J Wohlfahrt
email: julie.wohlfahrt@inra.fr

F Frechaud

B Gabrielle
email: benoit.gabrielle@agroparistech.fr

C Godard
email: c-godard@orange.fr

B Kurek

C Loyce

Characteristics of bioeconomy systems and sustainability issues at the territorial scale. A review

Keywords: social-ecological system, integrated assessment, territorial scale, landscape scale, conceptual framework Highlights: -Territorial bioeconomy systems are complex social-ecological systems

The bioeconomy is expected to be a key solution to supply societies with food and non-food products while replacing non-renewable resources and preserving natural ones. Sustainability of bioeconomy systems is currently an issue that has to be addressed. Current research dealing with the bioeconomy focuses primarily on technologies to improve biomass transformation and, with regard to sustainability, on simple and unitary bio-based value chains such as biofuel production from a single crop. In this paper, based on a literature review, we highlight the complexity of bioeconomy systems and propose a framework to support their sustainable development. We first review the key characteristics of bioeconomy systems: a wide variety of stakeholders with a limited vision of bioeconomy systems, flexibility but also rigidity of biomass feedstocks or transformation processes and a complex spatio-temporal layout.

Drawing on sustainability science, we show the relevance of the social-ecological concept to approach territorial bioeconomy systems' sustainably and develop an analytical framework to address sustainable development of territorial (local/regional) bioeconomy systems. This framework is based on two complementary representations of territorial bioeconomy systems, used to decipher their complexity. Finally, we outline an integrated assessment and modelling approach designed to tackle specific bioeconomy sustainability issues. This participatory approach has to take into account: i) the different sub-systems of territorial bioeconomy systems, their high level of interactions, their heterogeneity in terms of entities and processes involved and the circularity of matter and energy (production, transformation, use and recycling) with particular emphasis on the transformation sub-system and the logistics ii) the multiplicity and flexibility of stakeholders' nature, strategies and concerns, iii) the variety of spatial and temporal scales at play; iv) the effects of exogenous drivers like supra-regional policies and regulations, markets (e.g. prices of energies and biomass-based products) and climate.

Introduction

Strategies to develop an economy based on renewable biological resources, the bioeconomy, are currently implemented in many countries around the world. In 2012, the European Union defined five objectives for the bioeconomy that remained valid for the reviewed bioeconomy strategy in 2018: ensuring food security; managing natural resources sustainably; reducing dependence on non-renewable resources; mitigating and adapting to climate change; creating jobs; and maintaining European competitiveness (European Commission, 2012 and2018).

Developing the bioeconomy appears as a key policy to simultaneously embrace major societal issues of climate change, food security, fossil fuel dependence, scarcity of natural resources, and territorial and economic development on all scales, from the small territory to the national-continental scale [START_REF] Dubois | How sustainability is addressed in official bioeconomy strategies at international, national and regional levels: An overview[END_REF]. Sustainable production and use of biomass are indeed inherent to the bioeconomy proposition.

A major challenge for any bioeconomy therefore lies in our ability to assess how its development will successfully achieve these different objectives in real world situations, from biomass feedstock production to the recycling of biomass-based products.

Research in the field of bioeconomy is currently carried out primarily in the natural sciences and engineering, with the objective of developing industrial processes that optimize the uses of biomass [START_REF] Bugge | What Is the Bioeconomy? A Review of the Literature[END_REF][START_REF] D'amato | Green, circular, bio economy: A comparative analysis of sustainability avenues[END_REF]. As described by [START_REF] Bugge | What Is the Bioeconomy? A Review of the Literature[END_REF], research focuses on bio-technological or bio-resource views of the bioeconomy, meaning that investigations are mostly driven by the quest for technical solutions related to the production and transformation of biomass feedstocks. Relatively little research has been done toward an integrated assessment of bioeconomy impacts [START_REF] Golembiewski | The emerging research landscape on bioeconomy: What has been done so far and what is essential from a technology and innovation management perspective? Innovative Food Sci[END_REF]. The few studies that attempt to assess bioeconomy sustainability, taking into account biomass feedstock production's impacts on natural resources, mostly focus on dedicated agricultural biomass plantations, or on one biomass-based product [START_REF] Gabrielle | The environmental impacts of non-food biomass production through land-use changes: scope, foci and methodology of current research[END_REF], or on a single project such as the Global Bioenergy Partnership (GBEP) sustainability indicators [START_REF] Hayashi | A holistic sustainability assessment tool for bioenergy using the Global Bioenergy Partnership (GBEP) sustainability indicators[END_REF]. In so doing, they disregard the complexity of the whole bioeconomy system (Robeldo-Abad et al., 2016). The lack of monitoring, standards and tools for a holistic sustainable assessment of bioeconomy projects is also highlighted by the FAO [START_REF] Dubois | How sustainability is addressed in official bioeconomy strategies at international, national and regional levels: An overview[END_REF].

Our goal here is to provide a novel conceptual framework to address all bioeconomy systems' sustainability, considering their specific characteristics (e.g. the flexibility of biomass feedstocks and processes).

In this paper we consider bioeconomy systems as specific social-ecological systems which aim at producing, using and recycling biomass to satisfy the food, energy, material and chemical needs of a given population in a given geographical territory, while replacing partially or entirely non-renewable resources with biomass and ensuring sustainable management of natural resources. By analogy with a food system [START_REF] Capone | Food System Sustainability and Food Security: Connecting the Dots[END_REF]), a bioeconomy system operates in and is influenced by a given social, political, economic and environmental context. As proposed by the sustainability science community, using a socialecological framework allows for relationships between human and natural systems to be deciphered, in order to understand the system's behavior, assess its sustainability, and improve society's well-being [START_REF] Haberl | A socio-metabolic transition towards sustainability? Challenges for another Great Transformation[END_REF]. Considering that a social-ecological system at local/regional level is recognized as an appropriate level to deal with the particularities of the social and ecological contexts of action [START_REF] Wu | Landscape sustainability science: ecosystem services and human well-being in changing landscapes[END_REF][START_REF] Therond | A new analytical framework of farming system and agriculture model diversities. A review[END_REF][START_REF] Daher | Developing Socio-Techno-Economic-Political (STEP) Solutions for Addressing Resource Nexus Hotspots[END_REF], we focus on bioeconomy systems in a given biophysical, social, technical and economic context: the territorial context.

Our formal definition of a territorial bioeconomy system is a territory characterized by the presence of one or several bio-based value chains (e.g. bioenergy plants, bio-refineries) aimed at replacing non-renewable resources and partially dependent on local biomass feedstocks. This territorial bioeconomy system is embedded in: i) a non-specific food and non-food biomass production, use and recycling nexus, dependent on local and global networks; and ii) a local system of activities related to natural resources management and socio-economic development (see Figure 1). This operative concept is in line with the work of Moraine et al. (2017a) on territorial crop-livestock systems. It allows us to operationalize the sustainability assessment framework by focusing on bioeconomy systems' characteristics, while considering their embeddedness into a wider landscape system [START_REF] Pahl-Wostl | Governance of the water-energy-food security nexus: A multi-level coordination challenge[END_REF]. In the following sections, we first highlight the specific characteristics of bioeconomy systems that need to be addressed in order to improve their sustainability, based on a literature review.

