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Journal of Resources and Ecology >

2023 , Vol. 14 >Issue 1: 177 - 185

DOI: https://doi.org/10.5814/j.issn.1674-764x.2023.01.017

Ecosystem Assessment

Assessment of Restoration Technology in Typical Ecological Degradation Regions

  • WANG Shuang , 1, 2 ,
  • ZHEN Lin , 1, 2, * ,
  • XIAO Yu 1, 2 ,
  • WEI Yunjie 3 ,
  • HU Yunfeng 1, 2 ,
  • YOU Dongmei 1
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  • 1. Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Science, Beijing 100101, China
  • 2. University of Chinese Academy of Sciences, Beijing 100049, China
  • 3. School of Economics, Beijing Technology and Business University, Beijing 100048, China
*ZHEN Lin, E-mail:

WANG Shuang, E-mail:

Received date: 2021-11-01

  Accepted date: 2022-02-25

  Online published: 2023-01-31

Supported by

The National Natural Science Foundation of China(41977421)

The National Key Research and Development Program of China(2016YFC0503700)

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Abstract

In the face of increasingly severe ecological degradation in the typical fragile ecological regions around the world, many different ecological technologies (ET) have been developed. However, there is still a lack of any comprehensive analysis of these technologies and the effects of their implementation on regional ecological systems, and this largely limits the promotion of the excellent technologies and their applications. Based on the Web of Science core online database and specific literature screening criteria, 3409 papers were selected to summarize and analyze the development trends, research hotspots and regional comparisons of ecological technology effect research. Furthermore, 19 publications from 14 regions were selected to compare and analyze the effects of eight commonly applied ET: shelterbelt, artificial afforestation, water-saving irrigation, terrace, stereo-agriculture, contour tillage, ban/rest/rotational grazing and fallow/no tillage/minimum tillage. The results show four key features: (1) The research on the effect of ecological technology is still in the period of continuous development. (2) “Erosion” is the largest node in the keyword co-occurrence map of ecological technologies effect research, followed by “management”. (3) Most countries pay attention to the studies of “erosion” and “runoff”, although there are differences in research on the effects of ecological technologies in different countries. (4) The same technology could be applied to different regions but the effects varied, and the ecological technologies that have been implemented have generally achieved good restoration effects; however, the improper use of ecological technologies may bring negative consequences. This study provides important support for ecosystem restoration and improvement in the ecologically degraded areas in China and around the world, and it provides a reference for the export and introduction of excellent technologies.

Key words： ecological degradation; ecological technology; development stage; co-occurrence map; comparative analysis

Cite this article

WANG Shuang , ZHEN Lin , XIAO Yu , WEI Yunjie , HU Yunfeng , YOU Dongmei . Assessment of Restoration Technology in Typical Ecological Degradation Regions[J]. Journal of Resources and Ecology, 2023 , 14(1) : 177 -185 . DOI: 10.5814/j.issn.1674-764x.2023.01.017

