Drivers of carbon emissions and active layer thickening from boreal wildfires in a continuous permafrost region of Northeast Siberia

The circumpolar boreal biome is affected by increases in fire frequency and severity associated with climate warming. About 30% of the world&#8217;s terrestrial carbon (C) is stored in the boreal region. Fires can produce large C emissions when substantial amounts of aboveground and belowground biomass and soil organic matter are combusted. Quantification and understanding of the drivers of C combustion is crucial to better assess the role of boreal fires in the global carbon cycle.Despite the fact that the majority of boreal burned area occurs on the Eurasian continent, relatively few measurements of C combustion have been made in Eurasian boreal ecosystems. Here we synthetized data from 41 field sites collected during the summer of 2019 in Eastern Siberian larch forests. C combustion from surface and stand-replacing fires varied between 1.54 and 5.38 kg C/m2. Belowground pools contributed in average to 73.9% of total C combustion. C combustion was higher in open larch-dominated forests (Larix cajanderi) and open forests with a mixture of larch and pine (Pinus sylvestris). High severity crown fires were observed in dense larch-dominated forests, yet C combustion was in average 23% lower than in the open stands. To our knowledge, this study is the first to quantify C combustion from wildfires in a continuous permafrost terrain in Northeast Siberia. We also investigated the effects of fire weather and pre-fire stand characteristics (e.g., stand age, drainage conditions, overstory tree species composition) on C combustion.Because fires can also have a longer-term impact on permafrost environments through changes in surface energy balance and ground thermal regime, we also quantified active layer deepening in our study area. We measured thaw depth in 13 burned and 6 unburned sites one year after the fire. We explored the interactions between fire, vegetation, drainage conditions, and thaw depth. Our study shows that fire deepens the active layer, yet the magnitude of the effect is controlled by vegetation characteristics and topo-edaphic factors. Our findings provide insight to feedbacks between climate warming and boreal fires in permafrost-underlain larch forests in Siberia.

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Variability in above- and belowground carbon stocks in a Siberian larch watershed

Biogeosciences ◽

10.5194/bg-14-4279-2017 ◽

2017 ◽

Vol 14 (18) ◽

pp. 4279-4294 ◽

Cited By ~ 13

Author(s):

Elizabeth E. Webb ◽

Kathryn Heard ◽

Susan M. Natali ◽

Andrew G. Bunn ◽

Heather D. Alexander ◽

...

Keyword(s):

Aboveground Biomass ◽

Spatial Scales ◽

Siberian Larch ◽

Stand Age ◽

Permafrost Region ◽

Organic C ◽

Soil C ◽

C Storage ◽

C Stocks ◽

Thaw Depth

Abstract. Permafrost soils store between 1330 and 1580 Pg carbon (C), which is 3 times the amount of C in global vegetation, almost twice the amount of C in the atmosphere, and half of the global soil organic C pool. Despite the massive amount of C in permafrost, estimates of soil C storage in the high-latitude permafrost region are highly uncertain, primarily due to undersampling at all spatial scales; circumpolar soil C estimates lack sufficient continental spatial diversity, regional intensity, and replication at the field-site level. Siberian forests are particularly undersampled, yet the larch forests that dominate this region may store more than twice as much soil C as all other boreal forest types in the continuous permafrost zone combined. Here we present above- and belowground C stocks from 20 sites representing a gradient of stand age and structure in a larch watershed of the Kolyma River, near Chersky, Sakha Republic, Russia. We found that the majority of C stored in the top 1 m of the watershed was stored belowground (92 %), with 19 % in the top 10 cm of soil and 40 % in the top 30 cm. Carbon was more variable in surface soils (10 cm; coefficient of variation (CV)  =  0.35 between stands) than in the top 30 cm (CV  =  0.14) or soil profile to 1 m (CV  =  0.20). Combined active-layer and deep frozen deposits (surface – 15 m) contained 205 kg C m−2 (yedoma, non-ice wedge) and 331 kg C m−2 (alas), which, even when accounting for landscape-level ice content, is an order of magnitude more C than that stored in the top meter of soil and 2 orders of magnitude more C than in aboveground biomass. Aboveground biomass was composed of primarily larch (53 %) but also included understory vegetation (30 %), woody debris (11 %) and snag (6 %) biomass. While aboveground biomass contained relatively little (8 %) of the C stocks in the watershed, aboveground processes were linked to thaw depth and belowground C storage. Thaw depth was negatively related to stand age, and soil C density (top 10 cm) was positively related to soil moisture and negatively related to moss and lichen cover. These results suggest that, as the climate warms, changes in stand age and structure may be as important as direct climate effects on belowground environmental conditions and permafrost C vulnerability.

