17th–20th Century
6. Conclusions
By analyzing historical documents, regression analysis, model of pressure index on cropland, and geographic information system (GIS), this paper reconstructed spatial patterns of labor/household density, cropland area per capita, and pressure index on cropland at the county level in Shandong Province during the 17th–20th century. Following this, we analyzed the impacting process of climate change and the sustainability of cropland use during the different periods. The conclusions of this study are as follows:
There was a distinct spatial difference in labor/household density which showed the effect of land suitability for reclamation on the population distribution. There was a greater proportion of the population in the agricultural area of Northwest and Southwest Shandong as well as the Jiaolai Plain.
The population density of Shandong Province over the past 300 years has been increasing, especially in the three agricultural areas.
The spatial distribution of cropland area per capita in Shandong over the past 300 years has been relatively uniform. From the 19th century to the beginning of the 20th century, cropland area per capita decreased extensively and social vulnerability was strengthened. There was likely a threat to food security in Binzhou, Linyi, Jining, Laiwu, Taian, Yantai, Weihai, Jinan, Dezhou, Qingzhou.
The pressure index on cropland also showed a similar spatial distribution to cropland area per capita, but its threshold was lower than that in modern times. During the 19th century and the beginning of the 20th century, two high-value centers of pressure on cropland appeared in Middle Shandong and the Jiaodong Peninsula.
A warm climate was beneficial to driving an increase in population and agricultural development, which finally resulted in increasing pressure on the sustainability of cropland use. This increase in pressure on cropland was also related to the growth of the population as well as the spatial differences in land quality between plain and hill areas. The impacting process of climate change was sketched as following the flowchart shown in Figure 7: climate change—population and cropland area—cropland area per capita—food sustainability and society vulnerability—social stability.
Acknowledgments: This work was supported by the National Natural Science Foundation of China (Grant No.
41471156), the National Key Research and Development Program of China (Grant No. 2016YFA0602500), and the Strategic Priority Research Program from Chinese Academy of Sciences (XDA05080102).
Author Contributions:Yu Ye wrote this text and produced the figures. Xueqiong Wei, Xiuqi Fang and Yikai Li listed the references and help to edit the text.
Conflicts of Interest: The authors declare no conflict of interest.
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