Forgotten effects of active tourism activities in Spain on sustainable development dimensions

This research aims at exploring the impact of active tourism activities on sustainable development dimensions. The methodology applied was based on the Theory of Forgotten Effects, which involves the use of different matrices as a research method representing relationship between different elements. According to experts’ opinions, direct and indirect relationships effects caused by active tourism on sustainable development dimensions were evaluated. Particularly, the elements in the matrices were, on the one hand, types of active tourism activities by natural setting (ground, underground, water, underwater and aerial) and, on the other hand, dimensions of sustainable development goals (economic, social, environmental, cultural and governmental). The use of the Forgotten Effects Theory allowed us to analyse incidence relationships, both direct causalities identified by experts in the first place, and also significant linkages between elements in the matrices which had been overlooked initially but showed a strong incidence after applying the aforementioned research method (indirect causalities). Besides this identification of overlooked incidences or “forgotten effects”, another remarkable contribution of this pioneer work is in the selection of themes or objects of study included in the fuzzy metrics, as no other work relating active tourism activities and sustainable development dimensions was found in the literature.

Furthermore, tourism serves as a tool to raise awareness on social and environmental issues. In that respect, some works focus on the environmental education of tourism, dealing with how ecotourism and nature-based tourism promote tourist's environmental learning (Li et al., 2021), sensitivity (Canosa et al., 2020) and long-term behaviour of conservation (Ballantyne & Packer, 2011;Landon et al., 2019;Miller et al., 2020;Smith et al., 2019;Wilkins et al., 2018;Zeppel, 2008).
Although discussions and research on sustainability have taken place from decades ago (United Nations, 1987;Dixon & Fallon, 1989;Steer & Wade-Gery, 1993;Bramwell et al., 2017;Sharpley, 2000), recent policy frameworks such as the 2030 Agenda for Sustainable Development and alarming facts such as the increasing impacts of climate change (Backhaus et al., 2012;Intergovernmental Panel on Climate Change 2015;Scheyvens, 2018;Wesselbaum & Aburn, 2019) have put the issue of unsustainable lifestyles and human activities on the spotlight. Particularly in the Mediterranean area, experts, policymakers and the media point at sustainability-related issues concerning the tourism industry. For instance, according to the Tourism Research and Technology Center of the Balearic Islands (Andreu et al., 2003), the debate about sustainability of touristic activities is highly topical in mature destinations.
Concerns around how today's needs are met without preventing future generations to meet theirs have been addressed, at least, since the 80 s when the Brundtland report published one of the most referenced definitions of sustainable development (United Nations, 1987). However, it was only a few years ago when the 2030 Agenda for Sustainable Development was adopted by all members of the United Nations (2015) and provided a comprehensive and ambitious roadmap aimed at 17 Sustainable Development Goals (SDG) by year 2030.
As sustainability is a multidimensional term (Ratner, 2004), much debate has generated regarding the dimensions around the notion. The concept "Triple Bottom Line" has been widely applied to refer to the three typical dimensions of sustainability: environmental, social and economic pillars. Holden et al. (2014) suggest four dimensions associated with the Brundtland Report: long-term ecological sustainability, promoting basics needs, intragenerational equity and intergenerational equity. Sachs (1993) considers five dimensions: social, economic, ecological, spatial and cultural. Fosse and Le Tellier's (2017) also contemplates five categories: social, economic, environmental, cultural and governmental dimensions, linking them to the SDG. Other references, such as the framework presented by Fernández-Villaran et al. (2020), have included up to six dimensions of sustainability: environmental, social, economic, cultural, governance and territorial dimensions.
Many organizations have been developing indicators to measure outcomes in the different dimensions of sustainability from a regional perspective, such as the Sustainable Society Index, SSI (Van de Kerk & Manuel, 2008) or the European Tourism Indicator System, and from a private perspective, such as the Global Reporting Initiative standard. Thus, the discrepancies over the dimensions of sustainability are transferred to the definition of indicators to measure it, and the adoption of synthetic indicators, especially on the triple bottom line, is increasing (Cabello et al., 2019). A broad account of that increase is offered by Watróbski et al. (2018) and Ziemba (2018). More recently, Diéguez-Castrillón et al. (2021) present a bibliometric analysis of papers on sustainability indicators for tourism destinations published since 1995. The authors undertake a citation, co-citation and co-occurrence analysis, among others, to assess the evolution of the research topics over three subperiods and offer future lines of research, being one of them, the fulfilment of the SDGs.
