On the 20th, the reporter learned from the Qinghai Tibet Plateau Institute of the Chinese Academy of Sciences that researchers from the Institute and other units found that human activities had significantly reduced the plant diversity in eastern China since the Qin and Han Dynasties 2000 years ago by analyzing the plant pollen records in China. Relevant research results were published in the Journal of global change biology. Eastern China is an important agricultural origin in the world. The history of crop domestication and cultivation here can be traced back to the early Holocene 11500 years ago. However, there are still uncertainties in the start time and intensity of the impact of human land use on vegetation. "How to identify human impacts on vegetation and assess the intensity of impacts is a difficult problem for paleoecologists." Cao Xianyong, a researcher of the Qinghai Tibet Plateau Institute of the Chinese Academy of Sciences, introduced. Sporopollen is the general name of plant spores and pollen. Different sporopollen combinations can represent different vegetation communities. Under the action of wind and current, spores and pollen particles are gathered and buried in lakes, peats and other sediments, becoming a key to the reconstruction of ancient vegetation landscape. Palynologists can identify and count the spores and pollen buried in sediments one by one, and then combine the results of sediment chronology analysis to reconstruct the past vegetation landscape and land use history. Using a large number of stratigraphic and modern sporopollen data accumulated in China, researchers have carried out research on changes in plant diversity. It is found that under the influence of natural climate fluctuations, the sporopollen diversity in eastern China remained at a high level in most of the Holocene before 2000 years ago, although there was a certain range of fluctuations. However, since 2000 years ago, the sporopollen diversity in eastern China has decreased rapidly. "Compared with other periods of the Holocene, the climate fluctuation in the recent 2000 years is relatively weak. There is no doubt that the loss of plant diversity at this stage should be mainly caused by human land use." Cao Xianyong emphasized. In this regard, Cao Xianyong said that the Qin and Han Dynasties were a period of social transformation and cultural integration in China, and the first period of strong development in China's history. The rapid growth of population and agricultural development expanded the scope of vegetation damage and intensified the intensity of damage. Human deforestation and reclamation led to the reduction of the original forest area, and the replacement of farmland and secondary forest landscape began to appear on a large scale in eastern China and continue to expand. (Xinhua News Agency)