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Permafrost soils in arctic and boreal ecosystems store twice the amount of current atmospheric carbon that may be mobilized and released to the atmosphere as greenhouse gases when soils thaw under a warming climate. This permafrost carbon climate feedback is among the most globally important terrestrial biosphere feedbacks to climate warming, yet its magnitude remains highly uncertain. This uncertainty lies in predicting the rates and spatial extent of permafrost thaw and subsequent carbon cycle processes. Terrestrial ecosystem influences on surface energy partitioning exert strong control on permafrost soil thermal dynamics and are critical for understanding permafrost soil responses to climate change and disturbance. Here we review how arctic and boreal ecosystem processes influence permafrost soils and characterize key ecosystem changes that regulate permafrost responses to climate. While many of the ecosystem characteristics and processes affecting soil thermal dynamics have been examined in isolation, interactions between processes are less well understood. In particular connections between vegetation, soil moisture, and soil thermal properties affecting permafrost conditions could benefit from additional research. In particular, connections between vegetation, soil moisture, and soil thermal properties affecting permafrost could benefit from additional research. Changes in ecosystem distribution and vegetation characteristics will alter spatial patterns of interactions between climate and permafrost. In addition to shrub expansion, other vegetation responses to changes in climate and disturbance regimes will all affect ecosystem surface energy partitioning in ways that are important for permafrost. Lastly, changes in vegetation and ecosystem distribution will lead to regional and global biophysical and biogeochemical climate feedbacks that may compound or offset local impacts on permafrost soils. Consequently, accurate prediction of the permafrost carbon climate feedback will require detailed understanding of changes in terrestrial ecosystem distribution and function and the net effects of multiple feedback processes operating across scales in space and time.

We constructed a bi-directional reflectance distribution function (BRDF) observation system on a 25-m-high tower surrounded by mature larch forests at the foot of Mt. Yatsugatake, central Japan. The BRDF feature (strong/weak reflections in a backward/forward scattering areas) is related closely to the 3D structure and biophysical parameters of forests. However, because of the difficulty of observations, observational BRDF data of mature forests are scarce, except for those of Boreal Ecosystem –Atmosphere Study (BOREAS). We made BRDF observations 10 times during 2007 to ascertain BRDF characteristics in each season. For comparison to these BRDF data, a semi-empirical BRDF model (Ross–thick Li–sparse kernel model) was introduced. This model can reproduce the BRDF data fairly well under identical solar conditions in each season. Then, seasonal changes of the vegetation structure and possible relations with BRDF were discussed. They are summarized as follows: (1) The forest BRDF changes distinctly and seasonally depending on the phenology. (2) The forest BRDF is influenced primarily by clarity of the geometrical profile on the forest surface, which is affected by shadow. However, the forest BRDF might be influenced by other factors such as the physiological characteristics of leaves and slight change of vegetation structure such as forest floor conditions and leaf angles during summer. (3) Features of forest BRDF must therefore appear during summer when the crown shape is distinctive. Furthermore, BRDF features appear distinctly as seasons progress, e.g., by autumn leaves and defoliation, when the unevenness of forests increases. These findings can promote monitoring of vegetation using multi-angular satellite observations.

Changes in large herbivore distribution and abundance can have effects that potentially cascade throughout the trophic structure of an ecosystem. Little is known about these indirect trophic effects of ungulate herbivory, so the aim of this study was to investigate the role of red deer (Cervus elaphus) in determining the distribution and diversity of ground-dwelling beetles. We collected > 9000 beetles belonging to 149 species in a Western Norway boreal forest by pitfall trapping inside and outside red-deer exclosures placed along a gradient in herbivory intensity. Our study showed that red deer herbivory had a significant effect on structuring ground beetle communities in this boreal ecosystem. Key findings were that: (1) out of 17 beetle species represented by more than 100 specimens, four species benefited from red deer herbivory and associated impacts, while two were detrimentally affected; 2) red deer herbivory did not affect beetle abundance or alpha diversity, but increased local variation in beetle community structure (higher beta diversity); and 3) red deer browsing is important for the composition of the ground-beetle fauna. Herbivory improved the explanation of variation in beetle species composition on the forest floor by 40%. Given that herbivory is an indirect but central predictor of ground-dwelling beetle communities, it should be included in future studies or monitoring programs of red listed or keystone ground-dwelling beetles.

In the face of increasing temperature at high latitudes, ecosystem respiration (RE) is a key to determining sink and source dynamics of a boreal forest. In this paper, we analyzed four-year RE data obtained in an open black spruce forest—a typical boreal forest ecosystem with permafrost in Interior Alaska. RE measured as nighttime CO2 effluxes for both the ecosystem and the forest floor were clearly situated along the exponential temperature-dependent curve, except for the data obtained in extremely dry conditions in mid-summer. More than 93 % of RE data measured at nighttime with high vapor pressure deficit (VPD > 400 Pa) were lower than the values predicted from the temperature-dependent curve. Consequently, the year 2013 (with an unusually dry summer) had a 15 % lower amount of annual RE than that could be expected from the temperature-dependent curve without considering the effect of high VPD. The suppression of RE under dry conditions was also related to decreases in soil moisture and net ecosystem productivity. Finally, assuming daytime RE could be extrapolated from the temperature-dependent curves, annual daytime RE estimated with the effect of high VPD was decreased by up to 62% from RE estimated without the VPD effect. The down-regulation of RE presented in this study postulates a possible negative feedback for the carbon budget of boreal forests in response to climate warming.

