Abstract: Water shortage in China, particularly in the north and northwest of China, is very serious. The region accounts for half of the total area of China, but has less than 20% of total national available water resources. While the water shortage in this region is severe, irrigation water use efficiency is only about 40%, with a typical agricultural water use efficiency of about 0.46 kg m(-3). Excessive irrigation in Ningxia and Inner Mongolia has had a significant influence on downstream water users along the Yellow River. It is widely believed that an increase in the agricultural water use efficiency is the key to mitigating water shortage and reducing environmental problems. This paper reviews water-saving agricultural systems and approaches to improve agricultural water use efficiency in the and and semiarid areas of China. The paper will cover biological mechanisms of water-saving agriculture and water-saving irrigation technologies, including low pressure irrigation, furrow irrigation, plastic mulches, drip irrigation under plastic, rainfall harvesting and terracing, In addition, the paper addresses the compensatory effect of limited irrigation and fertilizer supplementation on water use efficiency and highlights the need to breed new varieties for high water use efficiency. Considerable potential for further improvement in agricultural water use efficiency in the region depends on effective conservation of moisture and efficient use of the limited water. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: Arid environments are characterized by limited and variable rainfall that supplies resources in pulses. Resource pulsing is a special form of environmental variation, and the general theory of coexistence in variable environments suggests specific mechanisms by which rainfall variability might contribute to the maintenance of high species diversity in arid ecosystems. In this review, we discuss physiological, morphological, and life-history traits that facilitate plant survival and growth in strongly water-limited variable environments, outlining how species differences in these traits may promote diversity. Our analysis emphasizes that the variability of pulsed environments does not reduce the importance of species interactions in structuring communities, but instead provides axes of ecological differentiation between species that facilitate their coexistence. Pulses of rainfall also influence higher trophic levels and entire food webs. Better understanding of how rainfall affects the diversity, species composition, and dynamics of arid environments can contribute to solving environmental problems stemming from land use and global climate change.

Abstract: The ‘pulse–reserve’ conceptual model—arguably one of the most-cited paradigms in aridland ecology—depicts a simple, direct relationship between rainfall, which triggers pulses of plant growth, and reserves of carbon and energy. While the heuristics of ‘pulses’, ‘triggers’ and ‘reserves’ are intuitive and thus appealing, the value of the paradigm is limited, both as a conceptual model of how pulsed water inputs are translated into primary production and as a framework for developing quantitative models. To overcome these limitations, we propose a revision of the pulse–reserve model that emphasizes the following: (1) what explicitly constitutes a biologically significant ‘rainfall pulse’, (2) how do rainfall pulses translate into usable ‘soil moisture pulses’, and (3) how are soil moisture pulses differentially utilized by various plant functional types (FTs) in terms of growth? We explore these questions using the patch arid lands simulation (PALS) model for sites in the Mojave, Sonoran, and Chihuahuan deserts of North America. Our analyses indicate that rainfall variability is best understood in terms of sequences of rainfall events that produce biologically-significant ‘pulses’ of soil moisture recharge, as opposed to individual rain events. In the desert regions investigated, biologically significant pulses of soil moisture occur in either winter (October–March) or summer (July–September), as determined by the period of activity of the plant FTs. Nevertheless, it is difficult to make generalizations regarding specific growth responses to moisture pulses, because of the strong effects of and interactions between precipitation, antecedent soil moisture, and plant FT responses, all of which vary among deserts and seasons. Our results further suggest that, in most soil types and in most seasons, there is little separation of soil water with depth. Thus, coexistence of plant FTs in a single patch as examined in this PALS study is likely to be fostered by factors that promote: (1) separation of water use over time (seasonal differences in growth), (2) relative differences in the utilization of water in the upper soil layers, or (3) separation in the responses of plant FTs as a function of preceding conditions, i.e., the physiological and morphological readiness of the plant for water-uptake and growth. Finally, the high seasonal and annual variability in soil water recharge and plant growth, which result from the complex interactions that occur as a result of rainfall variability, antecedent soil moisture conditions, nutrient availability, and plant FT composition and cover, call into question the use of simplified vegetation models in forecasting potential impacts of climate change in the arid zones in North America.

