Land Degradation & Development最新文献

China's ecological restoration projects aim to safeguard natural forests, improve the ecological environment, and achieve carbon neutrality. Previous studies at multiple scales have reported that the ecological projects contributed to enhancing carbon sinks. However, the effect of these projects on the carbon sinks has remained uncertain. Thus, we conducted a comparative analysis of nonlinear trends and influencing factors of carbon sink trends in the four ecological restoration project areas. Our findings suggested that the Pearl River shelterbelt program and middle reaches of the Yellow River shelterbelt program areas have experienced significant enhancements in ecosystem carbon sinks. The carbon sink exhibiting monotonically increasing trends and decreasing to increasing trends (positive shifts) accounted for 74.48% and 71.76% in these two shelterbelt program areas, respectively. However, less than half of the carbon sinks (41.38% and 31.80%, respectively) demonstrated monotonically increasing trends or positive shifts in the Yangtze River and Three North Shelterbelt program areas. The high background value of carbon sinks played a crucial role in the monotonically increasing trends of carbon sinks in the four ecological restoration projects. Additionally, in the Pearl River program areas, economic development and urban greening promoted the monotonically increasing trends of carbon sink. In the Yellow River program areas, CO₂ fertilization, appropriate warming, and increased precipitation were helpful to promote the carbon sink with monotonically increasing trends. Moreover, the positive shifts of the carbon sinks were attributed to the implementation of these two ecological restoration projects. However, the low temperature and drought hindered the enhancement of carbon sinks in the Three North program areas, and extreme climate (flood and drought) hindered it in the Yangtze River program areas. These findings can provide a comprehensive evaluation of the effectiveness of ecological restoration projects on terrestrial ecosystems and offer practical guidelines to achieve carbon neutrality.

Environmental and socioeconomic drivers would alter landscapes, bringing various effects with different directions and magnitudes. Demonstrating these driving effects is key to relieving the conflicts between territorial vegetation restoration and regional economic growth. However, the relationship between ecological protection and economic development due to landscape dynamics has not been systematically demonstrated as environment is difficult to quantify by the monetary value. In this article, we explored the changes in gross ecosystem product (GEP) in the Three Gorges (TG) reservoir area and constructed a conceptual framework to explicate its driving mechanism. Our results suggested that topographic, soil, and climatic factors positively impact on GEP through their important effects on vegetation structure, distribution, and succession. Additionally, reforestation policies promote the conversion of farmland and grassland to forestland in the TG reservoir region, which was the main contributor to enhancing GEP. Conversely, socioeconomic factors negatively impact GEP, of which effects were mainly manifested by changes in the proportion of ecological land. Therefore, it is essential to maintain a suitable land use proportion in this region to optimize GEP, and we proposed a landscape restoration program to enhance four ecosystem productions. This article provides a reference for land resource allocation for environmental protection and sustainable development in ecologically fragile areas.

Herbivore grazing affects plant growth and community structure in grasslands. This effect could be directly through foraging and dung/urine return or indirectly through plant–soil feedbacks (PSFs). Addressing the grazing effect on the feedback of plants can explicate the causes of community changes in the grazing system. However, how grazing and PSF interact to affect plant growth remains unclear. Here, we conducted a classic PSF experiment. In the conditioning stage, two native plant species (a grass Bromus inermis and a legume Medicago sativa) were planted in the field with four simulated grazing treatments (ambient, mowing, dung/urine addition, and mowing + dung/urine addition) in a meadow grassland of northern China. In the feedback stage, B. inermis and M. sativa were planted in the soils (both unsterilized and sterilized) from each treatment in the field experiment. Plant biomass of M. sativa showed positive feedback while B. inermis showed negative feedback across all the simulated grazing treatments. Simulated grazing (mowing and dung/urine addition) increased the positive feedback of M. sativa, while decreasing the negative feedback of B. inermis. The addition of dung/urine to the soil was found to have a significantly stronger impact on plant growth feedback compared to the effect of mowing. Dung/urine addition enriches the soil with higher levels of available nitrogen and phosphorus. Our results suggested that legume plants should have positive PSFs while grass should have negative feedback, which might be amplified by grazing because of the dung/urine fertilization effect. Our study improves the understanding of PSF effects on plant growth and community change in grazed grassland.

