Effects of vegetation restoration on distribution characteristics of heavy metals in soil in Karst plateau area of Guizhou

In southwest China, vegetation restoration is widely used in karst rocky desertification control projects. This technology can effectively fix the easily lost soil, gradually restore the plant community and improve soil fertility. However, the change law of soil heavy metals in the restoration process remains to be further studied. Therefore, in this work, Guizhou Caohai Nature Reserve as a typical karst area was taken as the research object to investigate the influence of vegetation restoration technology on repairing soil heavy metal pollution. The spatial distribution characteristics of soil heavy metals (chromium, nickel, arsenic, zinc, lead) before and after vegetation restoration in karst area were studied by comparative analysis and linear stepwise regression analysis. The main influencing factors and spatial distribution characteristics of heavy metals in karst area were further discussed. The results showed that: (1) heavy metals in karst soils are affected by surface vegetation, root exudates, microorganisms and leaching. Only heavy metals nickel (Ni) and lead (Pb) showed the tendency of surface enrichment and bottom precipitation enrichment in non-karst soils. Path analysis suggested that non-metallic soil factors such as soil bulk density (BD), total nitrogen (TN) and ammonium nitrogen (NH₄ ⁺-N) had direct effect on the content of heavy metals in soil. (2) The proportion of 0.25-2 mm aggregates in the surface soil of vegetation restoration belt was more than 40%, and the proportion of surface soil ≤2 mm aggregates in this increased to 83% and 88%, respectively, which could improve the soil structure and properties effectively. (3) Vegetation restoration effectively restored the nutrient elements such as carbon and nitrogen in the soil, and enhanced the soil material circulation. Furthermore the content of heavy metals in the surface soil higher than that in the 10-20 cm soil layer. Plant absorption, biosorption mechanism of microorganisms, coupling of root exudates, dissolution of soil soluble organic carbon and pH make the contents of heavy metals Cr, Ni and Pb in vegetation restoration belt slightly lower than those in karst soil. At the same time, affected by vegetation coverage, residual heavy metals in soil are further leached by surface runoff. Therefore, the content of heavy metals in soil could reduce combined heavy metal enrichment plants for extraction with remediation. This study elucidates the advantages and remedy mechanism of vegetation restoration in the remediation of heavy metal contaminated soils in Caohai area of Guizhou, and this plant activation and enrichment extraction remediation technology would be popularized and applied in the remediation of heavy metal contaminated soils in other karst areas.

Ecological function-oriented vegetation protection and restoration strategies in China's Loess Plateau

Potential natural vegetation (PNV) can provide a reference for vegetation protection and restoration. Previous studies often used PNV patterns as a reference; however, they ignored PNV ecological functions, impeding the establishment of function-oriented vegetation protection and restoration plans. To address this issue, this study used Loess Plateau of China as a case study to propose an ecological function-oriented vegetation protection and restoration framework based on PNV patterns and ecological functions. The results showed that PNV patterns, ecological functions, and their synergistic and trade-off relationships represented distinct spatial differences that would be largely influenced by climate change. This suggested that vegetation protection and restoration should be adapted to climate change. The protection and potential restoration regions for actual forest and grass were detected based on the stable PNV regions. Approximately 34.5%-41.4% of actual forest and 81.2%-82.3% of actual grass should be protected. Further, 13.9%-16.2% of actual forest and 14.7%-15.2% of actual grass have the potential to be restored to grass and forest, respectively, and lastly, the priority regions of forest and grass protection and potential restoration were determined according to a composite ecological functions index. Moreover, forest protection should be prioritized, followed by forest potential restoration, grass potential restoration, and grass protection. These results would be conducive to forest and grass protection and restoration of the Loess Plateau. The proposed framework is applicable to other regions of the world for developing vegetation protection and restoration strategies.

Soil properties under different ecological restoration modes for the quarry in Yanshan mountains of Hebei province, China

The ecological environment of quarry mining area is fragile, and the vegetation restoration cycle is long and difficult, so scientific and appropriate artificial vegetation is of great significance to ecological restoration. The purpose of this study was to evaluate the herbaceous and woody vegetation restoration, including Medicago sativa (Me), artificial miscellaneous grass (Mg), Rhus typhina (Rh), fruit orchard (Or) and Pinus tabulaeformis (Pi), to investigate the soil physicochemical properties and the structure of the microbial communities, and to reveal the correlation between them. The results addressed that Medicago sativa and artificial miscellaneous grass had significant effect on soil remediation, which were conducive to scientific and efficient ecological restoration, and could promote ecological restoration in the damaged ecosystems. While, the modes of Rh and Pi were not suitable for ecological restoration in this study area because they had strong allelopathy. Another arborous restoration mode of Or showed a better improvement effect (including soil nutrients, soil microbial diversity, etc.) than that of Rh and Pi. The findings also indicated that the herbaceous vegetation restoration modes of Me and Mg significantly increased the relative abundance of Proteobacteria, Acidobacteria, Actinobacteria bacteria, Ascomycota and Mortierllomycota fungi, and reduced the relative abundance of Firmicutes bacteria and Basidiomycota fungi. This study also revealed that the trend of bacterial localization in the fruit orchard, artificial miscellaneous grass and Medicago sativa was more obvious. Among many soil abiotic factors, the contents of organic matter, available nitrogen and pH were the most important factors affecting soil microbial community.

