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1. Controls over Fire Characteristics in Siberian Larch Forests

   https://doi.org/10.1007/s10021-024-00927-8  

   Webb, Elizabeth E; Alexander, Heather D; Loranty, Michael M; Talucci, Anna C; Lichstein, Jeremy W (September 2024, Ecosystems)
2. Siberian taiga and tundra fire regimes from 2001–2020

   https://doi.org/10.1088/1748-9326/ac3f07  

   Talucci, Anna C.; Loranty, Michael M.; Alexander, Heather D. (January 2022, Environmental Research Letters)

   Abstract Circum-boreal and -tundra systems are crucial carbon pools that are experiencing amplified warming and are at risk of increasing wildfire activity. Changes in wildfire activity have broad implications for vegetation dynamics, underlying permafrost soils, and ultimately, carbon cycling. However, understanding wildfire effects on biophysical processes across eastern Siberian taiga and tundra remains challenging because of the lack of an easily accessible annual fire perimeter database and underestimation of area burned by MODIS satellite imagery. To better understand wildfire dynamics over the last 20 years in this region, we mapped area burned, generated a fire perimeter database, and characterized fire regimes across eight ecozones spanning 7.8 million km²of eastern Siberian taiga and tundra from ∼61–72.5° N and 100° E–176° W using long-term satellite data from Landsat, processed via Google Earth Engine. We generated composite images for the annual growing season (May–September), which allowed mitigation of missing data from snow-cover, cloud-cover, and the Landsat 7 scan line error. We used annual composites to calculate the difference Normalized Burn Ratio (dNBR) for each year. The annual dNBR images were converted to binary burned or unburned imagery that was used to vectorize fire perimeters. We mapped 22 091 fires burning 152 million hectares (Mha) over 20 years. Although 2003 was the largest fire year on record, 2020 was an exceptional fire year for four of the northeastern ecozones resulting in substantial increases in fire activity above the Arctic Circle. Increases in fire extent, severity, and frequency with continued climate warming will impact vegetation and permafrost dynamics with increased likelihood of irreversible permafrost thaw that leads to increased carbon release and/or conversion of forest to shrublands. 

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3. Fire‐Induced Carbon Loss and Tree Mortality in Siberian Larch Forests

   https://doi.org/10.1029/2023GL105216  

   Webb, Elizabeth E; Alexander, Heather D; Paulson, Alison K; Loranty, Michael M; DeMarco, Jennie; Talucci, Anna C; Spektor, Valentin; Zimov, Nikita; Lichstein, Jeremy W (January 2024, Geophysical Research Letters)

   Climate change is intensifying the fire regime across Siberia, with the potential to alter carbon combustion and post‐fire carbon re‐accumulation trajectories. Few field‐based estimates of fire severity (e.g., carbon combustion and tree mortality) exist in Siberian larch forests (Larixspp.), which limits our ability to project how an intensified fire regime will affect regional and global climate feedbacks. Here, we present field‐based estimates of fire‐induced tree mortality and carbon loss in eastern Siberian larch forests. Our results suggest that fires in this region result in high tree mortality (means of 83% and 76% at Arctic and subarctic sites, respectively). In both absolute and relative terms, aboveground carbon loss following fire is higher in Siberian larch forests than in North America, but belowground carbon loss is considerably lower. This suggests fundamental differences in wildfire behavior and carbon dynamics between dominant vegetation types across the boreal biome. 

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4. Spatial patterns of unburned refugia in Siberian larch forests during the exceptional 2020 fire season

   https://doi.org/10.1111/geb.13529  

   Talucci, Anna C.; Loranty, Michael M.; Alexander, Heather D. (May 2022, Global Ecology and Biogeography)

   Abstract AimWildfire is an essential disturbance agent that creates burn mosaics, or a patchwork of burned and unburned areas across the landscape. Unburned patches, fire refugia, serve as carbon sinks and seed sources for forest regeneration in burned areas. In the Cajander larch (Larix cajanderiMayr.) forests of north‐eastern Siberia, an unprecedented wildfire season in 2020 and little documentation of landscape patch dynamics have resulted in research gaps about the characteristics of fire refugia in northern latitude forests, which are warming faster than other global forest ecosystems. We aim to characterize the 2010 distribution of fire refugia for these forest ecosystems and evaluate their topographic drivers. LocationNorth‐eastern Siberia across the North‐east Siberian Taiga and the Cherskii‐Kolyma Mountain Tundra ecozones. Time period2001–2020. Major taxa studiedCajander larch. MethodsWe used Landsat imagery to define burned and unburned patches, and the Arctic digital elevation model to calculate topographic variables. We characterized the size and density of fire refugia. We sampled individual pixels (n = 80,000) from an image stack that included a binary burned/unburned, elevation, slope, aspect, topographic position index, ruggedness, and tree cover from 2001 to 2020. We evaluated the topographic drivers of fire refugia with boosted regression trees. ResultsWe found no substantial difference in fire refugia size and density across the region. The fire refugia size averaged 7.2 ha (0.09–150,439 ha). The majority of interior burned patches exceed the potential wind dispersal distance from fire refugia. Topographic position index and terrain steepness were important predictors of fire refugia. Main conclusionsUnprecedented wildfires in 2020 did not impact fire refugia formation. Fire refugia are strongly controlled by topographic positions such as uplands and lowlands that influence microsite hydrological conditions. Fire refugia contribute to postfire landscape heterogeneity that preserves ecosystem functions, seed sources, habitat, and carbon sinks. 

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5. A nearly century long (1920-2017) Siberian alder (Alnus viridis ssp. fruticosa) secondary growth record near Sagwon Bluffs Alaska, USA

   https://doi.org/10.18739/A27M0421K  

   Drew, Jackson; Bret-Harte, Marion; Buchwal, Agata; Heslop, Calvin (January 2023, NSF Arctic Data Center)

   This data set contains measures of growth ring widths of Siberian alder (Alnus viridis ssp. fruticosa) from along the Sagwon Bluffs, Alaska, USA that was used to address how alder respond to temperature overtime and how plant age impacts their climate sensitivity. There are six individual files. One, the growth ring width data from each cross-section or part taken from an individual Siberian alder. Two, a data set of the detrended chronology with climate data over the period of 1920-2017. Three, a data set of individual detrended secondary growth with temperature and age data over the period of 1977-2016. Four, a data set relating individual alder's first 30 years of growth to temperature and the time period it started growth in. Five, a data set of detrended growth from cross-sections taken from each Siberian alder, age class information, and temperature. Finally, a data set containing the number of ramets, nodule biomass per area, and nitrogen fixation rate. 

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