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1. Goose grubbing and warming suppress summer net ecosystem CO₂ uptake differentially across high‐Arctic tundra habitats

   https://doi.org/10.1002/ecy.4498  

   Petit_Bon, Matteo; Beard, Karen H; Bråthen, Kari Anne; Lee, Hanna; Jónsdóttir, Ingibjörg S (January 2025, Ecology)

   Abstract Environmental changes, such as climate warming and higher herbivory pressure, are altering the carbon balance of Arctic ecosystems; yet, how these drivers modify the carbon balance among different habitats remains uncertain. This hampers our ability to predict changes in the carbon sink strength of tundra ecosystems. We investigated how spring goose grubbing and summer warming—two key environmental‐change drivers in the Arctic—alter CO₂fluxes in three tundra habitats varying in soil moisture and plant‐community composition. In a full‐factorial experiment in high‐Arctic Svalbard, we simulated grubbing and warming over two years and determined summer net ecosystem exchange (NEE) alongside its components: gross ecosystem productivity (GEP) and ecosystem respiration (ER). After two years, we found net CO₂uptake to be suppressed by both drivers depending on habitat. CO₂uptake was reduced by warming in mesic habitats, by warming and grubbing in moist habitats, and by grubbing in wet habitats. In mesic habitats, warming stimulated ER (+75%) more than GEP (+30%), leading to a 7.5‐fold increase in their CO₂source strength. In moist habitats, grubbing decreased GEP and ER by ~55%, while warming increased them by ~35%, with no changes in summer‐long NEE. Nevertheless, grubbing offset peak summer CO₂uptake and warming led to a twofold increase in late summer CO₂source strength. In wet habitats, grubbing reduced GEP (−40%) more than ER (−30%), weakening their CO₂sink strength by 70%. One‐year CO₂‐flux responses were similar to two‐year responses, and the effect of simulated grubbing was consistent with that of natural grubbing. CO₂‐flux rates were positively related to aboveground net primary productivity and temperature. Net ecosystem CO₂uptake started occurring above ~70% soil moisture content, primarily due to a decline in ER. Herein, we reveal that key environmental‐change drivers—goose grubbing by decreasing GEP more than ER and warming by enhancing ER more than GEP—consistently suppress net tundra CO₂uptake, although their relative strength differs among habitats. By identifying how and where grubbing and higher temperatures alter CO₂fluxes across the heterogeneous Arctic landscape, our results have implications for predicting the tundra carbon balance under increasing numbers of geese in a warmer Arctic. 

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2. Increasing Fuel Loads, Fire Hazard, and Carbon Emissions from Fires in Central Siberia

   https://doi.org/10.3390/fire6020063  

   Kukavskaya, Elena A.; Shvetsov, Evgeny G.; Buryak, Ludmila V.; Tretyakov, Pavel D.; Groisman, Pavel Ya. (February 2023, Fire)

   The vast Angara region, with an area of 13.8 million ha, is located in the southern taiga of central Siberia, Russia. This is one of the most disturbed regions by both fire and logging in northern Asia. We have developed surface and ground fuel-load maps by integrating satellite and ground-based data with respect to the forest-growing conditions and the disturbance of the territory by anthropogenic and natural factors (fires and logging). We found that from 2001 to 2020, fuel loads increased by 8% in the study region, mainly due to a large amount of down woody debris at clearcuts and burned sites. The expansion of the disturbed areas in the Angara region resulted in an increase in natural fire hazards in spring and summer. Annual carbon emissions from fires varied from 0.06 to 6.18 Mt, with summer emissions accounting for more than 95% in extreme fire years and 31–68% in the years of low fire activity. While the trend in the increase in annual carbon emissions from fires is not statistically significant due to its high interannual variability and a large disturbance of the study area, there are significantly increasing trends in mean carbon emissions from fires per unit area (p < 0.005) and decadal means (p < 0.1). In addition, we found significant trends in the increase in emissions released by severe fires (p < 0.005) and by fires in wetter, dark, coniferous (spruce, p < 0.005 and Siberian pine, p < 0.025) forests. This indicates deeper burning and loss of legacy carbon that impacts on the carbon cycle resulting in climate feedback. 

