Uphill or downhill?Cropland use change and its drivers from the perspective of slope spectrum

The continuous decrease of low-slope cropland resources caused by construction land crowding poses huge threat to regional sustainable development and food security.Slope spectrum analysis of topographic and geomorphic features is considered as a digital terrain analysis method which reflects the macro-topographic features by using micro-topographic factors.However,pieces of studies have extended the concept of slope spectrum in the field of geoscience to construction land to explore its expansion law,while research on the slope trend of cropland from that perspective remains rare.To address the gap,in virtue of spatial analysis and geographically weighted regression(GWR)model,the cropland use change in the Yangtze River Basin(YRB)from 2000 to 2020 was analyzed and the driving factors were explored from the perspective of slope spectrum.Results showed that the slope spectrum curves of cropland area-frequency in the YRB showed a first upward then a downward trend.The change curve of the slope spectrum of cropland in each province(municipality)exhibited various distribution patterns.Quantitative analysis of morphological parameters of cropland slope spectrum revealed that the further down the YRB,the stronger the flattening characteristics,the more obvious the concentration.The province experienced the greatest downhill cropland climbing(CLC)was Shannxi,while province experienced the highest uphill CLC was Zhejiang.The most common cropland use change type in the YRB was horizontal expansion type.The factors affecting average cropland climbing index(ACCI)were quite stable in different periods,while population density(POP)changed from negative to positive during the study period.This research is of practical significance for the rational utilization of cropland at the watershed scale.

Fifty years of Quaternary palynology in the Tibetan Plateau

Quaternary palynology in the Tibetan Plateau(TP)was initiated in the 1960s to meet the needs of economic development in western China.Pollen analysis was conducted for the first time on a 200-m long core of Quaternary lacustrine sediments taken from the main body of the TP in order to study pollen assemblages as well as vegetation and climate changes of glacial(cold)/interglacial(warm)periods.Pollen analysis of alpine snow and ice began at the first scientific expedition to the TP in the 1970s.After the 1980s,a series of international collaborative programs were carried out under Sino-French,Sino-German,Sino-Australian,and Sino-American cooperation,marking the integration of Chinese Quaternary palynology society with the international community.New methods for Quaternary palynology were gradually promoted and applied,changing the vegetational and climatic interpretation of Quaternary palynology from qualitative to quantitative.Since the 1990s,many palynologists have carried out extensive Quaternary palynological studies on fossil pollen sites of more than 60 lakes/sections and alpine glaciers in the TP to discuss the spatiotemporal vegetation changes and climatic and environmental evolution of the TP since the Pleistocene.Over the past half-century,Quaternary palynology in the TP has contributed to the establishment of the Chinese Quaternary pollen database and the study of vegetation and climate evolution since the Last Glacial Maximum(LGM)in the TP.Currently available pollen records revealed the spatial and temporal distribution of vegetation in the TP since the LGM,exhibiting expansions and shrinkages of forest,meadow,grassland and desert in different periods such as the LGM,the last deglaciation,and Holocene optimum period.The paleomonsoon reflected by paleovegetation since the LGM has undergone the changes of weak-strengthening-strong-weakening but still active-shrinking,which is mainly affected by solar insolation.

气候驱动下的晚全新世高山湖泊生态系统快速转变:来自中国北方高山湖泊沉积的首个枝角类记录证据

An increasing number of studies have shown that many alpine lakes have experienced rapid ecosystem transformations over the past^200 years[1–3].However,the mechanisms responsible for triggering these changes are often ambiguous in paleolimnological records and hence they are often debated.A major reason for this is that lake ecosystems are under increasing pressure from both anthropogenic activities and climate change.Possible means of distinguishing the effects of different regional drivers of lake ecosystem changes include the study of paleolimnological contexts which predate human activity,or the study of alpine lakes which are still largely unaffected by local human activity.

中国东西部降水跷跷板变化模式促使史前人类活动突破胡焕庸线

史前人类活动强度的分布显著受气候条件和地理格局的影响.人类活动能否突破地理环境的制约,又如何响应气候变化和技术发展是目前自然科学和社会科学共同关注的重大问题之一.在长时间尺度下寻找和发现人类活动与气候环境变化的关系,是回答上述问题的重要突破口.本文基于考古遗址;C数据概率密度、核密度等分析,揭示出以胡焕庸线为界的人类活动强度(人口)的分布模式:在新仙女木事件结束、东部地区开始驯化农作物后形成(距今约11400年前),并基本保持稳定;但在距今5200、3800和2800年前,胡焕庸线西部人类活动强度显著增加,分析认为这3次事件可能受到全新世中晚期我国东部降水相对减少而西部降水相对增加的跷跷板变化的影响,有助于人类向西部地区迁徙,气候变化可能对人类活动强度的时空变化产生深远影响.在研究史前人类迁徙的时空格局时,应考虑自然环境和人类社会发展的双重因素.

地层孢粉数据的远距离现代类比影响降水定量重建可靠性

Timing of the precipitation optimum in the Holocene for the semi-arid northern China affects our understanding of the temporal-patterns of the East Asian Summer Monsoon and its connection with precipitation in the monsoon fringe area.Discrepancies about when this occurs(early Holocene or mid-Holocene)exist in paleoclimate records based on various proxies and models.