André Torre
email: andre.torre.2@inrae.fr

Frederic Wallet
email: frederic.wallet@inrae.fr

Jiao Huang
email: jiao.huang@inrae.fr

A collaborative and multidisciplinary approach to knowledge-based rural development

Keywords: rural development, rural resilience, knowledge economy, territorial vision, collaborative research, multidisciplinary approach

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The place of rural areas in national socio-economic development remained uncertain for a long time. Rural development policies differed widely over time and from one country to another, emphasizing agricultural activities, industrialization, or services to the local population [START_REF] Torre | Rural development policies at stake: Structural changes and target evolutions during the last 50 years[END_REF]. Rural territories have recently been increasingly recognized as crucial, particularly in industrialized countries, for not only agricultural production but also recreational spaces, biodiversity preservation, natural areas, and local culture [START_REF] Kim | Natural amenities and rural development: Understanding spatial and distributional attributes[END_REF][START_REF] Torre | Regional development in rural areas. Analytical tools and public policies[END_REF]. Based on this multifunctionality, rural livelihood diversification contributes to meeting the needs of city dwellers and in-migrant rural households with an urban lifestyle and provides transition pathways for rural sustainability [START_REF] Smith | Socio-cultural representations of greentrified Pennine rurality[END_REF][START_REF] Wilson | Multifunctional' quality' and rural community resilience[END_REF]. It has become necessary to implement diversified rural policies that consider the specific characteristics and resilience of local territories [START_REF] Westlund | Social capital and sustainable urban-rural relationships in the global knowledge society[END_REF][START_REF] Pelucha | Expanding the ontological horizons of rural resilience in the applied agricultural research policy: The case of the Czech Republic[END_REF]. In other words, policymakers should explore smart rural development based on knowledge and innovation [START_REF] Naldi | What is smart rural development[END_REF].

However, there are several limitations to rural innovation and knowledge development. The concept of a Knowledge Economy has been debated and studied for decades [START_REF] Westlund | Social capital in the knowledge economy: Theory and empirics[END_REF]. A large body of work highlights innovations in large urban areas [START_REF] Grandadam | Places, spaces and the dynamics of creativity: The video game industry in Montreal[END_REF][START_REF] Secundo | Sustainable development, intellectual capital and technology policies: A structured literature review and future research agenda[END_REF]. Rural areas are deemed much less well-off and suffer from an insufficient innovation capacity because of a lack of knowledge suppliers, educational institutions, and adequate education among local actors [START_REF] Bock | Rural marginalisation and the role of social innovation; a turn towards nexogenous development and rural reconnection[END_REF]. The small population size and its sparse distribution over the rural territories also lead to a certain level of disconnection and weak network connectivity [START_REF] Fountain | Agrifood tourism, rural resilience, and recovery in a post-disaster context: Insights and evidence from Kaikōura-Hurunui, New Zealand[END_REF].

Many researchers criticize the above remarks as a typical but incomplete conception of the knowledge society which focuses mainly on formal, academic knowledge and technological innovation [START_REF] Rooney | Handbook on the Knowledge Economy[END_REF][START_REF] Neumeier | Why do social innovations in rural development matter and should they be considered more seriously in rural development research? -Proposal for a stronger focus on social innovations in rural development research[END_REF]. An essential part of rural knowledge relies on grounded know-how and networks of local actors with different objectives and goals from those in metropolises. Knowledge is less formal and more experiential in rural areas, where innovations are more rooted in the social and institutional fabric; the knowledge imported from outside is reinterpreted and reformulated to adapt to local realities [START_REF] Li | Bottom-up initiatives and revival in the face of rural decline: Case studies from China and Sweden[END_REF][START_REF] Šūmane | Local and farmers' knowledge matters! How integrating informal and formal knowledge enhances sustainable and resilient agriculture[END_REF]. Therefore, on the one hand, it is always important to introduce to rural territories the most recent progress in science and technology, such as digital technologies or electrical mechanization [START_REF] Cowie | Smart rural futures: Will rural areas be left behind in the 4th industrial revolution[END_REF]. On the other hand, public policy and actions need to support the emergence and development of local knowledge embedded in rural products, e.g., labeled local products or the Protected Designation of Origin [START_REF] Cañada | Quality certification, institutions and innovation in local agro-food systems: protected designations of origin of olive oil in Spain[END_REF], and practices and skills of the rural population, e.g., the short supply chains [START_REF] De Roest | Specialisation and economies of scale or diversification and economies of scope? Assessing different agricultural development pathways[END_REF].

The work on the Knowledge Economy for regional and rural development has increased extensively in recent years, focusing on innovative milieus [START_REF] Crevoisier | The Innovative Milieus approach: Toward a territorialized understanding of the economy?[END_REF], learning regions [START_REF] Asheim | The changing role of learning regions in the globalizing knowledge economy: A theoretical reexamination[END_REF], and other approaches to contribute to rural sustainability and resilience [START_REF] Li | Why some rural areas decline while some others not: An overview of rural evolution in the world[END_REF]. These approaches emphasize social innovation, local knowledge, and networks between local and external actors [START_REF] Cooke | Regionally asymmetric knowledge capabilities and open innovation: Exploring 'Globalisation 2'-A new model of industry organisation[END_REF][START_REF] Neumeier | Social innovation in rural development: identifying the key factors of success[END_REF][START_REF] Jones | Reimagining craft for community development[END_REF]. There is a strong demand for cross-boundary research across sectors and scales [START_REF] Eversole | Crossing boundaries in rural research[END_REF] to encourage collective learning through formal and informal knowledge interactions [START_REF] Tödtling | Innovation in knowledge intensive industries: The nature and geography of knowledge links[END_REF] and to support the development of innovation clusters [START_REF] Varis | Arriving at the dawn of the new economy: Is knowledge-based industrial renewal possible in a peripheral region?[END_REF]. However, several major problems need further consideration. For example, most previous research was about innovation in firms and industries or knowledge-based entrepreneurship in rural areas [START_REF] Richter | Rural social enterprises as embedded intermediaries: The innovative power of connecting rural communities with supra-regional networks[END_REF][START_REF] Kristensen | Social constructing of a rural bioeconomy cluster: The case of the Processum biorefinery complex in northern Sweden[END_REF]. A systemic vision is needed considering agriculture [START_REF] Arzeni | Analysis of farms characteristics related to innovation needs: a proposal for supporting the public decision-making process[END_REF], food system [START_REF] Martindale | From land consolidation and food safety to Taobao villages and alternative food networks: Four components of China's dynamic agri-rural innovation system[END_REF], forestry [START_REF] Weiss | Innovation governance in the forest sector: Reviewing concepts, trends and gaps[END_REF], rural living standards [START_REF] Jacobs | Producing knowledge to raise rural living standards: how universities connect with resource-poor municipalities in South Africa[END_REF], and other broad themes. There are still not many empirical reports about how knowledge-based initiatives are developed in the territories, what initiatives can facilitate the involvement of regional authorities and other partners, how the policy adapts to new urban-rural relationships, etc.

The experiences developed in the PSDR program ("For and On Regional Development") in France can hopefully provide meaningful responses to these questions. The program financed multiple research projects from its first generation, launched in 1996, to PSDR4, which closed in 2020. All projects followed several principles, such as solid interaction between regional partners and research institutes, co-definition of research themes, multi-and inter-disciplinary approaches, collaborative and participatory research between researchers and non-academic actors, and linkage with multi-level rural networks (Box 1). These research projects covered broad themes linked to agriculture, forestry, food, agroecological transition, and other issues in rural and peri-urban areas. The idea of the program is to enhance local techniques, introduce and adapt external knowledge, and, above all, encourage the emergence and development of local expertise, knowledge, and tools that territorial actors and other rural areas can use.

Box 1. A short introduction to the PSDR Program in France.

The PSDR ("For and On Regional Development") program (www.psdr.fr) was first launched in 1996 and recently closed its 4 th phase in 2020 (Table 1). Its first generation -DADP (1996)(1997)(1998) -established the basic principles of the program, including 1) Strong interaction between regional partners (e.g., the Regional Councils of participating regions) and research institutes (especially INRAE, the French National Institute for Agriculture, Food and Environment) in co-funding the projects and defining research themes; 2) Special attention to territorial development processes in rural and peri-urban areas directly or indirectly linked to agriculture, forestry, food, and other agroecological issues; 3) Collaborative research in partnership with local actors throughout all stages of the projects; 4) Research projects rooted in territories and interdisciplinary approaches combining social and natural sciences.