Abstract: Ecosystem dynamics in arid and semiarid climates are strongly dependent on the soil water availability which, in turn, is the result of a number of complex and mutually interacting hydrologic processes. This motivates the development of a process-based framework for the analysis of the soil water content in the root zone at the daily time scale. This paper reviews the results that the authors have obtained using a probabilistic–mechanistic model of soil water balance for the characterization of the seasonal regimes of soil moisture with different combinations of climate, soil, and vegetation. Average seasonal soil water content and level-crossing statistics have been used to study conditions of water stress in vegetation. The same framework has been applied to the analysis of the impact of interannual climate fluctuations on the seasonal regime of soil moisture and water stress. 2002 Elsevier Science Ltd. All rights reserved.

Abstract: Changes in resource availability can alter the functioning of ecosystems, especially with regard to both population dynamics and the cycling of organic matter and nutrients. At perhaps one end of the spectrum, arid and semi-arid ecosystems represent an extreme in which essential resource availability (e.g., water) is discontinuously available and the availability of these resources impact the ecosystem as discreet pulse events interspersed among long periods of limited resource availability. The objective of the special section that follows is to contribute to our understanding of how pulsed events shape population dynamics, species interactions, and ecosystem processes in arid and semi-arid ecosystems. There has been a renewed interest in recent years in the relationships between precipitation and ecosystem processes in arid and semi-arid lands. For many years, studies focused on the effects of mean precipitation, averaged at annual, seasonal, or monthly time scales. These studies suggested broad-scale relationships between precipitation amounts and seasonal distribution and the productivity of ecosystems (Le Houerou 1984; Le Houerou et al. 1988), or the plant functional type composition of water-limited systems (e.g., Neilson 1995; Smith et al. 1997). Though some researchers asked questions about the effects of single rainfall events early on (e.g., Went and Westergaard 1949; Beatley 1974; Sala and Lauenroth 1982), this perspective received wider attention only in the last decade, in part through the development of stable isotope tracer methods in plant ecology (e.g., Caldwell et al. 1985; Ehleringer et al. 1991; Lin et al. 1996). More recently, studies also have begun to focus on intra-seasonal precipitation patterns, asking whether variability in rainfall event size, frequency, and timing alone affect the biological processes in water-limited ecosystems (e.g., Goldberg and Novoplansky 1997; Knapp et al. 2002; Schwinning et al. 2003). With a view to addressing these questions, an international workshop was held at the University of Arizona in Tucson, USA (http://ag.arizona.edu/research/schwinn/ workshop.html). This special issue contains both peerreviewed synthesis papers that were generated through the collaboration of workshop participants, as well as original research contributions related to pulse dynamics in arid and semi-arid ecosystems. A generation ago, two major paradigms for understanding rainfall effects in water-limited ecosystems were published: (1) the pulse-reserve paradigm of Noy-Meir (1974) and co-workers, and (2) Walter’s (1971) two-layer soil water-partitioning model. Our understanding has advanced significantly since then, moving from the largely conceptual paradigms to an invariably more complex body of data and theory. Reynolds et al. (2004) critically review both paradigms, concluding that the accurate description of soil moisture dynamics is pivotal for addressing the dynamics of primary production and soil water partitioning. While Walter (1971) envisioned water partitioning in vertical space to govern major patterns of plant functional type distribution, Ehleringer et al. (1991) and Lin et al. (1996) have provided strong evidence of this spatial partitioning. Evidence is mounting that partitioning over time may be at least as important (Reynolds et al. 2004; Schwinning et al. 2004a, b). However, the consequences of the hydraulic redistribution of water for species S. Schwinning (*) School of Natural Resources, University of Arizona, Biological Sciences East 325, Tucson, AZ, 85721 e-mail: schwinn@Ag.arizona.edu