Irrespective of the number of dimensions, Tsaples and Papathanasiou (2021) point at two opposing approaches to sustainability: the dimensional approaches and the dualistic relationship between human and nature. As for the indicators, Tanguay et al. (2013) refers to the scientific approach to the development of indicators, which pursues a large amount of information, and the policy maker approach, based on consensus among stakeholders to reach a synthetic analytical tool.
Rather than assessing the sustainability measures in active tourism, the aim of this paper is to offer a profound debate with experts on to what extent the variety of activities of active tourism affects the main dimensions of sustainability presented in Fosse and Le Tellier's work (2017), which links them to the SDG. In particular, experts from sustainability and active tourism related fields provided their insights on the level of impact that different types of activities have on sustainability dimensions in Fosse and Le Tellier's framework.
Therefore, this work focused on the latter, while taking into consideration the 2030 Agenda as a universal landmark. Given the wide variety of sustainability issues included in this 2030 Agenda, which are addressed by multisectoral, global and interdependent goals intertwining three dimensions of sustainable development (economic, environmental and social), Fosse and Le Tellier's framework was considered to better serve the purpose and scope of this research. Yet, they still link sustainability issues in the Mediterranean to the SDG.
Regardless of the framework applied, a common challenge in research and academia arises, as to gaps and opportunities to conduct studies and generate evidence on SDGs-related topics (Scheyvens, 2018) such as the transference of sustainable development goals into national and local contexts, monitoring and evaluation of contributions and impacts on sustainable development by sectors, or the formulation of evidence-based good practices and recommendations in these regards.
The work presented in this paper intends to fill some of those gaps, to participate in the ongoing debate around sustainability and tourism, and to inform future practices with evidence-based outcomes. This work also aims to be the starting point of a research whose purpose is to explore actual and potential relationships between active tourism services and sustainable development objectives. The results of this study will allow informing decisionmaking and recommendations towards the realization of economic, environmental and social sustainable development goals. Haegeli (2016) underlined the dramatical increase of the popularity of outdoor recreation and nature-based tourism over the last decades and referred to several authors with publications on that area such as Cordell (2008) or TNS Opinion and Social (2010). Likewise, Rivera (2015) refers to active tourism as an emerging segment of strategic interest for some destinations in Spain, and Haegeli (2016) referred to Kuenzi and McNeely's statement about nature-based tourism being the "fastest growing sector of the global tourism industry". Despite this steady growth of the outdoor recreation industry and related businesses, Haegeli (2016) also acknowledged that academic research on this area has not evolved at the same pace; similar statement is made by Raikkonen et al. (2021). Durán (2015) recalled the high number of authors who question if the importance given to research on tourism in Spain can be compared with the importance that the sector has; and Vargas (2011) considered that research on tourism has a short academic tradition. Khanra et al. (2021) presented a bibliometric analysis of research in ecotourism since 1990, identifying the development of four major related thematic areas: ecological preservation, residents' interests, the carbon footprint and tourists' behaviour. The authors show the relationship via keywords' analysis among the following core topics: ecotourism, sustainable tourism, climate change, nature-based tourism, sustainable development, climate change and protected areas. As research gaps and future research, they point out at ecological preservation and carbon footprint as subjects to be addressed and at the application of new methods of research other than case studies and conceptual developments.

Literature review
Other concerning gaps have been identified in the relationship between tourism and its effects on society and the environment. The United Nations Environment Program (Fosse et al., 2017) revealed that in the Mediterranean region "the relationship between the economic benefits, usually captured by large international operators, and the induced social and environmental transformation at destination level remains problematic".