Background In the summer of 2015, hundreds of wildfires burned across the state of Alaska, and consumed more than 1.6 million ha of boreal forest and wetlands in the Yukon–Koyukuk region. Mapping of 113 large wildfires using Landsat satellite images from before and after 2015 indicated that nearly 60% of this area was burned at moderate-to-high severity levels. Field measurements near the town of Tanana on the Yukon River were carried out in July of 2017 in both unburned and 2015 burned forested areas (nearly adjacent to one-another) to visually verify locations of different Landsat burn severity classes (low, moderate, or high; LBS, MBS, HBS). Results Field measurements indicated that the loss of surface organic layers in boreal ecosystem fires is a major factor determining post-fire soil temperature changes, depth of thawing, and carbon losses from the mineral topsoil layer. Measurements in forest sites showed that soil temperature profiles to 30 cm depth at burned forest sites were higher by an average of 8–10 °C compared to unburned forest sites. Sampling and laboratory analysis indicated a 65% reduction in soil carbon content and a 58% reduction in soil nitrogen content in severely burned sample sites compared to soil mineral samples from nearby unburned spruce forests. Conclusions Combined with nearly unprecedented forest areas severely burned in the Interior region of Alaska in 2015, total ecosystem fire-related losses of carbon to the atmosphere exceeded most previous estimates for the state, owing mainly to inclusion of potential “mass wasting” and decomposition in the mineral soil carbon layer in the 2 years following these forest fires.

Positive net ecosystem productivity (NEP) extreme represents an extreme carbon sink in the terrestrial ecosystem. Studying positive NEP extremes and their control mechanisms is vital for a better understanding of the carbon cycle and mitigation of global warming. However, there are still challenges and difficulties in quantifying positive NEP extremes and finding optimal climate conditions to form them in China's terrestrial ecosystems. In this study, we used the Boreal Ecosystem Productivity Simulator (BEPS) to detect and reveal the control mechanisms of NEP extremes in China's terrestrial ecosystems. We found the positive NEP extremes occurred in 2002, 2012, and 2015, with the detrended NEP anomalies of 0.15 Pg C yr−1, 0.11 Pg C yr−1, and 0.09 Pg C yr−1, respectively. Also, the three positive NEP extremes contributed 70% of the NEP uptrend during 2000–2016. Evergreen needle-leaf forests and croplands in the subtropical-tropical monsoonal region played dominant roles in the positive NEP extremes, accounting for 34.2% and 32.6% in the positive NEP extremes on average, respectively. The relationship between the anomalies of Gross primary production (GPP) and NEP was significant (P 0.001). These results mean that GPP (rather than Re) played a decisive role in the positive NEP extremes. Also, the best climate conditions for carbon uptake in the subtropical-tropical region have temperature anomalies ranging from −1.0 to 0.5 °C, and precipitation anomalies ranging from 0 to 600 mm. This study provides new knowledge on the potential carbon sink scientific and technological support for mitigating climate warming in China's terrestrial ecosystem.

It remains challenging to interpret seasonal profile of vegetation dynamics from empirical indices NDVI and EVI for boreal forests due to confounding impacts of snow, soil and snowmelt in winter and spring. This work aims to characterize the seasonally snow-covered Howland boreal forest ecosystem in Maine, USA with the Moderate Resolution Imaging Spectrometer (MODIS) images. Vegetation cover fraction (VGCF), fractional absorption of photosynthetically active radiation (fAPAR) by all canopy components (fAPARcanopy), fAPAR by canopy chlorophyll (fAPARchl) and fAPAR by canopy non-chlorophyll components (fAPARnon-chl) were extracted from MODIS images in multiple years (2001 - 2014). Snow exposed during December to April. Top of canopy viewable snow cover fraction in April of multiple years varied between 0.02 and 0.16 (0.06 ± 0.04). Seasonal VGCF and fAPARcanopy showed a summer plateau (VGCF: 0.97 ± 0.01; fAPARcanopy: 0.90 ± 0.01). Both seasonal fAPARchl and fAPARnon-chl changed with time, and seasonal fAPARnon-chl had a bimodal shape. Spring VGCF varied between 0.54 and 0.69 (0.61 ± 0.04). Spring fAPARchl and fAPARnon-chl were 0.22 ± 0.03 and 0.21 ± 0.02, respectively. Peak summer fAPARchl was 0.58 ± 0.02. The lowest summer fAPARnon-chl was 0.32 ± 0.02. Replacing fAPARcanopy with fAPARchl to simulate boreal forest ecosystem gross primary production (GPP) could reduce uncertainties in GPP simulations.

Nitrogen (N) addition effects on boreal forest ecosystem are influenced by an interplay between N-form and N-dose. We hypothesize that trees take up organic N more efficiently than inorganic N and that unwanted side-effects of organic N are smaller. We predicted that 1) the tree growth response to arginine (ARG) addition is larger than to ammonium-nitrate (AN) and, 2) understory vegetation and ectomycorrhizal (EcM) changes following ARG addition are smaller than following AN addition. We investigated the effects of AN and ARG addition (50 and 150 kg N ha−1) during five years on tree growth, understory vegetation and EcM fungi in a Pinus sylvestris L. forest (c 50 years old) in northern Sweden. N addition increased tree growth and changed understory vegetation composition with few significant differences between AN and ARG. Differences in responses mainly occurred for the bryophyte Pleurozium schreberi which decreased more from ARG, and for EcM sporocarps, which sharply declined from AN, but not from ARG. We found very few differences in responses between AN and ARG addition with the exception of EcM and bryophytes. These species groups have several key functions in boreal forests and the differences in responses merits further investigations.

Boreal forests account for roughly one third of the carbon sequestered in terrestrial ecosystems, and the high-latitude boreal ecosystem they make up has been consequently vulnerable to recent climate change. This study investigated stem respiration of Alaska dominant black spruce trees in interior Alaska during the growing season of 2007. The continuous measurement of stem respiration was conducted in black spruce trees of four different ages (4.3, 7.2, 9.8, and 13.5 cm in diameter at breast height (DBH)) in interior Alaska, using a CO2 analyzer, a 12-V pump, chambers, and a data-logger. Mean stem respiration is 0.014 ± 0.006 mg CO2 m−2 s−1 (range 0.003–0.039 mg CO2 m−2 s−1) in different aged four black spruce trees, indicating remarkably temporal variations in stem respiration with temperatures in air and stem. We found that metabolism is 1.5-fold higher in the younger black spruce tree than in the older. Temperatures in air and stem are significant regulators in regulating stem respiration. The stand-level annual stem respiration simulated by Q10 value based on air temperature is 73.9 g CO2 m−2, corresponding to 5.0% of the ecosystem respiration (Re) estimated by eddy covariance tower in 2007. Our findings demonstrate that stem respiration is a significant component in the scale-up of the regional carbon budget in a black spruce forest of interior Alaska.

