Abstract: Interannual trends in annual and seasonal vegetation activities from 1982 to 1990 on a global scale were analysed using the Pathfinder AVHRR Land NDVI data set corrected by utilising desert and high NDVI areas. Climate effects on interannual variations in NDVI were also investigated using temperature and precipitation data compiled from stational observations. In the northern middlehigh latitudes, vegetation activities increased over broad regions because of a gradual rise in temperature. NDVI increases were also detected in the tropical regions, such as western Africa and south-eastern Asia. Plant photosynthetic activities on the other hand, decreased remarkably in some arid and semi-arid areas in the Southern Hemisphere, because annual rainfall decreased during this period.

Abstract: Most arid ecosystems have suffered from severe overexploitation by excessive wood harvesting, overgrazing, and agriculture, resulting in depletion of vegetation biomass and soil erosion. These changes are often difficult to reverse due to positive feedbacks that tend to stabilize the new situation. In this paper, we briefly review evidence for the idea that different states in these ecosystems might represent alternative equilibria and present a graphic model that summarizes the implications for their response to changing environmental conditions. We show how, in the light of this theoretical framework, climatic oscillations such as El Nino Southern Oscillation (ENSO) could be used in combination with grazer control to restore degraded arid ecosystems. We also present evidence that, depending on grazing pressure, ENSO episodes can trigger structural and long-lasting changes in these ecosystems.

Abstract: Although regional climates throughout much of the world appear to have become more arid in late Cenozoic time, sedimentation rates, and therefore presumably erosion rates, have increased. For sustained erosion of elevated terrain, at least where glaciers are not the major erosive agent, rivers must incise. Therefore bed-load transport by rivers should be a rate-limiting process in erosion. Theories of bed-load transport call for a threshold in either stream power per unit area or shear stress before the bed load can be moved, and most transport should be accomplished during high discharge. The frequency- magnitude distribution of floods shows that the ratio of magnitudes of, for example, 100 yr floods and annual floods is greater in arid than in humid environments. Thus, a shift toward more arid conditions may have increased relative magnitudes of rare floods or, conversely, increased the frequency of large floods. Such a shift, despite a decrease in precipitation and discharge, could have doubled incision rates, particularly in regions already quite arid.

Abstract: Banded vegetation patterns and related structures * Theories on the origins, maintenance, dynamics and functioning of banded landscapes * Specific methods of study * Runoff and Erosion Processes * Soil Water balance * Soil Biota in Banded Landscapes * Vegetation dynamics: recruitment and regeneration in two-phase mosaics * Multiscale Modelling of Vegetation Bands * Landscape Models for Banded Vegetation Genesis * Productivity of patterned vegetation * Towards Improved Management of Arid and Semi-Arid Banded Landscapes * Banded landscapes: Ecological Developments and Management Consequences

Abstract: Dust emission and wind erosion from arid and semiarid environments provide a major source of global atmospheric aerosols. Well-known relations between wind stress and saltation sand flux for sand sheets and relations between sand flux and dust emission by sandblasting have enabled construction of dust models that have only been partly successful in predicting atmospheric mineral dust concentrations. Most models of wind erosion assume that vegetation is evenly distributed. Through the use of field, Fourier transform, and semivariogram analysis, we show that mesquite dunelands in the Chihuahuan Desert of southern New Mexico, United States, have anisotropic shrub distributions. Elongated areas of bare soil, “streets,” which are aligned with the prevailing winds may partially explain discrepancies between observed and predicted atmospheric dust concentrations. Soils in the streets are not protected from winds blowing down the streets and may therefore produce more dust than if vegetation were more evenly distributed. Currently, few desert landscape evolution models take the role of wind explicitly into account. The existence of streets implies that wind plays a major role in the evolution of vegetated arid and semiarid landscapes with wind-erodible soils. Here wind acts in tandem with water to enforce islands of fertility centered around individual shrubs and may provide an explanation for reduced soil fertility observed in shrublands. Furthermore, in order for mathematical models of dust flux to be successful in these landscapes, new landscape models are required which incorporate the existence and orientation of streets.

Abstract: Chapters 22–24 of this Volume review the relationships between biological soil crusts and soil hydrology in the deserts of Israel, Australia, and North America, respectively. It is readily apparent that there are contradictions regarding the effects of biological soil crusts on arid land hydrology and soil stability. A logical approach to understanding some of the commonalities and disparities is to seek an understanding of how the crusts affect the processes of infiltration, runoff and erosion. Infiltration and runoff are closely related and inversely proportional, i. e., as more water infiltrates into the soil, less is available for surface runoff. This chapter discusses the effects of biological soil crusts on parameters known to control the partitioning of surface water between infiltration and runoff, as well as parameters related to soil erosion. These include soil physical and chemical properties, surface cover and roughness, below-ground biomass, soil hydrophobicity, and antecedent soil moisture content.

