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Dryland regions are particularly challenging for human survival over the course of deep time. This is true for institutionally complex communities as well as small-scale societies that have existed in semi-arid regions throughout the Holocene. This paper examines some of the successful strategies employed by small-scale mobile communities which enhanced their ability to thrive in drylands over the course of thousands of years. Small-scale societies living in drylands must rely on the transmission of Traditional Ecological Knowledge across generations. Some of this knowledge relates to the availability and use of wetlands and other more ephemeral water sources, the exploitation of a diverse range of resources, and the potential for natural storage of food resources as a buffer against regularly occurring drought years in these regions. We compare this understanding with our environmental archeological findings at the Mid-Holocene site of Zaraa Uul in the eastern Gobi Desert of Mongolia. At the site of Zaraa Uul, we show how hunter-gatherer groups returned to a campsite near the edge of a wetland environment over the course of at least two phases during the Mid-Holocene. Here they took advantage of a greater diversity of animal species and plants, including small-grained-grasses and sedges, which could enhance their caloric intake and increase the potential for storable commodities which could be collected as needed from their natural habitat. [ABSTRACT FROM AUTHOR]

The prediction of the impact of anthropogenic land use change on the climate system hinges on the ability to properly model the interaction between the heterogeneous land surface and the atmosphere in global climate models. This paper contains a review of techniques in general use for modeling this interaction in general circulation models (GCMs) that have been used to assess the impact of land use change on climate. The review includes a summary of GCM simulations of land cover change using these techniques, along with a description of the simulated physical mechanisms by which land cover change affects the climate. The vertical extent to which surface heterogeneities retain their individual character is an important consideration for the land-atmosphere coupling, and the description of a recently developed technique that improves this aspect of the coupling is presented. The differences in the simulated climate between this new technique and a technique in general use include the presence of a boundary layer feedback mechanism that is not present in simulations with the standard technique. We postulate that the new technique when implemented in a GCM has the potential to guide an improved understanding of the mechanisms by which anthropogenic land use change affects climate. [ABSTRACT FROM AUTHOR]

The origins of the word ‘desertification’, most commonly attributed to Aubréville's 1949 work on tropical African forests, may be traced back much earlier, to nineteenth-century French colonial North Africa. The concept of desertification was central to French colonial thinking about the North African environment. This paper argues that an environmental history of the Maghreb was constructed during the French colonial period which blamed local North Africans, especially pastoralists, for the deforestation and desertification of what was erroneously believed to have been a fertile, forested landscape in antiquity. This environmental narrative of destruction and decline was first fabricated during the early years of the French occupation of Algeria, and was invoked in Tunisia and Morocco as they were occupied. Founded on historical inaccuracies and environmental misunderstandings, this narrative helped to justify land expropriation, changes in land tenure, forest appropriation and the criminalization of traditional land use, all of which facilitated the colonial venture in the three Maghreb countries. [ABSTRACT FROM AUTHOR]

Wind erosion is one of the most important processes associated with land degradation and desertification in the arid, semi-arid and portions of the subhumid regions of China. The total land area experiencing wind erosion is approximately 160.74 x 104 km2, which is 16.7% of the national territory. Wind erosion is recognized as a great threat to land utilization and sustainable social and economic development. Documentation of wind erosion and its negative impacts in China dates back over 2000 years. Since the 1950s Chinese scientists have carried out an integrated investigation of the principal lands susceptible to wind erosion, and have undertaken many laboratory tests and field observations with respect to the stabilization and utilization of soil in desert areas. Since the late 1970s there has been an increasing concern worldwide regarding land desertification caused by climatic changes and human activities. Hence, wind erosion, one of the main processes of desertification, has attracted the attention of Chinese scientists to an even greater extent. Studies have been conducted to investigate the mechanics, causes and control techniques related to wind erosion using wind tunnel simulation tests and field observations in typical areas. Some encouraging achievements have been made. In this paper we summarize the main research results on wind erosion that have come to light in China in recent decades, and put forward some perspectives and suggestions to deal with problems in both research into and control practices of wind erosion in China. [ABSTRACT FROM AUTHOR]

This paper examines the mid- to late-Holocene (c. 6850-1160 cal. yr BP) environmental history of Sierra de Gádor in southern Spain. The local vegetation dynamics are reconstructed through the palaeoecological record obtained from a lacustrine deposit situated at 1530 m. Various hypotheses are considered to explain the vegetation dynamics apparent in the palaeoecological evidence, including climatic change, fire occurrence and human activity. Although the vegetation in this region is sensitive to climatic change, threshold events driven by ecological factors are also apparent. Climatic events include a thermo-mesophytic optimum with abundance of deciduous trees and maximum lake water level found from c. 6850 to 5500 cal. yr BP. In contrast, changes in the frequency of major fire episodes appear to have shaped interspecific relationships and vegetation change, especially from c. 4200 cal. yr BP onwards. Biotic properties of the ecosystem such as the inertia of established tree populations, interconnected with competition adjustments, appear also to have played a role. Over the last two millennia, overgrazing, combined with natural and/or human-set fires, appears to have pushed mountain forests over a threshold leading to the spread of grassland, thorny scrub, junipers and nitrophilous communities. [ABSTRACT FROM AUTHOR]

