John Dodson

Astronomical calibration of loess-paleosol deposits at Luochuan, central Chinese Loess Plateau

Abstract The 140 m loess–paleosol profile at Luochuan in the central Chinese Loess Plateau was sampled at 5-cm intervals in loess units and at 3 cm in paleosol units, in order to obtain a high resolution climatic record covering the past 2.5 million years. All samples were measured for magnetic susceptibility, which is regarded as a good proxy index of the East Asian summer monsoon strength. On the basis of the astronomical theory of Pleistocene climatic change, an age model of the Luochuan loess–paleosol sequence was developed by tuning the magnetic susceptibility record to time-series of insolation changes. The results show that the ages of the boundaries between the Malan and Lishi, and Lishi and Wucheng loess formations are 71 and 1320 kyr BP, respectively. The onset of loess accumulation is at 2470 kyr BP. Our age model was tested by comparing the orbitally derived ages with absolute age determinations of magnetic reversals, and cross-spectrum analyzing with solar radiation variations for summer at 65°N. These indicate that the calibration provides a reliable time scale for the Luochuan loess–paleosol deposit.

Predictability of biomass burning in response to climate changes

Climate is an important control on biomass burning, but the sensitivity of fire to changes in temperature and moisture balance has not been quantified. We analyze sedimentary charcoal records to show that the changes in fire regime over the past 21,000 yrs are predictable from changes in regional climates. Analyses of paleo- fire data show that fire increases monotonically with changes in temperature and peaks at intermediate moisture levels, and that temperature is quantitatively the most important driver of changes in biomass burning over the past 21,000 yrs. Given that a similar relationship between climate drivers and fire emerges from analyses of the interannual variability in biomass burning shown by remote-sensing observations of month-by-month burnt area between 1996 and 2008, our results signal a serious cause for concern in the face of continuing global warming.

Pollen-based quantitative reconstructions of Holocene regional vegetation cover (plant-functional types and land-cover types) in Europe suitable for climate modelling

We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1° × 1° spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.

The vegetation characteristics of the ‘Yuan’ area at Yaoxian on the Loess Plateau in China over the last 12 000 years

Vegetation history is a valuable tool to assist understanding of environmental changes, ecological restoration and human impact on the environment. This study discusses the pollen analysis of the Yaoxian section on the southern margin of the Loess Plateau in China. Based on the pollen diagram, the vegetation of Yaoxian shows four episodes of change, i.e. from steppe to humid-grassland, to steppe, to humid-grassland, and then to grassland, over the last 12 000 years. The vegetation of the ‘Yuan’ region (the large flat surfaces of the Loess Plateau) was herb and shrubland, even in sub-humid regions. Previously published pollen records from Weinan, Luochuan and Fuxian in the ‘Yuan’ area, using organic carbon isotopes (δ13C) and phytolith analysis, all similarly indicate that the vegetation was dominated by shrubs and herbs. Thus, steppe and grassland were the dominant vegetation types and there was no natural forest in the ‘Yuan’ region of the Loess Plateau during the Holocene, even not at the Holocene optimum.

Late Pleistocene Megafauna and Archaeology from Cuddie Springs, South-eastern Australia.

The Cuddie Springs site in south-eastern Australia provides the first evidence of an unequivocal association of megafauna with humans for this continent. Cuddie Springs has been known as a fossil megafauna locality for over a century, but its archaeological record has only recently been identified. Cuddie Springs is an open site, with the fossil deposits preserved in a claypan on the floor of an ancient ephemeral lake. Investigations revealed a stratified deposit of human occupation and fossil megafauna, suggesting a temporal overlap and an active association of megafauna with people in the lead up to the Last Glacial Maximum, when conditions were more arid than the present day. Two distinct occupation phases have been identified and are correlated to the hydrology of the Cuddie Springs lake. When people first arrived at Cuddie Springs, sometime before 30,000 BP, the claypan on the lake floor was similar to a waterhole, with five species of megafauna identified. Flaked stone artefacts were found scattered through this level. After the lake dried, there was human occupation of the claypan. The resource base broadened to include a range of plant foods. Megafauna appear to be just one of a range of food resources exploited during this period. A return to ephemeral conditions resulted in only periodic occupation of the site with megafauna disappearing from the record around 28,000 BP. The timing of overlap and association of megafauna with human occupation is coincident with the earliest occupation sites in this region. The archaeological evidence from Cuddie Springs suggests an opportunistic exploitation of resources and no specialised strategies for hunting megafauna. Disappearance of megafauna is likely to be a consequence of climatic change during the lead up to the Last Glacial Maximum and human activities may have compounded an extinction process well under way.

