Vegetation Changes in Southeastern Siberia During the Late Pleistocene and the Holocene

Abstract

Relationships between climate, species composition, and species richness are of particular importance for understanding how boreal ecosystems will respond to ongoing climate change. This study aims to reconstruct changes in terrestrial vegetation composition and taxa richness during the glacial Late Pleistocene and the interglacial Holocene in the sparsely studied southeastern Yakutia (Siberia) by using pollen and sedimentary ancient DNA (sedaDNA) records. Pollen and sedaDNA metabarcoding data using the trnL g and h markers were obtained from a sediment core from Lake Bolshoe Toko. Both proxies were used to reconstruct the vegetation composition, while metabarcoding data were also used to investigate changes in plant taxa richness. The combination of pollen and sedaDNA approaches allows a robust estimation of regional and local past terrestrial vegetation composition around Bolshoe Toko during the last ∼35,000 years. Both proxies suggest that during the Late Pleistocene, southeastern Siberia was covered by open steppe-tundra dominated by graminoids and forbs with patches of shrubs, confirming that steppe-tundra extended far south in Siberia. Both proxies show disturbance at the transition between the Late Pleistocene and the Holocene suggesting a period with scarce vegetation, changes in the hydrochemical conditions in the lake, and in sedimentation rates. Both proxies document drastic changes in vegetation composition in the early Holocene with an increased number of trees and shrubs and the appearance of new tree taxa in the lake’s vicinity. The sedaDNA method suggests that the Late Pleistocene steppe-tundra vegetation supported a higher number of terrestrial plant taxa than the forested Holocene. This could be explained, for example, by the “keystone herbivore” hypothesis, which suggests that Late Pleistocene megaherbivores were able to maintain a high plant diversity. This is discussed in the light of the data with the broadly accepted species-area hypothesis as steppe-tundra covered such an extensive area during the Late Pleistocene.

Late Quaternary Climate Reconstruction and Lead-Lag Relationships of Biotic and Sediment-Geochemical Indicators at Lake Bolshoe Toko, Siberia

“…The study site belongs to the Aldan Floristic Region (Kuznetsova et al, 2010) dominated by northern taiga consisting mainly of Larix accompanied by Picea and Pinus (Courtin et al, 2021).…”

“…Hydrochemical measurements performed during fieldwork are already published in detail in Biskaborn B. K. et al (2019). The study in hand is based on core PG2208 and additionally involves pollen time series published by Courtin et al (2021) from a core at 26 m water depth.…”

“…For creating a reliable model, we dated another set of bulk sediment samples at MICADAS radiocarbon laboratory at AWI using an acid treatment method outlined in Vyse et al (2020). All dating results are shown in detail in Courtin et al (2021) including the age-model for PG2133 used for pollen in their study.…”

“…We transformed the data to account for compositional data using centered log ratios (CLR) for single elements and additive log ratios (ALR) for ratios of two elements. (Courtin et al, 2021) was used in this study. The composite depth indicated as "Com.…”

“…Sedimentary pollen and their modern vegetation analogues have widely been used to reconstruct terrestrial summer temperatures (Biskaborn et al, 2016;Rudaya et al, 2016;Zhilich et al, 2017;Andreev et al, 2021). In our study design, we include a published pollen record from a parallel sediment core (Courtin et al, 2021) as additional independent proxy and counterpart to chironomid based air temperature reconstruction. Sediment-geochemical proxies that were analyzed from Bolshoe Toko surface sediments (XRF-gained elements, XRD-gained minerals, laser-derived grain-size distributions, organic carbon characteristics) are also used in support to biotic indicators.…”