Desert Expansion Research Articles

Active restoration efforts drive community succession and assembly in a desert during the past 53 years.

Regreening efforts in deserts have been implemented globally to combat land degradation and desert expansion, but how they affect above- and belowground community succession and assembly processes remains unknown. Here, we examined variations in plant and soil microbial community attributes along a 53-year restoration chronosequence following the establishment of straw checkerboard barriers (SCBs) in the Tengger Desert of China. This approach is a combination of fixing shifting sand and adding organic material (straw) simultaneously to expedite vegetation restoration by enhancing the success of plant establishment. Our findings revealed that the establishment of SCBs significantly triggered plant and soil microbial communities to gradually approximate those of the natural community along restoration duration. We observed positive and negative bidirectional shifts in plant and soil microbial community composition. Critical temporal threshold zones for relatively rapid changes in community composition were identified, with 2-15.5 years for plants, 0.5-8.5 years for bacteria, and 2-8.5 years for fungi. This suggests a delayed response of plant communities to restoration efforts compared with soil microbial communities. Both stochastic and deterministic processes regulated plant and soil microbial community assembly. Stochastic processes played a more important role in plant and fungal community succession, whereas deterministic processes primarily governed bacterial succession. In terms of deterministic processes, temporal variations in community composition mainly resulted from the intrinsic correlations among plant, bacterial, and fungal communities, as well as an increase in soil organic carbon (SOC) with restoration duration. Thus, temporal patterns and functional contributions of bacterial communities appear to be more predictable than those of plant and fungal communities during desert ecosystem restoration. This study emphasizes that plant-bacteria-fungi correlations and increasing SOC content are critical for accelerating community succession and promoting dryland restoration. Future studies should explore and integrate temporal variations and restoration effects of multiple ecosystem functions to better predict dryland development and resilience to global climate changes over a large temporal scale.

Analysis of Landscape Pattern Evolution and Impact Factors in the Mainstream Basin of the Tarim River from 1980 to 2020

The mainstream basin of the Tarim River serves as a vital ecological security barrier that prevents the merging and expansion of deserts and an important strategic corridor directly linking Qinghai and Xinjiang. With society’s development and climate change, ecological issues such as river interruption, vegetation degradation, and land desertification in the basin have notably intensified, and the ecological security is facing a critical test. Exploring the characteristics of landscape changes and their driving factors within the basin is crucial in improving the ecological environment system’s management. Based on land use data from 1980 to 2020, this study analyzed the characteristics of the spatiotemporal changes and pattern evolution of the landscape through a landscape transfer matrix and landscape pattern indices. It further revealed the impact factors of the landscape pattern through canonical correspondence analysis. The results showed that (1) in 1980–2020, the areas of desert, forest, farmland, and settlement landscapes increased, while the area of grassland landscape decreased, and the water landscape showed an “increasing–decreasing–recovery” pattern. The landscape transition types mainly included the transition from grassland to desert; mutual transitions among farmland, grassland, and forests; mutual transitions between water and grassland; and the transition from farmland to settlements. (2) The overall landscape pattern demonstrated increased fragmentation, shape complexity, and evenness with decreased aggregation. Furthermore, different landscapes exhibited distinct characteristics of landscape pattern changes; for instance, grassland landscape showed severe fragmentation, while desert landscape displayed the strongest dominance. (3) The landscape pattern was a result of the combined impact of natural and human factors, with the soil thickness (SOT), road density (ROD), annual actual evapotranspiration (AAE), population density (POD), and mean annual temperature (MAT) exhibiting significant influences. Specifically, the settlement and farmland landscapes were mainly influenced by the mean annual relative humidity (MAH), POD, GDP density (GDP), and distance to artificial water (DAW); the forest, grassland, and water landscapes were mainly influenced by the SOT, soil organic matter content (SOM), AAE, ROD, elevation (ELE), MAT, slope (SLP), and distance to natural water (DNW); and the desert landscape was mainly influenced by the DAW, DNW, SLP, AAE, SOT, SOM, and ROD. These findings can provide a scientific reference for landscape management and restoration, as well as sustainable social and economic development, in the mainstream basin of the Tarim River.

Plant root mechanisms and their effects on carbon and nutrient accumulation in desert ecosystems under changes in land use and climate.

