A 1640-Year Vegetation and Fire History of the Lake Haixihai Catchment in Northwestern Yunnan, Southwest China

Abstract

Vegetation and fire archives of the late Holocene are essential for understanding the importance of natural and anthropogenic forcings on past and future vegetation successions as well as climate changes. Here we present a 1640-year record of vegetation and fire history of the Lake Haixihai catchment in northwestern Yunnan, southwest China. Pollen and charcoal analyses as well as XRF (X-ray fluorescence) analysis of lacustrine sediments from Lake Haixihai were employed to reveal its regional vegetation, forest fire, and soil erosion intensity changes over the last 1640 years. The results show their significant changes attributed to both climatic conditions and human activities: The lake catchment witnessed the densest forests (including pine and hemlock forests, and evergreen broadleaved forests) and the weakest soil erosion of the last 1640 years as well as relatively frequent forest fires at 380–880 AD, when vegetation succession, forest fire, and soil erosion were mainly driven by natural forcings, i.e., climatic conditions. A significant and abrupt drop in forest density, minor changes in abundance of forest components, and gradually strengthening soil erosion occurred at the transition from 880 to 1040 AD, when anthropogenic forcings such as the development of agriculture and systematic deforestation gradually became dominant ones driving vegetation succession and soil erosion. After this transition, forest density and soil erosion intensity never returned to the level before 880 AD, implying that the modern landscape in the lake catchment was already established approximately at as early as ca. 1040 AD. No significant changes in forest component and density as well as forest fire and soil erosion occurred until 1940 AD. The most frequent forest fires, the strongest soil erosion, and low forest density after 1940 AD might be attributed partially to climatic conditions and partially to extensive deforestation around 1960 AD.