On the other side of the coin, the United Nations World Tourism Organization (United Nations, 2015) focused on the possibilities of tourism to support achieving the SDGs and identified specific contributions that this sector can make to each of them (Table 1).
The 2030 Agenda refers to three broad dimensions of sustainable development: economic, environmental and social (United Nations General Assembly, 2015); therefore, sustainable development goals can be grouped under these three dimensions.
The 2030 Agenda breaks down these dimensions down into different objectives, which in turn aim at achieving more specific development outcomes. The relationship between SDGs and development outcomes goes from the most generic level (the SGDs as global goals) to the most specific level of pursued results: development targets and indicators, which are key to measure results in each of the SDGs. For example, SDG 3 on health and wellness includes as a target "by 2030, reduce by one third premature mortality from noncommunicable diseases through their prevention and treatment, and promote mental health and well-being" and this will be measure through the indicator "mortality rate attributed to cardiovascular diseases, cancer, diabetes or chronic respiratory diseases". As presented in the following sections, this work focused on the sustainability dimensions level, in a preliminary approach to the research topic studied which intends to be further developed focusing on more specific aspects of sustainable development.
issues in the Mediterranean. The authors reviewed several policy frameworks, among which the 2030 Agenda, and focused on this geographical region to identify sustainability-related effects of tourism particularly affecting Mediterranean destinations.
Results from Fosse and Le Tellier (2017)'s analysis provided a basis for the design of the research methodology presented in Sect. 3; specifically, the sustainability categories presented in their study were included as such as part of the research method implemented in this work. Those categories or dimensions have been the starting point to analyse the view of experts on the effects that active tourism has on them. Table 1 Contributions of tourism to the SDGs. Source: adapted from UNWTO 2015 SDG 1. NO POVERTY: sustainable tourism, and its impact at community level, can be linked with national poverty reduction goals, those related to promoting entrepreneurship and small businesses, and empowering less favoured groups SDG 2. ZERO HUNGER: tourism can spur agricultural productivity by promoting the production, use and sale of local produce in tourist destinations and its full integration in the tourism value chain SDG 4. QUALITY EDUCATION: the sector can provide incentives to invest in education and vocational training and assist labour mobility through cross-border agreements on qualifications, standards and certifications SDG 5. GENDER EQUALITY: Tourism can empower women in multiple ways, particularly through the provision of jobs and through income-generating opportunities SDG 6. CLEAN WATER AND SANITATION: the efficient use of water in tourism, coupled with appropriate safety measures, wastewater management, pollution control and technology efficiency can be key to safeguarding this precious resource SDG 7. AFFORDABLE AND CLEAN ENERGY: by promoting long-term investments in sustainable energy sources, tourism can help to reduce greenhouse gas emissions and mitigate climate change SDG 8. DECENT WORK AND ECONOMIC GROWTH: by giving access to decent work opportunities in the tourism sector, society can benefit from professional development. Target 8.9 "By 2030, implement policies to promote sustainable tourism that creates jobs and promotes local culture and products" SDG 9. INDUSTRY, INNOVATION AND INFRASTRU CTU RE: the sector can incentivize governments to upgrade infrastructure and retrofit their industries, making them more sustainable SDG 10. REDUCED INEQUALITIES: tourism can be a powerful tool for community development and reducing inequalities if it engages local populations and all key stakeholders in its development SDG 12. RESPONSIBLE CONSUMPTION AND PRODUCTION: tourism can adopt sustainable consumption and production practices. Target 12b: develop and implement tools to monitor sustainable development impacts for sustainable tourism which creates jobs, promotes local culture and products SDG 13. CLIMATE ACTION: by lowering energy consumption and shifting to renewable energy sources, especially in the transport and accommodation sector, tourism can help tackle one of the most pressing challenges of our time SDG 14. LIFE BELOW WATER: coastal and maritime tourism, tourism's biggest segments, rely on healthy marine ecosystems. Target 14.7 aims to increase the economic benefits from the sustainable use of marine resources, including through sustainable management of fisheries, aquaculture and tourism SDG 15. LIFE ON LAND: sustainable tourism can play a major role […] in respecting terrestrial ecosystems, owing to its efforts towards the reduction of waste and consumption, the conservation of native flora and fauna, and its awareness-raising SDG 16. PEACE, JUSTICE, AND STRONG INSTITUTIONS: as tourism revolves around billions of encounters between people of diverse cultural backgrounds, the sector can foster multicultural and interfaith understanding SDG 17. PARTNERSHIPS FOR THE GOALS: due to its cross-sectorial nature tourism has the ability to strengthen private/public partnerships and engage multiple stakeholders-international, national, regional and local-to work together Table 2 captures those Fosse and Le Tellier's (2017) five categories of sustainability issues identified in the Mediterranean tourism sector, three of which equal the three aforementioned dimensions of sustainable development in the UN's 2030 Agenda: environment, society and economy.
