Philippe Le Coent

Coralie Calvet
email: coralie.calvet@inra.fr.

Claude Napoleone

Fabien Quétie

Philippe Le Coënt

Fabien Quétier

Challenges of achieving biodiversity offsetting through agri-environmental schemes : evidence from an empirical studyin Southern France

Keywords: Agri-environmental schemes, Biodiversity offsets, Conservation, No Net Loss Policies, Behavioral Economics

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

Introduction

Biodiversity offsetting (henceforth BO) is increasingly used in environmental policies as a way to halt or slow biodiversity losses caused by the development of infrastructure and urbanization, regarded as one of the major threats on biodiversity due to the species' habitat destruction and fragmentation [START_REF] Davenport | The ecology of transportation: managing mobility for the environment[END_REF][START_REF] Quintero | Biodiversity offsets and infrastructure[END_REF]. The principle of BO is to achieve a "No Net Loss" (henceforth NNL) of biodiversity by providing ecological gains at least equivalent to residual losses (Bull et al., 2013a). In many countries, as a regulatory requirement, BO is incorporated in a mitigation hierarchy aimed at first avoiding and minimizing residual losses, and then, in a last resort, offsetting residual impacts on biodiversity.

BO requirements appeared in environmental legislations of many countries in the 1970s, but they were rarely implemented in practice [START_REF] Mckenney | Policy Development for Biodiversity Offsets: A Review of Offset Frameworks[END_REF][START_REF] Quétier | No net loss of biodiversity or paper offsets? A critical review of the French no net loss policy[END_REF]. Recent regulatory developments and European or international initiatives to achieve NNL of biodiversity have strongly boosted the concept of BO worldwide.

Theoretically, the concept of BO offers a way to overcome the classic contradiction between economic development and biodiversity conservation. But in practice, the recent development of this principle is hampered by technical and operational problems that jeopardize its good application mainly due to problems of access to land (Jacob et al., 2014). In European countries, particularly in France where agriculture occupies a large share of non-urban land, the implementation of biodiversity offsets faces difficulties in finding and acquiring land [START_REF] Etrillard | Mesures de compensation écologique : risques ou opportunités pour le foncier agricole en France ?[END_REF]. This leads to conflicts, especially with farmers who try to maintain their activity in this fast-moving environment. In this context, implementing BO objectives through the acquisition of agricultural land is often seen as a major challenge to BO feasibility. Similar challenges are raised in many countries, where BO lead to restrictions on land uses and access to natural resources by local communities.

A possible way out of this problematic situation is to make the implementation of BO compatible with agriculture by involving farmers in BO schemes. The idea is to implement biodiversity offsets through voluntary agri-environmental contracts which we call Agrienvironmental Biodiversity Offsets Schemes (ABOS). Indeed, compared to land acquisition by a developer, which is commonly used in BO, ABOS only requires a temporary commitment of farmers to changing land use or adapting agricultural practices. It does not require either to cease the farming activity or to transfer land tenure rights from farmers to developers.

As compared to land acquisition, ABOS can therefore represent an opportunity for developers (and regulators) to facilitate the implementation of biodiversity offsets and reduce local conflicts. However, the use of agri-environmental schemes in the context of biodiversity offsets raises specific issues and challenges as compared to land acquisition with regard to NNL targets. A general requirement in BO is that, depending on the level of ecological losses that remain after avoiding and reducing the impact of a project, the developer is set by the State a mandatory target of ecological gains to achieve. The acquisition of land by developers provides long-term control over its use (and agricultural practices) that provides more security for the attainment of this mandatory target. However ABOS, which are voluntary short-term contracts with farmers, do not provide the same level of control.

We argue that the attainment of the BO objective of no net loss of biodiversity through ABOS, requires two conditions. The first one is the acceptability by farmers of ABOS contracts proposed by developers. The second one is the performance of ABOS contracts in terms of effectiveness. This scheme must indeed induce actual practice or land use change that lead to the expected environmental benefits and these must be sustained over time.

ABOS are similar to other contractual agreements widely used in environmental policies: Agri-Environmental Schemes (AES) and Payments for Environmental Services (PES). AES are voluntary contracts in which farmers are offered compensation payments for reducing the negative externalities of agricultural production or for producing positive externalities. AES are implemented in the Common Agriculture Policy (CAP) and are considered as the main policy instrument in the European Union to preserve biodiversity in agricultural landscapes [START_REF] Eea | High Nature Value Farmland -Characteristics, Trends and Policy Challenges[END_REF]. ABOS are a kind of AES designed for implementing BO requirements under NNL policies. ABOS can also be considered as a kind of Payment for Environmental Service (PES) in which a beneficiary (the developer) pays a provider (the farmer) for an environmental service: the compensation of residual biodiversity loss. These forms of contracts have been extensively studied in the literature, from which lessons can be drawn on the challenges of using ABOS to achieve NNL. This article sheds light on the opportunities and limits of using ABOS in NNL policies by asking the two following research questions:

Q1. What are the main determinants that influence the adoption of ABOS by farmers? Q2. What is the performance of ABOS to achieve biodiversity offset objectives?

To address these questions, we conduct an empirical analysis based on a case study located in Southern France. The literature on AES and PES acceptability identifies a diversity of determinants of adoption of contracts. To address our Question 1, we highlight the differences between AES/PES and ABOS and analyse in our empirical analysis whether these differences have an impact on the determinants of contract adoption. To address Question 2, we review the performance challenges faced by agri-environmental contracts in the literature and how they theoretically apply in the context of ABOS. Using a running ABOS programme as a case study, we subsequently analyse the performance of ABOS contracts through the lens of these challenges. While there is an extensive literature on PES and AES programs, to date, there has been no analysis of the use of agri-environmental contracts in the context of biodiversity offsets.

The article is organized into four main sections. First, we present the theoretical background of ABOS's challenges, in terms of acceptability and performance, which allow us to develop two research hypotheses. Then, we present the materials and method used in the empirical analysis to test the hypotheses divided into three subsections: (i) the case-study, (ii) the data collection, and (iii) the data analysis methodology. The third section presents the results of the empirical analysis and discusses these results by examining the opportunities and limits of ABOS in BO policies. The last section finally concludes on policy recommendations for ABOS implementation and research perspectives.

Background literature and research hypotheses

Definition of ABOS

We define ABOS as one or a set of voluntary contract(s) in which a developer pays one or several farmer(s) for changing their practices to provide ecological gains that will serve to offset residual impacts of one or several development projects. Intermediaries can be involved in establishing or managing the relationship between the developer and farmers. The public administration is typically involved in approving contracts or monitoring expected ecological gains.

BO policies generally involve a third-party transaction in which there are: 1) a buyer of an environmental service, the developer who legally must carry out biodiversity offsets to compensate for the ecological impacts he has caused, 2) a seller of the environmental service, the provider of ecological gains, and 3) a regulator who requires the purchase of offset and controls its implementation [START_REF] Scemama | L'émergence du marché de la compensation aux États-Unis: changements institutionnels et impacts sur les modes d'organisation et les caractéristiques des transactions[END_REF]. Thus, in this transaction, the farmer is the provider and the seller of the environmental service, and the developer is the beneficiary and the buyer of this environmental service used to comply with his offset requirements. The offset regulator is usually represented by two entities: at national level, by the Government that defines offset rules and requirements, and at local scale, by local authorities whose aim is to enforce environmental legislations (Figure 1).

Acceptability of ABOS

The acceptability of ABOS is a key challenge because developers need to find a sufficient number of voluntary farmers and a sufficient amount of agricultural land in order to reach the legally set BO objectives. In addition, considering that contracts are usually short-term (generally 5 years), the developer must be able do this several time during the legal duration of its biodiversity offset commitments.

The acceptability by farmers of agri-environmental contracts is well documented in the literature. There is particularly an extensive literature on the determinants of farmers' participation in AES proposed in the Common Agricultural Policy (CAP). The acceptability of agri-environmental contracts is influenced by a diversity of determinants that can be classified into four main groups: (1) farmer and farm socio-economic characteristics, (2) contract characteristics, (3) payment level and transaction and implementation costs, and (4) behavioral factors (see details in Appendix 1). Acceptability of ABOS may be influenced by the same determinants but the particularities of this scheme may modulate their importance or even reverse the direction. We present in this section the main determinants that may be particularly important in ABOS adoption:

Flexibility

The flexibility of contract design is among the key factors that facilitate adoption. Contracts that are more likely to be adopted have a shorter duration [START_REF] Bougherara | Farmers' preferences over compensation contract flexibility and duration: an estimation of the effect of transaction costs using choice experiment[END_REF][START_REF] Christensen | Determinants of farmers' willingness to participate in subsidy schemes for pesticide-free buffer zones--A choice experiment study[END_REF][START_REF] Louis | Coûts de transaction et adoption des contrats agroenvironnementaux Le cas des MAE territorialisées à enjeu DCE en Poitou-Charentes[END_REF][START_REF] Ruto | Investigating farmers' preferences for the design of agrienvironment schemes: a choice experiment approach[END_REF], leave more flexibility to farmers in plot selection [START_REF] Bougherara | Farmers' preferences over compensation contract flexibility and duration: an estimation of the effect of transaction costs using choice experiment[END_REF][START_REF] Ruto | Investigating farmers' preferences for the design of agrienvironment schemes: a choice experiment approach[END_REF] and in technical prescriptions [START_REF] Bougherara | Farmers' preferences over compensation contract flexibility and duration: an estimation of the effect of transaction costs using choice experiment[END_REF][START_REF] Christensen | Determinants of farmers' willingness to participate in subsidy schemes for pesticide-free buffer zones--A choice experiment study[END_REF][START_REF] Kuhfuss | Préférences individuelles et incitations collectives : quels contrats agroenvironnementaux pour la réduction des herbicides par les viticulteurs ?[END_REF][START_REF] Ruto | Investigating farmers' preferences for the design of agrienvironment schemes: a choice experiment approach[END_REF]. Besides, easiness to withdraw from the contract is also an important criteria in farmers' participation [START_REF] Christensen | Determinants of farmers' willingness to participate in subsidy schemes for pesticide-free buffer zones--A choice experiment study[END_REF]. In the CAP, contract design is generally framed by strict legislative and administrative rules limiting farmers' eligibility and leaving little flexibility for the adjustment of contracts' characteristics to specific contexts. BO programmes are generally operated at a limited geographical scale and ABOS are tailor-made according to a specific development project. ABOS are signed between farmers and a developer. Unlike classic AES, ABOS isn't bound by CAP rules that strongly constrain the flexibility of the contracting. Thus, it is expected that ABOS offer a more flexible way in the establishment of the agri-environmental contracts in accordance with offsets commitments.

