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Review

Knowledge Mapping Analysis of Karst Rocky Desertification Vegetation Restoration in Southwest China: A Study Based on Web of Science Literature

by
Xiaxia Lu
1,
Maoyin Sheng
1,2,* and
Mengxia Luo
1
1
Institute of Karst Research, Guizhou Normal University, Guiyang 550001, China
2
National Engineering Research Center for Karst Rocky Desertification Control, Guizhou Normal University, Guiyang 550001, China
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(10), 2235; https://doi.org/10.3390/agronomy14102235
Submission received: 19 August 2024 / Revised: 20 September 2024 / Accepted: 25 September 2024 / Published: 27 September 2024
(This article belongs to the Section Agricultural Biosystem and Biological Engineering)
Browse Figures
Versions Notes

Abstract

:
Karst rocky desertification (KRD) is a serious ecological and environmental issue, hindering the sustainable socio-economic development of the karst area. To scientifically control this issue, lots of studies on KRD vegetation restoration have been conducted in the past few decades. In the present study, a systematic review of the research progress and future trends in KRD vegetation restoration was conducted. The results showed the following: (1) Studies on KRD vegetation restoration began in the 1990s and could be divided into the four following stages: germination (1993–2002), initial development (2003–2010), steady growth (2011–2016), and rapid growth (2017–2023); (2) research hot topics included theoretical implications, vegetation restoration strategies and technologies, ecological responses to the KRD vegetation restoration, and the coupling of vegetation restoration with landscape resource enhancement; (3) the research frontiers were as follows: the classification and restoration effectiveness of KRD vegetation types, the impacts of KRD vegetation restoration on soil microorganisms and soil erosion, the influences of ecological engineering and land use on KRD vegetation restoration, and the relationships between KRD vegetation restorations and karst ecosystem structural functions. Finally, research prospects were proposed from the research methods, perspectives, content, and shortcomings. This study provided valuable references for in-depth research in the field of KRD vegetation restoration.

1. Introduction

Karst rocky desertification (KRD) is an important ecological and environmental issue, threatening the sustainable development of the regional socio-economy [1]. As a unique form of land desertification, KRD is characterized by the loss of surface vegetation and soil cover, leading to severe soil erosion, the extensive exposure of bedrock, decreased soil fertility, and a landscape resembling desertification [2,3]. Karst landforms are widely distributed around the world. The global karst area is approximately 22 million square kilometers, accounting for about 15% of the total land area [4]. China is one of the main distribution areas of karst landforms. Southwest China is one of the world’s three major concentrated and contiguous distribution karst areas [4]. The region has the largest area of exposed carbonate rocks, the most developed karst, and severe rocky desertification. Rocky desertification significantly threatens the living space of the people in this region, and is becoming the most serious ecological problem constraining the development of the area [5,6].
KRD control has been a part of the special ecological construction and protection project of Chinese government since 2008, which has achieved great success in increasing vegetation cover [6]. Compared to the situation in 1982, the vegetation cover of global terrestrial ecosystems has increased by 7.1% [7]. One of the largest increases in global vegetation biomass occurred in southwest China, where 4% of the global vegetation greening over the past two decades was located [8]. Recent global-scale evidence suggests that the direct human impact on global greening is 60%, including grazing, deforestation and policy measures [9,10]. A large number of studies have shown the trend in vegetation greening in the KRD areas in southwest China in the past 20 years, and pointed out that the vegetation greening in the KRD areas in southwest China is attributed to the afforestation and protection of natural forests [11,12,13]. In recent decades, the dramatic change in land-use type caused by ecological restoration projects is considered to be the driving force of vegetation greening in KRD areas in southwest China [14,15]. In addition, many studies have investigated the effects of climate on vegetation greening in KRD areas in southwest China. Due to the special geographical conditions of KRD areas in southwest China, research on the limiting factors of vegetation restoration has attracted extensive attention. Research in related fields has shifted focus from the formation mechanisms and ecological characteristics of karst to the vegetation restoration and ecological reconstruction of rocky desertification [16,17,18]. In recent years, karst rocky desertification has gradually become a research hotspot, with a significant increase in scientific research achievements.
Currently, a large number of studies have been conducted on the evolution process and law of rocky desertification, the plant distribution and nutrient cycling, the strategy of biology adaptation, the mechanism of productivity maintenance, and the adaptive rehabilitation of plant vegetation in KRD ecosystems [9,19,20,21,22]. The academic community has conducted extensive research on KRD vegetation restoration and achieved fruitful results [15,16,17]. Summarizing existing research results in a timely manner is of great significance for clarifying scientific research directions and guiding activities in rocky desertification vegetation restoration. Although some scholars have reviewed the results of KRD vegetation restoration from multiple levels, dimensions, and perspectives [18,19,20,21,22], quantitative reviews in this field are lacking. Innovative aspects of research include the selection of sample quantity and types, time span, perspectives on research content, research methods, and future prospects.
This article quantitatively analyzes a large amount of English literature on karst vegetation restoration in the Web of Science (WOS) database, transforming it into visual images. By systematically reviewing its development history and exploring its frontiers, combined with the current global ecological and environmental development and sustainable development, this article aims to provide valuable references for further studies on KRD vegetation restoration, and is of great significance for scientific KRD control.