From these identified issues, the authors formulated objectives to tackle each of them, as shown in Table 3. Considering that the purpose of this work was to explore current and potential contributions of active tourism to sustainable development, objectives rather than issues were approached (and included in the incidence matrices). The wording in terms of "objectives" instead of "issues" and the forward-looking perspective appeared to serve better such purpose.
Furthermore, the authors connect these dimensions to those SDGs which address related issues in each dimension. Through a crosscutting analysis of different frameworks, they identified the following links in Table 4.
As Table 4 presents, Fosse and Le Tellier (2017) found connections between objectives for sustainable tourism in the Mediterranean and most SDGs except those marked with an asterisk: SDG 3 on well-being, SDG 5 on gender and SDG 7 on energy. However, following UNWTO's analysis identifying contributions of tourism to all SDGs (United Nations, 2015), these originally missing SDG 3, 5 and 7 in Fosse and Tellier's work were also included in Table 4.
Most connections concentrate in the first three objectives for sustainable tourism in the Mediterranean, which correspond to the three dimensions of sustainable development in   Gibson et al. (2018) refer to it as tourism associated with practicing sports and offer some insights to how this research area has evolved. As stated by Araújo et al. (2012), active tourism, ecotourism, sports tourism or adventure tourism are used with confusing limits. Some associate it with activity, sports or mobility (Nasser, 1995) while others view it beyond that and consider it "meaningful experiences which connect human beings with outdoors" (Miranda et al., 1995). Where there seems to be consensus is in the fact that the area of nature-based tourism including physical activities for recreation has seen an increasing interest in recent years and configures a distinctive sector (Rivera, 2015). That is the case in Spain, where policy frameworks and legislation have been recently created around this sphere and active tourism is recognised as a distinctive area in the tourism industry (Government of Spain, 2018). From the demand's perspective, the trend of seeking active holidays with a dynamic and interactive character in Spain was identified, at least, since the early eighties (Miguel, 1984;Rivera, 2015). Lagardera (2002) defined active tourism as a consolidated alternative to traditional tourism consisting of the supply of recreational, sporting and cultural activities both on the coast and on the mountain, which require previous knowledge for doing them. In Triguero's (2010) PhD thesis, active tourism is in between sport practice, tourism activities and an interest in environment, and to have a multidisciplinary character which cannot be approached from a single perspective. From a narrower perspective, Araújo et al. (2012) defined active tourism as "sports activities of different physical intensity which use natural resources without degrading them" and propose a conceptual model where active tourism is regarded as part of the broader sector of nature-based tourism.
Despite conceptual differences in literature on active tourism and related fields, most Autonomous Communities in Spain have approved regulations where active tourism is referred to as a distinctive sector or subsector (Rivera, 2015). Common elements in their definitions include physical, sportive and adventure activities which are specialised, have a strong leisure or recreative component and are practised by using resources offered by nature in the environment where they take place.