Likewise, due to this flexibility, contract terms will probably be more easily renegotiated in a context of environmental or farm changes. The higher flexibility offered by ABOS will likely have a positive influence on farmers' acceptability.

Payment/Costs

The relationship between costs and payment amounts is a key issue to understand the adoption of agri-environmental contracts [START_REF] Brotherton | What limits participation in ESAs?[END_REF][START_REF] Drake | Farmers' attitudes and uptake[END_REF]. It is thus expected to similarly play a fundamental role for ABOS. A particularity, compared to AES, is that payments could theoretically be freely set during the transaction between the developer and farmers. The payment can therefore result from a trade-off between the contracting parties and not be set by public institutions1 . This agreement can foster the acceptability of ABOS by farmers. In addition, ABOS should generally present less administrative constraints and restrictions than AES, mainly due to simpler procedure and contract terms. This is likely to reduce transaction costs and could be therefore more easily adopted than AES.

Social norms

The role of social norms in the adoption of AES and pro-environmental practices has been recently highlighted (Kuhfuss et al., 2015). This factor may be an important determinant particularly for the adoption of ABOS and influence farmers' adoption in different ways. On the one hand, BO programmes are linked to the construction of infrastructure that may create local social and economic impacts, and may be associated with expropriation. These factors may create local resistance to any actions associated with the construction project and social pressure not to adopt ABOS. Linked to the opposition to the project itself (or to offsetting as a policy), we anticipate that social norms may modulate farmers' adoption. On the other hand, the large participation of farmers in such a large BO programme can positively influence the enrollment of other farmers in ABOS, through conformity and imitation effects.

Attitude towards the environment

This factor is one of the prominent factors that have been shown to influence adoption of agrienvironmental programmes [START_REF] Beedell | Using social-psychology models to understand farmers' conservation behaviour[END_REF][START_REF] Defrancesco | Factors affecting farmers'participation in agri-environmental measures: A northern Italian perspective[END_REF][START_REF] Delvaux | Adoption d'une MAE et consentement à recevoir des agriculteurs en région wallone[END_REF][START_REF] Ducos | Agri-environment contract adoption under fixed and variable compliance costs[END_REF][START_REF] Morris | Recruiting the New Conservationists: Farmers' Adoption of Agri-environmental Schemes in the U[END_REF][START_REF] Mzoughi | Farmers adoption of integrated crop protection and organic farming: Do moral and social concerns matter?[END_REF], although this importance is debated [START_REF] Lamine | Anticiper ou temporiser : injonctions environnementales et recompositions des identités professionnelles en céréaliculture[END_REF]. Considering that in ABOS the contract is presented as a transaction between a service buyer and a seller for the compensation of biodiversity damages linked to infrastructure development project, it is likely that ABOS are not considered as environmental programmes like in AES or PES, and thus do not involve pro-environmental behaviors to the same extent. We anticipate that the attitude towards the environment may have a rather limited importance in ABOS adoption.

Trust

Trust between contracting partners also facilitates participation in AES by reducing transaction costs both before and during the transaction [START_REF] Ducos | The asset specificity issue in the private provision of environmental services: Evidence from agri-environmental contracts[END_REF][START_REF] Ducos | Agri-environment contract adoption under fixed and variable compliance costs[END_REF][START_REF] Louis | Coûts de transaction et adoption des contrats agroenvironnementaux Le cas des MAE territorialisées à enjeu DCE en Poitou-Charentes[END_REF][START_REF] Peerlings | Farm choice between agri-environmental contracts in the European Union[END_REF]. In Europe, AES are generally struck between farmers and the State within the CAP framework. In the context of BO, developers that offer ABOS to farmers can also come from the private sector. Establishing trust and good relationships among these new actors is therefore a key challenge for the success of BO programmes. The perception of this trust relationship by individual farmer might therefore be an important factor to predict farmers' participation.

Performance of ABOS

As mentioned previously, the implementation of ABOS must respect mandatory outcomes in terms of ecological gains, which imposes a high level of effectiveness. This means that i) farmers must comply with contract requirements (compliance), ii) contracts must result in a real change of land use or agricultural practices (additionality), iii) land-use changes must actually lead to desired environmental outcomes (link between land use and environmental outcomes) and iv) changes must be sustained over time (permanence) (Bull et al., 2013b;Wunder, 2015).

We describe below the main challenges that will confront ABOS in relation to these four components.

Compliance

There is an information asymmetry between farmers and the developer in the actual implementation of actions on which they are committed. After the contract has been negotiated, it may be rational for farmers not to respect these terms (moral hazard) if the developer does not invest enough in monitoring compliance or does not impose stringent sanctions [START_REF] Ferraro | Asymmetric information and contract design for payments for environmental services[END_REF]. The implementation of a system of monitoring and control is costly for the developer.

He may therefore be tempted to implement a minimal control system that could result in very limited compliance by farmers. Whether or not regulators actually enforce offset requirements on developers will also be a major driver of developers' behaviour in this matter.

Additionality

Additionality means that farmers not only adopt land uses or agricultural practices that are contributing to the targeted outcome but ones that they would not have adopted in the absence of ABOS [START_REF] Wunder | Taking stock: A comparative analysis of payments for environmental services programs in developed and developing countries[END_REF]. Some farmers under ABOS may indeed adopt practices that are favourable for a species or habitat, affected by a development project's residual impacts, but that farmers would have adopted anyway. This "windfall effect" should be avoided as much as possible [START_REF] Chabé-Ferret | How much green for the buck? Estimating additional and windfall effects of French agro-environmental schemes by DID-matching[END_REF][START_REF] Kuhfuss | Do agri-environmental schemes help reduce herbicide use ? Evidence from a natural experiment in France[END_REF]. It does not bring ecological benefits and should not be taken into account in the estimation of NNL achievement.

Additionality is a key requirement for BO (Maron et al., 2015). If pre-contract diagnosis is not done properly, selected farmers may even get paid to implement practices that they were already implementing.

In sum, information asymmetries that are inherently associated with the use of agrienvironmental contracts, especially moral hazard and adverse selection, pose specific challenges for the use of this tool in BO, mainly for the issues of compliance and additionality [START_REF] Ferraro | Asymmetric information and contract design for payments for environmental services[END_REF].

Link between land use and environmental outcomes

Guaranteeing additionality in terms of actual land-use changes may not be sufficient to attain BO targets. It is indeed necessary that the modification of land use practices leads to the ecological gains targeted in the developer's offset commitments. Several aspects need to be considered here. First, changes in land use and practices included in ABOS requirements must actually lead to environmental benefits, which should be adequately quantified. This requires a solid understanding of the ecology of targeted species or habitats. Second spatial coordination may also be required in order to achieve ecological results. For some species, the spatial configuration of habitats is essential [START_REF] Forman | Some general principles of landscape and regional ecology[END_REF] and landscape-level approaches need to be included in contracts to achieve improvements in the conservation status [START_REF] Goldman | Institutional incentives for managing the landscape: Inducing cooperation for the production of ecosystem services[END_REF].

Permanence

According to the CAP objectives, AES are supposed to help farmers to sustainably adopt proenvironmental practices. But in practice, many farmers do not maintain their practices when the contract ends (Kuhfuss et al, 2015). In the case of ABOS, the main goal is to avoid no net loss of biodiversity. This implies that irreversible losses caused by development projects have to be offset by long-term ecological gains. Likewise, ecological measures usually require significant amounts of time to have significant and visible effects on species. There is therefore a major issue of maintenance of the ecological gains provided by farmers' practices in ABOS. One option could be to offer long-term contracts to farmers (20 years for example, or more) however the literature shows that contracts with long duration are generally not well accepted by famers [START_REF] Bougherara | Farmers' preferences over compensation contract flexibility and duration: an estimation of the effect of transaction costs using choice experiment[END_REF][START_REF] Christensen | Determinants of farmers' willingness to participate in subsidy schemes for pesticide-free buffer zones--A choice experiment study[END_REF][START_REF] Ruto | Investigating farmers' preferences for the design of agrienvironment schemes: a choice experiment approach[END_REF]. For instance, this solution has been rejected in our case study in which 5 year contracts have been offered. This permanence issue therefore implies either that the land-use modifications required in contracts are maintained after the term or that new contracts are periodically being signed with farmers for as long as the ecological impact of the infrastructure remains.

Research hypotheses

Based on this literature review, this article explores two hypotheses: H1. Determinants of adoption of ABOS differ from the ones of AES: it is likely that ABOS are more easily adopted due to higher flexibility and limited transaction costs. Social norms and trust may have an important role but that could be either positive or negative. Finally, we anticipate that the attitude towards the environment may not facilitate adoption in ABOS.

H2. Information asymmetries associated with agri-environmental contracts limit the performance of ABOS: issues of compliance, additionality and permanence put at risk the achievement of BO objectives through ABOS compared with land acquisition.

Materials and methods

In this section, we describe the methodology we have used to analyse our case study. We first present the case study and then we define how we analyse the two main issues of acceptability and performance of ABOS.

Presentation of the case study

We examine the use of ABOS for the implementation of a part of the biodiversity offsets required to compensate the ecological impact of building and operating a 80 km long mixed high-speed railway line between Nîmes and Montpellier, in Southern France. This project, named "Contournement Nîmes-Montpellier" (henceforth CNM project), was initiated in 2000 and in 2012, the construction and maintenance (25 years) was delegated to a private consortium named "Oc'Via", including the responsibility for the project's impacts on biodiversity.

Due to the size and location of the CNM project, there are large ecological impacts. In particular, the railway line crosses two Natura 2000 sites designated as Special Protection Areas under the European Habitats Directive as they harbour the largest population of Little Bustard (Tetrax tetrax L.) in France (Wolff, 2001a). The little bustard is a flagship species for the CNM project and its stakeholders (including the public administration) due to the significance of the impacted area on its conservation status.