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Variability in Above and Belowground Carbon Stocks in a Siberian Larch Watershed

10.5194/bg-2017-88 ◽

2017 ◽

Cited By ~ 1

Author(s):

Elizabeth E. Webb ◽

Kathryn Heard ◽

Susan M. Natali ◽

Andrew G. Bunn ◽

Heather D. Alexander ◽

...

Keyword(s):

Aboveground Biomass ◽

Spatial Scales ◽

Siberian Larch ◽

Stand Age ◽

Permafrost Region ◽

Organic C ◽

Soil C ◽

C Storage ◽

C Stocks ◽

Thaw Depth

Abstract. Permafrost soils store between 1,330–1,580 Pg carbon (C), which is three times the amount of C in global vegetation, almost twice the amount of C in the atmosphere, and half of the global soil organic C pool. Despite the massive amount of C in permafrost, estimates of soil C storage in the high latitude permafrost region are highly uncertain, primarily due to under sampling at all spatial scales; circumpolar soil C estimates lack sufficient continental spatial diversity, regional intensity, and replication at the field-site level. Siberian forests are particularly under sampled, yet the larch forests that dominate this region may store more than twice as much soil C as all other boreal forest types in the continuous permafrost zone combined. Here we present above and belowground C stocks from twenty sites representing a gradient of stand age and structure in a larch watershed of the Kolyma River near Cherskiy, Sakha Republic, Russia. We found that the majority of C stored in the top 1 m of the watershed was stored belowground (91 %), with 20 % in the top 10 cm of soil and 42 % in the top 30 cm. Carbon was more variable in surface soils (10 cm; coefficient of variation (CV) = 0.35 between stands) than in the top 30 cm (CV = 0.14) or soil profile to 1 m (CV = 0.12). Combined active layer and deep frozen deposits (surface – 15 m) contained 205 kg C m-2 (yedoma, non-ice wedge) and 331 kg C m-2 (alas), which, even when accounting for landscape-level ice content, is an order of magnitude more C than that stored in the top meter of soil and two orders of magnitude more C than in aboveground biomass. Aboveground biomass was composed of primarily larch (53 %) but also included understory vegetation (30 %), woody debris (11 %) and snag (6 %) biomass. While aboveground biomass contained relatively little (9 %) of the C stocks in the watershed, aboveground processes were linked to thaw depth and belowground C storage. Thaw depth was significantly negatively related to stand age, and variability of soil C in the top 10 cm was related to soil moisture and moss and lichen cover. These results suggest that as the climate warms, changes in stand age and structure may be as important as direct climate effects on belowground environmental conditions and permafrost C vulnerability.

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Climate warming and active layer thaw in the boreal and tundra environments of the Mackenzie Valley

Canadian Journal of Earth Sciences ◽

10.1139/e06-121 ◽

2007 ◽

Vol 44 (6) ◽

pp. 733-743 ◽

Cited By ~ 33

Author(s):

Ming-ko Woo ◽

Michael Mollinga ◽

Sharon L Smith

Keyword(s):

