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Ecological theory predicts the strongest ecosystem effects of herbivory when dominant and ecologically important species are consumed. Bilberry, Vaccinium myrtillus, is such a key plant species, attractive to many other species in the boreal forests, for example ungulate and invertebrate herbivores. Large herbivores may remove substantial biomass and alter plant quality and therefore affect abundance and populations of invertebrate animals sharing the same food plant. We combined experimental exclusion of ungulates with a browsing intensity gradient to investigate the 15-year effect of ungulate (Cervus elaphus and Ovis aries) browsing on bilberry plant size and on bilberry-feeding herbivorous larvae (Lepidoptera and Symphyta), in a Norwegian old growth boreal forest ecosystem. Bilberry ramets in exclosure plots had nearly nine times higher dry mass and three times higher abundance of invertebrates feeding on them than in ungulate-access plots. Sweep-netting data verified these findings as larval numbers were twice as high in exclosure plots. The pattern in the large herbivore effects on bilberry size and abundance of herbivorous larvae were identical along the browsing gradient. Differences in larval abundance between treatments, as indicated by leaf-chewing, increased during the 15-year study period, and the community fluctuations were larger when ungulate herbivores were excluded. The browsing effect was moderated by plant quality as larval densities were lowest on both heavily-browsed and non-browsed plants, and highest on ramets that had 50–74% of annual shoots browsed. Our study supports previous findings in that bilberry is relatively disturbance tolerant and may recover quickly, but that ungulates may compete with herbivorous larvae for food biomass. Additionally, our results strongly indicates that population insect community peaks and fluctuations are dampened by ungulate consumption. Our findings add to the understanding on how ungulates may structure forest ecosystems directly and indirectly.

In recent decades, global warming and nitrogen (N) deposition have been increasing obviously, which have led to some strong responses in terrestrial ecosystems, especially the carbon (C) cycle. The boreal forest occupies an important position in the global C cycle with its huge C storage. However, the impact of global change such as N deposition on boreal forest ecosystem C cycle has been not very clear. In order to solve this problem, the field experiment of N addition in a boreal forest has been built in the Greater Khingan Mountains of Northeast China since 2011. Four N addition gradients (0, 25, 50, 75 kg N ha−1 year−1) were set up to study the response of above- and belowground C pool to N addition. The results showed that the total forest C sequestration of low-, medium- and high-N treatments was 104.4 ± 5.9, 20.2 ± 2.7 and 5.3 ± 0.4 g C/g N, respectively. Aboveground trees were the largest C pool, followed by soil, roots and floor C pool. Low-N increased the input of C by promoting photosynthesis. Trees of Larix gmelini increased the investment in the belowground root system and increased the belowground C pool. High-N reduced the inter-annual litter biomass and decreased litter C:N that accelerated the decomposition of litter, resulting in a reduction in the floor C pool. Low-N increased total soil respiration, while medium- and high-N inhibited heterotrophic respiration and then increased soil C sequestration. The estimation of forest C pool provides valuable data for improving the C dynamic characteristics of boreal forest ecosystem and is of great significance for us to understand the impact of climate change on the global C cycle.

A quantitative understanding of the global gross primary productivity (GPP) and its responses to increasing CO2 levels is critical for quantifying the feedbacks of ecosystems to climate change. This study applied the daily boreal ecosystem productivity simulator (BEPSd) model to estimate the global GPP from 2000 to 2015, compare the estimated GPP with flux tower measurements and other GPP products to verify the estimation accuracy, and analyze the CO2 fertilization effect and conducted a spatial analysis of the effects of the spatiotemporal distribution of the CO2 concentration on the estimation of the GPP. The results showed that the estimates could capture the magnitude, amplitude, distribution, and variation in the GPP well compared with the flux tower measurements and other GPP products. In general, the terrestrial GPP increased as the atmospheric CO2 concentrations increased; however, the CO2 fertilization effect varied based on time and location and was constrained by climatic conditions. The increases in the lower latitudes were more significant than those in the middle and higher latitudes, and seasonal variation characteristics were observed in the middle and higher latitudes. Not considering the CO2 fertilization effect could underestimate the global GPP and its trend, while not considering the spatiotemporal distribution of the CO2 concentration could overestimate the global annual GPP. These results increase our understanding of the variations in carbon flux under future climate change, especially under the conditions of a changing atmospheric CO2 concentration.

Boreal forest in Canada has two main recurrent disturbances: one is fire and the other one is spruce budworm. The defoliation by spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) was first started in British Columbia of Canada in 1957 near Liard River. Budworm outbreaks were observed in the 1960’s to 1970’s and from the mid 1980’s to the present. Spruce budworm disturbance is one of the major issues of the forest management because of the potential losses of timber and non-timber resources in the boreal forest. To develop a sustainable management of the boreal ecosystem, mathematical modeling approaches for the budworm outbreak have been progressed. For this understanding, we propose a single species reaction-diffusion model appended with Holling type II functional response. In this paper, our main goal is to understand the spreading phenomenon of spruce budworm and subsequently identify its spreading velocity. In order to determine the spreading velocity, we focus on the one-dimensional traveling wave solutions of the model. Our results suggest that the minimal speed of traveling wave solutions can exhibit the spreading velocity of the spruce budworm in boreal forests.