An ecological remediation model combining optimal substrate amelioration and native hyperaccumulator colonization in non-ferrous metal tailings pond

The vegetation deterioration and pollution expansion from non-ferrous metal tailings pond have been found in many countries leading to water soil erosion and human health risk. Conventional ecological remediation technologies of mine tailings such as capping were costly and elusive. This study provided an economic and effective model as an alternative by substrate amelioration and vegetation restoration. A field experiment was carried out on a silver tailings pond in southwest China. Tailings substrate was ameliorated by adding organic matter (decomposed chicken manure, DCM), structural conditioner (polyacrylamide, PAM), water-retaining agent (acrylic acid-bentonite water-retaining agent, AAB), and heavy metal immobilizer (biofuel ash, BFA), which were optimized by laboratory experiment. Native heavy metal hyperaccumulator, Bidens pilosa, was colonized. Vegetation coverage and plant height of Bidens pilosa reached about 80% and over 30 cm respectively after 3 months, and the turbidity of tailings leaching solution decreased by 60%. The practice showed that the proportion of available heavy metals in tailings substrate was significantly lower than that in the soil surrounding mining area. Immobilization didn't have stabilization effect on Cd, Zn, and Pb, and As was only 0.002%, phytoremediation had stabilization effect of Cd, Zn, As, and Pb were 2.5-3.5%, 1-2%, 0.25-0.5%, and 0.25-0.75%. Phytoremediation was more effective significantly in controlling heavy metal pollution risk of tailings than immobilization. These results provided a new ecological remediation OSA-NHC model, meaning a combination of optimal substrate amelioration and native hyperaccumulator colonization, which could achieve vegetation restoration and augment heavy metal pollution control in non-ferrous metal tailings pond.

Response of spatio-temporal changes in sediment phosphorus fractions to vegetation restoration in the degraded river-lake ecotone

Phosphorus (P) is an essential element in the ecosystem and the cause of the eutrophication of rivers and lakes. The river-lake ecotone is the ecological buffer zone between rivers and lakes, which can transfer energy and material between terrestrial and aquatic ecosystems. Vegetation restoration of degraded river-lake ecotone can improve the interception capacity of P pollution. However, the effects of different vegetation restoration types on sediment P cycling and its mechanism remain unclear. Therefore, we seasonally measured the P fractions and physicochemical properties of sediments from different restored vegetation (three native species and one invasive species). The results found that vegetation restoration significantly increased the sediment total P and bioavailable P content, which increased the sediment tolerance to P pollution in river-lake ecotone. In addition, the total P content in sediments was highest in summer and autumn, but lower in spring and winter. The total P and bioavailable P contents in surface sediments were the highest. They decreased with increasing depth, suggesting that sediment P assimilation by vegetation restoration and the resulting litter leads to redistribution of P in different seasons and sediment depths. Microbial biomass-P (MBP), total nitrogen (TN), and sediment organic matter (SOM) are the main factors affecting the change of sediment phosphorus fractions. All four plants' maximum biomass and P storage appeared in the autumn. Although the biomass and P storage of the invasive species Alternanthera philoxeroides were lower, the higher bioavailable P content and MBP values of the surface sediments indicated the utilization efficiency of sediment resources. These results suggest that vegetation restoration affects the distribution and circulation of P in river and lake ecosystems, which further enhances the ecological function of the river-lake ecotone and prevents the eutrophication and erosion of water and sediment in the river-lake ecotone.

Vegetation restoration facilitates belowground microbial network complexity and recalcitrant soil organic carbon storage in southwest China karst region

Soil organic carbon (SOC) is an important component of soil ecosystems, and soils are a hotbed of microorganisms playing critical roles in soil functions and ecosystem services. Understanding the interaction between SOC and soil microbial community is of paramount significance in predicting the C fate in soils following vegetation restoration. In this study, high-throughput sequencing of 16S rRNA and ITS genes combined with ¹³C NMR spectroscopy analysis were applied to characterize SOC chemical compounds and elucidate associated soil microbial community. Our results indicated that the contents of SOC, total nitrogen, total phosphorus, microbial biomass carbon and biomass nitrogen, dissolved organic carbon, available potassium, exchangeable calcium and soil moisture increased significantly (P < 0.05) along with the vegetation restoration processes from corn land, grassland, shrub land, to secondary and primary forests. Moreover, the Alkyl C and O-alkyl C abundance increased with vegetation recovery, but no significant differences of Alkyl C were observed in different successional stages. In contrast, the relative abundance of Methoxyl C showed an opposite trend. The dominate phyla Proteobacteria, Acidobacteria, Actinobacteria, Ascomycota and Basidiomycota were strongly related to SOC. And, SOC was found to be the determining factor shaping soil bacterial and fungal communities in vegetation restoration processes. The complexity of soil bacteria and fungi interactions along the vegetation restoration chronosequence increased. Determinism was the major assembly mechanism of bacterial community while stochasticity dominated the assembly of fungal community. Bryobacter, Haliangium, and MND1 were identified as keystone genera in co-occurrence network. Besides, the dominant functional groups across all vegetation restoration processes were mainly involved in soil C and N cycles and linked to the enhanced recalcitrant SOC storage. Our results provide invaluable reference to advance the understanding of microbe response to vegetation restoration processes and highlight the impact of microbes on recalcitrant SOC storage.