Permafrost degradation due to climate warming would potentially increase the release of previously frozen soil carbon and change the carbon budget of the cold region ecosystem. The underlying permafrost degradation would be effectively mediated by soil surface freezing-thawing (FT) processes. Aboveground vegetation can regulate soil FT processes, however its effects on ground thermal transfer have not been well represented by ecosystem models. In this study, we improved the hydrothermal module of the Boreal Ecosystem Productivity Simulator (BEPS) through more careful parameterization of snowpack density, puddled water, soil organic matter and super-cooled soil water. The impacts of vegetation on the soil surface FT processes have also been investigated using the improved BEPS model and the measured soil temperature data at forest and grassland sites on the southern edge of permafrost region in Mongolia and northeastern China. The improved BEPS model performs better than the original model in simulations of soil temperature and soil FT processes. Smaller amplitudes of soil diurnal FT cycles were found in forest sites compared to grassland sites. Forest sites have delayed soil thaw timing and similar soil freezing time compared to grassland sites. Differences in snow depths and soil organic matter content due to distinct vegetation community structures have considerable influences on the disparity in soil FT processes. Thus, it is important to improve the simulation of the impacts of vegetation on soil surface FT processes for better forecasting the permafrost degradation.

The gross primary productivity (GPP) is the largest carbon flux in the terrestrial carbon cycle. Constraining GPP is critical for understanding the terrestrial carbon sources and sinks. In this study, we attempted to constrain the terrestrial GPP at regional to global scales through optimizing the key photosynthetic parameter (the carboxylation capacity at 25 °C, V c m a x 25 ) using solar-induced chlorophyll fluorescence (SIF) observations from the Orbiting Carbon Observatory-2 (OCO-2). The optimization was made within the Global Carbon Assimilation System (GCAS), in which the Boreal Ecosystem Productivity Simulator (BEPS) model was used to simultaneously simulate the global GPP and SIF in the process-based manner. Optimized V c m a x 25 shows a distinguishable spatial pattern, with the largest values over the crop regions. After optimization, V c m a x 25 of crop is significantly increased. Importantly, the optimized V c m a x 25 of different plant functional types (PFTs) show unambiguous seasonal variations. With these optimized V c m a x 25 , the simulated global GPP in 2015–2016 amounts to 119.1 PgC yr−1, close to the median value (121.3 PgC yr−1) of the observation-based estimates. Global GPP decreases by 8.3% relative to the value simulated using prior V c m a x 25 . In detail, GPP of crops increases by 16.4%, but it decreases over the other PFT regions, ranging from −4.4% over grasses to −34.0% over deciduous needleleaf forests. The spatiotemporal variations in the optimized PFT-dependent V c m a x 25 also reshape the seasonal cycle in GPP. We regard that it is an effective pathway to constrain GPP based on the satellite SIF and the process-based assimilation system, which can provide us an opportunity to better understand the terrestrial and global carbon cycle.

Implementing multi-use forest management to account for both commercial and non-commercial ecosystem services is gaining increased global recognition. Despite its spatial extent, and great economic and ecological values, few studies have evaluated the boreal forest and its management to assess the potential for simultaneous delivery of a suite of ecosystem services. Using data from a Swedish long-term experiment, this study explores how biodiversity of the ground vegetation and potential delivery of multiple ecosystem services (timber production, carbon [C] storage and non-timber forest products) are influenced by two common silvicultural practices (thinning, fertilization and their interaction). Diversity (diversity indices and species richness) of the ground vegetation was higher in thinned than in unthinned forest, a result attributable in part to six species of lichens that only occurred in thinned forest. In addition, supply of lichens for reindeer forage was three times higher in thinned forest. Fertilization negatively affected the lingonberry shrub (Vaccinium vitis-idaea). Timber production increased with fertilization, but decreased with thinning. The potential for C storage was highest in fertilized forests, which, apart from having the highest timber production, also supported the highest standing tree biomass. The silvicultural practices evaluated induced trade-offs among the ecosystem features studied as thinning increased biodiversity of the ground vegetation, production potential of wild berries and lichens, but reduced timber production and the potential for C storage. Fertilization had the opposite effect, promoting the potential for C storage at the expense of biodiversity and the ecosystem services delivered by the ground vegetation. Synthesis and applications. Increased multi-use potential is a common goal for forest management in many parts of the world. Our result shows that commonly used silvicultural practices can be used to determine the multi-use output, and might be applied to maintain, or even increase the multi-use potential of the boreal forest biome. Nevertheless, trade-offs among values were common, indicating that the multi-use potential will be limited at the site level. Allowing management objectives to vary across the landscape might, in such cases, be a preferable way to achieve high multi-use potential.

The understory plants of the boreal forests have evolved divergent strategies to succeed under low nitrogen conditions, with their ability to respond to nitrogen addition varying greatly. We examined the response of 5 key understory North American boreal forest species in the Yukon (4 shrubs and a herb) to low levels of nitrogen that could occur from natural pulses and to high levels that could occur because of anthropogenic deposition from either atmospheric deposition or as a management strategy to increase tree growth. We fertilized 240 one m2 plots for the three dwarf shrubs and one herb and 60 three m2 plots for one tall shrub at 0, 0.5, 1.0, 2.0, 4.0, and 17.5 g nitrogen/m2 in June 2004 and May 2005. We measured changes in cover, growth, leaf metrics, and berry production in three dwarf shrubs (Arctostaphylos rubra [deciduous] and A. uva-ursi and Empetrum nigrum [both evergreen]), one herb (Geocaulon lividum), and one tall shrub (Shepherdia canadensis). We predicted the first three would be strongly affected by variation in nitrogen levels but that neither Geocaulon (a hemi-parasite) nor Shepherdia (a nitrogen fixer) would be. To examine for long-term effects of nitrogen application, we also fertilized four 2.8 ha plots in 2004 and 2005 with 1.0 and 2.0 g/m2 and then measured berry production in 2006 and 2007 on the two Arctostaphylos species. Nitrogen addition at all levels had no effect on either Geocaulon or Shepherdia. There were general positive effects at low nitrogen levels and negative ones at high levels on the other 3 dwarf shrub species in a species-specific manner. There were marked year effects in some plant growth metrics and in berry production, emphasizing the role of climate, but also clear evidence that individual species tradeoff somatic growth for reproduction. There was a pronounced long-term negative effect of low nitrogen addition on the large plots, causing marked reductions in berry production in both Arctostaphylos species. We conclude that these dwarf shrubs are constrained to function optimally within a narrow range of nitrogen levels normally encountered, but are unable to cope with higher levels. Both Geocaulon and Shepherdia function independently of nitrogen limitation. Thus the life history adaptations of these understory plants to variation in nitrogen levels are species-specific and understanding their individual responses is key in predicting their fate and the biodiversity and organization of boreal forest ecosystem when challenged with higher anthropogenic levels of nitrogen.

