Research Progress and Hotspot Analysis of Low-Carbon Landscapes Based on CiteSpace Analysis

Abstract

Global climate change caused by carbon dioxide emissions has become a hot topic globally. It is of great significance to study how low-carbon landscapes can reduce carbon emissions and improve the ecological environment. In this study, CiteSpace software was used to conduct a bibliometric analysis of the research field. The analysis data were based on 2910 studies published in the research field from 2002 to 2023. By analyzing the number of publications in the research field, cooperation networks, keywords, etc., the research status, processes, and hotspots of low-carbon landscapes were systematically reviewed. The results show the following: (1) Between 2002 and 2023, low-carbon landscape research developed rapidly, gradually becoming a multidisciplinary field. A large number of studies were conducted by relevant institutions and scholars from 106 countries. (2) The research focuses on carbon emission reduction, renewable energy, life cycle assessment, etc. The research mainly goes through the following stages: theoretical research on low-carbon technology, the application of low-carbon technology, and the development of the low-carbon economy. (3) Research frontiers focus on low-carbon landscape emission-reduction technologies, low-carbon landscape research methods, and the development and application of low-carbon materials. This study deeply analyzes the research process of low-carbon landscapes and puts forward a research direction for low-carbon landscapes in future urban development, such as economic benefit assessments, ecosystem restoration and protection, social participation, and policy support, in order to provide a reference for low-carbon landscape research.

1. Introduction

With the advancement in global urbanization, global climate change caused by carbon dioxide emissions has affected human living space and become one of the most concerning global issues [1]. Cities contribute more than 70% of the global CO₂ emissions and two-thirds of the global energy consumption [2]. At the same time, cities are seen as major innovators and implementors of climate change mitigation and low-carbon development [3,4]. Low-carbon cities have become an important goal of global urban development, and the low-carbon development of cities plays an important role in global carbon emission reduction. Cities can influence carbon emissions through energy use, transportation, and other factors [5]. Urban low-carbon landscape construction is of great significance for improving ecological environment quality and promoting sustainable development [6]. A low-carbon landscape applies the concept and method of “low-carbon” to the landscape, with the aim of reducing carbon emissions in the entire process from landscape construction to later landscape management. Compared with ordinary landscape construction, it is more environmentally friendly and results in greater energy savings, higher resource utilization, reduced carbon emissions, the least damage to the natural environment, and the maximum protection of natural resources [7]. Previous research on low-carbon landscapes has covered a wide number of areas, such as land use [8], power systems [9], renewable energy [10], agricultural production [11], transportation [12], construction [13], and ecological planning [14]. People are increasingly concerned about the impact of carbon emissions on the living environment, which has prompted national governments and the international community to strive to achieve sustainable development and reduce the dependence on carbon emission activities [15]. Previous research on low-carbon development based on bibliometric analysis mainly involved a certain field or industry, such as the low-carbon economy [16,17,18], low-carbon transportation [19], or carbon emissions [20,21], and there is a lack of bibliometric analyses of low-carbon landscapes in the context of global urbanization. Therefore, it is necessary to review the current research status of low-carbon landscapes and reveal the evolution trend and future research development direction to promote more scientific and in-depth research on low-carbon landscapes and provide scholars with references for subsequent research.

In this study, bibliometric and scientific knowledge mapping methods using CiteSpace (6.2.R4) software were used to explore the research progress and research history of low-carbon landscapes. Although CiteSpace software is widely known in the field of bibliometrics, its innovative application to the specific and complex field of low-carbon landscapes is a breakthrough that fills the gap in the bibliometrics analysis of low-carbon landscapes in the context of global urbanization. This study used data obtained from a literature search of the Web of Science core database for the period from 2002 to 2023; it analyzed the annual number of publications, distribution of subject areas, national/regional collaborative networks, institutional collaborative networks, frequently cited literature, and so on, to sort out the current status of research in the field. Meanwhile, the research history, research hotspots, and research frontiers in the field were found through keyword co-occurrence, emergence analysis, and keyword time zone distributions. In addition, according to the comprehensive analysis of the research trend in this field, a further research direction for low-carbon landscapes was put forward. The purpose of this study is to review the research status, research hotspots, research process, research frontiers, and future research directions of low-carbon landscapes to provide references for improving the theoretical research into low-carbon landscapes and the in-depth research direction of low-carbon landscapes.

2. Materials and Methods

2.1. Data Collection

The Web of Science (WOS) is the world’s leading citation database, which has high academic research value and supports a wide range of information uses [22,23]. In this study, the Web of Science TM core collection was used as the data source, and the retrieval time was 25 August 2024. The search formula was TS = (landscape OR park OR green space OR plant OR urban ecology OR green infrastructure) AND TS = (low-carbon design* OR low-carbon plan*) AND LA = (English) NOT PY = (2024). A total of 3494 articles were retrieved. The literature was imported into CiteSpace software to delete duplicate content, and irrelevant items, such as news and conference announcements, were eliminated. Finally, 2910 studies were used as the basic data of this study.

2.2. Analytical Method

With the rapid development of science and technology, more and more visual analysis tools have been applied to review research, such as VOSviewer, CoPalRed, Bibexcel, Sci2, VantagePoint, CiteSpace, etc. All these tools support the literature co-citation analysis and keyword co-occurrence analysis, which can help us conduct the quantitative and objective analysis of related fields and reveal the quantitative relationship between various studies [24].

CiteSpace is an information visualization software developed by Dr. Chaomei Chen, a Chinese scholar from the School of Information Science and Technology of Drexel University in the United States, which is mainly used for the metrology and analysis of scientific literature data [25,26]. It combines bibliometrics methods, formation process visualization methods, and data mining methods to explore research hotspots, trends, and knowledge turning points in different disciplines [27]. In this study, CiteSpace 6.2.R4 (Figure 1) is used for the data visualization analysis of the relevant literature, including the annual number of publications, relevant cooperation networks, keyword co-occurrence, emergence analysis, etc., to present the status quo and development dynamics of low-carbon landscape research from an intuitive and clear perspective.

