| Summary: | The rapidly warming Arctic undergoes transitions that can influence global carbon balance. One of the key processes is the shift towards vegetation types with higher biomass underlining a stronger carbon sink. The shift is predicted by bioclimatic models based on abiotic climatic factors, but it is not always confirmed with observations. Recent studies highlight the role of disturbances in the shift. Here we use high-resolution remote sensing to study the process of transition from tundra to forest and its connection to wildfires in the 20 000 km(2) area in northwest Siberia. Overall, 40 % of the study area was burned during a 60-year period. Three quarters of the burned areas were dry tundra. About 10 % of the study area experienced two-three fires with an interval of 15-60 years suggesting a shorter fire return interval than that reported earlier for the northern areas of central Siberia (130-350 years). Based on our results, the shift in vegetation (within the 60-year period) occurred in 40 %-85 % of the burned territories. All fire-affected territories were flat; therefore no effect of topography was detected. Oppositely, in the undisturbed areas, a transition of vegetation was observed only in 6 %-15 % of the territories, characterized by steeper topographic slopes. Our results suggest a strong role of disturbances in the tree advance in northwest Siberia. Peer reviewed
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