The exchanges of water, energy and carbon between the land surface and the atmosphere are tightly coupled, so that errors in simulating evapotranspiration lead to errors in simulating both the water and carbon balances. Areas with seasonally frozen soils present a particular challenge due to the snowmelt‐dominated hydrology and the impact of soil freezing on the soil hydraulic properties and plant root water uptake. Land surface schemes that have been applied in high latitudes often have reported problems with simulating the snowpack and runoff. Models applied at the Boreal Ecosystem Research and Monitoring Sites in central Saskatchewan have consistently over‐predicted evapotranspiration as compared with flux tower estimates. We assessed the performance of two Canadian land surface schemes (CLASS and CLASS‐CTEM) for simulating point‐scale evapotranspiration at an instrumented jack pine sandy upland site in the southern edge of the boreal forest in Saskatchewan, Canada. Consistent with past reported results, these models over‐predicted evapotranspiration, as compared with flux tower observations, but only in the spring period. Looking systematically at soil properties and vegetation characteristics, we found that the dominant control on evapotranspiration within these models was the canopy conductance. However, the problem of excessive spring ET could not be solved satisfactorily by changing the soil or vegetation parameters. The model overestimation of spring ET coincided with the overestimation of spring soil liquid water content. Improved algorithms for the infiltration of snowmelt into frozen soils and plant‐water uptake during the snowmelt and soil thaw periods may be key to addressing the biases in spring ET.

In terrestrial ecosystems, leaves are aggregated into different spatial structures and their spatial distribution is non-random. Clumping index (CI) is a key canopy structural parameter, characterizing the extent to which leaf deviates from the random distribution. To assess leaf clumping effects on global terrestrial ET, we used a global leaf area index (LAI) map and the latest version of global CI product derived from MODIS BRDF data as well as the Boreal Ecosystem Productivity Simulator (BEPS) to estimate global terrestrial ET. The results show that global terrestrial ET in 2015 was 511.9 ± 70.1 mm yr−1 for Case I, where the true LAI and CI are used. Compared to this baseline case, (1) global terrestrial ET is overestimated by 4.7% for Case II where true LAI is used ignoring clumping, (2) global terrestrial ET is underestimated by 13.0% for Case III where effective LAI is used ignoring clumping. Among all plant functional types (PFTs), evergreen needleleaf forests were most affected by foliage clumping for ET estimation in Case II, because they are most clumped with the lowest CI. Deciduous broadleaf forests are affected by leaf clumping most in Case III because they have both high LAI and low CI compared to other PFTs. The leaf clumping effects on ET estimation in both Case II and Case III is robust to the errors in major input parameters. Thus, it is necessary to consider clumping effects in the simulation of global terrestrial ET, which has considerable implications for global water cycle research.

Light Use Efficiency (LUE), Vegetation Index (VI)-based, and process-based models are the main approaches for spatially continuous gross primary productivity (GPP) estimation. However, most current GPP models overlook the effects of topography on the vegetation photosynthesis process. Based on the structures of a two-leaf LUE model (TL-LUE), a VI-based model (temperature and greenness, TG), and a process-based model (Boreal Ecosystem Productivity Simulator, BEPS), three models, named mountain TL-LUE (MTL-LUE), mountain TG (MTG), and BEPS-TerrainLab, have been proposed to improve GPP estimation over mountainous areas. The GPP estimates from the three mountain models have been proven to align more closely with tower-based GPP than those from the original models at the site scale, but their abilities to characterize the spatial variation of GPP at the watershed scale are not yet known. In this work, the GPP estimates from three LUE models (i.e., MOD17, TL-LUE, and MTL-LUE), two VI-based models (i.e., TG and MTG), and two process-based models (i.e., BEPS and BEPS-TerrainLab) were compared for a mountainous watershed. At the watershed scale, the annual GPP estimates from MTL-LUE, MTG, and BTL were found to have a higher spatial variation than those from the original models (increasing the spatial coefficient of variation by 6%, 8%, and 22%), highlighting that incorporating topographic information into GPP models might improve understanding of the high spatial heterogeneity of the vegetation photosynthesis process over mountainous areas. Obvious discrepancies were also observed in the GPP estimates from MTL-LUE, MTG, and BTL, with determination coefficients ranging from 0.02–0.29 and root mean square errors ranging from 399–821 gC m−2yr−1. These GPP discrepancies mainly stem from the different (1) structures of original LUE, VI, and process models, (2) assumptions associated with the effects of topography on photosynthesis, (3) input data, and (4) values of sensitive parameters. Our study highlights the importance of considering surface topography when modeling GPP over mountainous areas, and suggests that more attention should be given to the discrepancy of GPP estimates from different models.

Drought has devastating impacts on agriculture and other ecosystems, and its occurrence is expected to increase in the future. However, its spatiotemporal impacts on net primary productivity (NPP) in Mongolia have remained uncertain. Hence, this paper focuses on the impact of drought on NPP in Mongolia. The drought events in Mongolia during 2003–2018 were identified using the Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI). The Boreal Ecosystem Productivity Simulator (BEPS)-derived NPP was computed to assess changes in NPP during the 16 years, and the impacts of drought on the NPP of Mongolian terrestrial ecosystems was quantitatively analyzed. The results showed a slightly increasing trend of the growing season NPP during 2003–2018. However, a decreasing trend of NPP was observed during the six major drought events. A total of 60.55–87.75% of land in the entire country experienced drought, leading to a 75% drop in NPP. More specifically, NPP decline was prominent in severe drought areas than in mild and moderate drought areas. Moreover, this study revealed that drought had mostly affected the sparse vegetation NPP. In contrast, forest and shrubland were the least affected vegetation types.

Atmospheric aerosols can alter the direct and diffuse components of global solar radiation, which further influences terrestrial gross primary productivity (GPP) via photosynthesis. To investigate ...