Quantitative analysis of vegetation restoration and potential driving factors in a typical subalpine region of the Eastern Tibet Plateau

Vegetation restoration is an essential approach to re-establish the ecological balance in subalpine areas. Changes in vegetation cover represent, to some extent, vegetation growth trends and are the consequence of a complex of different natural factors and human activities. Microtopography influences vegetation growth by affecting the amount of heat and moisture reaching the ground, a role that is more pronounced in subalpine areas. However, little research is concerned with the characteristics and dynamics of vegetation restoration in different microtopography types. The respective importance of the factors driving vegetation changes in subalpine areas is also not clear yet. We used linear regression and the Hurst exponent to analyze the trends in vegetation restoration and sustainability in different microtopography types since 2000, based on Fractional Vegetation Cover (FVC) and identified potential driving factors of vegetation change and their importance by using Geographical Detector. The results show that: (1) The FVC in the region under study has shown an up-trend since 2000, and the rate of increase is 0.26/year (P = 0.028). It would be going from improvement to degradation, continuous decrease or continuous significant decrease in 47.48% of the region, in the future. (2) The mean FVC is in the following order: lower slope (cool), lower slope, lower slope (warm), valley, upper slope (warm), upper slope, valley (narrow), upper slope (cool), cliff, mountain/divide, peak/ridge (warm), peak/ridge, peak/ridge (cool). The lower slope is the microtopographic type with the best vegetation cover, and ridge peak is the most difficult to be afforested. (3) The main factors affecting vegetation restoration in subalpine areas are aspect, microtopographic type, and soil taxonomy great groups. The interaction between multiple factors has a much stronger effect on vegetation cover than single factors, with the effect of temperatures and aspects having the most significant impact on the vegetation cover changes. Natural factors have a greater impact on vegetation restoration than human factors in the study area. The results of this research can contribute a better understanding of the influence of different drivers on the change of vegetation cover, and provide appropriate references and recommendations for vegetation restoration and sustainable development in typical logging areas in subalpine areas.

Different biomass production and soil water patterns between natural and artificial vegetation along an environmental gradient on the Loess Plateau

Loess Plateau (LP) is a vulnerable and climate-sensitive ecoregion. With the implementation of "Grain for Green" project (GGP), the vegetation cover has largely improved, while the contradiction between overconsumption of soil water and sustainability of restored vegetation is increasingly prominent, and further threatening the ecosystem sustainability and socioeconomic development. Understanding the different responses of relations of biomass production and soil water regimes between natural and artificial vegetation along environmental gradient will be crucial for sustainability of restored vegetation on the LP. Here, aboveground biomass (AGB) and soil water content (SWC) of natural and artificial vegetation were measured in steppe, forest-steppe and forest zone from 2008 to 2017 on the Yanhe River catchment. The results showed that artificial vegetation consumed more soil water than natural vegetation in steppe and forest-steppe zone, while it did not over consume soil water in forest zone. The AGB of natural vegetation in forest zone was significantly higher than that in steppe and forest-steppe zone. Steppe zone had serious overload of artificial vegetation (overload ratio: 5.35), while no overload occurred in forest zone. So, we suggest a cessation of artificial vegetation expansion in steppe zone. In steppe zone, planting artificial vegetation increased competition intensity between AGB and SWC, and the relative benefit tended to be AGB, their competition intensity was the highest. In forest zone, the trade-off relationship between AGB and SWC had no significant difference between natural and artificial vegetation, and the competition intensity between the AGB and SWC was the weakest. Optimal vegetation restoration approach would maintain the balance between vegetation restoration and soil water. To obtain social and ecological sustainability on the LP, vegetation suitability and suitable management along different environmental gradients should be considered and identified in the future revegetation project.

Driving factors of ecosystem services and their spatiotemporal change assessment based on land use types in the Loess Plateau

A clear understanding of the driving factors for different ecosystem services (ESs) is quite essential for sustainable ecosystem management. It is important to strengthen research in ESs and social sustainable development to identify the main driving factors of different ESs. This study assessed carbon sequestration (CS), water yield (WY) and soil conservation (SC) from 2000 to 2018 in the Loess Plateau using CASA (The Carnegie-AmesStanford Approach), InVEST (Integrated Valuation of Ecosystem Services and Trade-offs) and RUSLE (Revised Universal Soil Loss Equation) models. The spatial heterogeneity, trade-offs and synergies and driving factors were explored in the whole Loess Plateau. The results showed that the WY, CS and SC had increased from 2000 to 2018. The spatial relationships between WY and SC, SC and CS, and WY and CS were mainly synergistic. Annual mean precipitation (MAP) was the dominant driving factor of WY, while normalized difference vegetation index (NDVI) and slope (SL) had the strongest explanatory power for CS and SC. The LU was the most critical factor affecting the ESs in the different climatic zones. These results could act as a reference for decision-makers on how to control various influencing factors of ESs to improve the local ecology under local conditions.

