The Global Situation of Karst Desertification Research Based on Forest Ecology

Abstract

Karst desertification (KD) is a major ecological and environmental problem threatening human survival and development in karst areas. In order to explore the research situation and development trend of KD based on forest ecology, this paper provides a systematic literature review based on the CNKI and WoS databases, which involves search, appraisal, synthesis, and analysis. We performed a statistical and visual analysis of 2955 studies acquired between 1 January 1995 and 30 June 2023, including the time distribution of the studies, hot research trends, pivotal research clusters, literature co-citations, main publishing trends, and keyword bursts. The results show the following. (1) The literature shows a fluctuating growth trend, and the research trends are divided into accumulation, development, and expansion stages. (2) The pivotal research clusters comprised three major aspects: study area and method, driving and genetic mechanisms, and control technology and models. (3) KD research forms a China-centered research network, dominated by institutions and scholars in southwestern China. (4) Future research needs to solve a series of related scientific issues and technological needs for forest ecosystem function optimization, ecological product supply capacity enhancement, ecological product value realization, ecological industry formation, and rural revitalization in KD control. The purpose of this paper is to reveal research trends relating to KD and highlight the future direction of KD research and control.

1. Introduction

Karst comprises a variety of surface and underground landscapes and phenomena caused by the dissolution of soluble rocks by water, with a clear binary geomorphic structure [1,2]. Karst areas account for 15% of the global land and house approximately 1 billion people worldwide [1]. South China, central southern Europe, and eastern North America have become the three major karst areas in the world [3]. About one-seventh of China is made up of karst, which is distributed in the northeast, north, and southwest, especially from Yunnan in the west to Guizhou, Guangxi, and Guangdong in the east, and South China is the most continuous karst area in the world [4,5]. The various bare, semi-bare, and buried carbonate beds of developing karst cover 70% of the total area of China, of which the bare area covers 125 × 104 km² in 21 provinces (districts), accounting for 14% of the land area of China [6,7].

Karst desertification (KD) is an evolutional process of the land surface that causes deforestation, soil erosion, gradual exposure of rocks, and great loss of land productivity in prominent human–land conflicts, visually resembling a desert landscape due to unreasonable human socio-economic activities in the fragile ecological environment of the karst [8,9,10]. Since the 1980s, research on KD has increased gradually. At the 149th Annual Conference organized by the American Association for the Advancement of Science (AAAS), karst and desert edge areas were equally considered vulnerable environments [11]. Karst resources and environments are characterized by fragility, sensitivity, vulnerability, and low natural regeneration ability [1,12]. China’s karst areas are home to a large population, and the ecological environment and KD issues are gradually receiving more attention. Chinese scholars have successively introduced such terms as rocky mountain, stony mountain, rocky desertification, stony desertification, karst desertification, and karst rocky desertification [13,14,15,16,17,18]. Su et al. published the first paper on KD in Chinese [19]. Yuan published his first English paper on KD and brought international attention to the issue [20].

In recent years, KD research has attracted many scholars. Kangning Xiong, a geographer from Guizhou Normal University, defined the concept of KD, formulated the criteria for grading KD, researched the formation mechanism of KD [9], and pioneered scientific control models of KD such as “Huajiang”, “Bijie”, and “Qingzhen” [21,22,23]. He designed and led the construction of the ecosystem function optimization model and the technical path to enhance the supply capacity of ecological products, constructed the rural ecological industry revitalization model, and pointed out how to realize the value of these products [24,25,26,27]. Zhongcheng Jiang, a geologist from the Chinese Academy of Geological Sciences, studied the karst dynamic system [28], proposed a comprehensive strategy for the prevention and control of KD and soil erosion [29], and carried out a survey and research on karst carbon sinks [30]. He carried out an innovative comparative study, established a monitoring station network in the karst critical zone [31], and proposed the demonstration project of carbon sinks for KD control [32]. Kelin Wang, an ecologist from the Chinese Academy of Sciences, studied soil characteristics and vegetation adaptation in KD areas [33], established a monitoring and evaluation system for KD ecosystems [34,35], and researched the response of spatial and temporal changes in the value of ecosystem services to landscape patterns [36]. He innovated and established a scientific and technological poverty alleviation system for ecological control and poverty alleviation and development [37] and proposed a landscape change model to improve the study of karst hydrological and soil processes and landscape design [38]. Currently, key institutions and authors are designing and leading future research directions of KD. Therefore, it is of great significance to elucidate the research situation of KD and point out the direction of future hot research in order to improve the control of KD and improve the forest ecological environment.

At present, a large number of KD research and control projects have been carried out, involving KD driving mechanisms, spatial and temporal evolution, subsurface leakage of soil, the application of spatial technology, ecological restoration, soil and water conservation, the eco-industry, model demonstration, industrial poverty alleviation, control technology, evaluation systems, carbon sinks, ecosystem services, ecological products, and so on [39,40,41,42,43,44,45,46,47,48,49,50,51,52]. Although these works provide a great deal of research on KD control, there is a lack of understanding of the overall research trends in this field, and there is a need for an overview of research on KD. Reviews on KD, such as narrative literature reviews [53,54] and meta-analyses [55,56], provide an overview of only one relevant area of KD and rarely visually analyze the literature. There are also some reviews that only summarize the status and outlook of KD research in different regions [21,22], lacking a summary and discussion of the overall global research on the issue. Therefore, in this review, we adopt a systematic literature review approach and CiteSpaceV.6.2.R2 analysis to study the overall KD research trend based on forest ecology, providing insights for future research.

