Shrub mortality is accelerating globally, yet the mechanisms and thresholds driving vegetation mortality in dryland shrubs remain insufficiently understood. Caragana korshinskii Kom., a key species for dryland restoration in China, has experienced widespread die-off in recent decades. This study aimed to identify the important drivers of C. korshinskii mortality on the Loess Plateau, China. We surveyed 35C. korshinskii plantation plots (three 30m×30m subplots per sampling plot) across the western Loess Plateau. In each subplot, we measured the plant height, canopy diameter, and basal diameter of 30 randomly selected individuals and recorded the total number of live and dead shrubs to calculate the annual mortality probability (AMP). Environmental factors encompassing climate, soil, topography, and disturbance were compiled for each sampling plot. Spearman's correlation and ridge regression analyses were applied to determine the most driving factors. Piecewise linear models were then used to determine their breakpoints, and partial least squares path model (PLS-PM) was employed to quantify their effects on AMP. The results revealed that AMP exhibited a clear spatial gradient, decreasing from the west to the east across the study area. AMP decreased with increasing mean annual precipitation (MAP) but increased sharply when the MAP fell below 311mm, suggesting a discontinuous response around this statistical breakpoint. Similarly, AMP increased markedly when the mean annual temperature (MAT) exceeded its statistical breakpoint of 9.13°C. Higher total nitrogen (TN) was associated with a gradual decline in AMP, whereas wind speed and soil thickness were not clearly related. PLS-PM confirmed that MAP is the principal direct driving factor, with TN and MAT making secondary contributions. Our findings reveal that MAP is the key environmental driver of C. korshinskii mortality, with the statistical breakpoint (311mm) providing critical insights into vegetation stability and implications for the sustainable management and restoration of dryland ecosystems under climate change.
Dust emission is initiated when the wind friction velocity exceeds a surface-dependent threshold; however, whether low-, moderate-, or high-threshold surfaces contribute most to dust emission, particularly across the Gobi Desert, remains unclear. This study addressed this question by detecting dust emission point sources across southern Mongolia and northern China using nine years (January 2017–May 2025) of high- and moderate-resolution optical satellite imagery from Sentinel-2, Landsat-8/9, and Sentinel-3 through visual interpretation. We estimated effective threshold friction velocities (u*t) from Sentinel-1 C-band synthetic aperture radar (SAR) data and analyzed these values under dry spring conditions and during confirmed dust emission events. Our analysis of 4984 dust emission point sources revealed five major and nine minor dust source regions, primarily associated with lake basins, topographic depressions, mountain foothills, and gully systems. The major dust source regions included the Gaxun Nur Basin, Urad Rear Banner, and Alagxa Left Banner in China and the Ulaan Lake Basin, Orog Lake Basin, and Taatsiin Tsagaan Lake Basin in Mongolia. These regions exhibited moderate effective u*t ranging from 0.50 to 0.95m/s. In contrast, little or no dust emission was detected from mountain ranges characterized by high effective u*t (>1.20m/s) or from major sandy deserts (e.g., the Badain Jaran, Tengger, and Ulan Buh deserts), despite their extremely low effective u*t (<0.20m/s). Limited dust emission was observed in settings with moderate-to-high effective u*t (0.95–1.10m/s), such as mountain foothills and gully systems, and on surfaces with low-to-moderate effective u*t (0.20–0.50m/s). These findings indicated that frequent dust emission is confined to geomorphological settings with moderate effective u*t and active fluvial sediment supply, whereas mountain foothills and gully systems act as secondary, episodic sources because of their relatively high effective u*t. Identifying this moderate effective u*t range for frequent dust emission refines the representation of surface erodibility in dust emission models and highlights priority regions for future field-based measurements of sediment properties.
