Reconstructing The Chronology Of Paleo-biome Type Distribution In The Three-river Headwaters Region In China From The Middle Holocene

We examine spatial and temporal patterns of paleo-biome types in the Three-River Headwaters Region(TRHR,Sanjiangyuan)in China from the middle Holocene(6000BP).Biome is a collection of plants,animals and other groups living in similar environments.It is the basic element to describe the ecological environment and an important part of life on earth.it is of great significance to the study of ecology,geomorphology and civilization history.The TRHR is located in the northern Qinghai-Tibet Plateau,is the source of the Yangtze River,Yellow River and Lancang River(i.e.,the Mekong River in South Asia),is China's water source area,is the largest nature reserve and the first national park.The study of the spatial distribution of paleo biome types in the TRHR over time is beneficial to the protection of ecological environment,to the management of water resources,and to the study of relevant history.The existing methodology to identify paleo-biome types in a position is by judging the biomes from the species the pollen samples contain.This method,however,is not suited for regional scale,because high-resolution pollen records are lacked in space and time.The boundary of the biome distribution extracted through this way is thus fuzzy and the precision is low.In this study,we utilized a physiological biome model to simulate the chronology of the distribution of biome types.The climate inputs to this model were extracted from pollen data by modifying existing pollen transfer functions and by using complicated spatial and temporal interpolations.Through this,we reconstruct the chronology of the distribution of biome types with a time interval of every 50 years and a spatial cell size of 0.5 ? × 0.5?.The changes of the distribution of paleo-biome types here were mainly dominated by 36 patterns over 10 biome types.Among these,the tundra and the semi-desert were the main types and their exchanges were the main patterns in this region.Specially,the long-term direction of the evolution was from the tundra to the semi-desert,and from the tree group to non-tree group.It is also discovered that precipitation was the main driving force for changes of biomes,while temperature also had some influence.In addition,spatial heterogeneity of the evolution is identified in the TRHR,which means that in some time points,an opposite pair of changes of biome will appear in this region.The ecological evolution trend revealed by this study has been testified by some other studies,and the validity of the results is proved.However,the reconstruction of paleo biome type distribution in this study made use of some characteristics and distribution patterns of modern climate,thus introduced some uncertainties to the results,which should be solved in the future study.