The adaptive capacity of boreal tree species to thrive in a warming, more variable climate has significant implications for boreal forest ecosystem structure and function. Dendrochronological and other empirical data indicate reduced growth and increased mortality of white spruce (Picea glauca [Moench] Voss) growing in warmer, drier portions of its natural range in western North America due to recent climate change. Comparatively, little is known of potential climate change effects on white spruce in the more mesic, eastern portion of its range where mean annual precipitation is relatively high. In this study, we examined the potential long-term consequences of climate warming on annual rates of mortality and height growth of mature white spruce by substituting space for time using data from 10, 31- to 40-year-old large common garden experiments (CGEs) established in Ontario, Canada. Across these CGEs, white spruce was exposed to differences of up to 5.0 °C in mean annual temperature and 405 mm in mean annual precipitation. During a 12- to 16-year measurement interval, mortality increased from the colder, more northern CGEs to the warmer CGEs near the species’ southern range margin. Along this climatic gradient, white spruce was also exposed to more frequent, severe growing season moisture deficits, with southern CGEs sometimes subject to extreme drought events with a low probability based on historical occurrence. Our results indicate that the severity of recent growing season drought events at more southern CGEs may have exceeded the drought tolerance capacity of white spruce and resulted in significantly increased mortality and reduced height growth rates. These results suggest that with projected increases in temperature and frequency/severity of growing season drought by the end of this century, white spruce is likely to experience maladaptation over a larger portion of its range in Ontario and gradually retract from its current southern range edge.

Boreal forest fires emit large amounts of carbon into the atmosphere primarily through the combustion of soil organic matter1–3. During each fire, a portion of this soil beneath the burned layer can escape combustion, leading to a net accumulation of carbon in forests over multiple fire events4. Climate warming and drying has led to more severe and frequent forest fires5–7, which threaten to shift the carbon balance of the boreal ecosystem from net accumulation to net loss1, resulting in a positive climate feedback8. This feedback will occur if organic-soil carbon that escaped burning in previous fires, termed ‘legacy carbon’, combusts. Here we use soil radiocarbon dating to quantitatively assess legacy carbon loss in the 2014 wildfires in the Northwest Territories of Canada2. We found no evidence for the combustion of legacy carbon in forests that were older than the historic fire-return interval of northwestern boreal forests9. In forests that were in dry landscapes and less than 60 years old at the time of the fire, legacy carbon that had escaped burning in the previous fire cycle was combusted. We estimate that 0.34 million hectares of young forests (

AIM: Previous analyses of remotely sensed data detected the multimodality of the tree‐cover distribution of the boreal forest, and identified areas with potentially alternative tree‐cover states. This paper aims at investigating the causes of multimodality and multistability of the boreal forest, their influence on the asymmetric tree species distribution between Eurasia and North America, and whether multistability could be associated with recent greening trends in leaf area index (LAI) and normalized difference vegetation index (NDVI). LOCATION: Eurasian and North American boreal forests. TIME PERIOD: 2000–2010. MAJOR TAXA STUDIED: Boreal forest plant functional types. METHODS: We employ a conceptual model based on tree species competition to simulate the sensitivity of tree cover to stochastic disturbances and to changes in environmental factors. We include different plant functional types based on survival adaptations, and force the model with remotely sensed environmental data. We analyse the model as a dynamical system. We use metrics from statistics and information theory to compare the detection of alternative tree‐cover states and greening trends in LAI and NDVI. RESULTS: We find that multimodality and multistability can emerge through competition between different plant functional types. Additionally, our model is able to reproduce the asymmetry in tree species distribution between Eurasia and North America. Moreover, changes in permafrost distribution can be associated with phenomenological bifurcation points of the model. Finally, we find that the detection of multistable areas is not affected by recent vegetation trends, whereas shifts between alternative states could have affected the greening trends. MAIN CONCLUSIONS: Tree‐cover multistability in the boreal region can emerge through competition between species subject to periodic disturbances. Changes in permafrost thaw and distribution could be responsible for the asymmetry in tree species distribution between North America and Eurasia. Climate change and permafrost degradation could cause shifts in tree‐cover states and dominant species. Recent vegetation greening trends in multistable areas could have been affected by shifts between alternative states.

Grassland, as an important part of land cover, plays an important role in the global carbon cycle and carbon balance. Net ecosystem productivity (NEP) is a key indicator of the carbon cycle process and an important factor in assessing ecosystem security and maintaining ecosystem balance. In this paper, Boreal Ecosystem Productivity Simulator (BEPS) combining meteorological data, leaf area index, and land cover type data were used to simulate the grassland NEP of China from 1979 to 2008. This model was also used to analyze the responses to changes in climate factors, interannual variation in carbon conversion efficiency, drought stress coefficient, and water use efficiency of grassland in China. Results showed that from 1979 to 2008, the mean annual grassland NEP was 13.6 g C/m2 with weak carbon sinks. The grassland NEP distribution increased from northwest to southeast across China. Regions with NEP of > 0 (C sink) accounted for 73.1% of the total grassland area of China. The total C sequestration reached 26.6 Tg yearly, and grassland NEP was positive from 1979 to 2008. The annual changing characteristics were analyzed. Grassland NEP was positive with carbon sink from June to September, which was negative with carbon source in the remaining months. The carbon conversion efficiency and water use efficiency of the grassland increased significantly within 30 years. NEP showed positive correlation with precipitation (accounting for 74.2% of the total grassland area was positively correlated) but weakly positive correlation with temperature (50.2% of the case). Furthermore, significant positive correlation was found between grassland NEP and precipitation, especially in northeastern and central Inner Mongolia, northern Tianshan of Xinjiang, southwestern Tibet, and southern Qinghai Lake.

