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Only a few palaeo-records extend beyond the Holocene in Yakutia, eastern Siberia, since most of the lakes in the region are of Holocene thermokarst origin. Thus, we have a poor understanding of the long-term interactions between terrestrial and aquatic ecosystems and their response to climate change. The Lake Khamra region in southwestern Yakutia is of particular interest because it is in the transition zones from discontinuous to sporadic permafrost and from summergreen to evergreen boreal forests. Our multiproxy study of Lake Khamra sediments reaching back to the Last Glacial Maximum 21 cal ka BP, includes analyses of organic carbon, nitrogen, XRF-derived elements, sedimentary ancient DNA amplicon sequencing of aquatic and terrestrial plants and diatoms, as well as classical counting of pollen and non-pollen palynomorphs (NPP). The palaeogenetic approach revealed 45 diatom, 191 terrestrial plant, and 65 aquatic macrophyte taxa. Pollen analyses identified 34 pollen taxa and 28 NPP taxa. The inferred terrestrial ecosystem of the Last Glacial comprises tundra vegetation dominated by forbs and grasses, likely inhabited by megaherbivores. By 18.4 cal ka BP a lake had developed with a high abundance of macrophytes and dominant fragilarioid diatoms, while shrubs expanded around the lake. In the Bølling-Allerød at 14.7 cal ka BP both the terrestrial and aquatic systems reflect climate amelioration, alongside lake water-level rise and woodland establishment, which was curbed by the Younger Dryas cooling. In the Early Holocene warmer and wetter climate led to taiga development and lake water-level rise, reflected by diatom composition turnover from only epiphytic to planktonic diatoms. In the Mid-Holocene the lake water level decreased at ca. 8.2 cal ka BP and increased again at ca. 6.5 cal ka BP. At the same time mixed evergreen-summergreen forest expanded. In the Late Holocene, at ca. 4 cal ka BP, vegetation cover similar to modern conditions established. This stu

[Background] The global human footprint has fundamentally altered wildfire regimes, creating serious consequences for human health, biodiversity, and climate. However, it remains difficult to project how long-term interactions among land use, management, and climate change will affect fire behavior, representing a key knowledge gap for sustainable management. We used expert assessment to combine opinions about past and future fire regimes from 99 wildfire researchers. We asked for quantitative and qualitative assessments of the frequency, type, and implications of fire regime change from the beginning of the Holocene through the year 2300., [Results] Respondents indicated some direct human influence on wildfire since at least ~ 12,000 years BP, though natural climate variability remained the dominant driver of fire regime change until around 5,000 years BP, for most study regions. Responses suggested a ten-fold increase in the frequency of fire regime change during the last 250 years compared with the rest of the Holocene, corresponding first with the intensification and extensification of land use and later with anthropogenic climate change. Looking to the future, fire regimes were predicted to intensify, with increases in frequency, severity, and size in all biomes except grassland ecosystems. Fire regimes showed different climate sensitivities across biomes, but the likelihood of fire regime change increased with higher warming scenarios for all biomes. Biodiversity, carbon storage, and other ecosystem services were predicted to decrease for most biomes under higher emission scenarios. We present recommendations for adaptation and mitigation under emerging fire regimes, while recognizing that management options are constrained under higher emission scenarios., [Conclusion] The influence of humans on wildfire regimes has increased over the last two centuries. The perspective gained from past fires should be considered in land and fire management strategies, but novel fire behavior is likely given the unprecedented human disruption of plant communities, climate, and other factors. Future fire regimes are likely to degrade key ecosystem services, unless climate change is aggressively mitigated. Expert assessment complements empirical data and modeling, providing a broader perspective of fire science to inform decision making and future research priorities.

