Denilson Barbosa

Philip Bohannon

Juliana Freire

Carl-Christian Kanne

Ioana Mano- Lescu

Vasilis Vassalos

Masatoshi Yoshikawa

XML Storage

Synonyms

XML persistence; XML database

Definition

A wide variety of technologies may be employed to physically persist XML documents for later retrieval or update, from relational database management systems to hierarchical systems to native file systems. Once the target technology is chosen, there is still a large number of storage mapping strategies that define how parts of the document or document collection will be represented in the back-end technology. Additionally, there are issues of optimization of the technology and strategy used for the mapping. XML Storage covers all the above aspects of persisting XML document collections.

Historical Background

Even though the need for XML storage naturally arose after the emergence of XML, similar techniques had been development earlier, since the mid-1990's, to store semi-structured data ([EDS reference: Semistructured data]). For example, the LORE system included a storage manager specifically designed for semi-structured objects, while the STORED system allowed the definition of mappings from semistructured data to relations. Even earlier, storage techniques and storage systems had been developed for object-oriented data ([EDS reference: Object data models]). These techniques focused on storing individual objects, including their private and public data and their methods. Important tasks included performing garbage collection, managing object migration and maintaining class extents. Object clustering techniques were developed that used the class hierarchy and the composition hierarchy (i.e., which object is a component of which other object) to help determine object location. These techniques, and the implemented object storage systems, such as the O2 storage system, influenced the development of subsequent semi-structured and XML storage systems. Moreover, the above solutions or ad-hoc approaches had also been used for the storage of large SGML (Standard Generalized Markup Language, a superset and precursor to XML) documents.

Scientific Fundamentals

Given the wide use of XML, most applications need or will need to process and manipulate XML documents, and many applications will need to store and retrieve data from large documents, large collections of documents, or both. As an exchange format, XML can be simply serialized and stored in a file, but serialized document storage often is very inefficient for query processing and updates. As a result, a large-scale XML storage infrastructure is critical to modern application performance.

Figure 1a shows a simple graphical outline of an XML DTD ([EDS reference]) for movies and television shows.

As this example shows, XML data may exhibit great variety in their structure. At one extreme, relationalstyle data like title, year and boxoff children of show in Fig. 1a may be represented in XML. At the opposite extreme are highly irregular structures such as might be found under the reviews tag. Figure 2 shows a similar graphical representation of a real-life DTD for scientific articles. Since every HTML structure or formatting element is also an XML element or attribute, the corresponding XML tree is very deep and wide, and no two sections are likely to have the same structure.

XML processing workloads are also diverse. Queries and updates may affect or return few or many nodes. They may also need to ''visit'' large portions of an XML tree and return nodes that are far apart, such as all the box-office receipts for movies, or may only return or affect nodes that are ''close'' together, such as all the information pertaining to a single review.

A few different ways of persisting XML document collections are used, and each addresses differently the challenges posed by the varied XML documents and workloads.

Instance-Driven Storage

In instance-driven storage, the storage of XML content is driven by the tree structure of the individual document, ignoring the types assigned to the nodes by a schema (if one exists). In some cases, e.g., when documents have irregular structure or an application mostly generates navigations to individual elements, instance-driven storage can greatly simplify the task of storing XML content. One instance-driven technique is to store nodes and edges in one or more relational tables. A second approach is to implement an XML data model natively.

Tabular Storage of Trees A relational schema for encoding any XML instance may include relations child, modeling the parent-child relationship, and tag, attr, id, text, associating to each element node respectively a tag, an attribute, an identity and a text value, as well as sets that contain the root of the document and the set of all its elements. Notice that such a schema does not allow full reconstruction of an original XML document, as it does not retain information on element order, whitespace, comments, entity references etc. The encoding of element order, which is a critical feature of XML, is discussed later in this article.

A relational schema for encoding XML may also need to capture built-in integrity constraints of XML documents, such as the fact that every child has a single parent, every element has exactly one tag, etc.

Tabular storage of trees as described enables the use of relational storage engines as the target storage technology for XML document collections. While capable of storing arbitrary documents, with this approach a large number of joins may be required to answer queries, especially when reconstructing subtrees. This is the basic storage mapping supported by Microsoft's SQL Server as of 2007.

Native XML Storage Native XML storage software implements data structures and algorithms specifically designed to store XML documents on secondary memory. These data structures support one or more of the XML data models ([EDS reference to infoset/psvi/ XQuery data models]). Salient functional requirements implied by standard data models include the preservation of child order, a stable node identity, and support for type information (depending on the data model supported). An additional functional requirement in XML data stores is the ability to reconstruct the exact textual representation of an XML document, including details such as encoding, whitespace, attribute order, namespace prefixes, and entity references.

A native XML storage implementation generally maps tree nodes and edges to storage blocks in a manner that preserves tree locality, i.e., that stores parents and children in the same block. The strategy is to map XML tree structures onto records managed by a storage manager for variable-size records. One possible approach is to map the complete document to a single Binary Large Object and use the record manager's large object management to deal with documents larger than a page. This is one of the approaches for XML storage supported by the commercial DBMS Oracle as of 2007. This approach incurs significant costs both for update and for query processing.

A more sophisticated strategy is to divide the document into partitions smaller than a disk block and map each partition to a single record in the underlying store. Large text nodes and large child node lists are handled by chunking them and/or introducing auxiliary nodes. This organization supports efficient local navigation and tree reconstruction without, for example, loading the entire tree into memory. Such an approach is used in the commercial DBMS IBM DB2 as of 2007 (starting with version 9). Native stores can support efficiently updates, concurrency control mechanisms and traditional recovery schemes to preserve durability ([EDS reference ACID Properties]).

Figure 1b shows a hypothetical instance of the schema of Fig. 1a. The types of nodes are indicated by shape. One potential assignment of nodes to physical storage records is shown as groupings inside dashed lines. Note that show elements are often physically stored with their review children, and reviews are frequently stored with the next or previous review in document order.

Physical-level heuristics that can be implemented to improve performance include compressed representation of node pointers inside a block, and string dictionaries allowing integers to replace strings appearing repeatedly, such as tag names and namespace URIs.

Schema-Driven Storage

When information about the structure of XML documents is given, e.g., in a DTD or an XML Schema ([EDS references to XML Schema]), techniques have been developed for XML storage that exploit this information. In general, nodes of the same type according to the schema are mapped in the same way, for example to a relational table. Schema information is primarily exploited for tabular storage of XML document collections, and in particular in conjunction with the use of a relational storage engine as the underlying technology, as described in the next paragraph. In hybrid XML storage different data models, and potentially even different systems, store different document parts.

Relational Storage for XML Documents

Techniques have been developed that enable the effective use of a relational database management system to store XML. Figure 3a illustrates the main tasks that must be performed for storing XML in relational databases. First, the schema of the XML document is mapped into a suitable relational schema that can preserve the information in the original XML documents (Storage Design). The resulting relational schema needs to be optimized at the physical level, e.g., with the selection of appropriate file structures and the creation of indices, taking into account the distinctive characteristics of XML queries and updates in general and of the application workload in particular. XML documents are then shredded and loaded into the flat tables (Data Loading). At runtime, XML queries are translated into relational queries, e.g. in SQL, submitted to the underlying relational system and the results are translated back into XML (Query Translation). ([EDS references to XML publishing, XML query processing]) Schema-driven relational storage mappings for XML documents are supported by the Oracle DBMS.

An XML-to-relational mapping scheme consists of view definitions that express what data from the XML document should appear in each relational table and constraints over the relational schema. The views generally map elements with the same type or tag name to a table and define a storage mapping. For example, in Fig. 3b, two views, V1 and V2 are used to populate the Actors and Shows tables respectively. A particular set of storage views and constraints along with physical XML Storage. Figure 3. Relational storage workflow and example. storage and indexing options together comprise a storage design. The process of parsing an XML document and populating a set of relational views according to a storage design is referred to as shredding.

Due to the mismatch between the tree-structure of XML documents and the flat structure of relational tables, there are many possible storage designs. For example, in Fig. 3b, if an element, such as show, is guaranteed to have only a single child of a particular type, such as seasons, then the child type may optionally be inlined, i.e., stored in the same table as the parent.

On the other hand, due to the nature of XML queries and updates, certain indexing and file organization options have been shown to be generally useful. In particular, the use of B-tree indexes (as opposed to hash-based indexes) is usually beneficial, as the translation of XML queries into relational languages often involves range conditions. There is evidence that the best file organization for the relations resulting from XML shredding is index-organized tables ([EDS reference to Index Creation and File Structure]), with the index on the attribute(s) encoding the order of XML elements. With such file organization, index scanning allows the retrieval of the XML elements in document order, as required by XPath semantics, with a minimum number of random disk accesses. The use of a path index that stores complete root-to-node paths for all XML elements also provides benefits.

Cost-Based Approaches

A key quality of a storage mapping is efficiency -whether queries and updates in the workload can be executed quickly. Cost-based mapping strategies can derive mappings that are more efficient than mappings generated using fixed strategies. In order to apply such strategies, statistics on the values and structure of an XML document collection need to be gathered. A set of transformations and annotations can be applied to the XML schema to derive different schemas that result in different relational storage mappings, for example by merging or splitting the types of different XML elements, and hence mapping them into the same or different relational tables. Then, an efficient mapping is selected by comparing the estimated cost of executing a given application workload on the relational schema produced by each mapping. The optimizer of the relational database used as storage engine can be used for the cost estimation. Due to the size of the search space for mappings generated by the schema transformations, efficient heuristics are needed to reduce the cost without missing the most efficient mappings. Physical database design options, such as vertical partitioning of relations and the creation of indices, can be considered in addition to logical database design options, to include potentially more efficient mappings in the search space.

The basic principles and techniques of cost-based approaches for XML storage are shared with relational cost-based schema design.