3. Results and Discussion

3.1. Annual Number of Publications

The annual number of published papers is an important indicator reflecting the research evolution trend and research maturity in related fields. As can be seen from the literature search results, the database did not search the relevant literature on low-carbon landscape research before 2002. Since 2002, with the gradual popularization of the low-carbon concept and the continuous development of related technologies, academic research on low-carbon landscapes has gradually increased. Periodic changes and trend fluctuations in the time frame can also provide important clues for studying trend prediction. This section analyzes 2910 papers published between 2002 and 2023 and finds the number of papers published per year over the past 22 years, showing distinct stages. As can be seen from Figure 2, the research process is divided into three stages: (1) The initial development stage (2002–2007), with less than 25 papers per year. (2) The stable growth phase (2008–2020), during which the number of articles will begin to increase steadily, with an average of about 110 articles per year. (3) The rapid rise stage (2021–2023), during which the number of published papers increased significantly, with an average annual number of more than 400 papers. Many countries and regions have increased their policy support for low-carbon development after 2020. For example, the European Union has introduced stricter carbon emission targets and related green recovery plans, which explicitly emphasize the crucial role of landscapes in achieving low-carbon goals. On 22 September 2020, during the 75th session of the United Nations General Assembly, China put forward the “carbon neutrality” plan, which gained attention from scholars for the study of low-carbon landscapes, and the number of related articles has reached a peak in recent years, which further shows that the research direction of scholars is close to international hot spots. In addition, the application of big data analysis and artificial intelligence technology also provides new methods and means for low-carbon landscape research, accelerating the accumulation and dissemination of research results. From the increasing trend in the number of studies year by year, it can be inferred that the activity in the field of low-carbon landscape research continues to increase and may continue to grow in the future.

3.2. Subject Area Distribution

Research related to low-carbon landscapes covers 142 subject areas, and the number of disciplines with more than 100 publications is 17. Statistically ranking the top 10 subject areas in terms of the number of publications (

Table 1. Top 10 subject areas of this study in terms of publications.

Number	Subject Area	Number of Published Papers
1	Energy Fuels	1205
2	Environmental Sciences	877
3	Green Sustainable Science Technology	516
4	Engineering Environmental	405
5	Engineering Chemical	382
6	Environmental Studies	325
7	Materials Science Multidisciplinary	217
8	Thermodynamics	202
9	Engineering Electrical Electronic	174
10	Metallurgy Metallurgical Engineering	149

), the subject area with the highest number of publications is energy fuels (1205), followed by environmental sciences (877). There are also disciplines such as green sustainable technology, engineering environment, and engineering chemistry on the list, but with relatively few publications. The discipline of energy fuels is dedicated to the study of technologies and infrastructures related to low-carbon energy systems [28,29], as well as the impact of renewable energy sources on societal production [30,31]. The field of environmental sciences is more concerned with the impact of carbon emissions on the social environment and, secondly, carbon capture and sequestration (CCS) technology has also attracted the attention of many scholars [32,33,34]. Overall, energy fuels and environmental sciences occupy an important place in the research related to low-carbon landscapes.

3.3. National/Regional Cooperation Network

In the CiteSpace software, the author’s nationality was selected as the research object for analysis, the parameters were set to the default parameters of the software, and the time span was set to 2002–2023. Figure 3 shows the network of cooperation among countries. A total of 106 countries or regions have published relevant research studies. The basic information of the figure is N = 106, E = 781, and density = 0.1403. The size of the nodes in the figure reflects the number of papers issued by a country, the thickness of the node connections reflects the frequency of cooperation between countries, and the purple outer circle reflects that the country has a greater influence in the cooperation network.

Table 2. The 10 countries or regions with the highest number of publications and centrality in this study.

Number	Count	Centrality	Year	Countries	Count	Centrality	Year	Countries
1	972	0.18	2002	China	474	0.27	2002	USA
2	474	0.27	2002	USA	972	0.18	2002	China
3	291	0.14	2004	England	291	0.14	2004	England
4	167	0.14	2002	Germany	167	0.14	2002	Germany
5	136	0.09	2006	Italy	77	0.11	2003	France
6	132	0.04	2007	Australia	136	0.09	2006	Italy
7	117	0.09	2003	India	117	0.09	2003	India
8	109	0.08	2008	Spain	54	0.09	2006	Austria
9	108	0.07	2003	Canada	109	0.08	2008	Spain
10	104	0.05	2005	Japan	108	0.07	2003	Canada

lists the 10 countries or regions with the highest number of publications and centrality. The higher the centrality value, the greater the influence of the literature in the country or region [35]. The year indicates the first publication of relevant research literature in the country or region. The country with the highest number of publications is China (972), followed by the United States (474), England (291), and Germany (167). In terms of centrality, the United States (0.27), China (0.18), and England (0.14) occupy the top three spots, while France (0.11) and Austria (0.09) have a relatively high influence despite their small number of publications.

China is committed to studying how to improve the use efficiency of energy materials to better meet its environmental application and the impact of urban form changes on carbon dioxide emissions [36,37,38]. In addition, the United States mainly studies biofuels in low-carbon energy, as well as the separation and capture of carbon dioxide, so as to achieve the purpose of reducing carbon emissions [32,39,40]. England focuses on soil carbon sequestration research and the public acceptance of low-carbon energy facilities [29,41]. Overall, low-carbon landscape research has gained more attention from developed countries, with developing countries, with the exception of China and India, paying less attention to the field. However, country/regional cooperation network analysis is also influenced by a number of other factors. For example, publications published in English tend to be more widely disseminated and cited. This may make English-speaking countries appear more prominent in the network of cooperation, while the actual cooperation and influence of other language countries may be obscured to some extent. In addition, differences in the research priorities and directions of different institutions may affect the presentation of collaborative networks. Some institutions may focus on specific areas of research, and their partnerships are focused on countries or regions within that area.

3.4. Institutional Cooperation Network

The authors’ institution was selected as the research object for analysis, the parameters were set as the default parameters of the software, and the time span was set to 2002–2023. As can be seen from

Table 3. The 10 institutions with the highest number of publications and centrality in this study. Notes: CAS: “Chinese Academy of Sciences”; USDOE: “United States Department of Energy”; TU: “Tsinghua University”; NCEPU: “North China Electric Power University”; ICL: “Imperial College London”; UC: “University of California”; UCAS: “University of Chinese Academy of Sciences”; UL: “University of London”; SFITD: “Swiss Federal Institutes of Technology Domain”; CNRS: “French National Center for Scientific Research”; FDU: “Fudan University”; SJTU: “Shanghai Jiao Tong University”; INRAE: “French National Research Institute for Agriculture, Food and Environment”; IITS: “Indian Institute of Technology System”.