To design and size the offsets required for the CNM project, a specific loss -gain metric was used which combines area and habitat quality to determine "compensation units" (CU), defined as a unit change in habitat-quality on 1 hectare. Little Bustard habitat was assessed on a scale of 0 (unfavourable habitat) to 3 (highly favourable habitat), mainly on the basis of vegetation and agricultural practices. Thus, the destruction of a hectare of highly favourable habitat is a loss of 3 CU while the restoration of a hectare of favourable habitat (rated 2) to highly favourable habitat (rated 3) is a gain of 1 CU. In this example, 3 ha would be needed to offset the loss of 1 ha of Little Bustard habitat. Other combinations are possible depending on habitat quality before and after it is affected by the project or its offsets (destruction, degradation, restoration, etc.). This was considered an innovative approach at the time, given the dominance of area-based ratios in offset practice in France. The full method is described in Oc'Via's permit application and in [START_REF] Jacob | Vers une politique française de compensation des impacts sur la biodiversité plus efficace : défis et perspectives[END_REF].

The permit granted to Oc'Via requires that they offset the loss of 3279 CUs, meaning that he have to generate an extra 3279 CUs relative to a pre-impact baseline and maintain these until 2037. Most of the CUs are for agricultural habitats (95%), reflecting the types of habitats impacted and the importance given to the Little Bustard. The total amount of land required to achieve this depends on the amount of CU provided by the various land-use practices that are actually put in place and maintained by the developer. It was estimated that around 1668 hectares would have to be made more favourable for the Little Bustards, among which 500 hectares would be acquired and 1168 hectares would be contracted with farmers through ABOS. The required land for this could only be sought in specific areas in and around the Natura 2000 site.

The metric and exchange rules were developed only in 2013, several years after a significant number of farmers had been contracted to test the feasibility of ABOS to offset the expected impacts of the CNM project.

Presentation of the ABOS programme

Oc'Via's ABOS programme was set-up with the assistance by an ad hoc consortium formed by a regional nature conservancy / land trust (Conservatoire Régional des Espaces Naturels), a local bird conservation group (Centre Ornithologique du Gard), and the Chamber of Agriculture of the Gard area (CA30), a farmers' institution at the departmental level strongly involved in the technical and administrative support to farmers. This consortium (offset consortium, henceforth) was in charge of implementing, monitoring and enforcing ABOS, under the supervision of Oc'Via. The annual budget required for the payment of all ABOS is presently of 1564 M€.

The offset consortium defined and proposed a catalogue of 11 agri-environmental measures as possible ABOS contracts. ABOS payments are based on a fixed rate calculated based on average income foregone and additional costs tied to the implementation of the contract, and not negotiated between the parties to the transaction. This agreement, imposed by the local administration and promoted by farmers through the CA30, was set up to avoid excessive competition with other agri-environmental schemes, including AES and the needs of other developers with projects in the area.

In 2010, the offset consortium offered farmers the opportunity to participate in ABOS by sending a letter to 1100 farmers. The programme was opened to farmers for whom farming was their main or secondary activity, with no age restriction, and located in all the municipalities affected by the railway line. Farmers could choose the plots they volunteered to enrol in the program, and the measures they proposed to apply. The consortium received 124 propositions to participate in the offsetting program, corresponding to 2000 hectares among which they wanted to select 1150 hectares for implementing the ABOS. The consortium then set out a selection process to select the best plots to involve in ABOS based on three main criteria: the cost of the measure and an ecological rating of the plots. The ecological rating, which is different from the CU method, is a 1 to 4 score based on the location of plots (areas of known high densities of Little Bustards), plot size ("bigger is better") and the surrounding landscape (e.g. absence of hedges and nearby roads), as Little Bustards prefer large expanses of open habitat unbroken by visual obstacles. There was no clear and precise rule to select plots regarding these criteria; the selection was rather the result of a discussion between the consortium members and the buyer, Oc'Via. Following this selection process, the consortium selected 510 plots managed by 100 farmers and corresponding to 1160 ha.

In our case study, ABOS contracts have a five-year duration. Payments are given to farmers each year. The consortium set up a three-year monitoring and control plan of plots in which they are controlled without preliminary notice only once in three years. Enforcement rules are also very flexible. In case of non-compliance with requirements, farmers can receive lower payments, but no sanctions are foreseen. In case of technical problems related to the implementation of the technical specifications, farmers can renegotiate contract terms and even change measures. In worst cases, farmers can withdraw from the contract even during the contract duration. When the contract ends, farmers can decide to renew it or not on the same plots or to engage other plots. Compared to classic AES contracts, ABOS contracts are therefore much more flexible in terms of eligibility criteria, monitoring and enforcement.

Data collection and data analysis

The empirical study aims both at analysing determinants of farmers' acceptability and the performance of ABOS implemented for the BO programme of the CNM project. The methods used to analyse our two hypotheses are presented below.

Farmers' acceptability of ABOS

 Survey design

The issue of the acceptability of ABOS was analyzed through a survey carried out in early 2015.

The survey questionnaire was designed to determine factors that may explain two variables: i) whether farmers have adopted or not an ABOS, and ii) their intention to adopt an ABOS in the coming years. Survey questions were chosen based on factors that are considered to have an effect on the adoption of ABOS from the literature review on AES (see appendix 1 and section 2.1). The questionnaire covered the following topics: i) farmer and farm socio-economic characteristics, ii) contract flexibility, iii) transaction costs associated with the contract, iv) level of difficulty of the adoption of ABOS prescriptions, v) contract payment and their relation with costs, vi) attitude towards the environment, vii) social norms, viii) trust in the institutions involved in the contract, and ix) attitude towards BO. In most of the questions, farmers had to express their level of agreement with a statement ( "strongly disagree", "disagree", "agree", "strongly agree" or "do not know"). We deliberately avoided including a neutral point in our scales in order to prevent farmers from not expressing an opinion. The questionnaire is presented in appendix 2.

The questionnaire was designed in discussion with the stakeholders of the CNM project. It was tested in face-to face interviews with 4 farmers. The questionnaire was subsequently sent to all farmers that had been initially contacted by the Chamber of Agriculture of the Gard in 2010 when they were searching for voluntary farmers. It was sent to 1169 farmers by postal mail and by e-mail to those for which we had an e-mail address. Farmers were invited to fill the questionnaire on paper and send it back by postal mail or to fill the questionnaire directly online using Limesurvey. We received 39 questionnaires online and 106 questionnaires via postal mail. This 12.4% return rate is considered good for this type of survey in this field. Among the 145 questionnaires, 24 had to be discarded because they were very incompletely filled. Thus, 121 questionnaires could be analysed, among which 40 farmers had adopted the ABOS contract (henceforth referred as "adopters") and 81 had not (henceforth referred as "non-adopters").

 Analysis of acceptability

In our survey, two variables can be analyzed: the actual decision to adopt an ABOS and the intention to adopt one in coming years. The decision to adopt an ABOS was taken 5 years before the survey for most farmers, in 2010. The analysis of the determinants of adoption may therefore suffer from a strong endogeneity problem, i.e. it will not be possible to determine whether farmers adopted the ABOS because they were different or if they became different because they have adopted the ABOS. We therefore decided to focus our investigation on the intention of farmers to adopt an ABOS in the future, as we considered this to present less endogeneity issues and because the intention to perform a behavior is considered as one of the main predictors of behavior [START_REF] Ajzen | The theory of planned behavior[END_REF]. It captures the motivational factors that influence behavior, in other words it is an indication of "how hard people are willing to try, of how much of an effort they are planning to exert, in order to perform the behavior" -the stronger the intention, the more likely the behavior will be performed [START_REF] Ajzen | The theory of planned behavior[END_REF]. It was evaluated through the question "Do you intend to sign an ABOS in the coming years?" with the answer options "very unlikely" "rather unlikely" "rather likely" and "very likely" (see appendix 2). This variable however suffers from the limitations and biases of all stated preferences methodologies.

In this study, intention is an ordered variable (henceforth called 𝑦) coded from 1 to 4, however the difference between the different levels may not be constant. One option would be to turn this scale into a binary variable but it would partially collapse the diversity of intentions among farmers. We therefore decided to analyze this diversity using an ordered logit model.

We define a latent variable 𝑦 * , which is unobservable and defined by:

𝑦 * = 𝑋 ′ 𝛽 + 𝜖
where 𝑋 is a vector of variables that are considered to explain the intention to adopt an ABOS.

The intention 𝑦 takes the value j if the latent variable is comprised between two thresholds:

𝑦 = 𝑗 if 𝛼 𝑗-1 < 𝑦 * ≤ 𝛼 𝑗
The probability to choose level j can be defined by:

𝑝(𝑦 = 𝑗) = 𝑝(𝛼 𝑗-1 < 𝑦 * ≤ 𝛼 𝑗 ) = 𝐹(𝛼 𝑗 -𝑋 ′ 𝛽) -𝐹(𝛼 𝑗-1 -𝑋 ′ 𝛽)
where F is the logistic cumulative distribution function. This model produces one set of coefficients with (j-1) intercepts (3 in our case). The underlying ordered logistic assumption is that the relationship between each pair of outcome groups is the same. This is called the proportional odds assumption or the parallel regression assumption. An approximate likelihood-ratio test will be performed in order to verify that this assumption is verified. The description of the explanatory variables used to predict the intention to adopt is provided in appendix 3. Considering that there were missing values, the ordered logit estimation could only be done with 91 individuals out of the 121.

 Sample description

Descriptive statistics of our sample are provided in table 1. Compared to farmers of the Gard area, the sample presents a number of particularities. The sample has a higher proportion of organic farmers, of farms with more land and of cattle and field crop farm and less horticulture and fruit growing farms. These peculiarities could be due to contracts being offered only in certain areas of the Gard area. The population surveyed is therefore rather the farmers of these areas, but specific data on these farmers were not available. Another possibility is that farmers that had more interest in ABOS were more inclined to respond to the survey. This self-selection may partially bias responses. A way to manage this would have been to first estimate the probability to be part of the sample [START_REF] Vella | Estimating Models with Sample Selection Bias: A Survey[END_REF]), but we do not have access to individual data of farmers of the area for 2015.

ABOS performance

We analyzed the performance of ABOS in two ways. First, based on the survey, we studied the different challenges highlighted in the literature: compliance, additionality, link between land use and environmental outcomes, and permanence. These issues were addressed through a specific section in the farmers' questionnaire for the farmers enrolled in ABOS programme (see appendix 2). Questions mainly dealt with i) the level of modification of agricultural practices following contract adoption, ii) the criteria used by farmers to select the enrolled plots, and iii) farmers' intentions after the end of contract regarding reenrollment and maintenance of agriculture practices. Data analysis of the enrolled farmers' response is mainly based on descriptive statistics, in order to report their diversity of views. The ambition is therefore not to quantitatively analyze the impact of the programme but rather to identify challenges related to the programme's effectiveness. The issue of links between land use and environmental outcomes were mainly addressed during interviews with implementing partners and through the analysis of the database they provided.