2. Materials and Methods

2.1. Data Source and Processing

To ensure the authenticity, universality, and authority of the research data source, we selected the Web of Science journal articles, which are relatively authoritative in the field of scientific research. We conducted searches using keywords such as “karst + vegetation restoration”, “karst rocky desertification + vegetation restoration”, and “karst rocky desertification + vegetation restoration technology”. The data collection period was set from 1993 to 2023, with data retrieval ending on 30 September 2023. Based on the search criteria shown in Table 1, we initially obtained 752 literature sources. After reviewing the titles, abstracts, and keywords of the papers, we selected the initial literature data and then conducted a second round of screening to remove papers that were clearly irrelevant based on the research contents. Finally, a total of 739 papers were obtained.

2.2. Research Methods and Tools

Visualization maps and bibliometric analysis are new methods for scientific quantification research, developed in recent years. Currently, there are various visualization tools available, including Cite Space, VOS viewer, Net Draw, Hist Cite, and Bib Excel. Among them, Cite Space and VOS viewer are well-known for their excellent visualization effects and extensive data analysis capabilities [23,24]. VOS viewer is often more accurate in terms of author, institution, journal, and literature co-citation than Cite Space [25], but Cite Space can display the evolution and panorama of research fields through a timeline view. Therefore, this study utilizes these two software tools of Cite Space 6.3.R1 (Radsell University, Philadelphia, PA, USA) and VOS viewer 1.6.19.0 (Leiden University, Leiden, The Netherlands), combining bibliometric analysis, visualization maps, and content analysis methods to explore the spatiotemporal distribution and research frontier trends in the field of KRD vegetation restoration over the past 30 years, and to summarize the current research progress in KRD vegetation restoration.

2.3. Analysis Procedure

This study is divided into several steps, as shown in Figure 1: (1) Statistical analysis, including cluster analysis, time-series analysis and descriptive statistical analysis, used to process and analyze the relevant data and content of KRD vegetation restoration. The statistical characteristics can show that there is a research basis for the study of KRD vegetation restoration. (2) Collaborative analysis, including regional and author collaborative network analysis. The collaborative network reveals the correlations among the studies on KRD vegetation restorations. (3) Co-citation analysis, including journals, references and author co-citation network analysis, reflecting the research progress in the field of KRD vegetation restoration. (4) Hotspot analysis: a keyword co-occurrence network can reveal the potential hotspots and trends in KRD vegetation restoration in the future. (5) Constructing a comprehensive knowledge framework can help scholars quickly understand the comprehensive and systematic theoretical knowledge and logical structure of KRD vegetation restoration studies. The software Process On (https://www.processon.com/) (accessed on 15 September 2024) was used to draw the graphs. The data involved in the analysis come mainly from the top five most intense data volumes in each analysis graph.

3. Results

3.1. Temporal Distribution of the KRD Vegetation Restoration Studies

The temporal distribution of research findings reflects the development speed and stage changes in the field to a certain extent, and it is of significance for predicting development trends and studying dynamics [26,27]. Therefore, this study conducted an analysis of the temporal distribution of KRD vegetation restoration. As shown in Figure 2, the number of research achievements in KRD vegetation restoration has generally shown a pattern of growth over the past 30 years. The number of funding projects and the level of funding in China have steadily increased over the past decade, indicating that national attention to KRD vegetation restoration has reached a new high [15]. Additionally, research achievements and funding were mainly concentrated in the years 2011–2016, and the strong support from national funding projects has greatly promoted the restoration of KRD vegetation. Overall, the field has gone through roughly four stages, detailed as follows: germination (1993–2002), initial development (2003–2010), steady growth (2011–2016), and rapid growth (2017–2023). In the context of the gradual deepening and slowing down of research on KRD, systematically summarizing the development process related to vegetation restoration provides a good guiding role for subsequent research.
The evolution of the research context can better reveal the development and evolution of a field [22]. As shown in Table 2, although the restoration of KRD vegetation began as early as 1993, it did not receive significant attention from the academic community until after 2013. By combining stage characteristic analysis, the research context of KRD vegetation restoration can be outlined as follows.

3.1.1. Germination Period (1993–2002)

During this stage, the related concepts and explorations were in the initial stages, resulting in relatively few research outcomes. The high-frequency keywords during this period mainly included vegetation, forest, diversity, biology, and soil organic carbon, indicating that the exploration of KRD vegetation restoration began with keywords such as vegetation, forest, diversity, and soil organic carbon. However, the research content was still relatively limited, and the richness and depth of the research needed further development [14].

