Pollen Records Of Vegetation, Climate Changes And Human Activities During The Mid-Late Holocene From Peat Profiles In Daiyun Mountains, Fujian Province

As peat is a good indicator of climate changes in the past,the high resolution records of sporo-pollen are important to reconstruct paleoclimate and paleoenvironment in the southeast monsoon region.The peat from Daiyun mountains in the southeast monsoon region is sensitive to climate changes.In this paper,we choosed three peat profiles as study materials from Daiyun Mountains.According to chronology and environmental proxy index of pollen,we reconstructed nearly 9000 years' climate history of the study area,which can be divided four phases:(1)From 9 ka B.P.to 8 ka B.P.,pollen concentration was low in the whole section.Trees and shrubs decreased to a trough while herbs and fern spores were higher.Evergreen Quercus and Castanopsis were very low in this stage.Vegetation type was deciduous broad-leaved forest containing evergreen broad-leaved species,which indicated that climate was relatively cool and wet during the later period of the Early Holocene.(2)Pollen data showed that trees and shrubs were very high while upland herbs and wet herbs were low from 8 ka B.P.to 3 ka B.P..Coniferous forests decreased mainly composed of Pinus.Evergreen Quercus that lived in warm and wet environment was the peak in the whole section.Gramineae and Labiatae played a significant role in upland herbs while Ranunculaceae and Cyperaceae were higher in wet herbs.Vegetation type was broad-leaved trees containing a large number of evergreen species.The weather was warm and wet,which implyed this period is the appropriate stage of mid-Holocene.The stage from 6.9 ka B.P.to 5.5 ka B.P.was best of all epoch as combination of the heat and precipitation was nice,which was actually the Holocene optimum.Two cold events occured at 4.5 ka B.P.-4.1 ka B.P.and 8.2 kaB.P.(3)Trees and shrubs were high while herbs were low at 3 ka B.P.-2 ka B.P..Broad-leaved trees such as evergreen Quercus and Castanopsis were high while pinus was low.The vegetation type was the broad-leaved trees containing a lot of evergreen trees,suggesting the climate was warm and wet during the early period of the Late Holocene.(4)Trees and shrubs decreased and the herbs became dominant at 2 ka B.P.-0 ka B.P.In trees and shrubs,evergreen Quercus and Castanopsis are significantly reduced while pinus was high.The climate was changed from warm and wet to dry.Trees and shrubs decreased and Gramineae,charcoal concentration(>50 um)were increased in profile(DYS2)since 1ka B.P.,suggesting the climate was dry and cold and human activities were strengthened.The pollen records during the mid-late Holocene from the peats of Daiyun Mountains are well correlated with insolation in the northern hemisphere and the change of the East Asian monsoon.Why did the climate change to warm in mid-Holocene?This may be caused by insolation and the ENSO events may be a factor.There may be a strong linkage of global atmospheric CO2 and the climate during the mid-Holocene.