Fig. 3: Variations of the farming-pastoral ecotone and spatial distribution of ancient cities in the dust source region from the Han to the Ming Dynasties.
From: Asian dust-storm activity dominated by Chinese dynasty changes since 2000 BP
a, c, d, f Periods of unified dynasties with an increased number of cities (red dots) in the dust source region, which correspond to the northward movement of the farming-pastoral ecotone (purple broken line). b, e Periods of civil unrest with fewer cities in the dust source region, which correspond to the southward movement of the farming-pastoral ecotone. Ancient cities are interpreted as the permanent settlements of agricultural populations28. This is because nomadic populations are highly mobile, preventing the construction of such settlements, whereas settled agricultural populations are forced by necessity to build cities. The arrows indicate the direction of movement of the establishment of ancient cities. Distributions of loess (gray line shading), desert (yellow shading), and Gobi (dark gray shading) are also indicated. The blue dot indicates the location of Lake Gonghai and the blue line indicates the Yellow River. The distribution of ancient cities and the farming-pastoral ecotone are modified from ref. 31 and ref. 32, respectively. The figure was created using Arcmap 10.2.
