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1. Arctic sea ice retreat fuels boreal forest advance

   https://doi.org/10.1126/science.adh2339  

   Dial, Roman J ; Maher, Colin T ; Hewitt, Rebecca E ; Wockenfuss, Amy M ; Wong, Russell E ; Crawford, Daniel J ; Zietlow, Madeline G ; Sullivan, Patrick F ( February 2024 , Science)

   Climate-induced northward advance of boreal forest is expected to lessen albedo, alter carbon stocks, and replace tundra, but where and when this advance will occur remains largely unknown. Using data from 19 sites across 22 degrees of longitude along the tree line of northern Alaska, we show a stronger temporal correlation of tree ring growth with open water uncovered by retreating Arctic sea ice than with air temperature. Spatially, our results suggest that tree growth, recruitment, and range expansion are causally linked to open water through associated warmer temperatures, deeper snowpacks, and improved nutrient availability. We apply a meta-analysis to 82 circumarctic sites, finding that proportionally more tree lines have advanced where proximal to ongoing sea ice loss. Taken together, these findings underpin how and where changing sea ice conditions facilitate high-latitude forest advance.

    

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2. Disturbances in North American boreal forest and Arctic tundra: impacts, interactions, and responses

   https://doi.org/10.1088/1748-9326/ac98d7  

   Foster, Adrianna C. ; Wang, Jonathan A. ; Frost, Gerald V. ; Davidson, Scott J. ; Hoy, Elizabeth ; Turner, Kevin W. ; Sonnentag, Oliver ; Epstein, Howard ; Berner, Logan T. ; Armstrong, Amanda H. ; et al ( October 2022 , Environmental Research Letters)

   Ecosystems in the North American Arctic-Boreal Zone (ABZ) experience a diverse set of disturbances associated with wildfire, permafrost dynamics, geomorphic processes, insect outbreaks and pathogens, extreme weather events, and human activity. Climate warming in the ABZ is occurring at over twice the rate of the global average, and as a result the extent, frequency, and severity of these disturbances are increasing rapidly. Disturbances in the ABZ span a wide gradient of spatiotemporal scales and have varying impacts on ecosystem properties and function. However, many ABZ disturbances are relatively understudied and have different sensitivities to climate and trajectories of recovery, resulting in considerable uncertainty in the impacts of climate warming and human land use on ABZ vegetation dynamics and in the interactions between disturbance types. Here we review the current knowledge of ABZ disturbances and their precursors, ecosystem impacts, temporal frequencies, spatial extents, and severity. We also summarize current knowledge of interactions and feedbacks among ABZ disturbances and characterize typical trajectories of vegetation loss and recovery in response to ecosystem disturbance using satellite time-series. We conclude with a summary of critical data and knowledge gaps and identify priorities for future study.

    

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3. Understory plant diversity and composition across a postfire tree density gradient in a Siberian Arctic boreal forest

   https://doi.org/10.1139/cjfr-2020-0483  

   Paulson, Alison K. ; Peña, Homero ; Alexander, Heather D. ; Davydov, Sergei P. ; Loranty, Michael M. ; Mack, Michelle C. ; Natali, Susan M. ( May 2021 , Canadian Journal of Forest Research)

   null (Ed.)

   Cajander larch (Larix cajanderi Mayr.) forests of the Siberian Arctic are experiencing increased wildfire activity in conjunction with climate warming. These shifts could affect postfire variation in the density and arrangement of trees and understory plant communities. To better understand how understory plant composition, abundance, and diversity vary with tree density, we surveyed understory plant communities and stand characteristics (e.g., canopy cover, active layer depth, and soil organic layer depth) within 25 stands representing a density gradient of similarly-aged larch trees that established following a 1940 fire near Cherskiy, Russia. Understory plant diversity and mean total plant abundance decreased with increased canopy cover. Canopy cover was also the most important variable affecting individual species’ abundances. In general, tall shrubs (e.g., Betula nana subsp. exilis) were more abundant in low-density stands with high light availability, and mosses (e.g., Sanionia spp.) were more abundant in high-density stands with low light availability. These results provide evidence that postfire variation in tree recruitment affects understory plant community composition and diversity as stands mature. Therefore, projected increases in wildfire activity in the Siberian Arctic could have cascading impacts on forest structure and composition in both overstory and understory plant communities. 