Having gathered several definitions and delimitations around active tourism in the literature, for the purposes of this research, the most context-sensitive definition was adopted from Law 8/2012 on Tourism in the Balearic Islands: active tourism services are about delivering recreational, sporting and adventure activities which are practiced while making use of resources offered by nature in the environment where they are conducted, whether  Rivera's (2015) review of the active tourism sector in Spain and, in the Balearic context, the list of active tourism activities in Decree 20/2015 (Government of the Balearic Islands, 2015). The later includes, for instance, mountain bike (BTT in the Spanish acronym), canyoning, climbing, water skiing, speleology, ballooning, mountaineering, sailing, skydiving, canoeing, quads, equestrian tourism, bungee jumping, hiking, surf and windsurf. Besides these activities, Riviera's (2015) analysis includes others such as cycle tourism, archery, orienteering, rafting, scuba diving, skiing and snowboarding.
In order to categorize the wide variety of active tourism activities in a reduced number of typologies, the main five categories identified in the literature were selected for this work. Depending on the natural setting where the activity is practiced, the following five categories can be distinguished: aerial, ground, underground, water and underwater (Rivera, 2015;Lagardera, 2002; Government of the Balearic Islands, 2015). Following this classification, representative examples in each typology are ballooning, paragliding in aerial activities, hiking and cycle touring in ground activities, speleology and canyoning in underground activities, windsurf and canoeing in water activities, scuba diving, snorkelling in underwater activities.
Addressing the main thematic areas involved in this work, Sharpley's (2000Sharpley's ( , 2020 review of the development theory, provides an insightful discussion around the extent to which principles and objectives of sustainable development can be transposed to the specific context of tourism. In these regards, the author concludes that "tourism is widely perceived to be an effective vehicle for development, although […] the goals and inherent processes of "development" are largely overlooked in the tourism literature". In the later Sharpley's review (2020), the term of de-growth as an alternative approach to development is discussed. Moreover, as Khanra et al. (2021) mentioned "to sustain the attractiveness of a nature-based destination in the wake of climate change may provide important insights for the responsible authorities in ecotourism management". This equilibrium is stated as well by Ashraf et al. (2020) and Sánchez-Fernández et al. (2019) who referred to the importance of the destination's sustainability as a motive of attraction.
The concerns on the relationship between tourism and sustainable development (Sharpley, 2020; Fosse et al., 2017;Simo-Kengne, 2021), the necessity of developing academic research on nature-based tourism (Haegeli, 2016;Raikkonen, 2021) and the current significance of the SDG, served as the foundation for the following research question: To what extent can active tourism activities make contributions to the economic, environmental, social, cultural and governance dimensions of sustainability?
The methodology applied in this work is based on the Theory of Forgotten Effects, which involves the use of different matrices representing the relationship between different elements. According to experts' opinions, direct and indirect relationships of effects on sustainable development caused by active tourism are assessed. Research applying fuzzy decision-making has grown considerably since the publication, in 1965, of the work by Lofti A. Zadeh entitled "Fuzzy sets", from which fuzzy decision-making models began to be used to answer various problems analysed by social sciences (Barcellos de Paula and Gil-Lafuente, 2018). Based on Zadeh's work, the mathematics of uncertainty, and more specifically that of the Theory of Fuzzy Sets, has been used in Social Sciences fields, although over the last 50 years many researchers (Yager, 1993;Pedrycz, 1994;Xu, 2007 applications in different fields, such as business management, engineering, biology, medicine, geology, sociology, phonetics and music. Any problem in environments of uncertainty is likely to be treated through the Theory of Fuzzy Sets since, as time goes by, it becomes more and more feasible to introduce thought mechanisms such as sensations into formal schemes and opinions expressed in numbers. For Blanco-Mesa et al. (2016), the use of fuzzy logic helps the person responsible for making decisions in real uncertain environments in which the consequences of actions are not precisely known; as that is the case of the field studied in this work, the Theory of Forgotten Effects and Fuzzy Sets has been used as a methodology in the present document.
Thus, the tools and methodology used for a first assessment of relationships or effects between active tourism activities and sustainable development objectives are presented next.

Methodology
Fuzzy incidence, also referred to as fuzzy logic, was the methodological approach chosen for conducting this work. As presented by Linares-Mustarós et al. (2018), the idea of using fuzzy incidence or relationship matrices is to detect possible non-obvious influences of certain causes on certain effects. The application of this methodology in economic literature is regarded as "Forgotten Effects Research" (Alfaro-García et al., 2016;Linares-Mustarós et al., 2018). Given that objects of study in this work involve the economic sector of tourism and its actual or potential effects on development outcomes, fuzzy metrics serve the purpose of exploring such relationships.