KD is distributed to varying degrees across the karst areas of the world, especially South China karst. It threatens ecological security; restricts food production; exacerbates soil erosion; causes floods, droughts, mudslides, and landslides; and affects regional economic and social developments. Desertification not only worsens the ecological environment and production conditions but also destroys the basic conditions for human survival, making it difficult for one part of the soil and water to support one part of the population (Figure 1). In the 21st century, the Chinese government has begun to attach importance to controlling KD and has vigorously implemented control projects. At present, there is an urgent need to scientifically summarize KD research and control in order to highlight the direction for the next stage of the process. We systematically reviewed the global research situation of KD using a systematic literature review approach and visual analysis based on the literature related to KD on China National Knowledge Infrastructure (CNKI) and Web of Science (WoS) from 1 January 1995 to 30 June 2023. This paper aims to (1) clarify the development stage of KD research; (2) explore the hot research trends, pivotal research clusters, literature co-citations, and global publishing trends in the field of KD based on forest ecology; and (3) reveal the future direction of KD research and control. As a result, it is essential to scientifically summarize the literature, determine progress, analyze hotspots, and further promote KD control.

2. Materials and Methods

We used the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) protocol for a systematic search and review [57,58]. For scientific quantitative assessment, we used a systematic literature review framework including protocol, search, appraisal, and synthesis reports. The approach is characterized by transparency, portability, and replicability [59,60] and has been applied in various subject areas [61,62]. We used CiteSpaceV.6.2.R2 visual analysis to identify time zone visualization of hot keywords, timeline visualization of pivotal research clusters, time zone visualization of the literature co-citations and countries, institutions, and author collaborative mapping.

2.1. Protocol

In order to determine the scope of this study, we carry out the following: (1) count the number of studies based on six months of bibliometrics and divide them into research phases; (2) identify the hot keywords and hot KD research trends; (3) identify the pivotal research clusters on KD; (4) identify the literature co-citations; (5) establish which countries, institutions, and authors are involved in global KD research; and (6) establish the future research direction.

2.2. Search

The data in this study are sourced from the CNKI database and WoS core collection (

Table 1. Literature search strings.

Database	Search Terms (by Study Title, Abstract, and Keywords)	Number	Search Date
CNKI	“rocky mountain” or “stony mountain” or “rocky desertification” or “stony desertification” or “karst desertification” or “karst rocky desertification”	9289	15 October 2023
WoS	“karst rocky desertification” or “karst desertification” or “rocky desertification” or “stony desertification”	852	15 October 2023
Total		10,141	15 October 2023

). The retrieval period is from 1 January 1995 to 30 June 2023. In the CNKI database, using subject items for retrieval, the subject terms are “rocky mountain”, “stony mountain”, “rocky desertification”, “stony desertification”, “karst desertification”, and “karst rocky desertification”. Studies are selected based on sources (SCI, SSCI, EI, PKU, CSCD, CSSCI, Ph.D. dissertations, and master’s theses). In total, 9289 Chinese studies were retrieved. In the WoS core collection, using subject items for retrieval, the terms are “karst rocky desertification”, “karst desertification”, “rocky desertification”, and “stony desertification”. The types of literature included are journal articles and reviews, conference papers, theses, and books. In total, 852 English studies were retrieved.

As an important English literature database, WoS can retrieve the most authoritative articles related to KD. However, because KD research is mainly conducted in China, we also selected CNKI, which is the largest Chinese literature database, has the largest number of KD studies, and can retrieve the most comprehensive and important research. Thus, we chose the WoS and CNKI databases to retrieve studies. Because KD has multiple names, in order to maximize the inclusion of studies related to KD research, we tried to use all the synonymous terms for KD found in the two databases as search terms by extensively reading the literature.

2.3. Appraisal

We used inclusion and exclusion criteria to select research related to this review based on the initial search results (Figure 2). Inclusion criteria are as follows: (1) the search term should exist at least in the title, abstract, and keywords of the study; (2) studies in CNKI and WoS databases; (3) retrieve studies based on KD research in the literature; (4) studies in English or Chinese; (5) the types of studies include journal articles and reviews, conference papers, books, Ph.D. dissertations, and master’s theses; (6) studies published between 1 January 1995 and 30 June 2023. Exclusion criteria include (1) duplicates in the literature; (2) non-KD primary research studies; (3) unavailable literature; and (4) studies of low relevance to KD research. The specific methodology is based on the following screening criteria:

(1)

Searching for terms by time frame; study types included journal articles, reviews, editorials, books, doctoral dissertations, and master’s theses, and in total, 10,414 documents were retrieved;

(2)

Screening for duplicates and unavailable studies after the initial retrieve yielded a total of 9467 studies;

(3)

After checking the titles, abstracts, and keywords in the literature and excluding studies that were not on the topic of the review or had low relevance to the topic of the study, in total, 3494 studies were obtained;

(4)

After reading the literature after the eligibility criteria had been applied, research covering at least one study related to KD was screened, resulting in the acquisition of 2955 studies.

2.4. Synthesis Report

We screened the retrieved literature through a hierarchy of inclusion and search criteria, resulting in the inclusion of 2955 studies. We performed visual analysis and extensively read key research and found that the included literature extensively involved various countries, institutions, and authors related to KD research, ensuring data fairness. The keywords used in the literature are highly relevant to KD, and highly cited studies related to KD from both databases were included to ensure the reliability of the data. We found through CiteSpaceV.6.2.R2 analysis that the stage of development and change in the keywords of KD research coincides with the stage of time distribution of statistics-based studies, which can assist in the exploration of the hot research trends for KD. All the cluster parameters indicate significant clustering, so the analysis of the KD clusters is reasonable. The analysis of co-citation references in the literature reveals key studies. The analysis of the main publishing trends in this field of research reveals that key countries, institutions, and authors have published a large amount of research and have established collaborative relationships in the field of KD. Keyword bursts with the strongest citation indicate future research directions.

