Holocene wildfire regimes in forested peatlands in western Siberia: interaction between peatland moisture conditions and the composition of plant functional types

Feurdean, Angelica; Diaconu, Andrei-Cosmin; Pfeiffer, Mirjam; Gałka, Mariusz; Hutchinson, Simon; Butiseaca, Geanina; Gorina, Natalia; Tonkov, Spassimir; Niamir, Aidin; Tantau, Ioan; Kirpotin, Sergey

Abstract

Wildfire is the most common disturbance type in
boreal forests and can trigger significant changes in forest
composition. Waterlogging in peatlands determines the degree of tree cover and the depth of the burnt horizon associated with wildfires. However, interactions between peatland moisture, vegetation composition and flammability, and
fire regime in forest and forested peatland in Eurasia remain largely unexplored, despite their huge extent in boreal
regions. To address this knowledge gap, we reconstructed
the Holocene fire regime, vegetation composition, and peatland hydrology at two sites located in predominantly light
taiga (Pinus sylvestris Betula) with interspersed dark taiga
communities (Pinus sibirica, Picea obovata, Abies sibirica)
in western Siberia in the Tomsk Oblast, Russia. We found
marked shifts in past water levels over the Holocene. The
probability of fire occurrence and the intensification of fire
frequency and severity increased at times of low water table
(drier conditions), enhanced fuel dryness, and an intermediate dark-to-light taiga ratio. High water level, and thus wet
peat surface conditions, prevented fires from spreading on
peatland and surrounding forests. Deciduous trees (i.e. Betula) and Sphagnum were more abundant under wetter peatland conditions, and conifers and denser forests were more
prevalent under drier peatland conditions. On a Holocene
scale, severe fires were recorded between 7.5 and 4.5 ka with
an increased proportion of dark taiga and fire avoiders (Pinus
sibirica at Rybnaya and Abies sibirica at Ulukh–Chayakh)
in a predominantly light taiga and fire-resister community
characterised by Pinus sylvestris and lower local water level.
Severe fires also occurred over the last 1.5 kyr and were associated with a declining abundance of dark taiga and fire
avoiders, an expansion of fire invaders (Betula), and fluctuating water tables. These findings suggest that frequent,
high-severity fires can lead to compositional and structural
changes in forests when trees fail to reach reproductive maturity between fire events or where extensive forest gaps limit
seed dispersal. This study also shows prolonged periods of
synchronous fire activity across the sites, particularly during
the early to mid-Holocene, suggesting a regional imprint of
centennial- to millennial-scale Holocene climate variability
on wildfire activity. Humans may have affected vegetation
and fire from the Neolithic; however, increasing human presence in the region, particularly at the Ulukh–Chayakh Mire
over the last 4 centuries, drastically enhanced ignitions compared to natural background levels. Frequent warm and dry
spells predicted by climate change scenarios for Siberia in
the future will enhance peatland drying and may convey a
competitive advantage to conifer taxa. However, dry conditions will probably exacerbate the frequency and severity
of wildfire, disrupt conifers’ successional pathway, and accelerate shifts towards deciduous broadleaf tree cover. Furthermore, climate–disturbance–fire feedbacks will accelerate
changes in the carbon balance of boreal peatlands and affect
their overall future resilience to climate change

Citation

Feurdean, A., Diaconu, A., Pfeiffer, M., Gałka, M., Hutchinson, S., Butiseaca, G., …Kirpotin, S. (2022). Holocene wildfire regimes in forested peatlands in western Siberia: interaction between peatland moisture conditions and the composition of plant functional types. #Journal not on list, 18(6), https://doi.org/10.5194/cp-2021-125

• Journal Article Type: Article
• Acceptance Date: May 8, 2022
• Online Publication Date: Jun 3, 2022
• Publication Date: Jun 3, 2022
• Deposit Date: Oct 13, 2023
• Publicly Available Date: Oct 13, 2023
• Journal: Climate of the Past
• Peer Reviewed: Peer Reviewed
• Volume: 18
• Issue: 6
• DOI: https://doi.org/10.5194/cp-2021-125