We then develop our novel conceptual framework to assess the sustainability of territorial bioeconomy systems, identifying key scientific challenges in improving it.

Particularities of bioeconomy systems

Review methodology

In our research, the particularities of bioeconomy systems were identified based on an expert literature review conducted by the different authors, each of whom is specialized in a specific domain related to the bioeconomy. This method allowed us to cover a broad range of issues currently spread across disciplinary or thematic publications. The main domains encompassed by this review are green chemistry, bioenergy, cropping, farming and forestry systems, nonfood biomass chains and recycling, sustainability assessment, integrated assessment, and modelling of social-ecological systems.

2.2.The complexity of bioeconomy systems that scientists and decision makers struggle to grasp

Bioeconomy systems: a new concept, studied by a scattered community

Studies of bioeconomy systems mostly consider them through only one sectorial lens (e.g. increasing biofuel production based on corn, or recycling agro-industrial wastes, or diversifying crop uses), and focus in each case on a different sustainability issue, for instance GHG emissions, carbon storage, land use impacts, energy provision and/or healthy food production [START_REF] Gabrielle | The environmental impacts of non-food biomass production through land-use changes: scope, foci and methodology of current research[END_REF]. These studies are consequently scattered across the literature. Scientific journals tend to specialize in one specific issue, such as energy, biomass feedstock production or biodegradable polymers, and there are no leading journals dealing explicitly with the bioeconomy concept as a fully integrated complex and multiscale system. This increases the difficulty of identifying generic bioeconomy system studies and building a scientific community around this subject.

Systems that can be considered as bioeconomy systems currently stand at the crossroads between traditional sectors, mainly organized according to a single bio-based value chains, for example agriculture, forestry, energy or process engineering for chemistry and materials [START_REF] Székács | Environmental and Ecological Aspects in the Overall Assessment of Bioeconomy[END_REF]. The bioeconomy concept has moreover evolved over the years to comply with sustainability requirements, thus progressively integrating circular economy paradigms.

While bioenergy and biomaterial production plants have been a growing feature of many regions for a long time, only more recently have there been concerns about the complementarity of biomass feedstock production systems (e.g. regarding ecosystems services, see [START_REF] Therond | A new analytical framework of farming system and agriculture model diversities. A review[END_REF]Moraine et al. 2017a) or the optimization of resource use in the transformation processes (e.g. through cascading uses, see [START_REF] Bezama | Let us discuss how cascading can help implement the circular economy and the bioeconomy strategies[END_REF][START_REF] Olsson | Time to tear down the pyramids? A critique of cascading hierarchies as a policy tool[END_REF]. The territorial or landscape dimension of the bioeconomy, meaning the importance of developing bioeconomy systems at the local level, is also emerging along with the identification of this scale as the most relevant to grasp sustainability issues [START_REF] Wu | Landscape sustainability science: ecosystem services and human well-being in changing landscapes[END_REF].

Hence, there is currently very little knowledge regarding the realistic and integrated conditions of territorial bioeconomy systems development.

Multiple stakeholders and partial visions

Bioenergy projects' high rates of failure have been documented in the scientific literature (Buchholtz et al., 2009;[START_REF] Han | Small-scale bioenergy projects in rural China: Lessons to be learnt[END_REF], and examples of such projects that were discontinued or went bankrupt abound [START_REF] Belfiore | Benchmark of bioenergy permitting procedures in the European Union[END_REF]. The reasons for these failures are not always well understood. In this respect, the complexity of a territorial bioeconomy project that brings together diverse stakeholders, coupled with and the lack of involvement of local players, seem more decisive than technical issues (Buchholtz et al., 2009). [START_REF] Lewandowski | Securing a sustainable biomass supply in a growing bioeconomy[END_REF] highlights the fact that the bioeconomy requires a different, unfamiliar, business model compared to the fossil fuel economy, as it is based on different geographical conditions and many disconnected stakeholders. Indeed, the "in between" position of bioeconomy systems induces the development of disconnected projects, in which different stakeholders are in charge of parallel initiatives (e.g. municipal biogas projects supplied by local farmers; biorefineries operated by oil companies) on a wide range of scales from the field/farm to the international level [START_REF] Mccormick | Key barriers for bioenergy in Europe: Economic conditions, know-how and institutional capacity, and supply chain co-ordination[END_REF][START_REF] Cooper | Overview of the Chariton Valley switchgrass project: a part of the biomass power for rural development initiative[END_REF][START_REF] Madlener | Innovation diffusion, public policy, and local initiative: The case of wood-fuelled district heating systems in Austria[END_REF].

Geels' proposition of a multi-level perspective is relevant here to describe the multistakeholder layers of bioeconomy systems [START_REF] Geels | Technological transitions as evolutionary reconfiguration processes: a multi-level perspective and a case-study[END_REF][START_REF] Geels | Typology of sociotechnical transition pathways[END_REF]. Therefore, besides the primary actors of the bioeconomy value-chains (regime -e.g.: producer, transformers, users), the bioeconomy system depends on niche-innovation actors (e.g.: scientists, research institutions) proposing new solutions to replace non-renewable resources by biomass (e.g.: bioplastics, pyrogas from biomass) and improve biomass recycling (e.g.: developing nitrifying-enriched activated sludge to improve wastewater recycling systems, [START_REF] Sepehri | Effect of nitrifiers community on fouling mitigation and nitrification efficiency in a membrane bioreactor[END_REF]. The bioeconomy system is also under the influence of a sociotechnical landscape, composed of NGOs, political bodies, lobbyists, and influencing the orientation of bioeconomy development. Each bioeconomy stakeholder might have a partial vision of the bioeconomy system, as well as different goals and values [START_REF] Daher | Developing Socio-Techno-Economic-Political (STEP) Solutions for Addressing Resource Nexus Hotspots[END_REF].

The roles of bioeconomy stakeholders and organizations seem less specialized than in traditional globalized food or timber systems [START_REF] Borras | The rise of flex crops and commodities: implications for research[END_REF][START_REF] Therond | A new analytical framework of farming system and agriculture model diversities. A review[END_REF]. For example, farmers are biomass feedstock producers but can also be biomass buyers, transporters and energy producers (e.g.: on-farm biogas plant supplied by on-and off-farm biomass), biomass-based product consumers (e.g biofuels used for agricultural machinery) and recycling actors (e.g. farmers using biomass transformation waste to fertilize their crops).