Number	Count	Centrality	Year	Institutions	Count	Centrality	Year	Institutions
1	109	0.2	2002	CAS	109	0.2	2002	CAS
2	66	0.06	2010	TU	65	0.13	2003	USDOE
3	65	0.13	2003	USDOE	44	0.08	2002	UC
4	60	0.02	2015	NCEPU	66	0.06	2010	TU
5	44	0.08	2002	UC	19	0.06	2015	FU
6	44	0.02	2007	ICL	12	0.06	2003	INRAE
7	37	0.01	2008	UCAS	34	0.05	2016	UL
8	34	0.05	2016	UL	19	0.05	2004	IITS
9	33	0.04	2006	SFITD	33	0.04	2006	SFITD
10	25	0.03	2018	SJTU	22	0.04	2003	CNRS

, five of the top ten institutions are from China, with the Chinese Academy of Sciences having the most publications (109), followed by Tsinghua University (66) and the US Department of Energy (65). In terms of centrality, the Chinese Academy of Sciences (0.2) has the most influence, followed by the US Department of Energy (0.13) and the University of California (0.08). Figure 4 shows the cooperative relationship between institutions. The basic information of the figure is N = 522, E = 1072, and density = 0.0079. A total of 522 institutions around the world have participated in the research on low-carbon landscapes. As can be seen from the figure, institutions in this research field have formed a rich cooperative network, among which the two institutions that have contributed the most are the Chinese Academy of Sciences and the US Department of Energy, which have worked closely with several research institutions. In addition, although the University of California has a small number of publications, it has a greater influence in this field.

3.5. Frequently Cited Literature

Ranking the number of citations in the literature of studies related to low-carbon landscapes (

Table 4. The top 10 most frequently cited papers in this study.

Number	Author	Title	Year	Journal Name	Citations
1	Fargione, J [39]	Land clearing and the biofuel carbon debt	2008	Science	2590
2	Rumpel, C [42]	Deep soil organic matter—a key but poorly understood component of terrestrial C cycle	2011	Plant and Soil	1192
3	Raja, PB [44]	Natural products as corrosion inhibitor for metals in corrosive media—a review	2008	Materials Letters	781
4	White, CM [32]	Separation and capture of CO2 from large stationary sources and sequestration in geological formations—coalbeds and deep saline aquifers	2003	Journal of the AIR & Waste Management Association	598
5	de Jong, M [45]	Sustainable–smart–resilient–low-carbon–eco-knowledge cities; making sense of a multitude of concepts promoting sustainable urbanization	2015	Journal of Cleaner Production	594
6	Carroll, A [40]	Cellulosic biofuels	2009	Annual Review of Plant Biology	564
7	Sun, YN [36]	Effects of feedstock type, production method, and pyrolysis temperature on biochar and hydrochar properties	2014	Chemical Engineering Journal	534
8	Satapathy, AK [46]	Corrosion inhibition by Justicia gendarussa plant extract in hydrochloric acid solution	2009	Corrosion Science	552
9	Zhang, LF [47]	State of the art in evaluation and control of steel cleanliness	2003	ISIJ International	511
10	Santamaria, L [43]	Why are most aquatic plants widely distributed? Dispersal, clonal growth and small-scale heterogeneity in a stressful environment	2002	Acta Oecologica—International Journal of Ecology	490

), it can be found that the publication time of the ten most frequently cited studies is distributed in the period of 2002–2015, and seven of them are all concentrated in the period before 2010. Relevant research directions mainly focus on low-carbon energy, low-carbon technology, low-carbon materials, and low-carbon plants. For example, a paper by Fargione et al. [39] published in Science discusses the advantages of using biofuels as a low-carbon energy source (highest citation frequency of 2590). It has catalyzed a series of subsequent studies on biofuel production technologies, environmental impact assessments, and economic viability analyses. A paper published in Plant and Soil by Rumpel et al. [42] investigated the origin, composition, stabilization, and destabilization mechanisms of deep soil organic matter (cited 1192 times). By studying deep soil organic matter, we can better understand the microbial mechanism of soil carbon cycling so as to enhance the carbon sequestration capacity of soil. Santamaria et al. [43] revealed the low-carbon availability of aquatic plants and the reasons for its wide distribution. This article increases awareness of the importance of low-carbon plants in ecosystem services. In addition, the most frequently cited literature may not fully reflect the impact of certain types of publications. Some publications may have important practical value or social impact, but the number of citations is relatively small because their audience is mainly non-academic, for example, some technical reports, internal research results, or popular science articles.

3.6. Keyword Co-Occurrence Analysis

The co-occurrence analysis of keywords can reflect the research hotspot of low-carbon landscapes. In this section, CiteSpace software is used to select keywords as objects, and Pathfinder, Pruning sliced networks, and Pruning the merged network in the Pruning column are checked for visual analysis, while other parameter settings remain unchanged. The basic information in Figure 5 is N = 650, E = 981, and density = 0.0047. The size of the nodes in the figure represents the frequency of keyword occurrence, and the thickness of the lines represents the correlation strength between the nodes. The figure reflects the diversity and complexity of the research contents in this research field, and different research contents form certain connections.

Table 5. The 10 keywords with the highest posting volume and centrality in this study.

