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Abstract: Although numerous factors influence soil-water content, it is considered a key indicator of rangeland health. This paper investigates the effect of grazing on soil-water content using three treatments within the same soil association. The treatments, simulated holistic planned grazing (SHPG), rest-rotation (RESTROT), and total rest (TREST) applied stocking rates of 36, 6, and 0 animal days/hectare respectively. Soil-water content was measured continuously from 2006 to 2008 using 36 capacitance sensors. Statistical analyses revealed differences in percent volumetric-water content (%VWC) and in all treatments, the SHPG pasture had the highest %VWC. Mixed procedures models indicate strong environmental and treatment effects as explanatory variables for the observed difference in %VWC. Although results of vegetation cover analyses indicated no difference in percent shrub cover in the two production pastures (SHPG and RESTROT), percent litter cover differed in the latter years of this study. It was concluded that in addition to a variety of other factors, management decisions (grazing and rest) can have substantial influence upon soil-water content and that soil-water content can vary substantially as a result of animal impact and the duration of grazing. [Copyright &y& Elsevier]

Abstract: In the Tarim River Basin, the desert riparian forest vegetation is under high-temperature and aridity stress. However, the vegetation can grow continuously because of deep rooting that can reach groundwater, which can thus redistribute water into the upper soil profile. This paper describes patterns of hydraulic lift by Populus euphratica Oliv. and discusses its ecological effects. Our results show that the tap root sap velocity of P. euphratica Oliv. is positive during the day and night. However, a reverse sap flow was observed in the lateral roots during the night. The soil water content of the subsoil was higher than that of the topsoil at depths of 0–120cm. When the sap flow of the lateral roots was reversed at night, the soil water content clearly increased. In particular, at depths of 60–120cm, the soil water content at 4:00 was 28–38% greater than that at 16:00. The vapor pressure deficit was a factor that predominantly affected the root sap velocity, and the smaller vapor pressure deficit often facilitated a reverse sap flow in the lateral roots. Our findings demonstrate the hydraulic lift characteristics and ecological effects that occur in the desert riparian forest in extremely arid regions of middle Asia [Copyright &y& Elsevier]

Abstract: Australia has not always been arid, and the central desert was once well watered. This paper traces the changes in climate and vegetation, leading to the present aridity. At the beginning of the Cenozoic, continental Australia had a warm and humid climate, and the vegetation was mainly meso–micro-thermal (warm to cool temperate) rainforest. Central Australia experienced seasonal rainfall and there may have been limited aridity in the northwest. By the mid–late Eocene, rainforest in central Australia was restricted to the well-watered valley bottoms, with sclerophyll vegetation on the slopes and ridges. In the latest Eocene–earliest Oligocene, there was an abrupt cooling of ocean waters and the diversity of megathermal angiosperms decreased. The early–mid-Miocene was warm–humid and there was a considerable diversity of forest types. Woodlands and Casuarinaceae forests became more common. Central Australia was seasonal, with a very warm season of high evaporation. In Western Australia, regular flows in the palaeodrainage systems had stopped by the mid-Miocene and this marked the first major step towards aridity. The late Miocene was cool and dry, with a major reduction of rainforests and an increase of Eucalyptus/casuarinaceous sclerophyll forests in inland southeastern Australia. Regular burning became a feature of the eucalypt forests. Rainforest persisted, however, along the east coast and highlands of Australia. Central Australia became more arid with dry woodland and chenopod shrublands. Rainforests continued to decrease during the Pliocene and grasslands developed in central northern Australia. By the early Pleistocene, the modern climatic regime had been established, but precipitation was higher than today. Cycles of open, shrubland/grasslands/herbfields and wooded vegetation accompanied the arid glacial and humid interglacial cycles (respectively). About 0.5Ma, there was a change to a drier climate, but it was still wetter than today. The last glacial period was particularly harsh, and the present interglacial period is drier than the previous interglacial. Aridity has thus increased in a number of steps, following the first major step towards aridity in the early Miocene. Distinctive elements of the vegetation can be traced back to times when the arid zone was humid and supported rainforest. The elements, which have remained in arid regions, are the few that could tolerate or adapt to the drier climates. The taxa, which could not cope with these changing conditions, were eliminated from the arid regions. [Copyright &y& Elsevier]

Abstract: This paper analyses the role of climatic aridity on the spatial differences of vegetation activity and its inter-annual variability in a semi-arid region of the North East of the Iberian Peninsula. The vegetation activity was quantified by means of a monthly Normalized Difference Vegetation Index (NDVI) database from NOAA–AVHRR satellite images (1987–2000) at 1km2 of spatial resolution. Coefficients of variation (CoV) from temporal NDVI series were also calculated. The greater temporal variability of NDVI was recorded in areas with low vegetation cover (steppe and dry farming lands), whereas the lowest temporal variability of NDVI was recorded in the irrigated lands and forests located in the most humid areas. There is a strong and negative relationship between the CoV and the NDVI distribution, but we recorded important differences among land uses. Using maps of annual precipitation and temperature obtained by means of a regression-based method, we studied the influence of aridity on spatial patterns of NDVI and CoV values. The results show the high influence of aridity on the spatial distribution of vegetation activity in the Middle Ebro Valley. Aridity causes a general decrease of NDVI and an increase of CoV. Nevertheless, non-linear relationships between aridity and NDVI and CoV were recorded for the whole of the study area and for the different land uses. The relationships between aridity and vegetation patterns in the semi-arid region studied are discussed in depth. [Copyright &y& Elsevier]

Abstract: Science is frequently touted as the solution to dryland management problems, yet most management decisions are, by necessity, based primarily on expert knowledge and experience. This paper describes an integrated framework for organizing, synthesizing, and applying our growing understanding of aridland ecosystems using a flexible, multi-objective assessment, monitoring, and management approach. The framework is dual-purpose: (1) to coordinate the use of existing tools, resources, and diffuse knowledge, and (2) to facilitate the integration and application of new knowledge as it is developed. In particular, this framework must facilitate the integration of new knowledge about linkages among landscape units across scales. The framework includes five elements: (1) an ecological site-based approach for categorizing land based on soils and climate, (2) a repository for organizing existing data and knowledge about each ecological site, (3) conceptual models that organize information on the impacts of management and climate variability, and protocols for (4) assessing and (5) monitoring key ecosystem attributes fundamental to a variety of management objectives. Within this framework, basic and applied research are explicitly linked to management of arid and semi-arid ecosystems to more effectively articulate research questions and set research priorities. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to illustrate the importance of variation in water availability to temporal variation in vegetation dynamics in arid and semi-arid ecosystems. We hypothesize that fine-scale pulses of precipitation interact with longer scale variation in climate and weather to generate temporal variation in plant community composition. Arid and semi-arid regions exhibit great temporal variability in water availability as a result of variation in climate and weather at multiple scales and vegetation-soil water feedbacks. The scales of variation include: shifting climate regimes over centuries and decades, inter-annual variation in weather patterns, seasonal differences in winter and summer precipitation, and within-season variability in precipitation frequency and magnitude. In arid and semi-arid regions, pulses of rainfall are separated by intervening dry periods of variable lengths. This situation results in fluctuating availability of water that limits plant production and controls other ecological processes, such as rates of nutrient cycling. In some semi-arid and arid systems, temporal variation in water availability may create positive feedbacks that facilitate encroachment of C3 woody plant species into areas formerly dominated by C4 grasses. Our ability to predict these complex shifts in vegetation composition may be improved by including temporal variation in climate, weather, and ecosystem processes. [Copyright &y& Elsevier]