Deserts represent key carbon reservoirs, yet as these systems are threatened this has implications for biodiversity and climate change. This review focuses on how these changes affect desert ecosystems, particularly plant root systems and their impact on carbon and mineral nutrient stocks. Desert plants have diverse root architectures shaped by water acquisition strategies, affecting plant biomass and overall carbon and nutrient stocks. Climate change can disrupt desert plant communities, with droughts impacting both shallow and deep-rooted plants as groundwater levels fluctuate. Vegetation management practices, like grazing, significantly influence plant communities, soil composition, root microorganisms, biomass, and nutrient stocks. Shallow-rooted plants are particularly susceptible to climate change and human interference. To safeguard desert ecosystems, understanding root architecture and deep soil layers is crucial. Implementing strategic management practices such as reducing grazing pressure, maintaining moderate harvesting levels, and adopting moderate fertilization can help preserve plant-soil systems. Employing socio-ecological approaches for community restoration enhances carbon and nutrient retention, limits desert expansion, and reduces CO2 emissions. This review underscores the importance of investigating belowground plant processes and their role in shaping desert landscapes, emphasizing the urgent need for a comprehensive understanding of desert ecosystems.

Genetic and ecological differentiation of Caragana jubata (Pall.) Poir.

Caragana jubata (Pall.) Poir. is a cold-tolerant mountain shrub and important medicinal species of Fabaceae family with a disjunctive pan-Asian range. Sequences of the atpH-atpI and trnL-trnF intergenic spacers of chloroplast DNA and of the internal transcribed spacer region, ITS-1, of the nuclear ribosomal DNA were used to investigate the intraspecific evolution and phylogeography of this species. Eleven cpDNA haplotypes were identified. The population subdivision is very high (GST = 0.743, NST = 0.943), suggesting a distinct phylogeographic structure (NST > GST, P < 0.001). Phylogenetic analyses of the eleven haplotypes were clustered into four clades, consistent with their respective distributions in four separate regions: Tibet, Tien Shan, Buryatia and Magadan Region. This pronounced phylogeographic gap is also confirmed by nrITS data, however, there is some mixture of genotypes in the Magadan and Buryat populations. Genetic evidence suggests that the center of origin of C. jubata was Tibet and adjacent mountain systems, from where the species spread westwards along continuous mountain chains towards the Tien Shan and northeastwards to the coast of the Sea of Okhotsk and further northwards to Arctic. Divergence of Tien Shan populations of C. jubata may have been caused by climate change in the Pleistocene associated with increased aridity and expansion of deserts, while subsequent climate-induced cycles of range contraction/expansion increased geographic isolation and fragmentation of more northern populations. Marginal northern populations now occupy sites with the most favourable environmental conditions. Special attention is paid to the Okhotsk populations of this species preserved in Magadan Region.

Status quo analysis of the Aidar-Arnasay Lake System

The Aidar-Arnasay lake system, situated within a natural depression in the southern expanse of the Kyzylkum desert, southwest of the Shardara reservoir, constitutes a unique hydrological entity. Comprising drainless lakes sustained by inflows from the collector-drainage network and the Shardara reservoir, this system has, over the span of 50 years, accumulated an astonishing 2.5 times more water than all 53 reservoirs combined in the province. However, recent studies conducted to assess the water quality in the Aidar-Arnasay lake system have revealed alarming concentrations of pollutants. A comprehensive analysis of the water samples has unveiled significant exceedances across nearly all measured indicators. Notably, the general mineralization of water stands out as a critical concern, surpassing the permissible norm by more than 25 times. This excessive mineralization poses a severe threat to the biological diversity within the system, impacting the overall ecological health of the region. The repercussions of these heightened pollutant levels extend beyond mere water quality concerns, adversely affecting the delicate balance of the ecosystem. Urgent intervention and remediation efforts are imperative to mitigate the ecological consequences and preserve the integrity of the Aidar-Arnasay lake system, ensuring its sustainability for future generations.