Forest management strongly influences the carbon (C) budget of boreal forests and their potential to mitigating greenhouse gas emissions. A better quantification of the net changes of carbon pools with time since harvesting is necessary to guide the development of climate-friendly forest management practices. The objective of this study was to assess the evolution of forest C pools, with a special focus on detrital biomass, in an 80-year post-harvesting chronosequence consisting of 36 very homogenous stem-only harvested plots from a humid boreal balsam fir forest of eastern Canada. Dead wood C stocks comprised of snags, stumps, downed woody debris and buried wood averaged 37 Mg C ha−1 and evolved according to an upward-facing «boomerang» shape pattern throughout the chronosequence (rapid decrease in the first years followed by a constant increase until the end of the time horizon). In contrast, soil C stocks (FH and mineral) averaged 156 Mg C ha−1 and remain constant through time. Stand C sequestration increased rapidly in the early stages up to age 50 when it reached about 250 Mg C ha−1, and then continued to accumulate at a slower rate. The temporal trends observed in C pools suggest that C originating from aboveground dead wood (snags, stumps, downed woody debris) is either leaving the system (respired or leached) or transferred into buried wood, and does not appear to influence the C stocks of the fine fraction of the organic and mineral soil horizons. However, the ultimate fate of dead wood C is still poorly understood and further research is needed in this field. We recommend fixing the length of harvest rotation at a minimum of 50 years for this ecosystem to allow the build-up of its dead wood capital, and to promote dead wood retention on site. We also recommend including buried wood in carbon inventories as this pool represents an important share of the detrital C stock in these humid boreal forests.

Grassland carbon (C) sink/source evaluation is important to terrestrial ecosystem C cycling research. In this paper, boreal ecosystem productivity simulator (BEPS) model was used to simulate the net ecosystem productivity (NEP) of Inner Mongolia (IM) from 1982 to 2008. The coupling relation between NEP and climate factors was then explored. Results showed that the mean annual value of grassland NEP is 12.2 gC/m2/yr, and regions with NEP of >0 (C sink) accounts for 73.2% of the total grassland area of IM. Additionally, the total C sequestration reaches 0.35 Pg C yearly. NEP was positively correlated with precipitation (R = 0.31), and the positive correlation percentage accounted for 90% of total grassland area. But NEP was negative correlated with temperature (R = −0.11), and the negative correlation percentage was 72% of case. And the partial correlation coefficient between NEP and precipitation and between NEP and temperature was 0.30 and −0.06 respectively. Meanwhile, the monthly NEP of the grassland is obviously lagging behind the precipitation and temperature, and the lag time is both three months. We defined a precipitation differential (PD) parameter to explore the coupling relation between grassland NEP and precipitation. Generally, areas with positive PD are typically a C sinks (72% of the grassland area of IM). However, regions with negative PD are likely a C source (28% of case). The obtained mean PD value of IM is 18 mm, indicating that IM is a C sink. Further analysis showed that 69% of regions have positive PD and positive NEP, and 20% of regions have negative PD and negative NEP. This result confirmed that precipitation deficit restrains C sequestration. However, the rest of 11% of regions was sensitive area of carbon sink and carbon source transition. Among 8% of the regions (with negative PD but positive NEP) have insufficient precipitation, although other conditions (i.e., ecological restoration program) are favorable to C sink. Moreover, 3% of the regions (with positive PD but negative NEP) have sufficient precipitation, but have negative NEP because of inappropriate management or low temperature. Thus, appropriate measures that can convert a C source to a C sink are necessary. This paper can serve as a reference for policy makers for the efficient targeted implementation of ecological engineering.

Soil bacterial and fungal communities with different key ecological functions play an important role in the boreal forest ecosystem. Despite several studies have reported the microbial altitudinal distribution patterns, our understanding about the characteristics of the microbial community and the core composition of the microbiome in cold-temperate mountain forests is still limited. In this study, Illumina MiSeq sequencing was used to investigate the changes in soil bacterial and fungal communities in surface and subsurface soils along at an altitudinal gradient (from 830 m to 1300 m) on Oakley Mountain in the northern Greater Khingan Mountains. Altitude and soil depth had significant impacts on the relative abundance of Proteobacteria, Acidobacteria and Actinobacteria (dominant phylum for bacteria), and altitude had significant impacts on the Ascomycota, Basidiomycota and Mucoromycota (dominant phylum for fungi). The diversity of bacterial and fungal communities showed a monotonous decrease and increase with altitude. The influence of altitude on bacterial and fungal community composition was greater than that of soil depth. The variation of pH and dissolved organic nitrogen (DON) content in different altitudes were the main factors driving the bacterial and fungal community structure, respectively. There is no obvious difference between the network structure of surface and subsurface soil fungal communities, while the network of subsurface soil bacterial communities was more complex and compact than the surface layer. The network nodes mainly belonging to Proteobacteria and Actinobacteria are the key species in the two soil layers. Our results demonstrated that the altitude had a stronger influence on soil bacterial and fungal communities than soil depth, and bacterial and fungal communities showed divergent patterns along the altitudes and soil profiles.

Global warming threatens ecosystem functions, biodiversity, and rangeland productivity in Mongolia. The study analyzes the spatial and temporal distributions of the Net Primary Production (NPP) and its response to climatic parameters. The study also highlights how various land cover types respond to climatic fluctuations from 2003 to 2018. The Boreal Ecosystem Productivity Simulator (BEPS) model was used to simulate the rangeland NPP of the last 16 years. Satellite remote sensing data products were mainly used as input for the model, where ground-based and MODIS NPP were used to validate the model result. The results indicated that the BEPS model was moderately effective (R2 = 0.59, the Root Mean Square Error (RMSE) = 13.22 g C m−2) to estimate NPP for Mongolian rangelands (e.g., grassland and sparse vegetation). The validation results also showed good agreement between the BEPS and MODIS estimates for all vegetation types, including forest, shrubland, and wetland (R2 = 0.65). The annual total NPP of Mongolia showed a slight increment with an annual increase of 0.0007 Pg (0.68 g C per meter square) from 2003 to 2018 (p = 0.82) due to the changes in climatic parameters and land cover change. Likewise, high increments per unit area found in forest NPP, while decreased NPP trend was observed in the shrubland. In conclusion, among the three climatic parameters, temperature was the factor with the largest influence on NPP variations (r = 0.917) followed precipitation (r = 0.825), and net radiation (r = 0.787). Forest and wetland NPP had a low response to precipitation, while inter-annual NPP variation shows grassland, shrubland, and sparse vegetation were highly sensitive rangeland types to climate fluctuations.

