Anne-Charlotte Vaissiere

Fabien Quetier

Coralie Calvet

Harold Levrel

Sven Wunder

Biodiversity offsets and payments for environmental services: Clarifying the family ties

Keywords: Ecosystems, biodiversity offsets, payment for environmental services, conservation policies, economic incentives

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

Introduction

Biodiversity Offsets1 (BO) and Payments for Environmental Services2 (PES) are both innovative tools to address environmental problems. The literature on their design is rapidly expanding (e.g. [START_REF] Calvet | Tracking the origins and development of Biodiversity Offsetting in academic research and its implications for conservation: A review[END_REF][START_REF] Ezzine-De-Blas | Global Patterns in the Implementation of Payments for Environmental Services[END_REF]OECD 2013;[START_REF] Wunder | From principles to practice in paying for nature's services[END_REF]. Some authors have tentatively distinguished BO from PES (e.g. [START_REF] Hahn | Purposes and degrees of commodification: Economic instruments for biodiversity and ecosystem services need not rely on markets or monetary valuation[END_REF][START_REF] Maseyk | A disaggregated biodiversity offset accounting model to improve estimation of ecological equivalency and no net loss[END_REF], but the two are typically seen as intertwined, and often as generically identical instruments. For instance, [START_REF] Milder | Trends and future potential of payment for ecosystem services to alleviate rural poverty in developing countries[END_REF] see BO as a potential PES to alleviate rural poverty in developing countries and [START_REF] Salzman | The global status and trends of Payments for Ecosystem Services[END_REF] describe BO as "biodiversity PES programmes" (excluding several cases that they do consider as provision of a specific service). The widely referenced standard on BO developed by the Business and Biodiversity Offsets Programme (BBOP) ( 2012) states that 'one potential mechanism for securing the conservation outcomes needed for a biodiversity offset is payments for ecosystem services'. The BBOP adds that 'a range of people and organizations, from indigenous peoples and local communities, to farmers, NGOs, local authorities and protected area management boards, can be paid to deliver the specific conservation outcomes needed for the biodiversity offset to achieve no net loss (or a net gain)'. This standard conveys the progressive interest or need of including social aspects, such as poverty alleviation, equity or stakeholders' participation, to biodiversity conservation objectives.

From a regulatory perspective, some jurisdictions use terms to describe policies or instruments where BO and PES are being mixed together. For instance, in China, 'eco-compensation' is described as a "combination of 'ecological compensation' and 'payments for ecosystem services' " (Shang et al. 2018: 162). In France, parliamentarians recently recommended developing PES to pay farmers to deliver BO for developers, although PES are not mentioned in the country's Environmental Code as an option for BO implementation. Both the National Assembly [START_REF] Bassire | Rapport d'information sur la mise en application de la loi du 8 août 2016 pour la reconquête de la biodiversité[END_REF] and the Senate [START_REF] Dantec | Sur la réalité des mesures de compensation des atteintes à la biodiversité engagées sur des grands projets d'infrastructures[END_REF] argue that PES can help resolve some of the challenges of BO implementation in France, following the recent strengthening of No Net Loss requirements (Vaissière et al. 2018a), and in particular the acceptability of BO to farmers and farmland owners [START_REF] Calvet | Challenges of achieving biodiversity offset outcomes through agri-environmental schemes: evidence from an empirical study in Southern France[END_REF].

The confusion between PES and BO may be due to similarities in structure, such as a conditional payment for providing environmental services, and the shared reference to "market-based instruments" in some policy circles (e.g. Convention on Biological Diversity), as discussed by [START_REF] Boisvert | Market-based instruments for ecosystem services: institutional innovation or renovation[END_REF], Gómez-Baggethun and [START_REF] Gómez-Baggethun | In markets we trust? Setting the boundaries of marketbased instruments in ecosystem services governance[END_REF], [START_REF] Pirard | Market-based instruments for biodiversity and ecosystem services: a lexicon[END_REF] and [START_REF] Vatn | Markets in environmental governance. From theory to practice[END_REF].

In practice, it thus seems that BO are often included into a "large-umbrella" PES family and marketbased instruments. The need to improve the implementation of BO could lead to a hasty designation of BO as PES. However, as we will argue, BO and PES exhibit some quite distinct features. BO aim to counteract biodiversity losses from economic development by requiring developers to offset their impacts elsewhere through 'measurable conservation gains' (i.e. transforming financial payments into biophysical performance). PES are aimed at incentivizing/rewarding changes in land or resource-use practices, to deliver improved environmental outcomes, including biodiversity conservation, typically to a set of users willing to pay for incremental environmental services. The underlying rationale and logic of PES and BO is thus quite different: the latter is tied to an initial loss of biodiversity; the former to enhanced environmental service provision vis-à-vis a baseline scenario. Ecological equivalence and permanence are typically not key to PES design, yet matter greatly to achieving the stated 'No Net Loss' objective of many BO policies (Maron et al. 2018). As we will argue, this is not just an academic discussion over a miniscule conceptual facet, but has potentially weighty policy implications: misusing the (less strict) PES framework for guiding the (more impacting) BO implementation might ultimately jeopardize biodiversity outcomes. Conversely, there may also be important lessons for BO to be learned from PES. Thus, our first goal is to clarify the difference between PES and BO from a conceptual perspective, using case examples to illustrate them (Section 2). Indeed, [START_REF] Wunder | Payments for environmental services: some nuts and bolts[END_REF]2015) proposed to address the fuzziness of the PES concept by arguing for a fairly narrow definition of PES. Following the same footsteps, we see a need to clarify under what circumstances BO can be considered as PES. Secondly, we attempt to draw lessons from PES to enhance the performance of BO implementation (Section 3). We close with conclusions for practice and further research (Section 4).

Defining BO to enable a comparison with PES

Defining biodiversity offsets

The most commonly used BO definition is from IUCN, cf. ten Kate et al. ( 2004) that define biodiversity offsets as "conservation actions intended to compensate for the residual, unavoidable harm to biodiversity caused by development projects, so as to ensure no net loss of biodiversity (…) Before developers contemplate offsets, they should have first sought to avoid and minimize harm to biodiversity." (ibid: 13).

