How Can Rural Tourism Be Sustainable? A Systematic Review

: This investigation reviewed articles associated with sustainable rural tourism found on the Web of Science database over a 10-year span from 2009 to 2019. The 76 articles that were selected for their inclusion of the concept of sustainable rural tourism were listed in a comprehensive table, thereby revealing the research purpose, topics, detailed topics, research methods, and data source of the articles. The ﬁndings indicate that many papers on sustainable rural tourism were written from a holistic sustainability perspective without being biased towards any one of the environmental, economic, and social aspects. In the ﬁeld of rural tourism, it is essential to pay attention to interactions in all aspects of the environment, economy, and society, and to analyze them overall. In addition, this study conﬁrmed that e ﬀ orts to understand sustainable rural tourism from the customer perspective have been increased since customer loyalty is considered important for sustainability. This study is signiﬁcant in that, since it evaluated the knowledge status for the ﬁrst time through systematic review and applied content analysis to academic literature related to sustainability in the sector of rural tourism, it can expand and deepen the knowledge and understanding of related topics and raise awareness of a new research direction.


Introduction
Sustainable tourism has become recognized as a desirable goal in tourism development due to the addition of the concept of sustainability to tourism in order to reduce the negative impacts experienced during the tourism development process [1]. Sustainability-based tourism development models can evolve when they are able to meet the demands of locals, as well as respond to the needs of tourists [2]. Through tourist participation in activities in developed tourism, positive or negative factors are created, which affect the sustainability of environmental, social, and economic dimensions [3]. First of all, on the positive side, the development of tourist activities in rural areas can create verified positive effects: improvement of the quality of life for locals, creation of employment, preservation of cultural heritage, development of business networks, and enhancement of public image of the region [4]. Besides, through the development of rural tourism, there may be other positive effects, such as the opportunity to enhance the natural environment value, improvements related to public transport networks or public facilities, and the activation of cultural interactions [5]. However, there may be also negative effects, such as the overcrowding of public places and facilities, disruption of local people's lives, skyrocketing price of property ownership, safety concerns, environmental damage, increased waste, and overuse of resources [5]. These have negative impacts on the sustainability of rural tourism from social, economic, and environmental points of view. Sustainable rural tourism aims to raise the sustainability concerning the long term improvement of living standards by maintaining

Literature Review
Sustainable development was originally recognized for its importance as consideration for tourism research in regards to the environment and the natural resource limits of the Earth [17]. Sustainable development can be prescribed as development that meets the current generation's needs while maintaining the ability to satisfy the future generations' needs [18]. Hall [19] embodied the concept of sustainable development by establishing five basic principles: a holistic strategy and plan that encompasses environmental, social, and economic aspects; preserves essential natural ecology; development that maintains productivity in the future; balanced protection of biodiversity and human heritage; and seeks a balance between countries in terms of opportunity and fairness. Sustainable development was conducted in the early stages by emphasizing the environmental dimension, but it is recognized that social and economic dimensions are also important in achieving true sustainability [20]. This conclusion led to the widespread acceptance of the notion of sustainability being comprised of three basic elements: environmental, economic, and social [21]. The importance of comprehensively looking at these three dimensions has also been emphasized for the establishment of a sustainable development strategy [20]. In the end, sustainable development should not be restricted to just one aspect, but rather, it is a comprehensive system that encompasses the whole, such as environmental systems that preserve life resources, social systems that aim for equity, and economic systems for efficiency in resource use [22]. Data extraction forms were then designed to identify included articles and provide an overview of approaches to sustainable rural tourism research. Considering the quality of the study, each article was evaluated in a structured data extraction format. The data extracted included author, year, title, journal, abstract, keywords, research purpose, topics, detailed topics, research methods, and data source. In the next step, for the screening of articles, the context of the keywords presented in each article and the abstracts were analyzed. Through this process, articles could be divided into those that are fundamentally related to sustainable rural tourism and articles that are not related to sustainable rural tourism (for example, if the research area is not rural tourism or if the subject of the study is not associated with sustainability). The results show that 171 articles are fundamentally related to sustainable rural tourism. Finally, by analyzing the contents of the selected 171 articles, they were classified into those where sustainable rural tourism was addressed as the main issue of the study and those where it was treated as a supporting issue of the study. Finally, 76 articles covering the topic of sustainable rural tourism as the main issue were selected as the targeted material for the systematic review ( Figure 1). This screening process was conducted independently by the authors, and in the case of data discrepancies, consensus was reached through discussions between the authors of this review. source. In the next step, for the screening of articles, the context of the keywords presented in each article and the abstracts were analyzed. Through this process, articles could be divided into those that are fundamentally related to sustainable rural tourism and articles that are not related to sustainable rural tourism (for example, if the research area is not rural tourism or if the subject of the study is not associated with sustainability). The results show that 171 articles are fundamentally related to sustainable rural tourism. Finally, by analyzing the contents of the selected 171 articles, they were classified into those where sustainable rural tourism was addressed as the main issue of the study and those where it was treated as a supporting issue of the study. Finally, 76 articles covering the topic of sustainable rural tourism as the main issue were selected as the targeted material for the systematic review ( Figure 1). This screening process was conducted independently by the authors, and in the case of data discrepancies, consensus was reached through discussions between the authors of this review.