3.1.2. Initial Development (2003–2010)

In this stage, the research topic entered the academic domain, and the number of research outcomes showed a growing trend. The research content and scope were relatively diverse and rich. The research mainly involved patterns, trends, biodiversity, restoration, water, protection, communities, etc. [12,14]. Compared to the previous stage, the related research topics became more diverse and were the subjects of extensive discussions from scholars in various research fields, laying the foundation for continued in-depth research. Although biodiversity, water resources, plant communities, and protection were already considered during this period, there was still a need for further comprehensive development in the specific methods and theoretical aspects of KRD vegetation restoration [14,20].

3.1.3. Steady Growth (2011–2016)

This stage saw relatively mature research, with increasing research interest, a considerable number of research outcomes, and the emergence and deepening of emerging topics that enriched the mainstream research hotspots. The research content covered nutrients, organic carbon, ecological restoration, rocky desertification, vegetation restoration, climate change, land use, biomass, ecosystem services, etc. These topics characterized the divergence and diversity of research content during this period. In comparison to the previous two stages, there was not only a deep exploration in vegetation restoration but also macroscopic exploration in ecosystem restoration [18]. Interdisciplinary exploration in topics such as climate change, land use, and ecosystem services not only promoted the KRD governance and restoration but also gave it a clear positioning and new significance in the field of ecological environment [18,20].

3.1.4. Rapid Growth (2017–2023)

Building on the previous stages, this period experienced rapid growth, with research involving ecological stoichiometry, enzyme activity, microbial communities, green spaces, nutrient limitations, terrestrial ecosystems, random forests, etc. Research hotspots tended to focus on understanding microbial ecosystems such as enzyme activity and microbial communities through ecological stoichiometry methods, while also considering the spatial layout and functional characteristics of terrestrial ecosystems. Since 1993, the concept of KRD vegetation restoration has been gradually enriched with practical experience and sample data. Research methods have shifted from qualitative to quantitative, single-discipline to multidisciplinary integration, and from localized analysis to regional practice, evolving from small-scale governance to large-scale coordinated development [21].

3.2. Spatial Distribution of the KRD Vegetation Restoration Studies

3.2.1. Journal Published

The distribution of articles in journals can reveal the mainstream journals in the field of KRD vegetation restoration, while the distribution of commonly cited journals can indicate their influence and importance in academic research in this field [25,27]. As shown in Figure 3a, the 739 papers were sourced from 165 journals. Among them, journals with more than 20 articles each include “FORESTS” (35 papers), “Science of the Total Environment” (26 papers), “Ecological Indicators” (21 papers), “CATENA” (20 papers), indicating that research outcomes in high-quality journals in this field are relatively scarce. In Figure 3b, there are a total of 4242 journals that are commonly cited. Journals with common citation frequencies, exceeding 500 times, include “Science of the Total Environment” (897 times), “Soil Biology & Biochemistry” (768 times), “CATENA” (667 times), “Journal of Hydrology” (588 times), and others. Therefore, some international journals are paying attention to the research outcomes of rocky desertification vegetation restoration, but there is a lack of sustained attention. The number of articles in high-level journals is relatively small but is showing a steady growth trend. Journals such as “FORESTS”, “Science of the Total Environment”, “Soil Biology & Biochemistry”, “CATENA”, and “Journal of Hydrology” have the strongest impact in terms of publication and common citations.
Different journals emphasize different research topics. “FORESTS” mainly record “soil nutrients, soil multi-functional restoration”; “Science of the Total Environment” contains relatively rich topics, including “natural economy, social environment, vegetation ecology, hydrogeomorphology” and many other categories, but it still tends to topics such as “soil carbon sequestration and carbon sink function, temporal and spatial analysis of vegetation growth”. “Ecological Indicators” has many papers on macro-ecological quality assessment, such as “vegetation ecological corridor, landscape ecological security, forest vegetation productivity” and similar topics. These journals provide significant support and an essential platform for the research outcomes in KRD vegetation restoration over the past 30 years.

3.2.2. Author of Articles

The distribution of authors helps to understand the general distribution of main research energies in the field of KRD vegetation restoration, and the distribution of author coupling and common citations can reveal the cooperative relationships among authors with high impact and productivity [25,26,27]. As shown in Figure 4a, the 739 papers involve 1782 authors, with the top three authors in terms of publication numbers being KL Wang (54 papers), W Zhang (21 papers), and KN Xiong (20 papers); there are 14 scholars with more than 10 publications and 65 scholars with more than 5 publications. In Figure 4b, there are 13,722 authors who have been commonly cited, with the top three authors being XW Tong (244 times), ZC Jiang (172 times), and SJ Wang (134 times); there are 21 authors with 50 or more common citations. Leaders in the field of rocky desertification vegetation restoration, such as XW Tong, SJ Wang, PL Pu, L Deng, and DJ Li, have shown outstanding research quality and high common citation frequencies, indicating their high impact in the field of rocky desertification vegetation restoration. They play a crucial role in the subsequent development of the field, especially in the restoration of vegetation in rocky desertification areas.
According to the different colors of the nodes shown in Figure 4, the cooperation between different authors can be represented, and the authors of the same color system indicate cooperation. KL Wang-W Zhang-D Xiao-XY He was the most cooperative among several authors. KL Wang-W Zhang mainly explored “the relationship between soil microorganisms, soil nitrogen, soil organic matter and vegetation restoration”. YM Yue-XW Tong-JX Zhou-M Brandt Several authors mainly focus on the impact of ecological engineering and vegetation restoration, such as “climate change, community change, poverty transfer” and other studies. However, the external cooperation of these teams is relatively weak, which shows the relative independence of each research team. This means that although the research topic of vegetation restoration at KRD is multidisciplinary, the research topic is mainly studied independently by multiple teams in different disciplines. Therefore, teams from different disciplines should strengthen cooperation and promote interdisciplinary cooperation to find a breakthrough of vegetation restoration in KRD.

