| Wildfire is an important natural phenomenon in terrestrial ecosystems,which is closely related to climate change and human social development.The mechanism and influencing factors of fire are a widely concerned scientific issue.The research is of great significance for the prediction of fire evolution trend in the context of rapid climate change and the formulation of relevant prevention and control management policies,which also provides a unique perspective for exploring the evolution of human-land relationships.The regional climate systems along the middle part of the Silk Roads(Xinjiang)and the eastern part(Xi'an-Dunhuang)are very different,including the westerly region,monsoon-westerly transition region,and monsoon region.Natural vegetation in this vast area exhibits obvious geographical differentiation,including temperate desert,temperate grassland,warm temperate deciduous broad-leaved forest,etc.,which is sensitive to climate change.The region has a long history of human activities,diverse livelihood patterns,and obvious spatial and temporal differences in settlement intensity since the middle and late Holocene.Therefore,the study of the interaction among paleo-fire,climate,and human activities during the middle and late Holocene in the middle-east part of the Silk Roads will be helpful to understand the occurrence of fire activities and the driving mechanism behind them on centennial and millennial scales.It has important theoretical value and practical significance for fire prevention and control measures under the background of climate change in the future.In recent years,some important progress has been made in the study of paleo-fire in this region,which is valuable for understanding the evolutionary process and the law of paleo-fire activity in the past,while obvious deficiencies are still existing.Firstly,there are few paleo-fire records in the middle-east part of the Silk Roads,and their spatial distribution are heterogeneous.Secondly,the existing research haven't been well discussed combined with and archaeological data is insufficient,and the influence of human activities on the variation of paleo-fire frequency has not been well concerned.Thirdly,there is a lack of comparative analysis on the spatial-temporal differences of paleo-fire activities in a large space,and the understanding of the mechanism behind paleo-fire occurrence is not clear enough.In view of the problems above,this paper selected 5 lakes along the middle-east part of the Silk Roads with different longitudes.Using black carbon measurements in sediments as the main research method,combined with reliable core dating frameworks,the reconstruction of paleo-fire history in different climatic zones of the middle and late Holocene is carried out.The black carbon content of 641 samples was tested,and a total of 1923 black carbon,char,and soot data were obtained.The geochemical elements of292 sedimentary samples from 22 Neolithic-Bronze Age archaeological sites in Hexi Corridor were determined.On this basis,combined with the existing paleo-fire records in the study area,the relationships among paleo-fire and climate,vegetation and human activities in the study area is studied,and the difference of paleo-fire patterns in time and space during the middle and late Holocene and their possible driving mechanisms are discussed.Based on the research work above,the main conclusions and understandings are as follows:(1)There is significant spatial discrepancy in paleo-fire history in different regions of the middle-east part of the Silk Roads.In the monsoon region and the monsoon-westerly transition region,the intensity/frequency of paleo-fire revealed by black carbon fluxes in Yuhuangchi,Tianchi,Caodalian and Tian E Lake were generally lower during the middle Holocene and significantly increased during the late Holocene,with significant differences on the centennial scale.In the westerly region,the intensity/frequency of late Holocene paleo-fire revealed by black carbon fluxes from Kalakuli Lake showed a decreasing,rising and declining trend during 4200-3800 BP,3800-1400 BP and post-1400 BP,respectively.(2)The intensity/frequency of paleo-fire activity in the middle-east part of the Silk Roads is obviously different in space.The intensity/frequency of paleo-fire activity is the lowest in arid area,the middle level in humid and semi-humid area,and the highest level in semi-humid and semi-arid area.The intensity/frequency of fire is estimated to be the highest in areas with annual precipitation of 200-600 mm,Normalized Difference Vegetation Index(NDVI)of 0.4-0.6 and Net Primary Productivity(NPP)of 200-800 g C/m~2.(3)The paleo-fire activity in the middle-east part of the Silk Road was dominated by climate change and vegetation types on a millennial scale,and varied in different regions.Humidity was the main limiting factor for paleo-fire activity in the monsoon region and the monsoon-westerly transition region.The increase of drought degree in the late Holocene resulted in the expansion of flammable herbaceous vegetation,and the increase of temperature in winter and spring resulted in the increase of paleo-fire intensity/frequency.The main limiting factor of paleo-fire activity in the westerly is fuel availability.The increase of humidity promotes the growth of vegetation and provides more fuel supply for the occurrence of fire.Meanwhile,the rise of spring temperature promotes the growth of vegetation and is also conducive to the occurrence of fire,which leads to the increase of paleo-fire intensity/frequency.(4)Paleo-fire history is obviously influenced by human activities on the centennial scale in the middle-east part of the Silk Roads.There are differences in the action mode and time in different regions.The agricultural and metallurgical activities of slash-and-burn in Neolithic and Bronze Age probably led to the increase of paleo-fire intensity/frequency.In historical period,wars between different regimes had an important influence on the frequency of paleo-fire.In modern times,the rapid growth of population and arable land resulted in a general decline in fire intensity/frequency,which was related to the increase of landscape fragmentation and the decrease of combustible materials.In this stage,the influence of regional human activities on fire broke the previous pattern of long-term control of paleo-fire by climate change.(5)The paleo-fire activity in the middle-east part of the Silk Road has centennial and millennial cycles.On the centennial scale,paleo-fire activity is similar to the Gleissberg(50-80 years and 90-140 years)cycle of solar activity and the de Vries cycle of about 205 years.On the millennium scale,the paleo-volcanic activity in the monsoon and monsoon-westerly transition regions can correspond to the quasi-cycle of global thermohaline circulation of 1500-1800 years,while the westerly regions are very close to the“Eddy”cycle of solar activity of 1000 years.Therefore,changes in solar activity and its influence on ocean circulation and hydrological conditions(such as summer monsoon and westerly)drive periodic changes in fire activity at centennial and millennial scales in the study area.The characteristics and contributions of this paper are as follows:(1)the key historical records of paleo-fire in different regions of the middle-east part of the Silk Road during the middle and late Holocene are newly constructed,revealing spatial-temporal differences in the intensity/frequency of paleo-fire in this region;(2)The correlation mechanism between paleo-fire activity and climate change,vegetation and human activities during the middle and late Holocene in the middle-east part of the Silk Road was comprehensively discussed,and the main driving factors of paleo-fire activity in different periods in the middle-east part of the Silk Road were pushed forward.(3)Through spectral analysis,the understanding of historical variation cycle of paleo-fire in the study area is deepened. |
PDF Full Text Request