Anthropogenic activities profoundly influence carbon sequestration in the Eurasian Steppe. In particular, grazing has been identified as having a major effect on carbon sequestration. However, the extent to which grazing affects regional patterns or carbon sequestration is unknown. In this study, we evaluated the impact of regional grazing on grassland carbon sequestration using the Boreal Ecosystem Productivity Simulator (BEPS) and the Shiyomi grazing model. Model performances were validated against the results from field measurements and eddy covariance (EC) sites. Model outputs showed that in 2008, the regional net primary productivity (NPP) was 79.5 g C m −2 , and the net ecosystem productivity (NEP) was −6.5 g C m −2 , characterizing the region as a weak carbon source. The Mongol Steppe (MS) was identified as a carbon sink, whereas the Kazakh Steppe (KS) was either carbon neutral or a weak carbon source. The spatial patterns of grazing density are divergent between the MS and the KS. In the MS, livestock was mainly distributed in China with relatively good management, while in the KS livestock was mainly concentrated in the southern countries (especially Uzbekistan and Turkmenistan) with harsh environments and poor management. The consumption percentages of NPP in Turkmenistan, Tajikistan and Uzbekistan were 5.3, 3.3 and 1.2%, respectively, whereas the percentages in other countries were lower than 1%. Correspondingly, grazing consumption contributed to the carbon sources of Turkmenistan, Tajikistan and Uzbekistan by 11.6, 6.3 and 4.3%, respectively, while it weakened the carbon sink in Inner Mongolia, China and Mongolia by 1.6 and 0.5%. This regional pattern should be affected by different sub-regional characteristics, e.g., the continuous degradation of grassland in the southern part of the KS and the restoration of grassland in Inner Mongolia, China.

In an effort to ensure the sustainability of their forests, boreal forest managers often use forest planning models to make future projections of timber supply and other key services, such as habitat for wildlife. Projecting the fate of these services has proven to be challenging, however, as major uncertainties exist regarding the principal drivers of boreal ecosystem dynamics, including the future spatial and temporal distribution of wildfire and timber harvesting. Existing forest planning models are not well suited to dealing with this uncertainty because they produce deterministic projections based on central tendencies of these drivers. Here we present a new approach for incorporating uncertainty into forest management planning, which we demonstrate using two landscapes in the Canadian boreal forest. Our approach takes the assumptions contained within the latest forest management plans for each of these landscapes, including parameterizations of their deterministic forest planning models, and converts these assumptions into equivalent parameterizations of a stochastic, spatially-explicit state-and-transition simulation model (STSM). We then use Monte Carlo simulations with the STSM to “stress-test” the forest management plan with respect to a range of possible future uncertainties, including uncertainties in future levels and patterns of wildfire and timber harvest, along with the possible changes in wildfire that might result from future climate change. Our analysis demonstrates the importance of incorporating stochastic variability into projections of future ecosystem condition. The STSM projections that acknowledged variability in wildfire and timber harvest differed from the deterministic forest planning model projections that were based solely on mean values. Our analysis also suggests that there is an increased risk of shortfalls in timber harvest, for both boreal landscapes, associated with future projections for changes in wildfire due to climate change, and that management strategies aimed at reducing the future level of timber harvest offer an opportunity to mitigate these risks. We believe our approach provides a new risk-based framework for incorporating uncertainty into forest management, including the effects of climate change.

Bamboo forests are widely distributed in the tropical and sub-tropical regions, and have a great carbon sequestration capacity. However, the carbon dynamics of bamboo forest are still poorly understood. This study developed an algorithm for assimilating LAI dynamics based on an integrated ensemble Kalman filter using MODIS LAI data, MODIS reflectance data, and canopy reflectance data modeled by PROSAIL for two typical bamboo forests. The assimilated LAI was highly consistent with the observed LAI, yielding correlation coefficient ( r ) of 0.84 and 0.94 for Moso bamboo forest and Lei bamboo forest, respectively. Then, the spatiotemporal pattern of the CO 2 fluxes within bamboo forest were modeled for Zhejiang Province during 2011–2014 using the Boreal Ecosystem Productivity Simulator model driven by assimilated LAI. The modeled CO 2 fluxes were in agreement with the CO 2 fluxes measured by eddy covariance technology at two selected sites within the study region. Average r , absolute deviation, and root mean square error values were 0.77, 0.65 g C m −2 day −1 , and 0.82 g C m −2 day −1 , respectively. Bamboo stands with high Net Ecosystem Exchange (NEE) values were found to be distributed throughout mountainous areas in the northwest, southwest, and northeast of Zhejiang, while low NEE stands were located in the mountain basin areas, high altitude areas, and the majority of coastal areas. Among the eleven cities in Zhejiang Province, Hangzhou was the highest annual total NEE city (0.34 ± 0.06 Tg C yr −1 ), and Huzhou was the highest NEE density city (7.65 ± 1.02 Mg C hm −2 yr −1 ). The carbon sequestrated by bamboo forest was 1.74 Tg C yr −1 , accounted 6.36 Tg CO 2 yr −1 , which indicated the bamboo forested area in Zhejiang Province was a carbon sink. The spatial heterogeneity of CO 2 fluxes of bamboo forest can be revealed by an exponential semivariance model. The analysis of the model structure indicated that the spatial heterogeneity of CO 2 fluxes of bamboo forest was characterized by significant autocorrelation, with an average autocorrelation range of 3.00 km, however the effect of random factors (management levels, management measures, etc .) cannot be ignored. This is the first time that the CO 2 fluxes of bamboo forest in Zhejiang Province have been mapped and this study provides a new estimate of CO 2 fluxes in this region.