Correctness and Losslessness An important issue in designing mappings is correctness, notably, whether a given mapping preserves enough information. A mapping scheme is lossless if it allows the reconstruction of the original documents, and it is validating if all legal relational database instances correspond to a valid XML document. While losslessness is enough for applications involving only queries over the documents, if documents must conform to an XML schema and the application involves both queries and updates to the documents, schema mappings that are validating are necessary. Many of the mapping strategies proposed in the literature are (or can be extended to be) lossless. While none of them are validating, they can be extended with the addition of constraints to only allow updates that maintain the validity of the XML document. In particular, even though losslessness and validation are undecidable for a large class of mapping schemes, it is possible to guarantee information preservation by designing mapping procedures which guarantee these properties by construction.

Order Encoding Schemes Different techniques have been proposed to preserve the structure and order of XML elements that are mapped into a relational schema. In particular, different labeling schemes have been proposed to capture the positional information of each XML element via the assignment of node labels. An important goal of such schemes is to be able to express structural properties among nodes, e.g., the child, descendant, following sibling and other relationships, as conditions on the labels. Most schemes are either prefix-based or range-based and can be used with both schemadriven and instance-based relational storage of XML.

In prefix-based schemes, a node's label includes as a prefix the label of its parent. Dewey-based order encodings are the best known prefix-based schemes.

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The Dewey Decimal Classification was originally developed for general knowledge classification. The basic Dewey-based encoding assigns to each node in an XML tree an identifier that records the position of a node among its siblings, prefixed by the identifier of its parent node. In Fig. 1b, the Dewey-based encoding would assign the identifier 1.1.2 to the dashed-line year element. In range-based order encodings, such as interval or pre/post encoding, a unique {start,end} interval identifies each node in the document tree. This interval can be generated in multiple ways. The most common method is to create a unique identifier, start, for each node in a preorder traversal of the document tree, and a unique identifier, end, in a postorder traversal. Additionally, in order to distinguish children from descendants, a level number needs to be recorded with each node. An important consideration for any order-encoding scheme is to be able to handle updates in the XML documents, and many improvements have been made to the above basic encodings to reduce the overhead associated with updates.

Hybrid XML Storage

Some XML documents have both very structured and very unstructured parts. This has lead to the idea of hybrid XML storage, where different data models, and even systems using different storage technologies, store different document parts. For example, in Fig. 3b, review elements and their subtrees can be stored very differently from show elements, for example by serializing each review according to the dashed lines in the figure or storing them in a native XML storage system.

Prototype systems such as MARS and XAM have been proposed that support a hybrid storage model at the system level, i.e., provide physical data independence. In these systems, different access methods corresponding to the different storage mappings are formally described using views and constraints, and query processing involves the use of query rewriting using views ([EDS reference to Query rewriting using views]). Moreover, an appropriate tool or language is necessary to specify hybrid storage designs effectively and declaratively.

An additional consideration in favor of hybrid XML storage is that storing some information redundantly using different techniques can improve the performance of querying and data retrieval significantly by combining their benefits. For example, schema-directed relational storage mappings often give better performance for identifying the elements that satisfy an XPath query, while native storage allows the direct retrieval of large elements. In environments where updates are infrequent or update cost less important than query performance, such as various web-based query systems, such redundant storage approaches can be beneficial.

Key Applications

XML Storage techniques are used to efficiently store XML documents, XML messages, accumulated XML streams and any other form of XML-encoded content. XML Storage is a key component of an XML database management system. It can also provide significant benefits for the storage of semi-structured information with mostly tree structure, including scientific data.

Cross-references

  XML Storage.Figure 1. Movie DTD and example native storage strategy.

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XML Storage

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Figure 2. Graphical outline of a complex article DTD (strongly simplified).

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Oliver Frings

Jens Abildtrup

Claire Montagné-Huck

Salomé Gorel

Anne Stenger

Do individual PES buyers care about additionality and free-riding? A choice experiment

Keywords: Ecosystem services valuation, Additionality, Equity, Warm Glow, Free-riding, Payment vehicle

Based on a survey of the French population, this study investigates consumer preferences for forest ecosystem services (FES) provision towards efficiency and equity in the context of additionality, and differences in willingness to pay (WTP) for FES between a tax-based and a donation-based payments for ecosystem services (PES) scheme. We show that consumers prefer equity to strict additionality adherence, with this preference being significantly stronger among females. However, consumer preferences are heterogeneous, and respondents with a closer connection to forests express the opposite preference. Regarding WTP, we find no systematic difference between the two payment vehicles, though WTP does vary depending on how respondents perceive potential free-riding. When considering that non-contributors also benefit from a particular PES scheme, a small group perceived this as unfair and reacted by reducing their contribution. A second, significantly larger group interpreted this as an opportunity to contribute to the common good and showed a higher WTP, indicating a markedly altruistic attitude towards FES provision in French society. We conclude by discussing the role of altruism in PES, the dilemma posed by the partial economic and legal incompatibilities of additionality and equity, and the environmental impact of environmental credits when credit buyers do not account for additionality.

Introduction

Alongside the provision of wood, forests deliver a wide range of forest ecosystem services (FES) that do not necessarily have a market price but are of value to forest owners, local communities and the wider society [START_REF] Pearce | The Economic Value of Forest Ecosystems[END_REF]. The provision of these services is in many cases determined by decisions made by private forest owners and thus by the behaviour of individuals. In the absence of market prices and outlets for non-wood FES, expanding their provision may be beneficial to local stakeholders and society at large, but costly and unprofitable for private landowners [START_REF] Polasky | Implementing 1115 the optimal provision of ecosystem services[END_REF]. This lack of economic incentives for FES preservation and provision has led to market failures worldwide, involving over-exploitation of common pool resources and insufficient supply of non-market ecosystem services (ES) [START_REF] Hardin | The tragedy of the commons: The population problem has no technical solution; it requires a fundamental extension in morality[END_REF][START_REF] Lant | The Tragedy of Ecosystem Services[END_REF]. Assessing the demand for non-market FES can provide a basis for change to the management of private land through regulation and economic incentives, thus ensuring a more socially efficient FES provision.

A common way of bridging the gap between ES beneficiaries and landowner interests is through the establishment of payment for ecosystem services (PES) schemes, which are consensual, conditional arrangements between one or more 'sellers' and one or more 'buyers' over a well-defined ecosystem ser-Email address: oliver.frings@agroparistech.fr (Oliver Frings) vice --or land use hypothesised to provide that service (Wun-25 der, 2005).

Based on a framework for PES efficiency developed by [START_REF] Pagiola | Assessing the efficiency of payments for environmental services programs: A framework for analysis[END_REF], [START_REF] Engel | Designing payments for environmental services in theory and practice: An overview of the issues[END_REF] identified four main causes due to which PES systems can be economically inefficient: (1) Social inefficiency, which refers to funded management changes 30 where the costs exceed the social benefits of ES provision. As it is difficult or impossible to quantify the economic value of ES in many cases, this aspect is often not considered accurately. To address this form of inefficiency, this study is an attempt to provide approximations of the economic value of a range of 35 FES. (2) Lack of additionality, where additionality refers to a case where changes in management practices would not have been made without the funding of a corresponding PES programme. To this end, a historical benchmark is usually defined, on the basis of which an evaluation of a PES scheme's impact 40 on ES provision can be monitored and evaluated [START_REF] Ferraro | The Future of Payments for Environmental Services[END_REF]Blanco et al., 2021;[START_REF] Wunder | Payments for Environmental Services: Some Nuts and Bolts[END_REF]. A lack of additionality is considered to be particularly problematic when PES funding is tightly constrained. Despite the financial inefficiency of nonadditional PES schemes, they might still be socially efficient.

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In the present study, we focus on the importance of additionality for the population's willingness-to-pay (WTP). (3) Leakage, whereby undesirable activities are shifted to geographical zones outside the supported area, leading to an overestimation of the net ES provision of a PES project. (4) Lack of permanence, 50 where the provision of ES declines sharply when funding ends.

Our study follows two main objectives: Firstly, by contrast-ing a reward for sustainable behaviour that goes beyond the minimum legal standards and has already taken place at the forest owner's initiative (equity) with a more rigorous adherence to additionality, i.e., the exclusive consideration of future projects, we aim to assess whether consumers prefer efficiency (additionality) over equity. We also seek to investigate whether the corresponding consumer preferences are driven by socioeconomic variables. Secondly, by separately modelling the WTP for FES for a tax-based and a donation-based PES scheme, we intend to quantify the effect of the payment vehicle on the WTP. We then aim to assess whether altruism and free-riding concerns affect stated WTP values.

Previous work 65

2.1. Willingness to pay for FES Since the 1980s, numerous studies have estimated the willingness-to-pay (WTP) for different FES across the world. The Evri© database and the bibliographic analysis of [START_REF] Acharya | Global trend of forest ecosystem services valuation -An analysis of publications[END_REF] register more than a thousand records related to FES valuation. The oldest studies mostly applied the contingent valuation (CV) method, while more recently, choice experiments (CE) have become increasingly prevalent. These studies reveal that forests provide a broad range of ecosystem services and that there is a wide variation in reported economic value [START_REF] Elsasser | A bibliography and database on forest benefit valuation studies from Austria, France, Germany, and Switzerland -A possible base for a concerted European approach[END_REF](Elsasser et al., , 2016;;[START_REF] Binder | Payment for Environmental "Self-Service": Exploring the Links Between Farmers' Motivation and Additionality in a Conservation Incentive Programme in the Bolivian Andes[END_REF][START_REF] Mäntymaa | Integrating nature-based tourism and forestry in private lands under heterogeneous visitor preferences for forest attributes[END_REF][START_REF] Grammatikopoulou | The value of forest ecosystem services: A meta-analysis at the European scale and application to national ecosystem accounting[END_REF][START_REF] Taye | The economic values of 1145 global forest ecosystem services: A meta-analysis[END_REF]. Latterly, these economic valuations have been placed in the broader context of the implementation of PES schemes. Choice experiments have been used to assess consumer preferences for management and ecosystem attributes such as forest structure, composition of tree species, visibility of silvicultural interventions, habitat protection and peatland conservation, with some targeting the general population [START_REF] Horne | Multiple-use management of forest recreation sites: A spatially explicit choice experiment[END_REF][START_REF] Juutinen | Estimating the benefits of recreation-oriented management in state-owned commercial forests in Finland: A choice experiment[END_REF]Giergiczny et al., 85 2015; [START_REF] Ouvrard | Nudging Acceptability for Wood Ash Recycling in Forests: A Choice Experiment[END_REF] and others focusing on local communities [START_REF] Tolvanen | Preferences of Local People for the Use of Peatlands: The Case of the Richest Peatland Region in Finland[END_REF].