On the other hand, there is a wide diversity of stakeholders for each role within the bioeconomy system. For example, biomass-based energy production can be produced on farm (e.g. biogas plants), on large scales by companies (e.g. biofuel plants), but also on medium scales by public stakeholders (e.g. municipality heating systems). This complex stakeholder system represents a multi-level governance challenge [START_REF] Juerges | Soil governance in the transition towards a sustainable bioeconomy -A review[END_REF][START_REF] Pahl-Wostl | Governance of the water-energy-food security nexus: A multi-level coordination challenge[END_REF]. The required multi-level governance structures and attempts to build a common vision and sustainable management strategy between these stakeholders are still lacking (Pahl-Wostl, 2017).

2.3.Importance of policies in the development of bioeconomy systems

Under current market conditions and the absence of a clear "peak oil", most bioeconomy systems, especially the production of energy from biomass, do not appear to be pricecompetitive. Non-food biomass is a low-density and currently low-value product. The development of bioeconomy systems requires the articulation of biomass feedstock production, transport, processing, and use, and is therefore not competitive compared to energetically dense fossil fuels whose transformation processes have been developed over decades and are perfectly controlled. Fossil fuels benefit from a historically built economy of scale, due to mature processes initially developed without environmental constraints and because of the law of diminishing returns [START_REF] Priefer | Pathways to Shape the Bioeconomy[END_REF]. The reason for this relative non-profitability of bioeconomy systems on the current markets, especially compared to fossil fuel systems, might lie in the fact that negative externalities, which are considerable for fossil fuel systems, are not taken into account in such analyses [START_REF] Székács | Environmental and Ecological Aspects in the Overall Assessment of Bioeconomy[END_REF][START_REF] Olsson | Time to tear down the pyramids? A critique of cascading hierarchies as a policy tool[END_REF]. Furthermore, as bioeconomy systems must moreover meet sustainability expectations, it is very difficult to assess their profitability only with orthodox market-related profitability tools (net margins based on direct costs and prices).

Bioeconomy systems development furthermore relies on policies and public subsidies rather than on completely private initiatives [START_REF] Lewandowski | Securing a sustainable biomass supply in a growing bioeconomy[END_REF]. We can consider that one of the most spectacular bioeconomy systems is the use of sugar cane ethanol as biofuel in Brazil, initiated by the PROALCOOL programme in 1975. This initiative was first a political strategy to improve Brazil's energy self-sufficiency. In the last decade, renewable energy policies such as the European Renewable Energy Directive (2009/28/EC -European Parliament and Council, 2009) have also been implemented elsewhere to improve the sustainability of the energy supply [START_REF] Priefer | Pathways to Shape the Bioeconomy[END_REF]. The increase of biofuels incorporated into conventional fuel or bio-based electricity is supported in such cases by preferential price regimes and mandatory incorporation rates. [START_REF] Olsson | Time to tear down the pyramids? A critique of cascading hierarchies as a policy tool[END_REF] highlight the fact that, regarding bioeconomy systems, a difference should be made between market value and inherent value in order to properly inform decision makers and potential investors. The criterion of market profitability with respect to fossil systems, excluding negative externalities, seems to be irrelevant to bioeconomy systems, since these systems are developed under political impetus for environmental sustainability or energy sovereignty. There is therefore a need for indicators that reflect more fundamental properties than supply and demand.

2.4.Variability, flexibility and rigidity inherent to bioeconomy systems

Most of the scientific literature on bioeconomy systems or biomass feedstock production focuses on a "one product" and/or "one resource" view of the bioeconomy [START_REF] Gabrielle | The environmental impacts of non-food biomass production through land-use changes: scope, foci and methodology of current research[END_REF], and research and development in industry is mostly value-chain driven; Yet alternative resources and process flexibility are major characteristics of bioeconomy systems.

Biomass feedstock diversity and variability

Territorial bioeconomy systems can be based on a portfolio of alternative biomass feedstocks.

In the EU, biomass feedstock production is around 1.5 million tons per year, distributed between agricultural biomass (economic and residue production; respectively 471,928 and 436,856 thousand tones DM in 2013), fisheries biomass (1,459 thousand tones FM in 2013), algae biomass (143 thousand tones FM in 2013), forest biomass (511,544 thousand tones DM in 2013) and waste biomass (91,435 thousand tones DM in 2012;European Commission, 2019). Non-food biomass feedstocks, representing around two thirds of the total biomass produced in the EU, can be discriminated according to their origins and/or uses, for example first-generation or recycled biomass feedstocks, dedicated or flexible biomass feedstocks, main product or co-products, or agricultural, forest-based, or organic waste products. Some biomass feedstocks can be dedicated to non-food purposes (e.g.: sludges, forest biomass, dedicated energy crops) and others not (e.g.: cereals, oil bearing crops). Flex-crops are plants cultivated for several purposes: not only food or non-food markets [START_REF] Kline | Reconciling food security and bioenergy: priorities for action[END_REF][START_REF] Borras | The rise of flex crops and commodities: implications for research[END_REF]) but also different non-food markets. For example, triticale (Triticosecale Wittm., Poaceae) or oil palm (Elaesis guineensis Jacq., Arecaceae) can have several uses, depending on market opportunities. Triticale grains are mostly used for animal feed, whereas triticale straw can be used for bedding, heat and/or power, biogas, or as construction material, or can even be returned to the soil for carbon storage. Palm oil can be used for food purposes and also as a first-generation biofuel, whereas fruit stalks can be used for second generation bioethanol, heat and electricity production, or be returned to agricultural lands as organic inputs [START_REF] Bessou | Biofuels, greenhouse gases and climate change. A review[END_REF]. On the other hand, dedicated crops have a limited range of uses.

For example, Miscanthus x giganteus, a perennial crop, remarkable for its productivity under low-input (N fertilizer, pesticides) management [START_REF] Lewandowski | Miscanthus: European experience with a novel energy crop[END_REF][START_REF] Lewandowski | The development and current status of perennial rhizomatous grasses as energy crops in the US and in Europe[END_REF], is mostly used for energy production and has no food use.

From a farmer's perspective, establishing a crop dedicated to either food or non-food production commits land to one type of market (food or non-food), while flex-crops create the opportunity of choosing the end-use of one crop, depending on market conditions in the short term. The development of territorial bioeconomy systems should also increase the range of potentially marketable crops with new bioeconomy-oriented crops (energy crops, fiber crops) and will enable farmers to diversify their cropping systems. Increasing the diversity of plant covers and the length of rotations enables them to provide ecosystem services such as regulatory services associated with pest control [START_REF] Krupinski | Managing plant disease risks in diversified cropping systems[END_REF] or crop production [START_REF] Bending | Meeting the demand for crop production: the challenge of yield decline in crops grown in short rotations[END_REF]. Crop diversification can also help to improve the resilience of agroecosystems to the vagaries of climate and prices [START_REF] Lin | Resilience in agriculture through crop diversification: adaptive management for crop environmental change[END_REF].