1 Introdution

Intensive human activities and climate change have caused approximately 60% of global ecosystems to be degraded or deemed unsustainable (Millennium Ecosystem Assessment, 2005). Specific problems such as soil erosion, sandy desertification, karst desertification, and ecosystem degradation have exacerbated the severity of the situation, especially in arid and semi-arid areas (Zhen et al., 2010; Cross et al., 2019). The land area prone to desertification has been estimated to include 57%-65% of the total land area of dryland ecosystems worldwide (Lal and Baker, 1994; Lal, 2004), among them the total area affected by soil erosion, desertification, and karst desertification now constitutes at least one-fourth of the global land area (Lal et al., 2012). Almost 45% of the world’s agricultural land is located on drylands, mainly in Africa and Asia, but also in southern America, and they have been affected by negative land productivity trends which are considerably above global averages. Therefore, ecological degradation is a serious threat to regional ecosystems and sustainable development, and the most severe losses will be in Asia and Africa, where most of the world’s vulnerable populations live. China has some of the most fragile ecosystems in the world, and the land area with fragile ecological conditions accounts for 55% of the total land area (Zhen et al., 2020).
Consequently, various countries around the world have adopted corresponding ecological technologies (hereinafter referred to as “ET”) for managing fragile ecological regions. For example, the United States, Russia, Australia, and other developed countries have initiated many ecological protection projects since the beginning of the last century, with the aim of achieving optimal management for land use, comprehensive management of degraded areas, and promoting natural restoration (Zhen et al., 2010; Waters et al., 2017). China has rich natural resources, complex land use/coverage and natural conditions, coupled with a high level of human disturbance. This has led to the coexistence of different types of ecological degradation with a complex spatial distribution. Consequently, China has one of the most severe levels of erosion in the world (Zhen et al., 2019; Jiang et al., 2021). Since the 1950s, many ecological protection projects have been implemented in China, such as the Three North Shelterbelt Project, the Beijing-Tianjin Sandstorm Source Control Project, the comprehensive management of soil erosion in the Loess Plateau, and the ecological restoration of rocky desertification in the southern karst area. All of those ecological engineering efforts are composed of various ecological technologies. Specifically, since the “The Tenth Five-Year Plan”, 214 core technologies, 64 technology models, and more than 100 technology systems have been developed (Zhen et al., 2016). However, ecological restoration must recognize that most ecosystems are dynamic and hence restoration cannot be based on static attributes; therefore, developing effective and easily measured success criteria is a further important task (Hobbs and Harris, 2001).
It is worth noting that ET cannot be generalized, so it should fully consider the impact of climate change and the future human development direction. Only when the spatial heterogeneity is reflected in ecological restoration can the role and significance of ET be fully brought into play. Only by understanding the effects of different ET, can the typical ecological degradation areas be guided in choosing the ET that are more economical and efficient, have regional adaptability and are easily promoted, so as to save costs, improve the natural resources in ecological degradation areas (Zhen et al., 2019), and provide references for regional sustainable development.
However, due to many factors such as natural conditions, and environmental and system complexity, there is still a lack of understanding of the effects of ET implementation on the regional ecological system and regional differences. This largely limits the promotion of excellent technology and applications, which not only causes a waste of funds and manpower (Zhen et al., 2016), but also obscures the future developmental direction and evolutionary trend of ET. This paper analyzes the developmental stages of ET implementation effects by combining literature review and content analysis, and draws a keyword map based on Citespace to analyze the similarities and differences in research on ET effects in different countries and to clarify the effects of different ET in different countries. This study will provide important support for ecosystem restoration and improvement in ecologically degraded areas in China and throughout the world, provide a reference for the export and introduction of excellent technologies, and lay a foundation for the development of differentiated conservation and restoration schemes according to local conditions, all of which are conducive to the precise development of ecological technologies in the future.

2 Materials and methods

2.1 Data sources

All the papers were obtained from the Web of Science core online database, and the time span of the retrieval was 1900-2021. Considering our research objective to deeply understand the research hotspots, evolution laws and effects of ET, we defined two specific criteria for selecting the papers to be reviewed:
Criterion 1: Papers must assess at least one aspect of soil erosion, sandy desertification, rocky desertification or degraded ecosystem control practice, technology, or approach.
Criterion 2: Papers must assess at least one effect after the application of ET, including ecological, economic and social aspects.
The specific retrieval methods involved several steps. Considering the selectivity and accuracy of the literature, this paper adopted the combination of title, subject, and document type for retrieval, which can effectively eliminate a large number of irrelevant results in the retrieved literature. The search strategy was set to Title = (“benefit” or “impact” or “effect”) and Subject = (“soil erosion control” or “desertification control” or “degraded ecosystem” or “karst restoration\remediation” or “ecological programs” or “ecological rehabilitation technology”) and Language = (English) and Document type = (“Article” or “Review”). Ultimately, 3409 papers were selected, including the 14 most recent articles published in May 2021. The retrieved literature records were downloaded and saved as plain text files in the format of “Full Record and Cited References”, which were then used as the data samples for the analysis in this paper.