Abstract: Deserts, Land Use and Desertification.- River Diversion, Irrigation, Salinization, Desertification - an Inevitable Succession.- I: The Aral Sea Crisis.- The Aral Sea Crisis Region.- Flora of the Dry Seafloor of the Aral Sea.- Vegetation Dynamics on the Dry Seafloor of the Aral Sea.- Methods of Conservation and Restoration of Vegetation Cover on the Aral Sea Coast.- Vegetation Dynamics on the Syrdarya Delta and Modern Land Use.- Ecological Basis for Botanical Diversity Conservation within the Amudarya and Syrdarya River Deltas.- The Tugai Forests of Floodplain of the Amudarya River: Ecology, Dynamics and Their Conservation.- Soil Crusts in the Amudarya River Delta: Properties and Formation.- Irrigation and Land Degradation in the Aral Sea Basin.- Ecology of the Aqueous Medium in the Area Surrounding the Aral Sea.- Potable Water: Research into Seasonal Changes and Conditions in the Aral Sea Region.- II: Salt Stress.- Halophytes on the Dry Sea Floor of the Aral Sea.- Halophytes: Structure and Adaptation.- Environmental State and an Analysis of Phytogenetic Resources of Halophytic Plants for Rehabilitation and Livestock Feeding in Arid and Sandy Deserts of Uzbekistan.- Salinity: A Major Enemy of Sustainable Agriculture.- III: Impact of Grazing.- Remarkable Differences in Desertification Processes in the Northern and Southern Richtersveld (Northern Namaqualand, Republic of South Africa).- Colour Plates.- How Grazing Turns Rare Seedling Recruitment Events to Non-Events in Arid Environments.- Vegetation Degradation in Northeastern Jordan.- Impact of Grazing on the Vegetation of South Sinai, Egypt.- Arid Rangeland Management Supported by Dynamic Spatially Explicit Simulation Models.- IV: Desertification Processes and Monitoring.- Remote Sensing of Surface Properties. The Key to Land Degradation and Desertification Assessments.- Evaluation of Potential Land Use Sites in Dry Areas of Burkina Faso with the Help of Remote Sensing.- Degradation of the Vegetation in the Central Kyzylkum Desert (Uzbekistan).- Modern Geomorphological Processes on the Kazakhstanian Coast of the Caspian Sea and Problems of Desertification.- Anthropogenic Transformation of Desert Ecosystems in Mongolia.- Assessment of the Modern State of Sand-Desert Vegetation in Kazakhstan.- V: Reclamation.- Water-Harvesting Efficiency in Arid and Semiarid Areas.- The Effects of Landscape Structure on Primary Productivity in Source-Sink Systems.- Sedimentary Environments in the Desiccated Aral Sea Floor: Vegetation Recovery and Prospects for Reclamation.- Seeding Experiments on the Dry Aral Sea Floor for Phytomelioration.- Rehabilitation of Areas of Irrigation Now Derelicted Because of Strong Salinization in Ecologically Critical Zones of Priaralia.- Desert Soil Recultivation and Monitoring of (Phyto-) Toxicity: Pilot Project in Three Phases Lasting for 4 Years.- Contributions to a Sustainable Management of the Indigenous Vegetation in the Foreland of Cele Oasis - A Project Report from the Taklamakan Desert.- The Control of Drift Sand on the Southern Fringe of the Taklamakan Desert - an Example from the Cele-Oasis.- The Role of Biological Soil Crusts on Desert Sand Dunes in the Northwestern Negev, Israel.- Restoration of Disturbed Areas in the Mediterranean - a Case Study in a Limestone Quarry.- Indigenous Agroforestry for Sustainable Development of the Area around Lake Nasser, Egypt.- Ziziphus - a Multipurpose Fruit Tree for Arid Regions.- Root Morphology of Wheat Genotypes Grown in Residual Moisture.- Field Studies in Solar Photocatalysis for Detoxification of Organic Chemicals in Waters and Effluents.- VI: National Programs.- Activity of the Consulting Centre to Combat Desertification in Turkmenistan.- Desertification in China and Its Control.- Environmental Problems of the Southern Region of Kazakhstan.- National Strategy and Action Plan to Combat Desertification in Kazakstan.- VII: Social and Economic Aspects.- Economic-Demographic Strategies and Desertification: Interactions in Low-Income Countries.- Final Remarks.

