Anthropogenic and climatic drivers of alpine wetland degradation: a multi-scale perspective

Climate change and human activities are the two primary driving factors in the vegetation degradation process, and the assessment of their relative roles in vegetation degradation is important to understand the driving mechanisms of vegetation degradation. In this study, net primary productivity (NPP) was selected as an indicator to distinguish the relative roles of climate change and human activities in vegetation degradation and restoration from 2001 to 2010 in North Xinjiang, China. The potential NPP and the human appropriation of NPP were served as the indicator of the effects of climate change and human activities in vegetation degradation and restoration. The results showed that human activities were the dominant factor that induced vegetation degradation, accounts for 55% (153 720 km2) of the total degradation, whereas 25% (69 336 km2) of the total degradation resulted from climate change; the combination of human activities and climate change was the cause in 20% (55 429 km2) of the total degradation. In contrast, 61% (66 927 km2) of the total vegetation restoration was dominated by human activities and 29% (31 553 km2) was caused by climate change; the areas of vegetation restoration caused by the combination of human activities and climate change were 10 551 km2 (10%). The relative roles of the two factors possessed great spatial heterogeneity in five vegetation types. Climate dominated degradation expansion and human activities dominated vegetation restoration in forest. Both the degradation and restoration were dominated by human activities in grassland. In desert, degradation was dominated by human activities and vegetation restoration by climate. In cropland and crop/natural vegetation mosaic, degradation was dominated by both human activities and climate change and restoration was dominated by human activities. These results demonstrated that human activities played a demonstrably positive role in vegetation restoration, and ecological restoration projects were effective on mitigating vegetation degradation and also promoting restoration in the southern areas of North Xinjiang.

长江黄河源区湿地分布的时空变化及成因分析

Quantitative assessment of the contributions of climate change and human activities on vegetation degradation and restoration in typical ecologically fragile areas of China

Alpine wetland ecosystems, as important carbon sinks and water conservation areas, possess unique ecological functions. Driven by climate change and human activities, the spatial distribution changes in alpine wetlands directly affect the ecosystems and water resource management within a basin. To further refine the evolution processes of different types of alpine wetlands in different zones of a basin, this study combined multiple field surveys, unmanned aerial vehicle (UAV) flights, and high-resolution images. Based on the Google Earth Engine (GEE) cloud platform, we constructed a Random Forest model to identify and extract alpine wetlands in the Shule River Basin over a long-term period from 1987 to 2021. The results indicated that the accuracy of the extraction based on this method exceeded 90%; the main wetland types are marsh, swamp meadow, and river and lake water bodies; and the spatial–temporal distribution of each wetland type has obvious heterogeneity. In total, 90% of the swamp meadows areas were mainly scattered throughout the study area’s section 3700 to 4300 m above sea level (a.s.l.), and 80% of the marshes areas were concentrated in the Dang River source 3200 m above sea level. From 1987 to 2021, the alpine wetland in the study area showed an overall expansion trend. The total area of the wetland increased by 51,451.8 ha and the area increased by 53.5%. However, this expansion mainly occurred in the elevation zone below 4000 m after 2004, and low-altitude marsh wetland primarily dominated the expansion. The analysis of the spatial–temporal heterogeneity of alpine wetlands can provide a scientific basis for the attribution analysis of the change in alpine wetlands in inland water conservation areas, as well as for protection and rational development and utilization, and promote the healthy development of ecological environments in nature reserves.

The impacts of climate changes and human activities on net primary productivity vary across an ecotone zone in Northwest China

Quantifying the variability and changes in phenology and gross primary production (GPP) of alpine wetlands in the Qinghai–Tibetan Plateau under climate change is essential for assessing carbon (C) balance dynamics at regional and global scales. In this study, in situ eddy covariance (EC) flux tower observations and remote sensing data were integrated with a modified, satellite-based vegetation photosynthesis model (VPM) to investigate the variability in climate change, phenology, and GPP of an alpine wetland ecosystem, located in Zoige, southwestern China. Two-year EC data and remote sensing vegetation indices showed that warmer temperatures corresponded to an earlier start date of the growing season, increased GPP, and ecosystem respiration, and hence increased the C sink strength of the alpine wetlands. Twelve-year long-term simulations (2000–2011) showed that: (1) there were significantly increasing trends for the mean annual enhanced vegetation index (EVI), land surface water index (LSWI), and growing season GPP (R2 ≥ 0.59, p < 0.01) at rates of 0.002, 0.11 year−1 and 16.32 g·C·m−2·year−1, respectively, which was in line with the observed warming trend (R2 = 0.54, p = 0.006); (2) the start and end of the vegetation growing season (SOS and EOS) experienced a continuous advancing trend at a rate of 1.61 days·year−1 and a delaying trend at a rate of 1.57 days·year−1 from 2000 to 2011 (p ≤ 0.04), respectively; and (3) with increasing temperature, the advanced SOS and delayed EOS prolonged the wetland’s phenological and photosynthetically active period and, thereby, increased wetland productivity by about 3.7–4.2 g·C·m−2·year−1 per day. Furthermore, our results indicated that warming and the extension of the growing season had positive effects on carbon uptake in this alpine wetland ecosystem.

