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Ecological vulnerability is one of the core issues in the study of achieving sustainable development and is important for ecological conservation and environmental management, especially for ecologically vulnerable regions. Scientific assessment of ecological vulnerability can improve decision-making capacity and provide appropriate information for sustainable development. The Hexi Corridor is located in the inland northwest of China, and its ecological environment is very fragile. Under the influence of climate change and human activities, the Hexi Corridor is facing a crisis of ecological degradation. Therefore, this paper assessed the influence of various factors on ecological vulnerability, followed the principles of scientificity and data accessibility, and constructed a comprehensive assessment framework to reflect the spatio-temporal characteristics of ecological vulnerability in the Hexi Corridor from three aspects: natural factors, socio-economic factors and human interference factors so as to provide theoretical and practical guidance for regional ecological protection. The results showed that: (1) The ecological vulnerability of the Hexi Corridor was dominated by extreme vulnerability, mainly in the arid desert region, while mildly and lowly vulnerable areas were mainly distributed in the southern Qilian Mountains and the plain oasis region, which was closely related to its physical geography. The index values showed an overall decreasing trend, and the environmental situation was improving from 2000 to 2020. (2) The distribution of ecological vulnerability had obvious directional characteristics, and it gradually decreased from north to south. Moreover, it exhibited a significant positive spatial correlation, and its spatial aggregation pattern was basically consistent with the spatial distribution state. (3) Based on the spatio-temporal patterns of ecological vulnerability, the Hexi Corridor was divided into five zones: ecological core protection zone, integrated ecological monitoring zone, ecological optimization concern zone, ecological restoration management zone and ecological potential governance zone. Different environmental protection policies have been taken for different zones according to its basic conditions. Spatial principal component analysis (SPCA) method was used to analyze the ecological vulnerability factors based on the GIS technology. The partitions of ecological vulnerability for configuration and optimization has been classified and practical application. Geographic detector and national policies were considered for ecological vulnerability driver factors. [ABSTRACT FROM AUTHOR]

In responding to global ecosystem conservation and sustainable social development, numerous ecological restoration projects have been performed in ecologically vulnerable areas around the world, especially in semi-arid areas. Affected by local hydrothermal conditions, whether ecological restoration projects can achieve goals of balanced water-carbon enhancement as well as sustainable development in semi-arid areas is controversial. It is uncertain that to what extent the land use change caused by ecological restoration projects will affect the water-carbon imbalance. This research takes the Bashang Plateau Protection Zone (BPZ), a typical semi-arid area in Hebei Province of China, as a porotype to discover the spatial water-carbon changes and their contributing factors under ecological projects during 2000 to 2020 through root mean square deviation and random forest analysis. Results show: (1) In the past two decades, carbon sequestration in BPZ continued to improve while water conservation decreased significantly. The water-carbon imbalance regions in BPZ increased nearly 6.80 folds, from 338.60 km2 to 2642.38 km2. (2) Precipitation and temperature exerted the most significant impact on the formation of water-carbon imbalance regions, whereas the contribution of land use change could reach 40%, demonstrating that human activities were also strongly responsible for water-carbon imbalance. (3) Ecological restoration pattern of limiting afforestation and agricultural land expansion with priority restoration of grassland is beneficial to achieving water-carbon balance and sustainable goals of ecological restoration in semi-arid regions. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effects of appendages on the maintenance of viability and germination of the diaspores of the three shrubs Calligonum junceum (Fisch. et Mey.) Litv., Atraphaxis pungens (Bieb.) Jaub. et Spach. and Reaumuria soongarica (Pall.) Maxim. that have high potential for restoration of degraded temperate arid regions. It has been hypothesized that appendages on diaspores of A. pungens, C. junceum, and R. soongarica help maintain seed viability during dry storage at room temperatures and during moist storage in soil outdoors, but they inhibit seed germination. Fresh diaspores of each species were tested for germination; and diaspores with and without appendages were stored in moist soil outdoors in Xinjiang Province of northwest China; and dry diaspores at room condition for 4 months. Viability and percentage of diaspores with and without appendages that germinated during burial were determined. After burial or dry storage, diaspores with and without appendages were tested for germination. Regardless of storage condition, appendages had no effect on diaspore viability of C. junceum and A. pungens but significantly reduced mortality of R. soongarica diaspores by 50%. During burial outdoors, appendages inhibited germination of C. junceum diaspores but not of A. pungens; no diaspores of R. soongarica germinated. After burial, appendages inhibited germination of A. pungens diaspores but had no effect on C. junceum. Appendages had no effect on germination of R. soongarica diaspores after storage in both locations. To use these three species for revegetation, it is recommended that appendages should be removed from diaspores of C. junceum and A. pungens before storage and sowing, but appendages should be retained on seeds of R. soongarica. [ABSTRACT FROM AUTHOR]

