ALBERT

Description: Vegetation models are essential tools for projecting large-scale land-cover response to changing climate, which is expected to alter the distribution of biomes and individual species. A large-scale bioclimatic envelope model (RuBCliM) and an individual species based gap model (UVAFME) are used to simulate the Russian forests under current and future climate for two greenhouse gas emissions scenarios. Results for current conditions are compared between models and assessed against two independent maps of Russian forest biomes and dominant tree species. Comparisons measured with kappa statistics indicate good agreement between the models (kappa values from 0.76 to 0.69), as well as between the model results and two observation-based maps for both species presence and absence (kappa values from 0.70 to 0.43). Agreement between these multiple types of data on forest distribution provides confidence in the projected forest response to changing climate. For future conditions, both models indicate a shift in the dominant biomes from conifers to deciduous leaved species. These projections have implications for feedbacks between the energy budget, carbon cycle, and land cover in the boreal system. The distinct biome and species changes emphasize the need for continued investigation of this landmass that has the size necessary to influence regional and global climate.

Description: In recent years, the pan-Arctic region has experienced increasingly extreme fire seasons. Fires in the northern high latitudes are driven by current and future climate change, lightning, fuel conditions, and human activity. In this context, conceptualizing and parameterizing current and future Arctic fire regimes will be important for fire and land management as well as understanding current and predicting future fire emissions. The objectives of this review were driven by policy questions identified by the Arctic Monitoring and Assessment Programme (AMAP) Working Group and posed to its Expert Group on Short-Lived Climate Forcers. This review synthesizes current understanding of the changing Arctic and boreal fire regimes, particularly as fire activity and its response to future climate change in the pan-Arctic have consequences for Arctic Council states aiming to mitigate and adapt to climate change in the north. The conclusions from our synthesis are the following. (1) Current and future Arctic fires, and the adjacent boreal region, are driven by natural (i.e. lightning) and human-caused ignition sources, including fires caused by timber and energy extraction, prescribed burning for landscape management, and tourism activities. Little is published in the scientific literature about cultural burning by Indigenous populations across the pan-Arctic, and questions remain on the source of ignitions above 70∘ N in Arctic Russia. (2) Climate change is expected to make Arctic fires more likely by increasing the likelihood of extreme fire weather, increased lightning activity, and drier vegetative and ground fuel conditions. (3) To some extent, shifting agricultural land use and forest transitions from forest–steppe to steppe, tundra to taiga, and coniferous to deciduous in a warmer climate may increase and decrease open biomass burning, depending on land use in addition to climate-driven biome shifts. However, at the country and landscape scales, these relationships are not well established. (4) Current black carbon and PM2.5 emissions from wildfires above 50 and 65∘ N are larger than emissions from the anthropogenic sectors of residential combustion, transportation, and flaring. Wildfire emissions have increased from 2010 to 2020, particularly above 60∘ N, with 56 % of black carbon emissions above 65∘ N in 2020 attributed to open biomass burning – indicating how extreme the 2020 wildfire season was and how severe future Arctic wildfire seasons can potentially be. (5) What works in the boreal zones to prevent and fight wildfires may not work in the Arctic. Fire management will need to adapt to a changing climate, economic development, the Indigenous and local communities, and fragile northern ecosystems, including permafrost and peatlands. (6) Factors contributing to the uncertainty of predicting and quantifying future Arctic fire regimes include underestimation of Arctic fires by satellite systems, lack of agreement between Earth observations and official statistics, and still needed refinements of location, conditions, and previous fire return intervals on peat and permafrost landscapes. This review highlights that much research is needed in order to understand the local and regional impacts of the changing Arctic fire regime on emissions and the global climate, ecosystems, and pan-Arctic communities.

Description: Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land \nuse and climate have considerably reduced the scale of this system1 \n. Remote-sensing \nestimates to quantify carbon losses from global forests2\xe2\x80\x935 \n are characterized by \nconsiderable uncertainty and we lack a comprehensive ground-sourced evaluation to \nbenchmark these estimates. Here we combine several ground-sourced6 \n and satellitederived approaches2,7,8 \n to evaluate the scale of the global forest carbon potential \noutside agricultural and urban lands. Despite regional variation, the predictions \ndemonstrated remarkable consistency at a global scale, with only a 12% diference \nbetween the ground-sourced and satellite-derived estimates. At present, global forest \ncarbon storage is markedly under the natural potential, with a total defcit of 226\xe2\x80\x89Gt \n(model range\xe2\x80\x89=\xe2\x80\x89151\xe2\x80\x93363\xe2\x80\x89Gt) in areas with low human footprint. Most (61%, 139\xe2\x80\x89Gt\xe2\x80\x89C) \nof this potential is in areas with existing forests, in which ecosystem protection can \nallow forests to recover to maturity. The remaining 39% (87\xe2\x80\x89Gt\xe2\x80\x89C) of potential lies in \nregions in which forests have been removed or fragmented. Although forests cannot \nbe a substitute for emissions reductions, our results support the idea2,3,9 \n that the \nconservation, restoration and sustainable management of diverse forests ofer \nvaluable contributions to meeting global climate and biodiversity targets.

Description: Understanding what controls global leaf type variation in trees is crucial for \ncomprehending their role in terrestrial ecosystems, including carbon, water \nand nutrient dynamics. Yet our understanding of the factors infuencing \nforest leaf types remains incomplete, leaving us uncertain about the global \nproportions of needle-leaved, broadleaved, evergreen and deciduous \ntrees. To address these gaps, we conducted a global, ground-sourced \nassessment of forest leaf-type variation by integrating forest inventory \ndata with comprehensive leaf form (broadleaf vs needle-leaf) and habit \n(evergreen vs deciduous) records. We found that global variation in leaf \nhabit is primarily driven by isothermality and soil characteristics, while leaf \nform is predominantly driven by temperature. Given these relationships, \nwe estimate that 38% of global tree individuals are needle-leaved evergreen, \n29% are broadleaved evergreen, 27% are broadleaved deciduous and \n5% are needle-leaved deciduous. The aboveground biomass distribution \namong these tree types is approximately 21% (126.4\xe2\x80\x89Gt), 54% (335.7\xe2\x80\x89Gt), 22% \n(136.2\xe2\x80\x89Gt) and 3% (18.7\xe2\x80\x89Gt), respectively. We further project that, depending \non future emissions pathways, 17\xe2\x80\x9334% of forested areas will experience \nclimate conditions by the end of the century that currently support a \ndiferent forest type, highlighting the intensifcation of climatic stress on \nexisting forests. By quantifying the distribution of tree leaf types and their \ncorresponding biomass, and identifying regions where climate change will \nexert greatest pressure on current leaf types, our results can help improve \npredictions of future terrestrial ecosystem functioning and carbon cycling.