2.2 Data processing methods

CiteSpace is a Java application used for literature analysis and visualization in bibliometric analysis, and it is one of the most influential analysis tools. The software can be freely download from the website http://cluster.ischool. drexel.edu/~cchen/CiteSpace/download/, and the 3.9.R8 version was used in this article. This paper aims to explore the effects of ET, so it mainly adopted the co-occurrence network analysis (key words) and cluster analysis functions of the CiteSpace software. In order to meet the requirements for using these functions and refer to the existing research practices (Huang et al., 2020), the software parameters were set as follows: 1) Time Slicing covered 1952-2020, Years Per Slice = 1; 2) Keywords were used as Node Types; 3) In terms of Selection Criteria, this paper selected 80 items with the most frequently cited keywords or the highest frequency of occurrence from each section; and 4) This article selected “Pathfinder” on the Trim Settings to eliminate some redundant connections. Other settings remained as their defaults.
In addition, in order to comparatively analyze ET effectiveness between China and foreign countries, we selected eight commonly applied ET to analyze in this paper, including shelterbelts, artificial afforestation, water-saving irrigation, terraces, stereo-agriculture, contour tillage, ban/rest/rotational grazing and fallow/no tillage/ minimum tillage. Altogether, we reviewed and analyzed 19 papers from 14 regions which had applied those ET to compare their effects.

3 Results

3.1 Stage analysis of the development of ET effect research

The results show that the research on the effects of ET can be divided into three stages (Fig. 1): The initial exploratory period from 1952 to 1990, the rapid development period from 1990 to 2010, and the continuous development period from 2010 to the present. The reason why 1990 became a turning point is that the book Ecological Engineering, which was co-authored by scholars from China, the United States, Canada, Denmark and Japan and edited by Mitsch and Jorgensen (Mitsch and Jorgensen, 1989), was published in the United States in 1989, and it clearly proposed the research object, basic principle and methodology of this field. Since then, ecological engineering has been recognized as an emerging discipline by the international academic community (Yan and Wang, 2001), and research on the effects of ET has also shifted from the initial exploratory period to the rapid development period.
After 2010, the number of papers on the effect of ET increased significantly and this field entered a new stage of continuous development. The reason is that since the 1990s, as the population growth and utilization of resources continued to increase, countries around the world experienced different degrees of ecological environment problems and began to implement a series of ecological engineering/ technologies to deal with the ecological degradation in their respective ecological management problems, so the effect of ET research gradually became a focus. Examples include the Green Dam Project applied in five African countries during 1970-1990, Canada’s Green Program from 1990- 2000, The French Forestry Ecological Engineering applied from 1965 to the present, Social Forest Project in India from 1973 to present, Three-North Shelter Forest Program of China from 1978 to the present, and the “green wall” of Africa which was launched in 2007. These ecological engineering efforts have achieved remarkable results in the control of ecological degradation. For example, since the “green wall” of Africa was launched in 2007, more than 11.4×106 trees have been planted in Senegal and 2.5×104 ha of degraded land has been restored. Throughout the history of ecological control in all countries, ecological engineering is the carrier and ET is the implementation means to carry out comprehensive control, so it has become the essential way to defend against ecological crises and a series of ecological problems. Therefore, the research on the effect of ecological engineering/technology shows a trend of sustainable development, and has a great significance and function.
Fig. 1 Quantitative time series distribution of studies on the effectiveness of ET (1952-2020)