Progression mechanism of urban food desert and categorization of high‐risk blocks through the analysis of changes in food intake demand—A case study of Azabu and Takanawa districts of Minato‐ku, Tokyo, where the prices of grocery stores is rising due to redevelopment

AbstractWe analyzed the mechanism of urban food desert expansion based on data at the block level. According to the food demand curve, elasticity was high, and the nutritional food dietary decreased as store prices increased. The store prices within 500 m of the redevelopment site would tend to increase because luxury supermarkets would dominate, while over 500 m they would often tend to decrease because new non‐luxury supermarkets would compete for opening. There are two types of blocks with a high risk of food desert: A block surrounded by multiple redevelopments or a block whose store price has gone up considerably.

A systematic review on the morphology structure, propagation characteristics, resistance physiology and exploitation and utilization of Nitraria tangutorum Bobrov.

Nitraria tangutorum Bobrov., belonging to the family Nitrariaceae, is a drought-tolerant and salt-loving plant and has drawn attention for its good economic and ecological value. As one of the main group species and dominant species in China's desert and semi-desert regions, N. tangutorum possesses superior tolerance to drought, high temperature, cold, barren, high salinity and alkalinity and wind and sand. Its root system is well developed, with many branches and a strong germination capacity. Once buried in sandy soil, N. tangutorum can quickly produce a large number of adventitious roots, forming new plants and continuously expanding the shrubs, forming fixed and semi-fixed shrub sand dunes. Sand dune shrubs can trap and fix a large amounts of quicksand, prevent desert expansion and erosion, and play an important role in maintaining regional ecosystem balance and improving ecological environmental quality. In addition, the phytochemical screening studies report that N. tangutorum contains an abundance of various compounds including flavonoids, alkaloids, phenolic acids and polysaccharides. These compounds confer a range of beneficial bioactivities such as antioxidant, anti-inflammatory, anti-tumor, anti-fatigue, liver protection, neuroprotection, cardiovascular protection, lowering blood lipid, regulating blood sugar level and immunoregulation. The fruits of N.tangutorum also contain vitamin C, amino acids, minerals and microelements. It has been traditionally used as a nutritional food source and in folk medicine to treat diseases of the spleen and stomach, abnormal menstruation, indigestion, and hyperlipidemia. N. tangutorum, as a wild plant with medicinal and edible homology, possesses remarkable economic and medicinal values. This detailed, comprehensive review gathers and presents all the information related to the morphological structure, propagation characteristics, resistance physiology and exploitation and utilization of N.tangutorum, providing a theoretical basis for the researchers to conduct future in-depth research on N.tangutorum.

Spatial contrasts in mid-Holocene dune activities in deserts of northern China: Results from PMIP4 simulations in comparison with geological data

Numerous studies have explored paleoenvironmental conditions in China's dune fields around the mid-Holocene (MH), ∼6000 calendar years ago, often based on individual paleosol-aeolian sand depositional sequences and local-scale landscape dynamics. So far, continent-scale modeling studies have only indirectly assessed dune activation and stabilization processes via changes in simulated precipitation, net precipitation (precipitation minus evaporation), and effective moisture (precipitation divided by evaporation). Here we conducted a comprehensive study using gridded data on potential evapotranspiration, precipitation, and surface wind velocity from 13 climate models participating in the Paleoclimate Modeling Intercomparison Project phases 4 (PMIP4) and compared the model results with geological records. Our evaluation of spatial patterns of dune activity in northern China around the MH reveals that the intensity of annual MH dune activity exhibited significant differences between the eastern and western parts of Chinese deserts compared to those of the preindustrial period (PI). Dune activity was significantly weaker in the eastern region, while in the western part, it was considerably stronger. The key drivers of this disparity were the distinct spatial variations in near-surface wind speed and effective moisture between the two regions. Compared with the optically stimulated luminescence ages of the paleosol-aeolian sand sedimentary sequences derived from a compilation of geological records from 88 sites across northern China, the model results suggest that the weakening of dune activity and the process of dune stabilization in eastern China around the MH were mainly attributed to a significant increase in effective moisture and a concurrent decrease in near-surface wind speed due to the intensified East Asian summer monsoon. Additionally, the weakening of westerlies in western China resulted in reduced effective moisture, contributing to increased sand availability for dune development and subsequent desert expansion.

