Hans Tømmervik

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• Dr. scient (PhD)
• Senior Researcher at Norwegian Institute for Nature Research

Global temperature is increasing, especially over northern lands (>50° N), owing to positive feedbacks. As this increase is most pronounced in winter, temperature seasonality (ST)—conventionally defined as the difference between summer and winter temperatures—is diminishing over time, a phenomenon that is analogous to its equatorward decline at an...

Predicting the impacts of present global warming requires an understanding of the factors controlling plant biomass and production. The extent to which they are controlled by bottom-up drivers such as climate, nutrient and water availability, and by top-down drivers such as herbivory and diseases in terrestrial systems is still under debate. By ann...

The “greening of the Arctic” is among the world’s most significant large scale ecological responses to global climate change1. The Arctic has warmed at twice the rate of the rest of the planet on average in recent decades2 and satellite-derived vegetation indices have indicated widespread increases in productivity (termed “greening”) at high latitu...

Vegetation greenness has been increasing globally since at least 1981, when satellite technology enabled large-scale vegetation monitoring. The greening phenomenon, together with warming, sea-level rise and sea-ice decline, represents highly credible evidence of anthropogenic climate change. In this Review, we examine the detection of the greening...

Satellite data show increasing leaf area of vegetation due to direct factors (human land-use management) and indirect factors (such as climate change, CO2 fertilization, nitrogen deposition and recovery from natural disturbances). Among these, climate change and CO2 fertilization effects seem to be the dominant drivers. However, recent satellite da...

In an era marked by accelerating climate change, habitat loss, and shifting land use patterns, it is crucial to understand the intricate effects of multiple stressors on ecosystems. This long‐term study sheds light on the complex interplay between grazing and habitat characteristics on pasture dynamics and offers insights into how various stressors...

Arctic ecosystems are experiencing extreme climatic, biotic and physical disturbance events that can cause substantial loss of plant biomass and productivity, sometimes at scales of >1000 km². Collectively known as browning events, these are key contributors to the spatial and temporal complexity of Arctic greening and vegetation dynamics. If we ar...

The Arctic amplification affects the geology, cryosphere, and the total environment of high-latitude maritime influenced lands. This study synthesizes information on recent and future climatic changes within the Nordic boreo-arctic region. The study area includes Greenland, Iceland, and the central and northern parts of Finland, Norway (incl. Svalb...

This report is based on the results from a Nordic network project funded by The Nordic Joint Committee for Agricultural and Food Research (NKJ) during the years 2021-2022. This network was created to encourage further cross-border discussions about the prospects of winter feeding of reindeer. In reindeer husbandry winter feeding has increased durin...

Arctic observations in 2023 provided clear evidence of rapid and pronounced climate and environmental change, shaped by past and ongoing human activities that release greenhouse gases into the atmosphere and push the broader Earth system into uncharted territory. This chapter provides a snapshot of 2023 and summarizes decades-long trends observed a...

The European Arctic is commonly thought of as a pristine and homogeneous area. In reality, it is a diverse region experiencing growth relying on natural resource extraction. Despite local communities being primarily affected by industry activities, most socioeconomic impact assessments are conducted at the macro level. This study addresses this gap...

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 thes...

This report is based on the results from a Nordic network project funded by The Nordic Joint Committee for Agricultural and Food Research (NKJ) during the years 2021-2022. This network was created to encourage further cross-border discussions about the prospects of winter feeding of reindeer. In reindeer husbandry winter feeding has increased durin...

This report is based on the results from a Nordic network project funded by The Nordic Joint Committee for Agricultural and Food Research (NKJ) during the years 2021-2022. This network was created to encourage further cross-border discussions about the prospects of winter feeding of reindeer. In reindeer husbandry winter feeding has increased durin...

This report is based on the results from a Nordic network project funded by The Nordic Joint Committee for Agricultural and Food Research (NKJ) during the years 2021-2022. This network was created to encourage further cross-border discussions about the prospects of winter feeding of reindeer. In reindeer husbandry winter feeding has increased durin...

Reindeer (Rangifer tarandus) pastoralism utilizes vast boreo-arctic taiga and tundra as grazing land. Highly fluctuating population sizes pose major challenges to the economy and livelihood of indigenous herder communities. In this study we investigated the effect of population fluctuations on core provisioning and regulating ecosystem services in...