3.2.3. Country of Researchers

The paper published in the field of KRD vegetation restoration is measured by country, and it is concluded that the number of papers published in China is far more than other countries. As shown in Figure 5, among the 739 research results, China has 433 research results, accounting for 58.6% of the total number of papers. Therefore, China has the richest practical experience and theoretical results in the restoration of rocky desertification vegetation. The United States ranked second in the number of published papers (28), followed by the United Kingdom, Denmark, Australia, Canada and Germany, all of which showed strong development of karst topography and geomorphologic features.
Based on the node details shown in Figure 5, we can obtain some new findings. Specifically, several countries such as the United States, the United Kingdom, Denmark, Canada and Australia have a strong association and a cooperative relationship with China. China and the United States have mostly cooperated in the research topics of “vegetation restoration and soil water content, soil nutrients and enzyme activities, vegetation productivity, and vegetation carbon storage and carbon sink”. The cooperation between China and Denmark focuses on “evolution trend of vegetation restoration, ecological engineering and carbon sequestration”; In addition to conducting cooperative research on “soil nutrients and soil enzyme activities”, China and the UK also conducted cooperative efforts and exchanges on “vegetation restoration and abandoned farmland”. In short, the large ecological environment problem based on vegetation restoration will be the main cooperative topic of future research.

3.3. Research Hotspots of the KRD Vegetation Restoration Studies

The research hotspots in KRD vegetation restoration can be identified through keyword frequency and co-occurrence analysis, while the timeline view reflects the time span and development process of various clustering hotspots in this field [22,27]. Based on Figure 6, a total of 2531 keywords were extracted from 739 research papers. Cite Space categorized these main keywords into 12 clusters, depicted in Figure 7. Among them, keywords with a frequency of over 50 times include karst (105 times), vegetation restoration (86 times), vegetation (84 times), rocky desertification (70 times), restoration (70 times), land use (58 times), and others. The current research topics on KRD vegetation restoration are divided into seven categories, including climate change, soil organic carbon, soil moisture, ecosystem services, karst habitat, vegetation restoration, and karst ecosystem. Edge words in the keyword map represent the latest research topics, such as terrestrial ecosystems, microbial communities, ecosystem services, biodiversity, soil organic carbon, etc. In general, the research on KRD vegetation restoration has some shortcomings, such as a lack of concentrated research topics, keywords not forming clustered patterns, and insufficient in-depth studies on high-frequency keywords. By exploring and carefully reading the relevant literature based on Figure 6, the following conclusions can be further summarized.

3.3.1. Fundamental Theoretical Studies on KRD and Its Vegetation Restoration

Early European countries, such as Slovenia and Italy, focused on comprehensive research on karst geology. The current hotspots in this field are as follows: (1) vegetation restoration and environmental coupling research based on ecological stoichiometry [28,29,30,31], describing the impact of ecological environmental factors on biological characteristics from the perspective of plant geography; (2) using principles of community ecology to explore community types, structures, compositions, and species characteristics in KRD areas [32], identifying the ecological service functions of different vegetation, and proposing compensation and matching strategies tailored to local conditions as the basis for scientific vegetation restoration [33].

3.3.2. Technology Integration of the KRD Vegetation Restoration

Tailoring restoration strategies according to different geological environments, as shown in Table 3, included returning farmland to forest, afforestation on mountain slopes, artificial restoration, slope protection, forest and grass restoration, planting restoration techniques, etc., all forming specific restoration systems [34,35,36,37]. For example, in plant selection, it is necessary to carry out species screening and the cultivation of suitable vegetation in karst areas, as well as artificially induced cultivation, the optimization of drought-resistant plant communities, the composite management of vegetation, the characteristic cultivation of ecological derivative industries, etc. [38,39]. In the future, based on mechanism research, the further optimization of vegetation configuration measures should be carried out to form a scientific spatial-structure configuration pattern.

3.3.3. Responses of Ecological Process on the KRD Vegetation Restoration

Various factors such as soil, water, atmosphere, and temperature can trigger a series of chain reactions. Vegetation restoration can improve soil quality, and the soil quality restoration capacity of artificial forests in karst areas is superior to natural regeneration. During the vegetation restoration process, soil and different plant communities exhibit mutual responses in terms of their different physicochemical properties [40,41].