We divided the studies into time distribution of the literature, hot research trends, pivotal research clusters, co-cited references, main publishing trends, future research based on the statistics of the number of studies, and CiteSpaceV.6.2.R2 analysis of various aspects of the literature. In Section 3.1, we quantitatively analyze the number of studies based on six months of bibliometrics; in Section 3.2, we elucidate and analyze hot research trends; in Section 3.3, we analyze the pivotal research clusters; in Section 3.4, we find key research; in Section 3.5, we explore the main publishing trends and relationship networks; and in Section 3.6, we analyze the keywords with the strongest citation burst over the last decade, revealing future directions.

2.5. Research Tools

In the CNKI database, the export format of the literature is refwork, which exports research containing information, including titles, institutions, keywords, and authors. In the WoS database, the export format is a plain text file, and the recorded content is full records and cited references. CiteSpaceV.6.2.R2 is a visualization analysis software developed based on the Java by Professor Chaomei Chen and her team from Drexel University in Philadelphia, PA, USA. CiteSpaceV.6.2.R2 is used to visualize and analyze the literature. CiteSpaceV.6.2.R2 can be used to explore changes in research trends and pivotal research clusters in the research field by analyzing keywords and clusters in the literature, identifying key research, and exploring the network of collaborative relationships between countries, institutions, and authors [63]. We chose CiteSpaceV.6.2.R2 to clarify the research stage and then reveal the research hotspots, co-cited studies, and main publishing trends to obtain the current development trend in research on KD. In graph mapping, the size of the node circle represents the frequency size, and the thickness of connecting lines between nodes represents the strength of the relationship between each node. “Node Types” indicates the type of literature analysis, including keywords, institutions, and authors; “Year Per Slice” represents the standard for analyzing the year and time of the research. In this study, CiteSpaceV.6.2.R2 analysis was conducted based on one year as the standard; “g-index” represents the criteria for inclusion and exclusion of nodes; and Modularity Q and Silhouette S are the basis for judging the effectiveness of graph mapping. In pivotal research clusters, S > 0.5 indicates reasonable clustering, S > 0.7 indicates convincing clustering, and Q > 0.3 indicates significant clustering.

3. Results and Discussion

3.1. Time Distribution of the Literature

From 1995 to 2005, there was a slow and steady increase in the number of publications with accumulation, especially before 2000, when the number was very small. From 2006 to 2015, there was a fast, fluctuating increase in the number of studies with development. From 2016 to 30 June 2023, there was a steady sharp increase in the number of studies with extension. In 2022, the number reached its peak, with a study volume of 216 (Figure 3). The increasing literature suggests that the field of KD research is burgeoning, and the literature will expand further in the future.

According to the international state of karst forest ecology and the national strategies and local needs of China, the Five-Year Plan for national economic and social development of the People’s Republic of China and the National Science and Technology Plans have led the research trend of KD (Figure 4). From 1995 to 2005, there was a period of accumulation during which the exploration and publication of research subjects on KD were slowly increasing. One special subject on stone mountains has been set up in the Topic Project of the Key Science and Technology Tackling Program in the National 9th Five-Year Plan of China. During this stage, researchers were influenced by the policy and began to explore the theory of KD, which laid the foundation for the subsequent scientific definition of KD and the development of KD control strategies [11,16,19,20]. The current scale of the literature began to manifest itself after 2000. Two karst desertification topics were first set up in the Major Project of the Key Science and Technology Tackling Program in the National 10th Five-Year Plan of China to explore the theory, influencing factors, and control methods of KD. On the basis of research and improvement of basic theories, researchers have published studies on the driving and genetic mechanisms of KD, the application of monitoring technology, and experimental demonstration [9,10,64,65]. These results have guided KD control in Southwest China, and the topic has achieved initial results.

The period from 2006 to 2015 was a development stage of key research subjects and rapid fluctuations in the number of publications on desertification. The Major Project of the Key Science and Technology Supporting Program in the National 11th Five-Year Plan set up three key topics with KD control as the core, and the Major Project of the Key Science and Technology Supporting Program in the National 12th Five-Year Plan set up two key topics for desertification control, continuously refining and innovating relevant theories and practices. A large number of representative studies containing a high clustering degree of keywords appeared around 2006, entering a development stage from then on. During this stage, due to the improvement of theories and interdisciplinary research, focusing on the study of eco-efficiency and carbon sinks, socio-economic impacts and human–land coupling research were explored, and eco-poor alleviation, eco-tourism, and eco-civilization construction were carried out [66,67,68,69].

From 2016 to 2023, the research and publication volume of the project’s full coverage steadily increased and entered the expansion stage. The Major Project of the Key Research and Development Program in the National 13th Five-Year Plan has set up four key projects for KD control. The increased volume has also been influenced by international cooperation and regional coordinated development, research on cross-regional synergistic mechanisms for KD prevention and control, and ecosystem service function and value assessment [47,51,70]. KD evolution, forest and vegetation restoration, and ecological and economic benefits have always been the core contents for each stage.

3.2. Hot Research Trends

Based on the CNKI database, there are 431 nodes and 707 connections in the visualization graph (Figure 5). Based on the WoS database, there are 475 nodes and 2868 connections in the visualization graph (Figure 6). In CiteSpaceV.6.2.R2, “Node Types” is set to “Keyword”, “Year Per Slice” is set to “1”, and “Selection Criteria” is set to “g-index = 25”.