3.2 Keyword co-occurrence analysis in ET effect research

This paper mainly uses the keyword co-occurrence analysis of CiteSpace to draw the keyword co-occurrence map for ET effect research, and identify the main hotspots of current ET effect research (Fig. 2). The keyword “erosion” appeared in 698 cases and is the largest node in the Fig. 2, while it is also closely related to “runoff” (420 cases), “land-use change” (291), “yield” (179), and “carbon sequestration” (97). The node of “management” (400 cases) is large, and its share is closely related to “popularity station” (263), “vegetation” (205), and “productivity” (102). In addition, “tillage” (260 cases), “conservation tillage” (250), and “no-tillage” (227) are all related to tillage research and appeared frequently; “nitrogen” (299 cases), “organic-matter” (219), “infiltration” (150), and “organic-carbon” (120) are related to soil quality research and also appeared frequently. Keywords such as “carbon” (199 cases), “water” (186), and “biodiversity” (117) also become important nodes in the network due to their high frequencies of occurrence. Meanwhile, this research is also closely related to “climate-change” (133 cases).
These important nodes basically cover several main aspects of international ET effect research, that is the study of the types and factors influencing ecological degradation; the study of ET management, vegetation coverage and productivity; the research on individual ET; the influence of ET on soil quality; research on the impact of ET on the atmosphere, water and biodiversity; and research on the relationship between ET and climate change.
Fig. 2 A visualization of the keyword co-occurrence network in research on the effectiveness of ET

Note: Each circular node in the figure represents a keyword, the width of the line represents the frequency of keyword co-occurrence, a larger node represents a higher frequency of keyword occurrence, and a thicker line represents a higher frequency of co-occurrence between two keywords.

3.3 Differences in keyword co-occurrence in various countries

There are differences in the research on ET effects in different countries (Table 1), possibly due to the differences in physical geography (climate, terrain, etc.), development strategies and policies among countries. The high-frequency keywords of ET effects in the top 15 countries in terms of publication papers are listed in Table 1. The results are similar among countries in terms of the effects of ET, and most of them pay attention to the studies of “erosion” and “runoff”, which mainly include quantitative studies of soil erosion, soil loss, runoff and deposition. In addition, most countries pay more attention to soil conditions, including soil quality, soil organic matter, soil structure, soil moisture, soil microbial biomass, the changes and cycles of soil elements, and soil strength. Countries such as China, the United States, Spain, Germany, Italy, Brazil, Japan, India, Canada and France tend to focus on agriculture and farming systems. Due to the rich grassland resources and developed animal husbandry, Australia pays more attention to the research related to pastures; while Ethiopia pays more attention to studies on the effects of individual ET, such as afforestation and