Abstract: Scientists are still searching for possible unifying mechanisms to explain this range of spatial patterns (Tongway and Ludwig 2001), and an important question of this research is whether this range is the result of preexisting environmental heterogeneity, the result of spatial selforganization, or both (Klausmeier 1999; Couteron and Lejeune 2001; HilleRisLambers et al. 2001; Von Hardenberg et al. 2001). Here, we contribute to the ongoing debate about vegetation pattern formation in arid ecosystems by presenting novel, spatially explicit model analyses and results, extending on the work of HilleRisLambers et al. (2001). Our results show that these different vegetation patterns observed in arid ecosystems might all be the result of spatial self-organization, caused by one single mechanism: water infiltrates faster into vegetated ground than into bare soil, leading to net displacement of surface water to vegetated patches. This model differs from earlier model results (Klausmeier 1999; Couteron and Lejeune 2001; HilleRisLambers et al. 2001; Von Hardenberg et al. 2001) primarily in two ways: it is fully mechanistic, and it treats the lateral flow of water above and below the soil as separate, not independent, variables. Although the current model greatly simplifies the biophysics of arid systems, it can reproduce the whole range of distinctive vegetation patterns as observed in arid ecosystems, indicating that the proposed mechanism might be generally applicable. We further show that self-organized vegetation patterns can persist far into regions of high aridity, where plants would become extinct if homogeneously distributed, pointing to the importance of this mechanism for maintaining productivity of arid ecosystems (Noy-Meir 1973). Our analyses are based on the model first developed in HilleRisLambers et al. (2001)

Abstract: This publication provides planners, decision-makers and engineers with guidelines to sustain irrigated agriculture and at the same time to protect water resources from the negative impacts of agricultural drainage water disposal. On the basis of case studies from Central Asia, Egypt, India, Pakistan and the United States of America, it distinguishes four broad groups of drainage water management options: water conservation, drainage water re-use, drainage water disposal and drainage water treatment. The full texts of the case studies can be found on the attached CD-ROM.

Abstract: 1. Tectonics and Geology 2. Climatic Change and the Development of Landscapes 3. Climate at Present and in the Historical Past 4. Soils 5. Rivers, Lakes, Inland Seas, and Wetlands 6. Permafrost 7. Biodiversity and Productivity of Ecosystems 8. The Arctic Environments 9. Boreal Forests 10. Mixed and Deciduous Forests 11. Steppe and Forest-steppe 12. Arid Environments 13. The Mountains of Northern Russia 14. The Mountains of Southern Siberia 15. The Caucasus 16. The Mountains of Central Asia and Kazakhstan 17. Lake Baikal 18. The Far East 19. Radioactive Contamination 20. Environmental Impact of Oil and Gas Development 21. Air Pollution 22. The Aral Sea 23. Deforestation and Degradation of Forests 24. Nature Protection and Conservation List of Plant Names in Latin and English

Abstract: Widespread drought is among the most likely and devastating consequences of future global change. Assessment of drought impacts forecast by atmospheric models requires an understanding of natural drought variability, especially under conditions more arid than today. Using high-resolution lake-sediment records from the northern Great Plains, we show pronounced 100- to 130-yr drought cycles during the arid middle Holocene (8000 calendar yr BP). During drought phases, grass productivity declined, erosion and forbs increased, and fuel limitation reduced fire importance. Intervening humid decades saw grass production rise, with stabilization of soils and renewed fire as fuels became abundant. Although both C3 and C4 grasses declined during droughts, a lasting shift to C3 dominance occurred during a single drought -8200 calendar yr BP. During the more humid Late Holocene (2800 calendar yr BP), climate was less variable and without evident drought cyclicity. Consequently, drought severity during past, and possibly future, arid phases cannot be anticipated from the attenuated climate variability evident during contemporary humid phases. Our study demonstrates that agriculturally important grassland ecosystems respond sensitively to drought variability, uncertainty in which has profound implications for the future of these ecosystems.