Layer Thickness ◽

Active Layer ◽

Climate Warming ◽

Probability Distributions ◽

Organic Layer ◽

Active Layer Thickness ◽

Near Surface ◽

Ground Temperatures ◽

Thaw Depth ◽

Mineral Soils

The variability of maximum active layer thickness in boreal and tundra environments has important implications for hydrological processes, terrestrial and aquatic ecosystems, and the integrity of northern infrastructure. For most planning and management purposes, the long-term probability distribution of active layer thickness is of primary interest. A robust method is presented to calculate maximum active layer thickness, employing the Stefan equation to compute phase change of moisture in soils and using air temperature as the sole climatic forcing variable. Near-surface ground temperatures (boundary condition for the Stefan equation) were estimated based on empirical relationships established for several sites in the Mackenzie valley. Simulations were performed for typically saturated mineral soils, overlain with varying thickness of peat in boreal and tundra environments. The probability distributions of simulated maximum active layer thickness encompass the range of measured thaw depths provided by field data. The effects of climate warming under A2 and B2 scenarios for 2050 and 2100 were investigated. Under the A2 scenario in 2100, the simulated median thaw depth under a thin organic cover may increase by 0.3 m, to reach 1 m depth for a tundra site and 1.6 m depth for a boreal site. The median thaw depth in 2100 is dampened by about 50% under a 1 m thick organic layer. Without an insulating organic cover, thaw penetration can increase to reach 1.7 m at the tundra site. The simulations provide quantitative support that future thaw penetration in permafrost terrain will deepen differentially depending on location and soil.

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Mapping stand age dynamics of the Siberian larch forests from recent Landsat observations

Remote Sensing of Environment ◽

10.1016/j.rse.2016.10.033 ◽

2016 ◽

Vol 187 ◽

pp. 320-331 ◽

Cited By ~ 7

Author(s):

Dong Chen ◽

Tatiana V. Loboda ◽

Alexander Krylov ◽

Peter V. Potapov

Keyword(s):

Siberian Larch ◽

Stand Age ◽

Age Dynamics ◽

Larch Forests

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Status, Changes and Impacts of Permafrost on Qinghai-Tibet Plateau

10.5194/egusphere-egu2020-6246 ◽

2020 ◽

Author(s):

Lin Zhao ◽

Guojie Hu ◽

Defu Zou ◽

Ren Li ◽

Yu Sheng ◽

...

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Active Layer ◽

Climate Warming ◽

Global Climate ◽

Tibet Plateau ◽

Active Layer Thickness ◽

Permafrost Region ◽

Permafrost Degradation ◽

Qinghai Tibet Plateau

Due to the climate warming, permafrost on the Qinghai-Tibet Plateau (QTP) was degradating in the past decades. Since its impacts on East Asian monsoon, and even on the global climate system, it is fundamental to reveal permafrost status, changes and its physical processes. Based on previous research results and new observation data, this paper reviews the characteristics of the status of permafrost on the QTP, including the active layer thickness (ALT), the spatial distribution of permafrost, permafrost temperature and thickness, as well as the ground ice and soil carbon storage in permafrost region.The results showed that the permafrost and seasonally frozen ground area (excluding glaciers and lakes) is 1.06 million square kilometters and 1.45 million square kilometters on the QTP. The permafrost thickness varies greatly among topography, with the maximum value in mountainous areas, which could be deeper than 200 m, while the minimum value in the flat areas and mountain valleys, which could be less than 60 m. The mean value of active layer thickness is about 2.3 m. Soil temperature at 0~10 cm, 10~40 cm, 40~100 cm, 100~200 cm increased at a rate of 0.439, 0.449, 0.396, and 0.259&#176;C/10a, respectively, from 1980 to 2015. The increasing rate of the soil temperature at the bottom of active layer was 0.486 oC/10a from 2004 to 2018.The volume of ground ice contained in permafrost on QTP is estimated up to 1.27&#215;104 km3 (liquid water equivalent). The soil organic carbon staored in the upper 2 m of soils within the permafrost region is about 17 Pg. Most of the research results showed that the permafrost ecosystem is still a carbon sink at the present, but it might be shifted to a carbon source due to the loss of soil organic carbon along with permafrost degradation.Overall, the plateau permafrost has undergone remarkable degradation during past decades, which are clearly proven by the increasing ALTs and ground temperature. Most of the permafrost on the QTP belongs to the unstable permafrost, meaning that permafrost over TPQ is very sensitive to climate warming. The permafrost interacts closely with water, soil, greenhouse gases emission and biosphere. Therefore, the permafrost degradation greatly affects the regional hydrology, ecology and even the global climate system.