Abstract: . Mountain regions supply a large share of the world’s population with fresh water. Quantification of the hydrological significance of mountains, however, is subject to great uncertainty. Instead of focusing on global averages in advance, the present analysis follows a catchment-based approach using discharge data provided by the Global Runoff Data Centre (GRDC). The River Rhine originating in the European Alps is chosen as a first study area, revealing the hydrological relationship between mountainous and lowland regions in a well-documented area. Following the findings from this analysis, different aspects of runoff characteristics for a total of 22 case-study river basins world-wide have been investigated and compared, for a global view. The view has been extended through aspects of climate and human use of mountain runoff. The particular hydrological characteristics of mountain areas are characterised by disproportionately large discharges. In humid areas, mountains supply up to 20–50% of total discharge while in arid areas, mountains contribute from 50–90% of total discharge, with extremes of over 95%. The overall assessment of the hydrological significance of mountain areas reveals that the world’s major "water towers" are found in arid or semi-arid zones where they provide essential fresh water for a significant proportion of a quickly growing global population. Keywords: mountain hydrology, global comparative assessment, runoff, water resources, sustainability, Rhine River, European Alps

Abstract: Nitrogen (N) cycling was analyzed in the Kalahari region of southern Africa, where a strong precipitation gradient (from 978 to 230 mm mean annual precipitation) is the main variable affecting vegetation. The region is underlain by a homogeneous soil substrate, the Kalahari sands, and provides the opportunity to analyze climate effects on nutrient cycling. Soil and plant N pools, 15N natural abundance (δ15N), and soil NO emissions were measured to indicate patterns of N cycling along a precipitation gradient. The importance of biogenic N2 fixation associated with vascular plants was estimated with foliar δ15N and the basal area of leguminous plants. Soil and plant N was more 15N enriched in arid than in humid areas, and the relation was steeper in samples collected during wet than during dry years. This indicates a strong effect of annual precipitation variability on N cycling. Soil organic carbon and C/N decreased with aridity, and soil N was influenced by plant functional types. Biogenic N2 fixation associated with vascular plants was more important in humid areas. Nitrogen fixation associated with trees and shrubs was almost absent in arid areas, even though Mimosoideae species dominate. Soil NO emissions increased with temperature and moisture and were therefore estimated to be lower in drier areas. The isotopic pattern observed in the Kalahari (15N enrichment with aridity) agrees with the lower soil organic matter, soil C/N, and N2 fixation found in arid areas. However, the estimated NO emissions would cause an opposite pattern in δ15N, suggesting that other processes, such as internal recycling and ammonia volatilization, may also affect isotopic signatures. This study indicates that spatial, and mainly temporal, variability of precipitation play a key role on N cycling and isotopic signatures in the soil–plant system.

Abstract: The mean annual rainfall in southern Africa is found to explain over half of the observed variance in the stable nitrogen (N) isotopic signatures of C3 vegetation in southern Africa (r2=0.54, P<0.01). The inverse relationship between the stable N isotopic signatures of foliar samples from C3 vegetation and long-term southern African rainfall is found on a scale larger than previously observed. A modest relationship is found between stable carbon (C) isotopic signatures of C3 vegetation and rainfall across the region (r2=0.20, P<0.01). No such relationship is found between stable C and N isotopic signatures of C4 vegetation and rainfall. The explanation of the relationship between 15N in C3 vegetation and the mean annual rainfall presented here is that nutrient availability varies inversely with water availability. This suggests that water-limited systems in southern Africa are more open in terms of nutrient cycling and therefore the resulting natural abundance of foliar 15N in these systems is enriched. The use of this relationship may be of value to those researchers modeling both the dynamics of vegetation and biogeochemistry across this region. The use of the isotopic enrichment in C3 vegetation as a function of rainfall may provide an insight into nutrient cycling across the semi-arid and arid regions of southern Africa. This finding has implications for the study of global change, especially as it relates to vegetation responses to changing regional rainfall regimes over time.