Interactions of natural hazards and society in Austral-Asia: evidence in past and recent records

Abstract Interactions of some of the principal historical natural hazards with human populations in the Austral-Asian region are discussed both from the perspective of the impact of the hazard on humans as well as the effects of human activities and climate change on hazard magnitude and frequency. Basically, the former type of interaction is evident for most hazards, while the latter interaction is primarily confined to terrestrial and coastal flooding, erosion, landslides, sea level rise, drought, and fire. Social vulnerability to natural hazards is related to the resources available to cope with the hazard, level of economic development, the ability to predict the occurrence of a hazard and to adjust and adapt to conditions posed by the hazard, and planning measures embraced by societies. Historical chronologies are presented for a range of hazards. Problems in reconstructing historical records of natural hazards include: interpretations of oral records; lack of supporting artifacts; obliteration of evidence of chronic hazards by higher magnitude events; and the inability to distinguish between the effects of different hazards in sediment records. Nevertheless, useful examples illustrate the effects and awareness of volcanic activity and associated hazards, such as tsunami, by early Maori and subsequent development of avoidance strategies; the effects of widespread land use changes and increases in population on the occurrence of floods, landslides and gullies in China and New Zealand; and the effects of forest conversion and drought on fire hazards in Indonesia.

A late Quaternary record of environmental change and human impact from New Caledonia

A late Quaternary vegetation record is presented from a lowland site on the leeward southwest coast of New Caledonia. Plum Swamp is a backswamp on the Plum River at around 10 m a.s.l., just within the ultramafic terrain that dominates the southern third of New Caledonia. Pollen analysis, charcoal analysis, radiocarbon dating and stratigraphic analysis are employed to reconstruct the vegetation and sedimentary history of the valley. The vegetation record commences at around 20,000 yr BP and shows that from this time up until the late Holocene the valley was forested. The greater representation of taxa more prevalent at higher altitudes during the late glacial suggests a response to cooling and an enrichment of the lowland forest with more montane elements. The late glacial transition between 14,000 and 9000 yr BP is a period of instability within the valley when vegetation is disturbed by fire. Forest recovers after this and there is increasing stability until the arrival of people in the late Holocene at around 3000 yr BP. The initial colonisers of New Caledonia had a profound effect upon the vegetation of the valley, converting the lowland forest to a stunted and species poor maquis on the ultramafic sediments and Melaleuca woodland on the non-ultramafic substrates. However, sedimentary processes are relatively unchanged during this time. Dramatic geomorphic change does occur in the catchment though, during the latter part of the 20th Century as a consequence of mining. q 2001 Elsevier Science B.V. All rights reserved.

The history of mediterranean-type environments: climate, culture and landscape

This editorial introduction highlights four of the principal themes in late-Quaternary research on summer-dry, mediterranean-type environments: first, issues of historical biogeography, such as convergent evolution; second, the synchroneity of past climate change between and within different regions; third, how far mediterranean-type environments represent cultural constructs or pristine habitats; and, fourth, the environmental future of mediterranean-type regions - for example, whether past records can help inform our understanding of how their distinctive biotas and often fragile landscapes will respond to predicted climate change. These issues are illustrated from three of the worlds five mediterranean-type regions: the Western Cape Region of South Africa. South and Western Australia, and the Mediterranean Basin.

Holocene agriculture in the Guanzhong Basin in NW China indicated by pollen and charcoal evidence.

The emergence and rapid spread of agriculture from the early Holocene has made a great impact on the development of human societies and landscape change. Guanzhong Basin in the middle of Yellow River valley has a long continuous history of agriculture since the Neolithic. The pollen and charcoal records from Xindian in western Guanzhong Basin, together with the known distribution of archaeological sites, provide proxies to reconstruct the history of agricultural activity and landscape change. The concentration and percentage of Poaceae pollen increase from about 7700 yr BP ago and the concentration of charcoal shows the same trend. These records indicate that the ‘slash-and-burn’ cultivation for agriculture began around 7700 years ago. Between 7700 and 5500 yr BP, the evidence of cereal crops remained strong and charcoal concentration and archaeological sites increased greatly, which all indicate increased agricultural activity and the expansion of human populations. This was enhanced by the continuous development of new cultivation tools and techniques between 4700 and 3300 yr BP, especially in the Bronze Age of the pre-Zhou Dynasty. The original agricultural landscape had been settled after 3300 yr BP. Buckwheat became an important crop from around 5500 yr BP, perhaps because of increasing aridity. This is the earliest record of cultivated buckwheat in Neolithic China.

Environmental and cultural changes during the terminal Neolithic : Qingpu, Yangtze delta, eastern China

The lower Yangtze, eastern China, was colonized by several Neolithic and Bronze Age cultures giving rise to possibly the highest concentration of prehistoric sites in the world. Early Neolithic cultures in the delta region cultivated rice (Oryza sativa) and agricultural developments appear to have occurred throughout the Neolithic with abrupt socio-economic changes possibly associated with the terminal Neolithic. Given the extensive history of environmental exploitation and well-preserved archaeological sites, the Yangtze delta is an ideal setting to explore the complex interactions between humans and their environment. Multiproxies of environmental changes, namely pollen, charcoal and phytoliths, in a 14C AMS-dated sequence of sediments from an exposed profile at Qingpu, Yangtze delta, were investigated. 14C AMS dating indicates that the age range of the sedimentary sequence analysed is from c. 1800 to 6000 BP, and therefore encompasses the terminal Neolithic and subsequent Bronze Age in the region. This paper reviews this sediment-based evidence in the light of current understanding of human—environment interactions during a critical phase of the development of the Yangtze delta and associated human cultures.