Vegetation and climate history of the Tian Shan region of Xinjiang during the last millennium and their relations to past human civilization

Abstract

The arid Central Asia has long demonstrated a correlation between human activity and climatic fluctuations, particularly during the Holocene. However, Late Holocene palaeoclimate records remain sparse, limiting our understanding of the dynamic relationship between climate variability and human civilization over the past millennium. This study based on peat sediment samples from the Zhaosu Basin on the northern slopes of the Western Tian Shan Mountains, China, reconstructs vegetation and climate changes over the past millennium by employing precise dating techniques and high-resolution pollen analysis. The results were as follows: (1) grasslands have consistently dominated the northern slopes of the Western Tian Shan over the last millennium, as evidenced by the prevalence of pollen types, such as Artemisia, Chenopodiaceae, and Poaceae. During the Medieval Climate Anomaly (MCA, 1046–1288 ad), frequently fluctuating Artemisia/Chenopodiaceae (A/C) ratios indicated a transition from warm–arid to warm–humid conditions. This trend shifted during the Little Ice Age (LIA, 1288–1476 ad), marked by increased Picea pollen and positive principal component analysis axis 2 scores, suggesting a cooler and wetter environment. Pollen concentrations of arborvitae and shrubs peaked during the LIA (1476–1606 ad), alongside high Picea content, signaling an intensified cold and wet climate. (2) Historical records correlate climate conditions with patterns of human habitation and development. The warm, humid climate during the MCA (1046–1288 ad) coincided with the Song Dynasty, fostering population growth and cultural development on both slopes of the Tian Shan region. Conversely, during the LIA (1288–1606 ad), cooling temperatures and frequent conflicts triggered significant migrations, particularly to the northern slopes, (i.e., during the Yuan-Ming period) where conditions were more favorable. The center of gravity of the population relocated to the northern slopes of the Tian Shan Mountains. This shift promoted agricultural advancements in later periods, despite the challenges posed by the harsher climate.