stone dikes. In addition, the impact of ET on water resources is also of great concern in Australia, the United Kingdom, Belgium and Ethiopia. Land use changes in the management of ecologically degraded areas is of great concern in Germany, Italy and Japan. Spain, Germany, India and Belgium have conducted many studies on the relationship between ET and climate change. The relationships between ET and productivity and yield have been emphasized in the United States, Australia, Canada, India and France. In addition, there are also unique research hotspots in individual countries, such as the study of “Acidification” in the United States and the study of “Loess Plateau” in China. It is worth noting that the current research on the relationship between ET and water resources in China is relatively weak.
Table 1 Top 15 most productive countries and most frequently used keywords in effectiveness studies of ET
No. Country Number of published papers Keywords
1 China 1483 Soil erosion; Loess Plateau; Soil; Runoff; Afforestation; Vegetation coverage; Biodiversity; Organic carbon
2 USA 1118 Erosion; Conservation tillage; Soil quality; River quality; Runoff; Crop; No-till; Acidification
3 Australia 232 Tillage; Pasture; Grazing management; Soil; Erosion; Yield; Hydrology; Infiltration
4 Spain 201 Runoff; Mediterranean; Soil erosion; Soil carbon; Management; Climate-change; Soil quality; Vegetation
5 Canada 190 Tillage; Productivity; Zero tillage; Reforestation; Conservation tillage; Afforestation; Yield; Soil loss
6 UK 137 Erosion; Runoff; Management; Rehabilitation; Soil conservation; Ecosystem services; Afforestation; Water quality
7 Germany 124 Soil erosion; Soil; Organic matter; Management; Land-use change; Afforestation; Tillage; Climate-change
8 India 117 Zero tillage; Carbon sequestration; Productivity; Tillage; Soil; Climate change; System; Soil erosion
9 Belgium 113 Carbon; Erosion; Water; Biodiversity; Climate-change; Soil quality; Management; Rehabilitation
10 France 110 Soil erosion; Runoff; Herbicide; Soil quality; Mediterranean; Productivity; Conservation agriculture; Yield
11 Italy 97 Afforestation; Tillage; Runoff; Soil Erosion; Land use change; Soil organic matter; Soil management; Sedimentation
12 Netherlands 94 Tillage; Soil erosion; Runoff; Wind erosion; Soil loss; Sediment; Scale; Nutrient loss
13 Brazil 77 Runoff; No-tillage; vegetation; Water; Systems; Soil quality; Soil erosion; Reforestation
14 Japan 73 Soil quality; Soil organic matter; Microbial biomass; Biodynamic farms; Cropping systems; Shifting cultivation; Land-use change; Crop rotation
15 Ethiopia 63 Conservation agriculture; Watershed; Restoration; Drip irrigation; Soil loss; Water conservation; Stone bunds; Soil quality
In general, the ET effect studies in various countries indicate a lot of work mainly around water, soil, biodiversity, climate and humans, among which soil research is the most prominent, that is, soil erosion, runoff, soil loss, soil condition, land use change, etc. This is followed by the study of human activities, such as cultivation, management, productivity, yield, etc. The research on biodiversity, climate and water mainly includes vegetation cover changes, carbon and nitrogen cycles, and the utilization and protection of water resources.