Equity and additionality

PES are based on economic logic in a context of limited public resources; placing efficiency at the core of their implementation. In this sense, [START_REF] Karsenty | The Economic and Legal Sides of Additionality in Payments for Environmental Services: The Economic and Legal Sides 1035 of Additionality in Payments for Environmental Services[END_REF] argue that it is easier, more efficient and more effective to pay for the abandonment of unwanted practices than to reward already-established desired behaviour. This is in line with [START_REF] Wunder | The Efficiency of Payments for Environmental Services in Tropical Conservation[END_REF], who suggests that ES providers who have already behaved virtuously before 95 the implementation of a PES scheme should not automatically be eligible to claim compensation in the name of equity 1 . He argues that this systematisation could enable blackmail in the sense that corresponding ES suppliers could demand compensation in exchange for simply maintaining their ES provision,

1 By equity we refer to the interpretation of the law, including its application to specific cases, which allows it to be interpreted as an ideal, a guideline for balancing the interests to be taken into account [START_REF] Ikeme | Equity, environmental justice and sustainability: Incomplete approaches in climate change politics[END_REF][START_REF] Langlais | Le droit de la biodiversité à l'aune du développement durable ou l'ouverture à de nouvelles formes d'équité environnementale ? L'exemple controversé de la compensation écologique[END_REF] which in turn would drive up the cost of PES systems disproportionately.

However, this exclusion of virtually behaving ES suppliers from newly established PES schemes, causes PES potentially being perceived as unfair and highlights the risks associated 105 with strict adherence to the additionality criterion [START_REF] Sommerville | The role of fairness and benefit distribution in community-based Payment for Environmental Services interventions: A case study from Menabe, Madagascar[END_REF][START_REF] Martin | Measuring effectiveness, efficiency and equity in an experimental Payments for Ecosystem Services trial[END_REF][START_REF] Combe | Instruments Économiques et Protection de La Biodiversité : Analyse Juridique Des Mécanismes de Compensation Écologique et de Paiements Pour Services Environnementaux[END_REF]. The most important factor is the crowding-out effect, where a sentiment of injustice is created among those who were already behaving virtuously before the introduction of a PES, potentially leading 110 to ecological blackmail, where affected FES providers threaten to cease their FES provision in order to force financial compensation [START_REF] Binder | Payment for Environmental "Self-Service": Exploring the Links Between Farmers' Motivation and Additionality in a Conservation Incentive Programme in the Bolivian Andes[END_REF][START_REF] Ezzine-De-Blas | Payments for Environmental Services and Motivation Crowding: Towards a Conceptual Framework[END_REF]. In consequence, as [START_REF] Karsenty | Chapitre 5 -Du mésusage des métaphores. Les paiements pour services environnementaux sont-ils des instruments de marchandisation de la nature ?[END_REF] were able to show in two case studies in Central America, it is not always 115 possible to pursue strict compliance with additionality restrictions. In the first case it was decided already in advance to exclude additionality from the PES scheme, so that the risk of environmental blackmail that may have been formulated by those excluded would be avoided. In the second case, additionality 120 was initially enforced so that compensation was only granted for newly established plantations. The business-as-usual suppliers then threatened to chop down their preexisting trees in order to become eligible, which led to the removal of the additionality criterion from the project. This shows that also strict 125 compliance with additionality restrictions can lead to perverse behaviour, which in turn forces a relaxation or complete abolishment of additionality requirements. However, it is important to consider the differences between countries, as the socioeconomic context in France, for instance, is different from that of 130 these two cases. In this sense, [START_REF] Muradian | Reconciling theory and practice: An alternative conceptual framework for understanding payments for environmental services[END_REF] argues for consideration of PES within a broader institutional context, where equity is considered together with efficiency, a context which best corresponds to reality in the policy fields concerned.

Besides economic additionality, regulatory additionality, i.e.,

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going beyond existing regulations, must likewise be accounted for [START_REF] Karsenty | The Economic and Legal Sides of Additionality in Payments for Environmental Services: The Economic and Legal Sides 1035 of Additionality in Payments for Environmental Services[END_REF]. Simply rewarding compliance with environmental legislation risks complicating regulatory enforcement where no financial incentive is provided (Karsenty et al., 2014). The forest management measures we consider in 140 this study are not in conflict with regulatory additionality, as they are complementary to legal requirements.

Equity and gender

Many experiments have shown that women are more likely to be inequity averters opting for egalitarian compensation, while 145 men tend to be surplus maximisers [START_REF] Andreoni | Which is the Fair Sex? Gender Differences in Altruism*[END_REF]Kamas andPreston, 2012, 2015). Other studies show that men are more receptive to extrinsic incentives than women, who are generally more altruistic [START_REF] Brañas-Garza | Gender differences in altruism on Mechanical Turk: Expectations and actual behaviour[END_REF]. Thus we expected females to prefer equity over strict additionality.

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We also assumed that respondents with a closer connection to the forest would have a different stance on additionality. Beyond that, we did not have any prior hypotheses about French citizens' preferences for either strict additionality adherence or equity, as we were not aware of any empirical studies on this 2.4. The role of additionality -some empirical evidence [START_REF] Vedel | Forest owners' willingness to accept contracts for ecosystem service provision is sensitive to additionality[END_REF] show that the willingness to accept (WTA) among Danish forest owners for PES programs that increase biodiversity and recreational value for society depends strongly on additionality. For the extension of forest access, for example, those who had already opened their forest to the public had a WTA of around 0, while those who did not demanded 28€ per hectare per year for full access. However, on the side of ES buyers, Blanco et al. (2021) show in an experimental context that additionality leads to higher cost efficiency but not necessarily to a higher provision of public goods. Consequently, these two studies seem to indicate that there is a divergence between the WTA of ES providers and the WTP of ES buyers on the aspect of additionality.

Donations versus mandatory payments

To ensure incentive compatibility, there is a general consensus in the economic valuation literature that the payment instrument should be a mandatory one [START_REF] Carson | Incentive and informational properties of preference questions[END_REF][START_REF] Johnston | Contemporary guidance for stated preference studies[END_REF]. This eliminates the possibility of free-riding inherent to donation-based mechanisms [START_REF] Champ | Contingent valuation and incentives[END_REF]. From a theoretical point of view, it is therefore not guaranteed that a donation-based valuation study will provide the true economic welfare value of ES [START_REF] Kotchen | Reconsidering donations for nonmarket valuation[END_REF]. However, in some situations, voluntary donations may be the only acceptable payment vehicle among respondents [START_REF] Boyle | Contingent valuation in practice[END_REF], and real-world mechanisms for the provision of ES are often based on voluntary contribution and crowd-funding [START_REF] Bouma | Mind the gap: Stated versus revealed donations and the differential role of behavioral factors[END_REF].

Although the sensitivity of WTP to the payment vehicle is not a novel subject, a review of the existing literature indicates a need for a more thorough understanding of this matter: [START_REF] Ureta | Estimating residents' WTP for ecosystem services improvement in a payments for ecosystem services (PES) program: A choice experiment approach[END_REF] show that understanding respondents' preferences for the payment vehicle tends to support the implementation of a PES. [START_REF] Sonnenschein | Is one carbon price enough? Assessing the effects of payment vehicle choice on willingness to pay in Sweden[END_REF] examine policy-relevant differences in WTP between different payment vehicles for air and car travel: mandatory payments generate higher WTP than voluntary payments. This sensitivity has also been tested in the specific sector of forestry, confirming the specific role of payment vehicles on WTP indicators, reaching similar conclusions [START_REF] Weller | Preferences for forest structural attributes in Germany -Evidence from a choice experiment[END_REF][START_REF] Kreye | Does policy process influence public values for forest-water resource protection in Florida?[END_REF]. However, in a choice experiment on climate policy issues, [START_REF] Svenningsen | Testing the effect of changes in elic-1140 itation format, payment vehicle and bid range on the hypothetical bias for moral goods[END_REF] show that differences in WTP across samples have to be attributable to either the bid range or the elicitation format, with the payment vehicle having little or no effect on WTP.

In our study, we examine the WTP for a mandatory tax versus voluntary donations, the latter being inspired by a growing number of PES crowdfunding schemes [START_REF] Frey | Crowdfunding -revealing preferences for environmental goods[END_REF][START_REF] Wehnert | Crowdfunding for a sustainable future: A systematic literature review[END_REF] and initiatives to internalise positive forest externalities [START_REF] Chakrabarti | Making markets for private provision of ecosystem services: The Bobolink Project[END_REF][START_REF] Li | The performance of multi-type environmental credit trading markets: Lab experiment evidence[END_REF][START_REF] Rabotyagov | Testing the design variables of ECOSEL: A market mechanism for forest ecosystem services[END_REF]. [START_REF] Carlsson | Do hypothetical and actual marginal willingness to pay differ in choice experiments?: Application to the valuation of the environment[END_REF] compared real donations for environmental projects with WTP estimates via a hypothetical CE, and found no significant differences. We hypothesised that consumer WTP is lower for voluntary payment schemes than for mandatory ones, but not zero, so that WTP values in the context of a hypothetical voluntary payment scheme are not a suitable means for revealing a population's perception of the economic value of ES, but nevertheless provide a guide to the creation of voluntary PES markets.

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We also assumed that participants who anticipated the possibility of free-riding would have a lower WTP than those who did not [START_REF] Wiser | Using contingent valuation to explore willingness to pay for renewable energy: A comparison of collective and voluntary payment vehicles[END_REF].