3.3.4. Responses of Ecosystem Services on the KED Vegetation Restoration

Karst ecosystems not only have rich species diversity, unique landform landscapes, and cave resources, but also possess high aesthetic, scientific, ecological, and certain economic value [42,43,44,45]. Combining land use, spatial distribution patterns, regional planning, and other relevant policies, promoting the enhancement of the karst landscape value has become a focus of domestic karst research in recent years, and the selection, planning, and construction of geological parks and rocky desertification parks, especially, have become hot topics [46,47,48,49,50].

3.4. Frontier Trends in the KRD Vegetation Restoration Studies

The research frontier can represent the hot issues and mindsets of researchers in this field, reveal the latest frontier trends, and help to predict the evolution trend in the future [27]. Cite Space-Burstness (yin 1.0) was used to calculate strength values, and combines composite analysis with burst detection to explore cutting-edge research on vegetation restoration in karst rock de-certification (Figure 8 and Table 4). A co-citation network analysis shows that the key breakthrough literature in this field includes Tong et al. (2018) [51], Tong et al. (2017) [52], Wang et al. (2019) [53], Chen et al. (2019) [54], Brandt et al. (2018) [8], Jiang et al. (2014) [55], among others, and the co-cited literature mainly covers topics such as climate change, aquatic vegetation, ecology, succession regulation, geomorphology, limestone forests, karst wetlands, etc. Key breakthrough keywords include variability, community, southwestern China, soil properties, diversity, karst regions, land use, ecological restoration, etc., all of which represent the frontier topics in karst vegetation restoration over the past 15 years. The strongest breakthrough intensities are seen in variability, southwestern China, rocky desertification, diversity, etc., which are the hot topics that have emerged in the field of karst vegetation restoration in the short term.

3.5. Knowledge Framework

The results of this study indicate that KRD vegetation restoration involves a wide range of topics and research fields. Therefore, it is necessary to construct a systematic knowledge framework so that scholars can understand this field more effectively and conveniently. We built this knowledge framework on the basis of combing the research detailed in Figure 9. The basic elements of this knowledge framework include statistical analysis, cooperative analysis, co-citation analysis and hotspot analysis.
From the point of view of data statistical analysis, including author analysis, journal analysis, co-citation analysis, studies on KRD vegetation restoration began in 1993 and emerged after 2017, and can be divided into several stages: initial germination (1993–2002), initial development (2003–2010), steady increase (2011–2016) and rapid increase (2017–2023). From the perspective of journal distribution, “FORESTS”, “Science of The Total Environment”, “CATENA” and other indicators are at the forefront, indicating that they have a core position in this research field. In recent years, their research results have gradually won the attention and recognition of top international journals. From the perspective of author distribution, the 739 samples involved 1 782 authors and 13 722 co-cited authors. Although Wang L and Zhang W had the highest number of published papers, the level of published journals and the influence of their results still needed to be improved. Tong XW, Jiang ZC and other authors were cited the most, and the quality of scientific research results published by Tong XW, Wang SJ and Hu PL was relatively good. The above authors can be regarded as important founders. In terms of the number of national publications, China has a total of 433 (58.6%) of the total number of publications, far exceeding other countries, the United States ranked second, followed by the United Kingdom, Denmark and other countries, indicating that China has relatively rich scientific research results in the field of KRD vegetation restoration.
From the perspective of evolution and hot frontier analysis, the research on KRD vegetation restoration is gradually systematized, and the content perspective, sample scope, research level and research topics are gradually deepened and improved. From the perspective of research hotspots, there are the following four aspects: theoretical research on KRD and its vegetation restoration, research on the vegetation ecological restoration strategy system, research on the microscopic response brought by vegetation restoration, and research on the coupling of vegetation restoration and landscape resources. From the perspective of research frontier trends, it can be divided into six aspects: the classification of vegetation functions and restoration effectiveness, the response of vegetation diversity to soil mechanism in the KRD area, the ecological engineering promotion of vegetation growth in the KRD area, vegetation restoration and soil erosion fractures, soil heavy metal control, vegetation restoration and land-use policy in the karst area, vegetation restoration and karst ecological pattern, and ecosystem succession research.
In summary, research on KRD vegetation restoration has achieved fruitful results and is currently in a steady development period, laying a solid theoretical foundation for further exploration in the future. With the improvement of restoration technologies and the maturation of related data, there is a positive trend of mutual advancement. Based on this foundation, in order to further refine the scientific theory of KRD vegetation restoration and provide valuable references for future research, the following outlook is proposed.

