Hou Qishan Holocene Vegetation And Ecological Environment Evolution

From field investigation, the author has found that the Nanguanzhuang profile inZhouyuan region, which developed in holocene, consists of 3 palaesol layers, 3 loessbeds and 1 transitional layer. In this paper, stratigraphic structure is studied firstly andthe result shows that, from top to bottom the structure units are L₀¹, S₀¹, L_x¹, S₀², L_x²,S₀³ and Lt respectively. Secondly, 100 samples were gathered from Nanguanzhuangprofile and analyzed in laboratory using pollen analyses and charcoal content analyses,and the results are as followes:(1) >11 KaB.P.,stratigraphic unit is L₁, Concentricyats, Leguminosae, Gramineae,Compositae, Artemisia, Chenopodiaceae were the main pollen components when thevegetation was a desert-steppe. During this period, the annual temperature was about5-8℃, the rainfall was about 200-300mm and dry-cold was the climatic character. Atthat time, fire frequency is low for little calculation vegetation contain.(2) 11-8. 5 KaB.P., stratigraphic unit is Lt, the main pollen components includedGramineae, Leguminosae and Compositae, and the vegetation was a transitional zonefrom steppe to desert-steppe. During this period, the annual temperature was about 8-10℃ and the rainfall was about 300-450mm. Fire frequency is still limited for littlecalculation vegetation content in this period.(3) 8.5-7.4 KaB.P., stratigraphic unit is S₀³, the main pollen components includedGramineae, Leguminosae Ulmus and Cupressaceae while the vegetation was a steppewhich contained lots of Gramineae. During this period, the annual temperature wasabout 13-14℃ and the rainfall was about 600-750mm.(4) 7.4-6.8 KaB.P., stratigraphic unit is L_x², the main pollen components includedGramineae, Leguminosae, Compositae, Cupressaceae, Rosaceae and Concentricyats.There were 3 incidents when temperature were fallen and the vegetation wasdeteriorated to a desert-steppe, the annual temperature was fallen to about 9-10℃ andthe rainfall was about 300-400mm. This is the earlier period of Yangshao culture, thecontent of charcoal reaches to a peak value because of using fire for human'sproducing and living.(5) 6.8-6.0 KaB.P., stratigraphic unit is S₀², Leguminosae, Gramineae andCupressaceae were the main pollen components, the vegetation was a transitionalzone from forest-steppe to steppe, and the annual temperature was about 12-14℃ andthe rainfall was more than 600mm. During this period, Yangshao culture wasdeveloped and the content of charcoal maintain the peak value because of using firefrequently for human's producing and living.(6) 6.0-5.0 KaB.P., stratigraphic unit is L_x¹, Artemisia, Leguminosae, Ephedra andCupressaceae were the main pollen components and the vegetation was a desert-steppe. During this period, the annual temperature was about 8-12℃ and the rainfallwas about 250-400mm. At that time, Yangshao culture was deteriorated gradually andthe charcoal was fallen because of the short fire using.(7) 5.0-3.1 KaB.P., stratigraphic unit is the bottom part of S₀¹. Leguminosae,Compositae, Gramineae and Cupressaceae were the main pollen components, and thevegetation was a forest-steppe which contain some broad-leaved trees. During thisperiod, the annual temperature was about 12-14℃ and the rainfall was more than 600-750mm. Since this time, the content of charcoal was restored gradually.(8) < 3.1 KaB.P., From the earlier Zhou-dynasty to present, the content of charcoalreached a peak value and maintained because of the frequent using fire for human'sproducing and living.