Quantitative studies on charcoalification:Physical and chemical changes of charring wood

Charcoal is commonly preserved in both natural and artificial sediments,and is intensively used in paleontological,paleoenvironmental,and archaeological studies due to the abundant bio-information it contains.The biochemical properties of charcoal are also used for paleoclimatic reconstruction;however,the reliability of this approach has been challenged due to a lack of clarity on how physicochemical properties change during the charring process,as well as the temperatures required for charcoalification.To address this lack,in this study,Qinghai spruce and Chinese pine wood samples from the northeastern Tibetan Plateau were heated at different temperatures and for different lengths of time under restricted oxygen conditions.The reflectance;carbon,nitrogen,and oxygen content;and tracheid morphology were quantified before and after heating to assess changes related to the charring process.Archaeological charcoal remains were then evaluated to determine the charcoalification temperatures by comparing with the experimental results.The minimum temperature required for wood charcoalification was∼300℃,while temperatures recorded by archaeological charcoal were concentrated at 400-500℃.During the charring experiments,the tracheid cell walls gradually homogenized,and tracheid cell wall thickness and lumen area decreased by∼20%.On average,50%mass losses were observed;the carbon and oxygen content(%wt.)approximately changed from 47%to 60%and 48%to 35%respectively,while the nitrogen content(%wt.)fluctuated around 0.2%.The reflectance increased slightly from 0%to 0.5%.We propose that the charcoalification of wood tissue refers to charring(in restricted air)and carbonization(in the almost absence of air)when the wood is exposed to a heat source,which then finally transforms into a black,inert solid.This quantitative study provided valuable data and a thorough assessment of the process of wood charcoalification,as well as accurately estimated the feasibility of using charcoal physicochemical properties in paleoclimatic research.

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.

Spatiotemporal variation of agricultural patterns in different geomorphologic and climatic environments in the eastern Loess Plateau,north-central China during the late Neolithic and Bronze Ages

Human settlement and agricultural development are closely linked to local geomorphological and climatic environments.However,the variation in agricultural systems in different environmental and prehistoric contexts remains unknown.We report new archaeobotanical and radiocarbon dates from 34 Neolithic and Bronze Age sites in the Hutuo River Valley(HTRV)in north-central China and compare them with updated archaeobotanical studies in the Sushui River Valley(SSRV)and Henan Province(HNP),to explore the similarities and differences of agricultural patterns under different geomorphologic and climatic environments in north-central China.Our results reveal that humans consistently cultivated foxtail and broomcorn millet in the HTRV from the Miaodigou(6000–5700 cal.a BP)to the Shang-Zhou(3600–2256 cal.a BP)period,despite the introduction of wheat and barley into the area around 4000 a BP.Climate conditions and hilly landforms in the HTRV,SSRV and some parts of the HNP led people to develop foxtail and broomcorn millet dry land farming practices between 7000 and 3000 a BP.Alternatively,in other areas of the HNP,the climate conditions and alluvial plains enabled people to develop a mixed agriculture of millets,soybeans,and rice from 7000 to 4000 a BP,with the addition of wheat between 4000 and 3000 a BP.Farmers’different agricultural technologies and interactions with foreign cultures may have also influenced the formation of different agricultural patterns in the three regions between 7000 and 3000 a BP.Population growth during 7000–3000 a BP can explain the overall propensity of the higher-yield foxtail millet rather than broomcorn millet as the main cultivated crop.In the HTRV,however,higher proportions of broomcorn millet(as compared to the SSRV and HNP),may reflect the greater drought and heat tolerance of broomcorn millet,representing an adaptive agricultural strategy in the river valley.