Correspondingly, BBOP (2012: 13) states: "Biodiversity offsets are measurable conservation outcomes resulting from actions designed to compensate for significant residual adverse biodiversity impacts arising from project development after appropriate prevention and mitigation measures have been taken. The goal of biodiversity offsets is to achieve no net loss and preferably a net gain of biodiversity on the ground with respect to species composition, habitat structure, ecosystem function and people's use and cultural values associated with biodiversity."

These two definitions are the most frequently used in the academic literature on BO (Bull et al. 2013a;[START_REF] Calvet | Tracking the origins and development of Biodiversity Offsetting in academic research and its implications for conservation: A review[END_REF]. These definitions of BO are largely aspirational, in that they hinge on conditions for good (desirable) outcomes. In practice, the desired conditions that BO are to meet greatly differ according to the government regulations or internal (voluntary) policies adopted by corporations and conservation organizations. For instance, the scope of BO can range from biodiversity in general [START_REF] Bbop | Standard on Biodiversity Offsets. Business and Biodiversity Offsets Programme[END_REF] to very specific biodiversity components such as specific protected species, or certain wetland types [START_REF] Quétier | Assessing ecological equivalence in biodiversity offset schemes: key issues and solutions[END_REF]. In the case of voluntary BO, there is seldom any external verification that BO conditions are de facto met, beyond the agreed rules between the developer and the BO provider. Desirable socioeconomic outcomes (such as equity among stakeholders and costeffectiveness of public policies) are often ignored [START_REF] Bidaud | The Sweet and the Bitter: Intertwined Positive and Negative Social Impacts of a Biodiversity Offset[END_REF]Griffiths et al. 2018), and ecosystems services generally remain outside the scope of BO regulations [START_REF] Jacob | Investigating the inclusion of ecosystem services in biodiversity offsetting[END_REF][START_REF] Wawrzyczek | The ecosystem approach in ecological impact assessment: lessons learned from windfarm developments on peatlands in Scotland[END_REF]).

For research purposes, a useful definition should arguably reflect practices across variable ecological and institutional settings. Wunder (2015: 241) underlines the need of isolating desirable outcomes from definitions. For instance, including "additionality" in the definition of forest laws and protected areas would mean that an ineffective forest law or a "paper park"3 could not be labeled a "law" or a "protected area", respectively. Hence, a PES definition must be consistent and precise enough for generating empirical knowledge, distinctive in function from indirect positive incentives, robust to intertemporal variations in implementation, and simple enough to remember (ibid). Some analysts get close to this objective for BO, such as Maron et al. (2012:141-2): "compensating for losses of biodiversity components [or values] at an impact site by generating (or attempting to generate) ecologically equivalent gains, or 'credits', elsewhere (i.e. an offset site)". Following the [START_REF] Wunder | Revisiting the concept of payments for environmental services[END_REF] narrow definitional criteria, inspired by Max Weber's "ideal types" (Idealtypus), we propose to define BO as:

(1) the supply of an ecological gain (2) in response to an ecological loss (3) located in a compensation site distinct from the impacted site (4) following agreed-upon criteria for the ecological equivalence between gains and losses. This definition is arguably broad enough to include all types of offsets (both regulatory and voluntary) performed worldwide. It applies to future impacts, assessed ex-ante (e.g. in the context of environmental impact assessments and permitting), but also to impacts assessed ex-post (e.g. accidents, once they have occurred). It also covers 'averted-loss4 ' and 'restoration' offsets (Bull et al. 2013a) and it excludes scenarios of merely financial compensation. We deliberately do not specify who needs to offset ecological losses, and for which types of events, activities, projects, plans or programs. Nor do we delimit those who can provide ecological gains, and whether they need to hold property or land-use rights. Criterion (3) sets BO apart from other mitigation measures, such as avoidance and minimization (reduction), or the rehabilitation/restoration of the impacted area when operations end (decommissioning). As experience shows, although the underlying principles of BO (1, 2, 3) are simple, how to reach agreements between stakeholders regarding a tentative ecological equivalence (4) can be complex, yet decisive for BO outcomes [START_REF] Quétier | Assessing ecological equivalence in biodiversity offset schemes: key issues and solutions[END_REF]. The meaning of ecological equivalence is hotly debated [START_REF] Maron | Faustian bargains? Restoration realities in the context of biodiversity offset policies[END_REF], with some authors arguing that like-for-like requirements do not make any sense (e.g. [START_REF] Walker | Why bartering biodiversity fails[END_REF]).

Comparing the BO and PES definitions

Table 1 presents the differences and commonalities between BO, as defined above, and PES, as defined by [START_REF] Wunder | Revisiting the concept of payments for environmental services[END_REF]: "voluntary transactions between service users and service providers that are conditional on agreed rules of natural resource management for generating offsite services". When do biodiversity offsets respect the payment for environmental services definition?

The first part of Table 1 shows that the only PES criterion that BO always complies with is, as in any contract, conditionality upon agreed rules: BO is framed in terms of achieving equivalence with a biodiversity loss. A developer may meet BO goals through contracts with several service providers, on several pieces of land: in that case, the conditionality is to reach a given share of the ecological equivalence objective. The other PES criteria are only verified in some instances of BO, as described below.

Firstly, if the BO is implemented by the developer itself, the dichotomy between environmental service user and provider becomes obsolete: there is no transaction between actors. But the different steps to implement BO, e.g. requiring the finding, securing and managing of land for conservation are rarely conducted by developers themselves. Typically, they are contracted out to specialized firms, conservation organizations, landowners or users such as farmers. In this situation, the developer is the environmental service user (buyer and beneficiary of the ES) and there is a third-party provider (and seller) of the environmental service that delivers the BO requirements to the developer.