Number	Count	Centrality	Year	Keywords	Count	Centrality	Year	Keywords
1	271	0.05	2004	Energy	142	0.34	2003	Emissions
2	181	0.01	2012	Renewable energy	13	0.19	2006	Responses
3	178	0.02	2011	Performance	73	0.18	2002	Carbon
4	165	0.06	2008	Climate change	53	0.16	2013	Energy efficiency
5	156	0.01	2008	Life cycle assessment	6	0.14	2019	Nitric oxide
6	151	0.03	2009	Model	87	0.13	2011	Electricity
7	144	0.1	2010	Storage	36	0.13	2010	Carbon capture and storage
8	144	0.01	2011	Generation	83	0.12	2007	Biomass
9	143	0	2013	Optimization	51	0.12	2003	Coal
10	142	0.34	2003	Emissions	48	0.11	2012	Hydrogen

shows 10 keywords with the highest frequency and influence in this research field. The most frequent keywords include energy (271), renewable energy (181), performance (178), climate change (165), life cycle assessment (156), and model (151). These keywords received great research attention, but their centrality was generally low, indicating that their influence was small. Keywords with high centrality include emissions (0.34), responses (0.19), carbon (0.18), energy efficiency (0.16), nitric oxide (0.14), and electricity (0.13). Although these keywords appear less frequently, their influence is higher.

According to Figure 4 and Table 5, research hotspots in this research field include carbon emission reduction, renewable energy, life cycle assessment, and the development and application of low-carbon materials.

Reducing carbon emissions has become a topic of universal concern around the world, and it is also a goal that governments need to make efforts towards. In order to reduce urban carbon emissions, related research has invested more research efforts in many fields, such as buildings, energy, transportation, and agriculture. For example, with the help of sustainability indicators, GIS mapping, and city models, Tillie et al. concluded that densification and greening can help drive the transition of city centers to more livable, low-carbon cities [48]. Secondly, the progressive building envelope design method studied by Liu et al. can significantly decrease energy consumption and carbon emissions and promote the sustainable development of green and low-carbon buildings [49]. In addition, studies have shown that pumped storage hydropower is a low-cost, low-GHG emission energy storage technology that can be sited and designed to minimize negative social and environmental impacts [50]. Ye et al.’s research shows that a low-carbon transport-oriented urban spatial structure is conducive to reducing motor vehicle traffic and thus promoting energy conservation and emission reduction [51]. In addition, Guo et al.’s research shows that the reasonable adjustment of planting structures can effectively reduce carbon emissions and promote the process of low-carbon agricultural modernization [52].

The scale and proportion of renewable energy is gradually increasing with the rapid development of society, which is the development trend of today’s society, involving wind energy, solar energy, water energy, geothermal energy, biomass energy, and other disciplines. Studies have shown that microalgae anaerobic digestion is a promising environmental option for creating renewable energy for industrial and domestic needs [53]. At the same time, Meyers et al. developed a techno-economic evaluation method to compare the cost-effectiveness of solar thermal and electric steam compression heat pumps in process heat production [54]. In addition, Karschin et al. proposed a linear mathematical model for optimizing efficient cogeneration and district heating system planning in bioenergy villages [55]. The three-stage integrated scheduling method proposed by Ding et al. can make full use of wind energy and achieve the goal of the economic scheduling of power systems [56]. In addition, the Meyers et al. study compared the input costs and economic competitiveness of solar thermal and photovoltaic (PV) thermal energy for electricity demand [57].

Life cycle assessment (LCA) is a method of investigating and assessing environmental loads and assessing the environmental impact generated by all stages of a product or service. LCA has played a positive role in reducing environmental impacts, cutting costs, improving efficiency, and meeting stakeholder needs [58]. Similarly, LCA methods have been applied to eco-industrial parks for synergistic organic waste treatment and to improve the performance of low-carbon megacities and large cities [59]. In addition, urban parks play an important role in mitigating climate change as a source of carbon absorption. LCA estimates the life cycle carbon budget of urban parks based on land cover type and explores ecological design and construction strategies that minimize carbon emissions [60]. Alvarado et al. used LCA to assess the environmental impact of different wastewater treatment configurations in order to achieve resource recovery and energy efficiency improvement [61]. In addition, Wang et al. established a low-carbon economic operation model of the integrated energy system with carbon capture technology and analyzed greenhouse gas emissions of different energy chains in the integrated energy system using the life cycle assessment method, and the results showed that the reasonable planning of carbon trading markets and the transformation of high-carbon power plants could effectively promote the low-carbon development of the integrated energy system [62].

The development and application of low-carbon materials can reduce the negative impact of economic development on the ecosystem. Low-carbon materials generally have good performance, less consumption of resources and energy, less pollution of the ecological environment, and a high renewable utilization rate and degradable recycling rate. Research has shown that cannabis lime has excellent hygrothermal properties as a building material and is an ideal renewable, low-carbon material. It is characterized by low energy consumption, both during construction and during use, and offers opportunities for recycling at the end of its service life [63]. In addition, Nie et al. developed a model to calculate the carbon dioxide emissions of several low-carbon adhesives and ordinary Portland cement, and the results showed that CO₂ emissions in cement production could be further reduced by using a large number of auxiliary cementing materials, which also provided a valuable reference for the design of new low-carbon adhesives [64]. At the same time, the study of Shimamoto et al. showed that rice husk is a plant-friendly and durable structural material, which can replace cement in agricultural infrastructure to reduce carbon dioxide emissions and contribute to a low-carbon society [65]. Secondly, Sheng et al. achieved high-strength bonding at the interface of a bamboo shaving/magnesium chloride lightweight composite by mimicking the behavior of spiders catching flying insects. This material is an advanced composite for construction and decoration, and its low-loading characteristics can reduce carbon footprint calculations [66]. In addition, studies have shown that plant fiber composites have the advantages of abundant resources, low price, renewability, degradability, and high specific strength and specific modulus, and are widely used in low-carbon emission fields such as automobiles and buildings. They have played a positive role in reducing the impact on the ecological environment and promoting sustainable development [67].

These research hotspots have played a positive role in promoting urban planning and sustainable development. For example, urban planning policy makers can develop clear carbon emission targets for inclusion in urban planning standards based on the potential of low-carbon landscapes to reduce carbon emissions. Secondly, renewable energy research will promote the transformation of the urban energy structure, reduce dependence on traditional fossil energy, and reduce carbon emissions. In addition, the results of the life cycle assessment can be used as criteria and guidelines for the selection of urban construction materials to reduce energy consumption and environmental impact. Urban planning policy makers can formulate relevant industrial support policies to encourage enterprises to increase investment in the research, development, and production of low-carbon materials and incorporate the application of low-carbon materials into urban building codes and standards to improve the low-carbon level of urban buildings.

