Advances, Hotspots, and Trends in Outdoor Education Research: A Bibliometric Analysis

Abstract

Utilizing the Web of Science database as a retrieval source, this study employs CiteSpace software to conduct a visualization analysis of 8380 documents related to outdoor education published from 1994 to 2023. The findings reveal a phased increase in the volume of outdoor education research, with a shift in research themes from environmental governance to environmental education, ultimately concentrating on education for sustainable development that is characterized by significant temporal features. Initially dominated by publications from Europe and North America, the geographical distribution of research has gradually expanded globally. The core research theme centres around environmental education, with experiential education, outdoor learning, and education for sustainable development evolving concurrently. The network structure of research collaboration predominantly involves higher education institutions, with a noticeable shift from limited disciplinary research to interdisciplinary integration across multiple fields.

1. Introduction

Since the onset of the 21st century, the rapid advancement of modern urban development and digital technologies has led to diminishing human interactions with natural environments [1,2,3]. In his groundbreaking 2005 publication of “Last Child in the Woods: Saving Our Children from Nature-Deficit Disorder”, Richard Louv introduced the concept of “nature-deficit disorder”, which emphasises the growing issue of children’s separation from nature [4]. Moreover, data from the Office for National Statistics in the United Kingdom revealed that, as of 2017, less than one-quarter of all children in the United Kingdom met the daily minimum activity recommendations. Moreover, nature-deficit disorder contributes to a variety of physical and mental health problems, such as attention deficit disorder, obesity, decreased adaptability, school bullying, and depression. Against this backdrop, outdoor education, which involves educational activities in natural settings, has been determined to effectively strengthen communication between humans and nature and foster comprehensive development, thereby positioning it as an effective strategy to address the aforementioned mental health issues.

A substantial body of research confirms the positive effects of outdoor education on children and adolescents’ cognitive, emotional, and behavioural development [5]. Cognitively, it not only enhances attention [6], but it also increases innovation [7], expands thinking patterns [8], and strengthens memory [9]. Emotionally, outdoor education cultivates empathy [10], enhances a sense of belonging to society and nature [11], and alleviates psychological stress [12]. Behaviourally, it promotes a range of prosocial and environmentally friendly behaviours [13].

In recent years, nearly a century of academic research on outdoor education has explored various facets, including its value implications [14], teacher training, safety management, exploration of teaching techniques [15], practical applications, and factors affecting curricula. Despite the rich insights gained from comprehensive past studies, identifying research trends and developments through subjective analysis and traditional literature reviews has become highly challenging. Thus, scientific knowledge maps that analyse research hotspots in outdoor education offer researchers a clearer view of current research topics and challenges, and thus, as such, they provide strong guidance for future research initiatives.

2. Research Methods, Data Sources, and Indicator Description

2.1. Research Methods

CiteSpace 6.2.R6 (64-bit) Advanced is an information visualization software developed by Dr. Chaomei Chen, a scholar from the College of Information Science and Technology at Drexel University in the United States. This software focuses on the measurement and analysis of scientific data, providing a panoramic view of high-citation literature, research themes, and keywords in various knowledge domains. It allows for an intuitive exploration of the development trajectory, potential driving mechanisms, and cutting-edge advancements in related research [16].

Using CiteSpace 6.2.R6 (64-bit) Advanced, network visualization analysis was conducted on the publication regions, keywords, research themes, disciplines, institutions, and authors associated with outdoor education research, which clarified important topics, theoretical evolution paths, and significant research turning points in this field. Additionally, Origin 2024 (V 10.0.1.178 ) software was used to plot a line graph of annual publication volumes in outdoor education, thus allowing for an analysis of the overall publication situation.

In the field of outdoor education, core keywords, denoted by $\mathrm{M}\approx 0.749\sqrt{{\mathrm{N}}_{\mathrm{m}\mathrm{a}\mathrm{x}}}$, were identified via Price’s law. This law facilitates the focus on pivotal terms. In the equation, ${\mathrm{N}}_{\mathrm{m}\mathrm{a}\mathrm{x}}$ represents the frequency of the most commonly occurring node within the statistical period, and M represents the threshold value. A node is considered a core node when its occurrence frequency reaches or exceeds the value of M. All statistical results in this study are presented without rounding.

2.2. Data Sources and Indicator Description

2.2.1. Subject Word Source

To date, there is no unified standard for the definition of outdoor education. Given that different countries and regions have varying cultural and philosophical perspectives, the history, intrinsic meaning, and practical models of outdoor education also differ. This concept has been a focal point of research and discussion among scholars both domestically and internationally. Donaldson [17] defined outdoor education as “experiential learning that occurs in outdoor environments, for the outdoors and about the outdoors”. This classic definition was significant within its theoretical and practical context at the time and laid the groundwork for subsequent research. Over time, as theories and practices in outdoor education have evolved, scholars have recognized the limitations of this definition. Priest [18] questioned this classic definition and reshaped it via the metaphorical model of the “outdoor education tree” (Figure 1), further expanding the meaning of outdoor education. He identified six characteristics that outdoor education should embody: (1) it is a method of learning, (2) it is experiential, (3) it primarily occurs outdoors, (4) it requires the involvement of all senses, (5) it is based on interdisciplinary curriculum issues, and (6) it involves the relationship between humans and natural resources. Subsequently, Dr. Bisson [19] suggested that outdoor education should be viewed as an inclusive term rather than a singular theme. He employed the umbrella model to visually present this concept, arguing that this metaphor is more appropriate because outdoor education encompasses a range of methods and content rather than being confined to a specific domain. On the basis of this view, Bisson constructed a visual aid model—the “outdoor education umbrella” (Figure 2), which includes eight distinct elements, such as environmental education, adventure education, and wilderness education. This diversified perspective provides a more comprehensive framework for the study of outdoor education, thereby facilitating an understanding of its wide-ranging applications and practical significance.

