Abstract
Catastrophic fire years that have taken place during the last decade in Siberia, and more generally within the boreal forest, have been directly linked to global warming and had strong repercussions on boreal ecosystems and human populations. In this context the study of the past dynamics of these fires is essential for understanding their links with climate, vegetation and human activity changes on longer time scales than the last few decades. However, few studies on fire dynamics are available for Siberia, and none have been conducted for the entire Holocene period. This study presents the first fire history reconstruction of this area during the Holocene based on charcoals sequestered in sediments of two lakes located on the southern shore of Lake Baikal, in Siberia. The results show a similar trend in the two lakes, with high frequency and high peak magnitude during the Early Holocene and low magnitudes after 6500 cal. yr BP. This difference is interpreted as crown fires versus surface fires. According to pollen records (Dulikha, Vydrino, Ochkovoe) available near the studied lakes, a vegetation transition occurred at the same time. Picea obovata, which has a tree structure prone to crown fires, was dominant during the Early humid Holocene. After 6500 cal. yr BP, conditions were drier and Pinus sylvestris and Pinus sibirica became the dominant species; their tree structure favors surface fires. In addition to vegetation dynamics, the nearby pollen sequence from Dulikha has been used to provide quantitative estimates of past climate, indicating an Early to Middle Holocene climatic optimum between 8000 and 5000 cal. yr BP and an increase in temperatures at the end of the Holocene. These results have been compared to outputs from regional climate models for the Lake Baikal latitudes. Fire dynamics appear to have been more linked to the vegetation than climatic conditions. Over the past 1500 years, the greater presence of human populations has firstly resulted in an increase in the fire frequency, then in its maintenance and finally in its suppression, which may possibly have been due to very recent fire management, i.e., after ca 500 cal. BP.
Highlights
Boreal forest is a major component of the world’s forested area and represents around 25% of the forested ecosystem [1]
Crown fires jump from tree foliage to tree foliage and cause severe damage to the tree canopy, whereas surface fires spread on the ground without reaching tree foliage [5]
We have supposed that the magnitude of the peak is linked to the biomass burned which is linked to the fire regime [10,67]
Summary
Boreal forest is a major component of the world’s forested area and represents around 25% of the forested ecosystem [1] It is the world’s largest terrestrial biome, and is located in the northern hemisphere, in North America (mainly in Canada) and in Eurasia (Fennoscandia and Russia) [2]. Siberia covers three quarters of Russia (13.1 million km2), from the eastern side of the Ural Mountains to the Pacific Ocean This region is currently characterized by a continental climate and a high fire frequency [23,24]. These characteristics make Siberia a sensitive place in the context of global change, as wildfires tend to be more frequent in continental areas (global fire frequency could increase by over 37.8% during the period 2010 to 2039, according to global climate models based on the A2 emission scenario) [17,25,26]
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