Revegetation of coal mine degraded arid areas: The role of a native woody species under optimum water and nutrient resources

Ecological restoration of coal mine degraded soils across arid and semi-arid environments worldwide remains particularly challenging. We used a combination of greenhouse and field experiments to assess the potential role of a woody species, Ulmus pumila, in the restoration of degraded soils associated with coal-mining activities in the northwest China. We investigated how various combinations of water-nitrogen-phosphorus (W-N-P) resources affect multiple growth parameters in U. pumila. We found that several plant growth traits significantly improved with W-N applications, regardless of P inputs. Moderate-to-highest W-N-P doses increased net photosynthesis and transpiration rates, water use efficiency, stomatal conductance, chlorophyll and carotenoid contents under greenhouse conditions. A combination of high W together with low N-P applications led to high relative water content and net photosynthetic rates under field conditions. Increasing of N-P doses under W-shortage condition, aided U. pumila to enhance osmotic adjustments by increasing contents of proline and soluble sugar and also boost the activity of superoxide dismutase, peroxidase and catalase in leaf tissues to reduce accumulation of reactive oxygen species and malondialdehyde content in all conditions of greenhouse and field. Our study is the first to assess the optimum W-N-P resources in U. pumila and demonstrate that optimum growth performance could be obtained under W supplements corresponding to 90 mm year-1, N and P at 110 and 45 kg ha-1, respectively, under field condition. These findings can have far reaching implications for vegetation restoration of degraded areas associated with coal-mining activities across arid and semi-arid regions worldwide.

The spatiotemporal change of cropland and its impact on vegetation dynamics in the farming-pastoral ecotone of northern China

Due to the unfavorable soil conditions and water resources, the cropland use pattern in the farming-pastoral ecotone in northern China is complex. The program named "Grain for Green" has accelerated the cropland change. However, the complex cropland and retired cropland are challenging to monitor with remote sensing due to their spatially dispersed and easily confused with spectrally similar land use classes such as nature grasslands and non-cropped fields. Taking farming-pastoral ecotone in the northern foot of the Yinshan Mountains as a case study, we explored a classification approach for complex cropland and retired cropland, which was introduced as a specific land use class by using multi-temporal Landsat TM and OLI images with Google Earth Engine. During 1990-2000, cropland increased with a sharper growth and increased with a slower growth from 2001 to 2010, and then decreased significantly from 2011 to 2019, to lead the cropland area in 2019 was smaller than an area in 1990. We analyzed the spatiotemporal trajectories of retired cropland in 2019 using the Land Use Change Trajectory method to evaluate its source. In our finding, approximately 77% of retired cropland was labelled as cropland before 2019; albeit, not all retired cropland was converted from cropland. Moreover, we qualitatively assessed the vegetation dynamics in the study area by utilizing the long-term NDVI-mean value to reveal that vegetation coverage has shown a continuously increasing trend. It is related to the decline of cropland and the increase of retired cropland at the same rate. Our results highlighted that the "Grain for Green" program had led the vegetation restoration in the farming-pastoral ecotone. Our approach for monitoring cropland and retired cropland can improve the understanding of the driving factors and consequences of these critical land use change trajectories.

Effects of vegetation restoration types on soil nutrients and soil erodibility regulated by slope positions on the Loess Plateau

Soil degradation is significantly increased driven by soil nutrient loss and soil erodibility, thus, hampering the sustainable development of the ecological environment and agricultural production. Vegetation restoration has been widely adopted to prevent soil degradation given its role in improving soil nutrients and soil erodibility. However, it is unclear which vegetation type has the best improving capacity from soil nutrient and soil erodibility perspectives. This study selected three vegetation restoration types of grasslands (GL), shrublands (SL), and forestlands (FL) along the five slope positions (i.e., top, upper, middle, lower, and foot slope), to investigate the effects of vegetation restoration types on soil nutrients and soil erodibility. All vegetation restoration types were restored for 20 years from croplands (CL). We used comprehensive soil nutrient index (CSNI) and comprehensive soil erodibility index (CSEI) formed by a weighted summation method to reflect the effect of vegetation restoration on the improving capacity of soil nutrient and erodibility. The results showed the vegetation types with the highest comprehensive soil quality index (CSQI) at the top, upper, middle, lower and foot slope were FL (1.92), FL (1.98), SL (2.15), FL (2.37) and GL (3.93), respectively. When only one vegetation type was considered on the entire slope, SL (0.59) and FL (0.59) had the highest CSNI, the SL had the lowest CSEI (0.34) and the highest CSQI (1.89). The CSNI was mainly influenced by soil structure stability index (SSSI), sand content, silt + clay particles, and CSEI was controlled by soil organic matter (SOM), macroaggregates and microaggregates. Moreover, the CSQI was influenced by pH, silt and clay content, and biome coverage (BC). The study suggested the SL were advised as the best vegetation restoration type on the whole slope from improving soil nutrients and soil erodibility.

