The role of an international treaty in creating over time a sustainable network for interdisciplinary landscape approaches

Context. The European Landscape Convention (ELC) of the Council of Europe represents the rst international treaty that envisage all aspects when planning European landscapes. Through this convention, public authorities have been encouraged to adopt policies and measures at local, national and international level in order to protect, manage and properly plan landscapes in a sustainable manner. Objectives. Our study aims to provide a better understanding of the landscape governance research trends by using an innovative methodology to highlight ways to improve and optimize ELC implementation. Methods: For this, we analyzed published articles in international journals directly connected to ELC implementation between 2000 and 2020 (n=400). We use bibliometric indicators (i.e., publications, authors aliations) and co-occurrence analysis with overlay visualization in time (i.e. keywords), in order to discover the landscape research trends and evolution in the past 20 years. Furthermore, we extracted 119 articles that we review considering for each article the assigned different attributes in order to perform a more detailed analysis of the ELC aspects covered in research. Results: The ndings of our innovative analyses show the key player in promoting the European Landscape Convention principles in the research eld, along with the evolution in time of the most common trends of ELC by identifying the perspectives of landscape conservation in the future. Conclusions. This paper provides insights for integrating novel technologies and innovative landscape approaches in the future and for the landscape sustainability.


Introduction
The year 2020, besides the major change in human lives caused by the Covid-19 pandemic, also represents the celebration of 20 years since the implementation of the European Landscape Convention, something we do not want to forget. This unique international treaty that de ned the landscape as "a common resource and patrimony" (CE 2000a), is currently rati ed by 41 countries being considered the point from which research, policy management of landscapes and landscape practice related to key concepts for landscape sustainability (Brandt et al. 2012). This change pushed landscape science further into a different disciplines arena ), for instance: ecological approach (landscape ecology, biodiversity) or geography, geology, geomorphology, history, archaeology and landscape architecture or social, economic, cultural and why not political approaches.
This interdisciplinary approach has linked landscape science to planning, policies, management, and stakeholders involvement in order to nd solutions to improve local life conditions and landscape perception. If 10 years after the implementation of the European Landscape Convention (ELC) the IALE community ) raised the question of how ELC will be able to better integrate the concept of landscape among decision-makers and in the different sectoral policies dealing with the European territory. 20 years after its implementation, we still wonder if this step was taken and if the joint research -practical actions are still lacking (Hernández-Morcillo et al. 2017).
At rst, this treaty encouraged countries to identify and characterize their landscapes in order to identify and classify their landscapes for protection, management and planning (Chuman andRomportl 2010, García-Llamas et al. 2016). Due to the multidisciplinary nature of landscape research, several methods have appeared in the literature, which tried to quantify the landscapes. For example, (Simensen et al. 2018) in a systematic review show that there are multiple methods that can be used differently to characterize landscapes and depending on user needs. In addition to classical methods, dedicated tools have appeared, e.g. landscape inventories (Van Eetvelde and Antrop 2011, Santé et al. 2018), or webplatform for facilitating public participation such as: Public Participation GIS -PPGIS (Brown et al. 2014). Furthermore, the development of participatory scenario development process designed by stakeholders is encouraged (Santé et al. 2020).
By the clear and simple de nition of landscape seen as "areas, as perceived by people" (CE 2000b), people were encouraged to realize that they have an important role in the management of their landscapes (Conrad et al. 2019). This involvement is also supported by the 5th and 6th articles of the convention, where it is speci ed that the public involvement and participation is considered to be a key factor in developing these landscape policies (Santé et al. 2020). Citizen participation policies refer to actions, such as the conservation, protection, management and planning for different landscape types. These actions should be systematically integrated into regional and local planning policies (Brunetta et al. 2018). Also, landscape preferences of people could be the ideal tool for implementing these actions As in any research eld, collaboration in landscape planning, in policies implementation and in decisions concerning the landscape governance (Folkeson et al. 2013) between the general public, developers and the responsible public authorities, which should be an arena for the implementation of ELC (Sandström and Hedfors 2018), still remain a challenge.
Nevertheless, the network RECEP-ENELC (at local and regional authorities at European level) encouraged local authorities to consider ELC within planning policy and reactivate local communities' initiatives. But there is still a need to develop working groups to promote good practice, and existing networks (e.g., RECEP -ENELC, UNISCAPE, CIVILSCAPE networks) create stronger links between authorities, universities and civil society for the implementation of the ELC (EAI 2009). Furthermore RECEP-ENELC that could help implement the ELC within the territory through scienti c, technical and political support (Dempsey and Wilbrand 2016). In this paper, we use an innovative approach, namely network and co-occurrence analysis to investigate scienti c articles that discuss the European Landscape Convention implementation in order to answer the research question that envisages how the European Landscape Convention contributed to creating over time a network for interdisciplinary research approaches and also what are the points that need to be improved to optimize its implementation?