Material and methods

Questionnaire 220

Our analysis is based on a questionnaire sent to a representative sample of the French population. The questionnaire comprises five parts, where the first part includes questions on the socio-demographic characteristics of the respondent and also served to define the sample quota. The second and main part 225 of the questionnaire was a discrete choice experiment (CE), a widely used method in environmental valuation that serves to estimate preferences for project or policy attributes [START_REF] Mariel | Environmental Valuation with Discrete Choice Experiments: Guidance on Design, Implementation and Data Analysis[END_REF]. The CE is formulated as a choice between different policies supporting forest owners in restoring degraded 230 or climate-vulnerable forests, and is described in the following subsection. The third part of the questionnaire contains followup questions designed to help us understand the rationale behind respondents' decisions in the CE, along with some supplementary questions on preferences for forest restoration policies.

235

This part also includes a question designed to detect free-riding concerns and altruistic behaviour, in the same vein as [START_REF] Wiser | Using contingent valuation to explore willingness to pay for renewable energy: A comparison of collective and voluntary payment vehicles[END_REF]. The fourth and fifth parts include some questions on the respondents' attitudes and some additional socio-demographic characteristics.

240

To test whether there are differences in preferences and WTP between a mandatory and a voluntary payment vehicle, we created two versions of the questionnaire, to which each of the participants was randomly assigned. In the first version, the CE was formulated as a choice between public policies, where 245 participants were told that every French household would have to pay the same financial contribution if a policy was implemented, while in the second version, the CE was formulated as a choice of donation, where participants were told that the contribution was voluntary. The two versions of the questionnaire 250 are available in the supplemental material.

Choice experiment

The CE was conducted in the present French context, where large forest areas are facing deterioration due to droughts and insect infestations, along with current discussions and initia-255 tives to support forest restoration and adaptation to climate change (agriculture.gouv.fr, cnpf.fr). While most citizens have probably heard of or seen forest stands with dead spruces, they are less likely to be aware of the initiatives and discussions supporting forest restoration and adaptation. Therefore, we ex-260 plained this matter in an introductory text, which can be found in the questionnaire documentation.

In French forestry, owners of one or more parcels of land of 25 hectares or more are required to draw up a management plan (Article L.312-1, French Forestry Code) which must be approved by the administration. This document constitutes a road map for management of the forest for a period of 10 to 20 years. Otherwise, the forest is subject to the requirements of the administrative authorisation system (Article L.312-9, French Forestry Code), i.e., all logging must be authorised by the administration, except for wood for domestic use. A management plan is voluntary for an ownership of less than 25 hectares. A plan allows the owner to benefit from tax advantages related to the forest, access to public aid and certification of sustainable management. For an area of less than 10 hectares, it is also possible to voluntarily develop a management plan, which is approved by the administration. As property rights in France are generally highly protected, the choice of silvicultural measures depends largely on the individual owner or manager. There is no legal obligation in terms of species composition (except species classified as invasive), public accessibility, conservation of habitat trees or carbon sequestration. All choice experiment attributes are designed in a way so that legal additionality is ensured.

Choice experiment attributes

The six attributes and their levels describing the choice alternatives in the final version of the questionnaire are listed in Table 1 and are explained below. To ensure that the attribute explanations were read carefully, we added a question related to the respective attribute after each explanation. Participants were able to retrieve the attribute descriptions again on each choice card. The formulations of the attribute descriptions presented to the respondent in the questionnaire are documented in the questionnaire.

Forest type refers to the composition of species planted in a reforestation project. We included two options: (1) Mixed stand, described as very robust to climate change and composed of rather slow-growing native deciduous and coniferous species; and (2) Douglas fir, described as a fast-growing, high quality timber-producing and climate change-robust pure stand (single species stand). We emphasised that Douglas fir is not native to France. We hypothesised that the majority of respondents would prefer mixed stands. Annual CO 2 uptake described the additional CO 2 uptake that a respective reforestation scenario causes in the first 30 years after replanting in comparison to a reference scenario in which no active reforestation is being conducted. We included four levels: 0, 5, 10 and 15 tCO 2 per hectare per year. Linked to the different growth performances we had modelled beforehand, the possible annual sequestration values per hectare were set at 0-10 tCO 2 for the mixed stand and at 5-15 tCO 2 for the Douglas fir pure stand. The relatively large variation in sequestration values is rooted in the great diversity of site productivity in French forests. We hypothesised that respondents would prefer higher carbon sequestration values.

Recreation defined whether a funded forest owner is obliged to provide public access for non-motorised visitors. Two options were provided: (1) Accessibility ensured, and (2) Accessibility not ensured. The latter does not necessarily mean that the forest is inaccessible to the public. In fact, about 70 % of French private forests are currently accessible to the public, although forest owners in France are allowed to enclose their forests [START_REF] Agreste | Enquête sur la structure de la forêt privée en 2012[END_REF]. We hypothesised that participants would prefer funded forests to be guaranteed accessible.

Eligibility addressed whether consumers prefer efficiency 325 or rewards for sustainable behaviour, and more specifically, whether only strictly additional reforestation projects should be eligible or also those that were already managed at the owner's expense according to criteria meeting the PES guidelines before the PES was implemented. To facilitate understanding, we used 330 the levels (1) Future projects only and (2) Both past and future projects and explained that the former would lead to larger areas being covered with the same budget, while the latter would be regarded as a reward for sustainable behaviour. We did not have a hypothesis as to whether respondents would favour addition-335 ality or equity, but we assumed that such preferences would be determined by the respondents' socio-economic characteristics.

Biodiversity was related to the conservation of habitat trees. Two levels were given: (1) Additional habitats and (2) No additional habitats, where the former meant that at least three (the 340 French FSC standard is two trees and a legal minimum does not exist) habitat trees, defined as old living or dead trees, must be conserved per hectare of forestland. We hypothesised that participants would prefer habitat trees to be preserved in the forest.

Contribution to forest fund defined the annual contribution 345 per household (tax version) or donation (donation version) to be paid for a given project during ten years. Seven levels were considered: 4, 9, 15, 24, 34, 46, 60 and 80€. In the donationbased version we included the option that the donation commitment could be cancelled each year, as we considered that 350 most respondents would be unfamiliar with donations involving multi-year commitments and therefore that their choices would not truly reflect preferences for forest restoration. The values are based on cost estimates for reforestation projects, assuming that each French household pays into the fund and that 355 45,000 hectares are reforested. We expected consumers to try to keep their financial contribution as low as possible, and that the mandatory payment mechanism would yield higher WTP values than the voluntary mechanism. To ensure that our questionnaire was easily understandable to the respondents, and in particular that the CE attributes were relevant and understandable, we organised a focus group with participants not familiar with forestry or related fields. A key finding was that a location attribute (local versus no spatial constraint for restoration projects) was not considered important; it was thus omitted. It was also suggested that we should clarify that if a project criterion is that the forest should be accessible to the public, this should not include motorised access. Alongside these main comments, many suggestions were made on wording and layout, e.g., on the use of pictograms in the CE, which were taken into account in the subsequent revision of the questionnaire. We also ran two pilot trials, each including 200 responses.

We tested for scope sensitivity 2 by dividing respondents into two groups, where participants were told that either 45,000 hectares (Group A), or 90,000 hectares (Group B) would be restored with the fund. We expected higher WTP values for group B.

Statistical design

The choice tasks for the CE were obtained from an updated experimental design which was maximised for D-efficiency using the Ngene software (ChoiceMetrics, 2021), assuming a multinomial logit model. To set up the first pilot trial, we used priors (assuming only signs) for the attribute coefficients, which were based on our experience from the focus group and the literature. Based on these initial estimates, we designed a second pilot trial with updated priors and constraints. These estimates were then used to develop the design for the final launch. Here, the Carbon attribute was restricted to 0, 5, or 10 3 for the Mixed stand and 5, 10, or 15 3 for the Douglas fir.

Our design had two hypothetical alternatives and one optout option (not supporting forest restoration). An example of a choice card set is given in Figure 1. In total, we had 16 choice sets, which were divided into two blocks by Ngene, and respondents were randomly assigned to one of these two blocks.

Survey implementation

The data collection was conducted in May 2022 and targeted the whole French population. The questionnaire was distributed by the pooling agency Kantar France which samples participants from a standing panel. To ensure that the survey was representative, we set quotas for age groups, professions and gender, drawing on official French population statistics, on the basis of which participants were included in or excluded from 405 the survey. We were able to meet the quota as planned.

2 Scope sensitivity means that people's WTP increases when the quality or quantity of a non-market good increases [START_REF] Dugstad | Scope Elasticity of Willingness to pay in Discrete Choice Experiments[END_REF] 3 Annual CO 2 sequestration in tons per hectare 3.4. Econometric modelling

Data cleaning

To exclude 'speeders', we filtered out observations where the response time was less than 50 % of the median. A conditional 410 question was added to identify protest responses and was only shown to those who had always opted out in the choice experiment. Following [START_REF] Mariel | Environmental Valuation with Discrete Choice Experiments: Guidance on Design, Implementation and Data Analysis[END_REF], we then sorted all 'always-opt-out' responses into 'protest zeros' (e.g., "I did not understand the choices") and 'valid zeros' (e.g., "I prefer the 415 natural regeneration of forest stands.") and excluded the former from choice model estimation. To avoid overestimating WTP values, we also excluded respondents who did not consider the payment attribute important ('non-price sensitive'), as well as those who reported that they did not believe that the 420 survey would have an impact on real policy, i.e., those who did not believe that their decisions would have consequences ('non-consequential') [START_REF] Vossler | Truth in Consequentiality: Theory and Field Evidence on Discrete Choice Experiments[END_REF]. To test how the data cleaning influenced the results, we run a model with the unfiltered data set (Table A.10). 425

Modelling framework

The modelling is based on the random utility model (RUM) framework, which is a common approach in the analysis of discrete choice data [START_REF] Mcfadden | Conditional logit analysis of qualitative choice behavior[END_REF]. This model assumes that respondents select their most preferred alternative among the 430 I alternatives offered. The alternative that maximises the perceived utility, u nit , for respondent n in choice situation t is given by Equation 1:

u nit > u n jt , ∀ j i and where u n jt = X n jt β + ε n jt (1)
where j = 1, ..J, t = 1, ..T , and vector X n jt is a row vector of K attributes characterising alternative j, β is a column vector of K 435 parameters associated with these attributes, and ε i j is an error term that captures the utility unobserved by the researcher.

