Vegetation History And Dynamics In The Middle Reach Of The Yangtze River During The Last 1500 Years Revealed By Sedimentary Records From Taibai Lake, China
Pollen and charcoal records of a 150 cm long lake sediment core from Taibai Lake in the middle reach of the Yangtze River reveal seven major changes in regional vegetation over the last 1500 years. During the period c. ad 480–710, evergreen broadleaved forest dominated by Castanopsis/Lithocarpus and evergreen oaks occurred in the Taibai Lake catchment. From c. ad 710 to 1050, the vegetation shifted to a mixed conifer and broadleaved forest, with Pinus expanding at the expense of Castanopsis/Lithocarpus. Between c. ad 1050 and 1320, evergreen broadleaved forest reoccupied the studied area. From c. ad 1320 to 1650, the area of primary forest decreased markedly with synchronous reduction in broadleaved trees and Pinus. Between c. ad 1650 and 1740, the biomass declined rapidly, while secondary Pinus forest began to expand. During c. ad 1740–1950, forest extent increased slightly compared with the previous stage, but the landscape was still secondary forest with the minimum proportion of broadleaved trees. After c. ad 1950, the biomass in the surrounding area was very low, with vegetation types similar to that at present (secondary Pinus forest and mixed conifer and broadleaved forest). A detrended correspondence analysis (DCA) with 125 samples and 34 main pollen types is used to separate human and climatic impacts on vegetation. Then, the pollen assemblage, DCA, charcoal record, and magnetic susceptibility are combined to discuss the key factors inducing these vegetation changes. The vegetation changes were mainly controlled by the climatic changes, with the weak impacts of human activities before c. ad 1320. Since then, the intensity of human influences on vegetation increased gradually, entering a transitional period of main controlling factors of vegetation changes from nature to human activities. After c. ad 1740, the vegetation changes were chiefly controlled by human activities, and the climatic signal was weak.