The formation of large macroaggregates induces soil organic carbon sequestration in short-term cropland restoration in a typical karst area

Cropland restoration induces litter and root inputs and promotes the development of biological soil crusts (BSCs), which may promote aggregate formation and soil organic carbon (SOC) sequestration. However, litter, roots and BSCs have not been simultaneously considered when assessing soil aggregate and aggregate-associated SOC fraction responses to cropland restoration in subtropical areas. Here, we measured particulate organic carbon (POC) and mineral-associated organic carbon (MOC) in bulk soils and soil aggregates after 15 years of cropland restoration. Soil samples of cropland (CL) and four cropland restoration types (plantation forest [PF], forage grassland [FG], mixed plantation of forest and forage grassland [FF], and abandoned natural grassland [NG]) from depths of 0-30 cm were collected. Cropland restoration significantly increased SOC and POC in bulk soil at the 0-5 cm depth. However, only in FG did SOC significantly increase at depths of 5-15 cm, and POC significantly increased at depths of 5-30 cm. The large macroaggregate (5-10 mm and 2-5 mm) proportions increased significantly at the 0-15 cm depth after cropland restoration, and FG, FF and NG also increased the 5-10 mm aggregate proportions at the 15-30 cm depth. The SOC sequestration in bulk soil with cropland restoration was attributed to increases in the aggregate-associated organic carbon (AAOC) pool in large macroaggregates, which was mainly attributed to the increased aggregate amount rather than the increased AAOC concentration in large macroaggregates. Our results also indicated that an increase in aggregate-associated particulate organic carbon (AAPOC) led to an increase in AAOC. Variation partitioning indicated that the formation of large macroaggregates was controlled by the litter-moss-root interactive effect in this karst area. FG could be a better short-term cropland restoration strategy, increasing large macroaggregates in deeper soil layers better than the other vegetation types and promoting soil carbon sequestration in deeper soil layers.

Mapping annual land disturbance and reclamation in rare-earth mining disturbance region using temporal trajectory segmentation

Rare-earth mining has caused extensive damage to soil, vegetation, and water, significantly threatening ecosystems. Monitoring environmental disturbance caused by rare-earth mining is necessary to protect the ecological environment. A spatiotemporal remote sensing monitoring method for mining to reclamation processes in a rare-earth mining area using multisource time-series satellite images is described. In this study, the normalized difference vegetation index (NDVI) is used to evaluate the mining impact. Regression analysis is conducted to relate the HJ-1B CCD and Landsat 5/8 data to reduce the NDVI error related to sensor differences between different datasets. The analysis method of NDVI trajectory data of ground objects is proposed, and areas of environmental disturbance caused by rare-earth mining are identified. Pixel-based trajectories were used to reconstruct the temporal evolution of vegetation, and a temporal trajectory segmentation method is established based on the vegetation changes in different disturbance stages. The temporal trajectory of the rare-earth disturbance points is segmented to extract features in each stage to obtain the disturbance year, recovery year, and recovery cycle and evaluate the vegetation recovery after rare-earth mining disturbance. We applied the method to a stack of 20 multitemporal images from 2000 to 2019 to analyze vegetation disturbance due to rare-earth mining and vegetation recovery in the upper reaches of the Guangdong-Hong Kong-Macao Greater Bay Area, China. The results show the following. (1) Mining industry in the study area experienced rapid expansion before 2008, but growth slowed since the policies implemented by the government since 2009 to restrict rare-earth mining. (2) The continuous influence to the land caused by rare-earth mining can last for decades; however, the reclamation activities shorten the recovery cycle of mining land from 5 to 3 years.

Determination of the optimal ecological water conveyance volume for vegetation restoration in an arid inland river basin, northwestern China

Overexploitation of water resources has led to severe ecological degradation and even desertification in some arid inland river basins, northwestern China. To alleviate or restore the degraded vegetation ecosystem, ecological water conveyance (EWC) has become an important and effective measure. Scientific assessment of the impact of EWC on vegetation restoration and determination of the corresponding optimal EWC volume (EWCV) are important to formulate rational ecological water management. In this study, long time series normalized difference vegetation index (NDVI) was used to extract the restored vegetation area in Qingtu Lake area, a terminal lake in inland Shiyang River basin, northwestern China. The relationship between restored vegetation coverage and EWC was explored to determine the optimal EWCV. The restored vegetation area (RVA) increased dramatically in the first five years and became stable from 2016. The time lag of the response of RVA increase to EWC was about 2 years. A bell-shaped function between RVA and groundwater depth was obtained based on the results from Unmanned Aerial Vehicle (UAV) and micro terrain of the lake area. Based on the fitted function, five groundwater depth thresholds were obtained. The optimal groundwater depth in the hydrometric station was 2.91 ± 0.09 m for the maximal RVA (17.08 ± 3.25 km²). A polynomial function between the yearly EWCV and groundwater depth was developed and the EWCV thresholds corresponding to the groundwater depth thresholds were estimated. The optimal EWCV into Qingtu Lake was 2224.4 × 10⁴ m³ for the maximal RVA. The correspondingly optimal EWCV from Hongyashan Reservoir was 3271.4 × 10⁴ m³. The spatial distribution patterns of remotely sensed water surface and NDVI suggested that expanding the water-receiving area of conveyed water was useful to improve the vegetation growth. This study provides a reference for assessing the impact of EWC on vegetation restoration and determining the correspondingly optimal EWCV in arid inland river basins.

