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Based on the features of environment and the fact of successful artificial afforestation, the paper points out that the restoration of vegetation in Arid-hot valleys along the Jinshajiang River should be implemented mainly by planting sparse — arbor/ shrub/ tussock Combination. Four ways to restore vegetation in the area are given in the paper. [ABSTRACT FROM AUTHOR]

Warming of the climate system is unequivocal, and the change of climate variables will eventually have a great impact on vegetation cover and agricultural practices, especially in the arid area Xinjiang in China, whose agriculture and ecosystems are heavily vulnerable to climate change. In this paper, normalized difference vegetation index (NDVI) was used to study the vegetation growth and its response to climate change in Xinjiang. Firstly, two NDVI datasets (Global Inventory Modeling and Mapping Studies (GIMMS) and Moderate Resolution Imaging Spectroradiometer (MODIS)) were merged through a pixel-wise regression analysis to obtain a long time series of NDVI data, and then, relationships between yearly NDVI and yearly climate variables, and monthly NDVI and monthly climate variables were extensively investigated for grassland and cropland in northern and southern Xinjiang, respectively. Results show the following: (1) there was an increasing trend in NDVI for both grassland and cropland in both northern and southern Xinjiang over the past decades and trends were significant except that for grassland in northern Xinjiang; (2) precipitation and evaporation were more important than temperature for grassland in northern Xinjiang, while precipitation and temperature were more important than evaporation for grassland in southern Xinjiang and cropland in both northern and southern Xinjiang; (3) NDVI was highly correlated with accumulated monthly precipitation instead of monthly precipitation, and there was a lagged effect of precipitation, temperature, and evaporation on NDVI change. However, lagged effects were only significant in specific months. The results could be helpful to agricultural practices; e.g., based on lagged effect of precipitation, irrigation in July is very important for crop growth. [ABSTRACT FROM AUTHOR]

ABSTRACT The arid region in northwestern China covers 2·02 million square kilometres and is one of the most arid regions in the world. Positioned at the central part of the Eurasian Continent, this region experiences little influence from the Eastern and Southern Asian Monsoons and precipitation is formed mostly from westerly vapour. With a hyper arid climate, the annual precipitation in this region ranges from less than 20 mm at the oasis area to around 600 mm in the mountain regions, whereas potential evaporation can amount to 2000-3000 mm per annum. It is reported that strong evapotranspiration characterizes and dominates the water cycle in the arid basins. Nearly all the water resources of the oasis, where the human society exists, come from the mountain areas as river discharge from glacier/snow melting water, rainfall and subsurface flow from bedrock cracks. As a result, the hydrographs of the arid basins are affected by climate change via changes in precipitation partitioning (the ratio of rainfall and snowfall) and changes to seasonal distributions of precipitation and air temperature. These changes in turn directly affect the water yield and the vegetation response. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: An oasis is defined here as an efficient eco-geographical landscape that allows flourishing vegetation or human settlement due to a stable water supply in an arid region. The water resource is the major limiting factor impacting the oasis scale in arid regions. For discussion of the suitable scale of an oasis supported by a specific quantity of water resource, the Manas River Basin, a typical continental river basin in the arid region of China, was taken as the study object. Based on the remote sensing images and socio-economic data, the stability and suitable scale of oasis in 1976, 1987, 1998, 2010, and 2020 were analyzed using an oasis water-heat balance model. The results indicated that (1) the respective stability index (H 0) of 1976, 1987, 1998, and 2010 was 0.10, 0.15, 0.40, and 0.38, respectively, changing from an unstable level into a metastable level. (2) Under the guarantee of natural oasis ecosystem stability, the suitable scales of natural oasis in 1976, 1987, 1998, and 2010 were 697.2–1045.7 km2, 942.2–1413.3 km2, 2042.0–3063.0 km2, and 1428.2–2142.3 km2, respectively. The suitable scales of the total oases were 3681.3–4030.3 km2, 5259.1–5730.2 km2, 7654.5–8675.5 km2, and 8130.3–8844.4 km2, respectively. (3) If the artificial oasis scale remained unchanged from 2010, the suitable scale of the natural oasis in the Manas River Basin in 2020 would be 1695.8–2543.8 km2, and the suitable scale of the total oases would be 8398–9246 km2. With a reasonable proportion between natural and artificial oases, the suitable scales of each would be 3400.3–5100.5 km2 and 2266.9–3400.4 km2. This paper not only provides data for reasonable oasis planning of the Manas River Basin, but also provides a new direction for studies on the suitable scale of oases in arid regions. [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: Vegetation striped pattern is a common feature in semiarid and arid landscapes, which is seen as mosaics including vegetated and non-vegetated patches. Identifying scales of pattern in ecological systems and referring patterns to multi-scaled processes that create them are ongoing challenges. The aim of this paper is to study the vegetation patterns and their across-scale relationships between the vegetation and anisotropic topography (W–E and N–S) in 12 transects at Gurbantunggut desert. We used wavelet-based across-scale analysis for extracting information on scales of pattern for those transect data, evaluating their inherent structure, and inferring characteristics of the processes that imposed those patterns at across scales. The results show that, in W–E direction, the scales of vegetation pattern (C. ewersmanniana is at the scale 40m, H. ammodendron, at 35m) correspond to the dune ridge/dune valley sequences (appearing at distance of 40m), and vegetation on mesoscale and large scale are significant cross-scale correlation with topography on mesoscale and large scale in all W–E transects. In N–S direction, there is an irregular pattern of vegetation along the N–S irregular topography, and no unified cross-scale relationships between topography and vegetation on different scales in different transects. Moreover, cross-scale correlation analysis between topography and vegetation provides further detail on hierarchical structure and specific scales in space that strongly influenced the larger patterns. Knowledge of the cross-scale relationships between topography and vegetation could lead to better understanding and management of biological resources in that region. [Copyright &y& Elsevier]