Abstract: Banded vegetation patterns and related structures * Theories on the origins, maintenance, dynamics and functioning of banded landscapes * Specific methods of study * Runoff and Erosion Processes * Soil Water balance * Soil Biota in Banded Landscapes * Vegetation dynamics: recruitment and regeneration in two-phase mosaics * Multiscale Modelling of Vegetation Bands * Landscape Models for Banded Vegetation Genesis * Productivity of patterned vegetation * Towards Improved Management of Arid and Semi-Arid Banded Landscapes * Banded landscapes: Ecological Developments and Management Consequences

Abstract: Conditions in arid and semi-arid climates favor the formation of the most problematic collapsible soils. The mechanisms that account for almost all naturally occurring collapsible soil deposits are debris flows, rapid alluvial depositions, and wind-blown deposits (loess). Collapsible soils are moisture sensitive in that increase in moisture content is the primary triggering mechanism for the volume reduction of these soils. One result of urbanization in arid regions is an increase in soil moisture content. Therefore, the impact of development-induced changes in surface and groundwater regimes on the engineering performance of moisture sensitive arid soils, including collapsible soils, becomes a critical issue for continued sustainable population expansion into arid regions.

Abstract: The primary objective of this study was to assess the condition of a portion of Saudi Arabia's rangelands and evaluate the effects of grazing by the animal herds of indigenous nomads over the last decade Because of the desertic condition of these rangelands, changes in vegetation cover are more subtle than would be the case for other, less arid areas Consequently, a new analytic methodology for the detection of desertification of arid and hyper-arid rangelands was developed specifically for this project The conceptual framework for the analysis is the use of the coefficient of variation (COV) of the monthly Normalized Difference Vegetation Index (NDVI, maximum-value composite) as a measure of vegetative biomass change A higher NDVI COV for a given pixel (excluding cases of changes in land use) represents a greater change in vegetation biomass in the ground area represented by that pixel Linear regression was used to determine the trend in COV values for each pixel over the 12-year period for which da

Abstract: One of the more urgent global problems, particularly in arid and semi-arid regions of the world, is finding enough water and land to support the world’s growing food needs. By some estimates, an additional 500 million acres of new croplands are required over the next thirty years to feed burgeoning populations of the tropics and subtropics. Yet only 230 million acres are available in these areas for farming to expand. And, much of this land is forested and should realistically be preserved to maintain the integrity of remaining natural stands and ecosystem functioning. Furthermore, saline soils are a major problem of cultivated lands in semi-arid and arid areas. About 23% of the world’s 1.5 × 10 9 ha of cultivated land is saline and 37% is sodic. Approximately one third of the world’s irrigated land is salt-affected due chiefly to unsustainable irrigation practices. Freshwater resources are also being rapidly depleted and current agricultural irrigation practices are steadily increasing salinity levels in many regions. Rapid increases in population pressure are leading to greater utilization of remaining meager freshwater supplies for drinking, leaving even less for agriculture. In this complex scenario, it has become imperative to consider development of non-conventional agricultural technologies which might more effectively utilize degraded, marginal and saline lands for agriculture by using, the ‘so-called’, poor quality water (brackish water, seawater, and wastewater). An attractive option is the use of seawater or brackish water agriculture, and this has worked well in both inland and coastal sandy soils of some desert environments. Saline water aquifers exist in many arid lands of the world but these have been greatly under-utilized. This brackish water could be a major resource in saline agriculture to produce food, feed, and fiber and oil seeds on currently non-productive, saline arid lands. In further support of saline agriculture, there would be no shortage of water since seawater in the oceans makes up 97% of water on earth. Desert land is also plentiful, with around 43% of the earth’s total land surface being arid or semi-arid. A small portion of this (about 15%) is close to the sea and this would be convenient for growing crops using saline agriculture. This amounts to 130 million hectares of ‘new’ land that could arguably be brought into human or animal food production – without cutting down more forests or diverting scarce fresh water resources from current agricultural and community needs. Salt tolerant plants (halophytes, including salt marsh and mangrove plants) are highly evolved and specialised organisms with well-adapted morphological and physiological characteristics allowing them to proliferate in the soils possessing high salt concentrations. It is tempting to think we might exploit these plants for the better utilization of saline water, and for the rehabilitation of highly saline soils. Saline agriculture, however, must fulfill two conditions to be cost-effective. First, it must produce useful crops at yields high enough to justify the expense of pumping salty water. Second, researchers must develop successful agronomic techniques for growing saline, water-irrigated crops in a sustainable manner. These methods must also not contribute to further damage of natural environments. If applied successfully, this approach would lead to the domestication of wild, salttolerant plants for use as food, forage, and oilseed crops.