From the transformation point of view, crops and all non-food biomass materials are composed of the same building blocks (lignin, cellulose and hemicelluloses) constituting the plant cell walls. This material is known by the generic term "lignocelluloses". Lignocellulosic biomass feedstocks can therefore be classified according to their composition [START_REF] Krasznai | Compositional analysis of lignocellulosic biomass: conventional methodologies and future outlook[END_REF][START_REF] Van Der Weijde | Evaluation of Miscanthus sinensis biomass quality as feedstock for conversion into different bioenergy products[END_REF]. For instance, woody biomass feedstocks issued from forestry systems are composed of large amounts of lignin (20-28%), whereas biomass from agricultural systems can have lower or more variable amounts of lignin, depending on the crops and/or the crop part used: i.e. short rotation coppices (SRCs), stem or leaves from perennial plants like Miscanthus x giganteus, or triticale show an amount of lignin ranging from 20% to 5%. In addition to the gross chemical composition of the lignocellulosic biomass (lignin, celluloses hemicelluloses, mineral content, etc.), the quality of the biomass feedstock depends also on morphological and structural parameters, such as the integrity of the plant stem/organs or the state of degradation after harvesting or storage stages. These quality criteria can change the physical and chemical access to the polymers and molecules of interest for applications, and will impact further transformation pathways into fiber, polymers or molecules in biorefineries and for energy production routes (van der Weijde et al.

, 2017).

There is a trade-off between biomass quality and specific valuation processes that influence the number of technical steps (extraction, purification, effluent treatments or valorization, etc) hence the efficiency and the price of the transformation process [START_REF] Lynd | Cellulosic ethanol: status and innovation[END_REF]. For example, heat and power production processes based on combustion can be engineered to use different biomass products such as straw, whole plants (e.g. triticale or Miscanthus x giganteus) or wood [START_REF] Pang | Influence of lignocellulose and plant cell walls on biomass char morphology and combustion reactivity[END_REF]. Regarding biomass combustion, quality is generally based on biomass chemical composition, particularly lignin content, moisture content and physical characteristics like particle size.

For more integrated biorefinery systems, biomass quality management is more complex and variable. Such biorefineries extract several separated compounds from the biomass in cascades. Each compound requires specific characteristics for further use (molecules' purity; specific molecular mass for polymers; presence of inhibitors for fermentescible sugars).

Transformation units then have to manage biomass feedstock quality trade-offs regarding these different requirements.

Finally, using biomass feedstock of different nature and/or origin in the production process can be an option to improve supply flexibility according to markets and availability, if the industrial process is tailored to a wide range of feedstocks [START_REF] Borras | The rise of flex crops and commodities: implications for research[END_REF].

Transformation units have then to manage additional biomass quality variations linked to production and transport conditions of each biomass feedstock type and origin (i.e. climate or management variabilities) (see 2.5.1.).

In conclusion, biomass feedstock producers and transformers can then choose to produce and use either only one specific type or several types of biomass feedstocks, depending on their process constraints and objectives and for stability or flexibility purposes. The diversity and variability of biomass value-chains and biomass feedstock flows are thus key characteristics of a territorial bioeconomy system. The management of this diversity and variability in order to achieve sustainability objectives and ensure economic viability is one of the great challenges for territorial bioeconomy systems. However, it also provides managers with flexibility opportunities to deal with the variability of endogenous and exogenous contexts, and thus to increase the resilience of bioeconomy systems.

Rigidity and co-dependencies

Aside from diversity and variability, there are also dependencies that are entailed by specific biomass value-chains and that generate rigidity. For example, cascading uses of forest biomass theoretically places the priority on timber production (Vis et al., 2016). Once timber is extracted, the rest of the forest biomass is considered as residue (e.g. products of early thinning, small branches and leaves) that can be used for energy or chemistry purposes. The type of wood available for uses other than building material is then limited and can constrain the applicable transformation processes and therefore possible uses. Moreover, the quantity of timber exploited will determine the quantity of residues available for other uses. As decisionmaking on forest biomass harvesting is quite flexible compared to agricultural crops, which have to be harvested every year [START_REF] Sourdril | How to maintain domesticity of usages in small rural forests? Lessons from Forest Management Continuity through a french case study[END_REF], co-dependency of forest residues and timber production can increase uncertainty on biomass feedstock availability.

More generally, there is a co-dependency between territorial bioeconomy systems, food systems and traditional biomass-based systems that might be managed according to their own objectives and constraints. These systems can share biomass feedstocks, biomass harvest and transport logistics, and transformation plants (e.g. sugar cane transformation plants' energy can be supplied by sugar cane residues; storage facilities can be shared between various biomass feedstocks), as well as recycling logistics, processes and end-uses (e.g. digesting food processing waste in a biogas unit).

Spatio-temporal organization of bioeconomy systems

The multiplicity characterizing bioeconomy systems implies a consideration of the dependence between biomass feedstocks, processes and uses, given the temporal dynamics and spatial patterns of each of its components.

Bioeconomy spatial patterns

Many studies dealing with the spatial distribution of land-based biomass feedstock production assume that it follows biophysical land production potentials [START_REF] Rizzo | Miscanthus spatial location as seen by farmers: A machine learning approach to model real criteria[END_REF]. Forest or perennial non-food biomass crops are often supposed to be grown in low production potential soils (i.e. marginal soils) while fertile soils are preferentially dedicated to food crops, either according to the "food first" principle or based on economic assumptions that non-food feedstocks are less profitable than food crops [START_REF] Dauber | To integrate or to segregate food crops and energy crop cultivation at the landscape scale? Perspectives on biodiversity conservation in agriculture in Europe[END_REF][START_REF] Bogdanski | Making integrated food-energy systems work for people and climate. An overview[END_REF]. Although this kind of assumption is useful for understanding global tendencies [START_REF] Heck | Land use options for staying within the Planetary Boundaries -Synergies and trade-offs between global and local sustainability goals[END_REF], at the territorial scale biomass feedstocks' spatial distribution actually stems from the interaction of biophysical factors influencing productivity with producers' characteristics (e.g.: size of the estate), strategies regarding crops or biomass feedstocks spatial allocation, territorial scale logistical issues such as the location of water supplies or roads [START_REF] Poggi | Issues and challenges in landscape models for agriculture: from the representation of agroecosystems to the design of management strategies[END_REF][START_REF] Martin | Modeling farmers' choice of miscanthus allocation in farmland : a case-based reasoning model[END_REF] and historical legacy [START_REF] Genin | The Multiple Dimensions of Rural Forests: Lessons from a Comparative Analysis[END_REF]. This complexity leads to a large variety of biomass feedstock spatial patterns in specific territories.