2.2.2. Database Selection

Web of Science (WOS) and Scopus are currently the two most widely used literature databases in academia. WOS is renowned for its stringent journal selection criteria and comprehensive citation analysis capabilities, making it a staple for academic research, evaluation, and literature analysis. In contrast, Scopus is characterized by its broad disciplinary coverage and more flexible literature search features. However, the citation data of WOS is obtained through a rigorous selection process, ensuring the authority and accuracy of the data. Mongeon [20] found that the impact of WOS factor and other citation metrics are widely used in academic evaluations and better reflect the actual influence of research. Liu [21] in an investigation into the non-transparency of WOS usage, discovered that an increasing number of papers in their respective fields referenced WOS. Moreover, WOS’s impact factor and other citation metrics are widely applied in academic evaluations, providing a more accurate reflection of research impact. Singh [22] conducted a comparative analysis of the WOS, Scopus, and Dimensions databases, highlighting notable differences in terms of data comprehensiveness and selectivity, with WOS demonstrating the highest level of selectivity. Additionally, Birkle [23] demonstrated that WOS’s diversity and depth make it more advantageous for application in specific fields, offering researchers richer data results and analytical perspectives. Therefore, choosing WOS not only provides access to extensive literature resources but also offers superior applicability and advantages in specific research contexts.

2.2.3. Data Sources

When conducting research using bibliometrics, it is essential to provide a detailed explanation of the data sources and the coverage years of the sub-datasets. The WOS core dataset comprises ten sub-datasets, and many institutions may subscribe only to a customized subset of the entire core dataset. For instance, in the field of Information Science and Library Science, more than half of the papers that reference WOS and use “Web of Science Core Collection” as a data source do not specify which sub-dataset of the WOS Core Collection was used. This lack of transparency regarding data sources can hinder the reproducibility of related studies, particularly in bibliometric analyses [21]. Therefore, when utilizing WOS as a data source for bibliometric analysis, it is necessary to clearly state the selected sub-datasets and their coverage years. In this study, we utilized the following data sources: Science Citation Index Expanded (1982–present, coverage years for the subscribed sub-dataset), Social Sciences Citation Index (1999–present), Arts & Humanities Citation Index (1975–present), Conference Proceedings Citation Index-Science (1990–present), Emerging Sources Citation Index (2019–present), Current Chemical Reactions (1985–present), and Index Chemicus (1993–present).

Clearly, whether outdoor education is likened to a “tree” or an “umbrella”, analysing the historical evolution and cutting-edge topics of research solely using “outdoor education” as a search term is too narrow for a panoramic review of the relevant literature. Therefore, this study integrates related terms and expands upon keywords associated with outdoor education, such as “outdoor learning”, “outdoor teaching”, and “outdoor pedagogy”, aiming for a more comprehensive exploration of research outcomes related to outdoor education. In summary, this study employs the search query TS = outdoor education OR TS = outdoor learning OR TS = outdoor pedagogy OR TS = camping education OR TS = camping education OR TS = earth education OR TS = environmental education OR TS = wilderness education OR TS = outdoor adventure pursuits education OR TS = adventure education OR TS = challenge education OR TS = experiential education for the period 1994 to 2023. The data sources included Science Citation Index Expanded, Social Sciences Citation Index, Arts & Humanities Citation Index, Conference Proceedings Citation Index-Science, Emerging Sources Citation Index, Current Chemical Reactions, and Index Chemicus, utilizing the comprehensive online literature database WOS in the United States. This search yielded 8399 records, which, after deduplication and screening via CiteSpace 6.2.R6 (64-bit) Advanced, resulted in 8380 articles as data sources (Figure 3). In the adjustment of indicators, unless otherwise specified, the time slice is set to one year, with a threshold of K = 25 for extracting knowledge units in each time slice, employing the pathfinder and pruning sliced network methods, while all other indicators are set to default values. The search was conducted on 25 January 2024.

3. Research Results and Analysis

3.1. Progress in Outdoor Education Research

3.1.1. Annual Publication Volume

A line graph depicting the annual publication volume from 1994 to 2023 was created on the basis of data collated by CiteSpace 6.2.R6 (64-bit) Advanced (Figure 4). This graph reveals that overall publication activity in the field of outdoor education experienced fluctuating growth during the years examined. Notably, the publication volume reached its first and second peaks in 2004 and 2013, respectively, with a sharp increase after 2018. Therefore, these years have been designated key temporal milestones, and the related research has been categorized into four distinct phases.

(1)

Initial Development Phase (1994–2004)

During this period, the focus of outdoor education was predominantly on naturalistic stages within traditional educational, environmental, and ecological disciplines. Influenced by the level of theoretical development at the time, the overall publication output was relatively low but showed a gradual yearly increase, averaging 50 papers per year, with a minor peak occurring in 2004. An analysis of highly cited literature from this phase indicates that the main research theme was the impact of environmental education on pro-environmental behaviours [24].