Abstract: Biological soil crusts most often occur under harsh conditions that include extremes in temperature and light and at least periodic lack of water. They occur in almost all arid and semiarid ecoregions worldwide, and in local arid micro environments in other climates (e.g., temperate regions). Despite their widespread occurrence, comparing the biogeography and ecology of soil- crust biota and communities on a global basis is almost impossible. This is because most of the data were collected (1) using different methodologies, (2) using different taxonomic systems [e.g., using Drouet’s (1956) keys, where he combined genera], and/or (3) were focused on a single group of organisms (i.e., lichens, algae, cyanobacteria, or mosses) to the exclusion of other groups.

Abstract: In Australia, where approximately 80% of the land area is arid or semiarid, rainfall is the major factor limiting acridid populations. Rainfall is not only limiting in terms of quantity but also in being highly variable, both temporally and spatially. In this paper, the main adaptations seen in Australian Acrididae to overcome limiting rainfall are discussed with special reference to economically important species. In the arid to semiarid subtropics (lat 23–33°S) rainfall is slightly summer-dominant but extended dry periods can occur in any season. Chortoicetes terminifera, the main pest species, avoids dry periods through embryonic diapause or survives dry periods as quiescent eggs or adults. Migration is critical for survival as it allows locusts to locate areas of localized rainfall. Outbreaks are frequent and develop when enough rain falls to allow continuous breeding over three to four generations. In temperate areas of subcoastal southern Australia, summers are dry and most rain falls in wi...

Abstract: Banded landscapes are characterized by bands of dense perennial vegetation oriented parallel to the contour, separated by bare soil (Figures 11, 110, 112, this volume) They are widely distributed globally and have been studied in arid and semiarid climates of Sahelian Africa and the Middle East (White 1971; Wickens and Collier 1971), South Africa (van der Meulen and Morris 1979), Australia (Mabbutt and Fanning 1987; Tongway and Ludwig 1990), and North America (Cornet et al 1992) (1971) defined the common characteristics apparently necessary for the existence of a banded vegetation spatial structure These characteristics are now well known and include a semiarid climate and rainfall runoff as sheet-flow on gently inclined surfaces (chapter 1, this volume) Commonly, the band and interband zones have a similar soil type and texture but not always For example, some banded landscapes are located on soils with swell/shrink gilgai patterns and dynamics (Dunkerley and Brown 1995; Macdonald, Melville, and White 1999) The most common vegetation association in the bands is a mixture of grass and shrubs and/or trees (Slatyer 1961; Montana, Lopez-Portillo, and Mauchamp 1990; Seghieri et al 1997) but can be dominated by grass (Worral 1959), trees alone (Worral 1960), or chenopod shrubs (Macdonald, Melville, and White 1999)

Abstract: Publisher Summary This chapter discusses human dimensions of late Pleistocene/Holocene arid events in southern South America, where, examples from late glacial, and early and mid-Holocene archaeological sites in southern South America provide information about the human dimensions of past climate changes Particularly in semiarid areas with marginal food, and water resources, changes from humid to arid conditions coincided with major changes in human occupational, and cultural patterns The end of the first period of human occupation in central Chile coincided with rapidly increasing aridity, when trees were replaced by shrubs and herbs, the Pleistocene paleolakes disappeared, and the Pleistocene megafauna became extinct The Paleo-Indian hunters occupied ecological refuges around lakes, where the resources were concentrated in an environment under general water stress A similar process was observed 2000 years later in the Atacama Desert, and Altiplano of northern Chile, when the first period of human occupation came to an abrupt end, synchronously with the rapid desiccation of early Holocene paleolakes, and the disappearance of abundant water, vegetation, and animal resources The subsequent extremely arid mid-Holocene environments resulted in a general hiatus of human occupation in the Atacama basin, whereas widespread resettlement coincided again with a rise of the paleolake levels to the modern levels

Abstract: SUMMARY Currently, only 6% of the 15% of land in Afghanistan is usable and, if all the refugees were to return, problems of land ownership and adequacy of available land are inevitable. Natural forests have been severely degraded. Due to the nature of the topography and the arid climate, vast areas are subject to soil erosion. Loss of vegetation and soil humus have created ever more arid conditions. Abandoning the lands, poor reclamation schemes, overgrazing and destruction of vegetation for fuelwood have all caused desertifkation. The biological productivity of pastures has also deteriorated. This reduced productivity has affected livestock and has caused dramatic changes to the patterns of wildlife populations. Soil salinization and waterlogged lands are common. Farmland and pastures have been contaminated by landmines. Heavy concentrations of air-borne particulates and considerable amounts of transboundary pollutants from the Aral Sea have been found. Use of chemicals and the machinery of war have dama...