Each generation improved the strategy and approach of project management. For example, all projects were coordinated by a researcher-actor pair after the first experimentation carried out in DADP2 (2001DADP2 ( -2005)). All projects participated in one or more of the three joint working groups formally created in PSDR4 (2014-2020), following tentative initiatives in PSDR3 (2007PSDR3 ( -2011) ) to strengthen collaboration between projects. PSDR3 reinforced the requirement for improving the quantity and quality of scientific publications from the projects, with an independent national jury in charge of evaluating the projects and their results. There was also a shift in focus from knowledge dissemination to facilitating reuse from DADP2. The projects had extra funding for one year dedicated to knowledge transfer supported by a communications team at the program level in PSDR4. A book chapter about PSDR3 explained how the projects were selected and managed [START_REF] Wallet | Innovative governance and participatory research for agriculture in territorial development processes: Lessons from a collaborative research program (PSDR)[END_REF].

An increasing number of regions participated in the program, starting with those of specialty crops and services and followed by those of industrial field crops. The focus of the projects also extended beyond agricultural production to a wide variety of topics contributing to sustainable regional development, for example, food systems, value chains, farmland management, urban-rural relationships, natural resources, environment, climate change, territorial impacts assessment, and public policy. The research outline evolved to address the rising societal demand for agroecological transformation, food quality, circular economy, and the coordination of different goals. Many projects worked, stimulated by the reform of the Common Agricultural Policy (CAP) and the successive versions of the Green Deal, on the search for alternative agricultural systems and social structures to ensure a balance between agricultural, environmental, climate, and smart rural development objectives. The program aimed to contribute effectively to regional and territorial development by providing information, methods, and tools for local actors' decision-making and action, particularly within the framework of regional policy priorities.

In PSDR4, the 33 projects mobilized 128 research teams (universities, institutes, …), combining various disciplines of social sciences and natural sciences with an average of 4 teams per project. About 151 non-academic partner organizations were involved (on average 5 per project), including actors from the agricultural world, local and territorial authorities, decentralized services of the State, environmental organizations, industrial and service companies, fishing and forestry stakeholders, and others. There were more than 1,100 participants, of which 73% were researchers.

The TETRAE program ("Transition in Territories of Agriculture, Food and Environment", 2022-2027) succeeds the PSDR and retains the same structure and principles. TETRAE aims to promote transitions toward more sustainable territorial development. It revolves around three essential points: reasserting the central place of local territories in sustainable development, opening up the research towards the socio-economic world and civil society, and focusing on transitions under the Agriculture -Food -Environment -Health nexus. The objective of the paper is to present an overview of the PSDR approach during the last 25 years and the main findings of the projects for knowledge-based rural development and resilience. The goal is twofold: first, to present the new knowledge they bring to French rural territories regarding agricultural land governance and other issues; and second, to explain how this knowledge is locally created or reinvented based on local skills, cooperation between stakeholders, and the exploration of existing innovations. The structure of the paper is as follows. Section 2 is a literature review on rural development in the knowledge economy and an introduction to the PSDR approach. Section 3 presents the main results of the PSDR program in its most recent generation around five critical issues of rural knowledge and innovation. Section 4 discusses the contributions of a participatory and comprehensive research program like PSDR to rural innovation compared with other relevant initiatives in order to provide some general and critical thinking for future research and policy-making. Section 5 concludes the paper and opens ways for the future.

Knowledge-based rural development: a theoretical review and the PSDR problemdriven approach

This section presents a literature review on rural development challenges and the research and policy for a knowledge-based rural economy, followed by a conceptual introduction of the problem-driven approach of the PSDR program. This summarization of the PSDR approach aims to provide a tool that bridges the gaps in rural development between top-down knowledge and local innovation and between researchers and actors.

Literature review

Challenges of rural development

In the background of globalization and the growing mobility of capital and people, it has been widely noticed that rural areas are often marginalized in socio-economic development [START_REF] Bock | Rural marginalisation and the role of social innovation; a turn towards nexogenous development and rural reconnection[END_REF][START_REF] De Toni | Location matters. Are science and policy arenas facing the Inner Peripheries challenges in EU? Land Use Policy[END_REF]. Many are experiencing population decline and a downfall in private business, employment, and public services. The reasons are associated with the geographical and relational remoteness of rural areas due to limited socio-economic connections. The lack of knowledge institutions and links to them results in weak innovation systems in peripheral regions, demonstrating a low level of collective learning and insufficient capacity to absorb interregional knowledge spillover [START_REF] Pelkonen | How beneficial is a knowledge-based development strategy for peripheral regions? A case study[END_REF]. It is worth noting that initiatives increasing the connectivity of these remote areas without improving local innovation capacity may lead to the risk of resource-grabbing and rural gentrification [START_REF] Zoomers | The need for a less territorial, more people-centred and relational approach[END_REF].

Several large-scale studies of the European Territorial Observatory Network (ESPON) show the need to consider territorial disparity, diversity, and balance in rural research and policymaking. The EDORA findings highlight the different capacities at the micro-scale to respond to the "ubiquitous drivers" of rural change [START_REF] Copus | EDORA: European Development Opportunities for Rural Areas[END_REF]. The PROFECY final report shows a spatial variation between two main drivers of inner peripherality: a lack of access to regional centers and services and poor economic potential [START_REF] Noguera | PROFECY-Processes, Features and Cycles of Inner Peripheries in Europe (Inner Peripheries: National territories facing challenges of access to services of general interest)[END_REF]. The ESCAPE results suggest a diverse shrinking pattern and substantial intra-regional variation [START_REF] Copus | ESCAPE. European Shrinking Rural Areas: Challenges, Actions and Perspectives for Territorial Governance: Applied Research[END_REF]. The authors remind us that many European regions are declining due to relative disadvantage rather than absolute weakness compared with nearby regions.

Rural areas need to meet the rising societal demands, especially from urban citizens, for high-quality food, a circular economy, labeled local products, natural environment, and other services. The regulation of the CAP and the EU Green Deal has reinforced the requirement for agroecological transition and more sustainable development pathways. Rural resilience is no longer essentially linked to the agriculture sector but a question combining the environmental, territorial, and socio-economic dimensions [START_REF] Pelucha | Expanding the ontological horizons of rural resilience in the applied agricultural research policy: The case of the Czech Republic[END_REF]. Rural research needs to adapt to societal and policy needs. It remains a big challenge to coordinate multiple development goals and explore alternative agri-food systems. Therefore, the transformation resilience of rural areas becomes the key to preventing system crises [START_REF] Dwyer | AES presidential address, 2021: Policy analysis for rural resilience-Expanding the toolkit[END_REF]. When "business as usual" becomes impossible, the capacity of a rural territory to change its internal structure and feedback mechanisms toward a new healthy, dynamic, and efficient system will be crucial.

France faces these general challenges and some specific characteristics. The share of the agriculture sector in employment and the economy has diminished considerably. However, the role of agricultural activities remains essential in spatial planning and landscape management. France has experienced a significant evolution towards regional specialization in agriculture and rural economy [START_REF] Chatellier | Les logiques économiques de la spécialisation productive du territoire agricole français[END_REF]. Agri-food industrialization and exportation characterize the North-West and, to a lesser extent, the South-West parts. The North-East part relies more on an industrial tradition. In the South-East, on the contrary, specialty agricultural products and services contribute most to the local economy, e.g., labeled products, short supply chains, rural tourism, and second homes (Le [START_REF] Bras | Métamorphose du monde rural[END_REF]. Remote rural areas generally see a shrinking and aging population, but rural attractiveness tends to increase in the metropolitan outskirts and coastal areas under intense land pressure. As in the case of PSDR (Box 1), the regions of specialty agriculture were the first motivated to search for alternative production models and value chains. Those dominated by large-scale industrial crops and livestock are increasingly urged to break the socio-technical lock-in favoring intensive farming [START_REF] Meynard | Socio-technical lockin hinders crop diversification in France[END_REF] by the rising demands for agroecological transition, sustainability, and resilience. These territorial specificities of France call for heterogeneous research focus in cohesion with the regional context and multi-level coordination to facilitate exchange and collaboration among projects. The research outline and strategy of the PSDR program (Section 2.2) considered these specificities and relevant needs.