Mediterranean ecosystems contain some of the highest levels of plant diversity of any region on Earth and are amongst those believed to be most at risk from the consequences of global warming. Yet such ecosystems are not static and have responded to environmental changes at a variety of scales and from a variety of causes, particularly climatic and anthropogenic. The purpose of this paper is to review recent research on environmental change and ecosystem response. Long-term records are available to analyse changes over glacial-interglacial cycles, while high resolution records show the sensitivity and coupling of Mediterranean, North Atlantic and Greenland records. For the Holocene, there is continued debate about the relative impact of anthropogenic activity, but there is also increasing recognition that mediterraneantype ecosystems should not be regarded as fragile, degraded landscapes, but are disturbanceadapted. Nevertheless, conservation measures face increasing challenges from contemporary climate change and human pressures. Some insights into the identification of refugial areas, either in glacial times or for present-day conservation purposes, come from molecular biogeographical studies of past faunal and floral distribution. [ABSTRACT FROM AUTHOR]

This paper examines the rainfall conditions which have prevailed over Africa during the last two decades. Throughout this period rainfall has been abnormally low over most of the continent. These conditions are compared and contrasted with those which previously prevailed during historical and geologic times. A trend towards increasing aridity since about 1970 has been neither continuous nor apparent in all regions but is evident as an increase in the area affected by subnormal rainfall and in the size of the deficit in the semi-arid regions. These conditions contrast markedly with the 1950s and are unlike any which occurred earlier in the century, and may signal a major change in prevailing global- scale climate. The continental patterns of reduced rainfall are analogous to historical fluctuations, most notably those of the early nineteenth century, and are of relevance to understanding the causal mechanisms of climate change in the late Pleistocene. The patterns are supportive of an underlying climatic cause for recent desertification in Africa. [ABSTRACT FROM PUBLISHER]

The article examines and compares several explanations regarding mountain uplift and desertification in western North America. It is explained that most instances of mountain building in this area fall under either the Laramide uplift or the Neogene uplift. The author indicates his view that the uplift of the American Cordillera and the subsequent formation of deserts cannot be explained by any single event.

Pollen analysis is frequently used to build climate and environmental histories. A distinct Holocene pollen series exists for Chaco Canyon, New Mexico. This study reports linear modeling and hypothesis testing of long distance dispersal pollen from radiocarbon-dated packrat middens which reveal strong relationships between piñon pine (Pinus edulis) and ponderosa pine (Pinus ponderosa). Ponderosa pollen dominates midden pollen assemblages during the early Holocene, while a rapid shift to a much higher proportion of piñon to ponderosa pine pollen between c. 5440 and 5102 cal. yr BP points to an aridization episode. This shift is associated with higher δ18O values in Southwest speleothem records relative to the preceding millennium. The period of aridization is followed by a sharp increase in El Niño/Southern Oscillation events that would have caused highly variable precipitation and lasted until c. 4200 cal. yr BP. Bayesian change-point analysis suggests that this aridization episode led to stable ecotonal boundaries for at least 3000 years. The piñon/ponderosa transition may have been caused by punctuated multiyear droughts, analogous to those in the 20th century. The earliest documented instance of Zea mays cultivation on the Colorado Plateau is around c. 3940 14C yr BP (c. 4364 cal. yr BP) (Hall SA (2010) Early maize pollen from Chaco Canyon, New Mexico, USA. Palynology 34(1): 125–137) in Chaco Canyon. The introduction of this labor-intensive cultigen from Mesoamerica may have been facilitated by changes in the regional ecosystems, specifically by an increase in piñon trees, that promoted increasing human territoriality. Linear modeling and hypothesis testing can complement traditional palynological techniques by adding greater resolution in vegetation patterning to climate/environmental histories. [ABSTRACT FROM AUTHOR]