In order to fully exploit the panel structure of our choice data and to account for individual preference heterogeneity, we estimated a flexible mixed multinomial logit (MMNL) 440 model [START_REF] Revelt | Mixed Logit with Repeated Choices: Households' Choices of Appliance Efficiency Level[END_REF]. This allowed us to estimate individual-specific preference parameters and to account for non-standard substitution patterns between choice alternatives (relaxing the assumption of independence from irrelevant alternatives (IIA)), modelling preference heterogeneity as continu-445 ous distribution. We used an unrestricted model that allows for correlated random parameters so that both behavioural phenomena and scale heterogeneity are captured and biased utility estimates are avoided [START_REF] Mariel | A More Flexible Model or Simply More Effort? On the Use of Correlated Random Parameters in Applied Choice Studies[END_REF]. The mixed logit unconditional probability of respondent n choosing the se-450 quence of alternatives I = {i 1 , ..., i T } is given by Equation 2:

P n (I, θ) = T t=1 exp β ′ X nit j exp β ′ X n jt f (β θ) dβ (2)
where θ is a matrix of mean and variance-covariance for the distributions of the random parameters, and f is the density function for the random parameters, β . The corresponding log likelihood can be maximised using maximum simulated likelihood 455 ). For generating random draws we used the Modified Latin Hypercube Sampling (MLHS) method proposed by [START_REF] Hess | On the use of a Modified Latin Hypercube Sampling (MLHS) method in the estimation of a Mixed Logit Model for vehicle choice[END_REF]. This approach avoids unwanted correlation patterns, as generated, for example, by Halton draws, as well as larger simulation errors in the choice probabilities implied by uneven covering of the integration area, which can be caused by the randomness in the sequences when employing simpler pseudo-random draws, such as the pseudo Monte Carlo method [START_REF] Hess | On the use of a Modified Latin Hypercube Sampling (MLHS) method in the estimation of a Mixed Logit Model for vehicle choice[END_REF]. For each model, a number of 3000 MLHS draws were employed. In all models we assumed a normal distribution for the nonprice preference coefficients and a negative log-normal distribution for the payment coefficient. To control for the order effect, we included three alternative specific constant (ASC) values so that the two choice scenarios were considered separately. The ACS for opting out was fixed to 0. Each model was estimated multiple times, with the first run based on assumed starting values for the utility coefficients, and the subsequent runs based on the starting values of the corresponding previous estimation.

We selected the final model when we could not find significant changes in the model parameters as compared to the respective previous estimation. All variables included in the models are displayed in Table 4.

Preference-space models

We estimated three MMNL models in preference space, starting (1) with a base model without interaction terms. (2) For investigating the impact of socio-demographic variables on respondents' marginal utility with respect to additionality, we specified a model with interaction terms: Following our ini-tial hypotheses, we included gender (female) as well as respondents who themselves or their family own forests in France (forestowner ind fam), and those who feel very well informed about forests (very informed) as interaction terms in our model. The latter two groups were used as proxies for those partici-490 pants who have a closer connection to the forest. The interactions were carried out with the attribute variable additionality.

(3) To allow for an interpretation of the correlations of the base model, we followed [START_REF] Mariel | Interpreting correlated random parameters in choice experiments[END_REF] and estimated a model with negative choice attributes reversed. We then inter-495 preted only negative correlations as caused by behavioural phenomena. Here we interpreted those inversely that changed sign due to the previous reversal of the originally negative choice attributes. The corresponding model results can be found in Appendix A (Table A.9) 500

WTP-space models

To compare the marginal willingness to pay (mWTP) between the donation-based and tax-based payment vehicle, as well as the impact of altruism and free-riding concerns associated with a voluntary payment mechanism, we applied the 505 so-called WTP-space method. This allows for a direct derivation of the mWTP distributions, taking into account the heterogeneity in mWTP between respondents [START_REF] Train | Discrete Choice Models in Preference Space and Willingness-to-Pay Space[END_REF][START_REF] Scarpa | Utility in Willingness to Pay Space: A Tool to Address Confounding Random Scale Effects in Destination Choice to the Alps[END_REF]. We reformulated equation (1) to obtain [START_REF] Train | Discrete Choice Models in Preference Space and Willingness-to-Pay Space[END_REF]:

510 u n jt = α n (-X pn jt + X * n jt c n ) + ε n jt j = 1, .., J t = 1, ..., T (3)
where c n = β * n /α n and α n is the parameter on the payment variable for individual n, β * n is the vector of coefficients of the attributes variables, X * n jt without the payment variables, X pn jt . Note that this implies that the WTP (= c) is estimated directly and we also avoid the problem of unstable marginal WTP estimates based on ratios of parameters estimated in preferencespace models [START_REF] Thiene | Deriving and Testing Efficient Estimates of WTP Distributions in Destination Choice Models[END_REF].

The WTP-space models were estimated with sub-samples of the data set: The first two models were each estimated using only observations from the tax-based version and the donationbased version, respectively. For the other two models, only the donation-based version was used, and two further sub-samples were drawn, one containing only people who showed altruistic behaviour and the other comprising respondents who said they had reduced their WTP due to the possibility of free-riding. We then used two-tailed Student's t-tests to test for significant differences in mean WTP values between each pair of models. If either the variances or the sample sizes were significantly different between the pairs, we instead employed Welch's t-test. It should be borne in mind that potential differences may be due to (random) variations between observations in the different samples rather than to the payment vehicle or the respondent's attitude towards altruism and free-riding.

Due to the reduced sample size, we did not incorporate correlations between the choice parameters in the last two models, as otherwise the estimations would become unstable. 2 shows the sample used for estimation after data cleaning (subsubsection 3.4.1). We note that 43 % of respondents did not finish the questionnaire. This figure also includes respondents who were screened out due to the specified quotas. The relatively high proportion of drop-outs is most likely due to the screening process: It was difficult for the survey company to complete the quotas with young respondents and in the social professional categories of self-employed, managers and civil servants. As a result, many respondents who belonged to already completed groups were actively removed after the first out data cleaning, respondents' preferences differed slightly, but the observed signs and significance levels were the same (Table A.10) as compared to the base model estimated on the cleaned data set (Table 5).

Results

Respondent preferences 555

The results are largely in line with our preliminary assumptions: The price attribute is negative, respondents favour mixed forests over Douglas fir plantations, and prefer higher carbon uptake, increased biodiversity and guaranteed forest accessibility (Table 6). In all our models, as indicated by positive 560 alternative-specific constants, asc.alt1 and asc.alt2, which are constants included in the utility function for the hypothetical alternatives, respondents show a clear preference for one of the proposed scenarios relative to the status quo alternative. Furthermore, we demonstrate a clear preference for FES provi-565 sion, including recreation, biodiversity and carbon sequestration, as the corresponding coefficients are significantly positive in all models. However, these preferences are not homogeneous within the population, as indicated by the significant standard deviations in both the preference-space and WTP-space models 570 Table 4: Choice-specific and socio-demographic variables included in the models. More details are displayed in Table 3 and8.

Variable Description

Choice-specific f orest type Mixed forest = 1, 0 otherwise carbon Continuous variable ranging from 0 to 15 access Forest guaranteed publicly accessible = 1, 0 otherwise addition Strictly additional = 1, 0 otherwise biodiversity At least three habitat trees per hectare = 1, 0 otherwise Individual-specific f emale Female = 1, 0 otherwise f orestowner ind f am Forest owner, and/or family member owns forest = 1, 0 otherwise very in f ormed

Respondents who considered themselves very informed about forests = 1, 0 otherwise (Table 5, 6 and7). The unrestricted models also show significant correlations between a number of attribute coefficients.

However, given the model-immanent limitations in distinguishing between behavioural effects and scale heterogeneity, we could not distinguish for each of these whether they belonged to one or the other category. We could, however, identify positive behavioural correlations between forest type and additionality, biodiversity and additionality, and negative correlations between carbon and access, carbon and biodiversity, and access and biodiversity (Table A.9).

Additionality

A fairly large proportion of respondents (35 %), when asked directly, expressed a preference for rewarding sustainable behaviour over efficiency (additionality), while 55 % rated efficiency as more important and 10 % preferred neither option (Table 8). However, in both the base model and the additionality model, respondents show a significantly negative utility for additionality, indicating a preference for rewarding sustainable behaviour over economic efficiency in the choice experiment (Table 5). In line with our assumptions and the literature, we can show that respondents who feel very well informed about forests and/or own forests themselves or have a family as owners tend to prefer additionality, while female respondents seem to have an even clearer preference for rewarding sustainable behaviour as compared to the population as a whole. It should be noted, however, that the confidence level for the variable very informed is only 90 % (Table 5).

WTP in tax-based versus donation-based payment vehicles

Contrary to our original hypothesis, the mWTP values modelled with the WTP-space models are not systematically different between tax-based and donation-based subsets of the questionnaire (Table 6). Only the WTP for the choice attribute biodiversity differed significantly between the samples, being higher for the tax-based version.

By separately modelling the WTP of individuals who reported (a) altruistic behaviour and (b) those who stated they had reduced their WTP due to the possibility of free-riding (Table 8) in a WTP space model (Table 7), we show that the altruists do in fact have significantly higher WTP for forest type and carbon. The attribute biodiversity was only significant for 610 the altruistic group, while additionality was only significant for the free-riding group (Table 7). The only WTP value which is slightly higher in the group concerned by free-riding is corresponding to forest accessibility (access).

