Vegetation change and grazing activities since the middle Holocene in the Zoige Basin, eastern Tibetan Plateau, China

Abstract

Large herbivores of grazing activities are the most important production factor to maintain the permanent settlement of human beings in the high-altitude area of the Tibetan Plateau, China, and their population changes are the products of the interaction between climate change and human activities since the Holocene. Using pollen and fungal spore fossil records from a profile since mid-Holocene in the Zoige Basin, the history and controlling factors of vegetation change and grazing activities were revealed. The results showed that the history of vegetation change and grazing activities in the Zoige Basin could be divided into three stages: (ⅰ) During the period of 8.5–5.8 ka, alpine meadow dominated by Cyperaceae developed in the Zoige Basin with the highest tree pollen content and the best hydrothermal conditions. The low concentration of coprophilous fungal spore at this stage was probably related to wild herbivores. (ⅱ) During the period of 5.8–3.6 ka, the alpine meadow dominated by Cyperaceae developed further, the tree pollen content decreased slightly, and the climate began to change to drought, but the overall climate was still warm and humid. At this stage, coprophilous fungal spores occurred continuously and their concentration gradually increased, suggesting that there were human activities in the basin and grazing activities began at about 5.8ka. (ⅲ) During about 3.6–0 ka, the vegetation type changed to the desert steppe dominated by Chenopodiaceae and Asteraceae, and after 0.5 ka, the alpine meadow redeveloped. The pollen content of trees decreased significantly, and the climate was mainly cool and dry. Grazing activities, as represented by the concentration of coprophilous fungi spores, began to increase gradually after about 3.6 ka. There was a reverse correlation between grazing activities and the dry and cool climate in this stage. The dry and cool climate was one of the key factors to promote the development of grazing in the Zoige Basin. The research results further complement the evolution of human activities and environmental background in the eastern Tibetan Plateau, and have certain reference significance for understanding the impact of climate change on human survival strategies in the plateau environment.