Abstract: Landfill covers are critical to waste containment, yet field performance of specific cover designs has not been well documented and seldom been compared in side-by-side testing. A study was conducted to assess the ability of landfill final covers to control percolation into underlying waste. Conventional covers employing resistive barriers as well as alternative covers relying on water-storage principles were monitored in large (10 x 20 m), instrumented drainage lysimeters over a range of climates at 11 field sites in the United States. Surface runoff was a small fraction of the water balance (0-10%, 4% on average) and was nearly insensitive to the cover slope, cover design, or climate. Lateral drainage from internal drainage layers was also a small fraction of the water balance (0-5.0%, 2.0% on average). Average percolation rates for the conventional covers with composite barriers (geomembrane over fine soil) typically were less than 12 mm/yr (1.4% of precipitation) at humid locations and 1.5 mm/yr (0.4% of precipitation) at arid, semiarid, and subhumid locations. Average percolation rates for conventional covers with soil barriers in humid climates were between 52 and 195 mm/yr (6-17% of precipitation), probably due to preferential flow through defects in the soil barrier. Average percolation rates for alternative covers ranged between 33 and 160 mm/yr (6 and 18% of precipitation) in humid climates and generally less than 2.2 mm/yr (0.4% of precipitation) in arid, semiarid, and subhumid climates. One-half (five) of the alternative covers in arid, semiarid, and subhumid climates transmitted less than 0.1 mm of percolation, but two transmitted much more percolation (26.8 and 52 mm) than anticipated during design. The data collected support conclusions from other studies that detailed, site-specific design procedures are very important for successful performance of alternative landfill covers.

Abstract: As recently as 1950, 30% of the world's population lived in urban areas. By the year 2030, 60% of the world's population will live in cities, according to the United Nations (2001) World Population Prospects Revision Report. Urbanization is quickly transitioning communities from the natural rural vegetation to man-made urban engineered infrastructure. The anthropogenic- induced change has manifested itself in microscale and mesoscale increases in temperatures in comparison to adjacent rural regions which is known as the urban heat island (UHI) effect and results in potentially adverse consequences for local and global communities. One of the great challenges facing our current generation of scientists and engineers is how to support the growth of the new and existing arid urban centers in a sustainable manner. This is even more pronounced in arid regions, which will sustain the greatest rate of urbanization. This paper is focused on understanding the interdependency of the infrastructure used to support the growth of urban regions and their environmental, social and economic consequences with an emphasis on the rapidly urbanizing arid region of Phoenix, Arizona.

Abstract: This study estimated the current vegetation and soil carbon storage in China using a biogeochemical model driven with climate, soil and vegetation data at 0.5° latitude-longitude grid spatial resolution. The results indicate that the total carbon storage in China’s vegetation and soils was 13.33 Gt C and 82.65 Gt C respectively, about 3% and 4% of the global total. The nationally mean vegetation and soil carbon densities were 1.47 kg C/m 2 and 9.17 kg C/m 2 , respectively, differing greatly in various regions affected by climate, vegetation, and soil types. They were generally higher in the warm and wet Southeast China and Southwest China than in the arid Northwest China; whereas vegetation carbon density was the highest in the warm Southeast China and Southwest China, soil carbon density was the highest in the cold Northeast China and southeastern fringe of the Qinghai-Tibetan Plateau. These spatial patterns are clearly correlated with variations in the climate that regulates plant growth and soil organic matter decomposition, and show that vegetation and soil carbon densities are controlled by different climatic factors.

Abstract: The planting of sand-binding vegetation in the Shapotou region at the southeastern edge of the Tengger Desert began in 1956. Over the past 46 years, it has not only insured the smooth operation of the Baotou–Lanzhou railway in the sand dune section but has also played an important role in the restoration of the local eco-environment; therefore, it is viewed as a successful model for desertification control and ecological restoration along the transport line in the arid desert region of China. Long-term monitoring and focused research show that within 4–5 years of establishment of sand-binding vegetation, the physical surface structure of the sand dunes stabilized, and inorganic soil crusts formed by atmospheric dust gradually turned into microbiotic crusts. Among the organisms comprising these crusts are cryptogams such as desert algae and mosses. In the 46 years since establishing sand-binding vegetation, some 24 algal species occurred in the crusts. However, only five moss species were identified, which was fewer than the species number in the crust of naturally fixed sand dunes. Other results of the planting were that near-surface wind velocity in the 46-year-old vegetation area was reduced by 54.2% compared with that in the moving sand area; soil organic matter increased from 0.06% in moving sand dunes to 1.34% in the 46-year-old vegetation area; the main nutrients N, P, K, etc., in the desert ecosystem increased; soil physicochemical properties improved; and soil-forming processes occurred in the dune surface layer. Overall, establishment of sand-binding vegetation significantly impacted soil water cycles, creating favorable conditions for colonization by many herbaceous species. These herbaceous species, in turn, facilitated the colonization and persistence of birds, insects, soil animals, and desert animals. Forty-six years later, some 28 bird species and 50 insect species were identified in the vegetated dune field. Thus, establishment of a relatively simple community of sand-binding species led to the transformation of the relatively barren dune environment into a desert ecosystem with complex structure, composition, and function. This restoration effort shows the potential for short-term manipulation of environmental variables (i.e., plant cover via artificial vegetation establishment) to begin the long-term process of ecological restoration, particularly in arid climates, and demonstrates several techniques that can be used to scientifically monitor progress in large-scale restoration projects.