Methods
Our methodology consisted in extracting from Scopus database the articles that have in their title, abstract or keywords the mention of the European Landscape Convention. After data curation, we obtained 400 articles and created a database with the following aspects: Bibliographical information, Abstract & keywords, Author(s), Article title, Year, Source title, volume, issue, pages, Source & document type, Publication Stage, A liations, Author keywords and Index keywords. We created a network for the collaboration established for the promotion of the ELC research to understand the cooperation for landscape research driving factors (Rozylowicz et al. 2017, Hossu et al. 2018). Separately, we investigated the research productivity in order to identify the top journals in this eld. For the collaboration network, two countries were connected if they had at least 1 paper published together, isolated countries were not represented in the collaboration network. In this stage of our analysis, we used centrality metrics to identify the promotors of ELC at European and why not international level and highlight the countries with best position in the network to in uence (Everett and Valente 2016) (Abbasi et al. 2012). After uniformization of the dataset, we performed a co-occurrence analysis (Radhakrishnan et al. 2017) of the authors keywords evolution in time considering the average publication and of the criteria used in the reviewed publication. Keyword co-occurrence network based method helps to create a systematic review of scienti c literature by using visual analysis in order to directions to advance a particular scienti c domain (Radhakrishnan et al. 2017). Nevertheless, when using complex networks, the visual representation does not allow visibility of all nodes, this is why we chose to illustrate keywords that appear at least 2 times.
The results of this analysis will highlight the evolution of the ELC concepts will determine future directions of research and ways to improve the implementation of the principles of the convention by identifying the policy issues, gaps in landscape conservation and planning discussed in the literature (Pedroli et al. 2013, Roe 2013 Environmental Impact Assessment Review, Regional Studies, European Journal of Geography, Journal of Maps, Journal of Forest Economics, Ecology and Society, Journal of Agricultural Engineering, Landscape Online, Geosciences (Switzerland), Sustainability (Switzerland). In selecting the articles for review, we considered the type of the publishing journal, including some BDI recognized by the landscape ecology community. Another criterion was related to the ELC requirements and recommendations, described, or applied in these articles. The article excluded from this last analysis envisaged the following: the journal type (we excluded the Conference Proceedings and other papers with limited access, only presenting their abstract, in other language than English or those from the gray literature with very brief reference to the requirements of this treaty. The criteria (C1-C8) which were considered in the analysis, were chosen from the requirements promoted by ELC, respectively: i) C1-C3, de nition, characterization of landscapes (particularly values of landscapes); ii) C4-C5, to develop several assessment methodologies for delineate landscape units; iii) C6-C7, to recognizes the importance of public participation on decision-making and to establish procedures for the participation of the general public, in the de nition and implementation of landscape policies, the municipalities as an important instrument for the development and implementing of landscape policies. iv) C8 -networks established to promote the implementation of the ELC, a broad range of European stakeholders, such as political institutions, universities, and local and regional NGOs Or the ELC promotes collaboration between public agencies, NGOs and local communities.
The softwares used for analysis were R and Ucinet