Time zone visualization of hot keywords shows the KD research trends. In the accumulation stage (1995–2005), high-frequency and high-burst keywords included rock desertification (742), karst rocky desertification (489), soil erosion (114), karst areas (75), guizhou province (68), remote sensing (63), karst mountain region (35), southwest China (32), soil and water conservation (22), and ecological control (21). In the development stage (2006–2015), high-frequency and high-burst keywords included soil erosion (60), impact (55), land use (42), forest (39), models (36), benefit evaluation (27), comprehensive control (24), comprehensive treatment (19), human intervention (16), and huajiang (14). In the expansion stage (2016–2023), high-frequency and high-burst keywords included organic carbon (21), ecosystem services (14), ecological industry (13), poverty alleviation (12), agricultural products (11), karst ecosystem (10), green program (9), county demonstration (9), rural revitalization (8), and carbon sequestration (7).

In the accumulation stage (1995–2005), “rock desertification”, “rocky desertification”, and “karst rocky desertification” are the most frequent keywords, indicating that KD is a research focus in relation to the karst ecological environment [71,72]. The words “karst areas”, “karst mountain region”, “guizhou province”, and “southwest China” indicate that research, control, and monitoring of KD have been carried out in the karst areas of Southwest China. The initial ecological and economic benefits were achieved in this stage [73,74,75,76]. The words “dynamic monitoring”, “distribution characteristics”, “gis”, and “remote sensing” provide data support for establishing a grading and evaluation system for KD. Remote sensing and GIS have become the best choices for desertification monitoring [8,20,42,64,77,78] and provide detailed data for evaluation, especially for forest restoration [79]. Unmanned aerial vehicles equipped with remote sensing technology have become a research focus for the precise monitoring of forest vegetation structure, helping to better manage and protect forests in controlled areas [80,81,82]. The words “carbonate rock”, “karst forest”, and “soil” are important natural factors for identifying KD and its causes, as well as prerequisites for the control work [39,83,84,85,86,87,88]. The words “deforestation for arable land”, “soil erosion”, “soil and water conservation”, “ecological control”, and “ecological mode” have shown an implementation of control models and experimental demonstrations centered on forest vegetation restoration, and soil and water conservation [21,25,89,90,91,92,93]. “Artificial forests”, “artificial vegetation”, and “agroforestry” have made important contributions to carbon fixation and oxygen release, water and soil conservation, nutrient cycling, and coordinating forest vegetation community restoration with agricultural activities [49,94,95]. The trend of hot research indicates that Guizhou is a core area of KD research. The scientific definition, grading and control technology, and experimental demonstration of KD have laid the foundation for rapid development in the future.

In the development stage (2006–2015), the words “soil animals”, “soil thickness”, “soil moisture”, “soil erosion”, and “forest and plant” reveal the spatial distribution and changes in soil physicochemical and biological characteristics, which help to select vegetation for evaluation of the control and effects [29,41,65,96,97,98,99,100]. Forest vegetation transformation affects soil biology, soil physicochemical properties, and soil ecosystem services. The evaluation of the change in soil ecosystem services caused by the transformation is helpful in evaluating an ecological effect caused by forest degradation or restoration [50,101]. The words “population density”, “human intervention”, “human activities”, “land use”, and “afforestation model” have become the key factors for humans to reasonably develop and utilize resources and solve KD problems in terms of control [67,102,103,104,105,106,107]. The restoration effect of forest vegetation directly affects the ecological environment in the affected areas [88,108,109]. The words “alternative livelihoods”, “crops”, “benefit evaluation”, “rural poverty”, and “alleviate poverty through development” indicate that agricultural production is affected by KD, exacerbating rural poverty. As a result, an ecological industry poverty alleviation model for KD control should be established [49,66,110,111,112,113]. Characteristic forestry and agroforestry models improve land productivity, preserve soil and water, and greatly improve economic and ecological effects [44,114,115]. The words “comprehensive control”, “comprehensive treatment”, “forest vegetation restoration”, and “models” reflect the implementation of integrated control of KD in accordance with local conditions. Scientific models with scale demonstrations include the terms “Bijie”, “Qingzhen”, “Huajiang”, “Huanjiang”, and “Pingguo”, which have become the keywords [23,56,68,116,117,118,119,120]. As a result, universal eco-industry engineering models for KD control have been proposed by extending, applying, and expanding the scientific models in the future [121]. In the development stage, although high-frequency words do not account for much of the literature, the number of keywords is the highest. The trend of hot research indicates that research is constantly deepening and being refined. The driving factors and evolutionary mechanisms are one of the hotspots at this stage, indicating that many comprehensive management studies and scale demonstrations have been carried out in the desertification areas. The dynamic monitoring of soil physical, chemical, and biological characteristics provides important data and a theoretical basis for the control of KD. Control technology has gradually developed from mountain closure for afforestation to forest vegetation ecological restoration.