Desertification of arid and semiarid land is a severe environmental problem. Better understanding of the desertification process, in the context of changing climate and growing human activities, is essential for policy-making on desertification control strategies and land-use management in these environmentally sensitive areas. In this study, we analyze vegetation change and dune activity over the years 1981-2013 in Mu Us, a semiarid dune field in north-central China, using remote sensing techniques and geomorphic analysis. During this period, we have observed an increasing trend in vegetation greenness, indicated by the Normalized Difference Vegetation Index, which is consistent with the decreasing trend of the dune mobility index. Changes in dune morphologies in the study area indicate that dunes are being stabilized under vegetation growth, and this morphological change could potentially be used to detect the long-term trend in desertification. Based on a detailed analysis of both climatic and socioeconomic data, we found that the decadal changes in wind strength have significant impact on the long-term vegetation rehabilitation in the study area and that the short-term variations in vegetation growth are associated with interannual fluctuations in precipitation. Policy-driven, large ecological restoration projects implemented in recent decades can exert a positive impact on vegetation restoration, especially under favourable climatic conditions. This study implies that such climatic conditions may offer a window of opportunity for land regeneration in semiarid northern China. [ABSTRACT FROM AUTHOR]

The Temperature Vegetation Dryness Index (TVDI), a drought monitoring index based on an empirical parameterization of the Land Surface Temperature (LST)-Normalized Difference Vegetation Index (NDVI) space, has been widely implemented in a variety of ecosystems worldwide because it does not depend on ancillary data. However, the simulation of dry/wet edges in the TVDI model can be problematic because remote sensing images do not have sufficient pixels to identify the wetness and dryness extremes of different vegetation coverages. In this study, an improvement in dry/wet edge simulation was proposed, and a comparison of the original TVDI and the modified Temperature Vegetation Dryness Index (TVDIm) was performed for drought monitoring in Ningxia Province, which is a typical semi-arid region in China. First, the difference between the land surface temperatures in day and night (DLST) was used as an alternative to LST when building the TVDIm model. In addition, the wet edges were improved by removing outliers using a statistical method, and the dry edges were optimized by removing the "tail down" points in the NDVI range of 0.0-0.1. Here, the modeling process of TVDIm in 2005, one of recent extreme drought year is illustrated. The results show that both the TVDI and TVDIm can be used to monitor the temporal and spatial variations of drought, and the onset, duration, extent, and severity of drought can be reflected by TVDI and TVDIm maps. However, the magnitude of TVDI is higher than that of TVDIm, which could cause the TVDI-simulated drought condition to be elevated in normal years and underestimated in dry years. The TVDIm has higher coefficients of correlation with in situ meteorological drought index and agricultural drought statistical data than does the original TVDI, and it exhibits better performance in drought monitoring compared to that of the original TVDI in semi-arid regions of China. [ABSTRACT FROM AUTHOR]

