Climate change, vegetation history, and agricultural activity of Lake Li-yu Tan, central Taiwan, during the last 2.6 ka BP

Pollen record derived from the sediment core of Lake Li-yu Tan, central Taiwan, provides valuable information of vegetation history, climate change, and agricultural activity. Subtropical evergreen forests dominated the uplands surrounding this lake from 2.6 ka BP, indicating the climate was warm. However, the appearance of warm-temperate forest vegetation suggests two relatively cool periods, prior to 2.3 ka BP and between 1.6 and 1.2 ka BP. Based on the presence of cultivated pollen, including Poaceae (>40 μm), Lagerstroemia, and Melia, agricultural activity was expansive between 1.6 and 1.2 ka BP and from 0.6 ka BP. This study also provides the first charcoal record in Taiwan. Natural fires occurred frequently during the interval 2.6 to 1.7 ka BP, as shown by continuous and stable charcoal influxes. Decline in charcoal influxes elucidates that fires decreased during the interval 1.7 to 1.6 ka BP. Fire events resulting from agricultural activity occurred between 1.6 and 1.2 ka BP. The high fluctuation of charcoal influxes during this period also indicates charcoal production by humans, presumably near the lake, based on the appearance of large charcoal particles (>500 μm). Fires decreased gradually from 1.2 ka BP.