Abstract: The overgrowing population and the recent droughts are putting water resources under pressure and calling for new approaches for water planning and management if escalating con#icts are to be avoided and environmental degradation is to be reversed. As countries are using their water resources with growing intensity, poor rainfall increasingly leads to national water crises as water tables fall and reservoirs, wetlands and rivers empty. Global warming could cause further changes, further variability and further uncertainty. The UK Hadley Centre's global climate model was run at a spatial scale of 2)5 by 3)753 (latitude and longitude) grid squares to simulate the global climate according to scenarios of greenhouse gas concentration emission. Runs of the model assuming the emission scenario proposed by the Intergovernmental Panel on Climate Change in 1995 are analysed here for the 2050s time horizon. Outputs provide estimations of climate variables, such as precipitation and temperature, at a monthly time step. Those results, assumed representative of future climatic conditions, are compared to mean monthly values representative of the current climate and expressed in terms of percentage change. The results show that, for the dry season (April}September), by the 2050s, North Africa and some parts of Egypt, Saudi Arabia, Iran, Syria, Jordan and Israel, are expected to have reduced rainfall amounts of 20}25% less than the present mean values. This decrease in rainfall is accompanied by a temperature rise in those areas of between 2 and 2)753C. For the same period, the temperature in the coastal areas of the Mediterranean countries will rise by about 1)53C. In wintertime, the rainfall will decrease by about 10}15% but would increase over the Sahara by about 25%. Given the low rainfall rate over the Sahara, the increase by 25% will not bring any signi"cant amount of rain to the region. In wintertime, the temperature in the coastal areas will also increase but by only 1)53C on average, while inside the region it will increase by 1)75}2)53C. In southern Africa (Angola, Namibia, Mozambique, Zimbabwe, Zambia, Botswana and South Africa), results suggest an increase of the annual average temperature ranging between 1)5 and 2)53C in the south to between 2)5 and 33C in the north. The summer range is between 1)75 and 2)253C in the south, and increases towards the north to between 2)75 and 3)03C while the winter range is between 1)25 and 23C in the south, and increases towards the north to between 2)5 and 2)753C. On the other hand, the annual average will decrease by 10}15% in the south and by 5}10% in the north. The annual average decrease is 10%. However, some places will have an increase i.e. by 5}20% in South Africa in wintertime. In the Taklimakan region (Tarim Basin) west of China, the annual average temperature is shown to increase by 1)75}2)53C. Annual average rainfall should increase by 5}'25% in most of the region but decrease by 5}10% in some small parts. In summer, an increase by 5}15% is indicated in most of the region, and an increase by up to 25% or more during the wintertime. In the Thar Desert (India}Pakistan}Afghanistan), estimations suggest that the annual average increase in temperature ranges from 1)75 to 2)53C, ranging from 1)5 to 2)253C in winter and from 2 to 2)53C in summer. Annual average precipitation is shown to decrease by 5}25% in the region. The winter will have values closer to the annual average but the summer will have more decrease and most of the region will see a decrease closer to 25%.

Abstract: Both ecosystem carbon gain and nutrient availability are largely constrained by the magnitude and seasonality of precipitation in arid and semi-arid ecosystems. We investigated the role of precipitation on ecosystem processes along an International Geosphere Biosphere Programme (IGBP) transect in temperate South America. The transect consists of a contiguous precipitation gradient in the southern region of Argentinean Patagonia (44–45° S), from 100 mm to 800 mm mean annual precipitation (MAP) and vegetation ranging from desert scrub to closed canopy forest. Gravimetric soil water content tracked changes in seasonal and annual precipitation, with a linear increase in soil water content with increasing MAP. Above-ground net primary production (ANPP) increased linearly along the gradient of precipitation (ANPP = − 31.2 + 0.52 MAP, r2 = 0.84, p = 0.028), supporting the relationship that carbon assimilation is largely controlled by available water in these sites, and was in general agreement with regi...