With atmospheric reactive nitrogen (Nr) emissions increasing globally, research into Nr deposition has attracted increasing attention, especially in remote environments. These ecosystems are very sensitive to global change, especially enhanced Nr deposition. Forest environments, in particular, are highlighted because of their important ecological function. We quantified atmospheric Nr concentrations and deposition over four years of continuous monitoring in a southeast Tibetan boreal forest ecosystem, an ecosystem in which forest biomass and carbon density are high around the world. Average annual bulk Nr deposition was 3.00 kg N ha&minus, 1 y&minus, 1, with those of reduced and oxidized species estimated at 1.60 and 1.40 kg N ha&minus, 1, respectively. Bulk deposition of both NH4+ and NO3&minus, were controlled by precipitation amount: both Nr deposition and precipitation were highest in summer and lowest in winter. Dry deposition of NH3 and NO2 were 1.18 and 0.05 kg N ha&minus, 1, respectively. Atmospheric NH3 concentrations were in the range 1.15&ndash, 3.53 mg N L&minus, 1, highest in summer and lowest in winter. In contrast, no clear trend in seasonal NO2 concentrations was observed. Monthly NO2 concentrations were 0.79&ndash, 1.13 mg N L&minus, 1. Total Nr deposition (bulk plus dry) was 4.23 (3.00 + 1.23) kg N ha&minus, 1 in the forest. Reduced nitrogen was the dominant species. In conclusion, Nr deposition was in the range at which forest net productivity and carbon sequestration are sensitive to any variation in nitrogen input, so quantification of Nr deposition should continue and with greater detail.

The Atlantification of the European Arctic has been an increasingly discussed topic in polar science over the past two decades. The alteration of local marine ecosystems towards a more temperate state and the appearance/range expansion of subarctic-boreal species at higher latitudes is a complex phenomenon induced mainly by the changing properties of Atlantic water (AW) transported from the south. Areas under the direct influence of AW experience biological Atlantification of their communities on all trophic levels, resulting in the growing complexity of arctic food webs. Here, besides summarising the main documented messages of biological Atlantification, we take a critical view on the threat posed on Arctic marine communities. We take into account the formation of the Arctic marine fauna, as well as the nature of (re)colonisation of Arctic sites by boreal organisms when evaluating the extent of the issue. We take a look at the history of Arctic colonisations by boreal organisms in an attempt to identify ‘neonative taxa returning home’. We also highlight the role of floating plastic debris as an ‘instrument from the toolbox of the Anthropocene’ aiding the distribution of marine taxa.

Gross primary production (GPP) quantifies the photosynthetic uptake of carbon by the terrestrial ecosystem. Positive GPP extremes represent the potential capacity of the terrestrial ecosystem to uptake carbon dioxide. Studying the positive GPP extreme is vital for the global carbon cycle and mitigation of global warming. With increasing climate extreme events, many kinds of research focus on studying negative GPP and the negative impact of climatic extremes on GPP. There is still a lack of research on positive GPP extremes and whether climatic extremes could be beneficial to global carbon uptake. In this study, we used daily Boreal Ecosystem Productivity Simulator (BEPS) to simulate GPP of the global terrestrial ecosystem during 1982-2016 and combined TRENDY models to detect positive GPP extremes and investigate the effects of climate extremes on GPP. We found the results of the TRENDY models have large differences in some areas of the globe, and the BEPS model driven by remote sensing data could be more suitable for simulating the long-term time series of global terrestrial GPP. Compared to other plant functional types, grasslands contributed the most to positive GPP extremes, accounting for approximately 41.6% (TRENDY) and 34.8% (BEPS) of the global positive GPP extremes. The probabilities of positive GPP extremes caused by positive precipitation extremes were significantly higher than those caused by temperature and radiation in most areas of the globe, indicating that sufficient precipitation (not a flood) would boost the carbon uptake ability of the global terrestrial ecosystem to form positive GPP extremes. On the contrary, the partial correlation coefficients between temperature and GPP were negative in most areas of globe, suggesting that global warming will not be conducive to carbon uptake of the terrestrial ecosystem. This study may provide new knowledge on the global positive GPP extremes.

Boreal forests are one of the largest stores of carbon on Earth, and two-thirds of them are located in Siberia. Despite the fact that these forests have a significant influence on the global climate, they continue to remain understudied. Chernevaya taiga is a unique example of a highly productive Siberian boreal ecosystem. This type of forest is characterized by a series of unique ecological traits, the most notable of which are the gigantism of the perennial herbaceous plants and bushes, complete lack of moss cover on soil surface, and the type of soil it grows on, notable for its particularly high rate of decomposition of vegetative remains and low humic acid content. Abundant rainfall actively washes out nutrients from the top layers of the soil, but its fertility level remains very high. In fact, based on the existing data, it is twice as high as that of fertilized agricultural lands. In some ways the conditions within this type of forest closely resemble those observed in tropical rainforests. Microbiota associated with soil and plants represent an integral part of an interconnected system and contribute significantly to productive processes in soils. Its impacts on the environment require further study, since it could lead to discoveries that will help improve soil fertility without harming the natural environment.

