Pollen-based Vegetation And Climate Reconstruction From Chengde Area China, Over The Past 43,000 Years

Chengde area is located in the transitional zone between arid and semi-arid areas,which is an ecological barrier to block the invasion of wind and sand in Beijing-Tianjin-Hebei and an important water conservation area in Beijing-Tianjin-Tangshan.It is sensitive to the climate and environment change.In recent years,a series of ecological and environmental problems have appeared in Chengde area.How to restore the damaged ecosystem?Is it to plant trees or grass during revegetation?The study of historical vegetation can provide historical reference for answering this question.In this paper,Longhua profile and Mulan profile in Chengde area were selected for research.¹⁴C dating is used to establish the chronological framework of 43000 years,the sporopollen analysis of sediments is carried out to reconstruct the vegetation environment since 43000 years,the two profiles were divided into six stages and five sub stages.In the first stage（43536-24500 a B.P）,the climate was wet.In this stage,the percentage of trees was the highest in profile,the NAP/AP ratio was low,and the percentage of ferns is high.This stage can be divided into three sub stages:Sub stage 1a（43536-38500 a B.P.）has a warm and wet climate,the NAP/AP ratio is 2.65.The percentage of Pinus is the highest among trees.The percentage of Quercus,Betula and Ulmus is higher.The percentage of Rosaceae is the highest among shrubs,and the herbs are mainly Chenopodiaceae,Artemisia,Gramineae and Compositae.Sub stage 1b（38500-31000 a B.P.）,the climate was warm,wet,but slightly dry than previous sub stage.The NAP/AP ratio is 3.69.Compared with the previous sub stage the percentage of the warm-loving broad-leaved trees like Quercus,Betula,Ulmus,Corylus,Juglandaceae were all reduced which indicate that the climate was colder than previous stage.The increased of Chenopodiaceae also indicate drought compared with the previous sub stage.Sub stage 1c（31000-24500 a B.P）,the climate was cold and wet,and the NAP/AP ratio was 2.95.The percentage of Pinus,Picea and the ferns increase meanwhile Artemisia,Chenopodiaceae and Gramineae decrease compared with the previous sub stage.In the second stage（24500-11524 a B.P.）,the climate was dry.In this stage,the percentage of herbs was the highest in the profile.The NAP/AP ratio was higher,and the percentage of ferns was lower.This stage is divided into two sub stages:Sub stage 2a（24500-18000 a B.P.）had a cold and dry climate with a NAP/AP ratio of 3.81.The percentage of Picea is still at high level while Gramineae at low level.The percentage of Compositae,Caryophyllaceae increase and Artemisia,ferns decrease,which means a cold dry climate.Sub stage 2b（18000-11524 a B.P.）,the climate was warm and dry,and the NAP/AP ratio is 7.60.Compared with the previous sub stage the percentage of Picea,Artemisia and the ferns decrease meanwhile Quercus,Juglandaceae,Ericaceae,Chenopodiaceae and Gramineae increase,which means a warm and dry climate.In the third stage（9228-6000 a B.P.）,the climate was relatively warm and dry than previous sub stage.Compared with the previous stage the percentage of Carpinus,Juglandaceae,Ulmus,Betula which like warm increase while Ranunculaceae and ferns decrease,the percentage of Chenopodiaceae is still at high level.The pollen of shrubs is mainly the apricot which is suitable for living in dry climates.In the fourth stage（6000-2000 a B.P.）,the climate was warm and wet,the percentage of the warm-loving broad-leaved trees like Carpinus,Juglandaceae,Ulmus are still at high level.The percentage of Ericaceae,Gramineae and ferns decrease compared with the previous stage.In the fifth stage（2000-400 a B.P.）,the climate was less warm and wet than previous stage,compared with the previous stage the percentage of Quercus,Ulmus,Larix,Pinus,Ericaceae,Gramineae,Typhaceae increase while Artemisia and Chenopodiaceae decrease,the percentage of ferns is still at high level.Human activities have affected the original ecosystem,and agriculture developed.In the sixth stage（400 a B.P.-now）,the vegetation was greatly affected by artificial forest,and increased significantly in recent decades.The percentage of Betula,Ulmus,Larix and Pinus increase while Gramineae,Artemisia and ferns decrease compared with the previous stage.The vegetation of Bashang area is mainly herbs during the Holocene,and a large number of artificial forests have been planted in recent decades.However,the composition and structure of plantation trees are relatively simple and the planting density is high.In the future,it is necessary to choose native tree species that can adapt to the local natural conditions.Such as Larix,Picea,Quercus,Betula,Armeniaca sibirica and so on,these plants have high ecological and economic values and great comprehensive utilization potential.