Research and policy for a knowledge-based rural development

The creation and exploitation of knowledge have become the predominant engine in developing wealth and progress in the knowledge economy and society [START_REF] Peters | Three forms of the knowledge economy: Learning, creativity and openness[END_REF]. Previous research has revealed the following critical elements of knowledge-based rural development.

First, apart from technological innovation, social and cultural innovation is also essential in rural areas [START_REF] Dargan | LEADER and innovation[END_REF]. There can be divergent pathways for knowledge transfer and collective learning through formal and informal knowledge interactions [START_REF] Tödtling | Innovation in knowledge intensive industries: The nature and geography of knowledge links[END_REF][START_REF] Slee | An exploration of potential growth pathways of social innovations in rural Europe[END_REF]. [START_REF] Kristensen | Social constructing of a rural bioeconomy cluster: The case of the Processum biorefinery complex in northern Sweden[END_REF] propose a framework combining the function of social ties (e.g., bonding, bridging, and linking) to achieve organizational proximity in order to construct a rural cluster. Torre et al. ( 2020) suggest a regional strategy to focus on diversity and related variety in rural areas to facilitate inter-sector knowledge spillover and borrow size from more developed neighboring regions.

Second, rural innovation is steered from the bottom up and driven by local communities and initiatives [START_REF] De Toni | Location matters. Are science and policy arenas facing the Inner Peripheries challenges in EU? Land Use Policy[END_REF]Zoomer, 2022). It means identifying local needs and integrating local knowledge, strengths, and opportunities [START_REF] Bosworth | Identifying social innovations in European local rural development initiatives[END_REF][START_REF] Arzeni | Analysis of farms characteristics related to innovation needs: a proposal for supporting the public decision-making process[END_REF][START_REF] Kluvankova | Social innovation for sustainability transformation and its diverging development paths in marginalised rural areas[END_REF]. Thus, there should be a new perspective of governance connecting global and grassroots efforts [START_REF] Leach | Transforming innovation for sustainability[END_REF][START_REF] Eversole | Crossing boundaries in rural research[END_REF]. [START_REF] Pelkonen | How beneficial is a knowledge-based development strategy for peripheral regions? A case study[END_REF] suggest relying on existing networks and local resources to solve the problem of lacking dynamic clusters or knowledge suppliers in rural areas.

Third, the over-reliance on the local network may reduce creativity [START_REF] Varis | Arriving at the dawn of the new economy: Is knowledge-based industrial renewal possible in a peripheral region?[END_REF]. It is crucial to improve the "absorptive capacity" of the territory and individuals to exploit external knowledge [START_REF] Cohen | Absorptive Capacity: A new perspective on learning and innovation[END_REF]. Cooperation between local and external actors at regional or sub-regional levels is necessary [START_REF] Dahlström | Regional policies for knowledge anchoring in European regions[END_REF].

At the policy level, rural development has become the 2 nd Pillar of the EU's Common Agricultural Policy since Agenda 2000. A menu of measures is proposed to the Member States or regions to design Rural Development Programmes (RDP). Some have explicitly targeted to support knowledge transfer and innovation since 2007 [START_REF] Bonfiglio | Are rural regions prioritizing knowledge transfer and innovation? Evidence from Rural Development Policy expenditure across the EU space[END_REF]. The CAP is in continuous reform, and one central issue is reinforcing its contributions to regional growth and cohesion. The task remains challenging because the CAP is criticized as a cause of increasing territorial imbalance [START_REF] Esposti | Reforming the CAP: an agenda for regional growth[END_REF][START_REF] Bonfiglio | Are rural regions prioritizing knowledge transfer and innovation? Evidence from Rural Development Policy expenditure across the EU space[END_REF]. The RDP 2007-2013 integrated LEADER initiatives, a bottom-up method in the EU to reinforce the "links between actions for the development of the rural economy". Social innovation and networking are of central importance [START_REF] Dax | The Leader programme 2007-2013: Enabling or disabling social innovation and neo-endogenous development? Insights from Austria and Ireland[END_REF][START_REF] Georgios | Neo-endogenous rural development: A path toward reviving rural Europe[END_REF]. The integration into RDP has largely brought the small-scale and limited-budget LEADER program to the mainstream, though it is now showing a gradual decline [START_REF] Georgios | Neo-endogenous rural development: A path toward reviving rural Europe[END_REF]. At least 5% of RDP funding must go to actions based on Community-led Local Development (CLLD-LEADER). The EU regulations 2021/2115 for CAP Strategic Plans 2023-2027 reaffirm the importance of Agricultural Knowledge and Innovation Systems (AKIS) and locally led initiatives like LEADER.

The successive shifts of European regional development policies over the programming periods have underlined the difficulty in reconciling competitiveness and cohesion. Innovation, R&D, and other intangible factors have been emphasized as the engine of economic growth since the 1990s. The support for smart specialization and place-based initiatives for a decade tried to counter the harmful effects of the "wholesale" and one-size-fits-all approach centered on advanced technologies. However, existing strategies did not sufficiently consider territorial specificities, the role of infra-regional dynamics, and the quality of governance and intermediation systems at these scales. This defect calls for a reinforcement of knowledge production and dissemination mechanisms that stick more closely to the contemporary issues of rurality.

Policy evolution impacts the focus of the research (as mentioned in Box 1, Section 2.1.1) and, in turn, is influenced by the research, e.g., the assessment of territorial imbalance and the conception of social innovation mentioned above. Nowadays, huge amounts of data, reports, videos, etc., of the European Commission and the EU-funded research projects, e.g., Framework Programs, ESPON, and RURAGRI ERA-NET, are available on the websites. Thus, research can be closer to operational actors and provide them with case studies, development models, action points, databases, and networks. In France, research has successfully brought a territorial dimension to rural development policy by revealing the impacts of the territorial context on the performance of governance mechanisms. Researchers have also drawn the attention of policymakers to stakeholder diversity and the development of consultation tools promoting collaboration and learning dynamics. In addition, considering territorial configurations justifies place-based policies, which integrate the particularities of rural territories [START_REF] Torre | Rural development policies at stake: Structural changes and target evolutions during the last 50 years[END_REF].

Major problems and needs for knowledge-based rural development

The above review leads to the identification of several major problems for knowledge-based rural development nowadays, which needs to: i) be based on a systemic vision addressing a variety of subjects and their interdependence in rural areas, e.g., agriculture, food, ecological transition, rural well-being, adaptation, and resilience under the changing urban-rural relations.

ii) reconcile the targets of local territories and regional development in defining research themes and implementing projects. This reconciliation is essential for binding together different stakeholders and obtaining resources at regional and supra-regional scales.

iii) involve researchers and actors in different disciplines to address broad issues [START_REF] Lowe | Reflexive interdisciplinary research: the making of a research programme on the rural economy and land use[END_REF]. iv) develop collaborative research and bridge the gaps between research institutions (knowledge suppliers) and other actors in rural areas to promote territorial innovation [START_REF] Doloreux | Territorial innovation models: to be or not to be, that's the question[END_REF]. v) integrate informal and formal knowledge from local and external actors to avoid the risk of reduced creativity in an isolated system. Rural communities need to connect to global pipelines, which are trans-local knowledge linkages between regions and clusters [START_REF] Morrison | When do global pipelines enhance the diffusion of knowledge in clusters?[END_REF].

The PSDR approach

The work and results of the PSDR program can provide helpful solutions that respond to the needs presented in Section 2.1.3. The program was designed based on several principles, which became increasingly evident over subsequent generations (Box 1). These principles, aiming to produce scientifically rigorous knowledge directly usable by local partners or policymakers, can be grouped into five broad categories. Figure 1 presents how these principles potentially respond to the problems and needs in knowledge-based rural development: These research themes can be summarized into five categories: 1) governance of agricultural lands under increasing pressure in rural and peri-urban areas; 2) territorial attractiveness and well-being, including landscape preservation, cohesion, and competitiveness between regions and territories; 3) agroecological transition in the territories in light of local conditions and global changes, such as the evolution of agricultural practices and adaptation to climate change; 4) territorialized food systems in pursuit of food security, social benefits, and environmental sustainability; 5) bioeconomy and circular economy. Researchers and partners also participated in three joint working groups among projects to promote knowledge exchange between regions and produce general and transferable results and tools. These joint working groups focused respectively on: rural-urban relations around land use, attractiveness, and well-being, agroecological transition in different systems and territories, and innovation to boost circularity in the food and forestry systems and chains.