Nitrogen (N) input affects litter decay and ecosystem functioning. However, the mechanism of litter decay under temporal N-inputs has rarely been observed. Here we show that three-year experimental N-inputs significantly stimulated the rate of litter decay to some extent and then inhibited it with increasing N-inputs. The N-inputs affected the litter's mass loss by directly influencing the temporal stability of aboveground biomass (BS) and diversity while indirectly changing soil pH, C: N ratio, and synergistic interactions of soil, vegetation, and microbial traits. The BS has emerged as a significant regulatory factor for the litter decay of tropical grassland. The outcome of the present study will be helpful in predicting the global feedback of litter decay on the N inputs and the amount of N required for the sustainable functioning of the degraded tropical or similar grasslands.

To investigate the cracking behavior in the evaporation process of the soil surface with biochar as an additive, five experimental groups were established in the natural environment with 0, 12, 60, 120, and 170 g·kg⁻¹ biochar. The results of an investigation on organic matter and aggregations indicate that a high content of biochar can significantly improve the content of organic matter and the amount of soil aggregates. After adding 60 and 170 g·kg⁻¹ biochar, the content of organic matter increased by 19.47% and 84.12%, respectively, and the content of soil aggregates with an average diameter greater than 0.25 mm increased by 16.43% and 38.20%, respectively. The investigation also examines the evaporation and cracking characteristics of soils that contain biochar. The rate of evaporation is approximately a “step” type function with time. The rate of evaporation is observed in three stages: the rapid, decelerating, and final evaporation stages. In the rapid evaporation stage, the initial evaporation rate of the sample that contains biochar is increased on average by 46%. The fractal dimension and cracks rate are decreased by 22.95% and 20.99% with 120 g·kg⁻¹ biochar addition. This means that the increase of soil organic matter after adding biochar plays a crucial role in the stability of aggregates. As a soil conditioner, biochar has the ability to enhance soil water retention capacity and is a sustainable strategy to improve soil properties.

Cropland abandonment (CA) in China worsens the human-land conflict and endangers national food sustainability. Scientifically assessing cropland abandonment risk (CAR) can provide valuable information for early warning and prevention of CA. Despite the extensive literature on the identification, determinants, and consequences of CA, the research on CAR still needs to be improved, especially on a grid scale. Therefore, this study constructed an evaluation indicators system regarding farming conditions, socio-economic, and patch characteristics and used optimal parametric geographical detector and structural equation modeling to assess the CAR in China from 2010 to 2020. The results show China's CAR decreased from west to east. Very high and high CAR areas were in plateaus and mountains in western China. Medium CAR areas were mainly in central and southeastern China. Very low and low CAR areas were mainly in the Sichuan Basin and eastern plains. In 2010, the high and medium CARs accounted for a larger share of the area, 24.814% and 24.759%, respectively. The area share of very low, low, and very high CAR was 19.294%, 19.501%, and 11.633%, respectively. By 2020, both low and very high CARs increased, while the opposite was true for other grades of CAR. Very high CAR increased most evidently in the Loess Plateau. Although high CAR decreased, 43,327 km² of medium CAR was converted to high CAR. CAR's centers of gravity in China were located at the junction of the Loess Plateau and the Huang-Huai-Hai Plain and have shifted to the northwest by 5445.34 m. The findings will assist stakeholders in developing targeted cropland protection strategies to prevent CA and efficiently allocate resources for agricultural production.

Soil and groundwater contamination has always been a global concern. Contaminants are migrated and transformed in the soil and groundwater environments, which in turn pose potential environmental risks to humans. This paper describes four typical contaminants, including heavy metals, polycyclic aromatic hydrocarbons, microplastics, and perfluorinated and polyfluoroalkyl substances. Based on a systematic summary of the sources, hazards, and migration behaviors of these four contaminants, various existing remediation methods are analyzed, and the advantages and disadvantages of different methods are discussed. Finally, the future research prospects of soil and groundwater remediation are described, and the significance of the study of contaminant migration and remediation in the subsurface environment is emphasized. This research can help to provide theoretical and technical support for the study of contaminant migration and removal in soil and groundwater environments, and further improve the removal rate in actual contaminant sites.