4. Discussion

4.1. Studies on the Functionality of the KRD Vegetation

Studying the plant functional types in the karst landforms of China helps to understand the formation of karst vegetation and provides assistance for the restoration strategies of degraded ecosystems [58]. Factors such as rugged terrain, low rainfall, improper plant-species selection, and poor management greatly affect the effectiveness of restoration efforts in karst areas [52]. Based on land-use data and forest cover loss data, exploring the spatial patterns of forest protection and restoration, as well as the contribution of forest protection and restoration to vegetation greening, confirms the significant importance of forest protection and vegetation restoration [2,59]. In KRD areas, vegetation restoration can improve the overall soil water penetration, and the contribution of vegetation increase to the overall increase in soil water content is 38.2% [45], so it is necessary to affirm and strengthen the exploration of vegetation restoration function.

4.2. Response of Soil Microorganisms to the KRD Vegetation Restoration

The richness of soil microbial community is similar to the species richness of above-ground vegetation [46]; research on the impact of vegetation restoration on soil microbial carbon cycling confirms that the restoration of plant diversity is a key driver of changes in soil microbial carbon cycling in KRD areas, providing new insights into regulating soil carbon cycling in vegetation restoration [60,61]. Studying the response of KRD soil bacterial communities and soil properties to the natural vegetation restoration process [62,63,64], and exploring the accumulation, distribution, and mineralization of soil organic carbon and its unstable components in response to different vegetation restoration, provides support for carbon cycle intervention based on land use control [65,66,67].

4.3. Effects of Ecological Engineering on the KRD Vegetation

A series of ecological engineering projects, such as afforestation, will help prevent and improve the ecological environment. The turning point of the increase in vegetation greening in southwest China is consistent with the planning of the comprehensive control and restoration project of karst rocky desertification. Most of the vegetation recovery in karst areas is significant, and the proportion of karst vegetation greening increased to 81% due to human factors [68,69]. It shows that the change in land use in recent decades is mainly caused by karst ecological protection projects. At a certain regional scale, ecological engineering can reduce the risk of desertification by increasing vegetation cover and reducing the sensitivity of ecosystems [51]. While large-scale ecological protection projects are the main reason for vegetation growth, climate is also the key factor affecting vegetation growth in non-karst areas. Therefore, in the planning and evaluation of ecological engineering measures, the importance of climate and geological environment should be fully considered in addition to natural disturbance and human disturbance [70].

4.4. Effects of the KRD Vegetation Restorations on Soil Erosion and Heavy Metal Control

Studying the vegetation in karst limestone crevices to understand the impact and mechanisms of vegetation restoration on soil erosion (especially underground leakage) supports the prevention of water and soil loss and underground leakage in karst areas [71,72]. Researching the changes in soil heavy metals during vegetation restoration and the driving factors of soil environmental factors affecting plant functional traits provides technical references for using vegetation restoration to control karst soil heavy metal pollution [73].

4.5. Studies on Land-Use Policies in the KRD Vegetation Restorations

The increase in afforestation area in China mainly comes from forests and farmland, and strengthening land-use management is a key factor in greening the earth [54,55,56]. Under the unified management of land, manpower, water resources, and other resources, afforestation in karst areas is feasible [53,74,75]. In southern China, land management has increased vegetation cover, offsetting carbon emissions over the past 6 years. However, the transitional vegetation restoration and afforestation have led to challenges in carbon-sink services, such as forest growth saturation, competition for farmland for food production, and the depletion of water resources [75,76,77].
KRD vegetation restoration engineering is a complex interdisciplinary research system and a relatively broad research topic. In future in-depth research, attention should be paid to the study of plant adaptability, resistance, inhibitory capacity under environmental stress, and the inheritance and innovation of restoration technology practice experience should be strengthened. Under the macro-control guidance of national policies, land use should be carried out reasonably, and the question of how to balance ecological security and food security is a major issue that needs careful research. At the same time, the ecological vegetation restoration project in rocky desertification areas needs to effectively connect “rocky desertification vegetation restoration and rural revitalization development”.

