Review on boundary shift of farming-pastoral ecotone in northern China and its driving forces

The boundary of agriculture-animal husbandry ecotone in northern China has changed frequently by climate change and human activities. Quantitatively detecting the contributions of climate change and human activities to the boundary changes of the farming-pastoral ecotone in northern China has been a hot topic in the field of climate change. In recent years, an increasing number of studies have documented the boundary changes in the farming-pastoral ecotone in northern China. However, for a long time, there was not a unified definition of the farming-pastoral ecotone in northern China. Based on the related literatures, we systematically reviewed the definitions of the farming-pastoral ecotone in northern China from five respects. 1) The definition based on the substitute evidences, according to the information indicated in the historical literatures, archaeological events, pollen records, ice cores and tree-rings, the historical boundary of the farming-pastoral ecotone in northern China can be delineated. 2) The definition based on the field investigations, is according to the scholars’ field surveys of the farming-pastoral ecotone in northern China. 3) The definition based on the climatic factors, according to the range of the precipitation (such as the 400 mm isohyet), moisture, temperature and wind, the farming-pastoral ecotone in northern China can be draw accurately. 4) The definition based on the land use factors, according to the proportions of the grassland and cropland, the scope conforming to the farming-pastoral ecotone was selected. 5)The definition based on the comprehensive indicators, this method often combines the land use factors and climatic factors to define the scope of the farming-pastoral ecotone in northern China, besides this, the vegetation, the economic level and livelihood were also used to draw the outline of the farming-pastoral ecotone in northern China. Then we analyzed the contributions of the climate change and human activities to the boundary changes of the farming-pastoral ecotone in northern China. For the climate change, the boundary of the farming-pastoral ecotone in northern China changed northward during the warmer-wetter period and changed southward during the colder-drier period. For the human activities, the policies, increased population, developed economic levels, religion and diet structure were all the main driving forces of the boundary changes of the farming-pastoral ecotone in northern China. After that, we introduced the quantitative progresses of the previous researches on evaluation of the contributions of the climate change and human activities. However, there were four defects in assessing the contributions of climate change and human activities to boundary changes of the farming-pastoral ecotone in northern China, such as the lack of the comprehensive definition, the quantitative method, the systematical data and the reasonable explanation. Meanwhile, we obtained the solutions to the existing problems. For example, composited definition based on multi-factors, quantitative identification of driving forces at multi-scales, collection of high resolutions data and the detailed explanations of the mechanism of boundary change. Understanding the contributions of climate change and human activities to the farming-pastoral ecotone in northern China is essential for making comprehensive decisions concerning human adaptability to climate change in different regions; the study will be helpful to the management of reasonable land use and the mitigation and adaptation to climate change for the sensitive regions.