Strong interactions between research organizations and regional partners

Within the framework of the general topics selected at the national level, local research teams worked with policy and decision-makers to define the specific research subjects in each region. This smart development strategy is highly grounded in local problems and needs. Local teams first conducted some preliminary diagnostics about, for example, the depopulation processes in mountain areas, the agroecological transition through the development of pulse crops, and the short supply chains near the capital city of the region. The Regional Council provided at least 50% of the project funding. They followed their projects' progress with the coordinators of the PSDR program and participated in a regional monitoring and consultant committee. They expect to integrate the knowledge produced in the projects into regional policy-making.

Multi-and inter-disciplinary research projects

A partial or disciplinary approach can hardly meet the requirements of a global and systemic vision of the problems at the territorial level. PSDR research projects are interdisciplinary at two levels:

Recommended by the evaluation bodies of the program, the projects were proposed and carried out by multidisciplinary research teams. The general design and all work packages should include multidisciplinary research. For example, none of the projects had a purely economic or agronomic work package, and most projects engaged teams from social and natural sciences.

The projects in PSDR4 involved about 40 disciplines, including 10 in social sciences and 30 in natural sciences. The most frequent disciplines included economics, sociology, geography, agronomy, ecology, management, politics, and law.

Collaborative research and knowledge transfer to local actors

Each PSDR project was coordinated by a researcher and a non-academic partner and based on collaboration between research teams and local partners in defining research topics, theoretical framework, fieldwork, and the transfer of results. The 151 partners involved in the program included agricultural actors (e.g., cooperatives, groups of farmers, and the chambers of agriculture), local authorities (e.g., municipalities or groups of municipalities, department councils, and regional councils), decentralized bodies of the State for research, agriculture, and environment activities, territorial organizations (e.g., "Pays"), water agencies, Regional Natural Parks, and other actors in territorial development (e.g., environmental organizations, industrial and service companies, and fishing and forestry stakeholders).

The fifth year of PSDR4 was specifically dedicated to transforming scientific results into practical tools to promote knowledge transfer to local actors and other regions. The PSDR projects created about 1000 operational products, including thematic meetings and workshops, training courses for students, professionals, and the public, videos, e-books, manuals, software, databases, posters, etc. These products include good practice manuals for actors and territorial expertise guides to help local decision-makers select and elaborate public action. Most of them have been shared on social media and are freely available on the web.

Linkage with multi-level rural networks

The PSDR program is close to the European Innovation Partnership for Agriculture (EIP-AGRI) 1 in principles and structure, which has enabled their cooperation in the Rhône-Alpes region. The EIP-AGRI initiative comprises multi-stakeholder projects searching for practical and concrete solutions to a problem or an opportunity. It aims to facilitate the transfer of innovation and knowledge between countries in order to foster agroecological transition across Europe. The PSDR projects in the Rhône-Alpes region were also involved in the French Collective Mobilization for Rural Development (MCDR)2 program to support collaborative projects with a national or inter-regional dimension, promote network building, and contribute to rural development.

This joint coordination between the three initiatives in the projects has brought about fruitful results. Primarily, it indicates an approach for rural areas to create knowledge linkages with multiple rural networks across local, regional, national, and European levels. Teams with different targets worked jointly to organize workshops and produce practical documents sharing the results of innovative projects with various actors and policymakers. These partnerships echo the multi-level perspective on transitions [START_REF] Geels | Technological transitions as evolutionary reconfiguration processes: A multi-level perspective and a case-study[END_REF]. The production of practical knowledge favoring agroecology or short food supply chains has contributed to operational standards and strengthened their legitimacy in public policies and stakeholder strategies.

Results of the PSDR4 projects about rural knowledge and innovation linked to agriculture and food issues

The research of the PSDR projects in very different local territories leads to essential contributions to understanding the dynamic evolution and resilience of rural spaces and concrete proposals for public action. This section presents the key findings of the recently closed PSDR4 projects linked to five major issues in rural development among the broad research themes introduced in section 2.2.1. References to publications from the projects are provided in the text.

Governance of agricultural lands

Multiple PSDR4 projects studied the resilience of farming systems near the city, where agricultural lands face increasing urban pressures. They focused mainly on adaptation strategies and land management that help peri-urban farming to persist. The multidisciplinary PSDR approach facilitates a systemic vision combining research on land use management, social relations, and agroecological impacts, which contributes to identifying new opportunities and trade-offs in agricultural land governance under urban pressure.

First, land use studies reveal the difficulty of making land available for agricultural activities at the urban-rural interface. For example, downzoning from an urban development zone to an agricultural zone in land use planning means a loss of value for landowners and could lead to litigation in the administrative court (Le [START_REF] Bivic | Scheduling urbanization in rural municipalities: Local practices in land-use planning on the fringes of the Paris region[END_REF]. However, researchers have identified innovative practices of land ownership backing ("portage foncier") to help new farmers to get land for cultivation through the transfer of land use rights and diversified design of innovative agricultural projects [START_REF] Léger-Bosch | Changes in property-use relationships on French farmland: A social innovation perspective[END_REF]. One of the projects has created an interactive digital tool to manage local land resources for agricultural projects. It is an open web platform of collaborative mapping for local actors to report property initiatives.

Then, the research on social relations suggests recognizing the importance of local agriculture at the urban-rural interface following the change in eating habits and lifestyles in cities. For example, home gardens in metropolitan outskirts significantly contribute to the diet of working-class households, but their value has long been underestimated [START_REF] Darly | Home gardening and the social divide of suburban space: Methodological proposal for the spatial analysis of a social practice in the Greater Paris urban area[END_REF]. Farmland preservation in peri-urban areas can be integrated with local food strategies, which enables to rethink of the meaning and ways of sustainable urban planning [START_REF] Buyck | Bringing sustainable urban planning down to earth through food: the experience of the food transects of Grenoble and Caen[END_REF][START_REF] Kassis | Rethinking the place of agricultural land preservation for the development of food systems in planning of peri-urban areas: Insights from two French municipalities[END_REF]. In addition to farmers and other traditional actors, local municipalities, residents, and social services are increasingly engaged in agricultural and food issues. The relationship between society and agriculture is now growingly influenced by consumers and public authorities with rising interest in local food.

Other research on the ecological impacts of land use changes shows that the urban-rural interface, valley bottoms, and agricultural/industrial wastelands favor the production of ecosystem services and the preservation of biodiversity. These lands are conducive to agroecological transition. Researchers find that peri-urban areas with intermediate proportions of urban and agricultural lands [START_REF] Renaud | Non-linear effects of landscape on pollination service and plant species richness in a peri-urban territory with urban and agricultural land use[END_REF] and urban domestic gardens [START_REF] Levé | Domestic gardens as favorable pollinator habitats in impervious landscapes[END_REF] positively impact pollination and plant species richness. However, water contamination in peri-urban areas is more correlated with agricultural fertilizer and pesticides than urban land use. Thus, public policy should consider the environmental risk linked to agricultural activities [START_REF] Nélieu | Impact of peri-urban landscape on the organic and mineral contamination of pond waters and related risk assessment[END_REF]. These findings can provide pathways for change in public policies on biodiversity. Some foresight workshops between local institutional actors and other stakeholders have mobilized these results using a specific method AVEC® to draw "future landscapes" for interface areas like urban and peri-urban farmlands.

Attractiveness and well-being of the territories

The attractiveness of rural territories represents a significant issue in the public action of European countries in the last decades with increasing consideration of the well-being dimension. PSDR projects have developed a comprehensive approach to assessing territorial attractiveness. They investigate the basis for individual and collective well-being in a territory and how the two are articulated with each other and with territorial attractiveness. The wellbeing indicators and the surveys among local populations have made it possible to demonstrate the advantages of rural territories in terms of attractiveness.