(2)

Steady Development Phase (2005–2013)

This period saw a significant increase in the number of outdoor education publications, especially from abroad, with the volume exceeding 100 for the first time in 2008 and averaging 156 papers per year until reaching another minor peak in 2013. The majority of publications originated from the United States and European countries. From a bibliometric perspective, the substantial annual increase in publications during this stage can be attributed not only to growing public interest but also to the rising emphasis placed by the academic community on research outcomes. In particular, the quantity and impact of published papers became crucial metrics for evaluating researchers and institutions within research assessment systems. Additionally, the rise of the Open Access publishing model and the proliferation of online journals facilitated rapid dissemination of research findings to broader audiences, thereby driving the growth in publication volume. Visualization of citation themes through WOS highlighted environmental education as a predominant topic. The established direction involved disseminating environmental concepts, enhancing environmental knowledge, and improving environmental behaviours [25]. Research has focused on children and adolescents’ environmental knowledge, attitudes, behaviours, and values with respect to nature. The most cited studies investigated the social–psychological determinants of individual pro-environmental behaviours [26].

(3)

Rapid Growth Phase (2014–2018)

From 2014 to 2018, underpinned by rapidly advancing scholarly foundations and innovations in digital technology, the output of outdoor education research grew significantly, with an average annual publication volume of 289 papers. The primary contributors during this phase were the United States, Brazil, Australia, China, Canada, and the United Kingdom. The swift increase in publication volume during this phase was likely influenced by factors such as research funding across disciplines, emerging research hotspots, and academic evaluation systems [27]. Research in this phase deepened its integration with societal foundations and scientific technologies, exploring new domains such as mobile devices in outdoor education [28]. The theoretical approach increasingly embraced interdisciplinary issues, with methodologies expanding alongside the rise of artificial intelligence and algorithmic technologies, while the most referenced studies focused on the impact of integrating mobile devices with teaching on student performance [29].

(4)

Vigorous Development Phase (2019–Present)

Since 2019, in response to the global educational crises and sustainable development challenges, nations and organizations worldwide have escalated strategic planning to promote high-quality foundational education. Additionally, concerns over children and adolescents’ health due to the COVID-19 pandemic and increased screen time have further spurred scholarly attention [30,31,32]. The close associations between outdoor education and youth foundational education, environmental education, natural education, and sustainable development education have significantly increased the relevant research outputs, with an average annual publication volume of 900 papers. It is noteworthy that the primary reason for the abnormal increase in publications at this stage may be the growing popularity of outdoor education and heightened public interest. Moreover, this surge in publication volume is closely linked to changes in external environments as well as intrinsic motivations for academic research. For instance, Liu [33] finds a significant increase in the number of publications related to climate change research during certain years, which can be attributed to shifts in global climate policies and heightened public awareness. This gradual increase in publication volume reflects the interaction between societal demands and scientific research to some extent. The main research directions focus on three aspects:

(i)

environmental education and sustainable development

Environmental education seeks to raise awareness and foster action on environmental issues, with a focus on nurturing environmental consciousness and advancing sustainability. Ardoin’s research indicates that effective outdoor education not only imparts knowledge but also shapes the environmental attitudes, knowledge, and values of children and adolescents, equipping them with the skills to drive positive environmental actions [34]. The significance of environmental education is underscored by the growing global challenges such as climate change and biodiversity loss, which require public engagement beyond technological solutions. By instilling a sense of responsibility and sustainable development awareness in the younger generation, environmental education can contribute to addressing these issues [35]. Despite the ongoing integration of environmental education into sustainable development, methodological challenges persist in research. van de Wetering [25] notes the heterogeneity of study samples and the complexity of influencing factors, which result in varying effect sizes and hinder the drawing of consistent conclusions due to the diversity of research designs. The heterogeneity among different age groups, educational approaches, and research designs remains underexplored, posing challenges for future studies. Therefore, future research in environmental education should concentrate on key areas. Firstly, it is essential to delve into the components and methods that effectively enhance environmental education. While it is known to improve environmental knowledge, attitudes, intentions, and behaviours among children and adolescents, the specific impact of various educational methods remains unclear. Future studies should investigate the effectiveness of different methods, such as classroom learning, field trips, and community involvement, to identify the most influential components. Secondly, examining adaptation strategies across diverse cultural contexts is crucial. Opoku [35] highlights the interplay between human development and environmental sustainability, suggesting that future research should explore the implementation of environmental education in various cultural and socio-economic settings to meet sustainable development goals.

(ii)

mental health and personal development

Psychological well-being influences not just learning and work productivity, but also social engagement and emotional regulation. Research by Gladys Barragan-Jason [36] indicates that a connection with nature, both mentally and physically, positively affects mental and physical health. Outdoor education offers an enhanced natural learning context, which can boost attention, alleviate stress, bolster self-discipline, and heighten interest and enjoyment in learning, as well as encourage physical activity and fitness, thereby facilitating academic progress [6]. While the advantages of outdoor education for health and personal growth are well documented and broadly recognized, current research predominantly consists of short-term interventions with scant assessment of long-term outcomes. Longitudinal studies should be conducted to assess the enduring effects of outdoor education on mental health and social adjustment capabilities.

(iii)

educational practices and policy research

Through outdoor activities, students engage directly with nature, bolstering their environmental consciousness and stewardship while cultivating critical thinking, collaboration, and problem-solving abilities. This form of education, with its focus on practical experience, facilitates learning within authentic settings, enhancing students’ comprehension of sustainable development principles. Internationally, outdoor education is increasingly being recognized and integrated into educational frameworks. Sweden, for example, promotes environmental awareness and skill development through outdoor activities within its educational policies [37]. South Korea has revised its curriculum to emphasize key competencies in environmental education, focusing on the intellectual, personal, and relational skills required by students [38]. However, there may be discrepancies between existing curricula and the objectives of sustainable development education. Teachers often grapple with time and resource constraints, hindering the implementation of outdoor education and practical activities. Despite research highlighting outdoor education’s potential, there are limitations that future studies should address by examining policy –practice integration, teacher training, student capability development, and the comprehensive implementation of outdoor education across diverse cultural and educational settings.