Even when limited to one type of biomass feedstock, for example forest biomass, the diversity of landscape patterns is wide, as forests range from small-scale parcels to much larger expanses. According to a survey in nine European countries, forest parcels less than 1ha in size accounted for 61% of private forest parcels in 2006-2007, and forest parcels more than 100ha in size for 30% (UNECE, 2010). These parcels can also be spatially aggregated or scattered across the landscape following a more or less regular pattern.

Regarding biomass uses and transformation, non-food biomass can be used at different spatial scales, from the farm (e.g. biogas unit) to an international scale (e.g. large-scale biofuel production units based on imported resources). In between, several individual, collective or industrial initiatives for non-food biomass uses exist, such as collective heating systems based on local forest production [START_REF] Mccormick | Exploring a pioneering bioenergy system: The case of Enköping in Sweden[END_REF]), or regional co-generation plants based on local and imported biomass feedstocks [START_REF] Thrän | Global wood pellet industry and trade study 2017[END_REF]. Every biomass transformation plant defines its own strategy according to its goals (collective heating, oil market, etc.). In a given territory, these different transformation units may share parts of the biomass feedstock resources, markets and biomass residue recycling opportunities.

At global scale, biomass flows between world regions are significant. For example, wood pellets imported for EU consumption, mostly from North America, accounted for almost 30% of the total pellets consumed in the EU in 2014 (World Energy Council, 2016;[START_REF] Thrän | Global wood pellet industry and trade study 2017[END_REF]. Biomass feedstocks' growth conditions vary around the world, and especially between temperate and tropical regions. Biomass transformers are tempted to import biomass feedstocks to limit the costs and to ensure a steady supply of a certain type and quality of biomass feedstocks. On the other hand, high rates of biomass feedstocks exports could locally limit the development of territorial bioeconomy systems. It is important to examine the global bioeconomy spatial patterns, that is, the spatial distribution of biomass feedstock production, transformation and uses around the world, if we are to understand territorial bioeconomy systems' functioning. In other words, it is important to take on board indirect land-use changes (Searchinger et al.,08) and, more generally, telecoupling effects [START_REF] Liu | Systems integration for global sustainability[END_REF] between world regions via physical or economic processes.

Time-scale discrepancies

Biomass feedstock production is dependent on climate and ecosystem services such as nutrients, water and biological regulation. The time scales of biomass feedstock production and natural cycles can be very different. As several authors have pointed out, trade-offs have to be acknowledged between provisioning (i.e. increasing biomass production) and supporting (i.e. nutrient cycles, water cycle) ecosystem services [START_REF] Juerges | Soil governance in the transition towards a sustainable bioeconomy -A review[END_REF]. Addressing this time-scale discrepancy between production and natural cycles is particularly important with regard to bioeconomy systems because the increase of biomass production needed to meet bioeconomy goals increases the tensions between these short-and long-term processes.

Regarding primary land-based biomass feedstock production, agricultural biomass production cycles range between less than a year (e.g. intercrop cycles, such as sorghum sown in summer, are around three to four months in France) and a decade (e.g.: Miscanthus x giganteus can be grown for fifteen to twenty years). By contrast, forest biomass production is managed in a time frame of between ten and a hundred years, due to the slow growth rate of trees. Considering a diversified territorial bioeconomy system, biomass feedstock harvest and production can vary from intra-annual to pluri-annual cycles. Biomass feedstock producers' strategies regarding the choice of the feedstock produced and the scheduling of technical operations (e.g. forest thinning, type of harvest) can then be short-term for annual crop production or very long-term in the case of forests.

These time-scale discrepancies regarding biomass feedstock availability also depend on producers' behaviors when it comes to planting and harvesting biomass feedstocks. Biomass producers show a range of behaviors, ranging from risky to conservative, depending on the type of biomass feedstock produced, their own strategic profile, and the type of growers [START_REF] Bocqueho | Expected utility or prospect theory maximisers? Assessing farmers' risk behaviour from field-experiment data[END_REF]. For example, as the window for harvesting forest biomass is wide (several years), forest managers' willingness to harvest forest biomass is a key factor to understanding biomass feedstock availability dynamics [START_REF] Erickson | Woodlots in the rural landscape: landowner motivations and management attitudes in a Michigan (USA) case study[END_REF][START_REF] Nordström | Integrating multiple criteria decision analysis in participatory forest planning: Experience from a case study in northern Sweden[END_REF].

From a biomass transformer's point of view, ensuring the stability and regularity of the biomass feedstock supply for a biomass transformation plant requires one to take this diversity of production cycles into account. The duration for which harvested biomass feedstock can be stored, depending on the storage system and biomass feedstock quality -for example between fresh or dry feedstock -, should be factored into supply strategies. In addition to inherent characteristics of biomass feedstocks (see 2.4.1.), external hazards can also impact their availability dynamics, as can climatic events or market opportunities.

Concomitantly, the transformation activities in a bioeconomy have to comply with various time frames: short-term, for the competitiveness of the industries involved in the implementation of the bioeconomy; mid-term, for their capacity to adapt to new political, technological and societal constraints (i.e. food safety, zero petroleum-based plastics); and long-term, for the application of innovation processes in industrial integrated systems (e.g. reusable and recyclable biomass-based products). Biomass-based products have to be considered as the result of dynamic innovation processes where technical progress will open up new opportunities to better exploit the biomass potential for food and non-food goods, as well as new services. The dominant solutions proposed today in all subsystems may be discontinued or adjusted, according to innovations, and at different time scales.

Importance of logistics in bioeconomy systems

Managing biomass flows in a bioeconomy system implies the development and adaptation of logistical infrastructures able to regulate different production and consumption times and spatial frames. Logistics is considered to be a bottleneck when dealing with multiple, spatially scattered biomass feedstock resources [START_REF] Perrin | Integrated design and sustainable assessment of innovative biomass supply chains: A case-study on miscanthus in France[END_REF][START_REF] Lewandowski | Securing a sustainable biomass supply in a growing bioeconomy[END_REF]2015). The low density of biomass feedstocks compared to fossil fuels, for example, implies the improvement of logistical solutions in order to manage associated costs (e.g. spatial configuration of biomass feedstock processing / densification units). Biomass feedstock storage is usually a critical issue in the economics of bio-based value chains, in that it is supposed to buffer differences between seasonality of harvesting periods and of the demand for biomass-based products [START_REF] Kaut | BLOMST-An Optimization Model for the Bioenergy Supply Chain[END_REF].