3.7. Time Zone Distribution of Keywords

A keyword time zone distribution map can directly reflect the development of the research field in different periods. In this section, CiteSpace software is used to select keywords as objects, and Pathfinder, Pruning sliced networks, and Pruning the merged network in the Pruning column are checked for visual analysis, while other parameter settings remain unchanged. The basic information in Figure 6 is N = 650, E = 981, and density = 0.0047. Figure 6 shows the diversity and complexity of the development process of this research field, with new keywords generated every year. During the period from 2002 to 2023, the research journey in this field has undergone three stages of development.

The first stage (2002–2007): The high-frequency keywords in this phase reflect the research focus during 2002–2007, and also provide ideas for future research directions. This stage is dominated by theoretical research on low-carbon technologies, with research focusing on carbon dioxide emission-reduction technologies, the application of renewable energy, and the low-carbon value of plants. Carbon dioxide emission-reduction technology mainly focuses on carbon separation technology, carbon capture, and carbon storage technology. In addition, the application of renewable energy covers solar energy, wind energy, water energy, hydrogen energy, biomass, and other aspects. Moreover, studies have shown that the low-carbon value of plants is mainly reflected in nitrogen fixation, photosynthesis, and aerobic decay.

The second stage (2008–2018): In this phase, the research focus shifts to the application of low-carbon technologies, and many new keywords emerge. The main research contents include low-carbon city construction, life cycle assessment, and the development and application of low-carbon materials. Related studies explore the construction of low-carbon cities from the perspectives of urban spatial structure, transportation mode, land use, and landscape construction. In addition, studies have shown that the life cycle assessment of energy systems, power systems, organic matter waste conversion, and building materials plays an important role in reducing carbon emissions. Moreover, the development and application of low-carbon materials have had a positive impact on low-carbon landscape design.

The third stage (2019–2023): With the passage of time, during the period of 2019 to 2023, the new keyword volume gradually reduces. In this stage, the research focuses on the development of a low-carbon economy, including economic and technical analysis, integrated energy systems, dual-carbon policy, etc. Economic and technical analysis is an important part of exploring the development of a low-carbon economy, and also plays a role in promoting the optimization of integrated energy systems. In addition, carbon neutrality and carbon peaks have become key issues of public concern during this period.

3.8. Keyword Emergence Analysis

Through burst keywords, we can find that the research in a certain field presents an evolutionary trend from macro to micro, from single to diversified. The greater the burst intensity, the higher the frequency of the keyword in a certain period of time, indicating that there are more studies related to it in this period [68]. Using CiteSpace software, the pruning method is selected as Pathfinder, Pruning sliced networks, and Pruning the merged network, and the other parameters are default values. Figure 7 shows the top 25 burst keywords in the study, sorted by the year the burst began.

The early emergent keywords are as follows: low-carbon steel (8.5), mild steel (8.05), nitrogen (7.89), carbon capture and carbon capture storage (6.68), growth (5.33), aluminum (5.32), iron (5.3), climate change (5.22), plant extracts (4.6), and carbon (3.91). These emergent keywords had emergent durations of 4 to 10 years, overlapping each other in time. During this period, this research area actively carried out research related to the development and application of low-carbon materials and carbon reduction technologies. Low-carbon steel and mild steel represent an important research direction in the field of low-carbon materials, and in the context of carbon reduction, the development and application of these low-carbon steel materials are of great importance to reduce carbon emissions in the industrial sector. Although nitrogen is not directly related to the topic of carbon emission reduction, the treatment and emission of nitrogen in some industrial processes will also have an impact on the environment. The rational control of nitrogen emissions can synergistically reduce adverse climate impacts. In 1997, the United Nations created a plan called the Kyoto Protocol, which stipulated that countries around the world must work to reduce the amount of carbon dioxide they release into the air. Therefore, different countries have put forward different policies to reduce carbon dioxide emissions, and carbon emission-reduction technology has become a research hotspot. Among them, carbon capture and storage (CCS) technology is an important frontier in this research field.

The emergent keywords in the medium term are as follows: renewable energy (6.82), scenarios (6.52), integration (5.5), carbon capture (5.29), uncertainty (5.15), pilot plant (4.75), systems (4.62), CO₂ capture (4.2), and greenhouse gas emissions (4.17). The duration of the emergence of emergent keywords in this phase was between 2 and 4 years, with a gradual decrease in duration compared to earlier periods. This phase continued the research on carbon reduction technologies, and the scope of research expanded from fossil fuel power generation technologies to renewable energy power generation technologies such as wind, solar, hydrogen, and biomass. Therefore, more strategies and plans were put forward, such as using renewable energy for city electrification and the construction of low-carbon and climate-adaptive communities [69]. The emergence of renewable energy reflects the research field’s exploration of alternatives to traditional fossil energy. Studies in scenarios can help develop different carbon reduction strategies and plan future energy development paths. Integration emphasizes the integration and synergy of energy systems. Renewable energy is integrated with traditional energy systems to maximize energy efficiency and carbon reduction. Carbon capture remains one of the key technologies in the medium term, but its research focus is likely to be more focused on the optimization and practical application of the technology. In addition, life cycle assessment has become the international standard methodology for various resources, energy consumption, and environmental emissions, as well as for evaluating their environmental impacts.

The recent emergent keywords are as follows: techno-economic analysis (6.2), renewable energy sources (4.58), politics (4.1), power to gas (4.1), water electrolysis (4.01), and climate change mitigation (3.88). During this period, the world was plunged into an economic crisis due to the new coronavirus outbreak. Therefore, low-carbon economic development plays a very important role in achieving global economic recovery. The application of techno-economic analysis methods has become the focus of this research area. The focus on techno-economic analysis means that, when studying carbon reduction technologies and projects, more attention is paid to the economic and feasibility analysis of technologies. The continued development of renewable energy sources reflects the continuous attention and research on renewable energy. The emergence of politics shows that carbon reduction has become an important political issue. Governments promote carbon emission reduction by formulating policies and regulations, and political factors have an increasingly significant impact on carbon emission reduction. In addition, integrated energy systems are recognized as an effective means of increasing efficiency and reducing carbon emissions [70]. At the same time, electricity-to-gas technology has become an important research topic as an optimal way to increase the utilization of renewable energy.