5. Conclusions

This study used VOS viewer and Cite Space to analyze WOS publications for vegetation restoration in KRD. Through visual statistical analysis, cooperative analysis, co-citation analysis and hotspot analysis, the research status, research relevance, current research hotspot and its future evolution trend were revealed in this research field, which is helpful for scholars in understanding this research field dynamically and comprehensively.
The main conclusions from this study are as follows: (1) Early KRD vegetation restoration research mainly focused on theoretical exploration. In the last 10 years, quantitative research has mostly been used in land use, vegetation coverage rate and spatial distribution patterns, etc. However, most of the research data came from macro data, resulting in the lack of accuracy and timeliness of vegetation restoration research on rocky desertification. (2) Vegetation restoration in KRD is not only conducive to improving the ecological environment and maintaining the stability of the ecosystem, but more importantly, it can solve the contradiction between environment and production and life for the people living in this area by relying on ecological improvement. (3) KRD vegetation restoration is a systematic project, which needs to integrate cutting-edge methods in the fields of biostoichiometry, spatial statistics, geographical science, etc., to deeply study the frontier key contents of vegetation restoration and soil microorganisms, hydrology, soil erosion, pioneer plants, and ecosystem succession.
The study has several innovative features, listed as follows: (1) We used the visual network to review the research progress of KRD vegetation restoration from multiple perspectives, providing a wealth of valuable significance and improving the exploration efficiency of relevant researchers. (2) We constructed a comprehensive knowledge framework and showed the evolution of the topic in this field, providing a comprehensive knowledge map in this field, and helping readers quickly understand the current status of vegetation restoration. (3) We proposed the characteristics of future research, which may be a hot topic in this field, and provided a clear research path for subsequent exploration.
The study has some limitations, detailed as follows: (1) There are still great limitations in the cartographic software, such as the fact that the keyword meanings are repeated, but the combination is not recognized by the software, among others. (2) Because of the delay in the entry of papers on the platform, the results of the latest published papers were not statistically analyzed, and some valuable monographs were not included; in addition, the sample size of Chinese research results is too small to reach the amount needed for quantitative analysis, so there is a lack of quantitative statistical analysis of Chinese scientific research papers. (3) The research methods and technical means also need to be updated and improved. The combination of the number of papers’ statistics and knowledge graph analysis cannot fully cover the whole of the development in the research field.
Future studies could incorporate more methodological and practical investigations, expand the database and extend the timeline study to show more detailed results. In addition, studies in other languages can be further explored, more details of vegetation restoration in KRD can be given, and the research process of vegetation restoration in karst rocky desertification can be comprehensively evaluated and analyzed.

Author Contributions

Conceptualization, M.S.; methodology, M.S. and X.L.; software, X.L. and M.L.; validation, M.S. and X.L.; resources, M.S. and X.L.; data curation, M.S., X.L. and M.L.; writing—original draft preparation, X.L.; writing—review and editing, M.S.; visualization, X.L. and M.L.; supervision, M.S.; project administration, M.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Science and Technology Program of Guizhou Province (Qainkehe Zhicheng (2024]yiban120; Qainkehe Zhicheng (2023]yiban210), and the Project of Central Finance Guides Local Scientific and Technological Development (Qiankehe Zhongyindi (2023]028).

Data Availability Statement

No new data were created or analyzed in this study.

