An Integrated Study On Record Characteristics And Environmental Significance Of Locust Plagues In China During The Historical Period

Flood, drought and locust plague were the three biggest agricultural disasters in Chinese history. The three biggest disasters always led to various social crises such as hunger, epidemics, and wars. Both natural disasters and social crises would do great harm to agricultural and social-economic development. Meanwhile, they witnessed a hard but transcendent history in which Chinese people fought against natural disasters and social crises. Therefore, the process of Chinese social-economic development was a long struggle history.As the most frequent disasters in Chinese history, flood and drought which had a close relationship with climate change have been studied by many researchers for a long time. As for locust plague, more focuses should be paid to it. The reasons are as follows: First, the locust plagues registered in Chinese historical documents were caused by migratory locusts, especially Oriental migratory locust (OML), which had strong flying ability and could choose their food freely, so migratory locusts were hard to control. In addition, the causes of migratory locust plagues were rather complex and there were great difference of opinion from the past researches. Second, studies on historical locust plagues involved many specialization fields such as History, Biography and Geography etc. It was impossible to draw a comprehensive conclusion from a single field. Therefore these studies should be carried out under the leadership of the thought of integration, which was a nodus. Third, the relationship between locust plague and climate change was more complex than that between flood or drought and climate change. On many occasions, locust plague was caused by latent climate change, so more work should be done to disclose the secret between locust plague and climate change.This study was carried out in order to answer the questions full of disputes. Through collection and interpretation of Chinese historical documents that related with locust plague, we set up a Chinese historical locust plague database according to which the trend and characteristics of locust plagues were disclosed. As for the three subspecies of migratory locusts in China, we showed the sublevel regionalization map of them. According to the database and map above, we constructed many historical locust plague sequences and analyzed their periods with Wavelet Analysis Method. More work was done to deal with comparisons between locust plague sequences and sequences of other natural disasters, social crises, and climate proxies—mainly temperature and precipitation. At last, we drew a preliminary conclusion of the environmental significance of historical locust plagues. In a word, our study was an integrated study on record characteristics and environmental significance of locust plagues in China during the historical period, and the study was an integrated work based on historical data, geographical methods and biological explanation.The general results and conclusions are as follows:(1) The study period began with year 707BC in which the first locust plague had been registered in document and ended with year 1949AD after which pesticide was widely used to control the number of migratory locust. We collected 4346 locust plague records from 27 provinces of China (including Taiwan), with 1241 volumes of documents involved. In addition, 592 records of other pests were also gained. The frequencies of locust plague year in their whole period descended from Oriental migratory locust (OML), Tibetan Migratory Locust (TML), to Asiatic Migratory Locust (AML).(2) When collecting historical locust plague records, Network Search Method was used to deal with normative historical documents like official histories, which increased the efficiency and veracity, instead of reading word by word or page by page.(3) We dated the Eight Rises and Ten Falls of Chinese documents in history and drew a figure to indicate the uncontinuity and nonuniformity of Chinese historical documents. The first month of different calendars in Xia Dynasty, Shang Dynasty, Zhou Dynasty and Qin Dynasty was also discussed in order to establish a basis for the following study. In addition, the figures of locust plague frequency of the three subspecies of migratory locusts were drawn on 100-year scale.(4) We made a distinction of records of locust from other pests and listed their representative records. As for locust plague, we gained both ordinary records and special records like 24 suicide records and many natural enemy records.(5) According to the record characteristics of locust plagues, we raised several preliminary classification plans of historical locust plagues in the view of entomic taxology, physical geography regionalization, occurring time of locust plagues, and the hydrophilic distribution. According to the duration, extending scope, destroying degree, and impacts on human, we divide locust plagues into four grades: Occurrence Grade I, Impact Grade II, Harm GradeIII, Disaster GradeIV, with detailed explanation in a grade division table.(6) We made regionalization of Oriental migratory locust (OML) and Asiatic Migratory Locust (AML) in Gansu Province and made secondary regionalization of Oriental migratory locust (OML) among Shaanxi, Anhui and Jiangsu Province which step across the boundary of Qinling Mountains-Huaihe River. At the same time, generation, month, grade and stricken county of locust plagues were analyzed respectively. (7) We divided Oriental Migratory Locust Region into four spatial scopes: Core Region, North Region, South Region and Total Region in which we reconstructed three kind locust plague sequences of all regions respectively on 10-year scale. We analyzed the period of each sequence with Wavelet Analysis Method. In addition, record characteristics of Asiatic Migratory Locust (AML) and Tibetan Migratory Locust (TML) were also discussed and the corresponding sequences were constructed.(8) Considering the possible chain reactions after locust plagues, we made several comparisons between locust plague sequence and war sequence, epidemic sequence, dust storm sequence, rice price index, and flood sequence of Huaihe River. The results were as follows: First, locust plagues had well correlation with wars and epidemics, which indicated the causality among them. Second, locust plagues had well coherence with dust storms but it did not mean that cold background was indispensable for locust plagues. Third, locust plagues of Anhui had no overlapping year with floods of Huaihe River, which in reverse proved the coherence between locust plague and drought. Fourth, we found that rice price ascended always with a 1-3 year lag after locust plague, which inspected and verified the fact in history.(9) Through construction of next year tables of warm and cold winters in North and East China, we found the recurring probabilities of locust plagues in the two tables were 89/126=0.7063 and 64/85=0.7529, with a difference of 0.0466. The result indicated that locust plague did not have a positive correlation with both warm or cold winter, and locust plague sequence could not be used to reconstruct winter half-year temperature. Possible reasons were given in the respects of entomic physiology and ecology.(10) In a worldwide field of view, we made comparisons between several representative locust plague sequences and typical climate sequences. We found that locust plagues of Core Region had a well tele-connection with ENSO, and locust plague still had bad coherence with temperature, but good with drought.In a word, our study demonstrated that locust plague records could well represent drought for climate reconstruction, and locust plague had a well negative correlation with summer half-year precipitation instead of a positive correlation with winter half-year temperature. Therefore locust plague sequence would be a good proxy to reflect summer half-year drought. At the end, questions such as the collection of more documents, cooperation of different specialization fields, construction of Chinese Historical Locust Plague Geographic Information System, and other future work were discussed.