Abstract: Sediment coresfromLaike Zeribar intheZagrosMounitains ofwestemIranprovide arecord of changes inthediatomii flora since about40ka.ConduLctivity transfer functionis applied todiatom records fromii thelake indicate generally highei conduLctiVitv durin gtheLastGlacial Maxtmunm andLateglacial, especially between 15.0and10.5ka.Thts observation isconsistent withprevious interpretations ofrelatively arid con- ditions during this interval basedontheLakeZeribar pollen records. Oscillations between high- anid low- conducttvtty states during this interval additionally suLggest changes inprecipitation associated withmillennial- scale climiiate events, withrelatively dryconditions during theYounger Dryas. Diatom-inferred conductivity A isrelatively lowthroughout theHolocene. Shifts indiatomn composition occurin theHolocene record; however. minorvariations inreconstrtucted conduLctiVity arenotconsidered significant. SPECIAL ISSUE

Abstract: In an arid environment, the effect of evaporation on energy balance can affect air temperature recordings and greatly impact on degree-day calculations. This is an important consideration when choosing a site or climate data for phenological models. To our knowledge, there is no literature showing the effect of the underlying surface and its fetch around a weather station on degree-day accumulations. In this paper, we present data to show that this is a serious consideration, and it can lead to dubious models. Microscale measurements of temperature and energy balance are presented to explain why the differences occur. For example, the effect of fetch of irrigated grass and wetting of bare soil around a weather station on diurnal temperature are reported. A 43-day experiment showed that temperature measured on the upwind edge of an irrigated grass area averaged 4% higher than temperatures recorded 200 m inside the grass field. When the single-triangle method was used with a 10°C threshold and starting on May 19, the station on the upwind edge recorded 900 degree-days on June 28, whereas the interior station recorded 900 degree-days on July 1. Clearly, a difference in fetch can lead to big errors for large degree-day accumulations. Immediately after wetting, the temperature over a wet soil surface was similar to that measured over grass. However, the temperature over the soil increased more than that over the grass as the soil surface dried. Therefore, the observed difference between temperatures measured over bare soil and those over grass increases with longer periods between wettings. In most arid locations, measuring temperature over irrigated grass gives a lower mean annual temperature, resulting in lower annual cumulative degree-day values. This was verified by comparing measurements over grass with those over bare soil at several weather stations in a range of climates. To eliminate the effect of rainfall frequency, using temperature data collected only over irrigated grass, is recommended for long-term assessment of climate change effects on degree-day accumulation. In high evaporative conditions, a fetch of at least 100 m of grass is recommended. Our results clearly indicate that weather stations sited over bare soil have consistently higher degree-day accumulations. Therefore, especially in arid environments, phenology models based on temperature collected over bare soil are not transferable to those based on temperature recorded over irrigated grass. At a minimum, all degree-day-based phenology models reported in the literature should clearly describe the weather station site.

Abstract: Sodium monofluoroacetate (1080) is a commonly used vertebrate pesticide throughout Australia and New Zealand. However, little is known about the persistence of 1080 in arid environments, or whether soil microorganisms capable of defluorinating 1080 are present in soils from arid Australia. Soil samples (3 replicates) from central Australia were collected on seven occasions over an 8-month period, and the microorganisms capable of defluorinating 1080 were isolated. When grown in an inorganic medium containing 20 mM 1080 as the sole C source, 24 species were able to defluorinate 1080: 13 bacteria and 11 fungi. The abundance of these microorganisms appeared to be influenced by climatic conditions with the relative abundance of many species increasing after rain. The fungus Fusarium oxysporum had by far the greatest defluorinating ability, and defluorinated approximately 45% of added 1080 within 12 d. Defluorination of 1080 added to soil was significantly greater at pH 5.6 compared to pH 6.8, suggesting that the fungal species were important defluorinators in these soils. In a 28-d time course trial, defluorination of added 1080 by soil microorganisms appeared to asymptote after 21–28 d. The presence of these microorganisms in soil from central Australia indicates that 1080 can be used safely even in arid environments. 1080 is unlikely to persist in these soils, or to contaminate ground water. The implications of these findings with respect to the environmental safety of 1080 in other regions where 1080 baits are used are also discussed.