For example, Bourdeau-Lepage and Fujiki (2021) surveyed local people's perceptions of their living environment. They identified the key territorial components of well-being in rural areas, e.g., natural amenities, access to health services, and safety. They highlight that the decision-makers must consider the objective and subjective dimensions and the individual and collective dimensions of public policies and strategies. [START_REF] Tardieu | From supply to demand factors: What are the determinants of attractiveness for outdoor recreation?[END_REF] show that, besides socio-demographic characteristics, the biophysical context plays a prominent role in the recreational attractiveness of the territory and should also be considered in the recreation policy and planning. They claim that GIS-based mapping can be a valuable tool for valuing landscape services in people's daily decision-making. These results and tools help to develop participatory strategies to optimize well-being, renew landscape design, and contribute to public policies for improving territorial attractiveness.

Agroecological transition in the territories

PSDR projects conceive agroecological transition as the change of agricultural models to promote sustainable food systems that respect people's benefits and their environment, both at the farm and territorial level [START_REF] Charpentier | Intake, milk yield and grazing behaviour of stripgrazing Alpine dairy goats in response to daily pasture allowance[END_REF][START_REF] Magrini | Agroecological transition from farms to territorialised agri-food systems: issues and drivers[END_REF]. This approach combines technical and agronomic research and the mobilization of supporting services, consumers, and various other actors in local territories to improve farmers' knowledge and involvement [START_REF] Bouttes | Vulnerability to climatic and economic variability is mainly driven by farmers' practices on French organic dairy farms[END_REF]. The results show that, besides addressing the question "what is good in a biophysical sense", considering local actors' perception and participation is highly meaningful to the target of agroecological transition.

The work on biophysical dimensions shows that considering potential ecosystem services is a major lever of agroecological transition at all scales: regional, territorial, or farming systems [START_REF] Lopes | Spectro-temporal heterogeneity measures from dense high spatial resolution satellite image time series: Application to grassland species diversity estimation[END_REF][START_REF] Fauvel | Prediction of plant diversity in grasslands using Sentinel-1 and-2 satellite image time series[END_REF]. Many technical manuals have been developed to help farmers and agricultural advisers to understand the benefits of biodiversity to agriculture. PSDR teams investigated the autonomy of the farming systems, including cultivation, breeding, and the re-composition of the two. They have developed alternative systems that reconcile animal welfare with the health of the system at the farm and territorial levels while reducing dependence on synthetic inputs [START_REF] Forteau | Horses grazing with cattle have reduced strongyle egg count due to the dilution effect and increased reliance on macrocyclic lactones in mixed farms[END_REF]Guinet et al., 2020aGuinet et al., , 2020b;;[START_REF] Maxin | Cover crops as alternative forages for ruminants: nutritive characteristics, in vitro digestibility, methane and ammonia production[END_REF][START_REF] Mugnier | Why and how farmers manage mixed cattle-sheep farming systems and cope with economic, climatic and workforce-related hazards[END_REF]. Practical guides have been created to facilitate the construction of nitrogen-autonomous systems with farmers through design and conception workshops and the diagnosis of nitrogen losses in the fields.

Another big part of the work was about the involvement and cooperation of local actors in the transition processes, especially in sharing knowledge, learning, and accompanying projects. The results call to rethink the role of agricultural advisors in providing technical support for a systemic change, which needs to adapt to the singularity of the projects and local situations and develop knowledge for and with local actors [START_REF] Catalogna | Diversity of experimentation by farmers engaged in agroecology[END_REF]. Several practical tools of PSDR projects help different actors to understand the transition practices. For example, the Agroecology Dictionary is an online and evolving multimedia tool providing definitions of the main terms and concepts in agroecology. The Capflor® software is a digital decision support tool for grassland design. Other tools include multiple synthesis booklets on the conversion to organic agriculture, a video game around the practice of mixed breeds, etc.

Territorialized food systems

The PSDR4 work suggests a three-level approach combining conception, governance, and collective intelligence to territorialized food systems.

For the conception, researchers have revealed different forms of innovation that redefine the links between food, agriculture, and territory [START_REF] Galliano | The peripheral systems of eco-innovation: Evidence from ecoinnovative agro-food projects in a French rural area[END_REF]. The work shows differentiated dynamics of reterritorialization in the production, transformation, and distribution of food value chains [START_REF] Desquilbet | Organic food retailing and the conventionalisation debate[END_REF][START_REF] Madelrieux | Forms of territorial embeddedness in dairy value chains Case of the Chartreuse massif (French Alps): geographical and historical perspectives[END_REF]. This reconnection of agriculture, food supply, and people in local territories brings long-term benefits. It helps to define the trajectories of the Territorial Food Projects3 by combining individual and collective contributions.

PSDR results also show the importance of governance associated with these systems. Local elected officials and public actors play an essential role in structuring sustainable food systems through multiple levers such as collective catering, land management, or support for local agriculture [START_REF] Magrini | Agroecological transition from farms to territorialised agri-food systems: issues and drivers[END_REF][START_REF] Kassis | Rethinking the place of agricultural land preservation for the development of food systems in planning of peri-urban areas: Insights from two French municipalities[END_REF]. However, launching local food strategies beyond the modest and scattered initiatives is challenging. Civil society can be a remarkable driving force through collective and individual practices, e.g., food self-production and diet change for the sake of human and animal health [START_REF] Monier-Dilhan | Food labels: consumer's information or consumer's confusion[END_REF][START_REF] Duru | Trends in agri-food choices for health since the 1960s: the case of fatty acids[END_REF][START_REF] Morel-Journel | Selecting sorting centres to avoid long distance transport of weaned beef calves[END_REF]. The economic operators in charge of processing, distribution, and others still have a marginal place in food governance, though they can strongly influence the creation of territorial food systems.

In the end, the research shows a strong need for accompanying instruments and collective intelligence, which allow actors to rethink and implement changes in their territory. In this respect, the PSDR collaborative research projects, emphasizing the joint work between stakeholders, consultants, and research teams, have developed multiple tools promoting skills and knowledge learning, such as algorithms, chronicles, games, and good practice guides.

Territorial bioeconomy and circular economy

Unlike the traditional linear production processes, the secondary products or wastes are partly reused or recycled in the form of material or energy flows in the circular economy and bioeconomy. PSDR results underline the territorial dimension of the bioeconomy [START_REF] Vivien | The hijacking of the bioeconomy[END_REF]. Several projects worked on the deployment of local loops related to food issues and other agricultural and forestry activities. The production reterritorialization and the activation of territorial resources help to create an innovation ecosystem conducive to territorial resilience and local network creation.

These PSDR projects observe an active development of a circular economy in agriculture in France, especially the anaerobic digestion projects (Bourdin et al., 2020) and territory-based initiatives for improving circularities in forestry [START_REF] Fortin | The effect of stumpage prices on large-area forest growth forecasts based on socio-ecological models[END_REF][START_REF] Bessaad | How much does leaf leaching matter during the pre-drying period in a whole-tree harvesting system[END_REF][START_REF] Lenglet | Circularities and proximities within resource valuation systems: insights from territory-based initiatives in the forestry sector[END_REF]. These studies reveal the adaptation strategies of enterprises and cooperatives. They also demonstrate the acceptability of residents and other actors and the creation process of innovative eco-projects in rural areas. The results show that localization is a recurrent argument of circular economy projects for two main reasons. First, it allows a more environmentally friendly and economically efficient local loop than the longdistance transport of products and energy flows. Second, it calls for collaboration with different stakeholders in the territories, which reinforces territorial governance. It is important to consult not only the actors engaged in the bioeconomy projects but also the local population, who are sometimes opposed to certain initiatives, to ensure their agreement [START_REF] Bourdin | The role of a local authority as a stakeholder encouraging the development of biogas: a study on territorial intermediation[END_REF][START_REF] Niang | Territorial governance and actors' coordination in a local project of anaerobic digestion. A social network analysis[END_REF].

Discussion: implications for knowledge-based rural development and limitations

In a rural context marked by fewer actors in the innovation ecosystem, collaborative research projects like those in the PSDR program can be intermediaries promoting knowledge coproduction and transfer. They also contribute to the structuring of research communities, involving permanent actors who go beyond the framework and periods of the program.