Scope sensitivity 615

We tested for scope sensitivity by adding interactions between attributes and a dummy variable for participants who were told that the project would cover 90,000 hectares. Since we did not find a significant interaction (not reported here), we cannot reject the absence of scope sensitivity. One should there-620 fore be careful using our results for a welfare economic analysis if it is aimed at estimating the total WTP for forest restoration by the French population.

Discussion

Preferences and WTP for the restoration of French forests 625

In this study, we assessed the French population's preferences and WTP for forest restoration and adaptation projects in French private forests. We find that both preferences and WTP are highly dependent on policy formulation, i.e. the definition of what types of projects are eligible for financial sup-630 port. In line with our initial expectations, the population on average prefers mixed forest stands with native species over Douglas fir plantations. Additionally, projects with a high degree of carbon sequestration, which provide open access for recreational activities and preserve habitats for wild plants and ani-635 mals, are favoured. However, whether projects should be additional or should also include compensation for existing restoration projects is less clear. We also find significant preference heterogeneity for all forest project characteristics. As a consequence, crowdfunding-based PES companies can benefit from 640 a diversified portfolio of forest projects: Although the average donor prefers a native mixed forest, there is, e.g., a (small) market segment favouring fast-growing species no matter their origin.

The WTP for supporting PES projects in the tax-based subset 645 ranges from 23.43€ to 76.58€ per household per year, with the lowest value for a project with Douglas fir, an additional annual sequestration performance of 5 tCO 2 per hectare, no guaranteed forest access, and without habitat tree requirements. The highest value was achieved by projects with mixed stands, an additional annual sequestration performance of 10 tC0 2 per hectare, guaranteed public access and preserved habitat trees. The corresponding values for the donation-based subset are 25.06€ and 73.30€ per household per year. However, as our bid vector (4-80€) was oriented towards cost estimates for plausibility reasons, our WTP estimates may underestimate French consumers' true WTP.

Comparison with existing WTP estimates

In a survey on preferences for forest management alternatives affecting the recreational attractiveness of state forests in Finland, the estimated household WTP is at a similar level to that in our study [START_REF] Juutinen | Estimating the benefits of recreation-oriented management in state-owned commercial forests in Finland: A choice experiment[END_REF]. For example, households would pay 34-43€ annually to increase the width of scenic buffer zones along rivers and lakes and 16-21€ to increase the number of managed courting grounds for capercaillies. Also based on a CE, [START_REF] Müller | The valuation of forest ecosystem services as a tool for management planning -A choice 1095 experiment[END_REF] estimates an annual household WTP of 32€ in Switzerland to support forest owners to establish stands with mixed tree species (deciduous and coniferous) compared to pure conifer stands. This largely corresponds to the 23-27€ household WTP we find in the present study for mixed forests compared to Douglas fir stands. The total household WTP for forest programs promoting recreation, containing mixed tree species and showing no visual impacts of forest exploitation ranges from 107€ to 162€, depending on the region. [START_REF] Brey | Estimation of forest values using choice modeling: An application to Spanish forests[END_REF] estimated the WTP for increasing forestland 675 by 10 % in Catalonia through afforestation, applying a CE and focusing on the mWTP of forest attributes. They find an annual mWTP for allowing picnic and mushroom collection of 6€ and 13€ per individual, respectively. The WTP for storing 68,000 tC0 2 through afforestation is estimated at 12€ per year per per-680 son. In a valuation of different forest management scenarios for Aleppo pine forests in Catalonia, [START_REF] Varela | Social demand for multiple benefits provided by Aleppo pine forest management in Catalonia, Spain[END_REF] estimate the annual WTP per adult individual at 52-70€, depending on the scenario evaluated (focus on biodiversity, fire prevention, etc.), corresponding to annual hectare values of 683-2044€.

Scope sensitivity

We could not find a sensitivity to scope among the participants. We believe that this is due to (1) the difficulty of imagining area sizes on a regional level, and (2) the lack of a reference to compare with. This result also casts doubt on the per-hectare 690 WTP estimates of other CEs in the field of ES valuation investigating the consumer perspective, which were not specifically tested for scope sensitivity. This shows that improvements are called for in the currently established methodology. This finding seems particularly relevant because, as shown for 695 instance by [START_REF] Dugstad | Scope Elasticity of Willingness to pay in Discrete Choice Experiments[END_REF], unlike for Contingent Valuation (CV) studies, explicit testing for scope sensitivity is un- for large projects or entire countries, or for fiscally uniform areas in tax-based payment systems, which can then be used as direct policy recommendations. In a tax-based payment system, such total WTP values in a population could then be used to calculate area sizes that could potentially be treated with a corresponding PES system, if WTA values are available from FES providers. Additionally, in a donation-based payment mechanism, it is questionable whether assessing per-hectare values is truly necessary to aid in the establishment of markets for PES, as potential donors evidently lack the sophisticated ability to perceive spatial dimensions. In the context of this work, a follow-up study assessing per-hectare WTA values of forest owners for the same attributes could allow the estimation of total area sizes that could be treated with a potential tax or donation PES scheme in France.

The role of payment vehicles and free-riding concerns

We initially expected the possibility of free-riding in donation-based payment schemes to reduce consumers' WTP for FES. However, our results show that there is no systematic difference in the distribution of individual WTP between participants in the donation-based version compared to the taxbased version. This is in line with [START_REF] Svenningsen | Testing the effect of changes in elic-1140 itation format, payment vehicle and bid range on the hypothetical bias for moral goods[END_REF], who show that for the WTP for FES, especially those considered as rather "distant" by participants, the payment vehicle is of minor importance. In our case, this is probably due to the fact that, in their own words, only about 11 % of respondents had their WTP negatively affected by the possibility of free-riding. About 40 % responded that they do not care about the behaviour of others, they just want to contribute "something positive" themselves, and 28 % even said that it would be important for them for others to benefit from their contribution because they "want to contribute to the common good", suggesting an explicit altruistic attitude. We show that the group concerned about free-riding actually has a significantly lower 735 WTP than those who indicated altruist intentions (t-tests of the mean mWTP estimates). As opposed to several previous studies in which women were found to be more altruistic (Kamas andPreston, 2012, 2015;[START_REF] Brañas-Garza | Gender differences in altruism on Mechanical Turk: Expectations and actual behaviour[END_REF], we find a slightly higher share of males among the altruistic and free-740 riding-concerned respondents (Table 3). This is consistent with [START_REF] Andreoni | Which is the Fair Sex? Gender Differences in Altruism*[END_REF], who find that men are more inclined to be either perfectly selfish or perfectly selfless, they are slightly over-represented in both groups.

Similarly to [START_REF] Faber | Homo oeconomicus and homo 985 politicus in Ecological Economics[END_REF], [START_REF] Ojea | Altruistic, egoistic and biospheric values in 1105 willingness to pay (WTP) for wildlife[END_REF] 745 and many other studies in the field of ecological and environmental economics, our results challenge the assumption that a lack of incentive compatibility triggered by the possibility of free-riding significantly reduces consumers' WTP for public goods and common pool resources in an ES-related context.

750

We even found evidence that an awareness of other people benefiting from a donation can actually increase certain consumers' WTP, suggesting an altruistic attitude in sections of French society. This finding is consistent with Svenningsen and Jacobsen (2018), who applied both stated-hypothetical and revealed 755 preference methods and argue that concerns about free-riding would lower the WTP in a revealed preference context, while altruistic behaviour would increase it.

Another way of interpreting this would be to follow the argument of [START_REF] Nyborg | Homo Economicus and Homo Politicus: Interpretation and aggregation of environmental values[END_REF] and [START_REF] Faber | Homo oeconomicus and homo 985 politicus in Ecological Economics[END_REF], who distin-760 guish between two roles that a questionnaire participant can play: a) The classical 'homo oeconomicus' and b) the 'homo politicus', whereby the former mainly tries to maximise his personal (short-term) utility and the latter acts from the perspective of a "good citizen" who considers the common good when 765 making decisions. Nyborg argues that stated preference methods aimed at ES valuation specifically address the role of homo politicus, as such studies are embedded in an ethical/political context related to public goods and common pool resources, which by definition only benefit ES buyers in a non-exclusive 770 and indirect way. This is likely to result in higher WTP values compared to those that may be indicated from the homo oeconomicus' perspective. Our follow-up question (Table 8) would thus not only reveal the respective participant's attitude towards free-riding and altruism, but also which role he or she played when answering the questionnaire, whereby both aspects are barely distinguishable and probably linked with one another. [START_REF] Faber | Homo oeconomicus and homo 985 politicus in Ecological Economics[END_REF] identified a number of external conditions required for a person to adopt the role of homo politicus, such as a participatory and decentralised structure of political decision-making and the existence of a functioning public capable of exerting control upon the government. It is therefore important to bear in mind that the role someone plays in such a study--and also in real-life decisions--is likely to be related to the context, e.g., the type of political-economic system in which the decision-maker is situated, as both estimated and true WTP values may be influenced by this. As a result, we were able to provide further evidence that the payment vehicle is of little importance to consumers' WTP for FES, and we suggest that this indifference can be explained by respondents taking a "good are significantly more likely to be inequality-averters (Kamas andPreston, 2012, 2015;[START_REF] Brañas-Garza | Gender differences in altruism on Mechanical Turk: Expectations and actual behaviour[END_REF]. In contrast, owning forests, either as an individual or in the family, and feeling very well informed about forests, links to a preference for strict additionality adherence, while the remaining respondents are indifferent. This pronounced heterogeneity in consumer preferences also highlights that although PES is an economic and thus efficiency-oriented instrument, social and legal considerations cannot be disregarded in its design. Moreover, the fact that the majority of respondents prefer equity to additionality could indicate that consumers are more concerned with achieving a feel-good experience (warm glow) than with real environmental enhancements.

