Abstract: We carried out pollen/charcoal analyses on sediments of a 78cm core from Yangzonghai Lake to study vegetation succession, climatic change, and forest fire history over the past 1200 years in the catchment of Yangzonghai Lake, central Yunnan. The age-depth framework was established using an AMS ¹⁴C dating of plant remnants at the bottom and ²¹⁰Pb dating at the top. The results showed that: (1) There were four stages of vegetation changes in the catchment of Yangzonghai Lake over the past 1200: the first one was a warm and dry stage (780-1630 AD), when vegetation was dominated by mixed forest of pine and oak with few herbs; the second stage was a cool and wet stage (1630-1860 AD), when vegetation was still dominated the mixed forests of pine and oak, but with a decrease in the forest proportion and substantial fluctuations, and with a significant increase in herb proportion; it was followed by a cold and dry stage (1860-1950 AD) and the subsequent a warm and dry stage (after 1950 AD), when vegetation was strongly disturbed by human activities, which may have become the dominant factor driving vegetation. (2) Across the past 1200 years, a warm period (780-1630 AD) and a cold period (1630-1950 AD), corresponding to Medieval Warm Period and Little Ice Age respectively, occurred in the catchment of Yangzonghai Lake. Moreover, the hydrothermal conditions showed a pattern of warm dry and coldwet, which occurred almost synchronously in the adjacent areas such as Tiancai Lake and Erhai Lake in northwest Yunnan and eastern Qinghai Tibetan Plateau. During the whole warm period, temperature was stable with a little bit more fluctuation in the warmest stage from the middle of the 12th century to the middle of the 15th century. Climate during the Little Ice Age showed two periods, namely a cool-wet period from 1630 to 1860 AD and cold-dry period from 1860 to 1950 AD. The dominant forcing of climate change over the past 1200 years in the catchment of Yangzonghai Lake was solar forcing associated with regional and global ocean atmosphere coupling. (3) Forest fire increased gradually over the past 1200 years in the catchment of Yangzonghai Lake, a trend consistent with population growth and human activities, indicating that human activities have gradually become one of the dominant driving forces of environmental change.

Key words: gene regulation, crop growth, combined application of biochar and fertilizer, biochar, synergistic effects., roots