Evaluation of alpine wetland ecological degradation based on alpine wetland degradation index: A case study in the first meander of the Yellow River

The alpine wetlands on the eastern Qinghai-Tibet Plateau (EQTP) serve as a critical global ecological barrier. Under the dual pressures of climate change and human activities, these wetland systems face environmental challenges such as retrogressive succession, aridification, and desertification. Based on the Google Earth Engine (GEE) cloud computing platform, this study integrates high-resolution imagery, multi-source geoscience datasets, and field survey samples. Object-based image analysis (OBIA), logistic regression, and species distribution models (SDMs) were employed to systematically assess the spatiotemporal differentiation characteristics and key driving factors of alpine wetlands in EQTP. The results indicate that: (1) When applying OBIA classification to alpine wetlands, as image resolution increased from 30 m to 5 m, classification accuracy exhibited an improvement–saturation–fragmentation pattern. At a resolution of 10 m (Scale = 26), marsh wetland structures and spatial distribution characteristics were accurately identified, with a total wetland resource area of 17,454.56 km2. (2) Wetland distribution is driven by multiple factors, including climate (temperature, precipitation), topography (elevation, slope), and human activities (road density, settlement distribution). The best explanatory performance for driving forces was observed at a 500 m spatial scale (AUC = 0.81), confirming that climate factors predominantly govern long-term changes, while human activities significantly influence ecological patterns. (3) During 2021–2040, under a low-emission scenario, the area of highly suitable wetland zones was larger than under a high-emission scenario, with warming causing very high suitability zones to shift toward higher elevations. From 2041 to 2060, as regional warming intensified, the area of excellent suitability wetlands decreased. Between 2081 and 2100, the high-carbon emission scenario increased temperature in the high-altitude central study area, improving wetland suitability. This study proposes a GEE-based OBIA method for estimating alpine wetland resources, integrating logistic regression and SDMs to reveal the spatiotemporal differentiation mechanisms of alpine wetlands. The findings provide an effective technical framework for wetland research on the Qinghai-Tibet Plateau.

Alpine wetlands are critical ecosystems for global carbon (C) cycling and climate change mitigation. Ecological restoration projects for alpine grazing wetlands are urgently needed, especially due to their critical role as carbon (C) sinks. However, the fate of the C pool in alpine wetlands after restoration from grazing remains unclear. In this study, soil samples from both grazed and restored wetlands in Zoige (near Hongyuan County, Sichuan Province, China) were collected to analyze soil organic carbon (SOC) fractions, arbuscular mycorrhizal fungi (AMF), soil properties, and plant biomass. Moreover, the Tea Bag Index (TBI) was applied to assess the initial decomposition rate (k) and stabilization factor (S), providing a novel perspective on SOC dynamics. The results of this research revealed that the mineral-associated organic carbon (MAOC) was 1.40 times higher in restored sites compared to grazed sites, although no significant difference in particulate organic carbon (POC) was detected between the two site types. Furthermore, the increased MAOC after restoration exhibited a significant positive correlation with various parameters including S, C and N content, aboveground biomass, WSOC, AMF diversity, and NH4+. This indicates that restoration significantly increases plant primary production, litter turnover, soil characteristics, and AMF diversity, thereby enhancing the C stabilization capacity of alpine wetland soils.