Westerly aridity in the western Tarim Basin driven by global cooling since the mid-Pleistocene transition

To explore the relationship between the global cooling, westerlies, and central Asian aridity, we report ∼1.1 Ma local sedimentary environment changes according to physical-chemical parameters from an 800-m core (KT11) from the Kashgar region in the western Tarim Basin, China. Grain size end-member (EM) modelling is employed to quantify the processes of sediment transport and deposition. Four end members with modal values of 272 μm, 144 μm, 45.6 μm and 12.7 μm were extracted and explained 97.9% of the variance in the grain size data, corresponding aeolian dynamics, river energies, delta development and pedogenesis/long-term suspension components transported by wind or water, respectively. Four dominant sedimentation types, including lacustrine facies, delta facies, fluvial facies, and aeolian dunes, were identified through lithology and grain size frequency curves. The 1.1 Ma sedimentary successions experienced delta deposits interbedded with fluvial and aeolian deposits and lacustrines (1.1–0.6 Ma), alternating fluvial and aeolian facies with the occurrence of deltas and lacustrines (0.6–0.15 Ma), and aeolian facies interbedded with deltas and fluvial facies (0.15 Ma-present). Stepwise drying sedimentary conditions and enhanced desertification indicated by increasing rubidium/strontium ratios and proportion of aeolian sands, and decreasing total organic carbon since the past 1.1 Ma, implied intensified westerlies, likely resulted from ice volume expansion and ongoing global cooling according to geological record comparison and simulations during the Last Glacial Maximum compared to preindustrial conditions, which may have controlled the expansion of the permanent deserts in inland Asia. These persistent drying trends and intensified westerly circulation in arid regions during glacial periods after the mid-Pleistocene Transition indicated by larger amplitudes of aeolian sand proportion than prior to 0.6 Ma are similar to those in the interior monsoonal Asia, where the larger-amplitude of median grain size indicated enhanced Asian winter monsoon intensity and drier glacials.

Validation of MODIS Temperature and Emissivity Products Based on Ground-Based Mid-Wave Hyperspectral Imaging Measurement in the Northwestern Plateau Region of Qinghai, China

The climatic fluctuations in northern China exhibit remarkable variability, making it imperative to harness the power of MODIS data for conducting comprehensive investigations into the influences of desertification, desert expansion, and snow and ice melting phenomena. Consequently, the rigorous evaluation of MODIS land surface temperature (LST) and land surface emissivity (LSE) products takes on a momentous role, as this provides an essential means to ensure data accuracy, thereby instilling confidence in the robustness of scientific analyses. In this study, a high-resolution hyperspectral imaging instrument was utilized to measure mid-wave hyperspectral images of grasslands and deserts in the northwest plateau region of Qinghai, China. The measured data were processed in order to remove the effects of sensor noise, atmospheric radiation, transmission attenuation, and scattering caused by sunlight and atmospheric radiation. Inversion of the temperature field and spectral emissivity was performed on the measured data. The inverted data were compared and validated against MODIS land surface temperature and emissivity products. The validation results showed that the absolute errors of emissivity of grassland backgrounds provided by MCD11C1 in the three mid-wave infrared bands (3.66–3.840 μm, 3.929–3.989 μm, and 4.010–4.080 μm) were 0.0376, 0.0191, and 0.0429, with relative errors of 3.9%, 2.1%, and 4.8%, respectively. For desert backgrounds, the absolute errors of emissivity were 0.0057, 0.0458, and 0.0412, with relative errors of 0.4%, 4.9%, and 3.9%, respectively. The relative errors for each channel were all within 5%. Regarding the temperature data products, compared to the inverted temperatures of the deserts and grasslands, the remote sensing temperatures provided by MOD11L2 had absolute errors of ±2.3 K and ±4.1 K, with relative errors of 1.4% and 0.7%, respectively. The relative errors for the temperature products were all within 2%.

Tensile properties of six desert shrub species in Hobq Desert, China

Abstract Desert shrubs are often planted to control wind erosion, land desertification, and desert expansion. Their motions of bending and vibration can absorb and disperse kinetic energy of wind, so as to protect the erodible surfaces close-by. According to continuum mechanics, the quantification of mechanical properties of shrubs is critical to understand their dynamic behaviors. In this study, the conventional tensile tests of six dominant desert shrub species’ stems mainly sampled in the Hobq Desert of China are performed. It is found that the tensile strength of Tamarix ramosissima and Hedysarum scoparium are larger than others, whereas Caragana korshinskii and Hippophae rhamnoides are more flexible. And then, it is theoretically and experimentally proved that the tensile strength and Young’s modulus of these desert shrubs both decrease with the increase of diameter.

