Coprophilous Fungal Spores In Lake Sediments Recorded Holocene Pastoralism Development History In North China And Its Driving Factors

Pastoralism has long been the main livelihood in the northern steppe areas of China and the Qinghai-Tibet Plateau(QTP).However,there is a lack of archaeological evidence and documentary archives related to pastoral activity,and the evidence from animal archaeology,palaeoecology and animal genetics is ambiguous.Thus,the initiation and development of pastoralism in northern China,and its driving factors,remain unclear.The arable-pastoral ecotone in northern China is a region where pastoralism and agricultural civilization are interrelated,and it is also a key area for early cultural and technological exchange between the East and West.Thus,the area is ideal for studying the relationship between ancient humans and the environment,as well as the history of agriculture and pastoralism and their driving factors.The study area is ecologically fragile and experienced substantial climatic variability,triggering population migrations and the alternation of subsistence strategies during the historical period.Historical records of human activities in the region are scarce,and there is a sparsity of continuous and unambiguous records of relative changes in arable agriculture and pastoralism based on high-resolution records of climate and environmental changes.This makes it difficult to fully understand the shifts in subsistence strategies and their relationship with climatic and societal changes,and the relationship between human activities and environmental changes.To address these issues,16 modern herbivore dung samples and 10 surface soil samples from the northeastern QTP were investigated.Three sediment cores(with a total length of 23.13 m)from Gonghai Lake,Genggahai Lake and Tian'E Lake in northern China were also used as the research objects.1139 fungal spore samples from the three lake sediment cores and 520 pollen samples from the core from Tian'E were analyzed.A modern process investigation and previous research indicate that changes in the sedimentary content of coprophilous fungal spores,especially Sporormiella-type,can indicate changes in the large herbivore population and in the intensity of pastoralism.A record of changes in regional effective humidity was reconstructed,with an average resolution of ?7 years since 3.5 ka(1 ka = 1000 years),using the ratio of Artemisia and Chenopodiaceae from the sedimentary sequence of Tian'E Lake in the western Qilian Mountains.The history of agricultural activity was reconstructed with an average resolution of ?6 years during the historical period,based on changes in the crop pollen content of sediment cores from Gonghai Lake in Shanxi Province.In addition,archaeological evidence and historical documents,combined with palaeoclimatic and palaeoenvironmental records,were compiled in order to reveal the Holocene history of pastoralism in northern China and its driving factors.This compilation is used to evaluate the impact of climate and societal change on the intensity of pastoralism in northern China during the historical period.The principal results are as follows:(1)Sporormiella-type spores were dominant among the coprophilous fungal spores in the herbivore dung and surface soil samples,and changes in their content reflect changes in the herbivore population and the intensity of pastoralism.The Sporormiella-type record from Gonghai Lake is consistent with changes in the numbers of sheep and goats recorded in historical documents in recent decades;thus,the sedimentary record of Sporormiella-type can be as an indicator of variations in the size of the herbivore population on a longer time scale.(2)Records of Sporormiella-type coprophilous fungal spores in two sediment cores from Genggahai Lake in the Gonghe Basin and Lake Gonghai in northern China,were compared with fungal spore sequences from the Jiangxigou2 and Langgeri profiles in the Qinghai Basin,and with the cumulative probability of C-14 dates from animal bones(excluding pig bones)at archaeological sites in northern China.The results enable the population dynamics of large herbivores during the Holocene to be reconstructed,and they indicate that pastoralism appeared in the region at ?5.7–5.5 ka and was further intensified after ?4.2–4.0 ka.Combined with regional palaeoclimatic records,these findings suggest that the development of pastoralism in northern China was related to climate change: a warm and humid climate in Eurasian steppe areas generally occurred during the mid-Holocene,while a drought event at ?5.7–5.5 ka in some parts of the region may have prompted the expansion of livestock rearing into favorable grassland areas and facilitated the southward and/or eastward expansion of pastoral activity from the steppe regions of inner East Asia into northern China where the climate was warm and humid.An interval of cooler temperatures and drought conditions at ?4.2 ka may have further prompted the southward expansion of pastoral activity from high-latitude areas.The rapid intensification of pastoral activity after?3.6 ka may have been promoted by the wider use of horses in northern China.(3)The pollen and fungal spore records from Tian'E Lake in the western Qilian Mountains demonstrate that pastoralism intensity during the historical period is out-of-phase with that of changes in regional moisture.This suggests that the drier regional climate limited the development of arable agriculture in the lowlands of the Hexi Corridor,while forcing a shift in pastoral activity into the mountainous areas in the arid mountain-basin system on the northern margin of the QTP.A notable exception was a reduction of pastoral activity in the arid region with high mountains during 380–580 CE,caused by centennial-scale dry and cold climatic conditions,concurrent with a decrease of the human population.It is noteworthy that intensified pastoral activity occurred during 580–720 CE and after ?1920 CE,corresponding to a warmer and wetter climate and diverse subsistence strategies in the lowlands of the Hexi Corridor.In the semi-humid area,the records of fungal spore and crop pollen from Gonghai Lake show that a warm and humid climate promoted the expansion of arable agriculture in mountainous areas,corresponding to a phase of social stability and strong central government control,such as during the Sui and early–middle Tang Dynasties and the northern Song Dynasty.However,a cold climate and societal crises during the Wei,Jin Southern and Northern Dynasties and the Ming-Qing Dynasties limited the expansion of cultivated land and there was a shift to grazing as a subsistence activity.Time series analysis reveals that the arable farming phases had a longer periodicity than the pastoralism phases,possibly because of the greater resilience of farming activity to climate change and the attachment of agriculturalists to their land.A comparison of several records of pastoral intensity suggests that the arid climate may have limited the development of agriculture in low-altitude areas,while at the same time forcing the development and expansion of pastoral activity in mountainous areas.During the Sui and early–middle Tang Dynasties,with an increase in the regional population and diversification of subsistence strategies,pastoral activity also increased.These changes were promoted by relatively harmonious ethnic relations and the warm and humid.In the past few decades,a weakening of the intensity of pastoralism may be related to innovations in agricultural technology and the rational management of pasture resources and livestock.In addition,the different periodicities of pastoralism intensity from Tian'E Lake and Gonghai Lake during the historical period indicate that pastoralism intensity was not only affected by climate change but also by societal developments.In summary,this study provides several continuous and high-resolution lake sediment records of coprophilous fungal spores since the last deglaciation in northern China,and it also provides new evidence and an improved understanding of the development of pastoralism in northern China during the Holocene.It also,for first time,reveals changes in the cyclicity of agricultural and pastoral activity in northern China.A high-resolution pollen record from the western Qilian Mountains provides an improved climatic background for the reconstruction of human activities along the Silk Road.An improved understanding of the history of pastoralism and its driving factors in northern China also facilitates an evaluation of past changes in the regional vegetation and environment,the interactions between humans and the environment,and the environmental impacts of human activities.Independent records of arable agriculture and pastoral activity can help better understand the impact of human activities on land use,land cover changes,and soil degradation,and further provide an historical reference for understanding how ancient humans adapted and responded to changes in the climatic and environmental background,and to societal changes.