By adapting biomass transformation processes so that they can accommodate a flexible mix of biomass feedstocks with different cycle lengths, harvesting time windows, market opportunities or conservation dynamics, could allow biomass transformers to adjust their operation to fluctuating conditions, rather than relying on a single biomass feedstock or importing biomass from overseas. Morevoer, organizing territorial bioeconomy systems based on the industry 4.0 principles, especially interconnection and decentralized decisions and partial reliance on artificial intelligence to solve these complex logistical problems could improve the overall optimization of biomass uses (Salminen et al.,17).

Conceptual framework to assess bioeconomy systems' sustainability

Sustainability issues inherent to bioeconomy systems

Since the 2008 food crisis, environmental impacts and displacement effects from food to nonfood biomass production, inducing direct and indirect land use changes, have been under scrutiny [START_REF] Cherubini | Energyand greenhouse gas-based LCA of biofuel and bioenergy systems: Key issues, ranges and recommendations[END_REF][START_REF] Searchinger | Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change[END_REF]. The magnitude of these effects has been widely debated in the scientific community and policy arenas over the last decade, and led the EU, for example, to cap its production of first-generation biofuels in 2015 after having promoted it with the 2009/28/EC directive (European Parliament and Council, 2009). This decision, which was based on the precautionary principle in the absence of an objective framework capable of assessing this kind of impact, sent conflicting messages to bioeconomy developers and society.

A holistic sustainability assessment framework for the bioeconomy therefore seems to be critical to stabilize policies regarding it, and to ensure its sustainable development. As highlighted in the introduction, aside from replacing non-renewable by bio-based products, sustainable bioeconomy systems seek to reach objectives regarding food security (quantity, quality and availability), restoration or conservation of natural resources (including ecosystem services and biological diversity), economic competitiveness and, more generally, well-being.

The notion of bioeconomy encourages reflection on trade-offs between objectives at a much higher level of complexity than in a single bio-based value chain view (energy production, food production) or even in the Water-Energy-Food nexus [START_REF] Daher | Developing Socio-Techno-Economic-Political (STEP) Solutions for Addressing Resource Nexus Hotspots[END_REF][START_REF] Pahl-Wostl | Governance of the water-energy-food security nexus: A multi-level coordination challenge[END_REF].

3.2.Analytical framework of bioeconomy systems' sustainability issues

As seen above, the entanglement of resource uses, and of the production, uses and recycling of biomass-based products, along with stakeholders' roles and scales of action in a bioeconomy system creates a high level of complexity. To assess and ensure bioeconomy systems' sustainability, it is necessary first to develop an analytical framework to foster a sharable understanding of the way territorial bioeconomy systems function [START_REF] Berndes | Multifunctional biomass production systems -an overview with presentation of specific applications in India and Sweden[END_REF][START_REF] Mcginnis | Social-ecological system framework: initial changes and continuing challenges[END_REF]. Like [START_REF] Jones | Stocks and flows of natural and human-derived capital in ecosystem services[END_REF], we think that such a representation may help clarify where efforts are needed to improve system sustainability. In the following section, we present two complementary representations (non-equivalent models) of territorial bioeconomy systems, each providing key insights to decipher their key characteristics regarding sustainability. This figure is adapted from [START_REF] Marshall | A social-ecological framework for food systems research: accomodating transformation systems and their products[END_REF] and [START_REF] Mcginnis | Social-ecological system framework: initial changes and continuing challenges[END_REF]. Each specific bioeconomy system (i.e. focal action situation) is determined by natural, transformation and governance systems and entities (natural units, biomass-based products, bioeconomy stakeholders). Feedbacks (dotted arrows) account for transformation/influences from the focal action situation to first-tier components of the social-ecological system.

Figure 2 is an attempt to represent a bioeconomy system structure composed of several interacting bio-based value chains. Here we consider that a bioeconomy system is composed of several bio-based value chains, each composed of several subsystems inter-related through biomass flows: production system, storage and transport system, transformation system, distribution system, consumption. As highlighted above, these subsystems are articulated in a complex way (i.e.: a wide range of subsystem interactions are possible, yielding unexpected emerging properties), and their sustainable interactions with natural resources are at stake. Bioeconomy systems encompass different type of entities and processes: natural or seminatural entities such as soil-plant systems allowing biomass feedstock production; industrial entities such as biomass transformation plants and logistical systems; or social entities such as energy consumption networks.

The circularity of biomass flows is central, due to the need to preserve or restore natural resources (including ecosystem services). Recycling processes as well as energy own consumption along and across bio-based value chains are key elements to ensure sustainable bioeconomy systems. Accordingly, the development of territorial bioeconomy systems is convergent with the objectives of the circular economy. Industrial ecology is therefore a key to downscale bioeconomy general principles to the biomass transformation system, as the optimal transformation processes' organization to limit waste. [START_REF] Belletante | Optimal design of an efficient, profitable and sustainable biorefinery producing acetone, butanol and ethanol: Influence of the in-situ separation on the purification structure[END_REF][START_REF] Borras | The rise of flex crops and commodities: implications for research[END_REF][START_REF] D'amato | Green, circular, bio economy: A comparative analysis of sustainability avenues[END_REF].

The multiplicity of stakeholders involved in bioeconomy systems is partially shown in figure 2 but the representation of the diversity and overlapping roles of these stakeholders remains challenging. Moreover, this figure represents only the primary actors of bioeconomy systems.

Niche-innovation or sociotechnical landscape-related actors (e.g.: NGOs, research institutions) are not represented, for the sake of clarity, even though their impact on bioeconomy systems is crucial.

Figure 3 shows the structure of a bioeconomy system according to a now classical representation of first-tier components (or attributes) and focal situation actions of socialecological systems [START_REF] Mcginnis | Social-ecological system framework: initial changes and continuing challenges[END_REF][START_REF] Marshall | A social-ecological framework for food systems research: accomodating transformation systems and their products[END_REF]. Complementary to Figure 2, Figure 3 highlights the key components that determine bio-based value-chain configurations and interactions, including the different governance systems. Embracing the extended vision of social-ecological systems proposed by [START_REF] Marshall | A social-ecological framework for food systems research: accomodating transformation systems and their products[END_REF], we explicitly consider biomass transformation systems and biomass-based products as first-tier attributes of the bioeconomy system. Considering all territorial bioeconomy systems' first-tier attributes as either semi-natural or governance-related does not seem precise enough, as industrial processes or biomass feedstocks and biomass-based products distribution logistics are important for addressing sustainability and bioeconomy development issues. Therefore, considering transformation systems as part of the social-ecological system allows us to propose a more accurate solution for market-integrated systems such as bioeconomy systems, by eliciting the transformation-dependent situations in relation to natural and governance systems.

In conclusion, these two representations point out that, the interconnections between biomass value-chains, the circularity of biomass and energy flows, the heterogeneity of processes and entities of the system, the diversity of stakeholders, and the importance of the biomass transformation sub-system and the logistics are key issues to approach bioeconomy systems' sustainability.