Broadly, the forgotten effects methodology involves a direct effects matrix and a matrix of indirect effects or new incidences which results from other intermediate matrices. After obtaining the direct effect matrix, which shows incidences between causes and effects, a matrix relating to causes-causes incidences and another matrix relating to effects-effects incidences are also applied (Liu et al., 2019). The latter allow reformulating values in a new or composed cause-effects matrix which, compared to the original causes-effects matrix, can show differences between the values initially assigned by experts and the newly formulated values. When such differences are significant, a "forgotten" effect is found.
Tables 5, 6, 7 and 8 show each of the matrices typically used in Forgotten Effects methods. Once the above matrices of incidences have been created, direct and indirect incidences can be identified through the max-min composition or fuzzy composition (Blanco-Mesa et al., 2018).
Differences between the final composed matrix, or second-generation effects, and the direct incidence matrix created initially allows identifying causal relationships which were forgotten or non-obvious.
Incidence values in the matrices are given by experts according to their opinion on how significant they consider relationships between causes and effects to be. Usually, research using the Forgotten Effects Theory assign values between 0 and 1, being 0 the weakest and 1 the strongest influence. Table 9 shows the scale of numerical values and their corresponding linguistic meaning (Linares-Mustarós et al., 2018).
Following Mulet-Forteza et al. (2018) and Socias Salva et al. (2020), the methodological design of this document was carried out in several stages. In the first, based on the literature review carried out, the active tourism and sustainable development matrix was created. Types of active tourism activities were treated as causes and the dimensions of sustainable development as effects (Table 10). This matrix was sent to the experts to confirm its validity. Once a consensus was reached regarding the validity of the causes and effects represented in the matrix in Table 10, the next step was to collect Table 6 Fuzzy direct incidence matrix. Causes-Causes Table 7 Fuzzy direct incidence matrix. Effects-Effects Table 8 Max-mix composition matrix their opinions, through structured questions to a panel of experts on active tourism and sustainability. The panel of experts (11 in total), selected by means of a convenience sampling, brings together various profiles, devoted to areas related to active tourism and sustainability in various fields. It was made up of 5 researchers (two of them in areas related to physical activity and sports, one in the area of tourism and corporate social responsibility, another in the area of geography and sustainability and one in physical activities in nature); 4 people in consultancy (one from a Spanish consulting company offering environmental services, another one from an association offering tourism activities for people with disabilities in Spain, another consultant on tourism and sustainability, and other in active tourism); an expert in international aid and sustainable development goals; and finally, an ex-government expert in sustainable tourism. Although the incidence matrix methodology leaves room for selecting experts based on the criteria of the researchers (Mulet et al., 2018), in this case a balance was sought between representatives from the academic and business spheres, in addition to some representation of the political sphere. Therefore, the questionnaire was sent to 11 experts.
The main objective of the next stage of the data collection process was to validate the results initially obtained by the experts. For this, the experts were asked to analyse the answers given by their namesakes. Thus, the answers obtained by the researchers were Table 9 Scale of values for incidence matrices Null incidence 0 Practically null incidence 0.1 Almost null incidence 0.2 Very weak incidence 0.3 Weak incidence 0.4 Intermediate incidence 0.5 Fair incidence 0.6 Considerable incidence 0.7 Strong incidence 0.8 Very strong incidence 0.9 Absolute 1 forwarded to the rest on them so that they could analyse the logic of the evaluations obtained by the others. The same process was carried out for the rest of the experts with the same intention. The results of this review showed that the results initially given by a researcher were not consistent, specifically the one related to geography and sustainability, so the results of this expert were discarded. Thus, the number of validly obtained results is reduced to 10, 4 lectures, 4 consultants, an expert in international aid and sustainable development goals, and a former politician with a position in sustainable tourism. We consider that this number of experts is sufficient to carry out our work, since it is higher than that of other documents, as would be the case of the work of Mulet et al. (2018), who consulted 9 experts to carry out a similar study, but related to social economy companies, or that of Socias Salva et al. (2020), who consulted 8 experts to analyse the forgotten effects of worth-creating activities in hybrid business management models in non-profit organizations.