In this study, high quality soil moisture data derived from the Soil Moisture Active Passive (SMAP) satellite measurements are evaluated from a perspective of improving the estimation of the global Gross Primary Production (GPP) using a process-based ecosystem model, namely the Boreal Ecosystem Productivity Simulator (BEPS). The SMAP soil moisture data are assimilated into BEPS using an Ensemble Kalman Filter. The correlation coefficient (r) between simulated GPP from the sunlit leaves and Sun-Induced chlorophyll Fluorescence (SIF) measured by Global Ozone Monitoring Experiment–2 (GOME-2) is used as an indicator to evaluate the performance of the GPP simulation. Areas with SMAP data in low quality (i. e. forests), or with SIF in low magnitude (e. g. deserts) or both are excluded from the analysis. With the assimilated SMAP data, the r value is enhanced for Africa, Asia, and North America by 0.016, 0.013, and 0.013, respectively (p

New data are presented on unique refugia accounting for the high floristic diversity of dark conifer forests of the Northern Urals, which have some of the highest parameters of species saturation among boreal forests of northern Eurasia. Based on the results of analysis, the most significant biological factors have been revealed and their influence on boreal tall-herb and background plant communities has been evaluated.

A model is a simplification of our understanding of reality, but how much simplification is too much? We assessed model sensitivity for a new spatially-explicit individual-based gap model (IBM) SIBBORK to determine how spatial resolution (i.e., plot size) and explicit representation of light and space affect the simulated vegetation characteristics (e.g., structure and composition). The 3-dimensional (3-D) representation of light is the most computationally-expensive part of the simulation, so it is worthwhile to evaluate whether the time, resource and effort of spatial explicity improve predictive capabilities. In the simulation, gap dynamics occur at the plot-level, wherein a certain level of spatial homogeneity is assumed. Therefore, for the simulation of each ecosystem it is imperative to select the appropriate scale at which gap dynamics are simulated, i.e. the plot size. We conducted these sensitivity analyses and qualitatively compared model output to the descriptions of forest structure and composition at two different sites in central and southern Siberia. We systematically varied the plot size (100–900 m2) and found that a 100 m2 plot is most appropriate for the simulation of the central Siberian boreal forest ecosystem. Moreover, we found that the forest structure and composition simulated under the light environment generated using a 3-dimensional light ray tracing subroutine more closely resembled local and regional forest characteristics at both sites, whereas the growth and stand processes computed based on the simplified (1-D) light conditions approximated only large-scale (continental) average forest structure and biomass for the Eurasian boreal forest.

Boreal forest ecosystems are experiencing changes in plant productivity that are likely to continue with ongoing climate change. Transpiration (T) and canopy stomatal conductance (gc) are a key influence on plant productivity, and a better understanding of drivers and limitations of T and gc is necessary for constraining estimates of boreal ecosystem change. We describe patterns in T and gc of a deciduous conifer, Larix cajanderi, in an arctic boreal forest in northeastern Russia across three growing seasons from 2013 to 2015. We examine the influence of environmental drivers on gc using a phenomenological model. T was highly variable across days and varied between 0.03 and 0.75 L m−2 d−1. T and gc largely covaried with daily fluctuations in air temperature and vapor pressure deficit. gc was highly suppressed on days when the vapor pressure deficits exceeded 0.75 kPa with an average daily gc of 37.55 mmol m−2 s−1, and the average daily gc was almost double (71.25 mmol m−2 s−1) when vapor pressure deficits stayed below 0.75 kPa. Daily variation in gc was significantly related to air temperature, permafrost thaw depth, and past precipitation. The influence of past precipitation and permafrost thaw depth on gc indicates that belowground conditions relating to soil moisture status are a key limitation for T. Such limitations on gc and T suggest that soil water and plant water stress play an important role in plant productivity and water relations in far northeastern Siberia.

This study evaluates the large-scale seasonal phenology and physiology of vegetation over northern high latitude forests (40°–55°N) during spring and fall by using remote sensing of solar-induced chlorophyll fluorescence (SIF), normalized difference vegetation index (NDVI) and observation-based estimate of gross primary productivity (GPP) from 2009 to 2011. Based on GPP phenology estimation in GPP, the growing season determined by SIF time-series is shorter in length than the growing season length determined solely using NDVI. This is mainly due to the extended period of high NDVI values, as compared to SIF, by about 46 days (± 11 days), indicating a large-scale seasonal decoupling of physiological activity and changes in greenness in the fall. In addition to phenological timing, mean seasonal NDVI and SIF have different responses to temperature changes throughout the growing season. We observed that both NDVI and SIF linearly increased with temperature increases throughout the spring. However, in the fall, although NDVI linearly responded to temperature increases, SIF and GPP did not linearly increase with temperature increases, implying a seasonal hysteresis of SIF and GPP in response to temperature changes across boreal ecosystems throughout their growing season. Seasonal hysteresis of vegetation at large-scales is consistent with the known phenomena that light limits boreal forest ecosystem productivity in the fall. Our results suggest that continuing measurements from satellite remote sensing of both SIF and NDVI can help to understand the differences between, and information carried by, seasonal variations vegetation structure and greenness and physiology at large-scales across the critical boreal regions.

Human activity has more than doubled the amount of nitrogen entering the global nitrogen cycle, and the boreal forest biome is a nitrogen-limited ecosystem sensitive to nitrogen load perturbation. Although bryophyte-associated microbes contribute significantly to boreal forest ecosystem function, particularly in carbon and nitrogen cycling, little is known about their responses to anthropogenic global change. Amplicon pyrosequencing of the ITS2 region of rDNA was used to investigate how fungal communities associated with three bryophyte species responded to increased nitrogen loads in a long-term fertilization experiment in a boreal Picea abies forest in southern Norway. Overall, OTU richness, community composition, and the relative abundance of specific ecological guilds were primarily influenced by host species identity and tissue-type. Although not the primary factor affecting fungal communities, nitrogen addition did impact the abundance of specific guilds of fungi and the resulting overall community composition. Increased nitrogen loads decreased ectomycorrhizal abundance, with Amphinema, Cortinarius, Russula, and Tylospora OTUs responding negatively to fertilization. Pathogen abundance increased with fertilization, particularly in the moss pathogen Eocronartium. Saprophytic fungi were both positively and negatively impacted by the nitrogen addition, indicating a complex community level response. The overshadowing of the effects of increased nitrogen loads by variation related to host and tissue-type highlights the complexity of bryophyte-associated microbial communities and the intricate nature of their responses to anthropogenic global change. This article is protected by copyright. All rights reserved.