3.9. Literature Co-Citation Cluster Analysis

In this section, the cited literature is selected as the research object for cluster analysis, the time span is set as 2002–2023, and other parameters are set as the default parameters of the software. Figure 8 illustrates the literature co-citation clustering network for the top 10 in the ranking; the basic information of the graph is N = 1969, E = 6102, density = 0.0031, Q = 0.9205, and S = 0.9856. Modularity Q and average contour value S are two indexes that can be used to test clustering reliability [71]. Clusters with modularity Q > 0.3 and S > 0.5 are considered reasonable, and clusters with S > 0.7 are considered convincing. Therefore, the clustering results derived from the figure are plausible and structurally significant. As can be seen from Figure 8, the literature co-cited clustering labels mainly involve energy, technology, ecological environment, and other aspects, providing a rich perspective and direction for the study of low-carbon landscapes.

One cluster of labels is related to energy production and supply. These labels include conventional energy (#0 coalbed), low-carbon power and generation (#1 low-carbon power system and #2 power generation), and carbon capture and integrated energy systems (#4 incorporating carbon capture power plant and #6 integrated energy system). Although the traditional coal energy represented by coal seams has problems in terms of high carbon emissions, we cannot ignore its historical position and existing scale in the energy structure. It is crucial to investigate how to decarbonize the traditional energy extraction and utilization processes associated with coal seams. Low-carbon electricity and power generation is a key foundation for building a low-carbon landscape. Through carbon capture technology, carbon dioxide produced by power plants can be captured and stored, reducing its impact on the environment. The integrated energy system integrates multiple energy forms to improve energy efficiency and reduce carbon emissions. In a low-carbon landscape, integrated energy systems can provide clean, reliable energy support for a wide range of facilities and activities.

The second cluster of labels is related to technology and material application. Propulsion system technology (#3) is mainly concerned with the low-carbon development of the transportation sector. In a low-carbon landscape, optimizing the energy efficiency of transport systems is one of the keys. The development of efficient propulsion system technologies, such as the powertrain of electric vehicles, can reduce transport carbon emissions. The application of low-carbon steel (#8) as a material in landscape construction is also relevant to low-carbon goals. Choosing low-carbon steel for building structures, landscape facilities, etc., can reduce carbon emissions in the production and use of materials. At the same time, the research and development of new low-carbon materials is also an important direction to promote the development of low-carbon landscapes.

The third cluster of labels is related to ecology and environment. Aquatic plants (#5) play an important ecological role in low-carbon landscapes. They can not only absorb carbon dioxide and release oxygen but also purify water and improve the quality of the water environment. Through the rational use of aquatic plants, ecological wetlands, water features, and other landscape elements can be constructed, increasing biodiversity and enhancing the ecological value of the landscape. Mechanism (#7) research involves the internal principles and laws of various low-carbon-related processes in the ecosystem. For example, studying the carbon cycle mechanism and the energy flow mechanism of the ecosystem will help to better understand and optimize the ecological functions of low-carbon landscapes. In addition, label #9 reflects the latest research results and trends in the field. Through the attention and analysis of recent research, new technologies, methods, and concepts can be learned in time to provide the latest scientific basis and innovative ideas for the creation of low-carbon landscapes. At the same time, it can also promote communication, integration between different research directions, and the continuous development of the entire field.

3.10. Frontiers of Research on Key Issues

According to the time zone distribution of keywords and the analysis of the co-occurrence and emergence of keywords, it is found that the research frontier of low-carbon landscapes from 2002 to 2023 mainly focuses on three key issues: emission-reduction technology of low-carbon landscapes, research methods of low-carbon landscapes, and the development and application of low-carbon materials. However, CiteSpace is mainly based on the analysis of the existing literature, and it is difficult to effectively predict and discover those research directions and innovative ideas that have not been published or are in the process of being conceived. This, to some extent, limits its application value in the field of cutting-edge research and innovation.

3.10.1. Emission-Reduction Technology for Low-Carbon Landscapes

There is growing concern about the impact of greenhouse gas emissions on climate change, and reducing reliance on carbon-emitting activities is a goal of concerted efforts by governments and the international community [15]. Some studies have explored emission-reduction technologies for low-carbon landscapes, such as low-carbon energy technology [72], desulfurization technology [73], carbon capture and storage technology [74], nitrogen removal technology [75], gasification technology [76], and power-to-gas technology [77]. Among them, Posch et al. [78] pointed out that oxygen-rich combustion power plants, as one of the main technologies of carbon capture and storage, produced the lowest carbon dioxide purity. In addition, Yang et al. [79] proposed a new coal-glycol technology that significantly reduces carbon emissions and production costs compared to traditional processes. Feng et al. [80] confirmed that climate-smart agriculture (CSA) can effectively improve crop productivity, reduce carbon emissions, and enhance soil resilience to climate change. It can also be regarded as a promising practice for achieving food security and reducing carbon emissions. Denny et al. [81] showed that soil health improves the soil carbon sequestration capacity and that shifting from low-productivity pastures to carbon-based agricultural regeneration projects can help meet emissions targets. In addition, the large-scale use of biomass in energy-related applications is essential to reduce CO₂ emissions from fossil fuels. Cormos et al. [82] found that the direct chemical cycling of biomass has both high energy efficiency and an almost complete carbon capture rate (>99%). Xiang et al. [83] found that the transformation of traditional long-distance transportation in drainage systems and the biological treatment of terminal sewage can effectively reduce greenhouse gas emissions. Through low-carbon construction and operation technology, the greenhouse gas emissions of a mountain residential water system could be reduced by more than 30%. In addition, Ji et al. [84] developed an economical, efficient, and sustainable low-carbon urban sewage treatment technology, which effectively reduced carbon emissions in the process of urban sewage treatment. The technology enables mass and energy flow optimization through carbon management, resulting in high treatment efficiencies and low operational energy consumption, generating carbon emissions 4.1 times lower than conventional processes. So far, the emission-reduction technology of low-carbon landscapes is mainly applied to green energy technology, traditional fossil energy energy-saving emission-reduction technology, and other industry process energy-saving emission-reduction technologies. Among them, power, steel, construction, and other industries have become the key areas for the development of low-carbon emission-reduction technologies. In terms of maturity, some technologies have achieved certain results, but there is still room for improvement. For example, although low-carbon urban sewage treatment technology can effectively reduce emissions, it still needs to be improved in adapting to complex scenarios and large-scale promotion. In terms of scalability, most technologies have some potential but are limited by cost, technical adaptability, and other factors. The direct chemical cycle of biomass has high energy efficiency and a high carbon capture rate, but integration with other energy systems and cost control problems need to be solved for large-scale applications. Overall, these emission-reduction technologies require further research and practice to improve their performance and adaptability in different scale application scenarios.