Scientific and methodological proposal for investigating the sustainability of bioeconomy systems

As very significant growth of the bioeconomy is expected in the future, we have to be able to anticipate territorial bioeconomy systems' behavior, impacts and developments. Therefore, in addition to the analytical framework of bioeconomy systems' structure and functioning proposed above, managing and designing sustainable bioeconomy systems calls for adapted methodologies to understand and capture the dynamics involved.

4.1.Necessity of an integrated assessment and modeling approach

Embracing the complexity of the Food-Non-Food-Natural Resources nexus in territorial bioeconomy systems requires the development of multi-criteria, multi-level, ex-ante assessment approaches that identify tradeoffs and synergies intra-or inter-nexus as well as between sustainability domains [START_REF] Therond | A new analytical framework of farming system and agriculture model diversities. A review[END_REF]). An integrated assessment and modelling (IAM) approach seems to be the appropriate methodology to address bioeconomy systems' sustainability [START_REF] Hamilton | Integrated assessment and modelling: Overview and synthesis of salient dimensions[END_REF][START_REF] Ewert | Scale changes and model linking methods for integrated assessment of agri-environmental systems[END_REF]. It corresponds to a structured modelling-based way to integrate knowledge and to investigate ex-ante environmental, social and economic impacts of scenarios of the possible futures of social-ecological systems.

Regarding the characteristics of territorial bioeconomy systems highlighted in Parts 2 and 3, the integrated modelling approach should explicitly take into account: i) the different subsystems of territorial bioeconomy systems, their high level of interactions, their heterogeneity in terms of entities and processes involved, and the circularity of matter and energy (production, transformation, use and recycling), with particular emphasis on the transformation sub-system and the logistics; ii) the multiplicity and flexibility of stakeholders' nature, strategies and concerns; iii) the variety of spatial organization and temporal scales involved; and iv) the effects of exogenous drivers like supra-regional policies and regulations, markets (e.g. prices of energies and biomass-based products) and climate.

Modelling frameworks to assess bioeconomy systems' sustainability

Being able to model a territorial bioeconomy system to assess and anticipate its sustainability requires the combination of several modelling frameworks in the IAM approach.

First, spatially explicit modelling seems especially well-suited as bioeconomy systems are strongly linked to and dependent on the landscape composition and configuration (e.g. soilvegetal cover-climate interactions; impacts on natural resources; ecosystem services; logistic aspects see 2.5) [START_REF] Parrott | Agents, Individuals, and Networks: Modeling Methods to Inform Natural Resource Management in Regional Landscapes[END_REF][START_REF] Wu | Landscape sustainability science: ecosystem services and human well-being in changing landscapes[END_REF]. Spatially explicit modelling will be a central tool to manage the spatial organization of productions, bio-based value chains and, more generally, territories, and will help manage the optimization of uses and the alignment of the objectives of food and non-food production and natural resource conservation.

Second, different dynamic models have to be used to model the variety of dynamics and the associated temporal scales involved in bioeconomy systems, such as the seasonality of biomass feedstock productions, harvesting, markets for biomass-based products, or the logistics of biomass supply (see 2.5.2). Third, agent-based models are used to simulate the dynamics of social-ecological systems [START_REF] Rounsevell | Representing human behaviour and decisional processes in land system models as an integral component of the earth system[END_REF] as they can simulate the strategies of various types of stakeholders in relation to their own action situation (Parott et al., 2012), the evolutionary learning and out-of equilibrium dynamics [START_REF] Filatova | Spatial agent-based models for socioecological systems: Challenges and prospects[END_REF], and reveal emergent properties and processes at different levels [START_REF] Grimm | A standard protocol for describing individual-based and agent-based models[END_REF]Agent-based models are then central tools to consider modelling territorial bioeconomy dynamics.

Forth, considering the importance of logistics in bioeconomy systems sustainability (see 2.5.3), the modelling of the logistics -usually based on the minimization of operating costs [START_REF] Gold | Supply chain and logistics issues of bio-energy production[END_REF]-, should feature in other criteria that are relevant to assess bioeconomy systems' sustainability, such as environmental impacts (e.g. fossil energy consumption, greenhouse gases emissions), or social criteria (e.g. employment, operators' welfare) [START_REF] Perrin | Integrated design and sustainable assessment of innovative biomass supply chains: A case-study on miscanthus in France[END_REF][START_REF] Poggi | Issues and challenges in landscape models for agriculture: from the representation of agroecosystems to the design of management strategies[END_REF].

Fifth, indirect effects of bioenergy systems occurring beyond the region where they operate, through telecoupling, should also be taken on board (see 2.5.1., [START_REF] Liu | Systems integration for global sustainability[END_REF][START_REF] Verburg | Methods and approaches to modelling the Anthropocene[END_REF].

Sixth, the IAM approach will require the development of specific multi-criteria assessment (MCA) methods that allow for systematic comparison and ranking of alternative scenarios according to environmental, social and/or economic indicators for improving stakeholders' decision making processes (see 2.2.2.). The wide range of spatial and temporal scales and dimensions encompassed by territorial bioeconomy systems challenges MCA methods, as it requires them to integrate both multiple criteria, multiple organizational levels, and the spatial dimension [START_REF] Allain | How Do Multi-criteria Assessments Address Landscape-level Problems? A Review of Studies and Practices[END_REF].

Improving bioeconomy system monitoring

To be effective, the IAM approach has to be supported by high quality data from detailed monitoring of bioeconomy systems at local and global scales. Due to the wide variety of domains using non-food biomass feedstocks (biofuels, biomaterial, chemistry), and the relatively recent interest in bioeconomy systems as such, detailed data on real biomass feedstocks, flows and uses in bioeconomy systems are still scant. Efforts are needed to provide reliable data on the wide range of current and prospective uses and co-uses of these resources (e.g. location and supply plans of current biomass feedstocks users, potential of biomass transformation processes) and on the various biomass recycling processes. Dedicated local and global bioeconomy data monitoring and databases have to be developed.

On-going international initiatives currently pursue the goal of harmonizing models and methodologies to factor into land-use change effects [START_REF] Lotze-Campen | Impacts of increased bioenergy demand on global food markets: an AgMIP economic model intercomparison[END_REF], and may provide data to better approach trade-offs between local and global bioeconomy systems.

Increasing digitalization in biomass production, transformation, uses and recycling processes should improve the monitoring of the whole bioeconomy system. The IAM approach could then be integrated in a "smart industry"-like organization of territorial bioeconomy systems, allowing more decentralized, automated and intelligent solutions for a sustainable bioeconomy.

Involving stakeholders in the IAM approach

Sharing visions on bioeconomy systems

Assessing sustainability of bioeconomy systems, being able to anticipate the future, i.e. the IAM approach, and operating transitions towards a more sustainable bioeconomy system have to rely on stakeholders' vision and expectations. Stakeholders have to share a common vision of the current and future system to coordinate their actions and to manage cascading effects [START_REF] Duru | Designing agroecological transitions; A review[END_REF].

