Pollen-Based Quantitative Vegetation-Cover Reconstruction For Northern China During The Last 6000 Years

How is historical land-cover change driven by climate change? What is the trend of vegetation succession under the influence of human activities? Based on the relative pollen productivities data of north China and East Asian Pollen Database,the land-cover changes since 6ka in north China were quantitatively reconstructed using the Landscape Reconstruction Algorithm(LRA).On this basis,we analyzed the vegetation succession and its climate response,the distribution characteristics of forest vegetation in typical periods,and discussed the role of human activities in the process of vegetation succession since 6ka in north China.Climate change and human activity had played a major role in the succession of vegetation in northern China during the middle and late holocene.The results show that: At6k(cal.6k BP),the woody vegetation coverage of north China was the highest compared with other periods,deciduous broad-leaved forests dominated the mountains of the northeast China,the warm-loving tree species growth in north China plain,and agricultural activities appeared in the north China plain and Liao River plain.At 3k,coniferous forests increased in northeastern China,and forest decline in other areas,economic plants increased in north China plain,and human activities increased significantly.At 1.5k,under the influence of climate cooling and human activities,forest coverage generally declined,and herbs increased.In this period,the range of human activities increased,and agricultural production began to take shape.At 0.5k,woody plants increased in the mountainous areas,and human activities of deforestation and land reclamation increased.At 0.2k,cold-loving tree species increased and herbs decreased in northeastern China.Vegetation types changed little,and human activities were further enhanced.At 0.05 k,the deciduous broad-leaved forests increased in the mountains of north China,and the mixed coniferous broad-leaved forest developed in the mountains of northeast China,the broad-leaved trees in the plain were still reduced or unchanged,and the human activities were significantly enhanced.Deciduous broad-leaved forest and coniferous forest have distinct spatial distribution characteristics since 6ka in north China.During the middle Holocene,Quercus dominateddeciduous broad-leaved forests were widely developed in the mid-latitudes of the Northern Hemisphere;and Pinus dominated coniferous forests was located in warm temperate mountains.Then deciduous broad-leaved forests gradually shrink affected by the climate cooling,and distributed in the Yanshan mountain and the south of northeast plain.Coniferous forests gradually developed in the northeast of the Lesser Khingan mountains and Changbai mountains.In recent centuries,deciduous broad-leaved forests of the north China plain have been largely replaced by farmland.Coniferous forests moved northward driven by warm climate and human activity,and its distribution range and coverage were shrunk.With the warming of modern climate,deciduous broad-leaved forest increased in north China,and coniferous forest distribution shrink further.Vegetation development was significantly affected by climatic events.During the medieval warm period,the woody coverage changes were affected by climate change and human activities,deciduous broad-leaved forests increased in mountains where human activities were weak and coniferous forests generally decreased.The forest coverage in the plain has decreased where was affected by deforestation and land reclamation.During the little ice age,the growth of deciduous broad-leaved forest was restricted by the cold climate,and coniferous forest generally decreased.The vegetation succession in mountains was affected by climate change,and in the plains was affected by climate change and human activities.Human activities were mainly reflected in the decrease of forest vegetation and the emergence of farmland.Farmland existed in the north China plain and Liaohe plain 6,000 years ago.The stable agricultural activities were found in central and northeast China before3000 years,and human activities may have influenced forest coverage.In the Sui and Tang dynasties,the area of human activities expanded and agricultural was relatively mature.During the Ming and Qing dynasties,human activities had increased significantly with deforestation and land reclamation.