3.1.2. Geographic Distribution of Research in Outdoor Education

According to the CiteSpace 6.2.R6 (64-bit) Advanced visual bibliometric analysis, outdoor education research encompasses literature from 156 countries and regions. The United States holds a dominant position, contributing approximately 25.01% of the total publications, followed by Brazil with 915 articles (10.91%), Spain with 493 articles (5.88%), the United Kingdom with 484 articles (5.77%), Australia with 469 articles (5.59%), China with 446 articles (4.32%), and Canada with 428 articles (4.28%) (Figure 5). Drawing on the “Chronological Table of Science and Technology” and the Webster’s Biographical Dictionary, Japanese historians and physicists, such as Mitsuo Asai, have conducted statistical analyses of global scientific activities, defining a scientific centre as a country that contributes more than 25% to the significant global scientific achievements [39]. This criterion firmly establishes the United States as a scientific hub in the field of outdoor education, reflecting the country’s emphasis on the discipline and its robust research output facilitated by a comprehensive scientific research system.

A further analysis of the top 30 countries and regions in terms of publication volume reveals that Europe leads with 2649 articles, followed closely by North America with 2613 articles (2096 from the United States), South America with 1132 articles, Asia with 765 articles, and Oceania with 562 articles. This distribution indicates a research trend predominantly centred in Europe and North America, with collaborative global involvement focused in these regions.

Regional disparities in research may stem from a range of underlying factors. First, sociocultural factors play a significant role; New Zealand’s outdoor education is recognized for its progressive teaching philosophies and emphasis on environmental stewardship, prioritizing both academic instruction and practical engagement along with fostering a sense of social responsibility. This approach enjoys broad public support, laying a robust social groundwork for the advancement of outdoor education. Second, socioeconomic status is equally influential; regions with stronger economies typically invest more heavily in sports and education sectors than those that are less developed. The United States, leading globally in the sports industry, boasts an unmatched competitive edge in sports culture, underpinned by a substantial sports industry infrastructure and economic backing. Third, geographic and topographic characteristics are also pivotal; Wang [40] notes in a review of outdoor recreation that there are geographical patterns in author locations, with North America centred around the US and Canada, particularly in regions such as the Rocky Mountains, the west coast, the Great Lakes, and the east coast. Europe’s focus is on the UK, the Alps, and Northern Europe, while Oceania’s epicentre is on the east coast of Australia and New Zealand. Outdoor activities are contingent upon certain natural conditions, with regions abundant in natural resources often holding greater geographical benefits. Fourth, government policy support is instrumental in providing direction for outdoor education’s development. The UK’s outdoor education practices are particularly noteworthy, with a long-standing history of outdoor learning across various educational stages. Since 2012, the UK government has issued guiding documents on integrating outdoor learning into primary school curricula, outlining seven key themes including community involvement, partnerships, school improvement planning, leadership in teaching and learning, research utilization, professional development, and visionary leadership. Recently, the 25-Year Environmental Plan has pledged funding from the Department for Education to the Department for Environment, Food and Rural Affairs to increase access to nature among children, especially those from disadvantaged backgrounds, both in and out of school, to support their health and well-being. These policies and measures offer comprehensive guidance and support for the implementation of outdoor education by schools and educators.

3.1.3. Analysis of the Research Collaboration Network in Outdoor Education

An analysis of the structural characteristics of the publication authors and their collaboration networks illuminates the core group of authors and their collaborators within this field. In the author collaboration network maps, different colours signify distinct collaborative teams, and the number of connections indicate the closeness of team collaboration (Figure 6).

According to the core author calculation formula proposed by the American scholar Price in which n = 26 and M ≈ 3.81, authors of outdoor education papers who have published four or more papers are classified as prolific authors. The author research collaboration network map reveals the following: (1) there are many scholars in outdoor education research (with 1178 nodes and 821 connections and a network density of 0.0012), and some of these authors have formed stable research collaboration groups; (2) many authors constitute the main research teams with a high concentration, forming teams represented by Ardoin, Nicole M (26 papers), Bogner, Franz X (24 papers), Stern, Marc J (21 papers), and Powell, Robert B (20 papers). Moreover, Ardoin, Stern, and Powell are located within the same research team.

3.1.4. Disciplinary Distribution in Outdoor Education

The classification of disciplines within a field reveals the types of academic subjects involved and provides a clear, goal-oriented direction for research (

Table 1. Disciplinary distribution of research in the field of outdoor education over the past 30 years (1994–2023).