Vole population cycles are a major force driving boreal ecosystem dynamics in north - western Eurasia. However, our understanding of the impact of winter on these cycles is increasingly uncertain, especially because climate change is affecting snow predict - ability, quality, and abundance. We examined the role of winter weather and snow conditions, the lack of suitable habitat structure during freeze- thaw periods, and the lack of sufficient food as potential causes for winter population crashes. We live- trapped bank voles Myodes glareolus on 26 plots (0.36 ha each) at two different eleva - tions (representing different winter conditions) in southeast Norway in the winters 2013/2014 and 2014/2015. We carried out two manipulations: supplementing six plots with food to eliminate food limitation and six plots with straw to improve habitat structure and limit the effect of icing in the subnivean space. In the first winter, all bank voles survived well on all plots, whereas in the second winter voles on almost all plots went extinct except for those receiving supplemental food. Survival was highest on the feeding treatment in both winters, whereas improving habitat structure had no effect. We conclude that food limitation was a key factor in causing winter population crashes.

The forests of Newfoundland represent a unique type of boreal ecosystem with diverse environmental gradients that exercise strong control over disturbances and vegetation. We have assembled and analyzed a comprehensive database on disturbance history in Newfoundland. Defoliating insects, led by the eastern spruce budworm (Choristoneura fumiferana Clemens) and the hemlock looper (Lambdina fiscellaria Guenée), have the largest disturbance footprint on the island. Infrequent wildfires (fire cycle = 769 years) had a decisive role in driving forest succession, particularly in the Central Newfoundland Forest and Maritime Barrens ecoregions. We hypothesize that the historical disturbance regime in Newfoundland would not have enabled steady-state conditions, although the amount of old-growth forests and deadwood would likely have been greater than it is today. We argue that the implementation of the natural range of variation (NRV) concept in forest management for such non-equilibrium systems will be challenging in Newfoundland and in other regions of Canada. We propose guiding principles to adapt the NRV concept using ecological knowledge. If a sciencebased approach is desired, assumptions about NRV should be tested using a rigorous experimental design. We encourage the establishment of large-scale experiments in at least a portion of forestry operations to enable an ecosystem sciencebased approach.

The food systems of communities throughout Canada’s northern boreal forest are supported by the health of the surrounding land, animals, and waters. Traditional foods – those gathered, fished, and harvested from the land – remain the basis of community food systems. However, climate change is having profound negative impacts on both availability and accessibility to traditional food sources through its impacts on the ecological integrity of the boreal system. This has increased dependency on food purchased through the stores, and combined with other socio-economic factors, as well as the impacts of climate change on traditional food access, has contributed to the rise of food insecurity across the region. This chapter discusses the lack of assessment tools for the complex food systems found in northern communities, and the need for more holistic approaches to measurement that connect food systems, land, and ecosystem health. We discuss research being conducted with, and in, the community of Kakisa, Northwest Territories that highlights a community-driven assessment to understand the health of the boreal forest ecosystem. Kakisa, like many northern communities, sees the health of the boreal forest ecosystem as the most important part of the community’s food system. The well-being of northern communities therefore relies on the resiliency of the boreal forest and the ability of all aspects of the food system to support the overall form and function of the ecosystem.

Surface water browning affects boreal lakes in the Northern Hemisphere. This process is expected to increase with global warming. Boreal lakes are the most numerous lakes on Earth. These ecosystems are particularly sensitive to disturbances due to their low biodiversity compared to other aquatic environments. The recent darkening of surface water is expected to hinder key ecosystem processes, particularly through lower primary productivity and loss of biodiversity. However, studies based on long-term data collections have rarely been conducted on the ecological consequences of water browning on aquatic food webs, especially concerning its impacts on invertebrate communities. For the first time, our analysis based on two decades of data collection in Finnish lakes highlighted a relation between water browning and a decline in aquatic macroinvertebrate abundances. Aquatic invertebrates are the main food resource for many secondary predators such as fish and waterbirds, hence such effect on their populations may have major consequences for boreal ecosystem functioning.

Intercropping (IC) is a promising approach used to improve soil health and sustainable crop production. However, it is unknown whether IC improve the soil health status and biomass productivity of crops cultivated in podzols under cool climate in boreal ecosystems. Two silage corn and three forage soybean genotypes were cultivated either as inter or monocrop (MC) treatments in a randomized complete block design. IC resulted in 28% increase in total forage production (FP). A reduction in rhizosphere soil pH (RS-pH) was observed in the IC treatments. Conversely, the rhizosphere soil acid phosphatase (RS-APase) activity was significantly higher (26–46%) in the IC treatments and occurred concomitant with a significant increase in available phosphorus (RS-Pavailable) (26–74%) in the rhizosphere. Furthermore, IC enhanced the active microbial composition and strong positive correlations were observed between RS-Pavailable, RS-APase, microbial biomass and FP; while RS-pH was negatively correlated with FP, RS-APase and RS-Pavailable. These findings suggested silage corn intercropped with forage soybean could be a viable approach to enhance FP through improved active microbial community structure, RS-APase activity and RS-Pavailable when cultivated on podzols in cool climate boreal ecosystem.