3.4 Comparative analysis of ET effectiveness between China and foreign countries

In order to compare the effects of different ET for restoration, eight commonly applied ET were selected for analysis in this paper: shelterbelts, artificial afforestation, water-saving irrigation, terraces, stereo-agriculture, contour tillage, ban/rest/rotational grazing and fallow/no tillage/minimum tillage. The results show that the same ET could be applied to different regions, but that the effects varied (Table 2); and that the ET which have been implemented have often achieved good restoration effects in the control of ecological degradation, but the improper use of ET will also bring some problems.
The results show that shelterbelt ET can effectively reduce near-surface wind speed, improve vegetation coverage, and produce significant economic benefits (Table 2). For example, the Three-North Shelter Forest Program of China is the world’s largest ecological shelterbelt project, which has not only improved the vegetation coverage of northern sandstorm areas, but also increased the income of agricultural and tourism workers by increasing the number of employed people and expanding employment channels (Cao et al., 2020). Artificial afforestation is a widely used ET, mainly implemented to improve vegetation coverage and soil-water conditions, but improper selection of tree species may have negative consequences. For example, the improper selection of seedlings has led to tree deaths several years after planting, undermining the ecological restoration efforts in some parts of Kenya (Wade et al., 2018). Water-saving irrigation ET is suitable for soil erosion, desertification and degraded ecosystems. It can effectively improve vegetation coverage, biomass and yield, and it can also improve soil quality by increasing the soil water content, thereby reducing soil erosion. After the implementation of water-saving irrigation ET in China, more attention has been paid to the surface vegetation cover and economic benefits. It is worth noting that the irrigation efficiency will directly affect the effect of implementing the ET, such as the severe salinization of farmland in the Amu Darya Delta (Iran) due to excessive or inefficient irrigation water (Chen et al., 2020).
Table 2 Comparison of ET effectiveness between China and foreign countries
ET Effectiveness
China Foreign countries
Shelterbelt Compared with the area that in non-protected fields (11.0 m s-1), the wind speed in a shelterbelt can be reduced to 6.38-7.56 m s-1 (Fan et al., 2010); LAI and NDVI increased by 45.59% and 37.63%, respectively (Hu et al., 2021) Effectively reduce the economic losses from cyclones by half (approximately USD1025) per household compared to areas without mangroves (Ethiopia) (Mukai et al., 2021)
Artificial
afforestation		 The soil water content in the 0-10 cm soil layer increased obviously (increased by 244.90%). The yield per hectare is 1.8-4.3 times that of natural grassland, and the profit margin of hay production is 48% on average (Hu et al., 2020) The highest forest coverage rate is 95% (Kusar and Komac, 2019); In some parts of Kenya, improper selection of seedlings has led to tree death several years after planting, undermining the ecological restoration efforts (Wade et al., 2018)
Water-saving
irrigation		 Soil water storage and water use efficiency increased by 13.7% and 17.2%, respectively, in the 0-200 cm soil layer. The yield can be increased by 54.3% (Zhang et al., 2021) Reduced soil erosion by 0.1 t ha-1 yr-1 and river sediment by 38.03 m3 (Turkey) (Oguz et al., 2019); With 62% of irrigation water wasted before crop production, severe salinization of farmland occurred in the Amu Darya Delta due to excessive or inefficient irrigation water (Iran) (Chen et al., 2020)
Terrace The grain yield and direct economic benefit can be increased by 900 kg ha-1 and 847500 yuan, respectively (Shi et al., 2020) Terraces in Iran are potential areas for rainwater collection with a maximum rainfall that can be collected of 110 million m3 (Toosi et al., 2020); Due to immature terrace ET (e.g., application of acidic fertilizers such as rice straw and weeds), the soil K content is very low in the Philippines which indicates soil acidification (Ducusin et al., 2019)
Stereo-agriculture It can effectively increase nitrogen (14.76%) and phosphorus (15.52%) in surface water and promote vegetation growth; Reduces the potential risk of nitrogen and phosphorus losses in runoff (2.25 kg ha-1) (Wang et al., 2019) Sustainable crop production can be maintained with a 27% increase in rice yield and a 25% increase in protein content without the risk of heavy metal accumulation in soil (Japan) (Phung et al., 2020)
Contour tillage Compared with traditional tillage, the benefits of contour tillage in sediment and flow reduction in China were 35.86% and 49.02%, respectively (Jia et al., 2020) Soil organic matter content increased by 31%-51%, soil enzyme activity increased by 33% in the 15-30 cm soil layer, and soil functional diversity increased by 1.22-1.24 times (India) (Ghosh et al., 2019)
Ban/rest/rotational grazing Carbon storage, water conservation, and soil conservation increased by 45.66×104 t, 9351×104 t, 2091×104 t, respectively (Zhong et al., 2020); Community coverage increased by 6.21%- 7.93%, and aboveground biomass increased by 253.91-325.84 g m-2 (Xu et al., 2020) In Kazakhstan, Kyrgyzstan and Tajikistan, livestock storage decreased by 60.57%, 42.12% and 27.65% from 1991 to 2002, respectively (Chen et al., 2020); In southern Australia, surface vegetation coverage increased by 35%, and the runoff coefficient and sediment runoff decreased by 72% and 125%, respectively (Waters et al., 2019)
Fallow/no tillage/
minimum tillage		 Increase production by at least 50% can be achieved (Chen et al., 2020) Crop yields in south-western Australia increased by 30%-50%, and the return on investment between wheat yields and income benefits in Kazakhstan increased by 28% (Kassam et al., 2012)