Abstract: The PEP III Arid to Subarid Belt includes the largest hot desert in the world, the Sahara- Arabian desert and the Sahel zone. The region of interest extends south of the Atlas Mountains and south and east of the Mediterranean Sea to approximately 10 °N and shows a broadly zonal pattern with a varying seasonal distribution of precipitation. In the north (ca. 20–23 °N), rainfall results from the southward displacement of the midlatitude westerlies during winter whereas the south is governed by seasonal northward migration of the Intertropical Convergence Zone (ITCZ). Contraction and expansion phases of these presently semi-arid to hyper-arid desert areas result from significant changes in local precipitation. Palaeoenvironmental records from Northern Africa (north of 10 °N) and the surrounding seas document long-term changes in the magnitude and extent of the African monsoon in response to orbitally-forced changes in insolation. However, marine records as well as terrestrial palaeohydrological indicators (e.g., lakes, speleothems, rivers, pollen and charcoal) show that there have been changes in the hydrological cycle superimposed on the long-term waxing and waning of the monsoon which cannot be explained exclusively by changes in insolation. These fluctuations in space, time and magnitude were on a regional to continental scale. Here, we review available data on near-surface palaeohydrological indicators and vegetational changes in arid North Africa and the Arabian Peninsula as well as changes in the intensity of the South Asian Monsoon identified from marine sediments of the Arabian Sea. A comparison of regional environmental changes can clarify relations between the environment and changes in the Earth’s climate system. Each data-set is initially presented independently because they represent heteregeneous records from different regions and time periods and thereby emphasise their potential to provide evidence of continental chronostratigraphic palaeoenvironmental changes. Data-sets of lake status and vegetational change are complementary as they strongly reflect hydrological variation. Deep-sea sediments from the Arabian Sea were used to generate continuous records of oceanic upwelling, continental humidity, and dust and river discharge, that are closely related to palaeoenvironmental changes on the surrounding continents.After presenting the individual data-sets we compare the palaeoclimatic reconstructions derived from the different types of evidence.

Abstract: Chia seeds grown in different ecosystems of South America showed a significant difference in protein and oil contents, peroxide index and fatty acid composition. The main fatty acid was α-linolenic, which was lower in the Inter Andean Valley and Yungas ecosystems, and higher in the Great Chaco (Humid, Arid, and Semiarid) and the Atacama Desert. Copyright © 2004 Whurr Publishers Ltd

Abstract: Application of existing and novel management techniques can alter traditional livestock grazing patterns and significantly improve the sustainability of arid rangelands. Livestock often congregate and heavily graze riparian areas and other sensitive rangeland, while abundant forage remains in other areas. Increasing the uniformity of grazing can help protect fisheries, wildlife habitat, and other vegetative and watershed resources. For years, managers have improved grazing distribution in extensive arid pastures by developing new water sources. In addition, strategic supplement placement can be used to lure cattle to graze areas that typically receive little use. Placement of low-moisture molasses blocks in steeper areas that were far from water increased forage use by 14% at distances up to 600 m from supplement in foothill rangeland. Recent research has examined the potential of breed and individual animal selection to improve grazing distribution patterns. Cattle breeds developed in mountainous terrain utilize rugged rangeland more uniformly than breeds developed in more gentle terrain. In pastures that were grazed by cattle identified as "hill climbers" (previously observed on rugged terrain), more residual vegetation was left on gentle slopes and areas closer to water than in pastures grazed by cattle identified as "bottom dwellers" (previously observed on gentle terrain near water). Cattle may use rugged rangeland more uniformly after weaning and during periods when temperatures are more moderate and the forage is more homogeneous (spring, early summer, and autumn). Herding shows great promise for protecting sensitive rangeland. Preliminary data show that residual riparian forage in pastures where livestock were herded was up to two times higher than in a control pasture. The integration of herding and strategic supplement placement seems to be more effective than herding alone. Many concerns associated with the sustainability of grazing on arid rangelands can be resolved by manipulating livestock grazing behavior through management.