Data Analysis
To answer research question 1 (What are the general characteristics of studies related to sustainable rural tourism?), this study grouped the selected articles by several criteria. First, the number of publications per year and per region that pertained to related studies was analyzed. Next, the publishing trends of journals related to sustainable rural tourism were analyzed. Finally, the research methods and research perspectives that were applied to the related studies were explored.
In response to research question 2 (What are the structural characteristics in the intellectual dimension of research related to sustainable rural tourism?), this study draws a bibliographic map, which defined the co-occurrence of keywords that reveal the main scientific knowledge of each study [35]. To obtain the bibliographic map based on research keywords co-occurrence, the VOSviewer software associated with the technique of multidimensional scaling was utilized in this study [36]. The software applied mapping techniques to determine the location of keywords on the map and the clustering technique to create clusters through the allocation of frequently co-occurring keywords [37].

Data Analysis
To answer research question 1 (What are the general characteristics of studies related to sustainable rural tourism?), this study grouped the selected articles by several criteria. First, the number of publications per year and per region that pertained to related studies was analyzed. Next, the publishing trends of journals related to sustainable rural tourism were analyzed. Finally, the research methods and research perspectives that were applied to the related studies were explored.
In response to research question 2 (What are the structural characteristics in the intellectual dimension of research related to sustainable rural tourism?), this study draws a bibliographic map, which defined the co-occurrence of keywords that reveal the main scientific knowledge of each study [35]. To obtain the bibliographic map based on research keywords co-occurrence, the VOSviewer software associated with the technique of multidimensional scaling was utilized in this study [36].
The software applied mapping techniques to determine the location of keywords on the map and the clustering technique to create clusters through the allocation of frequently co-occurring keywords [37].
Concerning research question 3 (Which research topics interest sustainable rural tourism researchers?), the research topics from the selected articles related to sustainable rural tourism were analyzed. First, the research topics were categorized to grasp the overall tendency of research about sustainable rural tourism. Besides, the proportion of categorized topics was analyzed to confirm which topics were more significant in sustainable rural tourism research. Finally, the detailed topics covered in each category were analyzed to identify the specific research trends related to sustainable rural tourism.

Results
To address research question 1, the overall characteristics of the selected studies were analyzed. Over the 10-year period from 2009 to 2019, research on sustainable rural tourism steadily increased. From 2009 to 2016, an average of 0 to 7 sustainable rural tourism articles were published annually, and from 2017 to 2019, 13 to 21 papers were published each year ( Figure 2). This demonstrates that the interest in sustainable rural tourism has increased significantly over time. Concerning research question 3 (Which research topics interest sustainable rural tourism researchers?), the research topics from the selected articles related to sustainable rural tourism were analyzed. First, the research topics were categorized to grasp the overall tendency of research about sustainable rural tourism. Besides, the proportion of categorized topics was analyzed to confirm which topics were more significant in sustainable rural tourism research. Finally, the detailed topics covered in each category were analyzed to identify the specific research trends related to sustainable rural tourism.