3.10.2. Research Methods for Low-Carbon Landscapes

The research methods for low-carbon landscapes include literature analysis [85], the Delphi method [86], spatial analysis [87], the analytic hierarchy process [88], big data analysis [89], and life cycle assessment [90]. Among them, the life cycle assessment method is one of the most important research methods, which plays an important role in evaluating the impact of energy material utilization and waste discharge and evaluating environmental improvement. For example, Dong et al. [91] took Liuzhou, an industrial city in southern China, as an example and established an input–output model with the life cycle assessment method to evaluate the environmental benefits of the entire supply chain under the urban industrial symbiosis model. Guidi et al. [92] compared renewable energy technologies with traditional gas and coal technologies through life cycle assessment methods to determine the energy technologies with the least impact on the environment. Through this research method, Zhou et al. [93] found that reducing sludge landfills and increasing anaerobic digestion are effective ways to promote greenhouse gas emission reduction. At the same time, the life cycle assessment method has also been used to assess the impact of rural sewage treatment facility renovation on greenhouse gas emissions and carbon emission-reduction benefits [94]. Spatial analysis is mainly used in urban carbon emissions, low-carbon urban design, urban carbon sources, and carbon sinks and plays an important role in promoting the development of low-carbon cities. Some scholars have conducted relevant studies using this method. For example, Xia et al. [95] analyzed the correlation between urban carbon metabolism and the spatial change in urban form by combining spatial analysis with a landscape index, providing new ideas for low-carbon urban design. Peng et al. [96] evaluated the spatial siting potential of seven low-carbon energy power plants through spatial analysis and the analytic hierarchy process, providing guidance for the layout design of low-carbon energy power plants. In addition, with the deepening of research, the research method adopted by scholars is no longer a single system, but a research system composed of two or more research methods. In addition, Wu et al. [97] used natural experimental methods to review the research progress of green and low-carbon economics and found that, among many pollution problems, air pollution received the most attention, and the number of studies on climate change and energy issues was also increasing. Natural experimental methods are becoming more and more popular and diversified. In general, the combination of qualitative and quantitative empirical and evaluative research systems is favored by the majority of scholars.

3.10.3. Development and Application of Low-Carbon Materials

Low-carbon materials refer to materials that produce lower carbon emissions during production, use, and disposal. These materials play a key role in reducing negative impacts on the environment. The development and application of low-carbon materials are mainly concentrated in the construction industry, metal materials, energy production, and other fields. Low-carbon building materials, as an emerging industry in recent years, occupy an important position in building materials, and more and more low-carbon building materials are being developed, produced, and applied, such as eco-cement, bamboo and carbon wall paint, organic glass, and so on. Wu et al. [98] found that low-carbon plant-compatible ecological concrete is a new functional slope protection material that perfectly combines engineering protection and ecological restoration, and is more environmentally friendly, cost-saving, and energy-saving than traditional ecological concrete. Wiranata et al. [99] confirmed that coal fly ash and coal bottom ash are a viable solution as pavement base materials that can help develop transportation infrastructure with enhanced concrete durability and a reduced carbon footprint. Alaneme et al. [100] believe that mycelium-based composite materials are ideal materials in the field of building and construction, which have low energy consumption, low cost, biodegradability, and a series of attractive properties but need to be improved in terms of weather resistance, hydrophilicity, and scalability. In the field of metal materials, there has been much interest in research into low-carbon steel. For example, Lee et al. [101] compared the corrosion resistance of conventional mild steel, copper-containing mild steel, and stainless steel 409 and found that copper-containing mild steel has the highest corrosion resistance, and its surface corrosion product layer is denser and thicker than other steels. Guo et al. [102] found through dry–wet cycle tests that low-carbon microalloy bainite steel has better corrosion resistance than traditional weathering steel because the surface layer of the sheet has a uniform bainite structure. In the field of energy production, low-carbon materials can be used to improve the efficiency of energy production and reduce carbon emissions. For example, Lzydorczy et al. [103] found that extracts obtained from alfalfa and goldenrod could be used as renewable energy sources, producing lower carbon and hydrogen content. Bao et al. [104] summarized the application methods for low-carbon energy in rural landscape transformation planning and put forward measures and suggestions such as solar lighting, flat panel solar photovoltaic power generation, and solar water heaters. In general, in the construction industry, ecological cement and other materials have energy saving, environmental protection, and good engineering performance, and reduce the carbon emissions of the whole life cycle of the building. Low-carbon steel in the field of metal materials reduces maintenance costs and resource consumption due to its excellent corrosion resistance. Related low-carbon materials in the field of energy production can efficiently convert energy and significantly reduce carbon emissions and environmental impact. However, there is still room for further improvement in the performance optimization and environmental impact minimization of various materials.

