Mid-Late Holocene vegetation and hydrological variations in Songnen grasslands and their responses to the East Asian Summer Monsoon (EASM)

Abstract

Exploring the Mid-Late Holocene interactions between ecological and climate variations in semi-arid areas such as Songnen grasslands (northeastern China) provide insights into how future vegetation changes and hydrological variations may have an impact on semi-arid ecosystems, in general. In this study, we present a high-resolution palaeoecological dataset covering the past 7300 years. For this purpose, a peat section has been sampled from the shore of Dabusu lake situated in the southwestern part of the Songnen grasslands. We use pollen analyses to reconstruct the regional and local vegetation dynamics, and measure TOC (total organic carbon) and the degree of peat humification to study changes in regional and local biomass. Diatom analysis, grain size analysis, and CaCO3 contents are used to assess the water-table fluctuations of the Dabusu peatlands. The results show that from 7300 to 6000 cal BP, Dabusu peatlands were characterized by grasslands, dominated by Poaceae plants and high-water level. From 6000 to 910 cal BP, forest-steppes and dry-steppes dominated in the region alternatively. The water level of Dabusu peatlands experienced relatively low levels following an earlier rapid decline around 6000–5100 cal BP. Then after a slight increase between 5100 and 4000 cal BP, it remained at a relatively low level until 910 cal BP. After 910 cal BP, steppe vegetation dominated in the region and the water level of Dabusu peatlands slightly rose. By comparing these features with regional climate change, we show that EASM circulations might be the main driving forces controlling the regional paleovegetation dynamics and hydrological variations. This outcome is critical for the understanding of the long-term interactions between vegetation, hydrology, and climate of mid-latitude semi-arid grasslands.