The second approach we used to address ABOS performance is based on the analysis of the plot selection process. Considering that since the beginning (from 2011 to 2015) of the programme, we have information on 908 plots volunteered to be enrolled in the programme and that the consortium selected 510 of these plots, we decided to reconstruct the criteria that intervened in the plot selection through a statistical analysis. We especially wanted to determine the weight of ecological effectiveness (maximization of ecological benefits, in CU, and ecological rating) and economic efficiency for the developer (attainment of BO requirement at minimal cost ) in this selection. We collected data from the offset consortium on plots that farmers volunteered to enroll. Information available on these plots is the following: previous crop, ecological rating (see section 2.2), land area offered by the farmer, measure that the farmer proposed to adopt and associated payment. The plot database contains 908 plots that were submitted by farmers for enrolment. Among these, we have information for 829 plots.The remaining plots were rejected before field assessments were conducted.

We ran a logistic regression to estimate the probability of a plot to be selected based on the following explanatory variables: i) land area of the plot (SURF), ii) two effectiveness indicators, the ecological rating (ECORATE) and the amount of CU/ha brought by a plot (CU) and iii) an a cost-effectiveness criterion that is the cost per ha for a CU (COSTCU).

Results and Discussion

In this section, we present and discuss the results in two parts: first we analyze the determinants of farmers' acceptability of ABOS, and second, the performance of ABOS.

Determinants of farmers' acceptability of ABOS

The intention to adopt an ABOS is characterized by a normal-shaped distribution that is well suited for the use of an ordered logit model (Figure 3). Table 2. Logit estimation of the intention to adopt an ABOS in the coming years.

The results show that economic motivations play a crucial role in the intention to adopt ABOS as this is generally the case in AES. Farmers that perceive that it is easy for them to adopt (variable EASE) are more likely to have a high intention to adopt an ABOS in the future. The reasons are that the required practices fit well into their farming system, or because it is an opportunity to them to exploit an unused field plot or yet, or at the extreme, because they already have adopted this practice. In the same line high intenders perceive that the payment level proposed in contracts is interesting (PAYMENT).

Surprisingly, some advantages of ABOS, as compared to classic AES, such as higher flexibility (FLEX) and to a lesser extent lower transaction costs (TC), do not come out as significant determinants of the intention to adopt. This lack of influence may be due to different reasons.

First it could simply mean that flexibility is not fundamental for farmers in their choice to enroll.

Farmers may have not have been well informed of the advantages of ABOS contracts as compared to AES. This may partially be due a lack of information of farmers on some of the contract advantages. This study does not only consider the influence of socio-economic factors but also investigates the potential impact of behavioral factors. As anticipated, social norms especially seem to intervene in farmers' adoption. Farmers that consider important the enrollment of other farmers (NORMDESC) and farmers that think that the Chamber of Agriculture has a positive opinion on ABOS are more likely to participate (INSTOPINION). This large BO programme has led to the contracting (and acquisition) of a large area of farmland. Because of its size and its impact on local agriculture activities, the BO programme has also raised oppositions from some farmers' cooperatives and councilors. This maybe had a negative influence on the personal attitude of some farmers towards the programme (ATTITBO) and probably on their intention to adopt ABOS. Farmers that have a better general opinion of BO are more likely to adopt an ABOS.

Considering that the developer is a new stakeholder in agriculture contracting and that this type of scheme was new in the area, it was anticipated that trust variables (TRUST and TRUSTDEV) would play a significant role in adoption. However, it does not appear to be the case. As shown in psychology literature, peer influence is recurrently highlighted in empirical studies about farmer behavior (e.g. Burton, 2004). So, we think that the use by the developer of an offset consortium in which the CA30 had a strong involvement has limited the effect of this variable on the intention to enroll.

As we expected, the role of the attitude towards the environment (ENV) and the feeling of responsibility by farmers for the protection of threatened bird species (RESP) do not come out as significant determinant of the intention to adopt ABOS. The only variable that is positively linked with adoption is the fact to be member of an environmental association or to carry out nature activities, such as hiking, hunting or fishing (NATURE). This relatively low influence of environment susceptibility indicators may be due to the fact that farmers predominantly responded positively to environmental sensitivity questions: 89% agreed that protecting threatened bird species is a priority for the area and 85% that it is their responsibility to protect them. A more discriminating indicator of environmental susceptibility may have been necessary. Another interpretation could that for ABOS, in contrast to AES, adopting a contract may be strictly considered as a service transaction by farmers that therefore mobilize lower environmental considerations.

Finally, farmers that perceive that the programme will lead to an effective protection of threatened bird species are less likely to have a strong intention to adopt. This result is the only effect that goes against expectations. A possible interpretation may be that farmers that have the most positive opinion on the results of the programme may consider their future participation superfluous.

To conclude, this analysis of the determinants of the intention to participate in ABOS highlights the role of traditional factors known from studies of AES: high intenders tend to have a low profitability, to be more educated, to positively judge payments, to consider the implementation of ABOS requirements easy on their farm or to have already adopted a similar contract. Factors that differentiate ABOS and AES such as the perception of the flexibility of the contracts and transaction costs didn't have the expected influence. Behavioral factors such as the perception of social norms and the personal attitude towards BO, however, are key factors in the adoption of ABOS. However, the feeling of trust in contracting institutions does not seem to be critical.

Finally, the susceptibility to environmental issues does not seem to be a key factor in farmers' adoption of ABOS.

Performance of ABOS

In this section, we analyse the performance of ABOS in two different ways. We first present the results of the survey carried out with the enrolled farmers in ABOS based on the analysis of additionality, compliance, link between land use and environmental outcomes and permanence. Second, we analyse the influence of the plot selection process on the effectiveness and efficiency of the BO programme.

Analysis of the survey of farmers engaged in the AES programme  Additionality and compliance

In this section, we analyze questions that bring information on the magnitude of the change undertaken by farmers following their adoption of the contract. Replies to the question "How would you qualify the magnitude of the change of agricultural practice that you've had to undertake following your enrollment in the ABOS" are presented in table 3.

Intensity of practice change following ABOS adoption % of respondents

No change 19% Low change 39% Medium change 36% High change 6%

Table 3. Intensity of practice change following ABOS adoption. (N=36)

The results show that 58% of the enrolled farmers have declared not having made changes (19%) or low modifications (39%) to their practices following the adoption of the ABOS. In light of these results, the real additional effect of these ABOS on biodiversity is questionable.

We can suppose that the few changes declared by respondents did not produce the desired gains in habitat quality for the Little Bustard. This very low level of practice change for a majority of farmers can be due to the fact that farmers that were selected already implemented the practice before they enrolled (additionality issue) or can be due to the fact that farmers did not follow the requirements of the contract (compliance issue). Monitoring by the offset consortium in 2013 indicated only 75% conformity with the requirements of the ABOS, including 10% involuntary technical difficulties and 15% deliberate non-compliance [START_REF] Cen-Lr | Mise en oeuvre de mesures compensatoires en faveur de l'Outarde canepetie re dans la ZPS Costie res nîmoises -Rapport final du programme 2009-2013[END_REF].

These results are confirmed by the responses to the question "how did you select the plot that you submitted for enrollment", which are presented in table 4.

Farmers' plot selection criteria % of respondents

Plots that seemed ecologically relevant 61% Plots on which it seemed easy to implement the requires practices 61% Plots on which I was already implementing the practices 78% Plots with low productivity 2% Plots far away from the farm 5%

Table 4. Criteria quoted by farmers for farmers for the selection of plots they offered

These results confirm that a high proportion of farmers did not implement much change in their plots. Indeed, 78% of the adopting farmers indicated that they were already implementing the required practices on the plots before they enrolled them. Although qualitative, these results confirm that additionality and compliance issues that we theoretically emphasized in section 2.2 are indeed challenges for the use of ABOS to achieve BO objectives. For developers to deliver the ecological gains required to achieve the NNL objectives set by regulators, it is crucial that these challenges be addressed in future ABOS programmes. The analysis of the plot selection process that we conduct in the following section 4.2.2 sheds further light on this point.

 Link between land use change and the provision of ecological gains

As a condition to its permit, the developer, Oc'Via, had to generate 3079 CU by April 2015.

This was achieved with 500 ha of land directly acquired by the developer (generating 1015 CU + a bonus of 1 CU/ha for land it had under direct control through acquisition) and 1168 ha through ABOS contracts (generating 1550 UC).

However, this does not guarantee the attainment of ecological objectives in terms of conservation of the Little Bustard in and around the Natura 2000 site (Devoucoux, 2014). Our analysis of the plot selection database demonstrates the loose relationship between CU and ecological rating (Table 5). Somewhat surprisingly, plots with the lowest ecological rating do not lead to lower amounts of CU than plots with higher ratings.

 Permanence

Considering that contracts are signed for a period of 5 years and that the BO programme is legally supposed to ensure ecological benefits for a period of 25 years, the durability of benefits obtained through ABOS is a key issue. Two main dimensions of permanence are analyzed here:

1) whether farmers plan to sign a new contract after the end of their current contract (table 6),

and 2) what they plan to do in case their current contract ends and is not renewed (table 7).

Farmers' intentions after their current contract ends regarding the signature of a new contract

% of respondents

Stop ABOS 6% Sign again for the same area 56% Sign again for a smaller area 12% Sign again for a larger area 26% Table 6. Farmers' intentions after their current contract ends regarding the signature of a new ABOS contract (N=34)

Farmers' intentions regarding their agricultural practices in the absence of ABOS

% of respondents

Abandon the practices 36% Maintain the practices 36% Adopt other favorable practices 24%

Table 7. Farmers' intentions regarding their agricultural practices in the absence of ABOS (N=33)

Farmers generally seem to be satisfied with the contracts and 92% of the farmers plan to maintain or increase the land area under contract after their current contract ends. Thus, maintaining farmers under contract, during the period in which the developer needs to ensure offsets are effective is critical but seems achievable. However, only 36% of farmers would maintain the practices included in the requirement of their contract in the absence of ABOS.