Secondly, in Wunder's 2015 definition of PES, both the service user and provider must voluntarily engage in a contract. His paper discusses the collective organization of environmental services providers and/or users and the degree to which they reflect voluntary engagement by individual agents vs. collective action where not all individuals may pre-agree. This is also an issue in the context of BO. Some BO commitments by developers are voluntary in that they are not required by government regulation, but emerge from interactions with stakeholders [START_REF] Rainey | A review of corporate goals of No Net Loss and Net Positive Impact on biodiversity[END_REF]. When government regulations impose BO, these could be considered mandatory. BO providers are most often free to engage or not in a contract, making BO voluntary for the provider, but it is more difficult to describe the voluntary nature of the involvement of the providers in cases where their property or use rights are not well defined. If there are several BO providers, BO users can be said to voluntarily choose their service provider. However, this would not be enough to consider that a mandatory BO is voluntary from the BO user's side, meaning that the transaction is not fully voluntary, as required by the PES definition.

Thirdly, the PES definition mentions that "[environmental] services are generated offsite", meaning that the "ES [environmental services] beneficiaries are thus external to the physical site where ES provision is generated" (Wunder 2015: 242). In other words, the beneficiary does not own or hold property rights to the site where the environmental services are generated, as suggested by Karsenty & Ezzine de Blas ( 2016). In the context of BO, "offsite" usually means the offset is implemented on another site than the development project footprint5 , without considering land rights: what matters are the ecological criteria for equivalence, permanence, etc. Consequently, only BO carried out on land that the developer does not own or has no property or use rights to can be considered as "offsite", analogous to the PES definition of [START_REF] Wunder | Revisiting the concept of payments for environmental services[END_REF]. When land is bought by a developer for BO purposes and property rights are transferred to an environmental NGO for e.g. restoration and management activities, the situation still complies with the offsite (PES) definition, provided the developer continues to fund the management of the land now owned by the NGO, and thus keeps "buying" the environmental service. The points made above require a good understanding of property and land-use rights that vary considerably between countries6 . Where these are not well-defined or conflictive, determining whether a PES is being used to implement BO requirements can be hard to decipher. Figure 1 graphically represents the situations where BO initiatives fit under the PES definition.

Figure 1 -Verification of PES criterions for the possible BO schemes

When do payment for environmental services fit under a biodiversity offset definition?

The second part of Table 1 shows that PES do not have to comply with three of the four essential features of BO (addressing an ecological loss, respecting an equivalence between gains and losses, and being located in a distinct site from the impacted one) because, unlike BO, the goal of PES is not to address an ecological loss. Most of the BO definition is thus purposeless for PES. In PES, the environmental service can involve an ecological gain, but only those related to biodiversity might have a link with BO.

Beyond this comparison of definitions, BO and PES might be said to have different economic founding principles (see Box 1).

Box 1: The economic founding principles of BO and PES

Are BO as utilitarian as PES?

In economics, PES are based on a welfare approach [START_REF] Muradian | Reconciling theory and practice: an alternative conceptual framework for understanding payments for environmental services[END_REF]) whereby a consumer pays a provider (e.g. a farmer) to deliver a certain level of anthropogenic value (e.g. positive environmental externalities) from ecosystem management (e.g. farming practices). This is clearly utilitarian, with utility (a level of value or welfare) defined as the satisfaction provided by a good or a service to a consumer. On the contrary, BO is focused on providing in-kind ecological gains that address losses to species or habitats, independently of their anthropocentric values, and is thus not based on the utility concept. Our proposed definition, however, allows for utilitarian equivalence criteria to be considered, including the continued provision of certain ecosystem services [START_REF] Jacob | Investigating the inclusion of ecosystem services in biodiversity offsetting[END_REF] Does BO really conform to the polluter-pays principle? PES are generally tied to the 'beneficiary-pays' or 'provider-gets' principle (beneficiaries reward the maintenance or improvement of an environmental service by someone else). In turn, BO is often tied to the 'polluter-pays' principle whose foundations are in welfare economics (from Pigou and Kaldor-Hicks principle of compensation) and where the objective is to internalize externalities from pollutant activities using taxes, rather than ecological restoration, in order to get a monetary compensation corresponding to the level of loss of values induced by the pollution (Vaissière et al. 2017a). However, not only is BO not necessarily utilitarian in focus, but it excludes strictly financial payments to internalize negative externalities. It would be more appropriate to say that BO follows a 'polluter-restores' principle. Indeed, jurisdictions that allow developers to pay into funds that aim to pool BO resources often have a poor track record (e.g. Narain and Maron 2018) and these arrangements are better described as (green) taxes.

2.3 "Grey areas": when PES and BO share a common design

Using the PES definition of Wunder and the BO definition we have proposed, we show that BO and PES could be similar, in structure, only within very specific contexts and conditions (Figure 1): when a contract is set between a developer (or a collective organization) voluntarily deciding to implement BO and another agent (or a collective organization) voluntarily supplying a gain of biodiversity that is ecologically equivalent to the loss of biodiversity caused by the developer, due to pressure from stakeholders or the willingness of developers to develop and implement an internal set of values (or greenwash their image). And the gain of biodiversity has to be located in a site distinct from the one impacted by the development, and which the developer does not own or has no property or use rights over.

We have chosen four illustrations of previously studied test cases where the distinction between the structure of PES and BO could easily be blurred (Table 2). These are BO schemes, and we scrutinize whether they also hold PES features. Given our findings above (Table 1), conversely analyzing PES examples that are structurally not based on the principle of BO would be meaningless. Some PES schemes certainly share with BO the idea of "offsetting" environmental damages, such as in carbonbased PES initiatives 7 . Yet, the difference between them is that a PES programme does not pretend to assess in detail a specific, discrete underlying damaging activity 'prior to the cure', as certainly is the case for BO interventions.