The variation of rainfall runoff after vegetation restoration in upper reaches of the Yellow River by the remote sensing technology

In history, the Yellow River has been suffering from endless floods, which has brought great damage or destruction to agriculture, cities, and people's lives and property along the river. In this study, the rainfall and runoff characteristics of the Yellow River upstream (Tangnaihai and Lanzhou) after the vegetation restoration were analyzed. With the government implementation of ecological restoration policy since 1999, the vegetation cover in this area has been greatly improved and the normalized difference vegetation index (NDVI) shows a fluctuating increase, with the maximum value of 0.323 (in 2010) and the minimum value of 0.289 (in 2008). The trend of rainfall from 1948 to 2019 was increased, with an average increase of 1.747mm per 10 years. Before the implementation of ecological policy (1948 to 1999), the rainfall decreased by an average of 0.953mm per 10 years, and then increased by an average of 16.519mm per 10 years (2000 to 2019). From 1998 to 2017, the runoff increased by 11.13×10⁸m³ per 10 years (Tangnaihai) and 30.517×10⁸ m³ (Lanzhou) per 10 years, which was due to the increase in rainfall. Annual sediment discharge and annual average sediment concentration decreased by 0.002×10⁸t and 0.103 kg/m³ per 10 years in Tangnaihai, 0.081×10⁸t and 0.395kg/m³ per 10 years in Lanzhou respectively. The decreasing intensity of Lanzhou station was greater. The sediment runoff modulus of Tangnaihai and Lanzhou decreased by 1.4875 km²·year and 4.9439 km²·year respectively. The increase of vegetation has a decreasing effect on sediment discharge. The implementation of ecological restoration policy reduces the amount of sediment into the Yellow River and plays an important role in the protection of ecological environment in the Yellow River Basin.

Effects of Vegetation Restoration on Soil Enzyme Activity in Copper and Coal Mining Areas

Mining areas are suffering from serious environmental hazards, such as soil erosion, water pollution as well as land degradation. In this study, two types of mining areas in Anhui Province, China-one a copper mining area and the other a coal mining area-were selected to compare the soil properties under different vegetation restoration conditions, which can be generally classified into reclaimed and non-reclaimed areas. Soil catalase and urease activities and soil chemical properties were chosen to be the main indicators of soil quality. Principal component analysis was used to evaluate the overall soil fertility in the copper and coal mining areas. Results showed that in the copper mining area soil catalase activity was between 12.36 and 19.17 μg g^-1 h^-1 and urease activity was between 0.03 and 12.05 μg g^-1 h^-1. And in coal mining area, soil catalase activity was between 3.52 and 9.72 μg g^-1 h^-1 and urease activity was between 2.71 and 10.81 μg g^-1 h^-1. Moreover, soil catalase and urease activities in degraded areas were lower than those in reclaimed areas. Soil catalase activity and soil urease activity were significantly correlated with total potassium and total nitrogen, respectively. Soil quality in land types with vegetation restoration was higher than in non-reclaimed areas and old subsidence areas, while soil quality in the copper mining area was generally higher than in the coal mining area. Thus, the optimum measure in this region to ameliorate these degraded soils is vegetation restoration, which helps not only to improve the environment, but also to enhance soil quality in these degraded lands.

The convergence of species composition along the drawdown zone of the Three Gorges Dam Reservoir, China: implications for restoration

Many rivers across the globe are regulated by dams, resulting in a strong alteration of the plant community composition of the drawdown zone. But, how these changes happen along the drawdown zone is less understood. In this study, a multivariate analysis was used to explore plant composition and similarity along the drawdown zone of the Three Gorges Dam Reservoir (TGDR), China. The dominant plant species, species richness, indicator species, and growth form were compared among the upstream, midstream, and downstream of the TGDR. Moreover, variation partitioning was used to determine the relative importance of environmental factors and spatial factors. Results showed that only a few species contributed the most to the community composition of the study area, and there was an extreme similarity in the plant community composition across the three different river segments. Furthermore, the results of the linear regression model demonstrated a steady declining trend in species richness along the drawdown zone, with the lowest species richness in the downstream segment. In addition, variation partitioning revealed 11% and 8% of the species composition change under environmental and spatial factors, respectively. Our results suggested that the dam impoundment led to the convergence of species composition along the drawdown zone of the TGDR, and environmental filtering and dispersal limitation played an imperative role in shaping species composition. The study highlighted the importance of restoration activities in overcoming the barriers of seed dispersal and seedling establishment in the degraded drawdown zone ecosystem of the TGDR.