Gum arabic – A versatile natural gum: A review on production, processing, properties and applications

Gum arabic (GA) is the oldest gum known for its diverse application for more than 5000 years. The gum is produced from some species of Acacia , mainly growing/planted in arid and semi-arid regions of Africa and Asia. Sudan is the leading producer and exporter of GA in the world. GA is a mixture of potassium, magnesium and calcium salts of polysaccharide acid and is easily soluble in water. As it possesses a unique biochemical structure and properties, it finds application as a stabilizer, emulsifier, bulking agent, thickener, carrier, glazing and firming agent, humectant and antioxidant. GA is biocompatible and biodegradable, and its source is renewable. The people worldwide are now again feeling the necessity of using natural additives in products of human consumption, due to severe adverse effects of using synthetic additives. Such a shift in the human mindset has created additional demand for natural products like GA. This gum is produced in resource-constrained areas, where people are poor and need the creation of good livelihood options for improvement in their economic conditions. Apart from GA production, Acacia senegal trees help improve soil health and restrict climate change as well as expansion of desert in arid and semi-arid regions. Increasing production of GA by motivating farmers in arid and semi-arid regions to establish Acacia senegal plantations ; creating infrastructure for processing and value addition in the regions of GA production; and finding new application areas of GA are urgent needs of this vital sector. This consolidated review on GA covers the current research work on GA production, properties, processing, application and marketing, unlike several specific reviews considering the need of those who want to initiate research work/already working for this sector. • Gum arabic is a commercially important exudate gum from Acacia senegal trees. • It supports livelihood of resource constrained gum gatherers across the world. • Gum inducer method can be used for sustainable tapping with least damage to trees. • Gum arabic production, processing, properties and applications are discussed. • Biocompatibility of this gum makes it safe for food and medical applications.

PROGRESSION MECHANISM OF URBAN FOOD DESERT AND CATEGORIZATION OF HIGH_RISK BLOCKS THROUGH THE ANALYSIS OF CHANGES IN FOOD INTAKE DEMAND

We analyzed the mechanism of urban food desert expansion based on data at the block level. According to the food demand curve, the elasticity was high and the nutritional value diet decreased as the store prices increased. The store prices within 500m from the redevelopment would tend to increase because luxury supermarkets would dominate, while over 500m they would often tend to decrease because new non-luxury supermarkets would compete for opening. There are only two types of blocks with high risk of food desert: a block surrounded by multiple redevelopments or a block whose store price has gone up considerably.

Predicted expansion of sand deserts

Predicted expansion of sand deserts

Effect of Land Use/Cover Change on Soil Wind Erosion in the Yellow River Basin since the 1990s

“Ecological conservation and high-quality development of the Yellow River Basin” is one of the fundamental national strategies related to national food security and ecological security in China. Evaluating the impact of land use/cover change (LUCC) on soil erosion is valuable to improving regional ecological environments and sustainable development. This study focused on the Yellow River Basin and used remote sensing data, the soil wind erosion modulus (SWEM) calculated with the revised wind erosion equation (RWEQ), to analyze the impact of regional scale LUCC from 1990 to 2018 on soil wind erosion. The main conclusions are as follows: (1) The total area of cultivated land, grass land, and unused land decreased, with a total reduction of 11,038.86 km²; total areas of forest land and built-up areas increased, increased by 2746.61 and 8356.77 km2, respectively, with differences within the region in these LUCC trends at different periods. From 1990 to 2000, the area of cultivated land increased by 1958.36 km2 and built-up land area increased by 1331.90 km2. The areas of forestland, grass land, water area, and unused land decreased. From 2000 to 2010, the area of cultivated land and grass land decreased by 4553.77 and 2351.39 km², respectively, whereas the areas of forestland and built-up land significantly increased. From 2010 to 2018, the area of cultivated land and grass land continued to decrease, and the area of built-up land continued to increase. (2) Since the 1990s, the SWEM has generally declined (Slope1990–2018 = −0.38 t/(ha·a)). Total amount of wind erosion in 2018 decreased by more than 50% compared with the amount in 1990. During this period, the intensity of wind erosion first increased and then decreased. In terms of the SWEM, 90.63% of the study area showed a decrease. (3) From 1990 to 2018, LUCC reduced the total amount of soil wind erosion by 15.57 million tons. From 1990 to 2000, the conversion of grass land/forest land to cultivated land and the expansion of desert resulted in a significant increase in soil wind erosion. From 2000 to 2018, the amount of soil wind erosion decreased at a rate of about 1.22 million tons/year, and the total amount of soil wind erosion decreased by 17.8921 million tons. During this period, the contribution rate of ecological programs (e.g., conversion of cultivated land to forest land and grass land, ecological engineering construction projects, etc.) to reduction of regional soil wind erosion was 59.13%, indicating that ecological programs have a positive role in reducing soil wind erosion intensity. The sustainable development of the ecological environment of the Yellow River Basin should be continued through strengthening ecological restoration and protection, to further consolidate gains made in this fragile ecosystem. This study provides scientific and technological support and relevant policy recommendations for the sustainable development of the Yellow River ecosystem under global change.