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Increased Litter Greatly Enhancing Soil Respiration in Betula platyphylla Forests of Permafrost Region, Northeast China

Forests ◽

10.3390/f12010089 ◽

2021 ◽

Vol 12 (1) ◽

pp. 89

Author(s):

Hong Wei ◽

Xiuling Man

Keyword(s):

Soil Respiration ◽

Carbon Cycle ◽

Soil Carbon ◽

Northeast China ◽

Stand Age ◽

Permafrost Region ◽

Betula Platyphylla ◽

Litter Input ◽

Litter Manipulation ◽

And Control

The change of litter input can affect soil respiration (Rs) by influencing the availability of soil organic carbon and nutrients, regulating soil microenvironments, thus resulting in a profound influence on soil carbon cycle of the forest ecosystem. We conducted an aboveground litterfall manipulation experiment in different-aged Betula platyphylla forests (25-, 40- and 61-year-old) of the permafrost region, located in the northeast of China, during May to October in 2018, with each stand treated with doubling litter (litter addition, DL), litter exclusion (no-litter, NL) and control litter (CK). Our results indicated that Rs decreased under NL treatment compared with CK treatment. The effect size lessened with the increase in the stand age; the greatest reduction was found for young Betula platyphylla forest (24.46% for 25-year-old stand) and tended to stabilize with the growth of forest with the reduction of 15.65% and 15.23% for 40-and 61- year-old stands, respectively. Meanwhile, under DL treatment, Rs increased by 27.38%, 23.83% and 23.58% on 25-, 40- and 61-year-old stands, respectively. Our results also showed that the increase caused by DL treatment was larger than the reduction caused by NL treatment, leading to a priming effect, especially on 40- and 61-year-old stands. The change in litter input was the principal factor affecting the change of Rs under litter manipulation. The soil temperature was also a main factor affecting the contribution rate of litter to Rs of different-aged stands, which had a significant positive exponential correlation with Rs. This suggests that there is a significant relationship between litter and Rs, which consequently influences the soil carbon cycle in Betula platyphylla forests of the permafrost region, Northeast China. Our finding indicated the increased litter enhanced the Rs in Betula platyphylla forest, which may consequently increase the carbon emission in a warming climate in the future. It is of great importance for future forest management in the permafrost region, Northeast China.

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Emissions of nitrous oxide from continuous permafrost region in the Daxing'an Mountains, Northeast China

Atmospheric Environment ◽

10.1016/j.atmosenv.2018.10.045 ◽

2019 ◽

Vol 198 ◽

pp. 34-45 ◽

Cited By ~ 10

Author(s):

Weifeng Gao ◽

Yunlong Yao ◽

Hong Liang ◽

Liquan Song ◽

Houcai Sheng ◽

...

Keyword(s):

Nitrous Oxide ◽

Northeast China ◽

Permafrost Region ◽

Continuous Permafrost ◽

Daxing’An Mountains

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Response of Soil Moisture Change to Hydrological Processes in a Continuous Permafrost Environment

Hydrology Research ◽

10.2166/nh.1990.0018 ◽

1990 ◽

Vol 21 (4-5) ◽

pp. 235-252 ◽

Cited By ~ 16

Author(s):

Ming-ko Woo ◽

Philip Marsh

Keyword(s):

Active Layer ◽

Hydrological Processes ◽

Moisture Loss ◽

Moisture Regime ◽

Permafrost Environment ◽

Wetland Site ◽

Gamma Density ◽

Lateral Inflow ◽

Continuous Permafrost ◽

Moisture Storage

The moisture content of the active layer at three sites in a continuous permafrost area was measured using a twin-probe gamma density meter. The moisture storage status at these sites were related to various hydrological processes. Moisture was gained by meltwater and rainfall infiltration, but lost to evaporation in summer. Lateral inflow maintained a thick saturated zone at the fen (wetland) site. At the gravel site, there was a net moisture loss due to evaporation and lateral outflow. Moisture changes in the active layer during the summer were examined in terms of the water balance at the three sites. This established quantitative relationships between the moisture regime and the major hydrological processes in the permafrost environment.

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Vegetation Indices Do Not Capture Forest Cover Variation in Upland Siberian Larch Forests

Remote Sensing ◽

10.3390/rs10111686 ◽

2018 ◽

Vol 10 (11) ◽

pp. 1686 ◽

Cited By ~ 8

Author(s):

Michael Loranty ◽

Sergey Davydov ◽

Heather Kropp ◽

Heather Alexander ◽

Michelle Mack ◽

...