Rapid warming due to human-caused climate change is reshaping the Arctic, enhanced by physical processes that cause the Arctic to warm more quickly than the global average, collectively called Arctic amplification. Observations over the past 40+ years show a transition to a wetter Arctic, with seasonal shifts and widespread disturbances influencing...

A hyperspectral field sensor (FloX) was installed in Ad�ventdalen (Svalbard, Norway) in 2019 as part of the Svalbard Integrated Arctic Earth Observing System (SIOS) for monitoring vegetation phenology and Sun-Induced Chlorophyll Fluorescence (SIF) of high-Arctic tundra. This northernmost hyperspectral sensor is located within the footprint of a tow...

Vegetation has a profound impact on climate through complex interactions and feedback loops, where especially regulation of albedo, the ratio of reflected to incoming solar radiation, is important at high latitudes. How vegetation albedo varies along environmental gradients in tundra ecosystems is still not well understood, particularly for ecosyst...

Understanding drivers of space use and habitat selection is essential for management and conservation, especially under rapid environmental change. Here, we develop summer and winter habitat suitability models for the endemic wild Svalbard reindeer (Rangifer tarandus platyrhynchus). The High Arctic Svalbard tundra is currently subject to the fastes...

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 physiol...

Vegetation indices are corner stones in vegetation monitoring. However, previous field studies on lichens and NDVI have been based on passive sensors. Active handheld sensors, with their own light sources, enables high-precision monitoring under variable ambient conditions. We investigated the use of handheld sensor NDVI for monitoring pale lichen...

The global temperature is increasing, and this is affecting the vegetation phenology in many parts of the world. The most prominent changes occur at northern latitudes such as our study area, which is Svalbard, located between 76°30′N and 80°50′N. A cloud-free time series of MODIS-NDVI data was processed. The dataset was interpolated to daily data...

The circumpolar average peak tundra greenness value in 2022 declined from the record high values of the previous two years, but still represented the fourth highest value since 2000. Tundra greenness in 2022 was high in most of the North American Arctic, but unusually low in northeastern Siberia, consistent with persistent summer sea-ice in the adj...

The semi-domesticated nature of the reindeer (Rangifer tarandus L.) makes it a distinct case among the world’s herbivores. Here, we review the literature on how reindeer shape vegetation and soil carbon and nitrogen cycles in northernmost Fennoscandia. We first describe main historical events that shaped the present-day grazing patterns in the diff...

Although generally given little attention in vegetation studies, ground-dwelling (terricolous) lichens are major contributors to overall carbon and nitrogen cycling, albedo, biodiversity and biomass in many high-latitude ecosystems. Changes in biomass of mat-forming pale lichens have the potential to affect vegetation, fauna, climate and human acti...

The ecological evidence in the Fosen case - Analysis of reindeer use of winter pastures and consequences of wind power development

Calculation of lost and negatively influenced winter pastures due to establishment of wind power parks and connected electrical power lines in Fosen reindeer herding district.

For more than five decades, research has been conducted at Ny-Ålesund, in Svalbard, Norway, to understand the structure and functioning of High-Arctic ecosystems and the profound impacts on them of environmental change. Terrestrial, freshwater, glacial and marine ecosystems are accessible year-round from Ny-Ålesund, providing unique opportunities f...

Snow melt timing and the last day of snow cover have a significant impact on vegetation phenology in the Svalbard archipelago. The aim of this study is to assess the seasonal variations of the snow using a multi-sensor approach and to analyze the sensitivity of the Synthetic Aperture Radar (SAR) backscatter to vegetation growth and soil moisture in...

https://arctic.noaa.gov/Report-Card/Report-Card-2021/ArtMID/8022/ArticleID/936/Tundra-Greenness

The Arctic is one chapter from the State of the Climate in 2020 annual report and is available from https://doi.org/10.1175/BAMS-D-21-0086.1. Compiled by NOAA’s National Centers for Environmental Information, State of the Climate in 2020 is based on contributions from scientists from around the world. It provides a detailed update on global climate...

The Arctic is a region that is expected to experience a high increase in temperature. Changes in the timing of phenological phases, such as the onset of growth (as observed by remote sensing), is a sensitive bio-indicator of climate change. In this paper, the study area was the central part of Spitsbergen, Svalbard, located between 77.28 N and 78.4...

Near-surface remote sensing techniques are essential monitoring tools to provide spatial and temporal resolutions beyond the capabilities of orbital methods. This high level of detail is especially helpful to monitor specific plant communities and to accurately time the phenological stages of vegetation – which satellites can miss by days or weeks...