The vegetation patterns in high-latitude and high-altitude regions (HLAR) of the Northern Hemisphere are undergoing significant changes due to the combined effects of global warming and human activities, leading to increased uncertainties in vegetation phenological assessment. However, previous studies on vegetation phenological changes often relied on long-term time series of remote sensing products for evaluation and lacked comprehensive analysis of driving factors. In this study, we utilized high temporal resolution seamless MODIS products (MODIS-NDVISDC and MODIS-EVI2SDC) to assess the vegetation phenological changes in High-Latitude-Altitude Regions (HLAR) of the Northern Hemisphere. We quantified the differences in vegetation phenology among different land-use types and determined the main driving factors behind vegetation phenological changes. The results showed that the length of the growing season (LOS) derived from MODIS-NDVISDC was 8.9 days longer than that derived from MODIS-EVI2SDC, with an earlier start of the growing season (SOS) by 1.5 days and a later end of the growing season (EOS) by 7.4 days. Among different vegetation types, deciduous needleleaf forests exhibited the fastest LOS extension (p < 0.01), while croplands showed the fastest LOS reduction (p < 0.05). Regarding land-use transitions, the conversion of built-up land to forest and grassland had the longest LOS. In expanding agricultural areas, the LOS of land converted from built-up land to cropland was significantly higher than that of other land conversions. We analyzed human activities and found that as the human footprint gradient increased, the LOS showed a decreasing trend. Among the climate-related factors, the dominant response of phenology to temperature was the strongest in the vegetation greening period. During the vegetation browning period, the temperature control was weakened, and the control of radiation and precipitation was enhanced, accounting for 20–30% of the area, respectively. Finally, we supplement and prove that the highest contributions to vegetation greening in the Northern Hemisphere occurred during the SOS period (May–June) and the EOS period (October). Our study provides a theoretical basis for vegetation phenological assessment under global change. It also offers new insights for land resource management and planning in high-latitude and high-altitude regions.

Insights on the roles of climate and human activities to vegetation degradation and restoration in Beijing-Tianjin sandstorm source region

The Zoige alpine wetland on the eastern edge of the Tibetan Plateau is an important headwater area for the Yellow River Basin. The White and Black Rivers are two major tributaries in the Zoige Basin. However, the alpine wetland has experienced a rapid degradation due to human and other recent environmental changes in the region. The effects of climate variations and human activities on runoff in this region are still unclear. In this study, those changes in runoff were quantified and categorized using the hydrologic sensitivity analysis method and a monthly water balance model. The temperature index-based snow melting submodel was integrated into a monthly water balance model to account for the considerable snow meltwater from the wetland in the summer season. The nonparametric Mann-Kendall test was used to analyze the annual and seasonal climatic trends in the Zoige Basin. Results suggest that during the past 55 years (1957–2011), annual precipitation was significantly decreasing at a rate of −0.978 mm/year while the air temperature and potential evapotranspiration (PET) have increasing trends at the rates of 0.029°C/year and 0.755 mm/year, respectively. Using three change-point detection methods, one change point was detected at 1989 in the annual streamflow series (1960–2011) and was adopted to divide the data set into two study periods—the baseline period (1960–1989) and the human-induced period (1990–2011). The mean annual runoff depth from the White (Black) River in the baseline period was 448.9 mm (151.5 mm), while the mean of the human-induced period decreased by 28% (35%). It was determined that decreases in runoff between the two periods can be attributed to 55% (64%) from climate variations and 45% (36%) from human activities in the White River (Black River). Thus, climatic impact exerted more important influence on runoff decline in the Zoige wetland basin as compared to human activities. This study enhances our understanding of the changes caused by climate variations and runoff (and their contributing factors) in the alpine wetland.

Alpine wetlands play a role in water conservation, climate regulation, carbon sequestration, and biodiversity protection. However, due to the unique geological structure and climate characteristics of alpine areas, climate change is highly likely to have an impact on alpine wetlands and their ecosystems, including the abundance and distribution of local species. This paper focuses on analyzing the composition, quantity, and distribution changes of wetland organisms, including producers, consumers, and decomposers. The research findings indicate that, with the intensification of human activities and climate change such as global warming, despite the emergence of some new wetlands, many natural alpine wetlands on Qinghai-Tibet Plateau are facing shrinkage and are gradually retreating towards higher altitudes, latitudes, and wetter areas, which means the extinction of some plants and the shrinkage of wildlife habitats. Changes in wetland environment, such as drying, resulting from increased temperature and decreased precipitation, have led to a decline in biodiversity and degradation of alpine wetland ecosystems. Despite an overall increase in vegetation cover, wetland degradation has caused changes in plant species diversity and community composition. Climate warming have also affected wildlife migration and the activity of microorganisms. The changes in plateau wetlands are primarily shaped by climate conditions, while human activities act as accelerators, causing significant damage to wetland environments, leading to fragmentation and accelerated degradation. This paper proposes strengthening ecological monitoring and risk assessment in these regions, conducting further research, and promptly implementing necessary restoration measures to reduce the ecological risks caused by these changes.

Water quality determines protist taxonomic and functional group composition in a high-altitude wetland of international importance

Effects of climate change, coal mining and grazing on vegetation dynamics in the mountain permafrost regions