Climate change and global wood products demand raise concerns about boreal forest ecosystem resilience to natural disturbances and harvesting. A chronosequence experiment located in Foret Montmorency, Quebec was used to evaluate the effects of harvesting on carbon (C) recovery trajectories at the stand level over a period of 77 years in balsam fir-white birch stands. Empirical estimates of 19 Foret Montmorency forest carbon pools were compared with those simulated by the Carbon Budget Model (CBM-CFS3) to test model assumptions for predicting carbon dynamics in this forest. The model was initialized using forest inventory data, spatially explicit environmental conditions, and disturbance matrices designed to represent historical spruce budworm epidemics in Foret Montmorency. Over the chronosequence, total ecosystem C increased significantly (p = 0.05) following harvest from 211 Mg in year-zero to 279 ± 8 Mg C ha⁻¹ in year 67 (mean ± SE), suggesting that FM carbon pools were recovering to pre-harvest levels after seven decades. The CBM-CFS3 model predicted total ecosystem C stocks within 10% of the empirical mean at stand maturity; however, several predicted C pools deviated from field observations in both C amounts and trends over time. The greatest differences were in deadwood and soil C pools, suggesting that model initialization of dead organic matter pools did not adequately simulate the 1000-yr history of C-pool transfers and stand dynamics leading up to the harvest. Modifications to CBM-CFS3 initialization assumptions and default decay parameters may more accurately simulate long-term effects of natural disturbances on C pools for this forest region.

Porewater chemistry is an integrative measure of the physical, chemical, and biological processes occurring within peatland ecosystems, and therefore some chemistry measures (e.g., pH, calcium concentrations) have been used to classify bog vs fen peatlands. However, porewater sampling is often limited in spatial and temporal resolution, highlighting the need for a more comprehensive analysis of spatiotemporal variation in porewater chemistry. We examined depth profiles of porewater chemistry in four nearby peatlands that fall along a bog to rich fen gradient in northcentral Minnesota, USA. Porewater was sampled ~monthly during one ice-free season from three replicate piezometer nests per peatland to quantify temporal and spatial variability of those depth profiles. Porewater depth profiles of pH, calcium and total organic carbon concentrations, and δ18O-H2O varied along the bog to fen gradient, but total nitrogen and total phosphorus concentrations did not. Porewater chemistry was similar in the bogs and poor fen which were all quite different from the rich fen. In contrast, temporal and spatial variation in porewater chemistry, quantified using coefficients of variation, did not differ between bogs and fens despite the hypothesis that variation in porewater chemistry would be lower in fens than bogs due to the perennial throughput of large volumes of discharging groundwater in the rich fen. Spatial and temporal variability in porewater chemistry across all peatland types highlights the importance of collecting porewater samples in multiples over time in both near-surface and deeper peats. This variation can be important when scaling findings to the peatland scale, assessing the representativeness of peatlands within a larger landscape, and understanding variability in solute export to downstream ecosystems.

We studied the relationship of forest understory vegetation with nutrient contents of soil and tree leaves near Sokli phosphate ore in northern Finland, where the soil contains naturally high variation in phosphorus (P) contents. At most study plots boreal dwarf shrubs, bryophytes and lichen formed a dense mat under a mixture of sparsely growing Pinus sylvestris, Picea abies and Betula pubescens. However, some plots were dominated by B. pubescens and had a higher variety and number of forbs and grasses in the understory. The total P content in the soil humus layer explained the abundance and species composition of the vegetation slightly better than the total nitrogen content. The spatial variation in contents of soil elements was high both between and within plots, emphasizing the heterogeneity of soil. High contents of P in the humus layer (max. 2600 mg kg−1) were measured from the birch-dominated plots. As the P contents of birch leaves and leaf litter were also rather high (2580 mg kg−1 and 1280 mg kg−1, respectively), this may imply that the leaf litter of birch forms an important source of P to the soil.

Bamboo forests are an important part of the forest ecosystem, which has strong carbon sequestration potential and plays an important role in the global carbon cycle. As a key parameter for simulating the carbon cycle using forest ecosystem models, the quality of leaf area index (LAI) data has a direct influence on the accuracy of modelling results. Here, we used the particle filter (PF) algorithm and PROSAIL model to assimilate MODIS LAI products, which were then used to drive a boreal ecosystem productivity simulator model to simulate the bamboo forest carbon cycle. The results showed that the relationship between the assimilated and observed LAI values was very significant, with an R2 of 0.95 and an RMSE of 0.28, greatly improving the precision of MODIS LAI products. The R2 values for the gross primary productivity (GPP), net ecosystem exchange (NEE), and total ecosystem respiration (TER) simulated by the assimilated LAI values and observed carbon fluxes were 0.65, 0.45 and 0.70, respectively, and the RMSE values were 1.10 g C m−2 day−1, 1.00 g C m−2 day−1 and 0.35 g C m−2 day−1, respectively. Compared with the results of the carbon cycle simulated by non-assimilated LAI, the R2 values of the GPP, NEE and TER values that were simulated by assimilated LAI increased by 27.5%, 45.2% and 6.1%, and the RMSE values decreased by 29.9%, 23.7% and 22.2%, respectively. Therefore, coupling the PF and PROSAIL models can greatly improve the simulation precision for the large-scale bamboo forest carbon cycle. This study laid the foundation for simulating the carbon cycle over a large-scale bamboo forest based on low-resolution data in the future.

Forests regulate climate, as carbon, water and nutrient fluxes are modified by physiological processes of vegetation and soil. Forests also provide renewable raw material, food, and recreational possibilities. Rapid climate warming projected for the boreal zone may change the provision of these ecosystem services. We demonstrate model based estimates of present and future ecosystem services related to carbon cycling of boreal forests. The services were derived from biophysical variables calculated by two dynamic models. Future changes in the biophysical variables were driven by climate change scenarios obtained as results of a sample of global climate models downscaled for Finland, assuming three future pathways of radiative forcing. We introduce continuous monitoring on phenology to be used in model parametrization through a webcam network with automated image processing features. In our analysis, climate change impacts on key boreal forest ecosystem services are both beneficial and detrimental. Our results indicate an increase in annual forest growth of about 60% and an increase in annual carbon sink of roughly 40% from the reference period (1981-2010) to the end of the century. The vegetation active period was projected to start about 3 weeks earlier and end ten days later by the end of the century compared to currently. We found a risk for increasing drought, and a decrease in the number of soil frost days. Our results show a considerable uncertainty in future provision of boreal forest ecosystem services. peerReviewed