According to the influential 'environmental security' literature, supply-induced scarcity in the form of environmental degradation is a key driver of civil violence around the world. African drylands, especially the Sahel region, are allegedly among the areas most seriously affected by this development. Views of desertification and severe environmental degradation in the Sahel are held by environmental security scholars, despite the comprehensive literature questioning such ideas that has been published since the late 1980s. Instead of being steadily transformed towards more desert-like conditions through increasing population pressure, Sahelian environments are dominated by climatic fluctuations. This article first reviews the literature criticizing the idea of 'desertification' as it is applied on African drylands. Then, the article critically discusses the use of the Tuareg rebellion in northern Mali as an example of a supply-induced scarcity related conflict. The case study shows that the droughts of the 1970s and 1980s played a role in the rebellion, but the rebellion was not driven by supply-induced scarcity. Instead, the droughts led to the migration of young men to Algeria and Libya, where they were exposed to revolutionary discourses. There was already a strong feeling among nomads and Tuareg in Mali of being marginalized by state policies of modernization and sedentarization. Embezzlement of drought relief funds by government officials in Bamako added further to the anger felt by the young men who took up arms against the Malian state. The drought of the 1970s and 1980s was probably not a necessary condition for the rebellion to take place. Detailed case studies of armed conflicts, engaging with environmental research, may be necessary to further deepen our understanding of links, or lack of such links, between violence and environmental stress. [ABSTRACT FROM AUTHOR]

What was the environmental setting for changes in the settlement pattern of Adaïma, a mid-fourth to early-third millennium site in the Egyptian Nile valley? Analysis of charcoal collected from the archaeological soil was performed on contexts from several periods. The settlement was set up in an environment where the vegetation was probably more extended, with more wooded desert margins. Over 600 years, changes in the charcoal spectrum reflect a possible local desertification and the impact of human activities on the vegetation of the floodplain, perceptible in particular through the development of ruderal Calotropis procera. [ABSTRACT FROM AUTHOR]

Three sedimentary sequences from the southeastern littoral of the Iberian Peninsula have been palynologically studied. The results obtained show that during the Holocene no significant forest cover existed in the studied area, so that the different phases identified mainly show an alternation of shrub formations and steppe communities probably determined by limitations that are fundamentally bioclimatic. Highest values of arboreal pollen at the bottom of the San Rafael sequence would correspond to an older period, when the area appears to be dominated by shrub communities with a high proportion of wild olive, whereas at the beginnings of the Holocene it is dominated by steppe formations. Between 7000 and 4500 yr BP the Holocene optimum is recorded, with a significant degree of vegetational cover. This period ends abruptly with a radical transformation of the landscape that reflects the establishment of the steppe conditions that persist today, which lead to the marginalization of the maquis and the impact of intense erosion processes on a gradually deforested countryside. [ABSTRACT FROM AUTHOR]

Evidence of climatic variations and the impact of past farming was identified in a Holocene loess profile near Xi’an in the Guanzhong Basin, China. Detailed studies of the profile indicate that crop cultivation began at 7000 yr BP in the Neolithic and carried on to present in the area. Disturbance of the profile by cultivation has not masked evidence of changes in aeolian dust deposition and bio-pedogenic processes caused by climatic variations. Increased dust deposition indicates that a remarkable aridity phase occurred from 6000 to 5000 yr BP during the Holocene Megathermal (8500–3000 yr BP). The aridity and intensified aeolian dust deposition interrupted the formation of the brown soil developing under a warm-humid subtropical climate during the Megathermal. The palaeosol S0 , normally associated with the Megathermal period, is thus separated into two distinct soils, namely S0 1 and S0 2 . This variability in Megathermal climate may have been widespread across northwestern China. It is also possible that the marked decline in Neolithic culture in the periods of the middle and late Yangshao Culture (6000–5000 yr BP) in the Guanzhong Basin can be attributed to the climatic aridity at the time. [ABSTRACT FROM AUTHOR]

The study of desertification in China began in 1977 with the UN Conference on Desertification. Since then, much progress has been made. This article reviews progress over the last five years in China. A brief description of desertification research in China is given, and developments and changes in the definition of desertification described. Finally, the causes and patterns of desertification are discussed. [ABSTRACT FROM AUTHOR]

Transformations in terrestrial ecosystems are increasingly regarded as an important element of global change. Quantitative data on where, when and why land-cover changes take place globally are still incomplete. This article reviews recent approaches to the monitoring and modelling of deforestation and dryland degradation in tropical regions. The review highlights the requirement to tailor the investigation method to the specific research question of interest. Different techniques to monitor land-cover changes at regional scales are analysed. The following modelling scenarios are discussed and illustrated by specific studies: projection of future land- cover changes with descriptive models, explanation of land-cover changes with empirical models, projection of future spatial patterns of changes with spatial statistical models, test of scenarios on future changes in land-cover with dynamic ecosystem models, and design of policy interventions with economic models. The article stresses the needs for a better integration of social science knowledge in land-cover change models and for a comprehensive theory of land-use changes. [ABSTRACT FROM PUBLISHER]