In Sibirien wüteten in den letzten Jahren große Waldbrände. Neben der Bedrohung, die sie für menschliche Aktivitäten und Infrastruktur darstellen, könnten sie bei zunehmender Intensität und Frequenz auch eine einzigartige, von Permafrost geprägte Landschaft nachhaltig destabilisieren. Um mögliche Wechselwirkungen zwischen zunehmender Waldbrandaktivität und Waldstruktur auf langen Zeitskalen zu verstehen, werfen paläoökologisch Forschende einen Blick unter Wasser: In über lange Zeit abgelagerten Seesedimenten geben Verbrennungsprodukte Einblick in Waldbrandaktivitäten längst vergangener Zeiten.

The year 2021 set new records for wildfire extent in the Republic of Sakha (Yakutia) in eastern Siberia, Russia. Wildfire seasons in this unique region, characterized by its deciduous boreal forest and permafrost landforms, are becoming more intense. Some fires are threatening local communities, while their smoke covers vast stretches of land every summer, posing health risks to people even in the distance. At the same time, the larch trees of the eastern Siberian boreal forest stabilize the permafrost soils below as guardians of a continental-scale storage of terrestrial carbon. It is still largely unknown how the current trend of wildfire intensification will develop in the future, and how it will modify the structure of the boreal forests within the next decades to centuries. However, even though needed for a well-founded evaluation of long-term impacts of changing fire regimes, data on past trends of wildfire activity still remains scarce in eastern Siberia. Here, we present a new reconstruction of boreal fire and vegetation dynamics, spanning the last ca. 10.8 ka. Continuously analyzed macroscopic charcoal particles and a REVEALS-transformed pollen record from a sediment core from Lake Satagay (N 63.078, E 117.998) give insight into long-term trends and relationships between changes in fire regime and vegetation composition and coverage. The data indicates that modern larch-dominated forests co-exist with a lower severity fire regime, whereas early Holocene open larch-birch woodlands enabled increased charcoal accumulation and thus supported a higher severity fire regime. Considering the expected increase in tree mortality caused by wildfires and insect damage, likely to thin out currently denser tree stands, this fire-vegetation relationship suggests a potential upcoming positive feedback on intensifying fire regimes.

The permafrost-shaped landscape of Central Yakutia is particularly rich in thermokarst lakes, which provide important cultural and ecosystem services to the local population. Climate warming and an intensification of agriculture in alaas systems (i.e. mostly drained basins of large thaw lakes formed during the early Holocene under warm climatic conditions) in the Central Yakutian Lowlands may lead to pronounced changes in water resources, water quality, nutrient loading and biodiversity. This could in turn threaten the livelihoods of affected communities, who depend on functional alaas ecosystems. To better foresee potential future impacts of environmental changes on internal lake ecological processes, it is important to gain a better understanding of how thermokarst lakes reacted to such changes in the past. Here, we present a new paleoenvironmental reconstruction of ecological changes within Lake Satagay (N 63.078, E 117.998, Nyurbinsky District), covering the last ca. 10,800 years. We use sedimentological and XRF-derived geochemical parameters, in addition to the metabarcoding of sedimentary ancient DNA (sedDNA) for diatoms and aquatic plants, and microscopic diatom analyses, to evaluate sedimentological and biodiversity shifts throughout the Holocene. Our study revealed 53 diatom DNA sequence types and 53 species morphologically. High distributions of Stephanodiscus and Fragilaria, among multiple other diatom genera in the early Holocene, indicate that initial formation of this typical alaas lake occurred earlier than expected (i.e. before 10,800 BP). In recent millennia diatom abundance decreased and their community is almost exclusively composed of Pseudostaurosira and Fragilaria. Composition of aquatic plants show an overall dominance of Ceratophyllaceae and strong fluctuations in Potamogetonaceae likely related to lake level and water chemical changes. All proxies investigated support that lake conditions and biotic composition has been resilient since 4,000