Abstract: Hydrological disturbances, usually floods and drying, govern the distribution and abundance of biota and ecological processes in freshwater ecosystems. Reducing hydrological variability should reduce biodiversity and affect ecological processes. Many of Australia's rivers have reduced variability with river regulation, but some remain free flowing. We tested the variability hypothesis using waterbird communities on 12 floodplain lakes, paired into six systems distributed across half of the continent, over the period from 1983 to 2001. Half of the floodplain lakes were regulated (reservoirs) with stable water levels, while the remainder had unaltered hydrology. We analyzed in more detail the waterbird community within the Menindee system, using eight floodplain lakes, paired into four groups of flow regimes. Similar but less marked patterns occurred within the Menindee system. Overall, mean density (±1 se) on unregulated floodplain lakes was significantly higher (6.04 ± 1.64 waterbirds/ha), compared with r...

Abstract: Short-term measurements of carbon dioxide, water, and energy fluxes were collected at four locations along a mean annual precipitation gradient in southern Africa during the wet (growing) season with the purpose of determining how the observed vegetation‐ atmosphere exchange properties are functionally related to the long-term climatic conditions. This research was conducted along the Kalahari Transect (KT), one in the global set of International Geosphere-Biosphere Program transects, which covers a north‐south aridity gradient, all on a homogenous sand formation. Eddy covariance instruments were deployed on a permanent tower in Mongu, Zambia (879mm of rainfall per year), as well as on a portable tower in Maun (460mmyr � 1 ), Okwa River Crossing (407mmyr � 1 ), and Tshane (365mmyr � 1 ), Botswana for several days at each site. The relationships between CO2 flux, Fc, and photosynthetically active radiation were described well by a hyperbolic fit to the data at all locations except for Mongu, the wettest site. Here, there appeared to be an air temperature effect on Fc. While daytime values of Fc routinely approached or exceeded � 20lmolm � 2 s � 1 at Mongu, the magnitude of Fc remained less than � 10lmolm � 2 s � 1 when the air temperature was above 271C. Canopy resistances to water vapor transfer, rc, displayed an overall decline from the wetter sites to the more arid sites, but the differences in rc could be almost exclusively accounted for by the decrease in leaf area index (LAI) from north to south along the KT. Ecosystem water use efficiency (WUE), defined as the ratio of net carbon flux to evapotranspiration, showed a general decrease with increasing vapor pressure deficit, D, for all of the sites. The magnitudes of WUE at a given D, however, were dissimilar for the individual sites and were found to be stratified according to the position of the sites along the long-term aridity gradient. For example, Mongu, which has the wettest climate, has a much lower WUE for like levels of D than Tshane, which historically has the most arid climate. Given the similar inferred stomatal resistances between the sites, the disparate carbon uptake behavior for the grass vs. woody vegetation is the likely cause for the observed differences in WUE along the aridity gradient. The short-term flux measurements provide a framework for evaluating the vegetation’s functional adaptation to the long-term climate and provide information that may be useful for predicting the dynamic response of the vegetation to future climate change.

Abstract: The aim of this study was to analyze the main processes that determine changes in landscape patterns and vegetation cover from 1957-1994 to develop a model for land cover dynamics Land cover and landscape patterns were assessed and compared using aerial photographs taken in 1957, 1985, and 1994 Over this period, tall grass steppe and arid garrigues increased by 6% and 4%, respectively, while crop fields decreased by 15% and tall arid brush remained the same Over the same period, tall grass steppes and arid garrigues became less fragmented Changes in land use were triggered by socioeconomic forces, which were constrained by the underlying structure of the physical landscape The best preserved vegetation (tall arid brushes) was concentrated at higher elevations, with a pronounced slope, not oriented towards the sea, and in volcanic substrate Communities tended to be better preserved further away from towns and at lower house densities Tall grass steppe was present on more gradual sea-oriented slope and in calcareous substrate, and increased at higher elevations, although not far from the town but away from high anthropogenic influence Previous studies have revealed that traditional land uses of this landscape, particularly grazing, favoured the transition from tall arid brush to tall grass steppe In this study, we analyzed to what extent the underlying structure of the physical landscape imposes limitations to the vulnerability to human activity of the main vegetation types According to the data on the probability of vegetation transition over the 37-year period, the shift from tall arid brush to tall grass steppe appeared to be favoured by gradual slopes Tall arid brush recovered from either arid garrigues or tall grass steppes at steeper slopes Thus, steep terrain had a favourable effect on the formation of brushwood and more gradual terrain favoured tall grass steppe The prevalent trends were confirmed by a projection of a transition matrix over 100 years