Identifying vegetation restoration effectiveness and driving factors on different micro-topographic types of hilly Loess Plateau: From the perspective of ecological resilience

Vegetation restoration is an important way to improve the sustainability of the ecosystem in the hilly Loess Plateau. The variation of vegetation coverage, caused by the combined effects of meteorological factors and human activities, reflects the succession trend of regional ecosystems. Given the complexity and the diversity of landform in the hilly Loess Plateau, vegetation restoration is more affected by topographic factors. Nevertheless, few studies have considered the characteristics and trends of vegetation restoration under different micro-topographic types in the long-time series. From the perspective of ecological resilience based on the fractional vegetation cover (FVC), the trend, the hurst exponent, and the geographical spatial research were used to analyze the variation and future sustainability of vegetation restoration on different micro-topographic types for 20 years. Besides, the spatial autocorrelation, principal component analysis (PCA) and geographically weighted regression (GWR) were applied to identify the driving factors of vegetation restoration. The results showed: (1) the average of the overall regional vegetation coverage was 61.32%, and only 0.95% of the regional vegetation was degraded in the past 20 years. However, in the future, 69.87% of the area would be degraded from improvement, and 0.52% would be significantly decreased; (2) the vegetation coverage in descending order was as follows: ridge area with shady and steep slope, gully area with shady and steep slope, ridge area with sunny and steep slope, gully area with sunny and steep slope, gully area with shady and gentle slope, ridge area with shady and gentle slope, ridge area with sunny and gentle slope, gully area with sunny and gentle slope, valley area; (3) the difference of vegetation degradation among micro-topography was remarkable, and the valley area and gully area with sunny and steep slope have the greatest decrease; (4) the primary factors affecting vegetation restoration in the hilly Loess Plateau were temperature, moisture, soil quality, and social economical condition, and the dominant factors were various under different micro-topographic types and villages. Therefore, it is necessary to adjust ecological engineering measures by comprehensively considering the regional differences among dominant factors of vegetation restoration.

C4 herbs dominate the reservoir flood area of the Three Gorges Reservoir

Dam operations can dramatically degenerate riparian vegetation. To improve the restoration practices of reservoir riparian vegetation, it is important to understand which and how a dominant species physiologically and ecologically maintain high fitness in this type of ecosystems. We explored the compositional change of riparian plants during the long-term flood-dry-flood cycle in the reservoir flood area (RFA) of the Three Gorges Reservoir Area (TGRA), China. In total 769 vascular plant species (belonging to 415 genera in 122 families) existed in the study area before damming (prior to 2006, i.e. the natural riparian zone). Following damming (2008-2018), plant species diversity rapidly declined, with only 51 species identified in 2018 (45 genera in 22 families). Before damming, perennial herbs, annual herbs and shrubs co-dominated the study area. After damming, the proportion of shrubs decreased significantly, and the proportion of annuals to total plants increased by 20%. Alien invasive species proportion increased from 5% to 18%. Notably, the proportion of C₄ species increased significantly from 7% to 31%. Ten of the 16 dominant species in RFA since 2015 were C₄ Poaceae species. Our study indicates that dam construction could cause severe biodiversity loss of riparian plants and draw alien species invasion. Besides, C₄ herbs would dominate the RFA. A higher photosynthetic rate could help C₄ plants grow faster to cope with the nitrogen deficiency and short growth cycles in RFA. Hence, screening C₄ herbs for vegetation restoration might aid in maintaining biodiversity and ecosystem functions in flood-dry-flood reservoir flood areas.

Spatiotemporal tradeoffs and synergies in vegetation vitality and poverty transition in rocky desertification area

Vegetation recovery and poverty alleviation are critical problems in the karst national designed poor counties (NPDC) in southwest China. However, little information is available about the relationship between poverty and vegetation dynamics in these areas. In this study, we used remote sensing and statistical datasets from 2000 to 2015 to identify the relations between vegetation dynamics and poverty among the NPDC in southwest rocky desertification areas. We estimated the vegetation dynamics using the Normalized Difference Vegetation Index and poverty with the rural per capita net income. Local indicator of spatial association and the space-time transition type of poverty were applied to identify spatial patterns of the poverty spatial distribution relationship and transition. Also, poverty, natural and ecological governance factors were assessed using the Geo-detector method to uncover the driving factors of karst vegetation. The results showed that vegetation increased significantly (p < 0.05) in karst NPDC (82.82%) and rocky desertification control counties (78.77%). The karst NPDC was significantly clustered. The hot spots of rural per capita net income changed from west and north (2000) to only north (2015) and cold spots changed from east and south (2000) to only south (2015). The rural per capita net income spatiotemporal transition was higher in 2000 than in 2015. We found a weak synergy between vegetation change and poverty type transition in 42.86% of the browning counties, 45.45% in the slowly greening counties, and 43.65% in stable greening counties. However, 57.50% of counties in the quick greening counties showed a tradeoff relationship with the poverty type transition. The rocky desertification rate and ecological engineering measures affected vegetation dynamics importantly. The results will help decision-makers to understand the interdependence between vegetation and poverty. This will contribute to better policies formulation to tackle poverty in the karst rocky desertification area.