Toward a territorial vision of knowledge-based rural development

The PSDR approach underlines the importance of territorial innovation for knowledge-based rural development. It means to combine innovation processes connected with a given territory, in which actors organize themselves to develop new knowledge. As seen from the evolution of the CAP (Section 2.1.2), rural development is no longer considered merely an agricultural or a sectoral issue. The research and policy-making ask for strengthening a territorial vision. The PSDR program, just as its full name suggests (Box 1), emphasizes addressing territorial needs, focusing on territorial processes, and working with various related actors. The approach contributes to a comprehensive conception of a territorial vision for rural development, which should be multiscale, collaborative, and multidisciplinary. This multiscale vision allows it to combine top-down and bottom-up initiatives, integrate local and regional interests, actors, and resources, and connect internal and external networks. The collaborative approach facilitates research out of laboratories, focusing on problems and solutions close to the territory. Multiand interdisciplinary work is necessary to successfully address territorial problems, which are usually complex and multifaceted. Multidisciplinary projects may find new opportunities and trade-offs by making visible the relationship between agriculture, society, environmental issues, food security, and other subjects, as the examples in Section 3.1 show.

The PSDR results have confirmed previous observations that most innovation processes in rural areas are in social, cultural, and organizational dimensions [START_REF] Hargrave | A collective action model of institutional innovation[END_REF][START_REF] Chevalier | Innovation beyond technology: Science for society and interdisciplinary approaches[END_REF][START_REF] Moulaert | Advanced introduction to Social Innovation[END_REF]. Technological innovation, which always matters, is probably less central and often imported and adapted from outside of rural areas. Innovation is growing faster in rural territories because digital technologies are increasingly frequent at all stages of agricultural value chains [START_REF] Cowie | Smart rural futures: Will rural areas be left behind in the 4th industrial revolution[END_REF]. More importantly, local projects foster innovations in terms of short supply chains, land use management, and circular economy, which have improved the well-being of local communities. The PSDR results on agroecological transition demonstrate how the collective dynamics of actors (especially the groups of farmers), who are confronted with common problems associated with a specific territorial context, facilitate the generation of appropriate knowledge and more sustainable solutions. This idea about territorial innovation is consistent with social metabolism in addressing transition issues, which requires considering the entire flow of materials and energy needed to sustain all human activities [START_REF] Fischer-Kowalski | Social metabolism: a metric for biophysical growth and degrowth[END_REF].

Significance of a national research program like PSDR in the creation of a multidisciplinary and participatory community for rural knowledge and innovation

The PSDR experiences suggest the significance of a national program of its type in creating and maintaining a huge participatory community at the national level for rural knowledge and innovation. This community integrates a variety of research teams, practical actors, policymakers, and other partners and goes beyond the framework and periods of the program. The PSDR program was the first initiative in France of its type. The connection within the PSDR community has a multi-level structure. First, local research teams and actors cooperate closely within a project focusing on specific topics and problems of that territory. Second, the regional committee and project management team actively facilitate exchanges between projects in the same region. Third, the three joint working groups (Section 2.2.1) and the seminars, participatory workshops, and other scientific events organized at the program level promote knowledge exchange and cooperation at the national level.

The PSDR community kept growing over the past generations and became quite stably embedded and well-known in the territories. For example, some research projects carried out continuous social experimentation in PSDR3 and PSDR4. Local actors and research teams have become more familiar with the participatory research approach, methods, and joint territorial learning process. This working mode and associated cooperation network continue to exist in the next TETRAE, other research programs, and many policy initiatives. One example is the integration of the PSDR in the Rhône-Alpes region into the EIP-AGRI initiative (Section 2.2.5).

Thus, a national multidisciplinary and collaborative research program can make significant contributions to addressing rural challenges beyond the single project level. The active work of a multi-level coordination team has promoted effective knowledge exchange and cooperation between social and natural sciences and different territories. The intense national coordination can be a peculiarity of the PSDR program compared to other relevant European initiatives, e.g., the EU Framework Programs (European Commission, 2019), Horizon 2020, and ERA-Net RURAGRI. The national level is in proximity to the regions compared to the EU level, which makes the national level ideal for performing certain functions in territorial development and fostering knowledge and practice exchanges.

Limitations and future perspectives

The PSDR program shows the advantages of a multidisciplinary and collaborative approach, which mobilizes multiple research teams and local actors to produce new knowledge in favor of the evolution of perceptions and practices. But this type of project requires cognitive resources to translate local issues into research questions and transform scientific progress into practical tools. It also requires substantial human and financial resources because the project needs the regular presence of non-academic actors, which is sometimes difficult, especially for those strongly based on voluntary work. As the example of PSDR shows, the non-academic participants are usually the head of their organization, which call into question the potential for disseminating new knowledge to end-users. Another problem is the weak participation of civil society. Associations remain relatively few among PSDR partners. The participating associations are institutionalized representations of citizens and are sometimes far away from the local population. It is thus difficult for local people to have their opinions heard. The future design of collaborative research programs should consider these limitations.

Future programs must also pay attention to the complexity of regional development. The CAP measures [START_REF] Bonfiglio | Are rural regions prioritizing knowledge transfer and innovation? Evidence from Rural Development Policy expenditure across the EU space[END_REF] and the Cohesion Policy [START_REF] Berkowitz | The impact of the economic and financial crisis on the reform of Cohesion Policy 2008-2013[END_REF] have shown their limits in responding to the challenges of territorial imbalances. In this regard, future research and policy should recognize the spatial effects of knowledge-based territorial actions and networks. Can they bring solutions promoting cohesion between different regions, or do they aggravate inequalities? To what extent do they contribute to reconsidering rural-urban relations in the knowledge economy? The existing research often neglected the territorial dimension of transitions, and there is a call for a spatial perspective in transition studies [START_REF] Coenen | Toward a spatial perspective on sustainability transitions[END_REF].

A territorial vision of transitions is central to the objective of INRAE in transforming the PSDR into the TETRAE program. The future program deploys the systemic interdependencies between different fields (agriculture, food, environment, health, waste management, land use, etc.) and the tensions and potential collaborations between stakeholders. It will lead to the experimentation of solutions based on open innovation and the confrontation of expertise to identify new territorial configurations that foster mutually beneficial relationships between urban and rural areas. A further limitation that the future program will address is a reflection on social, cultural, and psychological barriers to agroecological transition and changes in production and consumption patterns of agri-food systems. It is important to analyze why the initiatives for change often need long-term involvement and can hardly be successful in the short term.

Conclusion

The paper presents the contribution of the PSDR program to collaborative knowledge creation and open innovation in rural territories of the vast majority of French regions for more than 25 years. The analysis of the program's basic principles and the main results obtained by the projects allows us to draw three main conclusions: i) the results are very rich and diverse, primarily related to the governance of agricultural lands, the territorial attractiveness and wellbeing, the agroecological transition in the territories, the territorialized food systems, as well as bioeconomy and circular economy; ii) the collaboration initiated from the outset of the projects between researchers and local partners is essential for a shared definition of research themes and collaboration between consortium members; iii) the funding specifically devoted to the transformation of results to scientific and practical products at the end of the projects is an essential condition for the success of the program.

The PSDR approach contributes to a comprehensive territorial vision for knowledge-based rural development. Yet there are several limitations. The PSDR program requires the substantial involvement of project coordinators at different levels, which is challenging to maintain over the long term without significant financial support. Moreover, the non-academic partners are mainly from the private, public, or associative sectors without the real involvement of civil society. These results question the relevance of the quintuple helix model [START_REF] Carayannis | Triple Helix, Quadruple Helix and Quintuple Helix and how do knowledge, innovation and the environment relate to each other?[END_REF] applied to contexts outside dense and high-tech urban spaces. Thus, the PSDR experiences underline that future participatory research needs to create conditions for the longterm involvement of field-based actors, including civil society, in innovative projects and promote knowledge dissemination beyond partners. Finally, future research should also pay attention to the complex spatial impacts of the territorialized rural initiatives and the transition of agriculture and rural areas at the request of the new CAP, the EU Green Deal, and the changing urban-rural relationships.

Fig. 1 .

 1 Fig. 1. The PSDR solutions to the problems in knowledge-based rural development (Source: Authors' original work).

Table 1

 1 A brief overview of the PSDR Program's past four generations.

	Program

generations Number of projects Number of participating regions* Budget Key progress in strategy and approach DADP (1996- 1998

					Establishment of basic principles (i.e.,
	)	21	3	No data	partnership with regional councils, collaborative research,
					interdisciplinarity)
					Experimentation of project
	DADP2 (2001-2005)	76	5	€ 6 M	coordination by a researcher-actor pair; a shift in focus from knowledge
					dissemination to facilitating reuse
					Increasing requirement for scientific
	PSDR3 (2007-2011)	36	10	€ 10 M	results of projects; experimentation of joint working groups; external
					evaluation by an international jury
	PSDR4 (2014-2020)	33	14	€ 11 M	One extra year for knowledge transfer; creation of a communications team at the program level
	*Regions before the French territorial reform effective on 1 st January 2016.

