Environmental changes and human impacts over the past 1200 years: Evidence from high-resolution pollen records from peat in the Yunnan-Guizhou Plateau, Southwest China

Abstract

Over the past millennium, the understanding of vegetation and climate changes in mountainous regions, driven by both natural and anthropogenic forces, remains unclear. In this study, we provide a high-resolution vegetation record spanning the past 1200 years from a subalpine peatland in the Niangniang Mountains, southwestern China. By analyzing pollen, charcoal, and loss-on-ignition from the peat sediment, we elucidate the interactions between vegetation, fire, and human impact. Our findings reveal that before 1150 CE, the mountains were covered with dense broadleaf forests and experienced minimal human activity. Natural forcings, primarily climatic conditions, drove vegetation succession and forest fires. After 1150 CE, the Human Influence Index (HII) increased sharply, coinciding with a rise in cereal-type pollen. Significant agricultural activities in the southwestern mountainous regions of China began after 1150 CE, which is later than those in the low-altitude lake basins of southwestern China. During the Medieval Climate Anomaly (MCA, 836–1400 CE), the Niangniang Mountains were characterized by warm and humid climatic conditions, a stable forested landscape, and a high peat carbon accumulation rate. Although human activities increased markedly during this period, the arbors did not undergo notable changes, and climate forcings continued to have a greater impact on vegetation than anthropogenic forcings. During the Little Ice Age (LIA, 1400–1800 CE), the regional vegetation landscape transitioned from dense forests to open grasslands as climate conditions became cold and dry, reducing peat carbon accumulation rate. This period also saw increased forest fires and significant human-driven deforestation, with anthropogenic forcings becoming dominant. After 1900 CE, vegetation changes were increasingly influenced by government policies. Comparison with major climate forcings and spectrum analysis have shown that variations in monsoon intensity, regulated by solar and volcanic activity, have influenced the climate and peat depositional environment in the Niangniang Mountains. Our research offers meaningful insights into forest conservation in the mountainous regions of the Yunnan-Guizhou Plateau.