Abstract: The presence of shrubs in arid lands creates spatial heterogeneity that affects the distribution and performance of annual plants; several possible mechanisms have been implicated. A preliminary survey in a chenopod shrubland in South Australia showed differences in the distribution of annual plants under canopies of Atriplex vesicaria and Maireana sedifolia (the two dominant shrub species) and open spaces. A series of experiments were conducted to test the potential contribution to these patterns of nutrient enrichment under shrubs, differential seed accumulation, stress reduction by the canopy, competition by shrub roots, and protection against grazing. The germinable soil seed-bank under A. vesicaria and M. sedifolia was different from that in open spaces, but these differences can only explain a fraction of the differences observed in the growing annual plant community in different microsites. The soil under A. vesicaria had higher total nitrogen content than soil in open spaces, whereas soil under M. sedifolia had lower available phosphorus than open spaces. Although annual plant densities under A. vesicaria were higher than in open spaces, experimental removal of shrubs increased their density, suggesting that shrub canopies inhibit annual plants in this system. Surprisingly, trenching of open areas close to shrubs (severing lateral shrub roots) decreased annual plant density. We suggest that water moves laterally through shrub roots, in a process akin to a hydraulic lift, increasing water availability for the annual plants. Exclusion of vertebrate grazers had a stronger effect on annual plant biomass in open spaces than under M. sedifolia, suggesting that this shrub provides shelter against herbivory. Overall our results show that shrubs can have simultaneously facilitative and inhibitory effects on the annual plant community through different mechanisms, but more importantly that different shrub species have different effects. This is a potential mechanism allowing for species coexistence of annual plants.

Abstract: In the arid southwestern United States, subtle differences in soil horizon development affect seasonal soil hydrology and consequently influence plant performance and community structure. We measured canopy development, population structure, and seasonal ecophysiology (predawn water potential, ψpd, and midday net photosynthetic assimilation, Anet) of two co-dominant warm-desert shrubs, the evergreen Larrea tridentata and drought-deciduous Ambrosia dumosa, in five Mojave Desert soils varying in surface and sub-surface soil development, and we used process-based soil hydrology modeling output to determine longer-term soil water dynamics underlying soil/plant responses. We hypothesized that ecophysiological performance would covary with plant development, which would reflect soil hydrological characteristics. Among three sites on alluvial fan deposits of different geological ages (Young Alluvial, <4000 yr BP; Intermediate Alluvial, ∼12 000 yr BP; Old Alluvial, ∼40 000 yr BP), total canopy volume of Larrea (c...

Abstract: This paper discusses several difficulties encountered in detecting and monitoring temporal changes in vegetation using multispectral imagery from airborne or spaceborne sensors. These difficulties are due to (1) temporal change in the vegetation state; (2) temporal change in the soil/rock signature; and (3) difficulty in discriminating vegetation from soil or rock background. The seasonal dynamics of soil and vegetation was investigated over two years on permanent sample plots in a natural fenced-off area in the semi-arid region (200 mm annual average rainfall) of the Northern Negev, Israel. Results show that temporal analysis of natural vegetation in semi-arid regions should take into account three ground features--perennials, annuals, and biological soil crusts; all having phenological cycles with the same basic elements--oscillation from null (or low) to full photosynthetic status. However, these cycles occur in successive periods throughout the year. The phenological cycle of perennial plants is relat...

Abstract: Dramatic changes in land use have occurred in arid and semi-arid lands of Asia during the 20th century. Grassland conversion into croplands and ecosystem degradation is widespread due to the high growth rate of human population and political reforms of pastoral systems. Rangeland degradation made many parts of this region vulnerable to environmental and political changes. The collapse of the livestock sector in some states of central Asia, expansion of livestock in China and intensive degradation of grasslands in China are examples of the responses of pastoral systems to these changes over the past decades. Carbon dynamics in this region is highly variable in space and time. Land use/cover changes with widespread reduction of forest and

Abstract: [1] Site-specific numerical modeling of four sites in two arid alluvial basins within the Nevada Test Site employs a conceptual model of deep arid system hydrodynamics that includes vapor transport, the role of xeric vegetation, and long-term surface boundary transients. Surface boundary sequences, spanning 110 kyr, that best reproduce measured chloride concentration and matric potential profiles from four deep (230–460 m) boreholes concur with independent paleohydrologic and paleoecological records from the region. Simulations constrain a pluvial period associated with infiltration of 2–5 mm yr−1 at 14–13 ka and denote a shift linked to the establishment of desert vegetation at 13–9.5 ka. Retrodicted moisture flux histories inferred from modeling results differ significantly from those determined using the conventional chloride mass balance approach that assumes only downward advection. The modeling approach developed here represents a significant advance in the use of deep vadose zone profile data from arid regions to recover detailed paleohydrologic and current hydrologic information.