In terms of the voluntary nature of the transaction, our BO examples show that transactions are seldom fully voluntary on the beneficiary side. Many respond to requirements for legal compliance, or anticipations thereof. The projects that are financially supported by lenders who have committed to the Equator Principles 8 , e.g. Ambatovy and Ngoyla mining projects, are required to apply the performance standards (PS) of the International Finance Corporation (IFC), and in particular PS6 on 7 For instance, the Dutch FACE Foundation has financed reforestation in tropical areas, such as the PROFAFOR programme in Ecuador [START_REF] Wunder | Decentralized payments for environmental services: The cases of Pimampiro and PROFAFOR in Ecuador[END_REF], to offset emissions from Dutch electricity companies. Of course, the focus here is not on biodiversity outcomes, which may be positive (e.g. in restoring highly degraded lands) or more dubious (e.g. when planting exotic species in high-altitude grasslands), but are only collateral to the main focus on carbon. The point is that such voluntary offsets are seen exclusively as a financing mechanism. 8 The Equator Principles constitute a risk management framework voluntarily adopted by financial institutions for determining, assessing and managing environmental and social risk in project finance. See: https://equatorprinciples.com biodiversity and natural resources. PS6 requires that the bank's clients implement a mitigation hierarchy of avoiding and minimizing impacts and offsetting any residual impacts on natural habitats to achieve no net loss or, in the case of critical habitats, a net gain of biodiversity (IFC 2012;[START_REF] Ambatovy | Sustainability report[END_REF]. The Ambatovy mining company also voluntarily accepted to become a BBOP pilot, which demonstrates commitment to BO and the goal of achieving no-net-loss and net-gains of biodiversity, and to communicating targets and progress. In addition, Madagascar's rapidly evolving environmental regulations may soon include stronger mitigation and offsetting requirements, so that future compliance contexts were perhaps anticipated. In the Contournement Nîmes Montpellier railway example (henceforth CNM)9 , the farmers are voluntary involved to provide ecological gains for BO through contracts as agri-environmental schemes funded by the developer.

It is notable that PES in practice are also often being applied in policy mixes, where payments are being conditioned upon cross-compliance with pre-existing (and partially overlapping) command-andcontrol interventions. This includes the European Union's Common Agricultural Policy whereby farmers are already eligible to agri-environmental payments and the emblematic case of Costa Rica's national PES scheme, which has been operated since 1996 [START_REF] Pagiola | Payments for environmental services in Costa Rica[END_REF]. It is thus also a question of whether we can analytically consider a particular environmental intervention as being independent, or whether we should rather see it as a component of an integrated policy strategy.

It can be hard to know if engagement was fully voluntary on the supply side. Landholders could be forced into giving up land or resource access rights to let developers implement offsets, becoming cases of displacement and resettlement from development projects that come with their own local requirements for 'compensation', as in the Ambatovy example [START_REF] Bidaud | Voluntary biodiversity offset strategies in Madagascar[END_REF][START_REF] Dantec | Sur la réalité des mesures de compensation des atteintes à la biodiversité engagées sur des grands projets d'infrastructures[END_REF][START_REF] Ambatovy | Sustainability report[END_REF]).In the Ngoyla example, there were no recognized land-use rights within the government-owned forest conservation concession prior to its attribution, but even within the government itself, the decision to assign the land to BO was not straightforward [START_REF] Ongolo | The politics of forestland use in a cunning government: lessons for contemporary forest governance reforms[END_REF]. Finally, as mentioned earlier, the collective organization of the suppliers or providers of the environmental service makes it difficult to be sure that all the individuals agree (free prior and informed consent) with the engagement in a BO programme.

There are always services users and service providers in our examples, as these were selected on their contract-based nature (entirely or partially). In the CNM example, the originally proposed BO scheme has to be spread in space and time across multiple short-term (5 year) contracts, for the full duration of the developer's 25 year BO obligations. This carries obvious risks [START_REF] Calvet | Challenges of achieving biodiversity offset outcomes through agri-environmental schemes: evidence from an empirical study in Southern France[END_REF]). In the Ambatovy example, there is a diversity of local stakeholders involved, with NGOs and government agencies acting as intermediaries. In the Ngoyla example, a public protected area agency acts as an environmental service provider to the developer. This contrasts with public agencies acting as buyers of environmental services, as is often the case in government-mediated PES. Interestingly, while in most PES and BO situations service users seek providers, mitigation bankers here anticipate the needs of service users. Beyond bespoke offsets implemented by a developer (with or without a service provider), mitigation banking has emerged since the late 1980s to overcome some of the challenges of offsetting impacts on wetlands in the USA.

Regarding conditionality, all the contracts in our examples include agreed criteria that are based on the ecological equivalence between biodiversity losses and gains. Of course, these criteria are more or less strict, and not always correctly applied. In the examples of CNM and mitigation banking, loss-gain approaches on ecological functions and/or habitat quality were used to determine the type and size of the BO. Because they are applied within an enforceable regulatory framework, the justification of the selected BO activities, monitoring and enforcement should be relatively high. The other two examples are voluntary BO with weaker governance structures.

Regarding the offsite nature of the BO (PES definition), it is easy to determine if the developer (user of the environmental service) has property rights or not on the site where the BO will be carried out. Each of our four examples has at least a part of its BO programme realized offsite. We acknowledge that the uncertainty about the land status on the provider side is often problematic, but the fact that the service provider owns or has property rights over the BO land, or not, is not actually important in defining the offsite nature (PES definition) of the scheme. Rather, we believe that this uncertainty raises more concerns as to the voluntary involvement of providers, as discussed in detail above.

Although not exhaustive, our selected examples illustrate quite contrasting BO situations: it is hard to find actual BO cases where the direct and voluntary requirements of Wunder's PES definition are met.