Global desert expansion during the 21st century: Patterns, predictors and signals

AbstractDesert expansion can cause tremendous damage to human wellbeing. However, the process of shifting from the non‐desert state to the desert state, a representation of a system regime shift, remains unclear on a global scale. Clarifying the underpinning patterns, predictors and signals of this process is of great value in advancing our understanding of both ecosystem resilience and sustainable development. Here, we combine the climate classification map and long‐term observational land cover data to assess the global desert distribution and its changes from 2000 to 2019. The identified desert areas covered approximately 7.53% of the global land in the past two decades. Only approximately 16.03% of these deserts showed expanding trends, especially in countries such as Tunisia, Tajikistan, and Peru. After assessing 26 climatic, ecological, and socioeconomic factors that could potentially influence desert expansion rates, vegetation cover diversity was identified as the strongest predictor in both hot and cold deserts, followed by cattle density in hot deserts and desert size in cold deserts. In addition, we also found that pronouncedly high fluctuations in vegetation productivity could serve as a possible signal for desert conversion. Our results provide not only a long‐term overview of current global desert changing patterns but also possible guidance for constraining desert expansion.

Threats and management options of the green belt natural forest, northwest lowlands of Ethiopia

The natural forest located across central Africa from Gambia (West Africa) to Ethiopia (East Africa) is believed to break the expansion of the great Sahara Desert towards the southern and south eastern Africa, as a green belt. However, natural and anthropogenic factors are challenging the existence of the forest. Thus, this study was conducted to investigate the spatio-temporal dynamics, threats and sustainable management options of the green belt forest (GBF) located in Ethiopia. Satellite imagery was used to assess the GBF cover dynamics between the year 1980 and 2020 using ERDAS IMAGINE software. ArcGIS software was used for spatial analysis and mapping. Field observation, focus group discussions, and questionnaire based interview were used to collect the required data and SPSS software was used for analysis. The result showed that farmland increased from 32% (in 1980) to 52% (in 2020), whereas, the GBF cover decreased from 58% (in 1980) to 39% (in 2020), with the overall classification accuracy and kappa coefficient of 86% and 81%, respectively. Re-settlement, large-scale agricultural investment, charcoal production, fuel wood, and road construction were among the important threats causing the GBF reduction. Investors, settlers, migrants, residents and day-workers are agents of the GBF cover reduction. To minimize deforestation and sustainably use the GBF local bylaws, delineating and keeping the GBF from human interferences, building awareness, enrichment plantation, and alternative firewood sources were identified as management options. Therefore, to maintain the GBF and break the expansion of the Sahara Desert, governmental and non-governmental organization and the local community ought to apply the recommended GBF management options.