Wildfires play an essential role in the ecology of boreal forests. In eastern Siberia, fire activity has been increasing in recent years, challenging the livelihoods of local communities. Intensifying fire regimes also increase disturbance pressure on the boreal forests, which currently protect the permafrost beneath from accelerated degradation. However, long-term relationships between changes in fire regime and forest structure remain largely unknown. We assess past fire-vegetation feedbacks using sedimentary proxy records from Lake Satagay, Central Yakutia, Siberia, covering the past c. 10,800 years. Results from macroscopic and microscopic charcoal analyses indicate high amounts of burnt biomass during the Early Holocene, and that the present-day, low-severity surface fire regime has been in place since c. 4,500 years before present. A pollen-based quantitative reconstruction of vegetation cover and a terrestrial plant record based on sedimentary ancient DNA metabarcoding suggest a pronounced shift in forest structure toward the Late Holocene. Whereas the Early Holocene was characterized by postglacial open larch-birch woodlands, forest structure changed toward the modern, mixed larch-dominated closed-canopy forest during the Mid-Holocene. We propose a potential relationship between open woodlands and high amounts of burnt biomass, as well as a mediating effect of dense larch forest on the climate-driven intensification of fire regimes. Considering the anticipated increase in forest disturbances (droughts, insect invasions, and wildfires), higher tree mortality may force the modern state of the forest to shift toward an open woodland state comparable to the Early Holocene. Such a shift in forest structure may result in a positive feedback on currently intensifying wildfires. These new long-term data improve our understanding of millennial-scale fire regime changes and their relationships to changes of vegetation in Central Yakutia, where the local population is

Wildfires, as a key disturbance in forest ecosystems, are shaping the world's boreal landscapes. Changes in fire regimes are closely linked to a wide array of environmental factors, such as vegetation composition, climate change, and human activity. Arctic and boreal regions and, in particular, Siberian boreal forests are experiencing rising air and ground temperatures with the subsequent degradation of permafrost soils leading to shifts in tree cover and species composition. Compared to the boreal zones of North America or Europe, little is known about how such environmental changes might influence long-term fire regimes in Russia. The larch-dominated eastern Siberian deciduous boreal forests differ markedly from the composition of other boreal forests, yet data about past fire regimes remain sparse. Here, we present a high-resolution macroscopic charcoal record from lacustrine sediments of Lake Khamra (south-west Yakutia, Siberia) spanning the last ca. 2200 years, including information about charcoal particle sizes and morphotypes. Our results reveal a phase of increased charcoal accumulation between 600 and 900 CE, indicative of relatively high amounts of burnt biomass and high fire frequencies. This is followed by an almost 900-year-long period of low charcoal accumulation without significant peaks likely corresponding to cooler climate conditions. After 1750 CE fire frequencies and the relative amount of biomass burnt start to increase again, coinciding with a warming climate and increased anthropogenic land development after Russian colonization. In the 20th century, total charcoal accumulation decreases again to very low levels despite higher fire frequency, potentially reflecting a change in fire management strategies and/or a shift of the fire regime towards more frequent but smaller fires. A similar pattern for different charcoal morphotypes and comparison to a pollen and non-pollen palynomorph (NPP) record from the same sediment core indicate that broad-s

Wildfires are an essential ecological process, located at the interface between atmosphere, biosphere, and geosphere. Climate-related changes in their appearance and frequency will shape the boreal forest of tomorrow, the largest terrestrial biome responsible for numerous important ecosystem functions. Changing fire regimes could also increase pressure on fire management and become a threat for humans living in Siberia. However, a lack of long-term fire reconstructions complicates the understanding of the main drivers in the larch-dominated forests of eastern Siberia. At the same time, this lack of long-term understanding also aggravates the validation of fire-vegetation models, and thus predictions of future changes of fire regimes in this vital region. Here, we present a new fire module being built for the individual-based, spatially explicit vegetation model LAVESI (Larix Vegetation Simulator). LAVESI is able to simulate fine-scale interactions in individual tree’s life stages and detailed population dynamics, now expanded by the ability of wildfires igniting and damaging biomass. Fire-vegetation simulations were computed around the catchment of Lake Khamra (SW Yakutia), which experienced forest fires in the years 2007 and 2014 according to remote sensing imagery. From the lake, we previously contributed a new, sedimentary charcoal-based fire reconstruction of the late Holocene. Testing the fire module at a current study site, where modern and historic data has already been collected, allows us to improve it, and look into ways in which the fire reconstruction might help inform the model, before eventually scaling it up to cover larger regions. This represents a first step towards a reliable fire-vegetation model, able to predict future impacts of fires on both the forests of eastern Siberia, as well as the humans living there.