Svalbard Integrated Arctic Earth Observing System (SIOS) is an international partnership of research institutions studying the environment and climate in and around Svalbard. SIOS is developing an efficient observing system, where researchers share technology, experience, and data, work together to close knowledge gaps, and decrease the environment...

Technical report; Van den Heuvel F, Hübner C, Błaszczyk M, Heimann M, Lihavainen H (eds) 2020: SESS report 2019, Svalbard Integrated Arctic Earth Observing System, Longyearbyen

The Arctic is experiencing an increased frequency of extreme events which can cause landscape-scale vegetation damage. Extreme event-driven damage is an important driver of the decline in vegetation productivity (termed ‘Arctic browning’) which has become an increasingly important component of pan-Arctic vegetation change in recent years. A limited...

Many reindeer herders in northern Norway use coastal pastures for grazing. Such use comes with challenges for herding flexibility, coastal grazing and traditional adaptation practices. We are addressing three of those challenges here, predominantly focusing on Nordland County. First, we look at how climate change affects the pastures through increa...

This paper inquires whether reindeer herders’ traditional knowledge (TK) provides a reservoir of precaution and adaptation possibilities that may be relevant to counteract climate change. As our core example, we used the milking of reindeer—which, in some areas, was practiced up until the 1950s–1960s—and the risk of getting foot rot disease (digita...

The reduction of cold temperature constraints on photosynthesis in recent decades has led to extended growing seasons and increased plant productivity (greening) in significant parts of Polar, Arctic and Boreal regions, here called northern lands. However, most territories within these regions display stable productivity in recent years. Smaller po...

The long-term satellite record (1982-2018) indicates "greening" across most Arctic tundra regions, especially Alaska's North Slope, mainland Canada, and the Russian Far East, but trends are not homogeneous, and some regions instead exhibit no trend or "browning," such as the Canadian Archipelago, southwestern Alaska, and parts of northwestern Siber...

In this study, we focused on three species that have proven to be vulnerable to winter stress: Empetrum nigrum, Vaccinium vitis-idaea and Hylocomium splendens. Our objective was to determine plant traits suitable for monitoring plant stress as well as trait shifts during spring. To this end, we used a combination of active and passive handheld norm...

Rapid climate change in Arctic regions is resulting in more frequent extreme climatic events. These can cause large-scale vegetation damage, and are therefore among key drivers of declines in biomass and productivity (or “browning”) observed across Arctic regions in recent years. Extreme events which cause browning are driven by multiple interactin...

As the Arctic warms, vegetation is responding, and satellite measures indicate widespread greening at high latitudes. This ‘greening of the Arctic’ is among the world’s most important large-scale ecological responses to global climate change. However, a consensus is emerging that the underlying causes and future dynamics of so-called Arctic greenin...

The Arctic marine ecosystem and the communities that depend upon it continue to experience unprecedented changes as a result of warming air temperatures, declining sea ice, and warming waters. Arctic Report Card 2019 draws particular attention to the Bering Sea region, where declining winter sea ice exemplifies the potential for sudden and extreme...

Eurasian forest cover at high northern latitudes (> 67°N) has increased in recent decades due to stimulatory effects of global warming, but other factors may be important. The objective of this study is to compare the importance of historical human exploitation and climate change. Periodic information on forest and tundra resources along with human...

Seasonality in photosynthetic activity is a critical component of seasonal carbon, water and energy cycles in the Earth system. This characteristic is a consequence of plant's adaptive evolutionary processes to a given set of environmental conditions. Changing climate in northern lands (>30°N) alters the state of climatic constraints on plant growt...

Ruminant fodder production in agricultural lands in latitudes above the Arctic Circle is constrained by short and hectic growing seasons with a 24-hour photoperiod and low growth temperatures. The use of remote sensing to measure crop production at high latitudes is hindered by intrinsic challenges, such as a low sun elevation angle and a coastal c...

Remote sensing, which is based on a reflected electromagnetic spectrum, offers a wide range of research methods. It allows for the identification of plant properties, e.g., chlorophyll, but a registered signal not only comes from green parts but also from dry shoots, soil, and other objects located next to the plants. It is, thus, important to iden...

Climate change-induced snow thaw and subsequent accumulation of ice on the ground is a potential, major threat to snow-dominated ecosystems. While impacts of ground-ice on arctic wildlife are well explored, the impacts on tundra vegetation is far from understood. We therefore tested the vulnerability of two high-arctic plants, the prostrate shrub S...