Factors controlling spatio-temporal variations of sandy deserts during the past 110 Years in Xinjiang, Northwestern China

Xinjiang, northwestern China, has the largest area of sandy desert landscapes in the northern hemisphere mid-latitudes and is known to be subject to so-called sandy desertification. Longer-term records of changes in the distribution of sandy desert landscapes are required to develop a more comprehensive understanding of mechanisms underlying their spatial and temporal dynamics. Here, we integrate a diverse range of data sources, including historical maps, documentary accounts, government statistics, remote sensing data, global climate reanalysis data, and field reconnaissance data, to reconstruct 110 years of spatial variations in sandy desert distribution in Xinjiang. Our results show that, overall, there has been a 22.3% reduction in the area of sandy desert in Xinjiang over the past 110 years. Cross-wavelet and linear regression analyses reveal that vegetation changes are the major determinants of sandy desertification during this period and that, in contrast to previous studies in the region, aeolian factors and human-induced degradation are less important drivers than previously reported. Ecosystem management has markedly constrained sandy desert expansion even against a background of population increase. The suggested comprehensive approach may be useful in improving understanding of sandy desert dynamics and associated desertification forcing mechanisms in arid and semiarid regions globally.

Aeolian sand accumulation and land desertification over the past 1,500 years as revealed by two aeolian dunes in the Beiluhe Basin on interior Qinghai-Tibet Plateau, SW China

As an important region of desertification in China, the Qinghai-Tibetan Plateau (QTP) has attracted great attention. However, the study of land desertification history at the millennia-scale on the interior plateau is grossly inadequate. In a severely and rapidly desertifying area in the Beiluhe Basin on the interior QTP, grain-size distributions, sand particle morphologies, and 7 available optically stimulated luminescence (OSL) ages of sand sediment from two fixed aeolian dunes were obtained by several laboratory tests. Combining these results with plateau paleoclimate and contemporary aeolian sand activities in several adjacent regions, two phases of evident enhanced aeolian sand accumulation corresponding to desert expansion over the past 1500 years in the study region were identified. The first enhanced phase (850–700 a B.P.) might have been closely related to suitable trapping of denser vegetation cover and degradation of permafrost on the QTP as a consequence of warm and wet climates. Reactivation of local older sediments caused by cold and dry climates might have been responsible for the second enhanced phase (1400–1200 a B.P.). Permafrost plays an important role in aeolian sand accumulation and desertification on the QTP. However, expansion (or degradation) of permafrost has not always prevented (or promoted) aeolian desertification development on the QTP since the Last Glaciation Maximum (LGM, 21–14–12 ka B.P.). The effects of permafrost on aeolian desertification are governed by numerous factors such as preceding and current climate conditions, locations of permafrost and aeolian sand activity, and trap conditions due to vegetation and topography.

Modeling of complex ecosystems, extension of deserts and violation of the short water cycle

The large ecosystems (region, country, and planet) have many properties common with complex systems. The main such characteristics include dynamic instability (e.g. weather dependence), weak causality (many possible causes per event) and event driven behavior (especially in arid and semi-arid areas). This paper focuses attention on modeling ecosystems by approaches used for complex systems.When modeling complex ecosystems, we usually encounter the following difficulties: partiality, large amounts of data and uncertainties of conclusions. It can be said that none of the known approaches solves these difficulties perfectly. The most common is the physical approach, sometimes reinforced by statistical procedures. The physical approach to modeling leads to a complicated description of phenomena associated with relatively simple geometry. A complicated description usually requires a large amount of data (measured or simulated) and thus more complicated calculations. If we assume emergences in the ecosystem, a physical approach is not appropriate at all. In the presented article we apply the approach of so-called structural invariants, which has the opposite properties: a simple description of phenomena associated with a more complex geometry (in our case pre geometry). It does not require as much data and calculations are simple. The price paid is a qualitative interpretation of the results, which carries a special type of uncertainty. The structural invariant used in the article is the invariant Matroid and Bases of Matroid (M, BM) in combination with Ramsey graph theory. In addition, the article introduces a calculus that describes the emergent phenomenon using two quantities - the power of the emergent phenomenon and the complexity of the structure that is associated with this phenomenon. The developed method is used for a novel application of modeling the process of desertification of Earth. In this approach, we understand desertification as an emergent evolutionary operation of the Earth's development. In the sequence of two large previous emergences (warming of the Earth about 11,700 years ago and drying of the earth beginning about6000 years ago), the time of possible further emergences related to the “desert expansion” operation is calculated. The second application of the method is the analysis of the operation “violation of Short Water Cycle” in the landscape and its possible contribution to the desertification.