In the expansion stage (2016–2023), the words “forest ecosystem”, “agricultural products”, “ecological industry”, and “ecological products” are the main trends in the control of KD, with a focus on breaking through the formation mechanism and process of derived ecological industries [27,45,52,122,123,124]. Collaborative development of forest ecosystem services and ecological industries is conducive to balancing ecological remediation and economic development [125,126,127,128]. It has become one of the highlights and hot spots of KD control and the ecological industry for discussion in terms of the words “afforestation effect”, “ecosystem services”, and “eco-products realization” at this stage [59,129,130,131,132,133,134]. The key lies in optimizing the forest ecosystem service function, enhancing the supply capacity of ecological products, and improving the forest ecological compensation mechanism [25,94,135,136]. Hence, the keywords “sustainable livelihood”, “poverty alleviation”, “rural revitalization”, and “county demonstration” have become a research focus in this stage, in contrast to the former stage [47,128,137,138,139,140]. The focus is on exploring the development and utilization methods of characteristic forestry and agroforestry, as well as balancing public welfare and profit attributes of ecological forests [44,95,114]. As China is becoming a moderately prosperous society in all respects, the eco-industry of KD control has become a future research trend in promoting rural revitalization. The high-frequency words “organic carbon”, “carbon sequestration”, and “low-carbon community” reveal the importance of low-carbon community construction, which promotes the construction of low-carbon communities in rural areas by achieving a low-carbon eco-environment, low-carbon productivity activities, and a low-carbon energy consumption structure [43,141,142,143,144,145,146]. Restoring arable land to forests effectively improves forest carbon sink function and carbon storage [147,148,149]. In the expansion stage, the focus is on the ecological secondary industries and poverty alleviation, with a greater emphasis on the application of new theories and high-tech methods, and the response to policies, with more environmental factors being considered in ecological restoration and more attention being paid to the control theory and application of ecosystem function and ecological services at the county level. Greater emphasis is placed on vegetation restoration for integrated ecological protection and the restoration of mountains, rivers, forests, farmlands, lakes, grasslands, and desertification. Eco-products focus on supply capacity improvement through qualitative and quantitative optimization of ecosystem functions.

3.3. Pivotal Research Clusters

Based on CNKI, the clustering theme display is set to 0–11, and the results are S = 0.8971 and Q = 0.6184 (Figure 7). Based on WoS, the clustering theme display is set to 0–9, and the results are S = 0.7212 and Q = 0.3964 (Figure 8).

The pivotal research clusters on KD are mainly discussed in terms of three aspects: study area and method, driving and genetic mechanisms, and control technology and model. The research sector comprises the following: forestry and ecology account for 33%, soil/water conservation and agroforestry for 19%, grassland and animal husbandry for 16%, land and natural resources for 15%, and others for 17%.

The research clusters related to the study area and method includes “karst area”, “rocky desertification area”, “Guizhou province”, and “remote sensing”. By analyzing high-frequency keywords behind the themes in the literature, we found that South China karst is diverse and typical, and Guizhou is the largest and most representative area with the most serious and prominent karst desertification problems, and the research on this has been centralized [40,150,151]. The spatial distribution and temporal variability of KD are pivotal research clusters [152,153,154]. The proportion of areas with varying degrees of desertification can be calculated, the evolution history can be analyzed [155,156], and the development trend can be monitored and evaluated in detail using remote sensing and GIS technologies to draw maps under complex karst conditions [157,158]. Moreover, the technology is very helpful for measuring complex forest structures, obtaining high spatial resolution in forest modeling, and monitoring forest change trends in desertification areas [80,81]. Research clusters indicate that Southwest China is the hardest-hit area of KD, but it is also the core area of KD research. KD research and control strategies originating from this region are useful for KD control in northern China as well as KD areas around the world.

The research clusters on driving and genetic mechanisms are “driving factors”, “deforestation for arable land”, “soil erosion”, “land use”, and “climate change”. The analysis of highly cited studies reveals that KD has destroyed the forest ecosystem, and soil erosion caused by human reclamation destroying forest vegetation is an important factor in the intensification of desertification [159]. Location detection of soil erosion with the level of rocky desertification is helpful for developing appropriate control measures [160]. Land use type is one of the factors that leads to different rates of rocky desertification [70]. Shrubs, other forests, low-coverage grasslands, steep-slope drylands, and unused land account for a large proportion of KD land [161]. Land use sustainability measures can effectively evaluate desertification control, reveal the desertification sensitivity to human activities under different land use types, predict an area of each sensitive type, and explore the desertification risk [162]. Water and soil loss is an important manifestation of the effect of human–land conflicts and global climate change [163]. Research clusters indicate high population pressure in the karst areas, large occupation of arable land by construction land, predatory development of natural resources, and disharmony of industrial structures with agriculture, forestry, and animal husbandry, forming a human–land system with regional advantages and socio-economic contrasts. Research clusters also reveal a reverse succession process of deforestation for arable land, soil erosion, bedrock exposure, and KD caused by unreasonable human activities in the fragile karst ecological environment.

The research clusters on control technology and model include “forest ecosystems”, “grasslands”, “agroforestry”, “soil organic carbon”, “drought stress”, and “karst water”. Forest ecosystems in karst areas face problems of KD, and forest restoration measures need to develop management programs based on different sensitivity levels [164]. Soil organic carbon and soil metabolic entropy play important roles in artificial vegetation in forest ecological restoration [69,146,165]. Forest vegetation restoration can increase soil stability and soil organic matter content [166]. Grassland is the last barrier to protect forest eco-environments in karst areas and plays an essential role in KD control [167]. Agroforestry provides ecological restoration and economic benefits, promotes the integration of eco-industry and ecosystem services, and forms a perfect model of ecological industry for rural development [45,168]. Drought-resistant tree species suitable for desertification habitats are selected to address periodic drought environments faced by vegetation based on knowledge of water consumption regularity and the drought resistance capabilities of afforestation tree species [169]. Forest ecological management is very helpful for solving a contradiction between karst water sustainable production and water use [170], for proposing efficient utilization and allocation of surface/groundwater resources and the optimization of natural plant communities and forest–shrub–grass allocation [48], and for establishing three-dimensional development models of ecological industries in syncline and anticline valleys for efficient utilization of water and soil resources, stable forest ecosystems and suitable characteristic forest ecological industries, and the development of economic tree species industries in forest ecological restoration [171]. Research clusters indicate that for this complex human–land system, technologies, such as forest and vegetation restoration and comprehensive control, are proposed to address the formation of artificial afforestation, mountain closure for afforestation and grass cultivation, artificial grass planting, grassland improvement, soil and water conservation, water resource development, rural energy optimization, ecological migration, and tourism resource development during the control process. Scientific and three-dimensional control approaches have been adopted in the fragile ecological environment, and ecological industry protection and restoration and precision poverty alleviation demonstrations have been carried out, basically achieving a coordinated development of ecology, economy, and society. The models of Bijie, Qingzhen, Huajiang, Shibing, Libo, Huanjiang, and Pingguo have been constructed and have had a nationwide influence. Forest ecological restoration work has made an important contribution to enhancing forest ecosystem stability and improving ecological function and services in the demonstration areas.