Results
Our results are focused on the extracted research articles concerning the implementation and role of the European Landscape Convention within landscape conservation and management. The core sources of the analyzed articles are presented in Fig. 1 Figure 2 illustrates a signi cant evolution of research done exclusively on ELC, especially after 2010.
In terms of country productivity on the papers discussing ELC implementation principles or best practice examples, stands out in the top the following countries: Italy, Spain, United Kingdom, Sweden, Poland, Germany, France, Norway, USA, Netherlands, Belgium, Czech Republic, Turkey, Denmark, Switzerland (see Supplementary Material Table 1). Among the countries that have produced scienti c articles on this subject but in a lower number maybe due to the fact that their countries have not rati ed the convention, we list: New Zealand, China, Japan, Serbia, Canada, Chile, Colombia, Iran, Kyrgyzstan and Lebanon (see Supplementary Material Table 1). Table 2), where we represented the cooperation established by the authors of the analysed articles considering their a liation. After investigating the betweenness centrality results we can see that countries such as: Norway, Spain, Sweden, and Denmark have the highest betweenness indicating the fact that they are the brokers for collaboration having the best position in the network. Considering the analyzed articles, United Kingdom was the leader in landscape research being the rst most coted country, followed by Belgium, Sweden, Netherlands and Italy. In terms of most important a liation of our investigated network in terms of productivity and that had a great academic impact, we mention the rst three positions, namely: Swedish University of Agricultural Sciences, Norwegian University of Life Sciences and Ghent University.

Figure 3 presents the analysed Country Collaboration network for ELC research (see Supplementary Material
The keyword network database investigated had initially 1314 authors keywords that were uni ed. After this, in order to generate a network with a good visualization, we selected as minimum number of occurrences of a keyword: 2, obtaining a nal graph of the most common 187 keywords used in landscape research (Fig. 4). Considering the evolution in time of the concepts discussed in the literature, there is a focus in the average publication year between 2012-2014 on concepts such as: land cover, heritage, character, landscape structure, restoration, territory, infrastructure. The middle cluster comprises keywords or concepts that have an average publication date between 2014 and 2016, this meaning that a concept could be in this group due to the fact that it is a concept discussed for the entire period of 20 years since the convention began to enter into force. In this cluster, we identi ed keywords such as: focus group, spatial planning, conservation, values, design, architecture. The newer research directions are highlighted by the keywords from the last cluster with an average year of publication after 2015, here we mention keywords such as: climate change, governance, human rights, community, commons, guidelines, policy, landscape education. Our keyword analysis shows that cultural landscape or landscape history have as average publication date between 2010 and 2015, other keywords such as: wind power, land use, regional planning have the average year of publication in 2014 and keywords such as conceptual framework, common agricultural policy and holistic approach have as average year of publication 2016.
As seen in Fig. 5, the most important criteria discussed in the investigated publications is C1: only the mention of the convention in the text (as a reference to the law), envisage the de nition of the landscape given by ELC is mentioned or discusses the implementation of ELC in general. The rest of them being used in the reviewed articles as follows: C2 found in 47.06% of cases, C6 42.86%, C7 37.82%, C3 38.66%, C5 28.57%, C4 24.37%, C8 15.97%. In Fig. 5, we also illustrate the connections between the criteria in the analyzed articles and in the graph (Fig. 5).

