Abstract
Abstract. 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 km2 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.
Highlights
Northwest Siberia is a region subject to a strong warming trend in summer as compared to the Arctic average
In order to assess climatic factors influencing vegetation dynamics, we studied the length and mean temperature of the growing season, which we define as the period with daily mean temperatures above +5 ◦C (Tchebakova et al, 1994)
In our analysis of vegetation dynamics, we focused on study area 1 which was most affected by fires
Summary
Northwest Siberia is a region subject to a strong warming trend in summer as compared to the Arctic average. According to the second assessment report on climate change in the Russian territory (Katsov et al, 2014), the winter warming trend in northwest Siberia (1972–2012) is 0.4–0.7 ◦C per decade, which is comparable to the trends reported for the entire Arctic. The summer trend is 0.8–1.0 ◦C per decade, double that reported for the entire Arctic. An increase in warm degree days favors a shift in vegetation type towards more southern species, i.e., transformation of tundra environment into shrubs and forest vegetation. Shrubs and trees decrease surface albedo and have a warming effect, especially in winter, but the higher amount of biomass will increase the terrestrial carbon sink. Forest ecosystems can enhance carbon uptake via complex atmosphere–biosphere feedback
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