This result raises the issue of the permanence of the ecological benefits obtained through ABOS after the legal period of 25 years.

Analysis of the plot selection process

When ABOS was launched in 2011 and in the following contracting phase in 2015, the amount of land that farmers volunteered to enroll was superior to the programme's target. To avoid competition with existing AES, a fixed price payment was chosen and plots were selected based on a multicriteria approach. This approach included the ecological rating and criteria that affect the cost of the programme for developers such as the relationship between the level of payment and the CU/ha 2 . The interests of the offset consortium and the developer were most likely not fully aligned and our results show which criteria prevailed in the plot selection process (Table 8).

The CU criteria was not used in the contractual phase in 2011 but was used in latter contractual phases. We nevertheless reconstruct the weight of these criteria throughout the selection process.

Table 8. Logit estimation of the plot selection choice

As expected, the ecological rating strongly intervened in the selection choice: plots rated at 3 or 4 had a significantly higher probability to be selected. However, we also show that the bigger the plot offered by a farmer the less chance it had to be end up being selected. This is unexpected considering that bigger plots were a priori more interesting from an ecological point of view and size was one of the criteria used in the selection process.

The amount of CU that a plot yielded does not have a significant effect on the probability of a plot to be selected. Cost-effectiveness (the cost to yield a CU), however, did have a significant effect: plots that generated costlier CU had a lower probability of being selected.

Using marginal effects, we can estimate that a plot that has the highest Euro/CU rate (1000€/CU) has 41.5% less chance to be selected than the plot that has the lowest rate (70 €/CU), while the plot that has an ecological rating of 4 has 45.8% more chance to be selected than a plot with an ecological rating of 1. Both criteria had similar effects on plot selection process. Furthermore, budget simulations show that, for the same CU target, if only the plots with highest ecological rating (4) had been chosen, the budget would have increased by 32%, while the budget would have decreased by 41% if only the cost-efficiency criteria would had been used.

From a purely economic standpoint, minimizing the cost of the programme should be the objective, as long as the CU target is achieved. In this case, the option of selecting plots based on cost-effectiveness, as would be done in an agri-environmental auction, would be the best option. On the other hand, considering the limits of CU as an ecological effectiveness indicator and reserves that we highlighted on additionality and compliance, a safe option to have more chance to reach NNL objectives would be to maximize the ecological favorability of selected plots. Indeed, in both cases the legal target in CU would have been attained, however the habitat created in the latter case would be much more favorable for the Little Bustard. The solution that was found is one that partially satisfies all parties but does not reflect a clear-cut political decision between minimizing costs and ensuring the attainment of BO objectives.

Conclusion and political implications

The main objective of this article was to analyse the opportunities and challenges of using agrienvironmental schemes in biodiversity offset implementation. Compared to land acquisition and management, ABOS present a number of advantages. First, it may be better accepted by farmers as it reduces pressure on the land market and represents an opportunity of additional revenue. Second, the use of ABOS reduces upfront costs for the developer, especially in context where the price of land is high. Third, the use of contracts allows greater flexibility and better adaptability of the offsetting system in case of environmental or institutional changes.

The main challenge of ABOS, as compared to land acquisition, is that the control of land use passes through a contract between the developer and farmers and is not under direct management. Yet, regulators require that developers achieve set targets of ecological gains, tied to the "No Net Loss" principle. Achieving BO objectives through ABOS therefore requires that i) a sufficient number of farmers accept to enrol in the programme and ii) that the contracts and their implementation are effective. However, information asymmetries that are inherently associated with agri-environmental contracts pose specific challenges for the use of this tool in BO, mainly in terms of compliance and additionality. In this paper, we identified the magnitude of these challenges through an empirical analysis of the ABOS programme put in place for a new railway line currently being built in Southern France. A survey of 145 farmers among those enrolled in the programme gave us insights into the determinants of their participation and into the effectiveness of the programme.

Our results suggest that the main determinants of acceptability are: i) classic economic factors (farmers with least compliance and opportunity costs, as well as farms in economic difficulty, are more likely to adopt), and ii) moral and social norms (the personal opinion on BO, the importance given to others' decision and the feeling that this decision is accepted by farmers' representatives). The importance of norms in the acceptability of ABOS is an aspect that should be considered in the implementation of ABOS. BO are a relatively new component in the permitting regime that is debated amongst farmers, farmer unions and politicians. Improving the general opinion on BO through continuous engagement by public authorities and environmental groups could strengthen and broaden support by other members of rural communities, which in turn may be an important element of success of future ABOS programmes.

The analysis of ABOS effectiveness reveals issues related to additionality. It would be interesting to undertake a quantitative impact evaluation in order to precisely quantify the magnitude of this problem. Additionality issues essentially stem from an adverse selection issue, which leads to the identification of farmers that cannot produce the environmental benefit in the most cost-effective way. [START_REF] Ferraro | Asymmetric information and contract design for payments for environmental services[END_REF] proposes 3 solutions to overcome this problem:

(1) acquire information on the environmental benefits that farmers can potentially offer and select them on this basis; (2) offer to farmers a menu of screening contracts; and (3) allocate contracts through agri-environmental auctions. In our case study, the first solution was privileged through a plot selection process that probably improved the additionality of the programme. However, due to the fixed-payment system calculated on foregone profits and additional costs, the payment system does not allow the payment of farmers according to the environmental, or BO, service they provide. Considering that there was a greater offer of plots by farmers than the final demand from the developer, the selection of plots and farmers could have been made through an auction mechanism (e.g. Latacz-Lohmann and [START_REF] Latacz-Lohmann | Auctioning Conservation Contracts: A Theoretical Analysis and an Application[END_REF]. A system with differentiated payment such as an auctioning mechanism would probably have improved additionality. Indeed, by paying less for contracts to low opportunity cost landowners, who are the most likely to adopt the practice even in the absence of a programme, the developer saves money to contract with higher opportunity cost landowners, who are more likely to participate and generate the desired biodiversity gains [START_REF] Ferraro | Asymmetric information and contract design for payments for environmental services[END_REF].

The analysis of the effectiveness of contracts also emphasized relatively high rates of noncompliance. Dealing with the issue of non-compliance would require a modification of the monitoring and enforcement system. Different theoretical contributions have studied how to determine the trade-off between environmental benefits, the cost of monitoring and the level of penalty. This trade-off essentially depends on farmers' risk aversion, with less monitoring efforts needed for risk averse farmers than for risk neutral ones when the level of sanctions is held constant [START_REF] Choe | Compliance Monitoring and Agri-Environmental Policy[END_REF][START_REF] Fraser | Moral Hazard and Risk Management in Agri-environmental Policy[END_REF][START_REF] Latacz-Lohmann | Moral hazard in agri-environmental schemes[END_REF][START_REF] Ozanne | Moral hazard, risk aversion and compliance monitoring in agri-environmental policy[END_REF]. In our case study, the high rate of non-compliance suggests that the level of penalty and the intensity of monitoring may not be sufficient. This could be due to the same consortium being in charge of design, implementation, monitoring and enforcement of the programme. It would therefore be necessary to raise monitoring efforts and strengthen enforcement to ensure compliance, possibly through third-party auditing. Another option that is frequently proposed in the literature is to shift from action-based contracts to result-rented contracts. This approach has been implemented in a number of countries, including for the protection of bird species (Burton and Schwarz, 2013). This approach would help solve the compliance issue but it shifts the risks of failure from the developer to farmers (or the offset consortium). This risk transfer is generally not well accepted by farmers (Burton and Schwarz, 2013).

In previous recommendations on compliance and additionality, we refer to research results in which agri-environmental contracts are modelled as a simple principal-agent model between farmers and the State. However, in our case, there is a principal-agent relationship between the developer and farmers, in the framework of ABOS, but there is also one between the regulator and the developer. In order to ensure that the developer actually cares about issues of additionality and non-compliance, the regulator must ensure that the incentives of the developer are aligned with the common society's interest. For example, the developer objective may not be to find a balance between farmer's compliance and monitoring costs but only to minimize the costs of monitoring. A monitoring and sanction system should therefore also be implemented by the State to ensure that developers adequately implement ABOS contracts. This idea of a cascade of principal-agent relationship for the implementation of BO through agri-environmental contracts, and the need to determine appropriate incentives for farmers and developers, could be the object of future theoretical developments.

Ensuring that additional land-use changes obtained thanks to ABOS actually lead to the required ecological gains is another important challenge. Knowledge is often limited and ecological equivalence and targets cannot be precisely set. The use of Compensation Units, based on the change of land use and practice modification, as in our case study, is an interesting approach to size BO requirements. However, because it does not take into account the local favourability (proximity to roads, presence of other groups of the same species, proximity of other favourable habitats), targets in terms of CU can be attained with very different levels of favourability of the resulting habitats and therefore different levels ecological gains. In the CNM case study, the selection of plots to be included in ABOS was based both on a local ecological indicator and the costs for the developer of the CUs this plot would yield. This equilibrium was found, probably due to the diversity of interest of the institutions involved in the plot selection process. Considering the uncertainties that still weigh on the sizing of biodiversity offsets, relying exclusively on metric approaches such as CUs would be hazardous.

It is therefore important that the State and/or ecological organizations are involved, in order to ensure ecological interests are taken into account to maximize the impact of the BO programmes.

Finally, our results show that although farmers may be ready to maintain their contractual agreements in the next period, very few would maintain their practice in the absence of financial support. In our case study, BO objectives are set for a period of 25 years, after which there is no guarantee from any party that offset measures will be sustained, although the loss of habitat is largely irreversible. Whilst it may be unreasonable to expect developers to finance compensation measure ad infinitum, such arrangements would place a considerable burden on public finances if every offset were to fall back on public funding once private sector obligation are through. The long-term financing of offsets is yet to be addressed in France.

I. Renseignements concernant votre exploitation

Figure 1 .

 1 Figure 1. Schematization of Agri-Biodiversity Offset Schemes (ABOS) as a transaction in biodiversity offset policies.

Figure 3 .