Sandy vegetation plays a critical role in maintaining ecological balance and combating desertification in arid regions. Accurately elucidating the vegetation dynamics and analyzing how it responds to the impacts of natural and human activity hold vital scientific significance for promoting the sustainable preservation and development of sandy lands. This research focuses on four major sandy lands (Hulun Buir, Mu Us, Horqin, and Otindag) in the typical fragile ecological zones of China, aiming to analyze the vegetation change and identify the contribution of driving factors to vegetation dynamics. Using normalized difference vegetation index (NDVI) data from the Google Earth Engine, we analyzed the spatiotemporal patterns of fractional vegetation cover (FVC) during the period 2000–2020. Furthermore, by integrating the optimal parameter-based geographical detector (OPGD) and structural equation modeling (SEM), we systematically assessed the relationships of natural factors and human activities with FVC changes. Compared with the period 2000–2010, FVC degradation in the Horqin and Mu Us sandy lands decreased by 5.74% and 3.49%, respectively, while FVC improvement increased by 6.12% and 1.24% during the period 2011–2020. Meanwhile, the Hulun Buir Sandy Land showed reductions in both degradation (14.92%) and improvement (0.08%), whereas the Otindag Sandy Land exhibited increased degradation (1.43%) and reduced improvement (0.41%). Climate was the dominant driver of FVC changes in the Hulun Buir and Otindag sandy lands, whereas human activity played a key role in the Horqin and Mu Us sandy lands. Specifically, temperature and precipitation were the key drivers in the Hulunbuir and Otindag sandy lands, while FVC dynamics in the Horqin and Mu Us sandy lands were mainly driven by land use intensity. These findings provide insights into vegetation dynamics and driving mechanisms in sandy land ecosystems, and offer practical implications for ecological management in vulnerable regions.
Understanding scale-dependent plant–plant relationships is essential for revealing population organization and species coexistence in extremely arid ecosystems. In this study, Calligonum mongolicum Turcz., a dominant sand-fixing shrub in mobile dunes of the Gurbantunggut Desert, Northwest China, was selected as the focal species to investigate its intra- and interspecific spatial relationships across multiple scales. Univariate, bivariate, and marked point pattern analyses combined with different null models were applied to characterize spatial patterns between different life stages, survival statuses, individual sizes, and co-occurring shrubs, and to evaluate the potential contributions of habitat heterogeneity and dispersal processes. The results show that the overall population and different life stages of C. mongolicum exhibited significant aggregation under the complete spatial randomness model, whereas the aggregation patterns were largely weakened after accounting for habitat heterogeneity and clustering processes. Adult–juvenile spatial associations showed clear scale dependence, whereas survival-related spatial patterns exhibited limited spatial dependence. After accounting for habitat heterogeneity, no persistent spatial pattern supporting strong adult-mediated facilitation or density-dependent effects was detected across most scales. Interspecific associations between C. mongolicum and co-occurring shrubs (Haloxylon persicum Bunge ex Boiss. & Buhse, Artemisia ordosica Krasch., and Ephedra distachya L.) also exhibited pronounced scale dependence, with positive associations mainly occurring at smaller scales and negative associations emerging at some larger scales. These findings indicate that the spatial organization of dominant desert shrubs is shaped by multiple ecological processes, including habitat heterogeneity, dispersal limitation, and potential biotic interactions, providing new insights into plant coexistence and population maintenance in extremely arid ecosystems.
Climate extremes strongly influence vegetation dynamics in arid and semi-arid regions, but the mechanisms of vegetation responses remain unclear. Using the Yellow River Basin, China as a case study, we integrated 20 extreme climate indices (11 precipitation-related and 9 temperature-related) and a drought index to assess vegetation responses to climate extremes. An integrated framework combining random forest (RF) and structural equation modeling (SEM) was applied to quantify lagged and cumulative effects and separate the relative impacts of climate change and human activities. The results indicated that: (1) vegetation greenness in the basin increased by 0.004/a, with nearly three-quarters of the area showing a statistically significant upward trend; (2) the frequency of extreme precipitation events increased, while extreme high-temperature events became more frequent and intense, and extreme low-temperature events showed little change; (3) drought exhibited the strongest lagged effect on vegetation, lasting up to 6.7 months, whereas individual extreme event mainly induced cumulative effects on normalized difference vegetation index (NDVI); (4) drought and precipitation primarily affected the duration of vegetation growth, while temperature mainly controlled its disturbance intensity, with diurnal temperature range (DTR) and extreme temperature indices being the most important; and (5) climate change and human activities jointly dominated NDVI increases over 89.5% of the vegetated area, highlighting the high sensitivity and spatial heterogeneity of vegetation responses. These findings improve our understanding of vegetation–climate thresholds in dryland ecosystems and provide a transferable framework for environmental impact assessment and adaptive ecosystem management in arid regions.