The EIP-AGRI is supported by the EU's Common Agricultural Policy (the European Agricultural Fund for Rural Development) and the European research and innovation program Horizon

The MCDR program is coordinated by the National Rural Network of France.

The Territorial Food Projects were introduced by the French Law for the Future of Agriculture, Food, and Forestry (LAAF) of 2014.

Acknowledgments

This work was supported by the PSDR4 Program (On and For Regional Development/Pour et Sur le Développement Régional), funded by the French National Institute for Agriculture, Food and Environment (INRAE) and ten French Regions, namely, Auvergne-Rhône-Alpes, Bourgogne-Franche-Comté, Bretagne, Centre-Val de Loire, Grand Est, Île-de-France, Normandie, Nouvelle-Aquitaine, Occitanie and Pays de la Loire. The authors thank all the participants of the projects, the coordinators at different levels, the members of the Scientific Committee, and other people who have contributed to the program and the activities of the projects. The authors are grateful for the valuable comments from the two anonymous reviewers.


Marie Orange

Pascal Tramoni

François-Xavier Le Bourdonnec

Sabine Negroni

Ana Ferraz

Maxime Remicourt

Anja Scheffers

Renaud Joannes-Boyau

Reconstructing obsidian consumption patterns in Neolithic Corsica: insights from the Listrella e Stabielle site

scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The sourcing analyses conducted by ED-XRF and LA-ICP-MS on the Listrella e Stabielle settlement have shown that the majority of the obsidian assemblage is originating from Sardinia, and more specifically from the SC source (72%, see Figure 4). The rest of the assemblage was attributed to the SA (21%) and SB2 (6%) sources, while two artefacts were matching the further source of Lipari (see location of the sources in Figure 1). The well-established occupation sequence of the Listrella e Stabielle settlement, attributed to the end of the middle Neolithic -beginning of the late Neolithic, is contemporary with a turning point in the history of the diffusion of the obsidian from Lipari and Sardinia. The first results obtained on the site might suggest that, during this period, north Corsican settlements could interact with the Tuscan region rather than the southern coast of France (Provence/Languedoc). Once combined with the typological and technological characteristics of the artefacts, the sourcing results obtained with ED-XRF and LA-ICP-MS on the Listrella e Stabielle settlement will help to bring further information on the obsidian economy of the region.

FOR

  ANY INQUIRIES PLEASE CONTACT M. ORANGE: m.orange.10@student.scu.edu.au In 2012 and 2015, preventive archaeological excavations have been conducted by the INRAP [Institut National de Recherches Archéologiques Preventives] on the Listrella e Stabielle settlement (Figure 1), located in the north-western part of the Corsican Island. The early occupation phase of this settlement is dated from the late 5 th millennium B.C., and is materialized by a small group of structures circumscribed by a sturdy wall. The obsidians excavated at the Listrella locus have been geochemically characterised by ED-XRF, while those from the Stabielle locus have been analysed by LA-ICP-MS. The ED-XRF analyses have been conducted at the IRAMAT-CRP2A, featuring a SEA6000VX High Sensitive X-Ray Analyzer from Seiko Instruments (cf. Lugliè et al., 2014). At SOLARIS (Southern Cross University), the LA-ICP-MS analyses have been conducted with an ESI NW213 Laser Ablation System coupled to an Agilent 7700x ICP-MS (Orange et al., submitted). The complementary use of both sourcing techniques, as well as the implementation of a newly conceived LA-ICP-MS protocol tailored to obsidian sourcing in the Mediterranean area, allowed the exhaustive geochemical sourcing of the assemblage in a limited amount of time.

Figure 2

 2 Figure 2 Comparison of the (Rb/Y) and (Sr/Y) log-ratios of 119 obsidian artefacts from the Listrella e Stabielle

Figure 3

 3 Figure 3 Comparison of the ( 85 Rb/ 89 Y) and ( 88 Sr/ 89 Y) log-ratios of 67 obsidian artefacts from the Listrella e Stabielle

Figure 3 ,

 3 Figure 3, by means of the comparison of the ( 85 Rb/ 133 Cs) and ( 137 Ba/ 133 Cs) log-ratios.

1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 Log(Rb/Y)

	SC (3)		6
			5
	SB1 (4)	SB2 (4)	4
			3
	SA (4)		2
			1
	Lipari (8)
			0
	Palmarola (7)	Listrella e Stabielle artefacts Obsidian sources	-1
		99% density ellipses
			-2

Log( 137 Ba/ 133 Cs) 2 2.5 3 3.5 4 4.5 5 Log( 85 Rb/ 133 Cs)

			SC (26)
		Yali (13)	(17) Melos	SB1 (15)
	Carpathians
	(16)
			SA (21)
		SB2 (18)	Lago
			Balata	di
			dei	Venere
	Antiparos		Turchi	(13)
	(11)	Lipari (7)	(25)
			e Stabielle artefacts
	Palmarola (7)	Obsidian sources 99% density ellipses


Thierry Aubert

Jochen Bardong

Omar Elmazria

Gudrun Bruckner

Badreddine Assouar

Iridium interdigital transducers for high-temperature surface acoustic wave applications

Keywords: high temperature, SAW, langasite, iridium I

Iridium is investigated as a potential metal for interdigital transducers (IDTs) in surface acoustic wave (SAW) devices operating at high temperatures. SAW delay lines based on such IDTs and langasite (LGS) substrate are fabricated and electrically characterized. The results show reliable frequency responses up to 1000°C. The strong increase of insertion losses beyond this temperature, leading to the vanishing of the signal between 1140 and 1200°C, is attributed to surface transformation of LGS crystal, consisting in relevant gallium and oxygen losses, as evidenced by scanning electron microscopy, energy-dispersive X-ray spectroscopy and secondary ion mass spectroscopy.

INTRODUCTION

In the last fifteen years, surface acoustic waves (SAW) devices have paid a lot of attention regarding the possibility to make wireless sensors working at high temperature (up to 1000°C) using this technology. Indeed, SAW devices are passive components requiring no embedded electronics neither power source to be wirelessly interrogated [START_REF] Reindl | Passive radio requestable SAW water content sensor[END_REF]. The choice of the constitutive materials is critical regarding the fabrication of such sensors. Concerning the piezoelectric substrate, langasite (La3Ga5SiO14 or LGS) is currently the most appropriate candidate. In fact, it has been intensively studied, demonstrating a good stability at high temperature, while being commercially available. In particular, Hornsteiner et al. recorded a SAW signal on LGS at temperatures as high as 1085°C for some minutes [START_REF] Hornsteiner | Surface acoustic wave sensors for hightemperature applications[END_REF]. Another remarkable result was obtained by Da Cunha et al. who successfully operated LGS-based SAW devices for more than 5½ months at 800°C [START_REF] Da Cunha | High temperature stability of langasite surface acoustic wave devices[END_REF]. Regarding the electrodes, numerous studies have shown the limitations of pure Pt thin films which experiment agglomeration phenomena from 700°C on, whatever be the nature of the adhesion layer [START_REF] Da Cunha | Enabling very high température acoustic wave devices for sensor and frequency control applications[END_REF][START_REF] Aubert | Behavior of platinum/tantalum as interdigital transducers for SAW devices in high-temperature environments[END_REF][START_REF] Bardong | Precise measurements of BAW and SAW properties of langasite in the temperature range from 25°C to 1000°C[END_REF].

Several successful strategies were proposed by Da Cunha et al., such as the use of a Pt/10%Rh alloy or codeposited Pt/10%Rh/ZrO2 composite, to avoid or at least slow down this process which turns the electrodes into a collection of separate beads [START_REF] Da Cunha | High temperature stability of langasite surface acoustic wave devices[END_REF]. They all help hinder self-diffusion of Pt which is the microscopic mechanism leading to agglomeration, by adding some well-chosen impurities into the Pt layer. Another way to obtain similar results might come from the use of more stable metals than Pt from a physical point of view, which means metals with a higher melting point and thus lower self-diffusion coefficients [START_REF] Kreider | High temperature materials for thin-film thermocouples on silicon wafers[END_REF].

