Vegetation Succession And Forest Fires Over The Past 13000 Years In The Catchment Area Of Yangzonghai Lake,Central Yunnan

Yangzonghai Lake is located in central Yunnan Plateau.It is adjacent to the edge of the southwest monsoon,its ecological environments are thus sensetive to climate change.A 1020-cm core?YZH-1?was taken from this lake to study environmental changes.The age-depth model for this core was established using 7 AMS ¹⁴C dates obatined from wood and leave remains.High-resolution pollen/charcoal analyses of samples from this core and numerical analyses?cluster analysis and principal component analysis?of pollen data reveal vegetation succession,climate change,and forest fire history over the recent 13000 years in the catchment area of Yangzonghai Lake.The catchment area of Yangzonghai Lake experienced seven stages of vegetation and climate changes as well as forest fires during the past 13000 years.1)13200-12100 cal.a BP,vegetation was dominated by evergreen and deciduous broadleaved mixed forest,indicating cool and wet conditions,and frequent forest fires occurred.2)12100-10540 cal.a BP,pine forest expanded and broadleaved forest shrank,showing colder and drier conditions than those in the previous stage,and forest fires still happened frequenctly.3)10540-9040 cal.a BP,pine forest continued to expand at the expense of broadleaved forest,indicating warmer and drier conditions than those in the stage 2,the occurrence of forest fires decreased;an extremely high Pediastrum influx at 10300-9620 cal.a BP,when pine forest shrank and evergreen broadleaved forest expanded,suggested a possible centennial-scale pluvial event.4)9040-4250 cal.a BP,the catchment area was occupied by pine forest and evergreen broadleaved forest together with Liquidambar forest,indicating a warm and relatively dry conditions;temperature rose to the highest over the past13000 years,and humidity was lower than that of the previous stages but it was higher than the present,but the forest fire frequency was low.5)4250-850 cal.a BP,an expansion of pine forest to its maximum together with a shrink of evergreen and deciduous broadleaved elements show a significant drop in temperature and humidity,and a little bit more forest fires than the preceding stage occurred in this period.6)850-290 cal.a BP,pine forest shrank,evergreen and decidudous broadleaved forest elements and upland herbaceous plants such as Poaceae,Ranunculaceae and Artemisia increased,hygrophilous Cyperaceae increased significantly as well,suggesting a drop in temperature and an increase in humidity;after 670 cal.a BP,an increase in Poaceae pollen implied the development of cultivated plants.7)290 cal.a BP to the present,pine forest expanded again,showing warmer and drier conditions than those in the preceding stage,the freqeuency of forest fire occurrence was relatively low.Our reconstructed vegetation,climate,and forest fire histories during the last13000 years in the catchment area of Yangzonghai Lake show that,the succession of vegetation mainly exhibits variations in the distribution range of pine forest and evergreen broadleaved forest;climate change is characterized by a changing pattern of warming,high temperature and cooling phases,and a trend of gradual decrease in humidity;in terms of forest fires,deciduous broadleaved forest materials easily cause forest fire,cold conditions result in frequent forest fire.