Holocene climate in Northern Urals (Komi Republic, Russia): a multi-proxy approach based on pollen and brGDGTs

International audienceThe functioning of the boreal forests of Russia is still little documented and little understood. It is governed by complex mechanisms that link climate, vegetation and disturbances, such as fires or human impact.In this presentation, we aim to provide robust reconstructions of the Holocene climate (temperatures and precipitation) of the Vychegda River basin in the Republic of Komi region, based on two different proxies: pollen assemblages and GDGTs (Glycerol Dialkyl Glycerol Tetraethers). This first study of GDGTs in this area corresponds to a preliminary step for the calibration of this proxy in peats. Higher temperatures and precipitation are recorded between 7000 and 4000 cal. yr BP (mean annual temperatures around 3°C and precipitation between 600 and 700 mm per year). This climatic optimum is in agreement with previous pollen-based climate reconstructions, and climate patterns in the neighboring Russian and Fennoscandia (Komi Republic - previous study-, Arctic Russia, Siberia and Northern Europe, Andreev and Klimanov, 2000; Golubeva, 2008; Seppä et al., 2009a). These results, in conjunction with the reconstruction of fire activity and vegetation dynamics in this region, led to a better understanding of the crossed influences of these factors. In particular, vegetation is mainly controlled by climate during the first part of the Holocene, while a threshold is reached on in fire frequency after 3500 cal. yr BP and this parameter has a greater impact on vegetation than climate. Over the past 600 years, the intensification of human activities led to overexploitation of the forest and an increase in its fire activity

Holocene climate in Northern Urals (Komi Republic, Russia): a multi-proxy approach based on pollen and brGDGTs.

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Did long-term fire control the coniferous boreal forest composition of the northern Ural region (Komi Republic, Russia)?

International audienceAim Documenting past vegetation dynamics and fire-vegetation relationships at a regional scale is necessary to understand the mechanisms that control the functioning of the boreal forest, which is particularly sensitive to climate change. The objective of this study is to document these interactions in the Komi Republic during the Holocene.Location Yaksha, Vychegda river basin, Republic of Komi, Russia. Taxon Plantae, gymnosperms, angiosperms.Methods Two palaeoecological approaches are combined, based (1) on pollen (this study) and charcoal analysis (recomputed from our previous analysis) applied to cores from two peatlands and (2) on a REVEALS model (a part of the Landscape Reconstruction Algorithm "LRA") applied to six regional pollen cores in order to obtain a regional estimate of vegetation cover during the Holocene. Results The pollen diagram produced locally from Yaksha was compared with the regional vegetation cover determined by REVEALS. Taxa such asAbiessp. andPinusspp. showed differences between the two approaches, but vegetation signals remain qualitatively consistent. From 10,000 to 6,000 cal. yr BP, the forest was mainly a light taiga (composed ofPinus sylvestrisandBetulaspp.) and low fire activity was recorded. From 6,000 to 3,500 cal. yr BP, a dark taiga (composed ofPiceaspp.,Abies sibiricaandPinus sibirica) was established due to favourable climatic conditions, despite higher fire activity. From 3,500 cal. yr BP onwards, the continuous increase in fire activity allowed for a gradual return of light taiga,Betulaspp., likely reinforced by human activities. The dynamics ofPiceaspp. andAbies sp. were asynchronous between the sites. ForPiceaspp., the hypothesis of local inter-site expansion distributed along stream corridors is supported by the data. ForAbiessp., a bias in REVEALS, and in climate cooling may explain disparities between sites.Main conclusions We found evidence that in the early and mid-Holocene, vegetation dynamics were probably more influenced by climate, as fire activity was low. During the late Holocene, fire activity and geomorphology, eventually augmented by human activities, increased in influence on vegetation dynamics and led to the predominance of the light taiga forest up to the present

Gradually increasing forest fire activity during the Holocene in the northern Ural region (Komi Republic, Russia)

International audienceIn many boreal regions of Russia the past natural variability of forest fire activity remains largely undocumented, preventing accurate assessment of the impact of current climate warming on forest ecosystem dynamics. This study aims to reconstruct the Holocene fire history of the northern Ural mountain foothills, in the Komi Republic, based on analyses of charcoal particles from peatland deposits and coupled with dendrochronological investigations. The results show that there was a gradual increase in forest fire activity during the past 11,000 years. Between 11,000 and 5100 cal. yr BP, the mean fire return interval (FRI) oscillated between 600 and 200 years. During this period, regional data showed that cold temperature, humid climatic conditions, combined with steppe vegetation between 11,000'9000 cal. BP, and then the development of spruce-dominated forest between 9300 and 4600 cal. yr BP, were less conducive to fires. After 5100 cal. yr BP, a gradual increase in drought conditions through reduced precipitations, associated with the establishment of a Scots pine forest favored fire frequency, with a mean FRI under 200 years (range, 200'40 years). Nowadays (since CE 1500), human activity induces an unprecedented fire activity with a mean FRI below 100 years (range, 100'40 years)