Qualitatively, volume diffusion phenomena, which lead to complete agglomeration in a matter of hours or less, are known to start around the Tammann temperature, which is defined as half the melting temperature of the material (both expressed in Kelvin) [START_REF] Aubert | Behavior of platinum/tantalum as interdigital transducers for SAW devices in high-temperature environments[END_REF][START_REF] Tiggelaar | Stability of thin platinum films implemented in high-temperature microdevices[END_REF]. In this context, iridium could be a material of first choice as it is a noble metal as platinum, with a melting temperature almost 700°C higher (2440°C versus 1770°C), which means a Tammann temperature close to 1100°C against 750°C in the Pt case. The main drawback of Ir is its tendency towards oxidation above 700°C in oxidizing environments [START_REF] Lisker | Effect of annealing in oxygen atmosphere on morphological and electrical properties of iridium and ruthenium thin films prepared by liquid delivery MOCVD[END_REF]. Recently, we confirmed the superiority of Ir to Pt with respect to agglomeration phenomena, as Ir interdigital transducers (IDT) on LGS substrate showed great stability after an annealing of 20h at 900°C under vacuum (5.10 -5 mbar of pressure), contrary to Pt ones [START_REF] Aubert | Behavior of platinum/tantalum as interdigital transducers for SAW devices in high-temperature environments[END_REF].

In this letter, we study Ir/Ti/LGS SAW delay lines at temperatures going from the ambient to 1200°C, by in-situ radio-frequency electrical measurements, coupled to scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS) and secondary ion mass spectroscopy (SIMS).

II. EXPERIMENTAL

To perform IDTs, 10 nm thick titanium as adhesion layer and 100 nm thick iridium films as electrodes were deposited by e-beam evaporation onto Y-cut LGS substrates (Witcore Company, Jinan, China). SAW delay lines were then fabricated by photolithography and ion beam etching. The devices were constituted of two identical IDTs, with 50 pairs of fingers and a wavelength λ fixed to 14 μm. The IDT center spacing, acoustic aperture, and finger width to space ratio were 65λ, 70λ, and 1:2, respectively. The SAW propagation path was along the X direction. The S21 parameters of these devices were recorded between room temperature and 1200°C under vacuum conditions (pressure: 2.10 -4 mbar). To do so, a specific setup was used [START_REF] Bardong | Characterisation setup of SAW devices at high temperatures and ultra high frequencies[END_REF]. The morphology of the device surface after high-temperature exposure was observed by SEM (Jeol 6500F), while the corresponding chemical composition was obtained by EDXS and SIMS (Cameca IMS 7F).

III. RESULTS AND DISCUSSION

Taking into account the high Tammann temperature of Ir and the previous successful tests at 900°C [START_REF] Aubert | Behavior of platinum/tantalum as interdigital transducers for SAW devices in high-temperature environments[END_REF], the first runs were focused on the determination of the highest operating temperature of the Ir/Ti/LGS SAW devices. The temperature was then increased as fast as possible (temperature ramp: 100°C/h) to the maximum temperature reachable in the oven (1200°C). Figure 1 shows the measured S21 frequency response at different temperatures. One can observe that insertion losses are quite constant up to 1000°C, with variations below 3 dB. Beyond this temperature, they increase quickly, inducing the loss of SAW signal after 1140°C. Consequently, as shown in figure 2, some other samples were heated from room temperature to 1050°C, just below the Tammann temperature of Ir, and then withstood a plateau at this level for several hours Figure 3 shows the corresponding frequency-versus-temperature curve. The latter is close to perfect parabola with temperature coefficients equals to +27 ppm/°C and -48 ppb/°C 2 for the first and second order respectively (reference temperature: 52°C). Quick aging of devices during this plateau can be deduced from the strong frequency drift visible on Fig. 3, coupled with an increase of the insertion losses at a rate of 6 dB/h, leading to the vanishing of the signal after 8h at 1050°C (Fig. 2). SEM images performed on heated samples after both electrical characterizations revealed comparable damages. In addition to showing a significant increase in roughness (Fig. 4a), langasite crystal surface also has numerous cracks (Fig. 4b). The chemical contrast between the substrate and the IDTs is very low, indicating likely the vanishing of the iridium thin film (Fig. 4b). EDXS confirmed this hypothesis, as only traces of Ir can be found on finger electrodes initial position (Tab. I). The presence of manganese and iron can also be noted. These elements are probably coming from the steel mantle of the RF cables used to interrogate devices. Last but not least, EDXS indicates that langasite crystals underwent huge losses in gallium. Such crystal degradation in vacuum was recently reported by Bardong et al. [START_REF] Bardong | Influence of packaging atmospheres on the durability of high-temperature SAW sensors[END_REF].

Schulz et al. observed as well this effect in air atmosphere, by surface exchange measurements, and attributed its origin to high Ga vapor pressure of gallium-containing compounds at high temperatures [START_REF] Schulz | Diffusion-related implications for langasite resonator operation[END_REF]. After 60h at 1050°C 14.8 0.9 10.3 0.9 0 3.9 0.7 SIMS measurements clarified this result, showing that there exists a Ga-depleted layer at the surface of the crystal, which is around 400 nm thick (Fig. 5). Moreover, SIMS also highlights significant losses of oxygen. Contrariwise to the Ga case, this lack seems not only to be located at the surface vicinity, but is quite homogeneous all along the 2 μm thick analyzed layer. This difference could be related to the fact that the diffusion coefficient of O in langasite is four orders of magnitude higher than the one of Ga [START_REF] Schulz | Diffusion-related implications for langasite resonator operation[END_REF], which involves a much smaller time for O to reach equilibrium than for Ga. Such oxygen losses in langasite and more generally in oxyde crystals have been intensively studied as they have important consequences on the conductive properties of such crystals [START_REF] Seh | Defects and transport in langasite I: acceptor-doped (La3Ga5SiO14)[END_REF]. Thus, in poor-oxygen environment, the following reduction reaction takes place, under which double charged oxygen vacancies and compensating electrons are formed in the crystal [START_REF] Rotman | Defect property correlations in garnet crystals[END_REF].

This model allows explaining easily the vanishing of the IDTs. Indeed, it appears that because of that crystal decomposition, the iridium thin film is permanently in close contact with oxygen-rich environment, which leads, at such temperatures, to its oxidation in the highly volatile IrO3 [START_REF] Chaston | Reactions of oxygen with the platinum metals[END_REF]. In summary, Ir/Ti/LGS SAW devices have been successfully operated at high temperatures up to 1140°C. They also showed a lifetime of more than 7h at 1050°C. Combination of SEM, EDXS and SIMS methods allowed attributing the devices failure to surface chemical transformation of langasite crystals, consisting in oxygen and gallium losses. In addition to altering the substrate properties, it also induces the oxidation of Ir electrodes, leading to their evaporation. Such troubles could be avoided by the use of nonoxide substrate, such as aluminium nitride, which has been shown to be a good candidate for such applications [START_REF] Aubert | Surface acoustic wave devices based on AlN/Sapphire structure for high temperature applications[END_REF]. In that case, Ir could be a first-choice material to make IDTs for SAW applications at high temperatures up to 1000°C. Another possibility to overcome those limitations could come from the use of an Ir/Rh alloy which is potentially usable in air atmosphere, where langasite is expected to be more stable [START_REF] Osamura | Development of new iridium alloy for spark plug electrodes[END_REF].

Fig. 1 .Fig. 3 .

 13 Fig. 1. Ir/Ti/LGS SAW delay line frequency response (S21 magnitude) at different temperatures

Fig. 4 .

 4 Fig. 4. SEM images of an Ir/Ti/LGS SAW device after 60h at 1050°C under vacuum conditions ((a) topography/(b) chemical contrast). IDT finger width is 2.3 μm. On the right half of the image is the bus bar on which the tip of a bonded Pt microwire is clearly visible (bottom-right corner).

Fig. 5 .

 5 Fig. 5. SIMS depth profile of LGS substrate. Solid and dotted lines refer to the same sample respectively before annealing and after 60h at 1050°C under vacuum conditions