Climate-Vegetation Changes And Human Activities History Of Gonghai Lake In Shanxi Province During Last 2000 Years

Based on Chronology and Palynology results of Gonghai Laike(GH09B) in Shanxi Province, we studied the vegetation evolution history and quantitative reconstructed(WAPLS method) climate changes of study area during last 2000 years. On these bases, we revealed the essence characteristic of climate-environment background of Gonghai Lake, discussed the changes of human activity intensity and its effects on vegetation community and ecological environment.The evolution of vegetation and climate in study area: During 54 B.C.-910 A.D., the vegetation belongs to conifer and broadleaf mixed forest, which was dominated by Pinus and associated with some broadleaf trees(such as Quercus, Betula, Ulmus and Salix); it can be inferred that the vegetation landscape was Forest-Montane meadow. The changes of climate indexes were relative steady, TANN changes between 6.2 to 8.9 ℃(average 7.7℃); and PANN was 460 mm. Before 600 A.D., climate was cool and wet; between 600 A.D. to 910 A.D., corresponding to the Tang Dynasty, climate was warm and wet. During 910 A.D.-1100 A.D., the vegetation dominated by Quercus and Pinus, and associated with some Ostryopsis; quantitative reconstruction results revealed a most warm period during last 2000 years, TANN was 8.5℃, MTCO was-7.3 ℃; and PANN decreased relatively; 1100 A.D.-1270 A.D., forest coverage increased dramatically, the vegetation transfer to typical conifer and broadleaf mixed forest, and mixed with some warm trees(Quercus, Betula, Ulmus and Juglans); PANN increased rapidly in study area(average 440 mm, at the peak of 505 mm). Accordingly, we inferred that the climate was warm and dry during 910 A.D.-1100 A.D, whereas warm and wet during 1100 A.D.-1270 A.D. Between 1270 A.D. to 1920 A.D., vegetation landscape of study area was montane meadow(dominated by Artermisia, Chenopodiaceae and Asteraceae), TANN, MTWA and MTCO were all decreased, and each was reduced 0.8 ℃, 0.6 ℃, 0.9 ℃, respectively; whereas PANN was also changed distinctly; which indicated dry and cold climatic conditions. During 1920 A.D. to 2008 A.D., the climate indexes showed an increased tendency, and TANN and MTCO with high values of 9.4 and-5.7 ℃, respectively. Influenced by warming effect, the compositions of forest and shrubs vegetation have been restored, there are montane meadow-shrubs dominated by Artemisia, Poaceae, Asteraceae, Hippophae and Spiraea around Gonghai Lake.With spectrum analysis method, we found that the changes of TANN in study area have about 250, 25, 17 and 12 years period oscillations, which was corresponding to solar variation(dominated by 200-220, 22 and 11 years period). It demonstrated that solar variation is the main factor influence climate changes in study area. However, ENSO, POD, volcanic activity, greenhouse gases and LUCC(Land-Use and Land-Cover Change) may also influence climate in study area, but there is no certain conclusion of the effects of these factors in difference stages, and further discussion and testify should be done.Meanwhile, the changes of arboreal pollen and crops pollen percentage showed that the content of crops pollen(mainly of Cereal Poaceae and Fagopyrum) grows increasingly during last 2000 years, indicated increasing human activity intensity. According to the changes of crops pollen percentage, we speculated that study area was controlled by northern minorities before the Sui and Tang Dynasty, and nomadism was the main agricultural production, the effects on natural vegetation was relatively weak. During the Sui and Tang Dynasty, the content of Cereal Poaceae pollen showed a peak value, which indicated the expansion of agricultural production. During the Northern Song to Qing Dynasty, the emergence of a large amount of Cereal Poaceae and Fagopyrum pollen showed intense human activity. Since 19 th century, the dramatically increase of Cereal Poaceae pollen revealed significant deforestation and land reclamation.Moreover, according to modern vegetation regionalization and climatic conditions, the study area should be conifer and broadleaf mixed forest(dominae by Pinus and associated with some broadleaf trees); But, effected by human activity since 20 th century, morden vegetation were dominated by Artemisia, Poaceae, Asteraceae, Hippophae and Spiraea around the Gonghai Lake. However, if climate becomes steadier, and the effects of human activity become weaker, the vegetation of study area should be transfer to Pinus dominated conifer and broadleaf mixed forest.