In the case of territorial bioeconomy systems, this issue is especially critical as the transition to a more sustainable bioeconomy relies on a massive reorganization -from linear to circular, from sectorial to cross-sectorial -and must include a wide range of stakeholders, from producers to consumers. In this shared-vision development process, stakeholders and scientists will have to define common and quantifiable objectives and performances that will ensure territorial bioeconomy sustainability [START_REF] Caron | Making transition towards ecological intensification of agriculture a reality: the gaps in and the role of scientific knowledge[END_REF] and underpin the sustainability assessment of the IAM approach. Reaching this shared vision of the bioeconomy system requires that stakeholders i) understand the functioning of the system as a whole and ii) transcend their individual interests.

Compared to other natural resource management issues (e.g.: water catchment protection, biodiversity conservation), the entanglement of biomass value-chains, and the diversity of entities and processes (see Part 3.) of bioeconomy systems require further efforts for stakeholders to reach this common understanding. The heterogeneity and multiple roles of stakeholders in the bioeconomy system (see 2.2.2.) may emphasize the importance of cognitive dissonance generally observed when individuals have to make choices regarding collective issues [START_REF] Duraiappah | Managing the mismatches to provide ecosystem services for human wellbeing: a conceptual framework for understanding the New Commons[END_REF]. This mis-match of values and interests might lead to inconsistent or conflicting decisions when collective organization is needed.

Methodological proposals

To trigger a shared vision of the bioeconomy system in the IAM approach, we call for participatory processes. Stakeholders' participation throughout conceptualization, modelling and assessment of the territorial bioeconomy system and future scenarios ensures: (i) that the multiplicity of interests and issues of the whole territorial bioeconomy system are considered;

(ii) that the required generic and local knowledge is integrated into a consistent representation of the system; and (iii) that participant stakeholders are helped to grasp the underlying assumptions, limitations and capabilities of the integrated model [START_REF] Voinov | Modelling with stakeholders[END_REF][START_REF] Voinov | Modelling with stakeholders -Next generation[END_REF]. More operationally, participatory processes will have to be employed at least at three crucial steps of the IAM implementation process, for the codevelopment of: (i) a shared and integrated representation model of the current situation (e.g. [START_REF] Murgue | Hybridizing local and generic information to model cropping system spatial distribution in an agricultural landscape[END_REF]Moraine et al. 2017b); (ii) scenarios of endogenous and/or exogenous changes [START_REF] Leenhardt | A generic framework for scenario exercises using models applied to waterresource management[END_REF][START_REF] Therond | Methodology to translate policy assessment problems into scenarios: the example of the SEAMLESS integrated framework[END_REF]; and (iii) the integrated assessment of scenarios (Moraine et al. 2017b;[START_REF] Allain | Spatial aggregation of indicators in sustainability assessments: Descriptive and normative claims[END_REF].

Moreover, increasing shared knowledge on how each bioeconomy stakeholder makes decisions regarding their own and collective issues regarding bioeconomy systems (e.g.: selfprofit and a collective biomass resource management) is an important step to capture cognitive dissonance and try to resolve it. For example, the importance of cross-sector collaboration regarding the forest products industry has been highlighted in several studies, as forest-based resources' optimal valuing can require processes of different natures (e.g. physical, chemical, biological), and therefore collaboration between existing sectors [START_REF] Guerrero | Cross-sector collaboration in the forest products industry: a review of the litterature[END_REF].

Conclusion

Bioeconomy systems' current sustainability assessment studies tend to be based on a limited view of the bioeconomy, focused on single bio-based value chains. They fail to offer an integrated approach to the territorial system under review. This narrow perspective produces a partial consideration of bioeconomy system's functioning, and of alternatives and sustainability issues which can generate controversies that discredit the potential of the bioeconomy for society as a whole. A specific sustainability assessment framework that takes into account bioeconomy systems' complexity is therefore needed to help decision and policy makers. We have highlighted key characteristics of territorial bioeconomy systems, such as the lack of knowledge surrounding the bioeconomy itself, the importance of policies for bioeconomy development, the variability and flexibility characterizing bioeconomy systems, and, more precisely, the multiplicity of resources and transformation processes, the co-dependencies between bio-based value chains, and the specific spatial and temporal patterns of bioeconomy systems. Based on this description, we have proposed an analytical framework informed by two representations of territorial bioeconomy systems that are useful to describe and decipher their organization and functioning, and to identify critical levers for sustainability. Finally, we have outlined a specific IAM approach to explicitly account for the diversity of stakeholders involved in bioeconomy systems, the range of options available to produce and transform biomass, and the interface of the human and technological components of these systems.

The next step will be to implement this IAM approach in territories, which will require: i) pluridisciplinary collaboration, especially regarding the coupling of models (biomass feedstock growth models, logistics optimization models, economic models, etc.), and ii) the involvement of all bioeconomy-related stakeholders.

While the IAM approach should help local and relatively short-term decision making regarding bioeconomy sustainability, some more fundamental issues have to be further investigated. The development of a sustainable bioeconomy able to replace non-renewable resources while supplying food to societies and preserving natural resources will depend not only on innovations in biomass transformation processes, but also on the organization of biomass feedstock production or biomass-based product consumption. Understanding the emergence of innovations and their interactions with existing bioeconomy systems to improve their sustainability seems important to anticipate the future of rural territories.

Figure 1 :

 1 Figure 1: Representation of a territorial bioeconomy system

Figure 2 :

 2 Figure 2: Bioeconomy system functioning and organization Sub-systems, biomass flows, stakeholders and main entities of a territorial bioeconomy system. S. stands for System. Arrows represent solid biomass flows. Green arrows represent biomass flows linked to the recycling process, and blue arrows represent biomass flows for energy own consumption options. Dotted arrows represent potential biomass transfers between bio-based value chains. The bioeconomy system encompasses entities of a different nature (human, industrial, natural, semi-natural). Examples illustrating the diversity of bioeconomy entities are given by the icons at the top of the figure. Stakeholders directly involved in the bioeconomy value chain are diverse and their relative participation varies regarding the subsystem considered. Icons at the bottom of the figure represent the three main categories of bioeconomy stakeholders: biomass feedstocks producer/farmers , companies , local communities . The size of each icon represents the relative importance of each type of stakeholders in the different bioeconomy subsystems. The biggest icon represents the fact that this type of stakeholder plays an important role (farmers for the biomass production step, companies for the transformation step and local communities / society for the consumption step), the fact that the three categories of stakeholders are represented for each step illustrate the diversity of roles each stakeholder can play in the bioeconomy system.

Figure 3 :

 3 Figure 3: Bioeconomy system as a social-ecological system

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