Boreal forest has played a role as sink of atmospheric CO2 due to the slow growth of black spruce; however, changes in source of atmospheric CO2 by forest fires and recent warming have significantly triggered modulation in physiological ecology and biogeochemistry over the boreal forest of Alaska. This chapter describes recent research findings in boreal forest ecosystem of Alaska: (1) the forest aboveground biomass (AGB) with field survey data and satellite data, (2) latitudinal gradients of phenology with time-lapsed camera and satellite data, (3) spatio-temporal variation of leaf area index (LAI) with the analysis of satellite data, (4) latitudinal distribution of winter and spring season soil CO2 emission, and (5) successional changes in CO2 and energy balance after forest fires. As a result, mapping of forest AGB is useful for the evaluation of vegetation models and carbon stock in the biogeochemical cycle. Latitudinal distribution of phenology understands the recent and future phenological changes including post-fire recovery forests. Interannual variation of LAI shows the leaf dynamics and near-surface remote-sensing approaches with the analyses of time-lapsed digital camera and satellite data. Spring carbon contributions are sensitive to subtle changes in the onset of spring. Vegetation recovery after forest fire is the major driver of the carbon balance in the stage of early succession. Increasing soil carbon emission in response to abrupt climate warming in Alaska is a significant driver of carbon balance.

A 3800 year-long radiocarbon-dated and highly-resolved palaeoecological record from Lake Fimon (N-Italy) served to investigate the effects of potential teleconnections between North Atlantic and mid-to-low latitudes at the transition from Marine Isotope Stage (MIS) 3 to 2. Boreal ecosystems documented in the Fimon record reacted in a sensitive way to millennial and sub-millennial scale Northern Hemisphere atmospheric circulation patterns. The high median time-resolution of 58 years allows the identification of five abrupt event-boundaries (i.e., main forest expansion and decline excursions) synchronous with the sharp stadial/interstadial (GS/GI) transitions within dating uncertainties. During Heinrich Stadial 3 (HS 3) we reconstruct more open and dry conditions, compared to the other GS, with a dominant regional scale fire signal. Linkages between local fires and climate-driven fuel changes resulted in high-magnitude fire peaks close to GI/GS boundaries, even exacerbated by local peatland conditions. Finally, palaeoecological data from the HS 3 interval unveiled an internal variability suggesting a peak between 30,425 and 29,772 cal BP (2σ error) which matches more depleted δ18O values in alpine speleothems. We hypothesise that this signal, broadly resembling that of other mid-latitudes proxies, may be attributed to the southward shift of the Northern Hemisphere storm tracks and the associated delayed iceberg discharge events as documented during other HS.

Fire severity affects both ecosystem N-loss and post-fire N-balance. Climate change is altering the fire regime of interior Alaska, although the effects on Siberian alder (Alnus viridis ssp. fruticosa) annual N-fixation input (kg N ha-1 yr-1) and ecosystem N-balance are largely unknown. We established 263 study plots across two burn scars within the Yukon-Tanana Uplands ecoregion of interior Alaska. Siberian alder N-input was quantified by post-fire age, fire severity, and stand type. We modeled the components of Siberian alder N-input using environmental variables and fire severity within and across burn scars and estimated post-fire N-balance using N-loss (volatilized N) and N-gain [biological N-fixation and atmospheric deposition]. Mean nodule-level N-fixation rate was 70% higher 11-years post-fire (12.88 ± 1.18 μmol N g-1 hr-1) than 40-years post-fire (7.58 ± 0.59 μmol N g-1 hr-1). Structural equation modeling indicated that fire severity had a negative effect on Siberian alder density, but a positive effect on live nodule biomass (g nodule m-2 plant-1). Post-fire Siberian alder N-input was highest in 11-year old moderately burned deciduous stands (11.53 ± 0.22 kg N ha-1 yr-1), and lowest in 11-year old stands that converted from black spruce to deciduous dominance after severe fire (0.06 ± 0.003 kg N ha-1 yr-1). Over a 138-year fire return interval, N-gains in converted black spruce stands are estimated to offset 15% of volatilized N, whereas N-gains in burned deciduous stands likely exceed volatilized N by an order of magnitude. High Siberian alder density and nodule biomass drives N-input in burned deciduous stands, while low N-fixer density (including Siberian alder) limits N-input in high severity black spruce stands not underlain by permafrost. A severe fire regime that converts black spruce stands to deciduous dominance without alder recruitment may induce progressive N-losses which alter boreal forest ecosystem patterns and processes.

Cyclic fluctuations in abundance exhibited by some mammalian populations in northern habitats ("population cycles") are key processes in the functioning of many boreal and tundra ecosystems. Understanding population cycles, essentially demographic processes, necessitates discerning the demographic mechanisms that underlie numerical changes. Using mark-recapture data spanning five population cycles (1977-2017), we examined demographic mechanisms underlying the 9-10-yr cycles exhibited by snowshoe hares (Lepus americanus Erxleben) in southwestern Yukon, Canada. Snowshoe hare populations always decreased during winter and increased during summer; the balance between winter declines and summer increases characterized the four, multiyear cyclic phases: increase, peak, decline, and low. Little or no recruitment occurred during winter, but summer recruitment varied markedly across the four phases with the highest and lowest recruitment observed during the increase and decline phase, respectively. Population crashes during the decline were triggered by a substantial decline in winter survival and by a lack of subsequent summer recruitment. In contrast, initiation of the increase phase was triggered by a twofold increase in summer recruitment abetted secondarily by improvements in subsequent winter survival. We show that differences in peak density across cycles are explained by differences in overall population growth rate, amount of time available for population growth to occur, and starting population density. Demographic mechanisms underlying snowshoe hare population cycles were consistent across cycles in our study site but we do not yet know if similar demographic processes underlie population cycles in other northern snowshoe hare populations.