Influence of the invasive shrub Nicotiana glauca Graham on the plant seed bank in various locations in Taif region, western of Saudi Arabia

Invasive species have been considered as one of the most serious threats to the biodiversity of various ecosystems, particularly in arid regions. The present study aimed to assess the influence of the invasive shrub Nicotiana glauca on the biodiversity of different habitats in Taif region, Saudi Arabia as well as to determine the highest habitat with seed bank of N. glauca. Soil samples were collected from three locations (Alwaht, Ash-shafa, and Ar Ruddaf), invaded with N. glauca, and analyzed for the soil seed bank. A soil seed experiment was designed in a greenhouse, whereby emerged plant seedlings were left to grow for three months and identified as well as the species density and biodiversity were assessed under and outside the canopy of N. glauca. Also, the floristic composition, life forms, and chorotype spectra of the plant species of the seed bank were analyzed. A total of 42 species, belonging to 23 families, were recorded in the soil seed bank. Asteraceae, Poaceae, and Cyperaceae were the major families (42.9%). The life form spectra of the recorded species were dominated by Therophytes (59.5%). Chorotype spectra analysis revealed that Mediterranean, Saharo-Arabian, and Irano-Turanian were the most represented elements. The species richness and evenness were higher outside the canopy, which indicates a negative effect of the invasive shrub N. glauca on the plant biodiversity in the study area, particularly in Ar Ruddaf location. This could be attributed to the competition or allelopathic effect of N. glauca. In contrast, the density of N. glauca seeds was higher under the canopy compared to outside. The soil nutrients and moisture under the canopy were higher than outside canopy. The present study provides a deeper understanding of the most susceptible habitats or communities to the invasion by N. glauca and thereby open the challenge toward control of this noxious plant and vegetation restoration.

Storm runoff generation in headwater catchments on the Chinese Loess Plateau after long-term vegetation rehabilitation

Storm runoff is important for maintaining surface water resources, while this function is significantly affected by land use and land cover changes, e.g., afforestation and reforestation. The Chinese Loess Plateau (CLP) has undergone large-scale vegetation rehabilitation, especially afforestation over the past 20 years. We hypothesize that afforestation has profoundly changed the amounts and mechanisms of storm runoff generation in headwater catchments on the CLP. To test this hypothesis, rainfall, soil moisture, and streamflow were monitored in a grass catchment and an adjacent forest catchment for two consecutive years. The objective of this study was to elucidate the varied mechanisms of storm runoff generation in these two contrasting revegetated catchments. Results showed that (1) average runoff coefficient in the grassland catchment (0.042) was approximately ten times higher than that in the forestland catchment (0.004), confirming the impact of catchment afforestation on the suppression of storm runoff generation. (2) Peak rainfall intensity was the first-order control of the runoff coefficient in the grassland catchment, but not in the forestland catchment. (3) Threshold values for antecedent soil moisture (~18%) and the sum of antecedent soil moisture index and event precipitation (~210 mm) were identified in the grassland catchment, above which storm runoff significantly increased. (4) Two extraordinary high runoff coefficient events were observed in the grassland catchment, one due to high peak rainfall intensity and strong surface runoff and the other due to high rainfall amount and high antecedent soil moisture. We conclude that long-term afforestation has changed the mechanisms and patterns of storm runoff generation, and different conditions of rainfall intensity, rainfall amount and antecedent soil moisture determined the hydrological connectivity between the upper hillslope and downhill gully in the catchment. This study deepens our understanding of the mechanisms and thresholds of storm runoff generation in headwater catchments on the CLP.

Effects of revegetation on climate in the Mu Us Sandy Land of China

The ecological environment in China's arid and semi-arid regions has been improving over the past few decades. Using the Mu Us Sandy Land (MUSL) as a case study, we examine the consequent climate feedbacks and the impacts of revegetation on regional climate by incorporating high-resolution remote-sensing vegetation data into the WRF-Noah model. From 2001 to 2010, although a small portion of the grassland was degraded in MUSL, vegetation overall improved, with green fraction and leaf area index increased and surface albedo decreased. The model simulation suggests a cooling of the near-surface temperature by 0.12-0.32 °C on average and up to >0.5 °C in summer, with a reduction in nighttime minimum of 0.15-0.46 °C and in daytime maximum of <0.13 °C. The cooling is accompanied by a slight increase in 2-m air humidity. The near-surface cooling and wetting are induced by revegetation-enhanced evapotranspiration, but they have insignificant effect on the local precipitation. The results of this study imply that while revegetation has positive effects on the ecological systems in MUSL, it bears the cost of an increase in evapotranspiration of 51 mm per summer, which may exacerbate the water shortages in the region.

Loess Plateau: from degradation to restoration

United Nations established 2021-2030 as the decade for ecosystem restoration and "prevent, halt and reverse the degradation of ecosystems worldwide". Ecosystem and land degradation are a global phenomenon. As a consequence of land degradation, in the late 1990s, the "Grain for Green Program" (GFGP) was established in Loess Plateau (China). It converted slope farmlands to forest or grassland over the, resulting in a visible "greening" trend. Other effects of GFGP on soil properties, land production, hydrological conditions, ecosystem services, and policy implications are the topics of this Special Issue. This Special Issue includes 17 contributions that cover recent research carried out in Loess Plateau in the mentioned topics at different spatial and temporal scales. The collection of papers presented in this Special Issue discusses critical issues in vegetation restoration and sustainable land management in the region. This Special Issue will contribute to United Nations strategy for ecosystems restoration.