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4. Perspectives on Sustainable Forest Management in Interior Alaska Boreal Forest: Recent History and Challenges

   https://doi.org/10.3390/f10060484  

   Morimoto, Miho ; Juday, Glenn ( June 2019 , Forests)

   Research Highlights: Interior Alaska boreal forest is still largely intact and forest harvest management, if applied appropriately across the forest landscape, can potentially mitigate the effects of climate warming, such as increasing wildfire and decreasing mature tree growth. Background and Objectives: This study examines historical relationships between forest growth and harvest in central boreal Alaska over the last 40 years in order to contribute to the development of sustainable forest harvesting practices. Materials and Methods: We compiled data from forest inventory and forest harvest and reforestation databases and analyzed harvesting intensity relative to growth. Results: Forest harvest management has relied heavily on natural regeneration due to a small profit margin. We found that volume harvested in the last 40 years was lower than volume growth; however, harvest activity was concentrated on the small road-accessible area and in the mature white spruce type. As a result, harvest activities need to be distributed geographically and by species in a way that prevents reduction of forest productivity or loss of ecosystem services. An expansion of the road network, or a shift in harvesting and utilization from white spruce to broadleaf would allow a significant increase in sustainable wood yield. Conclusions: There are two potential areas that could provide increased harvest, which contain a large amount of white spruce, birch, and aspen. Under rapid climate change, sustainable forest harvest management must consider the effects of fires, such as needs of salvage logging and a potential reduction of harvestable timber volumes due to damages. Forest harvest management could emulate natural fire disturbance and help reduce fuel amounts to prevent intensive and large-scale fires in the future in areas where fires are most aggressively suppressed. 

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5. The Boreal–Arctic Wetland and Lake Dataset (BAWLD)

   https://doi.org/10.5194/essd-13-5127-2021  

   Olefeldt, David ; Hovemyr, Mikael ; Kuhn, McKenzie A. ; Bastviken, David ; Bohn, Theodore J. ; Connolly, John ; Crill, Patrick ; Euskirchen, Eugénie S. ; Finkelstein, Sarah A. ; Genet, Hélène ; et al ( January 2021 , Earth System Science Data)

   Abstract. Methane emissions from boreal and arctic wetlands, lakes, and rivers areexpected to increase in response to warming and associated permafrost thaw.However, the lack of appropriate land cover datasets for scalingfield-measured methane emissions to circumpolar scales has contributed to alarge uncertainty for our understanding of present-day and future methaneemissions. Here we present the Boreal–Arctic Wetland and Lake Dataset(BAWLD), a land cover dataset based on an expert assessment, extrapolatedusing random forest modelling from available spatial datasets of climate,topography, soils, permafrost conditions, vegetation, wetlands, and surfacewater extents and dynamics. In BAWLD, we estimate the fractional coverage offive wetland, seven lake, and three river classes within 0.5 × 0.5∘ grid cells that cover the northern boreal and tundra biomes(17 % of the global land surface). Land cover classes were defined usingcriteria that ensured distinct methane emissions among classes, as indicatedby a co-developed comprehensive dataset of methane flux observations. InBAWLD, wetlands occupied 3.2 × 106 km2 (14 % of domain)with a 95 % confidence interval between 2.8 and 3.8 × 106 km2. Bog, fen, and permafrost bog were the most abundant wetlandclasses, covering ∼ 28 % each of the total wetland area,while the highest-methane-emitting marsh and tundra wetland classes occupied5 % and 12 %, respectively. Lakes, defined to include all lentic open-waterecosystems regardless of size, covered 1.4 × 106 km2(6 % of domain). Low-methane-emitting large lakes (>10 km2) and glacial lakes jointly represented 78 % of the total lakearea, while high-emitting peatland and yedoma lakes covered 18 % and 4 %,respectively. Small (<0.1 km2) glacial, peatland, and yedomalakes combined covered 17 % of the total lake area but contributeddisproportionally to the overall spatial uncertainty in lake area with a95 % confidence interval between 0.15 and 0.38 × 106 km2. Rivers and streams were estimated to cover 0.12  × 106 km2 (0.5 % of domain), of which 8 % was associated withhigh-methane-emitting headwaters that drain organic-rich landscapes.Distinct combinations of spatially co-occurring wetland and lake classeswere identified across the BAWLD domain, allowing for the mapping of“wetscapes” that have characteristic methane emission magnitudes andsensitivities to climate change at regional scales. With BAWLD, we provide adataset which avoids double-accounting of wetland, lake, and river extentsand which includes confidence intervals for each land cover class. As such,BAWLD will be suitable for many hydrological and biogeochemical modellingand upscaling efforts for the northern boreal and arctic region, inparticular those aimed at improving assessments of current and futuremethane emissions. Data are freely available athttps://doi.org/10.18739/A2C824F9X (Olefeldt et al., 2021). 

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