The fire season of 2020 in Siberia set a precedent for extreme wildfires in the Arctic tundra. Large fires burned in the carbon-rich permafrost landscape, releasing vast amounts of carbon, and changing land surface processes by burning vegetation and organic soils. However, little is known about the mosaics of burned and unburned patches formed by tundra fires and the underlying processes that generate them. In this study, we investigated six fire scars in the northeastern Siberian tundra using high-resolution PlanetScope imagery (3 m) to map burned fraction within the scars. We then used Bayesian mixed models to identify which biotic and abiotic predictors influenced the burned fraction. We observed high spatial variation in burned fraction across all tundra landforms common to the region. Current medium-resolution fire products could not capture this heterogeneity, thereby underestimating the burned area of fire scars by a factor of 1.1 to 4.4. The heterogeneity of the burn mosaic indicates a mix of burned and unburned patches, with median unburned patch sizes being smaller than 180 to 324 m². Pre-fire land surface temperature, vegetation heterogeneity and topography predicted burn fraction in our analysis, matching factors previously shown to influence large-scale fire occurrence in the Arctic. Future studies need to consider the fine-scale heterogeneity within tundra landscapes to improve our understanding and predictions of fire spread, carbon emissions, post-fire recovery and ecosystem functioning.

The effects of climate change on plants are particularly pronounced in the Arctic region. Warming relaxes the temperature and nutrients boundaries that limit tundra plant growth. Increased resource availability under future climate conditions may induce a shift from a conservative economic strategy to an acquisitive one. Following the leaf economics spectrum that hypothesizes a strategy gradient between survival, plant size and costs for the photosynthetic leaf area, light absorption of tundra plants may increase. We investigated climate change effects on light absorptance and the relationship between light absorptance (fraction of absorbed photosynthetically active radiation, FAPAR) and structural and nutritional leaf traits, performing a soil warming and surface soil fertilization experiment on two deciduous tundra shrub species. Our results show that fertilization and warming both increase light absorptance in Arctic shrubs and that FAPAR is correlated with leaf nutrients but not with structural leaf traits. This indicates an economic strategy shift of shrubs from conservative to acquisitive induced by warming and fertilization. We found species-specific differences: FAPAR was influenced by warming alone in Betula nana but not in Salix pulchra, and FAPAR was correlated with leaf phosphorus in B. nana but not in S. pulchra. We attribute this to water limitation of B. nana that generally grows in drier areas within the study site compared to S. pulchra. We conclude that FAPAR is a measure that opens up more possibilities to estimate nutritional leaf traits and nutrient cycles, plant economic strategies, and ecological feedbacks of the tundra ecosystem on broader scales.

The Arctic tundra biome is undergoing rapid shrub expansion (“shrubification”) in response to anthropogenic climate change. During the previous ~2.6 million years, glacial cycles caused substantial shifts in Arctic vegetation, leading to changes in species’ distributions, abundance, and connectivity, which have left lasting impacts on the genetic structure of modern populations. Examining how shrubs responded to past climate change using genetic data can inform the ecological and evolutionary consequences of shrub expansion today. Here we test scenarios of Quaternary population history of dwarf birch species (Betula nana L. and Betula Glandulosa Michx.) using SNP markers obtained from RAD sequencing and approximate Bayesian computation. We compare the timings of population events with ice sheet reconstructions and other paleoenvironmental information to untangle the impacts of alternating cold and warm periods on the phylogeography of dwarf birch. Our best supported model suggested that the species diverged in the Mid-Pleistocene Transition as glaciations intensified, and ice sheets expanded. We found support for a complex history of inter- and intraspecific divergences and gene flow, with secondary contact occurring during periods of both expanding and retreating ice sheets. Our spatiotemporal analysis suggests that the modern genetic structure of dwarf birch was shaped by transitions in climate between glacials and interglacials, with ice sheets acting alternatively as a barrier or an enabler of population mixing. Tundra shrubs may have had more nuanced responses to past climatic changes than phylogeographic analyses have often suggested, with implications for future eco-evolutionary responses to anthropogenic climate change.

Aim The Arctic ecosystems are exposed to amplified climate warming and, in some regions, to rapidly developing economic activities. This study assesses, models and maps the geographic patterns of community-level plant species richness in the Western Siberian Arctic and estimates the relative impact of environmental and anthropogenic factors driving these patterns. With our study, we aim at contributing towards conservation efforts for Arctic plant diversity. Location Western Siberian Arctic, Russia. Methods We investigated the relative importance of environmental and anthropogenic predictors of community-level plant species richness in the Western Siberian Arctic using macroecological models trained with an extensive geobotanical dataset. We included vascular plants, mosses and lichens in our analysis, as non-vascular plants substantially contribute to species richness in the Arctic. Results We found that the mean community-level plant species richness in this vast Arctic region does not decrease with increasing latitude. Instead, we identified an increase in species richness from South-West to North-East, which can be explained by environmental factors. We found that paleoclimatic factors exhibit higher explained deviance compared to contemporary climate, potentially indicating a lasting impact of ancient climate on tundra species richness. We also show that the existing protected areas cover only a small fraction of the regions with highest species richness. Conclusions Our results reveal complex spatial patterns of community-level species richness in the Western Siberian Arctic. We show that climatic factors such as temperature (including paleotemperature) and precipitation are the main drivers of plant species richness in this area, and the role of relief is secondary. We suggest that while plant species richness is mostly driven by environmental factors, an improved spatial sampling is needed to robustly assess anthropogenic impact on species richness. Our approach can be used to design conservation strategies and to investigate drivers of plant species richness in other arctic regions.

Aim The Arctic ecosystems are exposed to amplified climate warming and in some regions to rapidly developing economic activity. This study aims to identify, model and map the patterns of community-level plant species richness in the Western Siberian Arctic and the environmental and anthropogenic factors driving those patterns. With our results and methods, we aim at contributing towards conservation efforts for arctic species richness. Location Western Siberian Arctic, Russia. Methods We investigated the relative impact of environmental and anthropogenic factors on community-level plant species richness of the Western Siberian Arctic, using macroecological models trained with an extensive, newly assembled geobotanical dataset. We included vascular plants, mosses and lichens in our analysis, as non-vascular plants substantially contribute to species richness and ecosystem functions in the Arctic. Results We found that the mean community-level plant species richness in this vast Arctic region does not decrease with increasing latitude. Instead, we identified an increase in species richness from South-West to North-East, which can be explained by climatic, topographical and anthropogenic factors. We found that the lowest species richness is associated with a medium (≈ 35 km) distance to infrastructure while neighboring (<10 km) and remote (≈ 100 km) areas have relatively high species richness. We also show that the existing protected areas cover only a small part of the areas with the highest species richness. Conclusions Our results reveal complex spatial patterns of community-level species richness distribution in the Western Siberian Arctic. We suggest that the impact of economic activities on species richness is ambiguous and not limited to areas directly affected by infrastructure. We show that economic activities along with other factors contribute to heterogeneous distribution of species richness on a broad scale. Our approach and results can be used to develop nature protection strategies for other arctic regions facing similar challenges.