The topographic features and sedimentary environment potentially influenced the vegetation reconstruction in southwestern China since the MIS3

Abstract

A series of pollen records from southwestern (SW) China has provided substantial evidence for the reconstruction of paleovegetation and paleoclimate in the region since the Last Glacial Period (LGP). However, studies investigating the relationship between paleoclimate and ecosystem changes during MIS3 remain limited, thereby constraining our understanding of the response of vegetation to climatic fluctuations on the glacial–interglacial timescale. Moreover, in comparison to local–scale topographic pollen sources, traditional lake sedimentary environments introduce a higher degree of uncertainty into vertical vegetation reconstructions. Here, we present a pollen record derived from a peat core of the Niangniang (NN) Mountain Wetland, aiming to reconstruct biome and climate variations over the past 37 ka. Our findings indicate that during the LGP, the study area was predominantly covered by deciduous broadleaved forests (DBLF), with Quercus (D) and other Betulaceae taxa as the main components. Although a sedimentary hiatus occurred in the core sediments between 18.5 and 4.6 ka, it is still possible to infer that from the LGP to the late Holocene, the forests surrounding the NN wetland transitioned from DBLF to evergreen broadleaved forests (EBLF), which were predominantly composed of Castanopsis and Cyclobalanopsis. Over the past 2400 years, the rapid expansion of associated plants, including Poaceae and Pinus, along with secondary taxa such as Alnus, has driven a gradual transition to the Alpine Shrubland and Meadow (ALSM) biome. This shift is largely attributed to early human activities and fires. By comparing these results with other pollen and climate records, we conclude that DBLF expanded extensively at medium–to–high altitudes during the LGP, rather than evergreen sclerophyllous Quercus forest (ESQF). Consequently, previous estimates of mean annual temperature (MAT) based on pollen data may have been inflated from the Last Glacial Maximum (LGM) to the Holocene. In addition to the drivers operating at the glacial–interglacial scale, the Atlantic Meridional Overturning Circulation (AMOC) plays a pivotal role in modulating the variability of the Indian Monsoon precipitation, which in turn influences biome succession in SW China.