Discussions
The evolution of the research focused on ELC over time.
Important research journals focused on issues related to landscape ecology (e.g. Landscape Research, Landscape Ecology, Land Use Policy) have published research articles discussing ELC for the past 20 years (Figs. 1-2). At rst, this treaty encouraged countries to identify, characterize their landscapes and then propose them for protection and conservation, or to identify and classify their landscapes for protection, management and planning. The temporal analysis showed a progress with respect to the research focused on landscape science developed towards policy, management, and practice especially thanks to the implementation of the ELC, nevertheless a common agenda should be made in order to adapt and apply to better de ne these actions and to implement a holistic approach (Wu et  A treaty signed 20 years ago, the European landscape Convention produced unexpected effects in landscape research, planning. Of course, the implementation was done gradually and differently in European countries as well as the research in this eld (Fig. 3), referring to speci c national landscape management systems and it will be interesting to see how the next 10 years will look like for the research and practice established by the ELC, and especially if we are going towards a sustainable landscape.
The ndings of our temporal analysis show that before 2012, researchers encouraged landscape research in the following concepts: Landscape design (Nassauer and Opdam 2008), Landscape Character Assessment (Butler and Berglund 2012), land cover and use along with characterization of landscapes in different countries (Petrisor et al. 2010) or regions (Frondoni et al. 2011). After this period, in the next 10 years publications discussed the need of more involvement of local actors in landscape planning and the importance of collaborative processes in environmental management and governance of landscapes (Bixler et al. 2016a). Furthermore, in the last ve years (Fig. 4), it was registered a growth in subjects related to: landscape values important to be kept in time, important landscape ecology metrics and indices to be considered in climate change adaptation in a European Context, as well as ways to adapt urban landscapes (Sandström and Hedfors 2018) to sustainable blue green infrastructures (Lamond andEverett 2019, Iojă et al. 2021). In terms of productivity over time, our results showed a low productivity in high impact journals of some European countries, and maybe that is why we are also talking about uneven ELC implementation, as some countries have evolved a lot in researching innovative landscape analyses, while others are already very evolving, such as Italy, Spain, United Kingdom, Sweden, etc.
The emergence and implementation of ELC has generated the creation of networks for interdisciplinary approaches.
The implementation of the ELC contributed signi cantly for the awareness-raising (Riesco-Chueca and Gómez-Zotano 2013) of the landscape values (Fig. 2), among scientists, policymakers and the general public (Plieninger et al. 2015). The role of landscape ecologists was decisive in making the connections between scientists, researchers, practitioners and policymakers (Pinto-Correia and Kristensen 2013). Thus, our ndings showed that a bridge between disciplines was built, that led to an interdisciplinary research approach (Fig. 3). This collaboration led to the creation of diverse landscape assessment methods, indicators or PPGIS platform, integration of concepts such as multidisciplinarity (Fagerholm et  As shown by our co-occurrence ndings (Figs. [4][5], over the last 20 years, there has been a higher frequency of the analyzed elements envisaged by the rst 3 criteria (C1, C2, C3), referring to ELC generally mentioned as a legislative reference, considering the landscape according to ELC de nition, either encouraging local actors to be part of the decision process, ELC being considered as a policy instrument. These criteria were the most connected in the analyzed articles. This result draws attention to the need for greater promotion in the future of the following criteria in practice and in research: interdisciplinary methods of landscape assessment, along with perception research envisaging proper protection and management of the landscape, and especially implemented by municipalities or local authorities in collaboration with public stakeholders that should have the most important role in landscape planning and decision-making (Sandström and Hedfors 2018).

Conclusions
Our paper presents a retrospective of the research dynamics from the beginning of the implementation of the European Landscape Convention and until now, these being particularly important aspects in tracing the future of landscape planning and conservation. These ndings are achieved using topical innovative methods in the scienti c literature. as is the case of network analysis or co-occurrence keyword analysis.
A treaty signed 20 years ago has produced unexpected effects in landscape research, landscape planning or landscape policies. Of course, the implementation was done gradually and differently in European countries, referring to speci c national landscape management systems (De Montis 2014). The review of the investigated articles highlighted the fact that there is still a need for the transfer of good practices and clear policies for the implementation of the ELC depending on the landscape speci city. Moreover, creating networks among political institutions, universities, and local and regional NGOs, public agencies, local communities or working groups, to promote and why not improve ELC remains still a challenge (Bixler et al. 2016b), such shortcomings can also be covered by using network theory in future research that can improve ELC implementation (at international level and at local level), and further develop national landscape policies by integrating all interested actors on the one hand, and linking landscape ecology concepts with planning process on the other (Hersperger et al. 2021).
Given the digitization period that the entire planet is going through, maybe in the next 10 years, policy makers will consider proposing coherent examples that are easy to follow, especially for developing countries. Future policies should also envisage the creation at European or international level of a network to promote the interdisciplinary approaches along with novel technologies, which could stimulate the development of new research directions or could provide suitable solutions to landscape issues, considering past landscape planning mistakes. At the same time, the novel technologies and perspectives must consider at the same time past values, current perceptions, and future threats. All this, must be supported by an assumed collaboration to promote landscape sustainability and better communication of researchers' know-how to policy makers, landscape experts, architects, scholars and other practitioners.