Vegetation and fire anomalies during the last ~ 70 ka in the Ili Basin, Central Asia, and their implications for the ecology change caused by human activities

Abstract. Changes in vegetation characteristics and fire occurrence during the last glacial period offer an opportunity to better understand paleoclimate change and past human activities as well as the relationships among them. However, in central Asia, records of both vegetation and fire have rarely been obtained from the same profile. Here, for the first time, we present pollen and microcharcoal data collected together from the wind-blown loess Nileke section, representing the past ~ 70 thousand years (ka) in the Ili Basin, Northwest China, Central Asia. These records enable investigation of the pollen-based vegetation and microcharcoal-based fire proxies as well as their possible relationships with ancient human activities. The results show that the temperate herbaceous taxa remained at relatively low levels before 36 ka, whereas the temperate woody taxa, especially Cupressaceae, were abundant. At the same time, the fire frequencies were relatively low. After 36 ka, herbaceous taxa abruptly replaced Cupressaceae and the fire occurrence gradually increased. We named this change as the local vegetation degeneration event, because no equivalent changes have been identified anywhere else across Eurasia. Prior to the event, a period of intensified fire activity occurred between 47.5 and 36 ka, although the background fire activity was relatively low. We argue that the intensified local fire activity was the primary factor causing the vegetation event and was mainly driven by human activity. Following migrations from Africa after 200 ka, humans began to colonize the Ili Basin at least 47.5 ka ago, bringing their skills of fire control and consequential destruction of woody vegetation. Future analysis of first-hand archeological sites in this area will be an important step in supporting our hypothesis.