Drought disasters significantly threaten the stability of terrestrial ecosystems in arid and semi-arid regions. Although the impact of drought on vegetation has been extensively researched, there is still a lack of understanding regarding the ecological impacts of drought on the heterogeneous vegetation in northern China's arid and semi-arid regions. To investigate the spatial patterns of vegetation and differences in response to drought climate, the Normalized Difference Vegetation Index (NDVI) and Standardized Precipitation Evapotranspiration Index (SPEI) were used to determine vegetation characteristics and the seasonal sensitivity of vegetation types to drought response, as well as to identify the factors driving the sensitivity differences. In the study area, 83.1% of the vegetation exhibited a significant positive correlation with the drought index. The maximum correlation coefficient between vegetation and drought was 0.62, demonstrating that the majority of vegetation was influenced by drought. It was observed that different vegetation types responded differently to drought at varying spatial and temporal scales. The main drivers of vegetation response to drought in arid and semi-arid zones were quantified by using the random forest algorithm. The results indicated that climate and soil factors are the primary limiting factors. These findings enhance our comprehension of arid and semi-arid areas, the effect of drought on different plant species, and the factors that affect vegetation's response to drought. [ABSTRACT FROM AUTHOR]

Hot water extractable organic carbon (HWOC), the labile carbon component, is often used to indicate soil organic carbon (SOC) dynamics. Nevertheless, few studies have been carried out in arid climate areas which affects our full understanding of HWOC. Here, we investigated the change in HWOC in the topsoil of different ecosystems in the southern part of the Loess Plateau in the semiarid region of China and compared it with that in other regions. The HWOC concentrations of the study area (0-10 cm) were 0.27 ± 0.12 g C kg−1 and 0.19 ± 0.04 g C kg−1 in the natural and agricultural systems respectively, and the HWOC proportions were 1.38 ± 0.38% and 2.18 ± 0.22%. The HWOC concentration and proportion in the study area were much lower than the reported data in other areas, which may be affected by drought conditions. Irrigation could weaken the difference in HWOC between agricultural systems in different regions. Since HWOC is easily lost due to the impact of the arid climate, the soil carbon balance and carbon sequestration in arid and semiarid areas are relatively unstable, indicating that soil management should be improved in combination with water management. [ABSTRACT FROM AUTHOR]

Semi-arid regions belong to important ecological transitional zones with a high ecosystem vulnerability and sensitivity. In recent years, due to the influence of climate change and human activities, the land covers of semi-arid regions have experienced dramatic changes. Therefore, timely and accurate land cover mapping of semi-arid regions is of great significance. Deep learning has been a hotspot in land cover mapping; however, it requires a large number of labelled samples. To tackle this data-hunger issue, we resolve to a multi-gate semi-supervised learning (SSL) method that could use a huge number of unlabelled samples to improve the classification performance. Specifically, the proposed method consists of a probability gate, an uncertainty gate and a consistency gate, aiming to generate high-quality pseudo-labels from the unlabelled datasets. Experimental results from Zhangbei, China indicate that the proposed method yields a good performance with an overall accuracy of 90.31%, which is 4.31% higher than that of traditional supervised learning (SL) methods. Ablation studies also verify the effectiveness of the gated mechanism in selecting unlabelled data. [ABSTRACT FROM AUTHOR]