Ecosystem models have been widely used for obtaining gross primary productivity (GPP) estimations at multiple scales. Leaf area index (LAI) is a critical variable in these models for describing the vegetation canopy structure and predicting vegetation-atmosphere interactions. However, the uncertainties in LAI datasets and the effects of their representation on simulated GPP remain unclear, especially over complex terrain. Here, five most popular datasets, namely the Long-term Global Mapping (GLOBMAP) LAI, Global LAnd Surface Satellite (GLASS) LAI, Geoland2 version 1 (GEOV1) LAI, Global Inventory Monitoring and Modeling System (GIMMS) LAI, and Moderate Resolution Imaging Spectroradiometer (MODIS) LAI, were selected to examine the influences of LAI representation on GPP estimations at 95 eddy covariance (EC) sites. The GPP estimations from the Boreal Ecosystem Productivity Simulator (BEPS) model and the Eddy Covariance Light Use Efficiency (EC-LUE) model were evaluated against EC GPP to assess the performances of LAI datasets. Results showed that MODIS LAI had stronger linear correlations with GLASS and GEOV1 than GIMMS and GLOMAP at the study sites. The GPP estimations from GLASS LAI had a better agreement with EC GPP than those from other four LAI datasets at forest sites, while the GPP estimations from GEOVI LAI matched best with EC GPP at grass sites. Additionally, the GPP estimations from GLASS and GEOVI LAI presented better performances than the other three LAI datasets at crop sites. Besides, the results also showed that complex terrain had larger discrepancies of LAI and GPP estimations, and flat terrain presented better performances of LAI datasets in GPP estimations. Moreover, the simulated GPP from BEPS was more sensitive to LAI than those from EC - LUE, suggesting that LAI datasets can also lead to different uncertainties in GPP estimations from different model structures. Our study highlights that the satellite-derived LAI datasets can cause uncertainties in GPP estimations through ecosystem models.

Solar induced chlorophyll fluorescence has been shown to be increasingly an useful proxy for the estimation of gross primary productivity (GPP), at a range of spatial scales. Here, we explore the seasonality in a continuous time series of canopy solar induced fluorescence (hereafter SiF) and its relation to canopy gross primary production (GPP), canopy light use efficiency (LUE), and direct estimates of leaf level photochemical efficiency in an evergreen canopy. SiF was calculated using infilling in two bands from the incoming and reflected radiance using a pair of Ocean Optics USB2000+ spectrometers operated in a dual field of view mode, sampling at a 30 min time step using custom written automated software, from early spring through until autumn in 2011. The optical system was mounted on a tower of 18 m height adjacent to an eddy covariance system, to observe a boreal forest ecosystem dominated by Scots pine. (Pinus sylvestris) A Walz MONITORING-PAM, multi fluorimeter system, was simultaneously mounted within the canopy adjacent to the footprint sampled by the optical system. Following correction of the SiF data for O2 and structural effects, SiF, SiF yield, LUE, the photochemicsl reflectance index (PRI), and the normalized difference vegetation index (NDVI) exhibited a seasonal pattern that followed GPP sampled by the eddy covariance system. Due to the complexities of solar azimuth and zenith angle (SZA) over the season on the SiF signal, correlations between SiF, SiF yield, GPP, and LUE were assessed on SZA 2 = 0.3. The diurnal responses of SiF, SiF yield, PAM estimates of effective quantum yield (ΔF/Fm′), and meteorological parameters demonstrated some agreement over the diurnal cycle. The challenges inherent in SiF retrievals in boreal evergreen ecosystems are discussed.

Eastern Siberia is located at the centre of a continuous permafrost zone. The most prominent feature of this zone is its vast cover by deciduous coniferous boreal (taiga) forest. Underlying the boreal ecosystem is an extensive and massive ice layer within the permafrost (Yedoma), which was crucial for the development of large ground subsidence during the Holocene, which is closely related to ice volume loss. Therefore, scattered large grassland depressions (alas) and transitional topography under permafrost degradation (thermokarst) are also observed throughout central Yakutia. Extensive thermokarst evolution in this region has resulted in the development of successive thermokarst landforms. Thermokarst processes are enhanced by soil warming, indicating that both atmospheric warming and precipitation changes in summer and winter have had a marked effect on hydrothermal conditions within the active layer and upper part of the permafrost during recent decades. An increase in the mean active-layer depth of only a few tens of centimetres would release large amounts of water and carbon. Predicting permafrost landscape changes is not straightforward; it is hindered by uncertainty, by the need to consider combined ecosystem effects, by sociocultural interactions, and by hydrothermal processes. Permafrost landscape changes will have an impact on indigenous livelihoods, as has already been noted at local and regional levels. These permafrost-related influences will amplify feedback mechanisms between the climate and water and carbon cycles through permafrost degradation and concurrent boreal ecosystem changes.

The boreal biome is the largest of all terrestrial biomes, between the temperate and tundra zones. The climate is generally continental with short summers and cold winters, and permafrost can occur in the northern parts of this zone. Average precipitation tends to be low but water is seldom limiting. True boreal forest is far less species rich than temperate forest, and is dominated by coniferous trees such as spruces, firs, pines, and larches, whiles hardwoods, such as alders, poplars, birches, and willows, usually occur in dwarf form. Soils underlying conifers tend to be highly podzolized through acid leaching.

In this study, we simulated vegetation net primary productivity (NPP) using the boreal ecosystem productivity simulator (BEPS) between 2003 and 2012 over Northeast China, a region that is significantly affected by climate change. The NPP was then validated against the measurements that were calculated from tree ring data, with a determination coefficient (R2) = 0.84 and the root mean square error (RMSE) = 42.73 gC/m2·a. Overall, the NPP showed an increasing trend over Northeast China, with the average rate being 4.48 gC/m2·a. Subsequently, partial correlation and lag analysis were conducted between the NPP and climatic factors. The partial correlation analysis suggested that temperature was the predominant factor that accounted for changes in the forest NPP. Solar radiation was the main factor that affected the forest NPP, and the grass NPP was the most closely associated with precipitation. The relative humidity substantially affected the annual variability of the shrub and crop NPPs. The lag time of the NPP related to precipitation increased with the vegetation growth, and it was found that the lag period of the forest was longer than that of grass and crops, whereas the cumulative lag month of the forest was shorter. This comprehensive analysis of the response of the vegetation NPP to climate change can provide scientific references for the managing departments that oversee relevant resources.