 3 Figure 3. Frequency of farmers according to their intention to adopt an ABOS in the future (Obs: 111).

Farmers

  and farm socio-economic factors also intervene in the adoption. Farmers with higher education (EDUC) have stronger intention to adopt an ABOS. Considering that most ABOS measures require an extensification of agriculture activities, it is not surprising to see that farmers that are in a phase of activity reduction (ACTIVITYRED), such as land area reduction or planning to retire, generally have a stronger intention to adopt an ABOS (as compared to farmers that have not had significant change in the last 5 years). Similarly, farmers that suffer from a low profitability (PROFIT) of their farming activity may consider contract payment as an opportunity to have more regular revenues and are therefore in favor of adopting. Other factors have a less significant influence: younger farmers (AGE) and farmers that are in a new development project (NEWACTIVITY), such as a new production, the conversion to organic farming or farm size increase, are more susceptible to adopt an ABOS. Finally, farmers that had already enrolled in ABOS at the time of the survey are expectedly more likely to enroll in the future.

  Indeed, it is difficult to estimate whether the adoption of ABOS has actually led to an increase of the population of birds on enrolled plots and if it has compensated losses caused by the CNM project. Preliminary results show that the local landscape is reaching carrying capacity(Devoucoux, 2014) which makes it all the more important for offsets to maintain that carrying capacity as the railway line cuts through the Natura 2000 site. Simply displacing individual birds to favorable but unoccupied habitats won't be possible in those circumstances. The metric and exchange rules used to design and size the offset requirements for Oc'Via focus are suited to this challenge (with a focus on increases in habitat favorability per unit area) but remain based in expert judgement and the quantitative relationship between favorability and bird densities remains uncertain. It is premature to fully evaluate the actual ecological gains linked to ABOS in our case study.Another way to analyze the link between land use change and ecological is to compare the two ecological indicators used in the process. Specifically, the ecological rating takes into account local ecological characteristics (distance to a road or an urban area, presence or absence of population of little bustard before the enrollment, distance to other plots with favorable practices, presence or absence of hedges, plot area) while CUs is a broad indicators that focuses on land-use change within the plot.

□

  Les acteurs privés (entreprises, aménageurs, etc.) est votre opinion sur la compensation par des actions agricoles de dommages environnementaux occasionnés par la construction d'infrastructure ? -vous indiquer l'opinion des personnes ou organisations suivantes sur les contrats MAERFF et l'influence de cette opinion sur votre décision de signer un contrat MAERFF :V. Participation à d'autres programmes agro-environnementaux 30. Avez-vous déjà contractualisé un CTE ou CAD par le passé? □ OUI □ NON 31. Avez-vous été informé(e) de la possibilité de signer une MAEt Natura 2000 dans le cadre de votre dossier PAC ? □ OUI □ NON 32. Etes-vous actuellement en contrat MAEt Natura 2000? □ OUI □ NON 33. Si NON, pourquoi avez-vous choisi de contractualiser une MAERFF plutôt qu'une MAEt Natura 2000 ? (plusieurs réponses possibles) □ Plus grande flexibilité des contrats (durée, contrôles, sanctions…) □ La chambre d'agriculture m'a conseillé de plutôt signer une MAERFF □ Je ne suis pas éligible pour la signature d'une MAEt Natura 2000 □ Je n'ai pas constitué de dossier PAC et la signature d'une MAEt Natura 2000 aurait été trop compliquée □ Les mesures proposées dans le cadre des MAEt Natura 2000 ne convenaient pas à mon exploitation □ Je n'ai pas confiance dans les institutions qui financent et gèrent les contrats MAEt (Union européenne, Services de l'Etat)

□

  Des parcelles sur lesquelles il était facile pour moi de mettre en oeuvre les pratiques □ Des parcelles sur lesquelles je réalisais déjà les pratiques demandées dans le cahier des charges □ Des parcelles peu productives □ Des parcelles éloignées de mon exploitation □ 42. Si vous avez rencontré des difficultés pendant la durée de votre engagement, pouvez-vous préciser à quel niveau se trouvaient-elles ? (plusieurs réponses possibles) □ Pas de difficultés particulières □ Difficultés techniques et/ou agronomiques pour le respect du cahier des charges des MAERFF □ Difficultés dans l'organisation de l'activité agricole □ Manque de temps pour réaliser les actions □ Rentabilité insuffisante des parcelles engagées dans les MAERFF □ Valorisation difficile des cultures introduites (luzerne, colza) à ces difficultés avez-vous renégocié certains éléments du contrat ? □ OUI □ NON 44. Si OUI, sur quels éléments ont porté ces renégociations ? (plusieurs réponses possibles) □ Adaptation des actions de la mesure (par exemple modification des dates d'intervention) □ Changement de mesures □ Diminution des surfaces engagées □ Abandon du contrat □ Suspension temporaire du contrat □ Autres. Préciser : _______________________________________________________________ 45. Que pensez-vous faire à la fin de votre contrat MAERFF ? (une seule réponse souhaitée) □ Signer un nouveau contrat pour les mêmes superficies □ Signer un nouveau contrat pour une superficie plus importante □ Signer un nouveau contrat pour une superficie moins importante □ Ne pas signer de nouveau contrat 46. Que pensez-vous faire en ce qui concerne vos pratiques, si à l'avenir vous n'êtes plus en contrat MAERFF ? (une seule réponse souhaitée)

Table 1 .

 1 Descriptive statistics of the survey sample compared to the Gard Reference (Source: General Agriculture Census Agreste 2010).

	Variable	Modality	N	% of the 121 respondents	Reference (%)	Variable	Modality	N.	% of the 121 respondents	Reference
	Gender	Male		81.8	73.8	Main farm activity Field crops	16	13.6	4.5
		Female		18.2	26.2		Horticulture	10	8.6	10.9
	Age	Less than 40		18.2	16.9		Vine growing	61	52.1	53.8
		From 40 to 49		19.8	25.0		Orchard	4	3.4	13.2
		From 50 to 59		37.2	30.6		Livestock	17	14.6	6.6
		60 or more		24.8	27.6		Other	9	7.7	11.0
	Farm size	Less than 20 ha		31.4	67.5	Education	Primary	17	14.2	21.5
		From 20 to 50 ha		35.5	21.6		Secondary short	27	22.5	33.9
		From 50 to 100 ha		14.1	7.0		Secondary long	40	33.3	21.2
		From 100 to 200 ha		14.1	2.6		Superior	36	30.0	23.3
		200 ha or more	6	5.0	0.6
		Principal	100	84.8		Organic agriculture Yes	26	21.5	12
	Importance of farming	Secondary		14.4			No	95	78.5	88
	activity	Retired	1	0.9

Table 5 .

 5 Average CU/ha benefits for the different level of ecological rating.

Depending on the final plot selection, different levels of final ecological favorability can therefore be obtained with the same level of CUs. This simple table questions the idea of setting BO objectives on a "simple" generalized metric, such as CU. Although this metric can help determining the size of the BO efforts, it should be assorted with requirement on how to maximize ecological gains at the plot level.

  « J'ai confiance dans les institutions en charge du suivi et de la mise en oeuvre des contrats MAERFF (le Conservatoire des Espaces Naturels (CEN), le Centre Ornithologique du Gard (COGARD) et la Chambre d'agriculture du Gard) » Selon vous, quel est le principal acteur qui devrait se mobiliser pour agir en faveur des oiseaux menacés ? (une seule réponse souhaitée)□ Les acteurs publics (Etat, collectivités territoriales, etc.) □ Les agriculteurs