The development of the Asian monsoonal climate sparked a latitudinal shift in vegetation zones from the Oligocene to the Miocene. However, little is known about the history of the megathermal floristic response to the geologic events in key regions like subtropical China. Here, a species of Fabaceae, Ormosia cyclocarpa sp. nov., is recognised based on well-preserved fruits from the Miocene of Zhejiang in middle-subtropical China. This species features dehiscent, compressed suborbicular single-seeded pods with an intramarginal vein. Extensive comparisons with extant/fossil fabaceous taxa confidently support the present taxonomic consideration. Considering the extant distribution, diversity centre and regional climate history, the known fossil occurrences in southern China imply that Ormosia extended northwards during the Miocene from probable tropics of origin into subtropical China, where a once broad latitudinal arid zone prevailed throughout much of the Palaeogene. Such a changing phytogeographic pattern across tropical-subtropical China probably resulted from a drastic East Asian climate change around the Oligo-Miocene boundary, and closely coincided with the early-middle Miocene warming. The spreading of Ormosia and other tropical genera (e.g. Dipterocarpus, Shorea, Bauhinia, Dacrycarpus) sharing similar floristic history in subtropical China indicates a palaeotropical and Miocene origin for some clades of the extant East Asian flora. [ABSTRACT FROM AUTHOR]

Soil salinization is one of the main problems hindering the agricultural development in the arid and semi-arid regions. However, many previous studies of soil salinization monitoring failed to consider the impact of irrigation on soil salinity. To explore such impact, we used a UAV with a portable spectrometer to monitor the dynamic change of soil salinity before and after spring irrigation. In this study, 120 soil samples at the surface (0–10 cm) were taken in Shahaoqu Irrigation Area, Inner Mongolia, China, in mid-April (before spring irrigation) and mid-June (after spring irrigation), and the images of the four study zones A, B, C and D in this area were obtained from the UAV system. Based on these images, 25 spectral covariates (6 spectral bands, 16 spectral indices, and 3 two-dimensional indices) were calculated. Then, the sensitive spectral covariates were selected with such different variable selection methods as variable importance in projection (VIP), competitive adaptive reweighted sampling (CARS), and genetic algorithm (GA). Finally, Multiple Linear Regression (MLR) and BP neural network algorithm (BPNN) was used to establish models for soil salinity inversion, based on which salinity maps of the study area were plotted. The results showed that the soil salinity of the study zone A (covered with vegetation) increased while that of the other three zones decreased after the spring irrigation. The general tendency was: the higher the original soil salinity was, the more obvious decrease the soil salinity had after the irrigation. All the three variable selection methods improved the inversion model accuracy, but the GA-BPNN model had the best performance (RP2 = 0.78, RMSEP = 0.16, and RPD = 2.13 before spring irrigation; and RP2 = 0.80, RMSEP = 0.14, and RPD = 2.26 after spring irrigation). It indicated that relatively accurate regional salinity maps could be plotted based on the spectral indices selected by GA and the salinity inversion model built on BPNN. These results have certain reference for soil salinization monitoring and farmland irrigation using UAV multispectral remote sensing. [ABSTRACT FROM AUTHOR]

It is of great practical significance to thoroughly study the environmental changes and conduct desertification assessments of sandy lands to elucidate the formation and recovery mechanism of desertification. The purpose of this study is to evaluate the desertification process and its driving factors accurately and objectively, and compare the differences of desertification process in different areas. We used Moderate Resolution Imaging Spectroradiometer (MODIS) surface albedo (MCD43A3) and leaf area index (LAI) (MCD15A2H) products to calculate the desertification divided index (DDI) to reveal the spatial-temporal variation regularity of the four sandy lands in northern China during 2000–2017 as well as the correlation between desertification and precipitation. The results showed that the total desertification degree of sandy lands in northern China showed a downward trend during the study period. By grading the desertification level, it was found the decline trend of severe desertification and high desertification was relatively significant (p < 0.05). The spatial trend of the desertification level in sandy lands was significantly different, and the decreased area of severe desertification and high desertification in Mu Us sandy land was the largest (−0.042 × 104 km2 yr−1 and −0.052 × 104 km2 yr−1), while the interannual variation of the various desertification levels in Hulun Buir sandy land was small (±0.003 × 104 km2 yr−1). The precipitation and DDI were positively correlated in most areas (p < 0.05). Especially in Mu Us sandy land and Hunshandake sandy land, the proportional area of positive correlation between the precipitation and DDI was more prominent, accounting for 72.9% and 63.7%, respectively. This study had important decision-making significance for the effective management of sandy lands in arid/semiarid areas. [ABSTRACT FROM AUTHOR]