Acknowledgments

We would like to express our sincere gratitude to all editors, reviewers, and staff who participated in the review of this article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Analytical framework in the present study.
Figure 1. Analytical framework in the present study.
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Figure 2. The number of study papers and funded projects on KDR vegetation restorations between the years of 1993–2023. Note: The information for the funding amount is obtained from the Chinese National Natural Science Foundation.
Figure 2. The number of study papers and funded projects on KDR vegetation restorations between the years of 1993–2023. Note: The information for the funding amount is obtained from the Chinese National Natural Science Foundation.
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Figure 3. Linkages of journal published (a) and co-cited journals (b) in studies on the karst rocky desertification vegetation restorations.
Figure 3. Linkages of journal published (a) and co-cited journals (b) in studies on the karst rocky desertification vegetation restorations.
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Figure 4. Linkages of authors (a) and co-cited authors (b) in studies on the karst rocky desertification vegetation restorations.
Figure 4. Linkages of authors (a) and co-cited authors (b) in studies on the karst rocky desertification vegetation restorations.
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Figure 5. Author countries and their linkages in studies on the karst rocky desertification vegetation restorations.
Figure 5. Author countries and their linkages in studies on the karst rocky desertification vegetation restorations.
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Figure 6. Research hotspots in the knowledge map of studies on karst rocky desertification vegetation restorations.
Figure 6. Research hotspots in the knowledge map of studies on karst rocky desertification vegetation restorations.
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Figure 7. The time view of literature clustering by study keywords.
Figure 7. The time view of literature clustering by study keywords.
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Figure 8. Top 15 keywords with the strongest citation bursts. Note: The blue line segment in the figure represents the time when the keyword started, and the red line segment represents the time period when the keyword was strongly highlighted.
Figure 8. Top 15 keywords with the strongest citation bursts. Note: The blue line segment in the figure represents the time when the keyword started, and the red line segment represents the time period when the keyword was strongly highlighted.
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Figure 9. Knowledge framework of karst rocky desertification vegetation restoration [8,17,51,52,54,55,57].
Figure 9. Knowledge framework of karst rocky desertification vegetation restoration [8,17,51,52,54,55,57].
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Table 1. Literature retrieval conditions in the present study.
Table 1. Literature retrieval conditions in the present study.
Search CriteriaSearch Condition Setting
Deadline of literature published date30 December 2023
Time range1993–2023 (Year)
DatabaseWeb of Science database
Search strategy 1. Karst + vegetation restoration
2. Karst rocky desertification + vegetation restoration
3. Karst rocky desertification + vegetation restoration technology
Table 2. Literature clustering based on the study keywords.
Table 2. Literature clustering based on the study keywords.
Cluster NameCentralityTime PeriodClustering Keywords
#0 climate change0.9502012–2023nature reserve, climate change, drought
#1 soil organic carbon 0.9142005–2023soil organic carbon, NDVI
#2 karst critical zone observatory0.8711999–2015dynamics, agricultural soil
#3 community 0.8591999–2022abundance, forest soils, community
#4 soil moisture0.8372007–2017diversity, variability, conservation
#5 ecosystem services0.8701999–2022vegetation, biodiversity, patterns
#6 ecosystem service0.8682009–2022detection of change-point, karst area
#7 karst habitats0.8262010–2019water, loess plateau
#8 vegetation restoration0.9172014–2023vegetation restoration, moisture, matter
#9 manipulation of succession0.8852005–2021sequestration, microbial community
#10 karst ecosystem0.8722014–2023enzyme activity, karst ecosystem
#11 residual trend analysis0.8252013–2023impact, random forest
Table 3. Vegetation restoration technology for the different degrees of karst rocky desertification.
Table 3. Vegetation restoration technology for the different degrees of karst rocky desertification.
Ecological Restoration Technology
(Severe Rocky Desertification)		Economical Restoration Technology
(Slight—Moderate Rocky Desertification)
Close hillsides to facilitate afforestationBlanket ban
Half-round, half-forbidden		Economic forest and grass restoration technologymedicinal materials, fruit trees, spices, oil, beverage, timber, fiber, carbon planting
Artificial restoration technologyBiological crust
Green pioneer plant
Soil and water conservation plant
Afforestation and seeding		Feed crop remediation technologyHerbal feed
Woody feed
Slope protection technologyNitrogen fixing hedges
Soil and water conservation hedges
Plant slope protection
Planting bag
Spray seeding		Cultivation and restoration technology of melons, fruits and vegetablesStorable vegetable
Fresh vegetable
Flower plant planting restoration technologyFlower crop
Potted plant
Dried flower essential oil
Table 4. The highly cited and highly emergent studies.
Table 4. The highly cited and highly emergent studies.
FrequencyAuthorYearLiteratureMain IdeaStrength
105Tong XW2018Increased vegetation growth and carbon stock in China karst via ecological engineering [51]Ecological engineering can reduce the risk of rocky desertification by increasing vegetation coverage and reducing the sensitivity of ecosystems to climate perturbations.8.62
58Tong XW2017Quantifying the effectiveness of ecological restoration projects on long-term vegetation dynamics in the karst regions of Southwest China [52]The vegetation availability was higher in Guangxi Province, moderate in Guizhou province, and lower in Yunnan Province.11.96
46Wang KL2019Karst landscapes of China: patterns, ecosystem processes and services [53]Karst ecosystems are recovering with the improvement of ecosystem services, but hydrology, soil, human disturbance and landscape heterogeneity still need to be continuously explored.9.62
44Chen C2019China and India lead in greening of the world through land-use management [54]The increase in China’s green area mainly comes from forests and farmland, while India’s green area mainly comes from farmland. Human land-use management is a key factor in greening the planet.5.82
41Brandt M2018Satellite-observed major greening and biomass increase in south China karst during recent decades [2]The karst region of South China is one of the regions with the largest increase in vegetation coverage and aboveground biomass in the world.5.4
37Jiang ZC2014Rocky desertification in Southwest China: impacts, causes, and restoration [55]Under the unified management of land, manpower, water and other resources, afforestation in southwest China and even other karst areas is feasible.23.01
32Tong XW2020Forest management in southern China generates short term extensive carbon sequestration [56]Land management in southern China has increased vegetation cover and offset carbon emissions over the past six years, but at the same time faces carbon-sink service challenges such as forest saturation, competition for land for food production and water depletion.6.26
23Xiao KC2017Impacts of vegetation restoration strategies on soil organic carbon and nitrogen dynamics in a karst area, southwest China [57]Economic tree species and self-regenerating plantations may be equally effective in soil carbon sequestration.6.66
19Zhang YH2019Effects of vegetation restoration on soil quality in degraded karst landscape of southwest China [40]Vegetation restoration measures can significantly improve soil quality in karst areas of southwest China.6.12
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Lu, X.; Sheng, M.; Luo, M. Knowledge Mapping Analysis of Karst Rocky Desertification Vegetation Restoration in Southwest China: A Study Based on Web of Science Literature. Agronomy 2024, 14, 2235. https://doi.org/10.3390/agronomy14102235

AMA Style

Lu X, Sheng M, Luo M. Knowledge Mapping Analysis of Karst Rocky Desertification Vegetation Restoration in Southwest China: A Study Based on Web of Science Literature. Agronomy. 2024; 14(10):2235. https://doi.org/10.3390/agronomy14102235

Chicago/Turabian Style

Lu, Xiaxia, Maoyin Sheng, and Mengxia Luo. 2024. "Knowledge Mapping Analysis of Karst Rocky Desertification Vegetation Restoration in Southwest China: A Study Based on Web of Science Literature" Agronomy 14, no. 10: 2235. https://doi.org/10.3390/agronomy14102235

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