Relationships Between Modern Pollen/Charcoal And Vegetation/Fire In Northeastern And Central Yunnan

“The Present is the Key to the Past”.Understanding the relationships of modern pollen/charcoal with vegetation,climate and wildfire is the basis for the reconstruction of palaeovegetation,palaeoclimate,and paleofire in terms of fossil pollen/charcoal records.93 surface samples were thus collected from lakes and reservoirs in central and northeastern Yunnan for this purpose.Pollen/charcool analyses of these samples and numerical analysis of pollen data were then conducted to reveal relationships of modern pollen/charcoal with vegetation,climate and wildfire.Pollen analyses of lake surface samples show that arboreal pollen of modern pollen spectra from central and northeastern Yunnan is dominated by Pinus,followed by Alnus,Betula,Evergreen Quercus,and Lithocarpus/Castanopsis;herbaceous pollen is dominated by Poaceae,Polygonaceae and Cruciferae.Comparisons of modern pollen spectra with modern vegetation indicate that modern pollen spectra reflect regional and local vegetation around lakes and reservoirs well.The relatively low arboreal pollen percentages in some pollen spectra are associated with small forest cover and/or large deforestation of local vegetation.Some pollen spectra with high herbaceous pollen percentages are dominated by herbs such as Poaceae,Cruciferae,Leguminosae and Solanaceae,which are closely associated with human agricultural activities,indicating that local vegetation around sampling sites are strongly influenced by human agricultural activities.The difference of pollen types with high pollen percentages probably reflects the different plants of cultivated crops.The result of this study also reveals that modern vegetation is largely affected by human activities,as suggested by the principal component analysis(PCA)of modern pollen spectra.PCA results show that the first factor influencing modern pollen spectra in northeastern Yunnan is attributed to the intensity of human activities,and the second factor is attributed to temperature,a natural factor;the first and second factors affecting modern pollen spectra in central Yunnan are temperature and the intensity of human activities,respectively.Charcoal analyses show a marked difference in charcoal concentrations among lakes and reservoirs.The samples with high charcoal concentrations are generally related to the occurrence of large and prolonged fire events around sampling sites.However few samples with relatively high charcoal concentrations are from lakes and reservoirs around which no wildfires occurred in recent decades,this phenomenon may be related with some festivals such as the Torch Festival popularly-held in some national minorities.