The Red List of Ecosystems, proposed by the International Union for Conservation of Nature can determine the status of ecosystems for biodiversity conservation. In this study, we applied the Red List of Ecosystems Categories and Criteria 2.0 with its four major criteria (A, B, C, and D) to assess twelve dominant ecosystems in the Xilin River Basin, a representative grassland-dominating area in China. We employed Geographical Information Systems and remote sensing to process the obtained satellite products from the years 2000 to 2015, and generated indicators for biological processes and degradation of environment with boreal ecosystem productivity simulator. The results show that all twelve ecosystems in the Xilin River Basin confront varying threats: Artemisia frigida grassland and Festuca ovina grassland face the highest risk of collapse, sharing an endangered status, Filifolium sibiricum meadow grassland and Leymus chinensis grassland have a least concern status, while the remaining eight ecosystems display a vulnerable status. This study overcomes the limits of data deficiency by introducing the boreal ecosystem productivity simulator to simulate biological processes and the plant&ndash, environment interaction. It sheds light on further application of the Red List of Ecosystems, and bridges the research gap and promote local ecosystems conservation in China.

Boreal forests provide important ecosystem services, most notably being the mitigation of increasing atmospheric CO2 emissions. Microbial biodiversity, particularly the local diversity of fungi, has been shown to promote multiple functions of the boreal forests of Northeastern China. However, this microbial biodiversity-multifunctionality relationship has yet to be explored in Northeastern Canada, where historical environment have shaped a different regional pool of microbial diversity. This study focuses on the relationship between the soil microbiome and ecosystem multifunctionality, as well as the influence of pH and redox potential (Eh) on the regulation of such relationship. Structural equation modelling (SEM) was used to explore the different causal relationships existing in the studied ecosystems. In a managed part of the Canadian boreal forest, 156 forest polygons were sampled to (1) estimate the &alpha, and &beta, diversity of fungal and bacterial communities and (2) measure 12 ecosystem functions mainly related to soil nutrient storage and cycling. Both bacteria and fungi influenced ecosystem multifunctionality, but on their own respective functions. Bacterial &beta, diversity was the most important factor increasing primary productivity and soil microbial biomass, while reducing soil emitted atmospheric CO2. Environmental characteristics, particularly low levels of organic matter in soil, were shown to have the strongest positive impact on boreal ecosystem multifunctionality. Overall, our results were consistent with those obtained in Northeastern China, however, some differences need to be further explored especially considering the history of forest management in Northeastern Canada.

Rodents are classical model species to investigate spatial synchrony in population fluctuation. Yet, previous studies have been strongly biased geographically toward high latitude (boreal ecosystem) and limited in their spatial scale, i.e., few sampling sites separated by a few tens of kilometers. Both aspects currently limit our understanding of rodent population dynamics across space. In this study we investigate vole population synchrony at a large spatial scale in central Europe. We used long-term breeding success of a vole-eating raptor specialist, the European kestrel, as an indicator of vole abundance. We first demonstrate that the productivity of kestrels is highly dependent on the availability of voles and as such is a good proxy of vole abundance. Secondly, we assessed the spatial synchrony of kestrel productivity and its scaling. We found that kestrel productivity fluctuated synchronously at a large spatial scale, up to a distance of 300 km. This result suggests that vole populations in central Europe varied in synchrony at large spatial scales, similarly as in northern latitudes. The most likely mechanism resulting in such large scale synchrony of vole populations is synchronized density-independent environmental conditions.

Climate impacts agriculture in various complex ways at different levels and scales depending on the local natural crop growth limitations. Our objective in this study, therefore, is to understand how different is the atmosphere–biosphere exchange of CO2 under contrasting subtropical and boreal agricultural (an oilseed crop and a bioenergy crop, respectively) climates. The oilseed crop in subtropical climate continued to uptake CO2 from the atmosphere throughout the year, with maximum uptake occurring in the monsoon season, and drastically reduced uptake during drought. The boreal ecosystem, on the other hand, was a sustained, small source of CO2 to the atmosphere during the snow-covered winter season. Higher rates of CO2 uptake were observed owing to greater day-length in the growing season in the boreal ecosystem. The optimal temperature for photosynthesis by the subtropical ecosystem was close to the regional normal mean temperature. An enhanced photosynthetic response to the incident radiation was found for the boreal ecosystem implying the bioenergy crop to be more efficient than the oilseed crop in utilizing the available light. This comparison of the CO2 exchange patterns will help strategising the carbon management under different climatic conditions.

Plants have the capacity to alter their phenotype in response to environmental factors, such as herbivory, a phenomenon called phenotypic plasticity. However, little is known on how plant responses to herbivory are modulated by environmental variation along ecological gradients. To investigate this question, we used bilberry (Vaccinium myrtillus L.) plants and an experimental treatment to induce plant defenses (i.e., application of methyl jasmonate; MeJA), to observe ecological responses and gene expression changes along an elevational gradient in a boreal system in western Norway. The gradient included optimal growing conditions for bilberry in this region (ca. 500 m a.s.l.), and the plant's range limits at high (ca. 900 m a.s.l.) and low (100 m a.s.l.) elevations. Across all altitudinal sites, MeJA‐treated plants allocated more resources to herbivory resistance while reducing growth and reproduction than control plants, but this response was more pronounced at the lowest elevation. High‐elevation plants growing under less herbivory pressure but more resource‐limiting conditions exhibited consistently high expression levels of defense genes in both MeJA‐treated and untreated plants at all times, suggesting a constant state of “alert.” These results suggest that plant defense responses at both the molecular and ecological levels are modulated by the combination of climate and herbivory pressure, such that plants under different environmental conditions differentially direct the resources available to specific antiherbivore strategies. Our findings are important for understanding the complex impact of future climate changes on plant–herbivore interactions, as this is a major driver of ecosystem functioning and biodiversity., We used bilberry (Vaccinium myrtillus L.) ramets and an experimental treatment to simulate herbivory by inducing plant defenses (application of methyl jasmonate; MeJA), to observe ecological responses and gene expression along an elevational gradient in a boreal system in western Norway. Across all altitudinal sites, MeJA‐treated plants allocated more resources to herbivory resistance while reducing growth and reproduction, but this response to simulated herbivory was more pronounced at the lowest altitude. These results suggest that plant defense responses at both the molecular and ecological levels are modulated by the combination of climate and herbivory pressure, such that plants under different environmental conditions differentially direct the resources available to specific antiherbivore strategies.