Results
To address research question 1, the overall characteristics of the selected studies were analyzed. Over the 10-year period from 2009 to 2019, research on sustainable rural tourism steadily increased. From 2009 to 2016, an average of 0 to 7 sustainable rural tourism articles were published annually, and from 2017 to 2019, 13 to 21 papers were published each year ( Figure 2). This demonstrates that the interest in sustainable rural tourism has increased significantly over time. Regarding region, sustainable rural tourism-related research was found to be conducted in various regions (Table 1). Europe (37 papers, 48.7%) had the highest frequency, followed by Asia (28 papers, 36.8%). Spain (10 papers) in Europe and the People's Republic of China (12) in Asia led the research on sustainable rural tourism. In addition, North America, South America, Oceania, The Middle East, and Africa have recorded 1 to 3 publications each in the last 10 years. It shows that from a regional point of view, research related to sustainable rural tourism is focused on Europe and Asia.  Regarding region, sustainable rural tourism-related research was found to be conducted in various regions (Table 1). Europe (37 papers, 48.7%) had the highest frequency, followed by Asia (28 papers, 36.8%). Spain (10 papers) in Europe and the People's Republic of China (12) in Asia led the research on sustainable rural tourism. In addition, North America, South America, Oceania, The Middle East, and Africa have recorded 1 to 3 publications each in the last 10 years. It shows that from a regional point of view, research related to sustainable rural tourism is focused on Europe and Asia.
The 76 articles selected for review were published in various journals ( Table 2). The journals Sustainability (23 papers) and Journal of Sustainable Tourism (10)   For the selected 76 articles, three types of research methods were applied (Table 3). Quantitative analysis was used for 47 articles, qualitative analysis for 27 articles, and mixed analysis combining quantitative and qualitative analysis for 2 articles. Of the papers to which quantitative analysis was applied, 35 papers used questionnaire surveys as the primary research method, and 12 papers applied quantitative analysis on statistical data. Among the papers to which qualitative analysis was applied, studies that applied in-depth interviews (13 papers) were the majority, but there were also studies that applied Delphi (4 papers), participant observation (4 papers), qualitative analysis on textual data (5 papers), and focus group interviews (1 paper). Data sources for the 76 studies were found in the following order: residents (28 papers, 36.8%), secondary data (16 papers, 21.1%), tourists (15 papers, 19.7%), stakeholders (13 papers, 17.1%), and experts (4 papers, 5.3%).