	Affirmations					Niveau d'accord
	9. Vous êtes : □ Une femme 11. Quel est votre niveau d'étude ? □ Un homme L'engagement dans les MAERFF nécessite pour vous d'investir dans du matériel spécifique ou d'en louer Le fait que d'autres agriculteurs s'engagent également (machine ou matériel agricole, clôtures, etc.) dans les contrats MAERFF est important pour moi L'engagement dans les MAERFF nécessite beaucoup de remplir, signature contrat, etc.) d'accord d'accord d'accord d'accord temps pour les démarches administratives (dossier à Pas du tout Plutôt pas Plutôt Tout à fait	Pas du tout Pas du tout d'accord d'accord □ □ Pas du tout □ d'accord	10. Quel âge avez-vous ? ___________________ 12. Etes-vous exploitant agricole à titre : Plutôt pas Plutôt Tout à fait Plutôt pas Plutôt Tout à fait d'accord d'accord d'accord d'accord d'accord d'accord □ □ □ □ □ □ Plutôt pas Plutôt Tout à fait □ □ □ d'accord d'accord d'accord Je ne sais pas	Je ne sais Je ne sais pas pas □ □ Je ne sais □ pas
	□ Primaire (certificat d'études, BAA, CAPA) □ Secondaire court (CAP, BEP, BEPC ; BEA, BEPA) □ Secondaire long (Bac, BTA, BP) □ Supérieur (BTS, DUT, Ingénieur, BTSA) 13. Etes-vous membre d'une organisation agricole type syndicat des éleveurs ou cave coopérative (hors syndicat FNSEA ou confédération paysanne) ? □ OUI □ NON 15. Code postal du siège de l'exploitation : ___________________ 20. Comment évaluez-vous les montants proposés dans les j'allais faire prochainement sur l'exploitation □ III. Renseignements concernant les contrats MAERFF 17. Avez-vous été informé(e) de la possibilité de signer un contrat MAERFF ? Pas du tout □ □ □ □ L'engagement dans les MAERFF nécessite de se former d'accord (suivre des formations, participer à des réunions) □ « J'ai confiance dans la gestion des politiques agro-environnementales par les pouvoirs publics (Services de l'Etat, □ Principal □ Secondaire 14. Faites-vous ou avez-vous fait partie d'une association environnementale ou participez-vous à des activités de nature (type randonnée, chasse, pêche, etc.) ? □ OUI □ NON 16. Pensez-vous que quelqu'un reprendra votre exploitation après vous ? 21. Avez-vous vendu des terres agricoles dans le cadre □ □ □ □ □ OUI □ NON 18. Avez-vous signé un contrat MAERFF ? □ OUI □ NON Plutôt pas Plutôt Tout à fait □ Je ne sais d'accord d'accord d'accord pas □ □ □ □ Pas du tout Plutôt pas Plutôt Tout à fait Je ne sais Europe) » La mise en oeuvre des mesures des contrats MAERFF d'accord d'accord d'accord d'accord pas Pas du tout Plutôt pas Plutôt Tout à fait Je ne sais pas nécessite d'avoir recours à des personnes extérieures à l'exploitation (autres agriculteurs, prestataires de service) □ □ □ □ d'accord d'accord d'accord d'accord □ □ OUI □ NON Si OUI, par qui ? (plusieurs réponses possibles) □ Chambre d'agriculture □ Autre(s) agriculteur(s) Si OUI, en quelle année ? : __________ 19. Avez-vous l'intention de signer un nouveau contrat MAERFF ou MAEOC dans les prochaines années ? Pas du tout probable Peu probable Assez probable Très probable Pas du tout Plutôt pas Plutôt Tout à fait □ □ □ □ □ Je ne sais Les mesures proposées dans les MAERFF s'intègrent bien d'accord d'accord d'accord d'accord pas dans mon système d'exploitation □ □ □ □ 26. Pensez-vous qu'il est de votre responsabilité en tant qu'agriculteur d'agir pour la protection des □ Pas du tout Plutôt pas Plutôt Tout à fait oiseaux menacés ? Je ne sais Les mesures MAERFF représentent une opportunité de d'accord d'accord d'accord d'accord Pas du tout Plutôt pas Plutôt Tout à fait Je ne sais pas pas valoriser des parcelles non exploitées □ □ □ □ d'accord d'accord d'accord d'accord □ □ Coopérative ou organisation agricole □ Autre, préciser : ___________________ □ □ □ □ Les mesures MAERFF représentent une opportunité de mettre en oeuvre des actions que je faisais déjà ou que Pas du tout d'accord Plutôt pas d'accord Plutôt d'accord Tout à fait d'accord □ □ □ □ □ Je ne sais pas 27.
	1. Quelle est la Surface Agricole Utile (SAU) de votre exploitation (incluant les parcelles non exploitées) ? SAU = ___________ha dont __________ ha de luzerne 3. Quelle est l'activité principale de l'exploitation ? (une seule réponse souhaitée) □ Grandes cultures □ Arboriculture □ Viticulture □ Elevage □ Maraîchage □ Production fourragère □ Autres, préciser : ________________ 5. En quelle année vous êtes-vous installé(e) sur votre Affirmations La diversité des mesures proposées dans les contrats MAERFF est un avantage Pas du tout d'accord □ Les rémunérations proposées dans les contrats MAERFF sont intéressantes Pas du tout d'accord contrats MAERFF par rapport aux coûts des actions prévues dans les cahiers des charges ? Très inférieurs Plutôt inférieurs Egaux Plutôt supérieurs Très Pas du tout Il est important que la chambre d'agriculture participe à d'accord l'animation des MAERFF □ supérieurs □ □ □ □ □ Pas du tout Les actions mises en oeuvre dans le dispositif des MAERFF d'accord permettront de protéger les oiseaux menacés □ □ Les règles et les exigences des contrats MAERFF sont faciles à comprendre Pas du tout d'accord Pas du tout La protection des populations d'oiseaux menacés est d'accord importante pour notre territoire □ □ □ 22. Pouvez-vous indiquer si vous êtes en accord ou en désaccord avec les affirmations suivantes : (une seule 2. Quel est le statut de votre exploitation ? □ Exploitant individuel □ GAEC □ Autres formes sociétaires 4. Comment qualifieriez-vous le type d'agriculture que vous pratiquez sur votre exploitation ? (une seule réponse souhaitée) □ Agriculture conventionnelle □ Agriculture raisonnée □ Agriculture biologique 6. Quel est le nombre de personnes qui travaillent sur Niveau d'accord Plutôt pas d'accord Plutôt d'accord Tout à fait d'accord Je ne sais pas □ □ □ □ Plutôt pas d'accord Plutôt d'accord Tout à fait d'accord de la construction de la ligne LGV (incluant les expropriations) ? Plutôt pas Plutôt Tout à fait Je ne sais d'accord d'accord d'accord pas □ □ □ □ □ OUI □ NON Plutôt pas Plutôt Tout à fait Je ne sais d'accord d'accord d'accord pas □ □ □ □ Je ne sais pas □ □ □ □ Plutôt pas d'accord Plutôt d'accord Tout à fait d'accord Plutôt pas Plutôt Tout à fait Je ne sais d'accord d'accord d'accord pas □ □ □ □ Je ne sais pas □ □ □ □ □ □ □ □ faciles à mettre en oeuvre sur mon exploitation d'accord d'accord d'accord d'accord pas Les mesures proposées dans les contrats MAERFF sont Pas du tout Plutôt pas Plutôt Tout à fait Je ne sais Pas du tout Plutôt pas Plutôt Tout à fait Je ne sais Le statut foncier de mes parcelles est un obstacle à mon d'accord d'accord d'accord d'accord pas adhésion aux contrats MAERFF □ □ □ □ □
	exploitation ? : ______________________ 7. Comment jugez-vous la rentabilité économique de Pas du tout réponse souhaitée par affirmation) Il y a beaucoup de contrôles de la mise en oeuvre des d'accord mesures des contrats MAERFF □ 23. Pouvez-vous indiquer si vous êtes en accord ou en désaccord avec les affirmations suivantes : (1 l'exploitation (vous compris) ? ____________ 8. Avez-vous effectué d'importants changements Plutôt pas Plutôt Tout à fait Je ne sais d'accord d'accord d'accord pas □ □ □ □
	votre exploitation ? Pas du tout rentable Peu rentable réponse/affirmation) Les sanctions en cas de non respect des règles et des Assez rentable Très engagements des contrats MAERFF sont raisonnables rentable □ □ □ □ Il est facile de trouver de l'aide auprès des personnes en 24. Pensez-vous que les institutions qui financent les contrats MAERFF (RFF et Oc'Via) honoreront leurs dans votre système d'exploitation ces 5 dernières années ? (plusieurs réponses possibles) □ Pas de changement notable Pas du tout Plutôt pas Plutôt Tout à fait Je ne sais d'accord d'accord d'accord d'accord pas □ □ □ □ □ □ Développement d'une nouvelle activité □ Agrandissement Pas du tout Plutôt pas Plutôt Tout à fait Je ne sais d'accord d'accord d'accord d'accord pas charge des contrats MAERFF en cas de problème □ □ □ □ □ engagements ?
	Il est possible de renégocier les engagements des contrats MAERFF en cas de difficultés rencontrées ou d'évolution de d'accord d'accord d'accord d'accord Pas du tout Plutôt pas Plutôt Tout à fait Pas du tout d'accord	□ En cours de cessation d'activité ou de transmission de l'exploitation Plutôt pas d'accord Plutôt d'accord Tout à fait d'accord Je ne sais pas Je ne sais pas
	la situation de l'exploitation □	□	□	□	Pas du tout □	Plutôt pas □ Autre, préciser : __________________________ Plutôt Tout à fait Je ne sais □ □ □ □ □
	□ d'accord 25. Etes-vous en accord ou en désaccord avec les affirmations suivantes : □ II. Renseignements vous concernant Il est facile de se désengager des contrats MAERFF d'accord	□ d'accord	□ d'accord	□ pas

□

  Autres. Préciser : _______________________________________________________________ Personnes / Organisations Quelle est l'OPINION des personnes ou organisations suivantes sur les contrats MAERFF ? Est-ce que cette opinion a eu une INFLUENCE sur votre décision de signer un contrat MAERFF ?

	Pas du tout	Plutôt pas	Plutôt	Tout à fait	Je ne sais
	d'accord	d'accord	d'accord	d'accord	pas
	□	□	□	□	□
	Chambre agriculture 41. Sur quels critères avez-vous sélectionné les parcelles que vous avez proposées pour les contrats □ Positive □ Sans opinion / Je ne sais pas □ OUI □ Je ne sais pas
	MAERFF ?		□ Négative			□ NON
	Coopératives agricoles (Cocher les 2 principaux critères de la liste suivante) □ Positive □ Négative Critères de sélection □ Sans opinion / Je ne sais pas	□ OUI □ NON	□ Je ne sais pas Choix des 2 critères principaux
	Services de l'Etat locaux Des parcelles qui me semblaient intéressantes d'un point de vue écologique □ Positive □ Sans opinion / Je ne sais pas	□ OUI	□ Je ne sais pas
	(DREAL, DDTM)		□ Négative			□ NON
	Associations		□ Positive	□ Sans opinion / Je ne sais pas	□ OUI	□ Je ne sais pas
	environnementales		□ Négative			□ NON
	Elus locaux		□ Positive □ Négative	□ Sans opinion / Je ne sais pas	□ OUI □ NON	□ Je ne sais pas
	Autres agriculteurs		□ Positive	□ Sans opinion / Je ne sais pas	□ OUI	□ Je ne sais pas
			□ Négative			□ NON

It is to be noted that in our case study this difference was not observed because a fixed rate payment was used.

Acknowledgments

The authors wish to thank regional permitting authorities, RFF, Oc'Via, Biositiv and the offset consortium for their willingness to engage with the research and the questions raised here.

Specifically, the Chamber of Agriculture of the Gard must be thanked for giving us access to farmers and data on the enrolled plots. We also wish to thank all the farmers who took precious time to fill our questionnaire. This research was co-funded by the European Union's Seventh Framework Programme (FP7/ 2007-2013) under grant agreement 308393 'OPERAs' and by the ONEMA in the framework of the 2011 call for research projects "Changer les pratiques agricoles pour préserver les services écosystémiques", supporting the implementation of the French National Action plan Ecophyto 2018 under grant agreement 1073/2012 'Coud'Pouce'. The authors also wish to thank Naufel Mzoughi, Sophie Thoyer and Raphaële Préget and Thomas Menut for useful discussions.