The Arctic may seem remote, but the unprecedented environmental changes occurring there have important consequences for global society. Of all Arctic system components, changes in permafrost (perennially frozen ground) are one of the least documented. Permafrost is degrading as a result of climate warming, and evidence is mounting that changing permafrost will have significant impacts within and outside the region. This review asks: What are key structural and functional properties of ecosystems that interact with changing permafrost, and how do these ecosystem changes affect local and global society? Here, we look beyond the classic definition of permafrost to include a broadened focus on the composition of frozen ground, including the ice and the soil organic carbon content, and how it is changing. This ecological perspective of permafrost serves to identify areas of both vulnerability and resilience as climate, ecological disturbance regimes, and the human footprint all continue to change in this sensitive and critical region of Earth.

In temperate forests, red wood ants (Formica aquilonia) are considered ecosystem engineers affecting ecosystem properties and functions. Possible effects of F. aquilonia ants on species communities of invertebrates and plants were studied in the pine-dominated Geitaknottane forest reserve, Norway. Species richness of carabids, lichens and epiphytes (tree-living lichens and bryophytes) was negatively affected by ant mound density. Species of all groups, except for lichens and snails, were affected either positively or negatively by ant presence. Food availability and interference competition are plausible explanations of decreased species richness and negative species associations in carabids; while collecting, foraging and changed chemical environment may explain decreased species richness in lichens and epiphytes. Thirteen out of 15 plant and invertebrate species were weakly associated with ant mound density. Associations of only two species (Carabus violaceus and Drusilla canaliculata) were negative, while Pella humeralis and Agroeca proxima were associated positively and very strongly with ant mounds. Positive associations with ants of those invertebrates may be a response to excessive abundance of food and chemical mimicry.

Custom-built HNO3(g) passive diffusion-based samplers employing nylon filters were comprehensively quality assurance and quality control (QA/QC) tested, including analysis of the PTFE protective filters for potential bias. The passive samplers routinely quantified HNO3(g) mixing ratios in the Canadian boreal up to a factor of 20 lower compared to previous passive sampling dose-response determination and measurements. The use of appropriate blanks alongside field collections resulted in the detection of time-weighted mixing ratios as low as 5 parts per trillion by volume (pptv) over a monthly sampling period or 121 pptv over a 24-h sampling period. The nylon filters were tested for a single reuse to reduce resources required and no statistical difference between the measured mean value of reused and new filters between five replicates across four intercomparisons was found. This showed that a single nylon filter reuse in remote regions is sound as long as replicates are employed. The custom-built passive samplers were installed along the Newfoundland and Labrador – Boreal Ecosystem Latitudinal Transect (NL-BELT) to quantify mixing ratios of HNO3(g) in these forests. Samples generated monthly time-weighted average mixing ratios at the NL-BELT field regions. Samples were collected monthly across 15 months from the summer of 2015 through to the fall of 2016 on the order of tens to a hundred pptv. Across this time period the HNO3(g) mixing ratios ranged from 9 to 200 pptv – after incorporation of comprehensive field QA/QC – with seasonal maxima occurring during the early summer months. No consistent latitudinal trends were observed along the transect, except that the most northern region always corresponded to the lowest mixing ratios of HNO3(g) for a given observation period. Extracts of the protective PTFE filter and collocated measurements of temperature and humidity determined that previously uncertain effects on sampling accuracy likely result in a negative sampling bias of 10–30%. These unpowered devices are now demonstrated to be sensitive, affordable, simple, and redeployable for the continuous ultra-trace detection of HNO3(g) in regions such as the remote Canadian boreal forest.

Browsing by ungulates may induce plant responses and affect subsequent plant food quality for other animals. Populations of many deer species have increased to unprecedented levels in Europe and North America. In Norway, population densities of red deer (Cervus elaphus) have increased over the past decades, but little is known about how increased deer browsing pressure may change the palatability of key food plants for other taxa in the boreal ecosystem. We conducted a cafeteria experiment to assess if long-term deer-browsing intensity affected the palatability of bilberry (Vaccinium myrtillus) leaves for leaf-eating larvae (mainly Lepidoptera). We found that leaf-eating insect larvae preferred bilberry leaves from the lightly browsed bilberry plants; the larvae consumed twice as much leaf biomass from the lightly browsed plants than from the unbrowsed and moderately browsed ones, and four times more than from highly browsed plants. Larvae never selected leaves from highly browsed plants as their first choice. Our study suggests that browsing-induced changes in the quality of shared food plants may be important in mediating indirect interactions between browsers of widely separated taxa. Whereas low levels of long-term red deer browsing increases the palatability of bilberry leaves for leaf-eating larvae, high browsing pressure reduces food consumption. Whether changes in palatability lead to changes in population densities of leaf-eating larvae remains to be studied, but any such adverse effects could have cascading ecological consequences for insectivorous birds and mammals.