Discipline	Frequency	Centrality	Research Contents
EDUCATION AND EDUCATIONAL RESEARCH	3335	0.29	Theories of outdoor education, teaching methods, educational policies, and practices
ENVIRONMENTAL STUDIES	1675	0.12	Science, policy, and ethics within environmental education
ENVIRONMENTAL SCIENCES	1394	0.15	Physical, chemical, biological, and geological characteristics of the natural environment
GREEN AND SUSTAINABLE SCIENCE AND TECHNOLOGY	625	0.02	The intersection of outdoor education and sustainable development
EDUCATION, SCIENTIFIC DISCIPLINES	565	0.19	Psychological, sociological, and pedagogical issues during the process of outdoor education
ECOLOGY	430	0.06	Interactions between outdoor education and ecological environments
PHARMACOLOGY AND PHARMACY	301	0.10	Mechanisms of drug action, drug design, and therapeutics in the context of environmental education
BIODIVERSITY CONSERVATION	299	0.03	Conservation and restoration of biodiversity in environmental education
ENGINEERING, ENVIRONMENTAL	234	0.06	Environmental issues and engineering challenges in environmental education
INTERDISCIPLINARY SOCIAL SCIENCES	223	0.04	Societal impacts of outdoor education

). Using CiteSpace 6.2.R6 (64-bit) Advanced for a disciplinary analysis of outdoor education, the results revealed 207 network nodes. The ten most frequent nodes are as follows: education and educational research, environmental studies, environmental sciences, green and sustainable science and technology, education scientific disciplines, ecology, pharmacology and pharmacy, biodiversity conservation, engineering environmental, and interdisciplinary social sciences. Additionally, the field encompasses public environmental and occupational health, geography, water resources, multidisciplinary psychology, computer science, biology, multidisciplinary earth sciences, zoology, and forestry, among others. This demonstrates the broad distribution of disciplines within the field of outdoor education, thus reflecting a trend of gradually integrating educational and environmental sciences into other disciplines. The application of multidisciplinary and interdisciplinary theories and methods to address scientific questions in outdoor education has become a fundamental direction for future research.

3.1.5. Distribution of Institutions in Outdoor Education Research

Using the time-zone view feature of CiteSpace 6.2.R6 (64-bit) Advanced software, a temporal map of the institutions publishing in the field of outdoor education was created (Figure 7). In the parameter adjustment, the threshold for extracting knowledge units for each time slice was set to K = 5. The results revealed a modularity value of 0.9592 and an average silhouette value of 0.9991, indicating credibility. A total of 259 network nodes and 254 connections were generated, with a density of 0.0076. The research institutions are primarily composed of universities in Europe and America, with little cross-regional or cross-institutional collaboration. The top 10 institutions by publication volume are, in order, the University of North Carolina (94 papers), Florida State University (92 papers), Ohio University (82 papers), University of Wisconsin (64 papers), Monash University (63 papers), University of California (60 papers), Pennsylvania’s State System of Higher Education (57 papers), Federal University of Rio Grande do Sul (57 papers), University of Florida (53 papers), and University of London (49 papers). Early research institutions in 1994 included Purdue University, University of Wisconsin, etc., and more recent institutions include Uppsala University, Gothenburg University, and the Norwegian School of Sport Sciences in Sweden.

3.2. Research Hotspots and Trend Analysis

3.2.1. Co-Occurrence of Keywords in Outdoor Education Research

Keywords serve as concise summaries of a paper’s themes, and their analyses help researchers understand the core focus and themes within a domain (Figure 8). The keyword map generated by CiteSpace 6.2.R6 (64-bit) Advanced displays nodes representing keywords, where the size of a node indicates the frequency of the keyword’s occurrence, i.e., larger nodes signify more frequent occurrences. The thickness of the lines between nodes indicates the strength of co-occurrence, with thicker lines denoting stronger connections. The keyword map in Figure 6 generated 1062 nodes with 4091 connections, resulting in a network density of 0.0073, a modularity (Q value) of 0.4537, and a silhouette (S value) of 0.78. Generally, a Q value within the $[0,1)$ range and greater than 0.3 indicates significant clustering, whereas an S value greater than 0.5 suggests reasonable clustering, and an S value ≥ 0.7 denotes highly convincing clustering [41].

On the basis of the equation $\mathrm{M}\approx 0.749\sqrt{{\mathrm{N}}_{\mathrm{m}\mathrm{a}\mathrm{x}}}$, ${\mathrm{N}}_{\mathrm{m}\mathrm{a}\mathrm{x}}$ = 3160, and M is set to 42. Therefore, the threshold for keyword nodes is established at 42. Other key nodes include attitudes, students, knowledge, science, experiential education, sustainable development, and behaviour, among others, thus indicating these as central themes in outdoor education research (Figure 8). The main keywords, ordered by frequency, include environmental education (3,160 occurrences), education (610), attitudes (510), knowledge (505), experiential education (467), sustainable development (390), impact/impacts (375), outdoor education (370), behaviour (362), science (327), climate change (322), students (314), conservation (278), management (270), children (209), and more.

3.2.2. Thematic Analysis of Outdoor Education Research

Using keyword clustering as a basis, the evolution of themes in the outdoor education literature from 1994 to 2023 was analysed at five-year intervals (

Table 2. Thematic clusters in outdoor education research over the past 30 years (1994–2023).