3.4. Literature Co-Citations

Based on the CNKI database, Kangning Xiong, in the project “Research on Karst Desertification and Survey by Remote Sensing in Guizhou” funded by the Guizhou Provincial Department of Water Resources in 2000, systematically studied and proposed the definition, environmental effects and ecological poverty, control models, and technical measures of KD for the first time. Afterward, he led his team to publish the first monograph on KD research, a “Study on the karst desertification based on remote sensing and GIS”, with the Geological Press of China [9]. It has been widely recognized in the field. It has become the most frequently cited Chinese study in the field (1053 times), laying the foundation for KD research and control [104,115,172,173,174,175].

In CiteSpaceV.6.2.R2, “Node Types” is set to “Reference”, “Year Per Slice” is set to “1”, and “Selection Criteria” is set to “g-index = 25” (Figure 9). Through visualization of the co-citations in the literature, the most highly cited study is “Rocky desertification in Southwest China: Impacts, causes, and restoration” by Zhongcheng Jiang et al. (608 times), revealing that the karst rocky desertification has had significant negative impacts on the environment and socio-economic conditions at local and regional scales [176]. The study with the highest centrality is “Spatio-temporal evolution of rocky desertification and its driving forces in karst areas of Northwestern Guangxi, China” by Kelin Wang et al. (centrality 0.18), which points out that the driving forces behind rocky desertification have been increasingly influenced by human activities [177]. The work with the highest half-life is “How types of carbonate rock assemblages constrain the distribution of karst rocky desertified land in Guizhou Province, PR China: phenomena and mechanisms” by Shijie Wang et al. (half-life 4.5), which examines the spatial distribution of karst rocky desertified land and relates it to the different assemblages of basement carbonate rocks [178]. The work with the highest keyword burst is Jiang et al. (burst 20.73) mentioned above [176].

Studies with high citation frequency, centrality, half-life, and keyword burst reflect the strong academic influence, highlighting the hot issues of KD research trends at the time of publication and showcasing the key research stages. Synthesizing CNKI and WoS, before 2002, KD research comprised a discussion of basic theories, until Kangning Xiong’s team published the first monograph on KD, which defined the concept of KD and classified it while revealing the driving and genetic mechanisms [9]. Since then, from 2002 to 2014, a large number of highly co-cited and highly central studies have appeared, a large number of them focused on key subjects related to the concept of KD, drivers, the human–land relationship, GIS technology, and control models [10,124,172,176,177,178]. Research on the impact of natural and human factors on KD is highly popular, which forges an important research direction for KD. The period 2004–2009 for the literature on the high half-life indicates that the transition between the accumulation stage and the development stage is a key period for research on land use and the human–land relationship. The high-burst literature indicates a rapid increase in citation frequency around 2014, which has a certain representative effect on the pivotal research subjects in the development stage. The literature is beginning to focus on ecosystem services, forest succession, ecological restoration, climate change, carbon sinks, comprehensive control, poverty alleviation, and economic benefits [24,103,129,150]. Most of the literature on desertification is published in Chinese journals, with relatively few published in journals with high impact factors, such as “Nature” and “Science”. As a result, global cooperation in KD research should be strengthened, and studies should be published in highly influential international academic journals for studies of dynamic changes and forest ecological control of KD from a global perspective.

3.5. Main Publishing Trends

Visualization analysis was conducted on the studies in the WoS database, and the retrieved works came from 50 countries (Figure 10). The results show that China has an absolute advantage in the number of articles published, ranking first in the world, with 634 articles and 1.25 centrality. The second is the US, with a publication volume of 40 articles and a centrality of 0.04. The UK ranks third, with 14 articles and a centrality of 0.06. The others are Canada, Japan, Denmark, The Netherlands, Spain, Germany, etc. China has cooperative relationships with the US, the UK, Canada, and Germany in the study of KD. The US has cooperative relationships with Spain, France, and The Netherlands; the UK has cooperative relationships with Australia and Japan. The main countries of publication have KD distribution. Except for China, most countries and regions mainly study the interrelationships between rocky desertification and hydrology, ecology, and soil due to their mild degrees of desertification, low population density, and low human intervention [205,206,207].

Based on the CNKI and WoS databases (

Table 2. Top 10 institutions in terms of the literature on KD.

CNKI Institutions	Number	WoS Institutions	Number
Guizhou Normal University	584	Guizhou Normal University	167
Institute of Karst Geology, CAGS	154	Guizhou University	80
Institute of Geochemistry, CAS	138	Institute of Karst Geology, CAGS	54
Guizhou University	129	Institute of Geographic Sciences and Nature Resources Research, CAS	49
Southwest University	115	Institute of Geochemistry, CAS	43
Guangxi Normal University	80	Southwest University	41
Central South University of Forestry and Technology	69	Institute of Subtropical Agriculture, CAS	40
Guangxi University	61	China University of Geosciences	23
Southwest Forestry University	59	Research Institute of Forestry, CAF	23
Beijing Forestry University	57	Peking University	22

), Guizhou Normal University, including the State Engineering Technology Institute for Karst Desertification Control, the School of Karst Science, and the School of Geography and Environmental Sciences, ranks first with 751 papers. Guizhou University ranks second with 209 papers. The Institute of Karst Geology, Chinese Academy of Geological Sciences (CAGS), including the Key Laboratory of Karst Dynamics, MNR and GZAR, and the Key Laboratory of Karst Ecosystem and Treatment of Rocky Desertification of the Ministry of Natural Resources, ranks third with 208 papers. Institutions outside China, for instance, the University of Copenhagen and the University of Exeter, are major contributors.

