Vegetation Evolution And Its Response To Climate Change Recorded By A Peat Archive From The Western Guizhou Plateau

The western part of Guizhou is located in the central axis of the Yunnan-Guizhou Plateau,with widely distributed karst landforms and fragile ecological environment,this region are sensitive to climate and environmental changes.In this study,the peat core YJP01 from Yejiping peatland in western Guizhou,with a total length of 450 cm was selected as the research material.High-resolution dating results were obtained through high-precision AMS¹⁴C dating method.Based on sporopollen and charcoal analysis,and the measurement of water content,dry bulk density,loss on ignition and humification,and by high-resolution X-ray fluorescence（XRF）core scanning method to obtain the content of geochemical elements and chromaticity index,the evolution history of paleoclimate and paleoenvironment and vegetation dynamics since the late Holocene in Yejiping area was reconstructed.The representativeness environmental indicators were used for wavelet analysis and power spectrum analysis.In combination of the previous research results,this study also aims to explore the driving factors of climate and environmental changes,and to clarify the response process of vegetation to paleoenvironmental changes.The main findings are as follows:（1）The evolution history of vegetation in Yejiping area since the late Holocene had experienced five stages.Stage I,4730～3897 cal.a BP,with 4180 cal.a BP as the boundary,it can be divided into two sub-periods.In the early stage,there were sparse forests and grasses dominated by Betula and Corylus,and in the later stage,there was a cross-forest zone dominated by evergreen broad-leaved trees such as Evergreen-Quercus and Cyclobalanopsis;Stage II,1140～750 cal.a BP,evergreen and deciduous broad-leaved mixed forest dominated by Cyclobalanopsis,Evergreen-Quercus,Betula,Corylus,and Alnus;Stage III,750～500 cal.a BP,evergreen broad-leaved forests dominated by evergreen broad-leaved trees such as Castanopsis,Evergreen-Quercus,and Cyclobalanopsis;Stage IV,500～70 cal.a BP,evergreen and deciduous broad-leaved mixed forest dominated by Betula,Alnus,Corylus,and Deciduous-Quercus,with a large number of grasses;Stage V,1880～2018 AD,sparse forest and grass dominated by Gramineae,Artemisia,and Alnus.（2）The climate in the Yejiping area since the late Holocene also experienced a distinct variation.4730～3897 cal.a BP,this period can be divided into two sub-stages with 4180 cal.a BP as the boundary.The sporopollen assemblage and other indicators reflected that the climate was cold and dry in the early stage,but slightly warmer and humid in the later stage;1140～750 cal.a BP,the climate fluctuated significantly with the overall condition of slightly cooler;750～500 cal.a BP,it was in the Medieval Warm Period,and the climate was warm and humid;during Little Ice Age period at 500～70cal.a BP,,the climate gradually turned to cold and dry;Since 70 cal.a BP,the temperature increased,and the humidity also increased in the later period.In addition,the indicators of Yejiping peat recorded cold events at 4.2 ka BP and 1.1 ka BP,and revealed that the climatic characteristics of the Medieval Warm Period（1200-1450 AD）and the Little Ice Age（1450-1880 AD）were warm-wet and cold-dry,respectively.（3）The"warm-wet and cold-dry"temperature-humidity pattern in western Guizhou revealed by Yejiping peat during the Medieval Warm Period and the Little Ice Age is consistent with many paleoenvironment records,such as cave stalagmites,lacustrine deposit,and peat in eastern Yunnan,Guizhou,and northern Guangxi.However,it is different from the"warm-dry and cold-wet"temperature-humidity pattern in western Yunnan and southern Tibet,which are also significantly affected by the Indian monsoon.It can be seen that the climatic characteristics of the southwest region in China are different in spatial,and there is a boundary line roughly in the northeast-southwest trend.The temperature and humidity combination patterns on both sides of the boundary are different.（4）Through the principal component analysis of Yejiping peat pollen assemblages,PCA1 and PCA2 indexes were obtained and they can be used to reveal the variations of humidity and temperature,respectively.The wavelet analysis and power spectrum analysis show that the climate in Yejiping area is influenced by both the ocean-air coupling system inside the earth and the solar activity outside the earth.The climate control mechanism of the Medieval Warm Period and the Little Ice Age in Southwest China is obviously different.The climate of the Medieval Warm Period was mainly controlled by the Indian monsoon,while the humidity conditions in the west of the boundary line of the Little Ice Age were also affected by the south branch westerly wind.At the same time,it is also can be found that the period in the sporopollen records of Yejiping is similar to a variety of paleoclimate records those from the Yunnan-Guizhou Plateau.This result may be due to the fact that the Yunnan-Guizhou Plateau is more significantly affected by the Indian monsoon and the climate evolution is similar within a certain spatial scope.（5）The vegetation dynamics in the Yejiping area over the past thousand years has responded to climate change significantly,mainly manifested in changes in vegetation family and genus composition,spatial distribution of different plants,vegetation types and species diversity.In addition,in the mountainous area of western Guizhou where Yejiping is located,the intensification of human activities over the past thousand years has also affected the vegetation composition to a certain extent.The increase content of cereals in Poaceae during the relatively cold Little Ice Age shows that the agricultural planting activities increased during that period under the background of the implement of reclamation and other social factors.