In other words, in spite of the clear family ties, BO and PES are in this respect quite distinct10 . No: there are also 'on-site' and adjacent activities (forests in the mining concession, its buffer zones Yes: the faunal reserve is out of the mining concession Yes: the farmers' plots are outside of the footprint of the railway Yes: credits sold to developers that have impacts outside the footprint of the mitigation bank No: credits used by mitigation bankers for their potential own projects and a part of the Analamay-Mantadia Forest Corridor) Sources: (1) [START_REF] Ambatovy | Sustainability report[END_REF][START_REF] Bbop | Standard on Biodiversity Offsets. Business and Biodiversity Offsets Programme[END_REF][START_REF] Bidaud | Voluntary biodiversity offset strategies in Madagascar[END_REF]and 2017, von Hase et al. 2014, (2) Quétier et al. 2015a[START_REF] Quétier | Biodiversity offsets: Opportunities and challenges for managing cumulative impacts of large-scale land-based investments on Africa's forest landscapes and their biodiversity[END_REF][START_REF] Ongolo | The politics of forestland use in a cunning government: lessons for contemporary forest governance reforms[END_REF], (3) Quétier et al. 2015c, Calvet et al. 2019 (4) [START_REF] Levrel | Should we be wary of mitigation banking? Evidence regarding the risks associated with this wetland offset arrangement in Florida[END_REF][START_REF] Vaissière | Biodiversity offset markets: What are they really? An empirical approach to wetland mitigation banking[END_REF], Vaissière et al. 2017b 3 Lessons from PES for enhancing BO performance Despite the differences in structure presented in the previous sections, BO and PES share many common issues and challenges in design and implementation. A substantial literature discusses practical conditions and good practices for implementing BO (e.g. [START_REF] Quétier | Assessing ecological equivalence in biodiversity offset schemes: key issues and solutions[END_REF][START_REF] Bbop | Standard on Biodiversity Offsets. Business and Biodiversity Offsets Programme[END_REF]Bull et al. 2013a;[START_REF] Gardner | Biodiversity offsets and the challenge of achieving no net loss[END_REF][START_REF] Gordon | Perverse incentives risk undermining biodiversity offset policies[END_REF][START_REF] Moilanen | Fifteen operationally important decisions in the planning of biodiversity offsets[END_REF] and PES (e.g. Ezzine de Blas et al. 2016;Wunder et al. 2008;[START_REF] Ambatovy | Sustainability report[END_REF]. They share various preconditions and criteria for good outcomes, such as having relevant scope and spatial targeting (e.g. focusing on areas in urgent need of restoration or facing immediate threats), having measurable performance indicators, enforcing conditionality 11 (monitoring, sanctions for non-compliance, performance-based payments), or embedding actions in large-scale nature conservation approaches to enhance performance (threshold effects) and share costs (e.g. through shared monitoring and evaluation systems, etc.). A desirable characteristic for both PES and BO is payment differentiation (i.e. the price paid for a given action differs between providers) to improve cost-efficiency [START_REF] Calvet | Challenges of achieving biodiversity offset outcomes through agri-environmental schemes: evidence from an empirical study in Southern France[END_REF]for BO, Bamière et al. 2013 for PES) and 'additionality' of ecological gains with respect to a defined 'business as usual' baseline, or reference frame including e.g. historical/ projected rates of biodiversity loss, regulatory obligations, political commitments or previously funded actions (see Box 2).

Box 2: the important criteria of additionality in PES and BO [START_REF] Karsenty | The economic and legal sides of additionality in Payments for Environmental Services[END_REF] discuss the economic and legal dimensions of additionality for PES, which are very similar to those of BO, and are difficult to achieve in practice. Many PES projects focus on averting further losses by covering opportunity and/or management costs (Gómez-Baggethun & Ruiz-Pérez 2011; [START_REF] Chan | Payments for Ecosystem Services: Rife With Problems and Potential-For Transformation Towards Sustainability[END_REF], which means a credible counterfactual scenario must be agreed upon. On the contrary, investments in ecosystem restoration are often a hallmark of BO, especially when it is hard to make a case for 'averted loss' gains (see Quétier et al. 2015d). Indeed, offsetting development impacts through the conservation of existing biodiversity ('averted-loss') carries considerable risks of not halting long-term biodiversity loss, e.g. through cost-and motivationshifting [START_REF] Gordon | Perverse incentives risk undermining biodiversity offset policies[END_REF][START_REF] Maron | Faustian bargains? Restoration realities in the context of biodiversity offset policies[END_REF][START_REF] Wunder | When payments for environmental services will work for conservation[END_REF]. Regarding regulatory additionality, [START_REF] Karsenty | The economic and legal sides of additionality in Payments for Environmental Services[END_REF] relate cases where payments only served to facilitate the introduction of new regulations or prohibitions, making these more politically acceptable.

There is a growing concern that BO may only rarely meet their stated objectives (e.g. [START_REF] Maron | Faustian bargains? Restoration realities in the context of biodiversity offset policies[END_REF][START_REF] Curran | Is there any empirical support for biodiversity offset policy?[END_REF][START_REF] Lindenmayer | The anatomy of a failed offset[END_REF][START_REF] Bezombes | Do biodiversity offsets achieve No Net Loss? An evaluation of offsets in a French department[END_REF]) and that they may fail to be well integrated into their local socio-economic contexts [START_REF] Jacob | Investigating the inclusion of ecosystem services in biodiversity offsetting[END_REF][START_REF] Bidaud | Voluntary biodiversity offset strategies in Madagascar[END_REF][START_REF] Dantec | Sur la réalité des mesures de compensation des atteintes à la biodiversité engagées sur des grands projets d'infrastructures[END_REF][START_REF] Ambatovy | Sustainability report[END_REF]Griffiths et al. 2018). Although mentioned in good practice guidance, considerations of equity (i.e. BO winners and losers), stakeholder participation (i.e. inclusiveness in BO design and implementation), transparency in contract formulation (i.e. collectively defining the rules of the game) 11 There is an increasing focus on the conditionality of BO based on the achievement of the goal of ecological equivalence, while conditionality in PES is more often based on proxies [START_REF] Laurans | Les paiements pour services environnementaux. De la théorie à la mise en oeuvre, quelles perspectives dans les pays en développement[END_REF][START_REF] Gibbons | Should payments for biodiversity conservation be based on action or results[END_REF]Wunder et al. 2008). For instance, the recent French law on biodiversity adopts a result-oriented obligation (i.e. developers must show and monitor the ecological results they provided through BO), instead of a processoriented obligation, but it is still unknown how this new legal requirement will be implemented in practice. Similarly, species offsets under the US Endangered Species Act are sometimes managed using demographic indicators (Gamarra & Toombs 2018), although this is not a guarantee of overall success [START_REF] Sonter | Quantifying habitat losses and gains made by US Species Conservation Banks to improve compensation policies and avoid perverse outcomes[END_REF].