The top three authors in terms of publication volume were Kangning Xiong (257 articles, with an average centrality of 0.13), Shijie Wang (107 articles, with an average centrality of 0.07), and Yangbing Li (55 articles, with an average centrality of 0.01) (

Table 3. Top 10 authors in terms of the literature on KD.

CNKI Authors	Number	Centrality	WoS Authors	Number	Centrality
Kangning Xiong (Guizhou Normal University)	206	0.17	Kangning Xiong (Guizhou Normal University)	51	0.09
Shijie Wang (Institute of Geochemistry, CAS)	83	0.04	Kelin Wang (Institute of Subtropical Agriculture, CAS)	35	0.05
Yangbing Li (Guizhou Normal University)	55	0.01	Quanhou Dai (Guizhou University)	31	0.00
Zhongfa Zhou (Guizhou Normal University)	48	0.02	Shijie Wang (Institute of Geochemistry, CAS)	24	0.10
Shiyou Xie (Southwest University)	44	0.00	Xiaoyong Bai (Institute of Geochemistry, CAS)	23	0.00
Zhongcheng Jiang (Institute of Karst Geology, CAGS)	41	0.01	Yuemin Yue (Institute of Subtropical Agriculture, CAS)	22	0.00
Baoqing Hu (Nanning Normal University)	39	0.01	Xudong Peng (Guizhou University)	20	0.00
Xiebao Wu (National Forestry and Grassland Administration)	38	0.02	Yongkuan Chi (Guizhou Normal University)	18	0.00
Ziqi Liu (Guizhou Normal University)	37	0.00	Xianfei Huang (Guizhou Normal University)	14	0.06
Xinqiu Dan (National Forestry and Grassland Administration)	26	0.01	Zhenming Zhang (Guizhou University)	13	0.00

). In addition, Rasmus Fensholt at the University of Copenhagen and Jeroen Meersmans, Sophie M. Green, and Timothy A. Quine at the University of Exeter are important scholars in the study of KD.

The main academic teams (Figure 11 and Figure 12) include Kangning Xiong, Ziqi Liu, and Yongkuan Chi, who study the classification and grading of the karst desertification by remote sensing and GIS, the relationship between humans and land, the mechanism of formation, forest ecological industry and poverty alleviation, and the control models and technologies [9,45,65,68,162]. The author group that includes Shijie Wang, Xiaoyong Bai, and Zhenming Zhang, among others, is studying the driving mechanism and evolution process of KD, as well as its relationship with landforms, lithology, precipitation, and population [208,209]. The author group that includes Kelin Wang, Yuemin Yue, and Chunhua Zhang is studying karst landscape patterns and dynamic changes in KD, forest ecosystems, and service functions [33,127,189,191].

The global situation of KD research forms a China-centered research network. Southwest China research institutions and authors also occupy a dominant position and work closely together in terms of publication volume. KD issues are arising, to varying degrees, in the karst regions of the world. Throughout the world, there are KD landscapes experiencing degradation of their fragile environment in addition to those in China [102,170,210,211]. Scholars outside of China, such as M. Parise, U. Sauro, and D. Tuyet, among others, have studied the KD landscape that is driven by human activities [102,210,211], and R. Fensholt and J. Meersmans, among others, collaborated with Chinese scholars to study interrelationships between KD, on the one hand, and vegetation and soil, on the other [79,160]. However, the vast majority of institutions and authors studying KD are from China, and there is a scarcity of literature from other countries. This shows that other countries do not attach importance to KD research and that international cooperation on KD research is not close. In areas with insufficient literature representation, there is also a problem with KD, which requires international cooperation to attract regional attention. The implementation plan for KD control proposed by South China should not only strengthen cooperation and exchange among author groups but also expand to international and domestic cooperation with North China, Mediterranean coastal countries, the US, Russia, Australia, New Zealand, and Southeast Asia with a larger karst distribution, especially Vietnam, Laos, Cambodia, Thailand, Myanmar, and the rest of the Indochina Peninsula in the karst regions, which belong to the southern extension of South China karst, which has common ecological environment attributes and urgently require desertification research and control.

3.6. Future Research

The identification of cutting-edge research can provide researchers with the latest research trends and predict the future development direction of the research field. Identifying cutting-edge research typically involves analyzing changes in the frequency of keyword appearances in a study [212]. The stronger the keyword burst, the more attention it has received in the field in that particular time period. “Afforestation technology”, “afforestation”, “plant diversity”, “net primary production”, “green programs”, “conservation”, and “afforestation effects” show that forest vegetation conservation and restoration and high-quality green development are the latest research hotspots. “Ecosystem services”, “ecological products”, “governance models”, “karst ecosystems”, “ecological industry”, and “ecological restoration projects” show that ecosystem service function optimization, ecological product value realization, and ecological industry are the latest research hotspots. “Comprehensive evaluation”, “index systems”, “benefits analysis”, and “estimating ecological indicators” show that the evaluation of karst forest ecosystem function, the evaluation of the benefits of KD control, and measuring the value of ecological products are the latest research hotspots. “Human intervention”, “big data”, “soil organic carbon”, “ecological stoichiometry”, “influencing factors”, and “driving factors” show that big data application and ecosystem function driving ecological product supply capacity–ecological product–ecological industry development–rural revitalization chain mechanisms are the latest research hotspots (

Table 4. Top 12 keyword bursts with the strongest citations in the last decade on KD.