Fossil pollen records from 45 sites across China were evaluated and synthesized to document vegetation and climate change during Marine Isotope Stage 3 (MIS 3) at 60-27 ka and to understand the large-scale controls. During MIS3, vegetation type was dominantly forest in eastern China, forest steppe/meadow in the north and Tibetan Plateau, and steppe desert in northwestern arid China. We developed a semi-quantitative vegetation index to reflect change in plant abundance (by inferring the general climate conditions), with a vegetation score from 1 to 3 based on the different vegetation types inferred from pollen data at individual sites at intervals of 2,000 years. The reconstructed vegetation index shows higher values during MIS 3, especially during the period 53-40 ka, than at the Last Glacial Maximum. Our results also suggest that climate on the basis of vegetation change was cooler and drier during MIS 3 than during the Holocene optimum; however, MIS 3 vegetation was probably similar to modern vegetation. The close relationship between vegetation change, insolation and Asian summer monsoon strength suggests that climate variations, probably in both temperature and precipitation, are the primary drivers of regional vegetation change. Additional well-dated, high-resolution palaeoclimate records from many locations across China will be needed to understand the vegetation change and climate forcings on millennial and centennial scales within MIS 3. [ABSTRACT FROM AUTHOR]

Temperature has long been accepted as the major controlling factor in determining vegetation phenology in the middle and higher latitudes. The influence of water availability is often overlooked even in arid and semi-arid environments. We compared vegetation phenology metrics derived from both in situ temperature and satellite-based normalized difference vegetation index (NDVI) observations from 1982 to 2006 by an example of the arid region of northwestern China. From the satellite-based results, it was found the start of the growing season (SOS) advanced by 0.37 days year and the end of the growing season (EOS) delayed by 0.61 days year in Southern Xinjiang over 25 years. In the Tianshan Mountains, the SOS advanced by 0.35 days year and the EOS delayed by 0.31 days year. There were almost no changes in Northern Xinjiang. Compared with satellite-based results, those estimates based on temperature contain less details of spatial variability of vegetation phenology. Interestingly, they show different and at times reversed spatial patterns from the satellite results arising from water limitation. Phenology metrics derived from temperature and NDVI conclude that water limitation of onset of the growing season is more severe than the cessation. Phenology spatial patterns of four oases in Southern Xingjiang show that, on average, there is a delay of the SOS of 1.6 days/10 km of distance from the mountain outlet stations. Our results underline the importance of water availability in determining the vegetation phenology in arid regions and can lead to important consequences in interpreting the possible change of vegetation phenology with climate. [ABSTRACT FROM AUTHOR]

The Artemisia/Chenopodiaceae (A/C) ratio is assumed to be a useful index for reconstructing moisture changes in arid and semi-arid regions. Thorough modern pollen studies are still lacking to understand the reliability and limitation of A/C ratio as a moisture indicator, however. Here we review how well this ratio can be applied in arid and semi-arid China on the basis of new surface pollen data, previous data synthesis and other publications. Results indicate that variance in the A/C ratio can permit identification of modern vegetation types and that the A/C ratio generally has a positive relationship with annual precipitation. However, soil salinity, vegetation community composition, human activity and sample provenance (e.g. soil and lake sediments) will affect the values of the A/C ratio in different vegetation zones and therefore the A/C ratio is not comparable in different regions. We argue that the A/C ratio can only be used to reconstruct vegetation types and climate change in regions with precipitation <450–500 mm, and in steppe, steppe desert and desert areas. Careful studies should be undertaken to understand the modern pollen–vegetation–climate relationships in various regions before using the A/C ratio to interpret vegetation and climate. [ABSTRACT FROM AUTHOR]

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