Appendix

Appendix 1: Main determinants of adoption of agri-environmental schemes in the literature

Determinants Effect Reference

Farmer and farm socio-economic factors Area + [START_REF] Allaire | Contractualisation et diffusion spatiale des mesures agro-environnementales herbagères[END_REF][START_REF] Falconer | Farm-level constraints on agri-environmental scheme participation: a transactional perspective[END_REF][START_REF] Morris | Recruiting the New Conservationists: Farmers' Adoption of Agri-environmental Schemes in the U[END_REF]Wilson, 1997 Age - [START_REF] Bonnieux | Estimating the Supply of Environmental Benefits by Agriculture: A French Case Study[END_REF][START_REF] Chabé-Ferret | How much green for the buck? Estimating additional and windfall effects of French agro-environmental schemes by DID-matching[END_REF][START_REF] Ducos | Agri-environment contract adoption under fixed and variable compliance costs[END_REF][START_REF] Morris | Recruiting the New Conservationists: Farmers' Adoption of Agri-environmental Schemes in the U[END_REF][START_REF] Ruto | Investigating farmers' preferences for the design of agrienvironment schemes: a choice experiment approach[END_REF][START_REF] Vanslembrouck | Determinants of the Willingness of Belgian Farmers to Participate in Agri-environmental Measures[END_REF]Wynn et al., 2001 + (for measures with extensification) [START_REF] Drake | Farmers' attitudes and uptake[END_REF] Education + [START_REF] Allaire | Contractualisation et diffusion spatiale des mesures agro-environnementales herbagères[END_REF][START_REF] Chabé-Ferret | How much green for the buck? Estimating additional and windfall effects of French agro-environmental schemes by DID-matching[END_REF][START_REF] Louis | Coûts de transaction et adoption des contrats agroenvironnementaux Le cas des MAE territorialisées à enjeu DCE en Poitou-Charentes[END_REF] Wilson, 1997

Contract characteristics

Short duration + [START_REF] Bougherara | Farmers' preferences over compensation contract flexibility and duration: an estimation of the effect of transaction costs using choice experiment[END_REF][START_REF] Christensen | Determinants of farmers' willingness to participate in subsidy schemes for pesticide-free buffer zones--A choice experiment study[END_REF][START_REF] Louis | Coûts de transaction et adoption des contrats agroenvironnementaux Le cas des MAE territorialisées à enjeu DCE en Poitou-Charentes[END_REF][START_REF] Ruto | Investigating farmers' preferences for the design of agrienvironment schemes: a choice experiment approach[END_REF] Flexibility on plot selection by farmers + [START_REF] Bougherara | Farmers' preferences over compensation contract flexibility and duration: an estimation of the effect of transaction costs using choice experiment[END_REF][START_REF] Ruto | Investigating farmers' preferences for the design of agrienvironment schemes: a choice experiment approach[END_REF] Flexibility on technical prescriptions + [START_REF] Bougherara | Farmers' preferences over compensation contract flexibility and duration: an estimation of the effect of transaction costs using choice experiment[END_REF][START_REF] Christensen | Determinants of farmers' willingness to participate in subsidy schemes for pesticide-free buffer zones--A choice experiment study[END_REF][START_REF] Kuhfuss | Préférences individuelles et incitations collectives : quels contrats agroenvironnementaux pour la réduction des herbicides par les viticulteurs ?[END_REF][START_REF] Ruto | Investigating farmers' preferences for the design of agrienvironment schemes: a choice experiment approach[END_REF]

Payment level and costs

Payment superior to costs [START_REF] Brotherton | What limits participation in ESAs?[END_REF][START_REF] Drake | Farmers' attitudes and uptake[END_REF] Low compliance and opportunity costs + [START_REF] Delvaux | Adoption d'une MAE et consentement à recevoir des agriculteurs en région wallone[END_REF][START_REF] Louis | Coûts de transaction et adoption des contrats agroenvironnementaux Le cas des MAE territorialisées à enjeu DCE en Poitou-Charentes[END_REF][START_REF] Vanslembrouck | Determinants of the Willingness of Belgian Farmers to Participate in Agri-environmental Measures[END_REF]Wynn et al., 2001.

Transaction costs - [START_REF] Ducos | The asset specificity issue in the private provision of environmental services: Evidence from agri-environmental contracts[END_REF][START_REF] Falconer | Farm-level constraints on agri-environmental scheme participation: a transactional perspective[END_REF][START_REF] Peerlings | Farm choice between agri-environmental contracts in the European Union[END_REF][START_REF] Vatn | An institutional analysis of payments for environmental services[END_REF] Asset specificity - [START_REF] Ducos | The asset specificity issue in the private provision of environmental services: Evidence from agri-environmental contracts[END_REF]Rorstad et al., 2007 Previous participation in similar schemes + [START_REF] Allaire | Contractualisation et diffusion spatiale des mesures agro-environnementales herbagères[END_REF][START_REF] Chabé-Ferret | How much green for the buck? Estimating additional and windfall effects of French agro-environmental schemes by DID-matching[END_REF][START_REF] Louis | Coûts de transaction et adoption des contrats agroenvironnementaux Le cas des MAE territorialisées à enjeu DCE en Poitou-Charentes[END_REF][START_REF] Kuhfuss | Le dispositif des MAEt pour l ' enjeu eau : une fausse bonne idée ?[END_REF]

Behavioral factors

Attitude towards the environment + [START_REF] Beedell | Using social-psychology models to understand farmers' conservation behaviour[END_REF]Defrancesco et al., 2007;[START_REF] Delvaux | Adoption d'une MAE et consentement à recevoir des agriculteurs en région wallone[END_REF][START_REF] Ducos | Agri-environment contract adoption under fixed and variable compliance costs[END_REF][START_REF] Morris | Recruiting the New Conservationists: Farmers' Adoption of Agri-environmental Schemes in the U[END_REF][START_REF] Mzoughi | Farmers adoption of integrated crop protection and organic farming: Do moral and social concerns matter?[END_REF] [START_REF] Fielding | Explaining landholders' decisions about riparian zone management: the role of behavioural, normative, and control beliefs[END_REF][START_REF] Beedell | Explaining farmers' conservation behavior: Why do farmers behave the way they do?[END_REF] Trust between contracting partners + [START_REF] Ducos | The asset specificity issue in the private provision of environmental services: Evidence from agri-environmental contracts[END_REF][START_REF] Ducos | Agri-environment contract adoption under fixed and variable compliance costs[END_REF][START_REF] Louis | Coûts de transaction et adoption des contrats agroenvironnementaux Le cas des MAE territorialisées à enjeu DCE en Poitou-Charentes[END_REF][START_REF] Peerlings | Farm choice between agri-environmental contracts in the European Union[END_REF] Risk aversion + (because AES bring a secured revenue) [START_REF] Fraser | On the Use of Targeting to Reduce Moral Hazard in Agri-environmental Schemes[END_REF][START_REF] Karsenty | Paiements pour services environnementaux et biodiversité dans les pays du sud[END_REF] Determinants Effect Reference -(uncertainty) regarding the future of AES) [START_REF] Slangen | How to organise nature protection by farmers[END_REF][START_REF] Sumpsi | An integrated approach to agricultural and environmental policies: a case study of the Spanish cereal sector[END_REF] Trust in the results of the programme + [START_REF] Gibbons | Offsets for land clearing: No net loss or the tail wagging the dog?[END_REF][START_REF] Karsenty | Paiements pour services environnementaux et biodiversité dans les pays du sud[END_REF] Appendix 2: The questionnaire sent to farmers.

Enquête sur les mesures MAERFF (mesures outardes) proposées aux agriculteurs suite au projet de contournement ferroviaire de Nîmes-Montpellier

Dans ce questionnaire, il vous est demandé de répondre aux questions selon votre situation ou votre opinion.

Pour répondre aux questions, il vous suffit de cocher une ou plusieurs case(s) selon les questions. Nous vous prions de bien vouloir répondre à TOUTES les questions qui vous concernent. L'absence de réponse à certaines questions pose en effet des problèmes dans le traitement des données.

Intensity of change

EASE

Ease to change perception index. The proposed measures are: easy to implement on my farm fit well in my farming system an opportunity to exploit unused fields ...an opportunity to be supported for practices I had already adopted or planned to adopt Continuous: sum of variables below 1=Agree; 0=Disagree or no opinion 1=Agree; 0=Disagree or no opinion 1=Agree; 0=Disagree or no opinion 1=Agree; 0=Disagree or no opinion

Contract payment

PAYMENT

The proposed payment level is interesting 1=Agree; 0=Disagree or no opinion

Attitude towards the environment

ENV

The protection of threatened bird species is a priority for our area 1=Agree; 0=Disagree or no opinion


domain: math info sdv shs

text:
Sara Maqrot

Simon De Givry

Gauthier Quesnel

Marc Tchamitchian

Mixed Fruit-Vegetable Crop Allocation Problem using MIP

Keywords: Agroecology, spatial and temporal crop allocation problem, binary quadratic programming, mixed integer programming, Benders decomposition

Agroforestry systems are one of the sustainable approaches that have received considerable research attention over the past with a view to ensure high productions, ecosystem services and environmental benefits. These systems combine two principal land-use sciences : agriculture and forestry. However, to our knowledge, none of the several studies conducted on agroforestry systems has specifically examined the combination of vegetable crops with fruit trees using a mathematical programming approach. Accordingly, the aim of the present study is to design mixed fruit vegetable cropping systems, represented as a spatial-temporal crop allocation problem. Nonetheless, unlike existing studies in which allocation concerns only annual crops [1, 2], our approach allocates both annual and perennial crops on the same land while optimizing above-and belowground interactions resulting from this combination (see Fig. 1).

To assess the validity of different modeling choices to design mixed fruit-vegetable cropping systems, we built a first prototype using a Binary Quadratic Programming (BQP) formulation of the Mixed Fruit-Vegetable Crop Allocation Problem (MFVCAP) [3]. The aim of this preliminary work was to examine the ability of state-of-the-art exact solver IBM ILOG cplex v12.6.1 in solving MFVCAP in order to support farmers in their crop allocation strategies. Depending on various modeling simplifications (without crop rotation nor crop dispersion) and preferences (equal importance to above-and belowground interactions), cplex was able to solve a small piece of land divided into 10 × 10 land units, each one contains either a tree or a crop (among 6 possible ones, plus bare soil), over a time horizon divided into three periods of four seasons (except the first period with only one season starting in autumn, see Fig. 3).

We further improved the results by exploiting a Benders decomposition of the problem. The master problem deals only with tree positioning and is a 0/1 linear program. The BQP objective function becomes linear in the continuous subproblem by exploiting the fact that it depends only on the quantity of crops assigned to land units having shade, root or nothing (see Fig. 2). The final spatial-temporal allocation of crops can be found in post-processing. This decomposition allows us to reformulate the MFVCAP into a Mixed Integer linear Program. The same 10 × 10 problem could be solved in 6 seconds compared to 405 sec. in the original BQP formulation using a 4-core computer.

Further research remains to be done in order to extend our model, e.g., by taking into account crop rotations in order to avoid soil depletion and to increase pest and disease natural regulation, and to solve larger instances (going from 15-by-15 to 100-by-100 land units).

Références

[1] M Akplogan, S de Givry, JP Métivier, G Quesnel, A Joannon, and F Garcia. Solving the crop allocation problem using hard and soft constraints. RAIRO -Operations Research,

FIG. 1 -

 1 FIG. 1 -Example of above-and belowground interactions between crops and trees