appear to get less attention in BO design and implementation than in PES (a rare example is Griffiths et al. 2018). [START_REF] Roussel | Compensation Écologique et Agriculture : Est-Ce Compatible ?[END_REF]), Vaissière et al. (2018b) and [START_REF] Calvet | Challenges of achieving biodiversity offset outcomes through agri-environmental schemes: evidence from an empirical study in Southern France[END_REF] analyse the use of contract-based BO with farmers in France, and showed that poor contract design conveys significant risks. The lack of additionality is a well-documented risk and in the case of CNM: [START_REF] Calvet | Challenges of achieving biodiversity offset outcomes through agri-environmental schemes: evidence from an empirical study in Southern France[END_REF] revealed that 58% of the enrolled farmers in the BO programme declared that they had not made significant changes to their practices. Also, 78% of the farmers contracted out plots on which they were already conducting the targeted agricultural practices revealing they might be benefiting from an undeserved 'windfall effect'12 . In such cases, poor farmers' selection process (selecting those with the lower opportunity costs) and weak contract enforcement (especially no sanctions and weak monitoring) were both of major importance. Given these risks, PES may thus provide a variety of practical experiences for improving socio-economic design and outcomes from contract-based BO implementation. Below, we discuss in this light three main PES lessons (good practices but also pitfall to avoid) in relation to our four practical BO examples.

Firstly, PES are considered more sustainable if they are permanent, i.e. the induced change of practice/ behavior continues even after payments stop [START_REF] Karsenty | The economic and legal sides of additionality in Payments for Environmental Services[END_REF]. For instance, Locatelli et al. (2007) found that the Costa Rican PES program has improved local awareness about ecosystem services, even after payments have ended. This element is of particular importance in the context of BO where the ecological losses that must be offset are often permanent. Considering BO contracts as time-bound investments aimed to lastingly transform the behavior and practices of the enrolled stakeholders could provide the necessary long-term ecological gains even after the BO requirements of developers stop. In the Ambatovy example, the developer's rural capacity-building activities could be considered such a long-term investment. In the CNM, contracts are short-term (5 year renewable 5 times). [START_REF] Calvet | Challenges of achieving biodiversity offset outcomes through agri-environmental schemes: evidence from an empirical study in Southern France[END_REF] found that one-third of the farmers involved in the BO program do not anticipate changing their practices after the contract ends, but one-third will keep them. This raises concerns regarding the permanence of the ecological gains, although short-term contracts also make the BO program more flexible vis-à-vis unanticipated institutional (agricultural policies) and environmental (climate) changes [START_REF] Calvet | Challenges of achieving biodiversity offset outcomes through agri-environmental schemes: evidence from an empirical study in Southern France[END_REF]Bull et al. 2013b).

Secondly, motivations and behavioral factors have been widely considered in PES schemes, featuring roles and responsibilities (e.g. [START_REF] Clot | Payments vs. compensation for ecosystem services: do words have a voice in the design of environmental conservation programs[END_REF][START_REF] Brimont | Between incentives and coercion: the thwarted implementation of PES schemes in Madagascar's dense forests[END_REF] in the Malagasy context) and flexible "menus" to meet performance requirements (e.g. [START_REF] Fleury | Flowering meadows," a resultoriented agri-environmental measure: technical and value changes in favour of biodiversity[END_REF][START_REF] Andrello | Paying for conservation: a bioeconomic analysis of land use effects on the viability of an endangered species, Eryngium alpinum L[END_REF]. More recently, this question is being studied in BO contexts too. [START_REF] Calvet | Challenges of achieving biodiversity offset outcomes through agri-environmental schemes: evidence from an empirical study in Southern France[END_REF] revealed the influence of social norms on farmer enrolment into the CNM program. Le [START_REF] Coent | Compensating Environmental Losses Versus Creating Environmental Gains: Implications for Biodiversity Offsets[END_REF] showed that purely biodiversity-framed BO contracts made farmers expect higher payments, flagging sensitivity towards environmental issues. It is widely recognized that BO implementation benefits from the involvement of specialized organizations, dedicated to conservation and more likely to be selfmotivated by successful implementation. Under IFC performance standards, for example, project proponents are required to actively engage in partnerships with conservation NGOs for the implementation of their biodiversity actions, including BO. It was the case for Ambatovy which partnered with Conservation International and would have most likely been so for Ngoyla, for which the Cameroonian authorities now get technical assistance from the World Wildlife Fund. These NGOs act as intermediaries with local communities, for which motivations and behavioral factors remain important success factors. In addition, it is worth mentioning that the NGOs themselves are not immune to influence: using BO as a recurrent source of financing for their conservation programs exposes them to a risk of crowding out other sources of funding [START_REF] Gordon | Perverse incentives risk undermining biodiversity offset policies[END_REF][START_REF] Maron | Does it matter why we do restoration? Volunteers, offset markets and the need for full disclosure[END_REF].