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3. Increased melt from Greenland’s most active glacier fuels enhanced coastal productivity

   https://doi.org/10.1038/s43247-025-02599-1  

   Wood, Michael; Carroll, Dustin; Fenty, Ian; Bertin, Clément; Darby, Basil; Dutkiewicz, Stephanie; Hopwood, Mark; Khazendar, Ala; Meire, Lorenz; Oliver, Hilde; et al (December 2025, Communications Earth & Environment)

   Abstract Seasonal phytoplankton blooms in Greenland’s coastal waters form the base of marine food webs and contribute to oceanic carbon uptake. In Qeqertarsuup Tunua, West Greenland, a secondary summertime bloom follows the Arctic spring bloom, enhancing annual primary productivity. Emerging evidence links this summer bloom to subglacial discharge from Sermeq Kujalleq, the most active glacier on the Greenland Ice Sheet. This discharge drives localized upwelling that may alleviate nutrient limitation in surface waters, yet this mechanism remains poorly quantified. Here, we employ a high-resolution biogeochemical model nested within a global state estimate to assess how discharge-driven upwelling influences primary productivity and carbon fluxes. We find that upwelling increases summer productivity by 15–40% in Qeqertarsuup Tunua, yet annual carbon dioxide uptake rises by only  ~3% due to reduced solubility in plume-upwelled waters. These findings suggest that intensifying ice sheet melt may alter Greenland’s coastal productivity and carbon cycling under future climate scenarios. 

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4. Decadal increases in carbon uptake offset by respiratory losses across northern permafrost ecosystems

   https://doi.org/10.1038/s41558-024-02057-4  

   See, Craig R; Virkkala, Anna-Maria; Natali, Susan M; Rogers, Brendan M; Mauritz, Marguerite; Biasi, Christina; Bokhorst, Stef; Boike, Julia; Bret-Harte, M Syndonia; Celis, Gerardo; et al (August 2024, Nature Climate Change)

   Abstract Tundra and boreal ecosystems encompass the northern circumpolar permafrost region and are experiencing rapid environmental change with important implications for the global carbon (C) budget. We analysed multi-decadal time series containing 302 annual estimates of carbon dioxide (CO₂) flux across 70 permafrost and non-permafrost ecosystems, and 672 estimates of summer CO₂flux across 181 ecosystems. We find an increase in the annual CO₂sink across non-permafrost ecosystems but not permafrost ecosystems, despite similar increases in summer uptake. Thus, recent non-growing-season CO₂losses have substantially impacted the CO₂balance of permafrost ecosystems. Furthermore, analysis of interannual variability reveals warmer summers amplify the C cycle (increase productivity and respiration) at putatively nitrogen-limited sites and at sites less reliant on summer precipitation for water use. Our findings suggest that water and nutrient availability will be important predictors of the C-cycle response of these ecosystems to future warming. 

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5. Simulating dynamic fire regime and vegetation change in a warming Siberia

   https://doi.org/10.1186/s42408-023-00188-1  

   Williams, Neil G.; Lucash, Melissa S.; Ouellette, Marc R.; Brussel, Thomas; Gustafson, Eric J.; Weiss, Shelby A.; Sturtevant, Brian R.; Schepaschenko, Dmitry G.; Shvidenko, Anatoly Z. (December 2023, Fire Ecology)

   Climate change is expected to increase fire activity across the circumboreal zone, including central Siberia. However, few studies have quantitatively assessed potential changes in fire regime characteristics, or considered possible spatial variation in the magnitude of change. Moreover, while simulations indicate that changes in climate are likely to drive major shifts in Siberian vegetation, knowledge of future forest dynamics under the joint influence of changes in climate and fire regimes remains largely theoretical. We used the forest landscape model, LANDIS-II, with PnET-Succession and the BFOLDS fire extension to simulate changes in vegetation and fire regime characteristics under four alternative climate scenarios in three 10,000-km2 study landscapes distributed across a large latitudinal gradient in lowland central Siberia. We evaluated vegetation change using the fire life history strategies adopted by forest tree species: fire resisters, fire avoiders, and fire endurers. Annual burned area, the number of fires per year, fire size, and fire intensity all increased under climate change. The relative increase in fire activity was greatest in the northernmost study landscape, leading to a reduction in the difference in fire rotation period between study landscapes. Although the number of fires per year increased progressively with the magnitude of climate change, mean fire size peaked under mild or moderate climate warming in each of our study landscapes, suggesting that fuel limitations and past fire perimeters will feed back to reduce individual fire extent under extreme warming, relative to less extreme warming scenarios. In the Southern and Midtaiga landscapes, we observed a major shift from fire resister-dominated forests to forests dominated by broadleaved deciduous fire endurers (Betula and Populus genera) under moderate and extreme climate warming scenarios, likely associated with the substantial increase in fire activity. These changes were accompanied by a major decrease in average cohort age and total vegetation biomass across the simulation landscapes. Our results imply that climate change will greatly increase fire activity and reduce spatial heterogeneity in fire regime characteristics across central Siberia. Potential ecological consequences include a widespread shift toward forests dominated by broadleaved deciduous species that employ a fire endurer strategy to persist in an increasingly fire-prone environment. 

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