Next, an expert-type was elaborated, based on the values indicated in Table 9, to build a matrix of direct incidences (Mulet et al., 2018) (Table 10), following the Kaufman and Gil algorithm (Kaufman & Gil, 1988;Gil-Aluja et al. 2009). Respondents' answers were weighted according to their level of specific knowledge and experience on active tourism and sustainable development; thus, values in the matrices incorporate such differences in expertise.
Subsequently, to obtain the accumulated effects of the first and second generation, a new diffuse incidence matrix was developed, composing the matrix of Tables 11, 12 and 13, whose results are presented in Table 14. Finally, and similarly to what was done in the papers of Mulet et al. (2018) and Socias Salva et al. (2020), to isolate the effects of secondgeneration influences, the algebraic difference between the results of the matrix included   Tables 14 and 11 has been made. In this way, we obtained an indirect diffuse incidence matrix (Table 15) which only brings to light second-generation effects, that is, it reveals the degree to which some causal relationships have been ignored (Socias Salva et al., 2020).

Results
Following the analysis of experts' responses and values obtained in the incidence matrices, relevant findings arose. Initially, direct effects in the causes-effects matrix (Table 11) captured a concentration of significant incidence-value 0.9 or "strong incidence" in the scale-under economic effects columns, especially with regard to terrestrial and aquatic activities (a2 and a4, respectively). The experts also obtained strong incidences (value 0.8) in the columns of economic and cultural effects; in particular, strong effects caused by aerial activities in cultural sustainable development were identified as well as strong effects of ground, underground and underwater activities in economic sustainable development. Slightly weaker but still considerable incidences (0.7) were found between aerial activities and environmental and economic dimensions of development, between aerial and ground activities and social development, and between underground and underwater water activities and economic development. Experts also provided answers regarding the intensity of relationships among causes and relationships among effects, i.e. they assigned a value according to the extent to which they considered that each cause affects the rest of causes, and so they did for valuing how influencing they consider each effect to the for the rest of effects. Tables 12 and 13 present results of these causes-causes and effects-effects matrices.
In the cause-cause matrix (Table 12), it can be seen how influential certain causes are on other causes. Letting aside cells in the matrices showing the obvious absolute incidence between the same causes-values "1" in the diagonal-the highest influential relationships were assessed to be between water activities and underwater activities. Furthermore, a considerably strong incidence was found between ground and underground activities, and between ground and water activities.  As for effects-effects incidences, experts' responses pointed at the relationship between economic and governance dimensions of sustainable development as the most intensively linked. The connection between the economic and the environmental dimensions of sustainable development objectives was also considered to be a considerable incidence.
These incidences directly identified by experts in their responses are the so-called first-generation effects, while indirect incidences, found through the composition presented next, are second-generation effects. Through overlapped significant relationships in cause-cause and effects-effects matrices, a new fuzzy incidence matrix was formulated in the max-min composition (Table 14).
The max-min composition matrix allows comparing resulting values and those values initially assigned by experts. Those incidences whose value changes significantly are showing "forgotten effects" or overlooked strong relationships between elements in the matrix (Table 15). Table 15 shows differences between first-generation and second-generation effects, i.e. changes in the effects that experts considered active tourism activities to have on certain dimensions of sustainable development objectives.
The following incidences increased its value considerably: effects of ground activities on environmental development objectives, and effects of underground and water activities on governance. Table 16 captures these indirect or forgotten effects as well as direct effects.