As [START_REF] Karsenty | The Economic and Legal Sides of Additionality in Payments for Environmental Services: The Economic and Legal Sides 1035 of Additionality in Payments for Environmental Services[END_REF] show, the feeling of being evicted from a PES scheme due to additionality requirements can lead to cases of blackmail on the part of FES providers, which may even cause an affected PES scheme to fail. Equity at the expense of additionality, on the other hand, leads to a multiplication of eligible FES providers, which ultimately reduces a PES scheme's economic efficiency. [START_REF] Vedel | Forest owners' willingness to accept contracts for ecosystem service provision is sensitive to additionality[END_REF], however, demonstrate that the WTA of forest owners for non-additional projects is close to zero. This, in combination with the high WTP for non-additional projects among parts of the population, can be interpreted as an opportunity to create win-win situations: Non-additional reforestation projects could be supported with relatively low funds so that large areas can be covered while avoiding major efficiency losses due to the lack of additionality. Here, however, it is essential not to lose too many funds in transaction costs.

Moreover, studies across various contexts suggest that peo-825 ple tend to chalk up their prosocial behaviour as a kind of social surplus in order to subsequently justify antisocial or morally dubious actions [START_REF] Monin | Moral credentials and the expression of prejudice[END_REF][START_REF] Merritt | The strategic pursuit of moral credentials[END_REF][START_REF] Brañas-Garza | Moral cleansing and moral licenses: Experimental evidence[END_REF][START_REF] Sass | Moral Self-Licensing and the Direct Touch Ef-1125 fect[END_REF][START_REF] Clot | Moral self-licencing and social dilem-955 mas: An experimental analysis from a taking game in Madagascar[END_REF][START_REF] Engel | A little good is good enough: Ethical consumption, 975 cheap excuses, and moral self-licensing[END_REF]. This so-called 'moral self-830 licensing dilemma' is particularly delicate for voluntary, nonadditional PES programmes, where the absence of an effective behavioural change on the part of FES providers could result in a net deficit of prosocial behaviour at the societal level. In this respect, one could consider requiring PES projects that fo-835 cus on carbon sequestration to always be additional, so that a net CO 2 emission increase caused by moral self-licensing in combination with non-additional carbon sequestration projects is avoided at the societal level.

Generally, if there is no strict additionality obligation, there 840 is a risk of environmental law losing its power, which can also lead to a logic of blackmail in remuneration. Thus, either way, there may be tensions and risks of blackmail, or even of net losses in FES supply. These PES-inherent moral dilemmas, which transcend technical issues, suggest the inclusion of stake-845 holder participation and interdisciplinary dialogue in their design process. Consequently, eligibility criteria should be specified on a case-by-case basis, rather than being dictated by onedimensional objectives or general consumer preferences.

Conclusion 850

We show that consumers are willing to pay for both additional and non-additional projects in tax-and donation-based PES schemes. Their respective preferences are heterogeneous for all attributes studied. Given consumers' rejection of additionality and their lack of spatial understanding, as we found 855 when testing for scope sensitivity, they seem to have difficulties--or little interest--in assessing the environmental effectiveness of PES projects. This may also imply that consumers' decisions are aimed at a feel-good factor (warm glow) rather than actual ecological enhancements. Thus, our study can be 860 interpreted as a call for stricter regulation of FES markets, especially when it comes to carbon sequestration projects where moral self-licensing could lead to a net increase in CO 2 emissions. However, given the pronounced altruistic attitude and high WTP for FES that we observed, this work also allows for 865 some optimism: Consumers seem willing to contribute financially to a greater supply of FES. In addition, the pronounced heterogeneity in consumer preferences allows for the establishment of diverse markets in which a wide variety of FES can be traded.

870

In light of these findings, we propose that further assessments are needed of the impact of warm glow, free-riding and altruism, and the moral self-licensing dilemma in tax-based and donation-based PES schemes in the context of additionality. We also suggest including real payments and identifying the WTA 875 of FES providers for the FES and eligibility criteria analysed in this work, so that appropriate spatial estimates of the areas potentially covered by a respective PES can be calculated.

Figure 1 :

 1 Figure 1: Example choice card

  685

  Methodology, Writing -original draft, Data curation, Formal analysis, Writing -reviewing and editing. Jens Abiltrup: Supervision, Resources, Conceptualisation, Investigation, Writing -original draft, Project administration, Validation, Writingreviewing and editing. Salomé Gorel: Writing -original draft.ness models and mechanisms for the sustainable supply of and payment for forest ecosystem services', under the umbrella of ERA-NET Cofund ForestValue (Horizon 2020 research and innovation program grant agreement Nº773324/ANR-19-SUM2-0001-04). Also, the UMR BETA is supported by a grant overseen by the French National Research Agency (ANR) as part of the 'Investissements d'Avenir' program (ANR-11-LABX-0002-01, Lab of Excellence ARBRE). In addition, funding was provided by the French National Association for Research and Technology (ANRT) (ANRT-2020/1360) and the Orion Program, a government grant administered by the ANR to support Oliver Frings' research internship (ANR-20-SFRI-0009).

Table 1 :

 1 Description of the DCE attributes and the respective levels.

	Attributes	Levels
	Forest Type	Mixed stand, Douglas fir
	Annual CO 2 uptake 0, 5, 10, 15 tCO 2 /ha/year
	Recreation	Accessibility ensured, accessibility
		not ensured
	Eligibility	Only future projects; both past and
		future projects
	Biodiversity	Extra habitats in the form of at least
		three habitat trees per hectare, no ex-
		tra habitats
	Payment	Annual financial contribution per
		household of 4, 9, 15, 24, 34, 46, 60
		or 80 euros

Table 2 :

 2 Data cleaning (more detailed description in subsubsection 3.4.1).

		#	%
	Total	4426	100
	Not completed	1905	43.04
	Completed	2521	100
	Speeders	340	13.49
	Protesters	64	2.54
	Non-consequential	247	9.80
	Non-price sensitive	392	15.55
	Sample used for analysis 1709	67.79
	No. of choices	41016 100
	Opt out choices	14043 34.24
	4.1. Data and respondents' characteristics
	Table

Table 3 :

 3 Descriptive statistics, showing percentages for the sample as compared to the French population statistics (Pop.)

		Response	Sample	Sample	Pop.
			[n]	[%]	[%]
		Age
		18-24	186	10.88	10.50
		25-34	244	14.28	14.44
		35-44	280	16.38	15.77
		45-54	308	18.02	16.40
		55-69	423	24.75	23.35
		older than 70	268	15.68	19.56
		Socio-professional categories
		Farmer, craftsman, manager,	541	26.39	28.1
		civil servant
		Employees and workers	481	28.15	28.10
		Pensioners and others	773	45.23	43.90
		Gender
		Female	896	52.43	52.35
		Male	805	47.10	47.65
		Did not identify as either	6	0.35	-
		Did not wish to answer	2	0.12	-
		Altruists (donation sample)
		Total	230	28.19	-
		Female	109	26.27	-
		Male	118	29.72	-
		Free-riding concerned (donation sample)
		Total	86	10.54	-
		Female	40	9.64	-
		Male	46	11.59	-
		page of the questionnaire. The survey population statistics are
	550	displayed in Table 3. When estimating an MMNL model with-

Table 5 :

 5 Preference-space MMNL base model without interactions and MMNL model for investigating the impact of individual specific variables on respondents' marginal utility with respect to additionality.

	Coefficient	Utility estimates (s.e.) base model Utility estimates (s.e.) additionality model
	asc.alt1	2.202 * * * (0.109)	2.211 * * * (0.105)
	asc.alt2	2.092 * * * (0.107)	2.101 * * * (0.104)
	f oresttype	0.842 * * * (0.073)	0.843 * * * (0.065)
	sd. f oresttype	1.410 * * * (0.089)	1.423 * * * (0.071)
	carbon	0.720 * * * (0.094)	0.703 * * * (0.006)
	sd. f oresttype.carbon	0.027 (0.017)	0.024 (0.083)
	sd.carbon	1.300 * * * (0.111)	1.291 * * * (0.074)
	access	0.386 * * * (0.065)	0.366 * * * (0.048)
	sd. f oresttype.access	-0.104 (0.089)	-0.116 * * * (0.078)
	sd.carbon.access	-0.063 (0.084)	-0.061 (0.079)
	sd.access	1.028 * * * (0.084)	1.015 * * * (0.069)
	addition	-0.256 * * * (0.051)	-0.123 * * * (0.028)
	sd. f oresttype.addition	0.076 (0.069)	0.080 (0.067)
	sd.carbon.addition	0.334 * * * (0.066)	0.338 * * * (0.064)
	sd.access.addition	0.182. (0.114)	-0.1617 * (0.078)
	sd.addition	0.576 * * * (0.083)	0.530 * * * (0.077)
	addition. f emale	-	-0.1219 * (0.072)
	addition.very in f ormed	-	0.155. (0.118)
	addition. f orest ownerind f am -	0.326 * (0.143)
	biodiversity	0.419 * * * (0.058)	0.413 * * * (0.047)
	sd. f oresttype.biodiversity	0.202 * (0.091)	0.189 * * * (0.065)
	sd.carbon.biodiversity	0.474 * * * (0.072)	0.475 * * * (0.068)
	sd.access.biodiversity	0.197 * * (0.078)	-0.215 * * * (0.072)
	sd.addition.biodiversity	-0.678 * * * (0.136)	-0.757 * * * (0.064)
	sd.biodiversity	0.399. (0.289)	0.203 * * (0.085)
	log.payment	-0.893 * * * (0.145)	-1.9170 * * * (0.121)
	sd.log. f oresttype.payment	-0.163 (0.275)	-0.066 (0.140)
	sd.log.carbon.payment	0.098 (0.513)	0.015 (0.073)
	sd.log.access.payment	0.384 (0.601)	0.211 * (0.093)
	sd.log.addition.payment	0.195 (0.767)	0.126. (0.081)
	sd.log.biodiversity.payment	0.954 * * (0.344)	1.937 * * * (0.120)
	sd.log.payment	1.711 * * * (0.112)	0.446 * * * (0.093)
	n individuals	1709	1709
	n choice situations	13640	13640
	n inter-individual draws	3000 (mlhs)	3000 (mlhs)
	n estimations	3	3
	Log-likelihood (final)	-10994.23	-10981.74
	Adj.Rho 2 vs equal shares	0.2644	0.2650
	Adj.Rho 2 vs observed shares	0.2184	0.2191
	AIC	22046.46	22027.49
	BIC	22264.56	22268.15
	. p<0.1; * p<0.05; * * p<0.01; * * * p<0.001