Intellectual Structure Based on Keywords
To answer research question 2, this study examined the keywords related to sustainable rural tourism research ( Figure 3). Keyword co-occurrence was analyzed using the VOSviewer software [36]. The first main keyword was rural tourism and agriculture. Pursuing a win-win relationship with rural tourism and agriculture can be a primary way to increase the sustainability of rural tourism [38]. Providing rural tourism products by strengthening the link between rural tourism and agriculture can greatly contribute to improving the economic and ecological sustainability of rural areas [39]. Farmers who not only participate in the busy farming season, but also in the peak tourism season can enhance livelihood sustainability by maximizing the synergistic relationship between The first main keyword was rural tourism and agriculture. Pursuing a win-win relationship with rural tourism and agriculture can be a primary way to increase the sustainability of rural tourism [38]. Providing rural tourism products by strengthening the link between rural tourism and agriculture can greatly contribute to improving the economic and ecological sustainability of rural areas [39]. Farmers who not only participate in the busy farming season, but also in the peak tourism season can enhance livelihood sustainability by maximizing the synergistic relationship between rural tourism and agriculture [40]. The keywords related to rural tourism and agriculture were "diversification" and "enterprises". From the perspective of agricultural diversification, a wide range of initiatives that pursue sustainable rural tourism can be found, varying between farm-based activities and rural tourism activities related to rural, natural, and cultural resources [41]. Rural tourism based on agricultural diversification not only makes it possible to supplement agricultural income with tourism income, but also protects the environment and guarantees the agricultural system [41]. The related keyword "enterprises" creates new rural tourism experiences, increases the value of the places, beautifies the properties owned in the countryside, and preserves the local culture [27]. In order to meet the diverse needs of tourists of rural tourism, not only farmers' efforts, but also entrepreneurs' efforts to attract tourists with attractive rural tourism programs must be added [25].
The next main keyword was tourist satisfaction. Tourist satisfaction with rural tourism can be defined as their evaluation of the difference between the expectations they had before visiting and the experiences they had while visiting [42]. Satisfaction after experiencing rural tourism is an important factor in making rural tourism sustainable because it increases customer loyalty to the destination [43]. Tourists' satisfaction, as well as the conservation of nature, the quality of life of the locals, cultural development, and economic improvement, are important drivers that make sustainable rural tourism possible [44]. The surrounding keywords related to satisfaction were "products", "experience", and "destination image". First, "products" and "experience" in the field of tourism can be considered to be service quality by tourists' evaluation of a standardized service delivery process related to tourism experiences [26]. Since there can be many factors that make up customer satisfaction, it is very important to check the association between the former and the latter [45]. Next, "destination image" can be defined as tourists' involvement level in a specific place, formed through the destination experience [46]. It can be also an important factor influencing customer satisfaction and loyalty to destinations [47].
The next main keyword was community. The active involvement of the community, which is the major operator of rural tourism, is an important factor in ensuring the sustainability of rural tourism [48]. Community is a key body that can protect the natural environment of rural areas, preserve the cultural identity of the region, and help provide economic benefits to residents [49]. Community involvement helps to avoid negative socio-cultural changes that may occur due to rural tourism development and maximizes economic benefits by redistributing the benefits obtained from rural tourism [50]. Community participation can affect tourist experiences in rural tourism [51]. Keywords related to community were "attitude", "perceptions", and "ecotourism". The effectiveness and efficiency of sustainable rural tourism development can vary depending on the "attitude" and "perceptions" of the community about rural tourism development [50]; they are factors that influence the level of community participation in rural tourism development [52]. The keyword "ecotourism" indicates that environmental sustainability should be reflected in the efforts of the community towards achieving sustainable rural tourism [53]. The sustainability of rural tourism destinations should be estimated from the point of view of the balance between the needs of rural tourists and the environment [12]. The assessment of environmental sustainability can derive a sustainable eco-tourism management strategy [54].
The final main keyword was indicators. Indicators for measuring sustainability for rural tourism should be able to objectively and accurately assess the status of sustainable development and be scientifically strong and reliable [55]. Furthermore, it should be verifiable and easily accessible to decision-makers [56]. Indicators that measure the status of development can increase the efficiency of management for sustainable rural tourism [57]. Keywords related to indicators were "livelihood sustainability" and "quality of life". The keyword "livelihood sustainability" demonstrates that the assessment of economic sustainability should be reflected in indicators of sustainable rural tourism development [53]. Rural tourism can be a driving force for economic income and employment opportunities that promote livelihood [58]. Rural tourism can be sustainable when the needs of rural destinations can be exchanged for economic constraints [59]. In addition, the keyword "quality of life" indicates that social sustainability, such as improving the quality of life of residents and communities, should be reflected in indicators for sustainable rural tourism development [55]. Rural tourism development has positive or negative impacts on the social life of the community and it also changes the rural environment [60]. There is a need to prevent departure and increase the social sustainability of the community [61]. It is also important to maintain and develop a local traditional culture that can be damaged by rural tourism to promote social sustainability [26].

Research Topics
In response to research question 3, the research topics found in the 76 articles were analyzed. The selected articles related to sustainable rural tourism had different types of research topics. The research topics can be divided into five categories: holistic, environmental, social, economic, and customer. Among them, 31 studies (40.8%) used holistic as the topic, 19 used environmental (25.0%), 10 used social (13.2%), 10 used economic (13.2%), and 6 used customer (7.8%) (see Figure 4). The proportion of studies dealing with holistic sustainability was significantly higher than that of other topics. This indicates that social and economic aspects, as well as the environmental aspects, are comprehensively considered in research related to sustainable rural tourism, although in general, the environmental aspect is emphasized when it comes to sustainability. It can be said that the lens of holistic sustainability is actively used to analyze the phenomenon in the rural tourism sector. In view of individual research topics, there was slightly more research on environmental sustainability. Studies on social sustainability, economic sustainability, and customer sustainability were evenly distributed.