Rank	1994–1998	1999–2003	2004–2008	2009–2013	2014–2018	2019–2023
1	#0Environmental Education	#0Environmental Education	#0Environmental Education	#0Environmental Literacy	#0Experiential Education	#0Outdoor Learning
2	#1Insect Conservation	#1Landscape Ecology	#1Sustainable Development	#1Sustainable Development	#1Political Ecology	#1Ecosystem Services
3	#2Environmental Management Systems	#2Fuzzy Modelling	#2Critical Pedagogy	#2Environmental Attitude	#2Environmental Knowledge	#2Higher Education
4	#3Social Impact Assessment	#3Outdoor Recreation	#3Environmental Behaviour	#3Citizen Science	#3Land Education	#3Circular Economy
5	#4Classroom Animals	#4Educational Programs	#4Experiential Education	#4Global Warming	#4Pharmacy Practice	#4Education for Sustainable Development

). The analysis revealed that environmental education has consistently been a focal point, maintaining a central position in the field. The theme of sustainable development emerged between 2004 and 2008, re-emphasizing its significance in subsequent periods (2014–2018 and 2019–2023), with scholars gaining a deeper understanding of the relationships among individuals, society, and the environment. The research themes associated with environmental education expanded from insect conservation and classroom animals from 1994–1998 to landscape ecology, sustainable development, and ecosystem services in subsequent years, shifting from a singular focus on animal conservation to a comprehensive perspective considering environmental, social, economic, and cultural factors. Between 1994 and 2013, although environmental education remained the predominant theme, other topics, such as curriculum, experiential education, and outdoor learning, gained prominence in 1999–2003 and 2004–2008, indicating a diversification of outdoor education that emphasized other educational forms as well as the significance of practice and direct experience in education. The clustering analysis of themes over nearly three decades suggests that future research in outdoor education will likely continue to develop towards an integrated, global, and practice-oriented approach.

3.2.3. Analysis of Emerging Keywords in Outdoor Education Research

Emerging keywords are those that see a significant increase in usage over a short period, aiding researchers in identifying sudden research hotspots and identifying trends and potential future directions within the field. The emergence map displays “begin” and “end” markers indicating the start and end times of keyword surges, respectively, whereas “strength” denotes the intensity of the emergence, with higher values indicating greater impact during the period. The analysis in CiteSpace 6.2.R6 (64-bit) Advanced identified the top 30 emerging keywords with the highest prominence (Figure 9), with conservation showing the highest intensity over 18 years (1998–2016) and a prominence of 29.77, indicating its extensive focus within the field of outdoor education. The least intense emerging keyword is “nature relatedness”, beginning in 2019, with a prominence of 4.96. Keywords with over five years of prominence, ordered from highest to lowest intensity, include environmental education, conservation, education for sustainable development, patterns, nature conservation, ecology, ecological paradigm, perspective, and introductory pharmacy practice experience, thus reflecting sustained academic interest in these research directions within the field of outdoor education.

4. Discussion

4.1. Development Trajectory: From Environmental Governance to Environmental Education and Focus on Sustainable Development

According to annual publication statistics, research on outdoor education over the past 30 years can be broadly divided into four stages, specifically, the initial development period (1994–2004), steady development period (2005–2013), rapid growth period (2014–2018), and vigorous development period (2019 to present). This research development trajectory not only reflects the academic community’s gradually increasing attention to outdoor education but also mirrors the global awakening and evolution of environmental consciousness.

In the 1960s, due to the acceleration of urbanization, natural resources were severely damaged [42]. The publication of Silent Spring in this context triggered widespread social concern about environmental issues and spurred a wave of in-depth studies on environmental pollution and governance [43]. Subsequently, nations began to gradually emphasize environmental pollution management. This phase of the environmental movement could be characterized by the conflict between economic growth and natural resources, where development was seen as necessitating environmental degradation, with a focus on pollution control and conservation efforts. This led to an upsurge in research on environmental pollution and management worldwide, prompting nations to increasingly prioritize environmental pollution control. Over time, concerns expanded to include ecosystem protection and climate change, leading to a recognition that economic progress should not come at the expense of natural resources. This shift led to educational initiatives aimed at improving environmental consciousness. In 1975, the at the Belgrade Conference of the United Nations Educational, Scientific and Cultural Organization (UNESCO) defined environmental education as an understanding and care for the ecological interdependence of economic, social, and political aspects in urban and rural areas, thus providing everyone with the knowledge needed to protect and enhance the environment, and fostering appropriate values, viewpoints, responsibilities, and skills to promote new patterns of environmental behaviour among individuals, groups, and society at large [44]. Following this, environmental concerns shifted from pollution management to preventive education, with developed countries pioneering a new model of environmental education characterized by university leadership, multiparty cooperation, and community participation [45]. This transition influenced the content and direction of environmental education, moving it towards a practice- and action-oriented approach. Following extensive accumulation and reflection, the United Nations Conference on Environment and Development in 1992 proposed a program focused on education for the environment and development and adopted significant documents such as the Rio Declaration on Environment and Development, Agenda 21, Framework Convention on Climate Change, and Convention on Biological Diversity, and thereby established a path for harmonious development between humans and nature for the benefit of future generations. From this point, “environmental education has transitioned to education for sustainable development”, with sustainability gradually becoming the core purpose of environmental education [46], driving profound changes in its content and methodology. This approach is more comprehensive, encompassing environmental, social, economic, and cultural dimensions, and aims to cultivate global citizenship, emphasizing interdisciplinary learning and exploring interconnections and dependencies among the environment, society, and economy.

In recent years, the convergence of environmental and sustainable development education has given rise to a new educational philosophy that underscores the intrinsic link between ecological civilization and sustainable development—the balance among the environment, economy, and society. France has been a forerunner in sustainable development education since the 1970s, striving for comprehensive coverage in basic education and integrating innovative disciplinary approaches in higher education. Germany’s interactive and heuristic teaching methods in sustainable development education, along with the integration of volunteer culture, provide valuable insights for public engagement. These experiences indicate that the successful implementation of environmental education relies not only on policy support but also on broad social participation and practical exploration. Drawing on the environmental education policies and outcomes of countries like the United States, Germany, and Japan offers valuable lessons. The United States’ National Park environmental education system, after over a century of development, has established a mature legal framework and management mechanisms to cater to diverse visitor needs, offering a reference for environmental education in national parks [47]. Germany’s focus on fostering public participation and interactive, engaging educational methods in sustainable development education provides insights for improving environmental education approaches [48]. The successful experience of environmental education in Japanese elementary schools highlights the importance of nurturing students’ environmental awareness and practical abilities as key to enhancing educational effectiveness [49].