Keyword(s):

Carbon Storage ◽

Vegetation Change ◽

Vegetation Index ◽

Forest Cover ◽

Global Climate ◽

Vegetation Indices ◽

Temporal Trends ◽

Siberian Larch ◽

Field Observations ◽

Larch Forests

Boreal forests are changing in response to climate, with potentially important feedbacks to regional and global climate through altered carbon cycle and albedo dynamics. These feedback processes will be affected by vegetation changes, and feedback strengths will largely rely on the spatial extent and timing of vegetation change. Satellite remote sensing is widely used to monitor vegetation dynamics, and vegetation indices (VIs) are frequently used to characterize spatial and temporal trends in vegetation productivity. In this study we combine field observations of larch forest cover across a 25 km2 upland landscape in northeastern Siberia with high-resolution satellite observations to determine how the Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI) are related to forest cover. Across 46 forest stands ranging from 0% to 90% larch canopy cover, we find either no change, or declines in NDVI and EVI derived from PlanetScope CubeSat and Landsat data with increasing forest cover. In conjunction with field observations of NDVI, these results indicate that understory vegetation likely exerts a strong influence on vegetation indices in these ecosystems. This suggests that positive decadal trends in NDVI in Siberian larch forests may correspond primarily to increases in understory productivity, or even to declines in forest cover. Consequently, positive NDVI trends may be associated with declines in terrestrial carbon storage and increases in albedo, rather than increases in carbon storage and decreases in albedo that are commonly assumed. Moreover, it is also likely that important ecological changes such as large changes in forest density or variable forest regrowth after fire are not captured by long-term NDVI trends.

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Consequences of permafrost degradation for Arctic infrastructure – bridging the model gap between regional and engineering scales

The Cryosphere ◽

10.5194/tc-15-2451-2021 ◽

2021 ◽

Vol 15 (5) ◽

pp. 2451-2471

Author(s):

Thomas Schneider von Deimling ◽

Hanna Lee ◽

Thomas Ingeman-Nielsen ◽

Sebastian Westermann ◽

Vladimir Romanovsky ◽

...

Keyword(s):

Climate Change ◽

Climate Warming ◽

Strong Increase ◽

Permafrost Degradation ◽

Key Factors ◽

The Road ◽

Model Based ◽

Linear Infrastructure ◽

Continuous Permafrost ◽

Gravel Road

Abstract. Infrastructure built on perennially frozen ice-rich ground relies heavily on thermally stable subsurface conditions. Climate-warming-induced deepening of ground thaw puts such infrastructure at risk of failure. For better assessing the risk of large-scale future damage to Arctic infrastructure, improved strategies for model-based approaches are urgently needed. We used the laterally coupled 1D heat conduction model CryoGrid3 to simulate permafrost degradation affected by linear infrastructure. We present a case study of a gravel road built on continuous permafrost (Dalton highway, Alaska) and forced our model under historical and strong future warming conditions (following the RCP8.5 scenario). As expected, the presence of a gravel road in the model leads to higher net heat flux entering the ground compared to a reference run without infrastructure and thus a higher rate of thaw. Further, our results suggest that road failure is likely a consequence of lateral destabilisation due to talik formation in the ground beside the road rather than a direct consequence of a top-down thawing and deepening of the active layer below the road centre. In line with previous studies, we identify enhanced snow accumulation and ponding (both a consequence of infrastructure presence) as key factors for increased soil temperatures and road degradation. Using differing horizontal model resolutions we show that it is possible to capture these key factors and their impact on thawing dynamics with a low number of lateral model units, underlining the potential of our model approach for use in pan-Arctic risk assessments. Our results suggest a general two-phase behaviour of permafrost degradation: an initial phase of slow and gradual thaw, followed by a strong increase in thawing rates after the exceedance of a critical ground warming. The timing of this transition and the magnitude of thaw rate acceleration differ strongly between undisturbed tundra and infrastructure-affected permafrost ground. Our model results suggest that current model-based approaches which do not explicitly take into account infrastructure in their designs are likely to strongly underestimate the timing of future Arctic infrastructure failure. By using a laterally coupled 1D model to simulate linear infrastructure, we infer results in line with outcomes from more complex 2D and 3D models, but our model's computational efficiency allows us to account for long-term climate change impacts on infrastructure from permafrost degradation. Our model simulations underline that it is crucial to consider climate warming when planning and constructing infrastructure on permafrost as a transition from a stable to a highly unstable state can well occur within the service lifetime (about 30 years) of such a construction. Such a transition can even be triggered in the coming decade by climate change for infrastructure built on high northern latitude continuous permafrost that displays cold and relatively stable conditions today.

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