Abstract: Establishing plants in deserts can be challenging even with supplemental irrigation. The low relative humidity, extreme temperatures, lack of consistent rainfall, tremendous rate of evaporation, and high wind speeds common in desert environments all play important and interrelated roles in water loss from desert soil and plants. These factors make it critical that restorationists use the most appropriate and cost-effective means to deliver water to the root zone of newly planted plants in order to maximize survival and growth. In this paper, I discuss the pros and cons of standard and alternative means of watering plants. This information is derived from experiences that my colleagues and I have had using these systems in the desert areas of southern California and from the experiences of researchers in other countries.

Abstract: This is the first extensive study of soil protozoa of arid lands. Twenty-six samples from litters, soils, termitaria, and a cyanobacterial crust, collected from central and south Australian arid lands, were analyzed for numbers and species of gymnamoebae, ciliates, and testacea. Amoebae ranged from 1,000-5,000/g of material, and were two orders of magnitude more abundant than ciliates. Both groups increased in abundance and species richness from bare soils through spinifex to mulga to chenopod vegetations. Testacea ranged 900-5,000/g with similar species richness throughout vegetations, but reached 11,900/g with a doubling of species in a refugium in Kings Canyon. The most prevalent species of amoebae, ciliates, and testacea were taxa associated with ephemeral and disturbed habitats (r-selection). The cyanobacterial crust might be considered a micro-refugium because it contained a number of non-encysting protozoa, including Thecamoeba sp. and Nassula picta, feeding on cyanobacterial filaments. The numbers and species richness of protozoa under shrubs were greater than in bare soils, supporting the resource island hypothesis that desert plants create soil heterogeneity by localizing soil fertility under their canopies.

Abstract: In any dam siting study in arid regions, rainfall records, runoff measurements and their greatest magnitudes are very important. Unfortunately, the data are scarce and, therefore, empirical approaches and charts obtained from similar regions in other parts of the world are necessary for complete applications. The lack of observed data presents the major problem for runoff modelling in arid regions. These regions have characteristically high rainfall intensity and consequent flash floods with large amounts of sediments. Occurrence of rainfall is sporadic, both temporally and spatially, which makes the interpretation of the rainfall-runoff relationship quite difficult. Flood estimations play a significant role in dam siting from the point of view of water availability. This paper presents the basic calculations of floods and sediment amounts that are necessary in dam siting and construction in an arid area by considering the southwestern part of the Kingdom of Saudi Arabia.

Abstract: Vegetation cover is a major feature for ecological system. The change of vegetation cover in large area is mainly caused by climate and human activities. The Yellow River, the second largest river in China with a basin of 752,443 km2, includes semi-arid and arid environment. Therefore, it is necessary to study the change of vegetation cover in the Yellow River Basin, which will help us understand climate influences and impacts of human activities. In order to understand the change of vegetation cover in the Yellow River Basin and its influencing factors, we use the data of AVHRR-NDVI and the information of 76 meteorological stations in the Yellow River Basin covering 1982-1999 to analyze their spatial distribution and dynamic change in spring, summer and autumn. On the basis of calculating the NDVI mean deviation and Moisture Index (MI) mean deviation, we study the feature of MI mean deviation, the speed of NDVI mean deviation and the correlation between them. Finally, some conclusions are drawn. Firstly, the climate was relatively humid from 1982 to 1992 and relatively dry since 1993. The environment in the Yellow River Basin tended to be desiccated, but the vegetation cover is increasing. Secondly, the correlation between NDVI mean deviation and MI mean deviation demonstrates that the humid climate was helpful for vegetation cover. Thirdly, the average speed of vegetation cover increase was 0.58%. The speed of vegetation cover increase in the loess region and catchment area is 0-3.8%, which shows the achievement of ecological measurements in China. The vegetation cover in desert and riverhead region is decreasing, the speed of which is 0-3.0%, a reflection of the climate change.