4.2. Global Dynamics: From Parity Between the US and Europe to a Global Melting Pot

An analysis of research regions indicates that outdoor education studies are concentrated mainly in Europe and North America, with the United States leading in publication volume and forming a pattern of diffusion from the US and Europe to the rest of the world. Academic research on outdoor education has not originated in any specific country but has gradually developed and expanded across multiple nations. The modern development of outdoor education has benefited from key individuals and organizations, such as the outdoor training centres established by German educator Kurt Hahn in Aberdovey, Wales, during World War II, marking a significant milestone in the history of outdoor education; the forest schools in the UK; and the Outdoor Leadership School in the US. The Association for Experiential Education has also greatly advanced the development of outdoor education. Academically, as a specialized field, the theoretical models of outdoor education have continually evolved due to increasing practice. For example, at the beginning of the 20th century, Australia focused on educational reforms centred on national curriculum revisions [50,51], and the UK’s “Education Act of 1944” incorporated outdoor education into its national curriculum, recognizing its significant role in the development of children and adolescents. These measures greatly propelled the development of outdoor education.

Moreover, the diversification of outdoor education has benefited from two main aspects. First, there are different educational philosophies and purposes. For example, the UK’s forest schools aim to “foster resilient, creative, and compassionate individuals who value the natural world (including humans and nonhumans) and are committed to the welfare of all living beings” [52]; the US Outdoor Leadership School emphasizes environmental conservation, travel skills, outdoor survival and safety skills, and team assistance and aims to cultivate leaders for outward-bound schools; the Wilderness Education Association advocates taking responsibility for the protection of wilderness resources to increase the quality of outdoor activities and develop a curriculum for the certification of outdoor leaders; the Association for Experiential Education is dedicated to developing experiential learning methods, and promoting research in practice education and experiential education; and theme-based adventure education has promoted the integration of outdoor education into the school education system, cultivating students’ spirit of cooperation through team collaboration strategies. Second, there are different organizational forms and models. In the US, outdoor education is regarded as an important educational form and is supported by professional guides and organizational institutions such as wilderness education centres and outdoor leadership schools. In Germany, outdoor education is reflected in the summer homework for adolescents. In other words, students are expected to complete reports on cave exploration and surveys on flora and fauna as the main content of their holiday homework. Similarly, in France, outdoor camping activities are a major part of vacations, whereas in Japan, orienteering and other outdoor activities are popular and youth outdoor classrooms are established [53].

4.3. Research Themes: Environmental Education as the Most Extensive, with Multiple Educational Forms Developing Simultaneously

Keyword co-occurrence and clustering analysis reveals that research on outdoor education focuses primarily on environmental education, attitudes, knowledge, experiential education, sustainable development, behaviour, and climate change, among other factors. Although it is widely agreed that increasing environmental knowledge, fostering environmental attitudes, and enhancing environmental awareness to improve environmental behaviours has been achieved [54,55,56], academic research continues to deepen, gradually recognizing the limitations of a single form of education, particularly with respect to practical effectiveness. Researchers such as Kagawa F have reported that although students generally hold positive attitudes towards environmental issues, their commitments to personal changes in behaviour are often limited to relatively superficial light green actions, such as recycling, resource conservation, and green commuting. In promoting deeper social change in understanding and action, the efforts appear relatively lacking [57]. Initially, the core focus of environmental education has concentrated on macrolevel themes such as biodiversity, conservation, and ecology. However, as times have developed and research has deepened, the research fields of environmental education have gradually become refined and extended to more specific areas, such as schools, youth, natural connections, and environmental sustainability. This trend reflects that environmental education is moving from traditional knowledge transfer to a greater focus on direct interactions and personal experiences between students and the natural environment.

It is evident that environmental knowledge, attitudes, and awareness promote, to a certain extent, environmental behaviours, but this influence is complex and multidimensional. Simply relying on the transfer of knowledge may not directly translate into effective environmental behaviour. To achieve more comprehensive educational objectives, environmental education should, beyond fostering knowledge, attitudes, awareness, and values, place greater emphasis on direct interactions between children and adolescents and the natural environment through field trips, adventure education, outdoor camping, and outdoor recreation, thereby enhancing their environmental perceptions and sense of responsibility. Ultimately, students’ environmental awareness is not only key to their personal development but also has a profound effect on the environmental sustainability of future societies [55]. Then again, from recent thematic clustering regarding outdoor education, the largest theme cluster from 2019–2023 is outdoor learning, which indicates that academic interest in the form of outdoor education is changing and is no longer limited to the singular field of environmental education, but rather, it is gradually expanding to a wider range of educational forms. This trend not only reflects the diverse development of research in outdoor education but also highlights the necessity of exploring diverse educational models within environmental education.

4.4. Cooperative Layout: Numerous Researchers and a Predominantly University-Based Research Cooperation Network Structure

Cooperative network graph analysis indicates that the field of outdoor education has formed several core research teams, with teams led by such prominent scholars as Bogner, Ardoin, Powell, and Stern. Among these teams, Ardoin, Stern, and Powell belong to the same research group. They have systematically assessed various types of residential environmental education programs and reported that the students who participated in these programs experienced significant short-term improvements in environmental responsibility, character development, and leadership. More importantly, these positive effects were still significant in follow-up evaluations three months later [58,59,60,61]. This research not only highlights the significant short-term benefits of environmental education for student personal growth and environmental awareness but also reveals its potential long-term impact.