Abstract: Arid regions are expected to undergo significant changes under a scenario of climate warming, but there is considerable variability and uncertainty in these estimates between different scenarios. The complexities of precipitation changes, vegetation - climate feedbacks and direct physiological effects of CO2 on vegetation present particular challenges for climate change modelling of arid regions. Great uncertainties exist in the prediction of arid ecosystem responses to elevated CO2 and global warming. Palaeodata provide important information about the past frequency, intensity and subregional patterns of change in the world's deserts that cannot always be captured by the climatic models. However, it is important to bear in mind that the global mechanisms of Quaternary climatic variability were different from present-day trends, and any direct analogies between the past and present should be treated with great caution. Although palaeodata provide valuable information about possible past changes in the vegetation - climate system, it is unlikely that the history of the world's deserts is a key for their future.

Abstract: Publisher Summary This chapter focuses on the effects of global climate change on the size and position of geographic ranges and the richness and composition of bird communities. Plenty of evidence demonstrates that range boundaries of birds are correlated with climatic factors. In general, the northern range limit of species seems to be influenced rather by abiotic factors such as cold temperatures. The southern range limit of species appears to be determined by climatic factors such as heat or lack of water in arid regions and by biotic factors in more humid regions. For communities, increases in species richness are predicted for northern latitude and high-elevation sites and declines of species richness in arid regions. With increasing winter temperature, declines in the proportion of migratory species in bird communities have been predicted and observed. The chapter uses these results to evaluate consequences for the conservation of birds. Conservation consequences of global climate change are especially high threats to species in arid environments, expected movements of species out of protected areas and increasing land use conflicts.

Abstract: Aim To assess the correspondence between current avian distributions in the lowlands of northern South America with respect to the hypothesized importance of sea level rise and other events over the past 15 million years on speciation. Location Tropical lowlands of north-western South America. Methods To establish which bird taxa may have originated in each area of endemism, I examined the ranges of all bird species occurring in the Pacific and the Caribbean lowlands. To determine land and sea distribution during a sea level rise of 100 m in north-western South America and eastern Central America, I traced the 100 m contour line from the Geoatlas of Georama and the Global 30-Arc-Second Elevation Data (GTOPO30) produced by the US Geological Survey. Results During a sea level rise of ∼100 m, marine incursions would have occurred from the Caribbean Sea and the Pacific Ocean. Several areas of tropical forest and dry/arid vegetation would have been isolated, currently known as the Darien, Choco, Nechi, Catatumbo, Tumbesian and Guajiran areas of animal and plant endemism. Main conclusions A large part of the high diversity of forest and nonforest birds and other animals and plants in the Pacific rain forest and the Caribbean woodland likely arose as the result of sea level rises, dispersal and other geological and climatic events.

Abstract: Tooth, S., Nanson, G. C. (2004). Forms and processes of two highly contrasting rivers in arid central Australia, and the implications for channel-pattern discrimination and prediction. Geological Society of America Bulletin, 116 (7-8), 802-816 RAE2008

Abstract: The zonal climate pattern associated with the Hadley cell circulation is best exemplified in northern Africa, with its Mediterranean northern tip, subtropical Sahara desert, and belts of monsoonal and equatorial climates related to the seasonal migration of the Intertropical Convergence Zone (ITCZ). In the past, astronomical forcing has been the prime factor driving the meridional shifts of these climate belts, but feedback processes from oceans and land surfaces have amplified and modified the direct effects of insolation changes.