Holistic
If studies that address the topic of holistic sustainability are classified, they consist of those related to the term "sustainability indicators" for rural tourism (17.1%), and "awareness investigation" (14.5%) and "case study" (9.2%) for sustainable rural tourism. First, "sustainability indicators" are the subjects of studies that suggest the direction of sustainable rural tourism management by developing and applying indexes to evaluate the sustainability of rural tourism from various perspectives. To derive indicators for evaluating the sustainability of rural tourism, surveys

Holistic
If studies that address the topic of holistic sustainability are classified, they consist of those related to the term "sustainability indicators" for rural tourism (17.1%), and "awareness investigation" (14.5%) and "case study" (9.2%) for sustainable rural tourism. First, "sustainability indicators" are the subjects of studies that suggest the direction of sustainable rural tourism management by developing and applying indexes to evaluate the sustainability of rural tourism from various perspectives. To derive indicators for evaluating the sustainability of rural tourism, surveys were conducted on the following populations: residents [53,[62][63][64][65], experts [55,66,67], stakeholders [68,69], and tourists [70]. The indicators were mainly divided into economic, environmental, and social aspects of sustainable rural tourism. Next, studies with the subject of "awareness investigation" explored what influences sustainable rural tourism development by examining the attitudes and perceptions of verified stakeholders on sustainable rural tourism development. Several studies have investigated what the drivers of sustainable rural tourism for residents are [41,[71][72][73][74][75][76][77]. Other studies explored tourists' perceptions and attitudes about rural tourism as a sustainable development strategy [78,79]. In the holistic dimension, the last research topic is "case study". These studies analyze the success factors of cases that have developed sustainable rural tourism. They present a development model for sustainable rural tourism through case studies [28,80,81] and also explore the interaction between rural tourism and sustainable rural development [30,82,83] (see Table 4). Studies on cases of preventing rural residents from leaving through rural tourism and increasing social sustainability of the older population in the community.

Environmental
Studies on the topic of environmental sustainability can be divided into those that specifically deal with sustainability in terms of "physical environment" (7.9%) and those that explore sustainability concerning "ecological environment" (17.1%). First, studies related to "physical environment" analyze the transportation accessibility and transportation systems that increase the sustainability of rural tourism [85,86], cases of rural tourism used as a tool to increase the sustainability of agricultural land [87], and studies on developing the ways to preserve and promote cultural heritage in a rural area [88][89][90]. The second sub-topic in terms of environment is the "ecological environment". Studies related to "ecological environment" examine the relationship between rural tourism development and environmental protection from a sustainable rural tourism perspective [91][92][93][94][95][96], suggest the direction of development for strengthening the link between rural tourism and agriculture [39,[97][98][99], and also analyze communication strategies to drive rural tourism tourists toward green behavior [100][101][102].

Social
Studies on social sustainability can be distributed in detail between those dealing with "social stability" (5.3%) and "local community" (7.9%). First, studies on "social stability" analyze the effect of rural tourism on population influx from a social sustainability perspective. They examine cases that prevented rural residents from leaving rural areas due to the opportunities presented through rural tourism [103], research other cases in which social sustainability was increased for the older population in the community through rural tourism [104], and analyze cases in which traditional villages were revitalized from social and cultural perspectives [105]. The second detailed topic of social sustainability is the "local community". Studies related to the "local community" focus on finding the role of the local community in sustainable rural tourism. They analyze the factors that determine the sustainability of social perspectives for local communities [107], derive a community participation development model for sustainable rural tourism [50,61,108], and seek the way to make rural tourism sustainable through the use of the traditional life culture of the local community [109,110].

Economic
The detailed topics of the study on economic sustainability consist of "tourism income" (10.5%) and "new income generation" (2.7%). First of all, research related to "tourism income" focuses on analyzing the sustainable livelihoods of local people through rural tourism income. They measure the economic effect of rural tourism [111][112][113], evaluate the economic sustainability of rural households in response to seasonal changes [58,114,120], and suggest strategies for the sustainability of households based on rural tourism [38,115]. The second detailed topic is "new income generation". Studies based on the sub-topic of "new income generation" focus on analyzing cases of creating new sources of income for rural tourism. They examined cases that promoted economic sustainability by grafting the traditional resources of regions, such as tea and the application of food heritagization, to rural tourism [116,117].