CNKI Keyword	Year	Burst	WoS Keyword	Year	Burst
afforestation technology	2013	1.11	ecological product	2014	2.78
comprehensive evaluation	2013	1.44	ecosystem services	2014	3.06
index system	2013	2.75	afforestation	2016	1.5
benefit analysis	2014	1.02	estimating ecological indicators	2016	2.55
governance model	2014	2.29	plant diversity	2019	1.84
human intervention	2015	2.28	net primary production	2019	1.84
big data	2017	1.83	karst ecosystem	2019	2.27
ecological industry	2018	2.93	soil organic carbon	2019	3.4
ecological stoichiometry	2018	3.66	green program	2020	1.08
influencing factors	2019	3.95	conservation	2020	1.19
afforestation effect	2020	1.12	ecological restoration projects	2021	1.28
driving factors	2021	1.6	projects	2021	1.92

).

The keyword bursts with the strongest citations indicate a higher level of research interest in the research field, and they suggest future research directions. With the 14th Five-Year Plan of China, the government put forward a more demanding strategy, which promotes the integrated control of KD, requiring research on KD to provide scientific and technological support for the transformation of South China karst to high-quality green development. That is, according to a series of related scientific issues and technological needs for forest ecosystem function optimization, ecological product supply capacity enhancement, ecological product value realization, ecological industry formation, and human wellbeing improvement based on rural revitalization in KD control, researchers should conduct full-chain design, integrated arrangement, and modular promotion for systematic research that focuses on basic frontier research, common key technology development, technological application and demonstration, and industrialization extension. The first goal is, based on forest ecosystem functional traits and health evaluation, to clarify the improvement mechanisms of system resilience from vulnerability regulation, system stability from structural adjustment, system safety capacity from carrying capacity regulation, and eco-product supply capacity from ecological asset revitalization. The second goal is to reveal the driving mechanisms of the ecosystem function optimization for service balance/synergy and ecosystem services (i.e., eco-product value realization of ecological material products, regulatory services, and cultural services) in terms of ecological industry development and, hence, the ecological industry’s effect on rural revitalization. The last goal is to propose an ecosystem service rural revitalization model with strategies and paths of the eco-product value realization to conduct application demonstration and verification extension, which will provide a scientific basis and technological support for consolidating poverty alleviation achievements and promoting rural revitalization in KD control areas.

3.7. Limitations

This section notes some key points regarding the limitations of this paper. Firstly, the studies retrieved for this review only cover the period from 1 January 1995 to 30 June 2023, and ignore the latest and older literature. We only searched the CNKI and WoS databases, and there are studies in other databases that we did not retrieve. We have removed unavailable literature, newspapers, patents, and technical reports, as these may lead to incomplete and one-sided research. Secondly, other researchers have also reviewed the literature on KD [213,214] but have used fewer search terms. We have tried our best to include the various synonymous terms for KD as search terms in our search, and we have obtained more studies. However, due to the complexity and limitations of literature database search engines and search methods, our search of the literature related to KD is incomplete. In terms of research in general, it has little impact on the KD research trend and the exploration of pivotal research clusters. Finally, this study is based on our summary and analysis of statistical and visual mapping, which, while trying to remain objective, is still subjective.

4. Conclusions

This paper is based on CNKI and WoS retrieval and screening, which ultimately resulted in 2955 studies being included in our review. The following conclusions are drawn based on the systematic review approach and visual analysis. (1) The research is divided into three phases in terms of the number of studies with a slow and steady increase and accumulation with a thematic exploration of sub-projects, fast fluctuating increases, and development with a project in a key field, and a steady and sharp increase and extension with full coverage of the program. (2) The hot research trend shows that in the accumulation stage, hot research is on scientific definition, classification, and grading, as well as control technology and model demonstration; in the development stage, hot research is on driving factors and evolutionary mechanisms, comprehensive control research, and scale demonstrations; and in the expansion stage, hot research is on ecological industries and poverty alleviation, ecological protection and vegetation restoration, and ecological product supply capacity enhancement. (3) The pivotal research clusters are study area and method, driving and genetic mechanisms, and control technology and model. (4) The high citation frequency, centrality, half-life, and burst literature are all from China and belong to institutions and authors with more research on KD. (5) China is the most influential country in the world in terms of KD research, and Southwest Chinese institutions and authors have the highest number of studies and lead the global trend. (6) Ecosystem function optimization, the improvement of ecological product supply capacity, ecological product value realization, the formation of the ecological industry, the driving mechanism of the ecological industry on rural revitalization, and the ecosystem service rural revitalization model are the hot future research directions.

There is a problem of KD distribution to varying degrees across karst areas around the world, and the literature on KD in countries outside of China shows that there is a lack of research on the driving mechanisms of local desertification formation and KD control in these countries. KD research should strengthen international exchange and cooperation, which can promote innovation and the exchange of technologies and models for KD control and ecological restoration and promote comprehensive control projects in countries that urgently need KD control. Natural disasters, poverty, food issues, and ecological security caused by KD affect the sustainable development of many countries around the world. Research on KD should strengthen interdisciplinary studies, such as humanities and social sciences, climate and meteorology, and ecology and environmental science; expand disciplinary boundaries and perspectives; and contribute to the design of comprehensive KD control plans.