Thirdly, PES are widely expected to allocate contracts equitably (e.g. [START_REF] Pascual | Exploring the link between equity and efficiency in payments for environmental services: a conceptual approach[END_REF]. For BO, more attention should also be given to the socio-economic consequences of area selection, given that similar tradeoffs between efficiency and equity abound [START_REF] Bidaud | Voluntary biodiversity offset strategies in Madagascar[END_REF]. [START_REF] Bidaud | The Sweet and the Bitter: Intertwined Positive and Negative Social Impacts of a Biodiversity Offset[END_REF][START_REF] Bidaud | The local costs of biodiversity offsets: Comparing standards, policy and practice[END_REF] found some positive impact on local wellbeing in the case of the Ambatovy BO program, but also that timing and beneficiaries were not always matching those suffering negative impacts. In the mitigation banking example, aggregation of BO supply in a single 'bank' sometimes led to the impacted areas and 'banks' being quite distant (e.g. averaging 40 km in Florida - [START_REF] Levrel | Should we be wary of mitigation banking? Evidence regarding the risks associated with this wetland offset arrangement in Florida[END_REF]. The potential redistribution effect in terms of ecosystems services between users of the impacted site and beneficiaries from the restored one must receive due consideration (Vaissière et al. 2017b).

Agri-environmental PES schemes, land trusts and easements [START_REF] Merenlender | Land trusts and conservation easements: Who is conserving what for whom?[END_REF]), public-private partnerships for conservation [START_REF] Thackway | Public/private partnerships and protected areas: selected Australian case studies[END_REF][START_REF] Saporiti | Managing national parks: how public-private partnerships can aid conservation[END_REF], community-based conservation and other forms of 'private' protected areas [START_REF] Carter | Private protected areas: management regimes, tenure arrangements and protected area categorization in East Africa[END_REF]) can all potentially provide lessons for BO implementation. But BO come with specific requirements that must be remembered when investigating implementation options. Due diligence is needed to ensure that BO is not interpreted as just another financing mechanism (e.g. [START_REF] Maron | Interactions between biodiversity offsets and protected area commitments: avoiding perverse outcomes[END_REF].

Conclusion

Biodiversity Offsetting (BO) and Payments for Environmental Services (PES) are often considered jointly as innovative ways to tackle the ongoing biodiversity crisis, and BO are by many observers considered generically as a type of PES, i.e. falling under the same umbrella of intervention. We have argued above that this would generally be a misuse: compared to the most common definition of PES [START_REF] Wunder | Revisiting the concept of payments for environmental services[END_REF], there are few circumstances in which BO can structurally be considered as PES, especially because the PES inherent voluntariness criterion from both sides is hardly ever respected in BO. In terms of our initial intention of clarifying the family ties, we can thus conclude that PES and BO are neither twins nor siblings; they are probably best compared to two fairly "distant cousins": some founding material is clearly shared between them, while other of their respective characteristics are fundamentally different.

Why then is it fairly common that PES and BO are put under the same umbrella? This perhaps forms part of the confusion around the so-called "market-based instruments" [START_REF] Pirard | Classifying market-based instruments for ecosystem services: A guide to the literature jungle[END_REF][START_REF] Gómez-Baggethun | In markets we trust? Setting the boundaries of marketbased instruments in ecosystem services governance[END_REF], an arguably excessively broad term under which many instruments constitute economic incentives or resource allocation mechanisms in which markets properly defined actually play no role [START_REF] Pirard | Market-based instruments for biodiversity and ecosystem services: a lexicon[END_REF][START_REF] Wunder | When payments for environmental services will work for conservation[END_REF]. Hence, the scope for conceptual confusion is noteworthy. By claiming to directly offset residual damages from a directly paired environmentally polluting impact from development activity, BO interventions thus come to share much more in the responsibility of the paired loss impacts than would be the case for PES: a PES intervention is generally deemed to be successful if it manages to produce more environmental services than a business-as-usual baseline, but it is not directly (though sometimes indirectly) used to justify environmental losses prior to the remedying action. No wonder, then, that we need stricter standards for the aggregate environmental benefits of BO than we do for PES schemes: we need to make sure with much more vigor that on balance the adopted impact compensation mechanism is not tantamount to a greenwashing operation.

On the other hand, the design and implementation of contract-based BO can indeed draw valuable lessons from PES experience. Contract design and enforcement matter for successfully converting developers' commitments into measurable conservation outcomes. Also, PES social impacts, safeguards, and side-objectives have been more holistically looked into than for BO. Hence, as BO implementation is continuously expanding, it would be unwise to turn a blind eye to PES.

Still, care is also needed to avoid invalid extrapolations from blindly transferring lessons from one tool to the other. Neither PES nor BO are 'silver bullets' for biodiversity conservation and important organizational and legal limitations need to be considered when choosing a contract-based BO approach and the relevance of lessons from PES must be assessed for the specific purposes of BO. In this context, practical research on the contracting of BO implementation to third parties is also needed so that responsibilities are not lost or diluted, and monitoring and enforcement are not rendered impossible.

The implications of BO failure for biodiversity are stronger for BO than for PES, given that the former entails a direct, and often locally irreversible frontloaded loss of biodiversity, while the latter can be flexibly be interrupted whenever the parties would no longer agree on a service provision contract. Development projects with impacts on biodiversity can go forward on the basis of expected BO outcomes that can be made insecure when dependent on voluntary contracts with land-owners and land-users, as in a PES scheme. If a PES scheme has not been specifically designed for biodiversity purposes, it also cannot be used as a BO setup. The differences in the founding principles of PES and BO matter and safeguards are needed to avoid the risks of uncompensated biodiversity loss that could arise from confusing BO and PES. This is why it was important to clarify how they differ.

Table 1 -BO vs. PES comparison through their definitions I. When do BO respect PES criteria?

 1

	Definition of PES	Applicability of PES criterion to BO
		For the developer
		No, if requirements for BO are mandatory
	Voluntary transactions	Yes, if requirements for BO are voluntary
		For the environmental service provider
		Yes, if there is a provider
	[Environmental] service user	Yes, when the offset is carried out by an external provider
	[Environmental] service provider	No, when the offset is carried out by the developer
	Conditionality based on agreed rules	Yes (ecological equivalence)
		Yes, if the offset is also carried out offsite (as
	Generate offsite services (offsite as per PES definition)	per the BO definition) -unless the developer has land rights over both sites No, if the offset is carried out onsite (as per the
		BO definition)

II. When do PES respect BO criteria?

	Definition of BO	Applicability of BO criterion to PES
	Ecological gain	Yes, if an environmental service is provided to generate the ecological gain
	Ecological loss	Not Applicable: usually no ecological loss in PES
	Located in a compensation site distinct from the impacted site	Not Applicable
	Agreed criteria on ecological equivalence between gains and losses	Not Applicable

  ).