4 Discussion

In the face of increasingly severe ecological degradation in typical fragile ecological regions around the world, great efforts have been made in ecological restoration, and numerous ET have been developed, which plays a key role in controlling and mitigating ecological degradation (Zhen et al., 2019). However, systematic research on the effect of ET implementation and its regional differences is still insufficient, and there is a lack of overall categorization of the effects of ET and characterization of the regional differences (Zhen et al., 2010). Based on Citespace and a literature database, this study has delineated the developmental stages and research hotspots of ET effect research in different regions, and used eight applied commonly ET to compare and analyze the effects of different ET for restoration, but they have not been compared precisely. Therefore, the focus of the next step will be to continue carrying out the quantitative analysis of ET implemented in different countries or regions, and to convert the units of the comparative effects into uniform units (for example, the unit of sediment runoff is t ha-1) to make them more comparable. The method of data collection in this study may have ignored some information about ecological restoration because the criteria are relatively subjective, while different criteria might yield different results. However, by sorting out and summarizing the developmental stages of ET effect research, building the keyword co-occurrence map and comparing the effects of domestic and foreign technologies, this study plays a role in the screening of future ecological restoration technologies, and provides a reference basis and theoretical support for the input and output of excellent technologies.
Many studies have implied that ecological restoration is a long-term task and the design, selection and application of ecological technologies must focus on the specific degradation issue, phase and degree of degradation and its drivers, as well as relevant local conditions including economic, cultural, policy and institutional settings (Zhen et al., 2019; Cao et al., 2020). This paper is consistent with existing research in that there are differences in the research on the effects of ET in different countries, and the same technology could be applied to different regions with varying effects. This means that most ecosystems are dynamic and restoration cannot be based on static attributes (Hobbs and Harris, 2001). Meanwhile, there have also been many cases in which ecological restoration failed or performed poorly, and the reasons mainly include a lack of technology or knowledge to support the optimal application and management of the approach, an inadequate climate, or insufficient land, labor, investment, or related resources (Lal et al., 2021). Therefore, considering the relationship between the patterns of future human development and ecological restoration is essential in further research.
The Chinese government has put forward that the core of regional ecological restoration is to repair the relationship between humans and nature, and emphasized that this should be based on the characteristics of the regional land use structure and the main problems make a difference designing in the best strategy. Therefore, it is particularly important to clarify the advantages, limitations and implementation effects of different ecological technologies. This knowledge can guide typical ecological degraded areas in choosing more economical and efficient ecological technologies with regional adaptability and easy popular acceptance, so as to save ecological restoration costs, improve the natural resources in ecologically degraded areas, and ultimately promote the sustainable development of the local economy and ecological environment (Zhen et al., 2016). This paper can provide support for screening the ecological technologies that are suitable for different regions and ecological objectives, and the key technologies that are suitable for major national ecological projects in the future.
It is worth noting that the current research on ecological restoration mostly emphasizes the analysis and evaluation on the basis of the original ecological technology with the goal of “restoring the ecological environment to its original state”, but there is a lack of linking ecological restoration to the future human development pattern, which undermines the design, selection and application of appropriate ecological technologies for the region. With the development of society, nature-based restoration should be given priority, whenever and wherever possible, as the main solution for promoting the construction of an ecological civilization in the world (Zhen et al., 2020). Therefore, follow-up research should fully consider the coordinated development of humans and the environment, rather than blindly pursuing the restoration of the ecological environment to its original state (Hobbs and Norton, 1996). In addition, ecological degradation should be fully restored by new means such as ecological big data, remote sensing, GIS and UAV, so as to provide a realistic basis for ecological protection and restoration in various countries and regions around the world.

5 Conclusions

Based on the bibliometric analysis of a literature database, this study analyzed the developmental trends of ET effect research, used the keyword co-occurrence map to explore the ET effect research hot spots and analyzed such research in different countries. Furthermore, eight commonly applied ET were selected to compare and analyze the effects of different ET for restoration. This analysis led to four main conclusions.
(1) The research on ET effects can be divided into three stages: the initial exploratory period from 1952 to 1990, the rapid development period from 1990 to 2010, and the continuous development period from 2010 to the present.
(2) In the keyword co-occurrence map of ET effect research, “erosion” is the largest node, followed by “management” and then keywords related to tillage research (such as “conservation tillage” and “no-tillage”). The keywords “carbon”, “water”, and “biodiversity” also became important nodes in the network due to their high frequencies of occurrence.
(3) Most countries pay attention to the studies on “erosion” and “runoff”, which mainly include quantitative studies of soil erosion, soil loss, runoff and deposition. However, maybe due to the differences of physical geography, development strategies and policies, there are differences in the research on ET effects in different countries.
(4) The same technology can be applied in different regions but with varying effects, and the ET that have been implemented have generally achieved good restoration effects, although the improper use of ET may bring negative consequences.
Therefore, subsequent research should fully consider the dynamics of ecosystems and the coordinated development of humans and the environment, rather than blindly pursuing the restoration of the ecological environment to its original state based on static attributes.

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