Refined chronology of prehistoric cultures and its implication for re-evaluating human-environment relations in the Hexi Corridor,northwest China

The reconstruction of high-resolution chronologies for prehistoric cultures is a prerequisite for understanding the history of human evolution and its relationship with environmental change, and is valuable for exploring the trajectory of transcontinental cultural exchanges in prehistoric time. The Hexi Corridor of northwest China was one of the earliest centers for long-distance culture exchange in the prehistoric world. The timing and sequence of cultural changes in this area remains poorly understood resulting from the lack of radiometric age control. This paper presents a refined radiocarbon(14 C) chronology to resolve the timing of human occupation and cultural evolution in the Hexi Corridor. Radiocarbon dating of crop remains, which have an annual life cycle, has the advantage of eliminating problems such as the carbon stored in ‘old wood’. As a result,14C dates from crop remains are used to test the validity of the14C dates derived from charcoal, bone and plant remains. The resultant database of ages is modelled using the Bayesian approach. The updated chronology presented in this paper shows generally good agreement with the original dates used to constrain cultural evolution in the Hexi Corridor. However, the occupation of the corridor by the Shajing and Shanma Late Bronze Age-Early Iron Age cultures appears to have taken place ~300 years later than previously thought. On the basis of comparing this updated chronology of cultural evolution with palaeoclimatic and historical records, it is proposed that the collapse of the Shajing and Shanma cultures occurred as a result of geopolitical impact rather than climate change.

人类活动改变了中亚1000年以来的火-气候关系:来自4200年的沉积物记录

火灾深刻地影响着人类的生产生活.中亚地区对气候变化响应敏感且有着悠久的放牧活动历史,然而由于缺乏高分辨率的火灾记录,该地区长时间尺度的火-气候-人类活动间的关系仍不清楚.本文通过对新疆卡拉库里湖泊(38.439°N, 75.057°E;3645 masl)沉积物中的黑碳含量分析,重建了该地区首条高分辨率(~20年)的晚全新世火灾记录.综合古气候记录对比分析表明, 4200~1000 a BP,在年代际、百年际和千年际尺度上,湿润期对应火灾多发期;1000 a BP以来,在百年际和千年际尺度上,湿润期对应火灾少发期.我们认为,中亚地区草原火灾的变化受控于湿度所影响的植被载荷的变化,而人类活动(如牧业和农业)很可能通过减少地表生物量而抑制了近1000年来的火灾活动,打破了长期以来气候控制火灾变化的模式.本研究对以草原为主的中亚地区火-气候-人类活动之间的相互作用提供了有益的认知,有助于未来火灾管理政策的制定.

Detecting anthropogenic impact on forest succession from the perspective of wood exploitation on the northeast Tibetan Plateau during the late prehistoric period

Human activities are usually considered to have had impacts on forest degradation and/or changes of forest composition in the past.The Tibetan Plateau,an environmentally sensitive area,has witnessed a high intensity of human activities since the late Neolithic,but the evidence is still incomplete concerning how human activities affected the environment,especially vegetation changes.This may result,in part,from the fact that research on prehistoric wood utilization by humans in the northeast Tibetan Plateau(NETP)is scarce,especially from the perspective of charcoal analysis,which is an archaeological index directly related to human activities.To fill this gap,we report new data here concerning charcoal analysis from 24 archaeological sites dated 5200–2300 a BP in the NETP,where this period saw remarkable environmental and social changes.By coupling the results with published paleoenvironment records(especially pollen),we aim to explore the utilization of wood and its spatial-temporal changes,as well as the anthropogenic impacts on past forest dynamics in the NETP.The results suggest that the wood resources collected by humans were mainly needleleaf trees(Picea L.and Pinus L.),broadleaved trees(Populus L.,Salix L.,and Betula)as well as shrubs(Hippophae L.and Tamarix L.),and that these were distributed around the human habitation areas.There was a clear spatial difference in the woody assemblage collected by humans in the period 3600–2300 a BP.This was likely related to the diversity of natural environments in local areas,but there was an abnormal spatial pattern of forest composition with broadleaved trees dominant above 2500 masl caused not by climate change,but by the rapid increase of human settlement and wood collection in high altitude areas of the NETP since 3600 a BP.

粟种子和花序的新发现揭示粟在传播中的表型分异

晚全新世粟的传播是史前食品全球化的重要组成部分,对欧亚大陆农业生产体系、先民食物组成以及文明发展进程产生深远影响.但是粟传播的时间、路线和模式并不清晰,而且很少有研究涉及粟在传播过程中表型对新环境的响应和适应,以及这类表型变化可能产生的农业效应.本文根据245个粟直接测年数据的贝叶斯年代模型分析结果,提出粟向我国西部传播的"西北线"和"西南线",明确粟非"波浪式推进"的传播模式.分析有明显降水梯度的28个遗址中12977粒成熟炭化粟种子的测量值,发现距今5165年以来粟在适应不同降水背景下,各遗址间种子群体存在复杂的无规律的差异,但总体上种子尺寸和形状中值波动较小,缺乏指向性变化趋势,基于此提出该时间段粟产量增加主要依靠种子粒数增加而非单粒种子尺寸增大的新认识.另外,遗址五堡和米兰干燥粟种子测量结果也支持种子表型性状多样化但总体相对稳定的结论.但五堡粟花序尺寸小,呈直立柱状,而米兰粟花序大,呈纺锤弯曲形态,有复杂的分枝结构.这些被发现的完整干燥粟花序,突破了以往只依靠种子来推测粟表型多样化表现的有限认识,为揭示粟表型分化及其产生的农业效应提供了极为关键的实证材料.