Overall, these results show the presence of non-obvious effects of active tourism activities on sustainable development dimensions, especially regarding environment and governance issues. Initially, these areas of sustainable development had not been highlighted as strongly affected by active tourism activities; however, the use of the forgotten effects methodology revealed these overlooked significant incidences. To a lesser degree, some indirect effects on social and cultural issues have also been found, although the experts captured more precisely the incidences that are generated in these areas-that is, forgotten effects of water activities on cultural development with an increase in the incidence degree from 0.6 up to 0.8 (strong incidence) and forgotten effects of underground and water activities on social development with an increase of 0.1 on the incidence degree, which makes it a considerable incidence. Finally, the results of Table 16 indicate that the experts captured all the incidents generated by active tourism activities regarding economic development.

Conclusions
As presented throughout this paper, the purpose of exploring relationships between active tourism activities and sustainable development dimensions was achieved through the forgotten effects method. Those effects were identified by a variety of experts from sustainability and active tourism related fields, providing their perceptions on the influence that diverse types of active tourism activities have on sustainability dimensions. First-generation effects in direct incidences matrices showed those relationships which experts assessed as the strongest, that is: the effects that all the activities analysed (aerial, ground, underground, water and underwater) have on economic development; the effects that aerial and ground activities have on social development; the effects that ground, underground and underwater activities have on cultural development (causes-effects matrix); and the influence of the economic dimension of sustainable development goals on the governmental dimension (effects-effects matrix).
Interestingly, the methodology of the incidence matrices has revealed other additional strong relationships: first, the forgotten effects that all activities, except aerial ones, have on the sustainable development goals related to the environment. Second, the forgotten effects that all activities have in governance. The latter effects may be since only one expert on the panel is directly related to this activity. Third, we find indirect effects of water activities on cultural goals. To some extent, certain indirect effects on social and cultural issues were also found, such as those caused by underground and water activities on social development.
Furthermore, responses may have been biased towards the most typical types of activities or those which experts know the most; for instance, ground and water activities where the two typologies where the strongest incidences concentrated. By contrast, underground activities were overlooked as first-generation effects while appeared to have significant second-generation effects in two dimensions of sustainable development: environmental and governmental objectives.
A less expected forgotten effect was the incidence of ground activities on environmentrelated sustainable development objectives. Despite assumptions and hypothesis that could be drawn from the reviewed literature regarding the potential causalities of most practiced activities such as hiking and activities alike on the ground (Rivera, 2015), experts did not assigned a strong incidence of these on environmental objectives initially. The fact that the forgotten effects method made this relationship appear as a strong second-generation effect, shows how appropriate this methodology can be for incorporating relevant connections between studied elements which had been overlooked. In this case, the generation of indirect incidences through the max-min composition seems to link back to literature underlying actual and potential effects of frequent ground activities on the environment.
All in all, direct and indirect incidences leave ground, underground and water activities as the most influential ones to sustainable development goals, according to this work. Despite limitations involved, such as the complexity and interdisciplinarity of elements studied, steps towards the testing of the said hypothesis have been made. Contributions of certain types of active tourism activities to dimensions of sustainable development goals can be envisaged, although further work will be necessary to continue generating robust evidence in these regards.
Given the variety of elements encompassed in the studied subjects-active tourism activities and sustainable development objectives-future research will break down categories in specific activities and particular objectives. Thus, we pursuit a deeper analysis of the effects of active tourism activities on objectives for sustainable tourism in the Mediterranean. Future work using a major number of categories in the matrix-specific active tourism activities instead of typologies and specific sustainable development goals instead of dimensions-will allow discerning possible differences in relationships between elements which were treated equally under the same category in this work. Thus, more precise and extensive matrices will allow valuing the intensity of incidences differently depending on the particular activity and on the particular goal presented in the matrices. They may also bring light to some of the unanswered questions in this first work, such as those around missing strong incidences in social development goals or the forgotten effects found. From a wider perspective, future work in this line will try and narrow the research gap around sustainable development through active tourism. Following this work, next pieces of research will be conducted through incidence matrix which relate more specific features in the active tourism sector with particular sustainable development outcomes.
Future research will aim to develop and apply more complex fuzzy incidence matrices which better represent and inform an also complex reality.
Funding Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.

Declarations
Conflict of interest It is an original manuscript. It has not been published in any other journal nor it has been submitted simultaneously elsewhere.
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