Table 6 :

 6 WTP-space MMNL models, one each for the split samples of tax-based and donation-based payment vehicles

	Coefficient	mWTP estimate (s.e.) for tax-based	mWTP estimate (s.e.) for donation-based
		(mandatory) payment vehicle [€/year]	(voluntary) payment vehicle [€/year]
	asc.alt1	22.190 * * * (1.448)	23.820 * * * (1.624)
	asc.alt2	21.065 * * * (1.481)	22.605 * * * (1.592)
	f oresttype	26.574 * * * (2.871)	23.283 * * * (3.421)
	sd. f oresttype	40.551 * * * (5.871)	42.168 * * * (4.300)
	carbon	1.804 * * * (0.292)	1.847 * * * (0.191)
	sd. f oresttype.carbon	1.244 * (0.616)	1.313 * * * (0.298)
	sd.carbon	2.989 * * * (6.874)	3.503 * * * (0.428)
	access	9.988 * * * (2.070)	10.778 * * * (2.703)
	sd. f oresttype.access	0.696. (0.499)	0.936 * * * (0.260)
	sd.carbon.access	0.049 (0.276)	-0.136 (0.422)
	sd.access	21.468 * * * (1.886)	18.565 * * * (2.963)
	addition	-1.215 (4.833)	-1.645 (1.839)
	sd. f oresttype.addition	3.579 (0.297)	0.312 (0.250)
	sd.carbon.addition	6.941 * * * (0.184)	0.571 * (0.289)
	sd.access.addition	1.810 (0.288)	-0.539 * * (0.202)
	sd.addition	12.244 * * (4.131)	12.851 * * * (2.426)
	biodiversity	14.784 * * * (3.226)	12.332 * * * (1.499)
	sd. f oresttype.biodiversity	1.371 * * (0.437)	1.398 * * * (0.285)
	sd.carbon.biodiversity	1.365 * * * (0.173)	1.898 * * * (0.247)
	sd.access.biodiversity	0.549 * * (0.225)	0.502 * (0.301)
	sd.addition.biodiversity	-0.752 (0.978)	-0.178 (0.329)
	sd.biodiversity	12.535 (13.610)	11.055 * (6.230)
	log.payment	-0.678 * * * (0.117)	-0.794 * * * (0.082)
	sd.log.payment	1.095 * * * (0.211)	1.262 * * * (0.121)
	n individuals	891	814
	n rows in database	7128	6512
	n inter-individual draws	3000 (mlhs)	3000 (mlhs)
	n estimations	4	4
	Log-likelihood (final)	-5803.18	-5267.55
	Adj.Rho 2 vs equal shares	0.2559	0.2604
	Adj.Rho 2 vs observed shares	0.2101	0.2133
	AIC	11654.35	10583.1
	BIC	11819.27	10745.85
	. p<0.1; * p<0.05; * * p<0.01; * * * p<0.001

Table 7 :

 7 WTP-space MMNL models, one for the split samples of respondents who reported contributing more (altruism) or less (free-riding) when considering that also non-contributors benefit from a corresponding PES programme. p<0.05; * * p<0.01; * * * p<0.001

	Coefficient	Altruism estimate (s.e.) [€/year]	Free-riding estimate (s.e.) [€/year]
	asc.alt1	25.945 * * * (2.683)	29.039 * * * (5.775)
	asc.alt2	25.766 * * * (2.590)	26.965 * * * (5.548)
	f oresttype	31.382 * * * (2.522)	9.011 * * * (1.725)
	carbon	1.689 * * * (0.187)	0.600 * * * (0.1601)
	access	14.228 * * * (2.689)	16.141 * * * (1.673)
	addition	-1.406 (6.602)	-3.102 * (1.699)
	biodiversity	10.068 * * (3.332)	1.863 (1.639)
	log.payment	-1.346 * * * (0.246)	-0.397. (0.265)
	sd. f oresttype	54.341 * * * (9.586)	31.798 * * * (1.548)
	sd.carbon	4.250 * * * (0.870)	3.977 * * * (0.4395)
	sd.access	24.288 * * * (7.262)	24.616 * * * (2.525)
	sd.addition	20.695 * * (8.440)	21.921 * * * (2.093)
	sd.biodiversity	23.989 * * * (4.043)	18.237 * * * (1.567)
	sd.log.payment	1.622 * * * (0.357)	1.545 * * * (0.2782)
	n individuals	230	86
	n choice situations	1840	688
	n inter-individual draws	3000 (mlhs)	3000 (mlhs)
	n estimations	4	4
	Log-likelihood (final)	-1478.42	-548.57
	Adj.Rho 2 vs equal shares	0.2617	0.2557
	Adj.Rho 2 vs observed shares	0.1496	0.2254
	AIC	2984.84	1125.14
	BIC	3062.08	1188.61
	. p<0.1;

*

Table 8 :

 8 Follow-up questions, with the first two presented to all respondents and the third only to those assigned to the donation-based subset.When you donate to a project, it benefits everyone, including non-payers. Has this influenced your decisions? No, I didn't care about the behavior of others, I only wanted to contribute something positive myself.343 42.14 814 No, I was not aware of the fact that others benefit without paying anything.155 19.04 Yes, I would have donated more if I had known that others would also donate, because it is not fair if only I pay but others who pay nothing also benefit from the restored forests. (Free-riding concerned)

	Response

Table A .

 A 9: Preference-space MMNL model for interpreting correlations, where additionality and payment were reversed p<0.05; * * p<0.01; * * * p<0.001 Table A.10: Preference-space MMNL model estimated with the entire uncleaned data set p<0.05; * * p<0.01; * * * p<0.001

	Estimate (s.e.) 1.805 * * * (0.090) 1.724 * * * (0.090) 0 0.057 (0.056) 1.603 * * * (0.067) 0.018 * * (0.005) 0.076 * * * (0.009) -0.140 * * * (0.006) 0.104 * * (0.043) 0.122 * (0.068) -0.159 * (0.072) -0.978 * * * (0.0659 0.484 * * * (0.036) -0.274 * * * (0.058) 0.139 * (0.060) 0.004 (0.071) -0.521 * * * (0.081) 0.052 (0.042) 0.403 * * * (0.063) -0.537 * * * (0.063) -0.182 * * (0.071) -0.480 * * * (0.123) 0.625 * * * (0.120) -1.304 * * * (0.181) 0.645 * * * (0.085) 0.280 * * * (0.041) 0.051 * (0.025) 0.109 * * * (0.029) 0.012 (0.017) -0.026 * * (0.009) 1705 13640 3000 (mlhs) 4 -11725.84 0.2156 Adj.Rho-squared vs observed shares 0.1665 asc.alt1 asc.alt2 asc.optout f oresttype sd. f oresttype carbon sd. f oresttype.carbon sd.carbon access sd. f oresttype.access sd.carbon.access sd.access addition sd. f oresttype.addition sd.carbon.addition sd.access.addition sd.addition biodiversity sd. f oresttype.biodiversity sd.carbon.biodiversity sd.access.biodiversity sd.addition.biodiversity sd.biodiversity log.payment sd.log. f oresttype.payment sd.log.carbon.payment sd.log.access.payment sd.log.addition.payment sd.log.biodiversity.payment sd.log.payment n individuals n choice situations n inter-individual draws n estimations Log-likelihood (final) Adj.Rho-squared vs equal shares AIC 23509.68 BIC 23727.79 . p<0.1; Estimate (s.e.) asc.alt1 2.191 * * * (0.083) asc.alt2 2.154 * * * (0.082) asc.optout 0.000 f oresttype 0.564 * * * (0.046) sd. f oresttype 1.240 * * * (0.056) carbon 0.509 * * * (0.043) sd. f oresttype.carbon 0.096. (0.072) sd.carbon -1.170 * * * (0.058) access 0.248 * * * (0.036) sd. f oresttype.access -0.071 (0.064) sd.carbon.access 0.014 (0.065) sd.access -0.812 * * * (0.058) addition -0.295 * * * (0.032) sd. f oresttype.addition 0.065 (0.056) sd.carbon.addition 0.236 * * * (0.052) sd.access.addition -0.099. (0.065) sd.addition 0.500 * * * (0.062) biodiversity 0.215 * * * (0.039) sd. f oresttype.biodiversity 0.290 * * * (0.053) sd.carbon.biodiversity -0.447 * * * (0.054) sd.access.biodiversity -0.167 * * (0.067) sd.addition.biodiversity -0.524 * * * (0.056) sd.biodiversity -0.415 * * * (0.065) log.payment -0.233 * * * (0.015) sd.log. f oresttype.payment -0.024 * * * (0.006) sd.log.carbon.payment -0.013. (0.010) sd.log.access.payment -0.020 * * (0.007) sd.log.addition.payment -0.078 * * * (0.008) sd.log.biodiversity.payment 0.289 * * * (0.014) sd.log.payment -0.060 * * * (0.007) n individuals 2521 n rows in database 20168 n inter-individual draws 3000 (mlhs) n estimations 4 Log-likelihood (final) -16093.1 Adj.Rho-squared vs equal shares 0.2724 Adj.Rho-squared vs observed shares 0.2557 AIC 32244.19 BIC 32473.64 . p<0.1;

* *

matter.

Funding

This work was supported by the NOBEL project 'Novel busi-

citizen" position (homo politicus).

Equity and additionality

We show that being female is significantly related to a particularly strong advocacy of equity. This is in line with the literature on gender differences in equality, which shows that women