	Agreed criteria on ecological equivalence
	between gains and losses	LEGEND
	Biodiversity offset (BO)	Conditional on agreed rules Criteria of the PES definition :
				A voluntary transaction
	Mandatory BO for		Voluntary BO for	A service user and provider
	the developer		the developer	Generation of offsite services
				Verification of the criterions :
	BO implemented	BO voluntarily implemented	Verified
	by the developer	by an external provider	Not verified
	Onsite (BO def)	Offsite (BO def)	Offsite (BO def)
	on land that the	on land that the	on land that the
	developer owns or	developer owns or	developer does not own
	has property or use	has property or use	or has no property or use
	rights over	rights over	rights over
	= Onsite (PES def)		= Offsite (PES def)

Table 2 -

 2 Features of selected BO examples

		Ambatovy (1)	Ngoyla (2)	CNM (3)	Mitigation banking (4)
	Details of the example
	Country	Madagascar	Cameroon and Congo	France	Florida, United-States
	Project	Nickel and cobalt mine: extraction	Iron ore mines of Mbalam and	Railway bypass of 80 km in Southern	Several development projects
		site, 220 km pipeline, processing	Nabeba: extraction sites,	France called the "Contournement	(infrastructures, housing, beach
		plant on the coast, extension of the	infrastructure to transport the ore	Nîmes-Montpellier" (CNM);	nourishment, etc.)
		port at Toamasina; in operation	to the coast 500 km away; the	construction completed in 2017
		since 2012	projects were put on hold in 2014
			but are now being reconsidered
	Residual	The footprint includes the loss of	Total footprint is around 15,000 ha,	About 2000 ha of mainly agricultural	Cumulative losses of wetland
	biodiversity	about 2000 ha of native forest, with	including over 2000 hectares of old-	land harboring endangered species	area and functions
	impact after	risks of additional induced impacts	growth rainforest, with
	avoidance and	from population influx	considerable risks of induced
	reduction		impacts from population influx
	measures
	BO program	Averted loss offset: conservation of	Averted loss offset: conservation of	Restoration offsets: changes in	Mostly ecological restoration
		existing forests in 5 sites totaling	164,000 ha of mostly previously	agricultural practices or farmland use to	but also several averted loss
		more than 18,000 ha. This includes	unlogged old-growth forest in	provide favorable habitats for the little	programs:
		working with forest authorities and	southern Cameroon. The mining	bustards. As of April 2019, about 1200	a specialized offset provider,
		a conservation NGO to ensure:	company bid for and won this	ha of agri-environmental biodiversity	the mitigation "banker",
		-Strict protection from	forest concession as a 'conservation	offset contracts with more than 100	voluntarily undertakes
		deforestation by ranger patrols	concession', against a competing	willing farmers covering over 500 farm	ecological restoration and/or
		-Training of local communities to	proposal by Wildlife Works to sell	plots. In addition, the developer also	conservation actions on his or
		new rules for local multifunctional	carbon credits in the context of	purchased 512 ha of farmland for	her land, to then sell publicly
		use (e.g. establish woodlots within	REDD+. It was designated as a	conversion into favorable land-cover	authorized 'credits' to one or
		the forests, where wood collection	Faunal Reserve in 2014 (Ministerial	that was leased to farmers for	typically several developers.
		was permitted and managed)	Decree 2014/2383), in agreement	management.	When the mitigation bank is
		-Rural development program to	with the government, and		sold out (i.e. all the credits
		generate alternative revenue	management handed over to the		have been sold), the land is
		streams to compensate for	Ministry of Forests		often transferred to a NGO or
		restrictions on forest uses (e.g.			another environmental
		training farmers to intensify rice			stakeholder to carry out the
		production, introduce poultry			long term management plan
		farming, etc.)

We use BO to refer indiscriminately to Biodiversity Offset(s) or Biodiversity Offsetting.

The term Payment for 'Ecosystem' Services is being used mostly as a synonym, but is on aggregate slightly less popular in the literature[START_REF] Wunder | Revisiting the concept of payments for environmental services[END_REF]. We use PES to refer indiscriminately to Payment for Environmental Service(s).

A "paper park" refers to an administratively declared protected area that de facto enjoys no or only negligible protection: it only exists "on paper" (e.g. Di Minin & Toivonen 2015).

'Averted losses' offsets rely on ecological gains from the avoidance of impending damages, e.g. through protection measures, rather than from purposely restoring a degraded ecosystem (that would be 'restoration' offsets).

However, in the particular example of mining, BO implemented in areas within a mining concession but outside the footprint of the mine could be said to be "offsite". Concessions can be very large, and mining companies generally do not have full land-use rights on the full extent of the concession.

For instance, the common law considers the property rights as a bundle of rights and the roman law considers property rights as a full ownership.

The CNM project is a large-scale BO program involving hundreds of farmers in southern France to offset the ecological impacts of a new 80 km high-speed railway line managed by Oc'Via, the developer. For further information see[START_REF] Calvet | Challenges of achieving biodiversity offset outcomes through agri-environmental schemes: evidence from an empirical study in Southern France[END_REF].

Of course, alternatively, a broader definition of PES (e.g.[START_REF] Muradian | Reconciling theory and practice: an alternative conceptual framework for understanding payments for environmental services[END_REF], Froger et al 2016) may well include cases where the voluntary nature of the transaction, on the provider or the user side, is blurred, enabling some BO to be categorized as PES with specific requirements in terms of offsite services. However, the more restrictive definitions of both BO and PES that we have used here are more helpful in differentiating the two instruments.

The 'windfall effect' describes a situation where someone receive a reward for doing nothing additional.