3.10.4. Correlation and Synergy of Key Issues

In the previous section, we discussed the three key aspects of low-carbon landscape emission-reduction technology, research methods, and the development and application of low-carbon materials. However, these fields do not exist in isolation; there are many potential overlaps or synergies. The first is the synergy of emission-reduction technologies and research methods. For example, life cycle assessment, as an important research method, provides a powerful tool for the assessment and optimization of emission-reduction technologies. In addition, in the study of urban carbon emissions, the combination of spatial analysis and emission-reduction technology can better plan urban transportation, buildings, and other infrastructure and realize the reasonable distribution of carbon sources and carbon sinks, thus improving the emission-reduction effect of the whole city. The second is the mutual promotion of emission-reduction technology and low-carbon materials. For example, the development and application of low-carbon materials provide a key material foundation for emission-reduction technologies. In addition, the continuous progress of emission-reduction technology has put forward higher requirements for the performance and quality of low-carbon materials, thus promoting the research, development, and innovation of low-carbon materials. The third is the guiding role of the research method in the development and application of low-carbon materials. For example, literature analysis can provide an understanding of the research status, development trend, and existing problems of low-carbon materials by combing and analyzing the existing research literature related to low-carbon materials and providing theoretical support and research ideas for the research and development of new low-carbon materials. In addition, big data analysis can collect and analyze a large number of data related to low-carbon materials, such as material performance parameters, market demand data, etc., and explore potential performance optimization directions and market opportunities through data analysis. Understanding and leveraging these synergies will help drive comprehensive development and innovation in the low-carbon landscape to achieve better emission reductions and sustainable development goals.

3.11. Future Research Direction

The low-carbon landscape is the development direction of future cities and an important way to achieve carbon emission reduction. With the speeding up of urbanization, the city has become the main source of environmental pollution in the world; an increasing number of scholars and policy makers have begun to pay close attention to low-carbon landscapes and related research and policy making. At present, low-carbon landscapes have accomplished some achievements in theory, technology, and practice. Based on the above analysis, the authors believe that the further research direction of low-carbon landscapes can include the following contents:

The first is the economic benefit assessment of low-carbon landscapes. Assessing the economic costs and benefits of low-carbon landscapes and exploring their sustainability in the long term is crucial for policy makers and planners to decide whether to adopt low-carbon landscape options. In addition, economic benefit assessment also plays an important role in optimizing resource allocation, risk assessment, and promoting innovation and improvement. Some studies on the economic benefit assessment of low-carbon landscapes have been carried out, such as low-carbon power systems [105,106], mild steel iron [107], and low-carbon energy [108]. At present, the economic benefit assessment of low-carbon landscapes still remains at the local scale of a few industries. In future research, the economic benefit assessment of low-carbon-landscape-related industries should be carried out and strengthened, especially in areas closely related to urban life, such as low-carbon gardens, low-carbon transportation, low-carbon buildings, etc. Through an accurate economic benefit assessment, the government can formulate tax incentives, subsidy policies, etc., to guide social capital to flow to low-carbon landscape projects and promote the green development of the city. Low-carbon landscape projects can enhance the resilience of cities and ecosystems and reduce the negative economic impacts of climate change. Economic evaluation can help us to quantify the toughness benefits and provide the basis for investment decisions.

The second is ecosystem restoration and conservation in low-carbon landscapes. With the development of human society, the ecological environment has suffered serious damage, and the stability of the ecological system has been seriously threatened. Ecosystem restoration and protection is a comprehensive process aiming to promote improvements in the ecological environment and sustainable development. It can increase carbon sinks and reduce landscape carbon emissions through vegetation restoration, wetland protection, and other means. In recent years, relevant studies have attracted wide attention from scholars, such as encouraging ecosystem restoration through carbon sink trading [109] and promoting ecosystem restoration by relying on an ecological afforestation model of an ant forest [110]. However, the quantitative analysis of low-carbon landscape ecosystem restoration and protection is still lacking in systematic and in-depth discussion. It can be seen that the quantitative analysis of carbon sinks may be the future research direction and focus. In addition, environmental education and public participation in ecosystem protection should also be highlighted so as to enhance people’s awareness of ecosystem value and protection awareness. Many countries and regions around the world have set policy goals for ecological conservation and restoration, such as increasing forest cover and protecting wetlands and biodiversity. Ecosystem restoration and conservation in low-carbon landscapes can directly support the implementation of these policies. In addition, they can also increase carbon sinks and reduce greenhouse gas concentrations in the atmosphere through means such as vegetation restoration and wetland protection.

The third is the social participation and policy support of low-carbon landscapes. Strengthening social participation, cultivating low-carbon awareness, and formulating policies and regulations to support low-carbon development are important guarantees to promote the construction of the low-carbon landscape. At present, the main problems include low social participation, insufficient binding and scientific policy goals, and the lack of effective social participation mechanisms. Some relevant studies have been carried out, such as community residents’ awareness of and participation in low-carbon behaviors in daily life [111], and the impact of the carbon emission trading system on low-carbon energy investment [112]. Therefore, future research could investigate how to promote the public’s perception of the low-carbon landscape and engagement, pay more attention to the impact of relevant policies on different fields and industries, and put forward specific suggestions for further promoting low-carbon development. Countries around the world are actively promoting sustainable development and the green transformation of society, as well as encouraging public participation in environmental protection and low-carbon actions. The public’s low-carbon awareness and behavior can directly affect the reduction in carbon emissions. By strengthening social participation and the education publicity of low-carbon landscapes, the public’s awareness of and responsibility for climate change can be enhanced, and the popularization of low-carbon lifestyles can be promoted. The government needs to develop and implement a series of policy measures, such as carbon emission limits, renewable energy subsidies, and green building standards, to promote the implementation and promotion of low-carbon landscape projects.

4. Conclusions

Using the CiteSpace Scientific Knowledge Visualization Graph software, this study analyzes the literature on low-carbon landscapes published in the WOS database between 2002 and 2023. Through the analysis of the annual number of publications, subject field distribution, cooperation network, keyword co-occurrence and emergence, keyword time zone distribution, and other aspects, the authors find that, since 2008, low-carbon landscape research has entered a period of rapid development, and the number of published documents has increased year by year. A study involving 141 subject areas, including fuel energy and environmental science, occupies the dominant position. Relevant institutions and scholars from 106 countries or regions participated in the low-carbon landscape research, among which the main contributors were China and the United States. Research hotspots include carbon emission reduction, renewable energy, life cycle assessment, and the development and application of low-carbon materials. The research frontiers mainly focus on three key issues: emission-reduction technology of low-carbon landscapes, research methods for low-carbon landscapes, and the development and application of low-carbon materials. This study deeply analyzes the research process of low-carbon landscapes, reviews the research directions and emphases in each stage, and puts forward the possible research directions for the future, which lays a foundation for scholars to carry out more research on low-carbon landscapes.