Pollen assemblages and anthropogenic influences in the central and western regions of Yunnan Province

The goal of this study was to provide information on the representation of pollen taxa and the human impact on vegetation by exploring the relationship between modern pollen and vegetation in the central and western regions of Yunnan Province of China. A total of 120 modern pollen samples were collected throughout the study area. The surface pollen assemblage was divided into eight pollen zones (Zones I-VIII) based on vegetation types. We analyzed the palynology and determined the hemeroby levels of each zone in the area. Our results showed that human activity is one of the most important factors that can result in the damage of natural vegetation and increase anthropochory and secondary plants. The hemeroby levels of the surface pollen samples were mainly euhemerobic except for Zones I, II, and VI, which indicates a strong and continuous anthropogenic influence in the central and western regions of Yunnan Province in recent decades. The lowest hemeroby values were observed in Zone I samples, which were collected from Mengla and Jinghong. These areas are in the Xishuangbanna region, which is the most biodiverse region in China and has been well preserved since 1959. Therefore, the extent of human influence of a region can be estimated from the degree of hemeroby established from pollen data, which can be used in the future for nature conservation. (C) 2018 Elsevier B.V. All rights reserved

Vegetation, fire, and climate history during the last 18500 cal a BP in south-western Yunnan Province, China

High-resolution pollen and charcoal records from Qinghai Lake in south-western China are presented. The records reveal variations in vegetation, fire and climate history since 18 500 cal a BP. The results show that seven significant vegetation changes are recorded, which are responses to climate changes and/or fire events. Frequent and intensive fires occurred during the periods 17 900–15 000, 13 000–11 500 and 4280–980 cal a BP, corresponding to relatively dry climatic conditions. Combined with the climatic record from Tiancai Lake, the regional climatic changes since 18 500 cal a BP in western Yunnan Province are reconstructed. Namely, the Heinrich Event 1, the Bølling–Allerød warm period and the Younger Dryas event during the last deglaciation are ubiquitous in western Yunnan Province. The start of the Holocene is recorded at 11 500 cal a BP. The Holocene climatic optimum occurred between 8450 and 4280 cal a BP. After 4280 cal a BP, the climate deteriorated, accompanied by evidence for human impact. Based on this study, we consider that vegetation and climatic changes since 18 500 cal a BP in south-western Yunnan Province are primarily driven by September and average summer solar insolation, with some associated influence from regional sea-surface temperature and sea-level rise