Recent large-scale fire events in Siberia have drawn increased attention to boreal forest fire history. Boreal forests contain about 25% of all global biomass and act as an enormous carbon storage. Fire events are important ecological disturbances connected to the overarching environmental changes that face the Arctic and Subarctic, like vegetation dynamics, permafrost degradation, changes in soil nutrient cycling and global warming, and act as the dominant driver behind boreal forest’s landscape carbon balance. By looking into past fire regimes we can learn about fire frequency and potential linkages to other environmental factors, e.g. fuel types, reconstructed temperature/humidity or geomorphologic landscape dynamics. Unfortunately, fire history data is still very sparse in large parts of Siberia, a region strongly influenced by climate change. The Global Charcoal Database (www.paleofire.org) lists only a handful of continuous charcoal records for all of Siberia, with only three of those featuring published data from macroscopic charcoal as opposed to microscopic charcoal from pollen slides. We aim to reconstruct the late Holocene fire history using lacustrine sediments of Lake Khamra (SW Yakutia at N 59.99°, E 112.98°). It covers an area of c. 4.6 km² with about 22 m maximum water depth, located within the zone of transition from summer-green and larch-dominated to evergreen boreal forest. We present the first continuous, high-resolution (c. 10 years/sample) macroscopic charcoal record (> 150 μm) including information on particle size and morphology for the past c. 2200 years. We compare this to complementary information from microscopic charcoal in pollen slides, a pollen and non-pollen palynomorph record as well as μXRF data. This multi-proxy approach adds valuable data about fire activity in the region and allows a comparison of different prevalent fire reconstruction methods. As the first record of its kind from Siberia, it provides a long-term context for c

Even though wildfires are an important ecological component of larch-dominated boreal forests in eastern Siberia, intensifying fire regimes may induce large-scale shifts in forest structure and composition. Recent paleoecological research suggests that such a state change, apart from threatening human livelihoods, may result in a positive feedback on intensifying wildfires and increased permafrost degradation [1]. Common fire-vegetation models mostly do not explicitly include detailed individual-based tree population dynamics. However, setting a focus on patterns of forest structure emerging from interactions among individual trees in the unique forest system of eastern Siberia may provide beneficial perspectives on the impacts of changing fire regimes. LAVESI (Larix Vegetation Simulator) has been previously introduced as an individual-based, spatially explicit vegetation model for simulating fine-scale tree population dynamics [2]. It has since been expanded with wind-driven pollen dispersal, landscape topography, and the inclusion of multiple tree species. However, until now, it could not be used to simulate effects of changing fire regimes on those detailed tree population dynamics. We present simulations of annually computed tree populations during the past c. 20,000 years in LAVESI, while applying a newly implemented fire module. Wildfire ignitions can stochastically occur depending on the monthly fire weather. Within the affected area, fire intensity is mediated by surface moisture. Fire severity depends on the intensity, with scaled impacts on trees, seeds and the litter layer. Each tree has a chance to survive wildfires based on a resistivity estimated from its height and species-specific traits of bark thickness, crown height, and their ability to resprout. The modelled annual fire probability compares well with a local reconstruction of charcoal influx in lake sediments. Simulation results at a study site in Central Yakutia, Siberia, indicate that the incl