Earth climate has gradually warmed up since the last glacial maximum some 20,000 years ago. With appropriate climate conditions, production mode and lifestyle of ancient people gradually changed from the early collecting, fishing and hunting to the later settled production with farming agriculture.
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| Hindcasted past distribution of natural vegetation during (A) the Last Glacial Maximum (LGM) and (B) the Mid-Holocene (MH) and (C) the proportion (%) of each vegetation type (LGM: dark blue line; MH: orange line; modelled: dark gray line). In (C), the proportion (%) of a vegetation type was calculated as the ratio of its distribution range relative to the terrestrial area of China [Credit: Wang et al. 2017] |
This change in production and lifestyle was closely related to the environment variations at that time, and had a great impact on the development of human civilization.
In order to better understand the variations of vegetation with climate fluctuation since the last glacial maximum in Southern China, as well as the impact of human activities on vegetation, researchers from the Chinese Academy of Sciences (CAS) carried out a pollen study for 20 drilling cores in some of the less researched areas. They selected pollen data from 14 sites for the restoration of vegetation over the past 20,000 years.
The research team gave for the first time the vegetation zoning maps around 18 ka BP, 9 ka BP and 6 ka BP, respectively, and the distribution characteristics of plants in each zone/subzone were described.
They found that the variation of vegetation in Southern China since about 20,000 years generally coincided with the changing process of global climate after the last glacial maximum. Temperate vegetation around 18 ka BP could extend southward to the present south subtropical subzone, reflecting that the nature of vegetation still retained some climatic characteristics of the previous glacial period, although the climate had begun to warm up at that time.
«During the Holocene megathermal, the characteristics of vegetation in the study area are rather distinct, which indicates similar features around both 9 ka BP and 6 ka BP. This reflects the general trend of global warming at that time on the one hand, and the overall control of southeast monsoon and southwest monsoon in Southern China on the other hand,» said Prof. WANG Weiming from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS). It was speculated that the long-term strong monsoon climate since 9 ka might be the main reason for the dominant vegetation distribution at that time as well as its gradual convergence with the present.
High-resolution palynological study showed that although some climatic events since the last glacial maximum had been documented in some stratigraphic profiles, they had limited impact on the overall nature of local vegetation. In addition to the global climate change, the vegetation in the study area was also affected by the evolution and development of monsoon climate, said Dr. CHEN Wei from NIGPAS.
«Human activities are not clearly reflected in 9 ka BP and 6 ka BP vegetation maps, which indicates that early farming activities have little influence on the original vegetation. The impact of human activities on vegetation is generally earlier in the middle and lower reaches of the Yangtze River than in the other areas of Southern China, and the impact is more distinct,» said LI Chunhai from the Nanjing Institute of Geography and Limnology of CAS.
According to Dr. SHU Junwu from NIGPAS, the rise of sea level during the Holocene megathermal might also affect the distribution of vegetation at that time. Large-scale transgressions were recorded in Lake Dongqian, Lake Baima and Lake Xianghu in the early Holocene.
The study, published in Science China: Earth Sciences, was supported by the Strategic Priority Research Program of Chinese Academy of Sciences and the National Natural Science Foundation of China.
Source: Chinese Academy of Sciences [June 04, 2019]
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