Customer
The detailed topics of research on sustainability in terms of the topic of the customer can be divided into "customer loyalty" (6.5%) and "customer characteristics" (1.3%). First, research on "customer loyalty" concentrates on finding tourists' loyalty that enables sustainable rural tourism. They measure how much loyalty a customer has toward rural destinations [26,43] and tourists' satisfaction by establishing factors affecting the satisfaction experienced from rural tourism [44,118,119]. The second detailed topic of the research related to customer sustainability is "customer characteristics". For rural tourism to become sustainable, it is necessary to continuously attract tourists in the long term through sustainable management in rural areas [82]. To increase the sustainability of rural tourism, having loyal tourists with the intention to revisit and recommend to others is a very important factor of rural tourism [121]. Given the fierce competition of rural tourism, much care must be taken to secure and retain loyal visitors to ensure the long-term development of rural tourism [122]. The loyalty of customers to rural tourism destinations immediately improves the economic stability of the community and immediately reinforces the welfare of residents [47]. Furthermore, customer loyalty leads to environmental improvements, as it must provide natural and cultural resources in well-preserved rural areas to sustain tourists [26]. Losing loyal customers may jeopardize rural tourism enterprises' survival [123]. Rather than inducing new customers to visit tourist destinations, increasing loyalty of existing customers to induce repeated visits is an efficient use of communication resources [26]. Research associated with "customer characteristics" centers on analyzing sustainable consumer behavior for rural tourism. In this regard, a segmentation study on the rural tourism market based on sustainable customer behavior was conducted [47].

Conclusions and Implications
This study examined various aspects of understanding sustainability in the rural tourism sector and extensively reviewed the literature by applying the topic of sustainable rural tourism (see Appendix A). It analyzed 76 articles from 29 journals published from January, 2009, to December, 2019, through systematic review and detailed content analysis. The selected papers were divided into 11 detailed topics according to the classification system developed for this study. The results of this systematic review will help researchers and on-site rural tourism providers easily access publications on sustainable rural tourism, thereby contributing to narrowing the knowledge gap in sustainable rural tourism. It can also help them choose an approach for future research in the field of sustainable rural tourism and build a framework.
There are several key points that this study found in the literature related to sustainable rural tourism. First of all, research on sustainable rural tourism has been increasing steadily for about 10 years, as observed from 2009 to 2019. In particular, sustainable rural tourism centered on Europe and Asia has been treated as an important research topic in those regions. This means that sustainable rural tourism has become an increasingly important topic with the passage of time. Second, in general, the concept of sustainability applied to rural tourism is interpreted and implemented differently, depending on the researchers [124]. In this study, it was revealed that more than 40% of papers on sustainable rural tourism were carried out from a holistic sustainability perspective. It shows that sustainability in the rural tourism sector is understood and applied as a holistic concept without being biased to any one of the environmental, economic, and social aspects. In the field of rural tourism, it is important to pay attention to interactions in all aspects of the environment, economy, and society, and to analyze them overall. Third, this study confirmed that efforts have been made to understand sustainable rural tourism from the customer perspective. Studies on tourists' loyalty and satisfaction, that enable sustainable rural tourism, reveal these efforts. It means that, in order to become a sustainable rural tourism destination, it is indispensable to ultimately gain the tourists' hearts. Fourth, the detailed tendency of research related to sustainable rural tourism was confirmed. In the field of sustainable rural tourism, studies using environmental sustainability as a topic deal with sustainability in the "physical environment" and "ecological environment". Research on the topic of social sustainability, in detail, deals with "social stability", which analyzes the effect of rural tourism on population inflow from the perspective of social sustainability, and the "local community", which seeks the role of the community in sustainable rural tourism. The study on economic sustainability shows a tendency to focus on "tourism income", which analyzes the sustainable livelihood structure of local people through rural tourism income and "new income generation", which analyzes the cases in which new income sources are created. Finally, research on the customer dimension consists of topics related to "customer loyalty" and associated with "customer characteristics".
This study has some limitations, despite the aforementioned contributions. First, the data used in this review were collected only from the Web of Science; thus, studies on sustainable rural tourism from other journals were not utilized. This limits the opportunity to obtain broader information on sustainable rural tourism. Future studies should make efforts to find a wider range of journals covering sustainable rural tourism. The next limitation is that, although most articles are written in English, this study only reviewed English language written papers dealing with sustainable rural tourism. This also means that a more diverse and in-depth analysis of sustainable rural tourism research was not made. Lastly, since there were several detailed topics within the topic of sustainable rural tourism, it was impossible to analyze 76 studies under a single framework to identify discrepancies in the research results and suggest the causes for them. It is desirable for future research to make efforts to generate a new conceptual framework and new knowledge by analyzing the consensus and inconsistency of the results of selected studies with more specific systematic review research topics in the sustainable rural tourism field.       [117] To analyze the relationship between regional specialty tea and rural tourism in terms of sustainability