Climate change is one of many ongoing human-induced environmental changes, but few studies consider interactive effects between multiple anthropogenic disturbances. In coastal sub-arctic heathland, we quantified the impact of a factorial design simulating extreme winter warming (WW) events (7 days at 6–7°C) combined with episodic summer nitrogen (+...

DOI: 10.1201/9780429489617-1

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 flux...

The socioeconomic causes of land use change are complex. They are highly context dependent, but most often studied through case studies. Here, we use a quasi-experimental paired block design to investigate whether better access to wage income leads to more visible land use around 28 settlements in six regions of the circumpolar Arctic. We mapped vi...

The ericoid shrub Vaccinium myrtillus is one of several deciduous boreal plants that respond to larval defoliation by compensatory production of a new set of leaves within the same growing season soon after defoliation. This new set is termed as ‘secondary leaves’. The physiological performance and longevity of secondary leaves is poorly understood...

In 2017, the dominant greenhouse gases released into Earth's atmosphere-carbon dioxide, methane, and nitrous oxide-reached new record highs. The annual global average carbon dioxide concentration at Earth's surface for 2017 was 405.0 ± 0.1 ppm, 2.2 ppm greater than for 2016 and the highest in the modern atmospheric measurement record and in ice cor...

In the years 2014–2016 biomonitoring studies were conducted in the forest areas of south and north-eastern Poland: the Karkonosze Mountains, the Beskidy Mountains, the Borecka Forest, the Knyszyńska Forest and the Białowieska Forest. This study used epigeic moss Pleurozium schreberi and epiphytic lichens Hypogymnia physodes. Samples were collected...

Extreme winter events that damage vegetation are considered an important climatic cause of arctic browning—a reversal of the greening trend of the region—and possibly reduce the carbon uptake of northern ecosystems. Confirmation of a reduction in CO2 uptake due to winter damage, however, remains elusive due to a lack of flux measurements from affec...

Arctic shows no sign of returning to reliably frozen region of recent past decades Despite relatively cool summer temperatures, observations in 2017 continue to indicate that the Arctic environmental system has reached a 'new normal', characterized by long-term losses in the extent and thickness of the sea ice cover, the extent and duration of the...

Remote sensing is a suitable candidate for monitoring rapid changes in Polar regions, offering high-resolution spectral, spatial and radiometric data. This paper focuses on the spectral properties of dominant plant species acquired during the first week of August 2015. Twenty-eight plots were selected, which could easily be identified in the field...

The exact cause of population dieback in nature is often challenging to identify retrospectively. Plant research in northern regions has in recent decades been largely focussed on the opposite trend, namely increasing populations and higher productivity. However, a recent unexpected decline in remotely-sensed estimates of terrestrial Arctic primary...

Icy surfaces impose challenges for northern societies, wildlife and agriculture. However, there have been relatively few studies of the impacts of anoxic ground ice on non-agricultural plants. During the winter of 2009–2010, an extreme winter warming event led to thick ground-ice layer development in the world’s northernmost botanical garden in Tro...

After the publication of the research paper by Anderson et al. [1], a reanalysis of the data showed that mistakes had been introduced in the calculation of the greenness indices and the filtering for outliers prior to the statistical analysis.[...]

The study area of Finnmarksvidda is Norway’s largest mountain plateau, located in the arctic/alpine-boreal transition area. The area is also a central winter grazing area for the reindeer herds of the indigenous Sámi people. This study develops a bioclimatic-based model to simulate future potential vegetation, with focus on forest types. The model...

The Oribatida of High Arctic Svalbard are faunistically relatively well known, but the distribution, density, stage structure and other population parameters of most species are unknown. Here we focus on two ceratozetid species, Diapterobates notatus (Thorell, 1871) and Svalbardia paludicola Thor, 1930, and investigate the summer density, stage and...

The migratory tundra caribou herds in North America follow decadal population cycles, and browsing from abundant caribou could be expected to counteract the current climate-driven expansion of shrubs in the circumpolar tundra biome. We demonstrate that the sea ice cover in the Arctic Ocean has provided a strong signal for climate-induced changes on...

Heavy metals and radioactive compounds are potentially hazardous substances for plants, animals and humans in the Arctic. A good knowledge of the spatial variation of these substances in soil and primary producers, and their sources, is therefore essential. In the samples of lichen Thamnolia vermicularis, Salix polaris and Cassiope tetragona, and t...