Additionally, multiple universities have made significant contributions to the field of outdoor education. Statistics indicate that research institutions such as the University of North Carolina, Florida State University, and Ohio State University in the US have high publication volumes and diverse research content. Research at the University of North Carolina has focused on evaluating and exploring the impact of outdoor education programs on adolescents’ environmental awareness, self-efficacy, and leadership development [62,63,64]. Florida State University has explored how environmental education enhances students’ environmental awareness [65], attitudes, and behaviours and how outdoor education programs and practices promote biodiversity conservation and sustainable development [66]. Finally, Ohio State University’s research has focused on exploring the effects of experiential learning, environmental education, and outdoor education programs on enhancing changes in students’ environmental awareness, skills, and behaviour [67,68,69].

4.5. Subject Distribution: From Limited Disciplinary Research to Multidisciplinary Integration and Interdisciplinary Fusion

Research discipline analysis indicates that the field of outdoor education is increasingly characterized by a trend towards multidisciplinary integration and interfield fusion, with education and environmental studies as the leading disciplines. The developmental process of disciplinary integration in outdoor education has been previously discussed. In English, terms such as “interdisciplinary”, “multidisciplinary”, or “cross-disciplinary” are commonly used to describe studies that involve two or more academic disciplines aimed at innovating beyond the boundaries of established fields. This concept was first introduced in 1926 by Woodworth, a psychologist at Columbia University, who, in the context of Western literature from the 1920s and 1930s, highlighted research involving multiple disciplines aimed at innovation.

Through a comprehensive analysis of interdisciplinary research development in outdoor education, with environmental education as a prominent theme, the inherent logic is reflected in five prominent aspects.: (1) Unity of purpose. The core goal of education is to foster cognitive, emotional, and behavioural development in children and adolescents, and thereby enhance their environmental awareness and sense of responsibility. Moreover, environmental science and ecology are committed to promoting environmental protection and sustainable development, with both fields sharing highly consistent objectives. (2) Interdependence. Education provides the theoretical foundation and practical methods for nurturing environmental awareness among children and adolescents, whereas environmental science and ecology offer scientific knowledge about natural environments and ecosystems. This interdependent relationship enables the blending of disciplines. (3) Disciplinary fusion. As outdoor education emphasizes experiential learning within natural settings, it also requires an integrated application of educational methodologies, environmental protection philosophies, and ecological science. This synthesis enables outdoor education to more effectively achieve its educational goals while also fostering the integration of related disciplines. (4) Policy-driven. With the increasing severity of global environmental issues and the emergence of sustainable development goals, educational authorities are recognizing the importance of incorporating environmental and ecological education in the school’s curricula. (5) Complementary methodologies. The combination of research methodologies from education with those from environmental science and ecology provides a more comprehensive perspective for analysing and addressing societal challenges.

5. Conclusions

Outdoor education is an integral part of the national curriculum in most Western countries, a reality that emphasises its importance. Accelerating the theoretical and practical research on outdoor education curricula and establishing national and locally adapted professional standards for outdoor education not only aligns with the research trends in outdoor education but also responds to the urgent need for new curricula to be established by the latest round of basic education reforms. A systematic analysis of the academic literature in the field of outdoor education from 1994 to 2023 was conducted via CiteSpace 6.2.R6 (64-bit) Advanced software. This study revealed that outdoor education research has undergone a significant transformation from environmental governance to environmental education and then to a focus on sustainable development, thus ultimately delineating four stages, namely, preliminary development, steady growth, rapid expansion, and vigorous development. This reflects the shift from merely imparting knowledge to promoting education that fosters sustainable development. Moreover, the United States holds a leadership position in outdoor education research that has established a research pattern centred on Western countries, whereas global research interest has gradually increased, presenting a scenario of diverse scholarly voices. Additionally, while environmental education remains a core research theme, experiential education, outdoor learning, and sustainable development practice education have also garnered widespread attention. A tight network of academic collaboration reflects the extensive cooperation and communication in outdoor education research within the academic community. Outdoor education research continues to expand its disciplinary boundaries, constructing a new interdisciplinary research system based on education, environmental studies, and ecology. Future research in outdoor education is expected to continue evolving towards a comprehensive perspective, a global outlook, and a practice-oriented approach.

This study has certain limitations: (1) Data collection was not comprehensive, as we only collected and utilized studies published in English within the WOS database, resulting in a narrow scope of data sources. WOS primarily covers literature in English, with relatively limited coverage of non-English and regional publications [70]. Consequently, many research outputs from non-English speaking countries may not be adequately recorded or cited, diminishing their influence and visibility in the global academic community. Additionally, WOS focuses on journal indexing, with limited coverage of books and conference proceedings [71], which may affect the comprehensive assessment of research outcomes in disciplines that rely more heavily on these formats for academic communication. (2) Under identical data conditions, different parameter settings in CiteSpace 6.2.R6 (64-bit) Advanced for data analysis may lead to variations in research results. (3) Relying solely on subject keywords may not encompass all relevant lexical variants, potentially resulting in the omission of significant data. Therefore, we recommend that future researchers consider using multiple databases for literature collection to facilitate a more comprehensive analysis in their citation and dataset management efforts.