The START is based upon primarily published data, from a special issue of Ambio containing 13 articles by more than 180 scientists
State of the Arctic terrestrial biodiversity report (2021) - Chapter 3.1 Vegetation
Vegetation indices (VIs), which describe remotely sensed vegetation properties such as photosynthetic activity and canopy structure, are widely used to study vegetation dynamics across scales. However, VI-based results can vary between indices, sensors, quality control measures, compositing algorithms, and atmospheric and sun–target–sensor geometry corrections. These variations make it difficult to draw robust conclusions about ecosystem change and highlight the need for consistent VI application and verification. In this Technical Review, we summarize the history and ecological applications of VIs and the linkages and inconsistencies between them. VIs have been used since the early 1970s and have evolved rapidly with the emergence of new satellite sensors with more spectral channels, new scientific demands and advances in spectroscopy. When choosing VIs, the spectral sensitivity and features of VIs and their suitability for target application should be considered. During data analyses, steps must be taken to minimize the impact of artefacts, VI results should be verified with in situ data when possible and conclusions should be based on multiple sets of indicators. Next-generation VIs with higher signal-to-noise ratios and fewer artefacts will be possible with new satellite missions and integration with emerging vegetation metrics such as solar-induced chlorophyll fluorescence, providing opportunities for studying terrestrial ecosystems globally.
Optical vegetation indices for monitoring terrestrial ecosystems globally
Abstract Droppings of Svalbard reindeer (Rangifer tarandus platyrhynchus) could affect the carbon and nitrogen cycles in tundra ecosystems. The aim of this study was to evaluate the potential of reindeer droppings originating from the winter diet for emission and/or absorption of methane (CH4) and nitrous oxide (N2O) in summer. An incubation experiment was conducted over 14 days using reindeer droppings and mineral subsoil collected from a mound near Ny-Ålesund, Svalbard, to determine the potential exchanges of CH4 and N2O for combinations of two factors, reindeer droppings (presence or absence) and soil moisture (dry, moderate, or wet). A line transect survey was conducted to determine the distribution density of winter droppings at the study site. The incubation experiment showed a weak absorption of CH4 and a weak emission of N2O. Reindeer droppings originating from the winter diet had a negligible effect on the exchange fluxes of both CH4 and N2O. Although the presence of droppings resulted in a short-lasting increase in N2O emissions on day 1 (24 h from the start) for moderate and wet conditions, the emission rates were still very small, up to 3 μg N2O m−2 h−1.
Potential of Svalbard reindeer winter droppings for emission/absorption of methane and nitrous oxide during summer