Pollen-based land cover changes reveal temporal and spatial differences of human activity in north-central China during the Holocene

Abstract

Beginning in the middle to late Holocene, anthropogenic land cover change has had a profound impact on both regional and continental environments. Hence, assessing temporal and spatial differences in the intensity of human activity in different regions and geomorphologic contexts has become a focus of current global change research. Here we use two representative pollen records from different geomorphologic units in North China (Lake Gonghai in the mountains, and Lake Daihai in a large basin) together with a novel methodology to quantitatively reconstruct Holocene land cover changes. The results indicate diverse vegetation succession patterns in different regions and geomorphologic contexts. In the Daihai basin, the vegetation cover changed relatively little, maintaining values of 45–50%, and only increased during the interval of 8–5.1 ka, when it attained a maximum of 67%. In the Gonghai area, the vegetation cover remained at a higher level at 70–80% for an extended interval, before decreasing substantially to 58% after 1.4 ka. We propose that changes in the intensity of human activities was a major cause of the observed regional disparities in vegetation succession. Comparison of the results with records of prehistoric human activity shows that, prior to 5.1 ka, land cover change (especially of the vegetation composition) in the Daihai basin evolved naturally, under the influence of climate. Then, during ∼ 5.1–2.8 ka, a transitional stage occurred, driven by both climate change and human activities. Finally, from ∼ 2.8 ka to the present, human activities dominated the pattern of vegetation change. In contrast, land cover change in the alpine Gonghai area was controlled by natural processes until 1.4–1.3 ka, when human activities exceeded the influence of natural variability and became the dominant factor controlling local vegetation development. In larger basin/plain areas, the favorable climatic conditions of the mid-Holocene promoted increased human activity; while later, population pressure, the increased demand for resources, and political factors may have triggered the diffusion of human populations from basins to the mountains or previously undeveloped areas, with resulting effects on their vegetation succession. The anthropogenic impacts have dominated the natural environment of mountainous areas in north-central China for at least the last 1,300 years.