Global food security is being threatened by the reduction of high-quality cropland, extreme weather events, and the uncertainty of food supply chains. The globalization of agricultural trade has elevated the diversification of non-grain production (NGP) on cultivated land to a prominent strategy for poverty alleviation in numerous developing nations. Its rapid expansion has engendered a multitude of deleterious consequences on both food security and ecological stability. NGP in China is becoming very common in the process of rapid urbanization, threatening national food security. To better understand the causal mechanisms and enable governments to balance food security and rural development, it is crucial to have a clear understanding of the spatiotemporal dynamics of NGP using remote sensing. Yet knowledge gaps remain concerning how to use remote sensing to track human-dominated or -induced long-term cultivated land changes. Our study proposed a method for detecting the spatiotemporal evolution of NGP based on Landsat time-series data under the Google Earth Engine platform. This approach was proposed by (1) obtaining the union of cultivated lands from multiple landcover products to minimize the cultivated land omission, (2) constructing multi-index dynamic trend rules for 3 representative types of NGP and obtaining results at the pixel level, while adopting the continuous change detection and classification algorithm to Landsat time series (1986–2022) to determine when the most recent change occurred, (3) minimizing the noise by object-oriented land use–land cover classification and mode filter approaches, and (4) mapping the spatiotemporal distribution of NGP. The proposed methodology was tested in Jiashan, located in Zhejiang Province (eastern China), where NGP is widespread. We achieved a high overall accuracy of 95.67% for NGP type detection and an overall accuracy of 85.26% for change detection of time. The results indicated a continued increasing pattern of NGP in Jiashan from 1986 to 2022, with the cumulative percentage of NGP increasing from 0.02% to 20.69%. This study highlights the utilization of time-series data to document essential NGP information for evaluating food security in China and the method is well-suited for large-scale mapping due to its automatic manner.

The groundwater table depth, which is typically shallow in coastal areas, is one of the decisive conditions impacting soil salinization. The influence mechanism of shaollow groundwater table depth change on the evolution of saline-alkali land is still unclear.  In this study, Huanghua City, a coastal city of the Bohai Sea in China, was selected as the research area, and four wells with groundwater table depths ranging from shallow to deep were studied. The groundwater table depth was divided into three levels based on the average groundwater table depth over 30 years, namely shallow, medium, and deep. We analyzed the influence of changes in groundwater table depth in each well on the evolution of saline-alkali land within a radius of 2 km. The results showed that changes in groundwater table depth did not cause conversion between saline-alkali land grades in shallow areas, whereas, in medium-depth areas, changes in groundwater table depth caused conversion among saline-alkali land grades. In deep areas, changes in groundwater table depth did not affect the conversion of moderate/heavy saline-alkali land to non-mild saline-alkali land. The lower limit and upper limit of the groundwater table depth response threshold of saline-alkali land were found to be 1.35 and 3.58 m, respectively, in this coastal area. When the groundwater table depth of saline-alkali land remains lower than 1.35 m for a long period, it will become heavily salinized, one appropriate treatment measure in this instance is to plant saline-alkali tolerant plants beacause improving saline-alkali land by reducing the groundwater table depth is a challenge. When the groundwater table depth of saline-alkali land remains greater than 3.58 m for a long period, changes in groundwater table depth will not influence the gradual reduction of salinization, the saline-alkali land should be properly irrigated and drained to avoid secondary salinization caused by the groundwater level rising to the upper limit of the response threshold. When the water depth in saline-alkali land remains between 1.35 and 3.58 m for a long time, the degree of salinization will change with the change in water depth, the underground water depth can be reduced under a subsurface drainage system in order to treat the saline-alkali land. The research results can provide a scientific basis for improvement of saline-alkali land.

The soil seed bank is one of the most important ecological indicators to evaluate and monitor the ecological restoration process of plant communities. We aimed to analyze the influence of two different ecological restoration techniques on the diversity and floristic composition of the soil seed bank and of standing vegetation, in two 4-year-old areas under forest restoration around bauxite mining, Southeast Brazil. A total of 30 soil samples were collected in each area (SPN—forest restoration by seedling planting in rows and nucleation techniques between planting rows and SP—forest restoration by seedling planting in rows). The samples were transported to a shade house and evaluated for 6 months, where germinated individuals were counted and identified weekly. A floristic census of shrub/tree species was conducted to assess the diversity of standing vegetation. The results indicated that the soil seed banks of the two areas are floristically similar (predominance of pioneer, herbaceous, and native origin species). The two restoration techniques did not differ in their effects on the species composition of the soil seed bank, mainly due to the restoration age. However, when analyzing the standing vegetation, 38 species were recorded in SPN, while only 20 species were in SP. This result demonstrates that nucleation techniques contributed to the increase in species diversity in SPN. We conclude that combining seedling planting in rows with nucleation techniques (topsoil transposition, direct seeding, and artificial perches) can enhance species diversity in standing vegetation, improve forest functionality, and consequently enhance the potential for forest restoration.