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WWF Italia Onlus, Lega Italiana Protezione Uccelli Onlus, Gruppo di Intervento Giuridico Onlus, Italia Nostra Onlus, Forum Ambientalista and FC and Others, by G. Viglione and N. Tsuno, avvocati,

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the Italian Government, by G. Palmieri, acting as Agent, and by G. Palatiello, avvocato dello Stato,

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the Czech Government, by M. Smolek, J. Vláčil and L. Dvořáková, acting as Agents,

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the European Commission, by G. Gattinara and C. Hermes, acting as Agents,

1

This request for a preliminary ruling concerns the interpretation of Article 6 of Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora (OJ 1992 L 206, p. 7; ‘the Habitats Directive’).

2

The request has been made in proceedings between, of the one part, WWF Italia Onlus, Lega Italiana Protezione Uccelli Onlus, Gruppo di Intervento Giuridico Onlus, Italia Nostra Onlus, Forum Ambientalista and FC and Others and, of the other, the Presidenza del Consiglio dei Ministri (Presidency of the Council of Ministers, Italy) and Azienda Nazionale Autonoma Strade SpA (ANAS) concerning the legality of the decision of 1 December 2017 by which the Consiglio dei Ministri (Council of Ministers) found that the preliminary project for a road link north of Rome (Italy) using the ‘green route’ between Monte Romano Est (Italy) and Tarquinia Sud (Italy) was compatible with environmental requirements, and of the decision of 28 February 2018 by which the Comitato Interministeriale per la Programmazione Economica (Interministerial Economic Planning Committee, Italy) (‘the CIPE’) approved that preliminary project.

3

The seventh recital of the Habitats Directive states that ‘all the areas designated, including those classified now or in the future as special protection areas pursuant to Council Directive 79/409/EEC of 2 April 1979 on the conservation of wild birds [OJ 1979 L 103, p. 1], will have to be incorporated into the coherent European ecological network’.

4

Article 1(l) of the Habitats Directive defines ‘special area of conservation’ as ‘a site of Community importance designated by the Member States through a statutory, administrative and/or contractual act where the necessary conservation measures are applied for the maintenance or restoration, at a favourable conservation status, of the natural habitats and/or the populations of the species for which the site is designated’.

5

Article 3(1) and (2) of that directive provides:

‘1.   A coherent European ecological network of special areas of conservation shall be set up under the title Natura 2000. This network, composed of sites hosting the natural habitat types listed in Annex I and habitats of the species listed in Annex II, shall enable the natural habitat types and the species’ habitats concerned to be maintained or, where appropriate, restored at a favourable conservation status in their natural range.

The Natura 2000 network shall include the special protection areas classified by the Member States pursuant to Directive 79/409/EEC.

2.   Each Member State shall contribute to the creation of Natura 2000 in proportion to the representation within its territory of the natural habitat types and the habitats of species referred to in paragraph 1. To that effect each Member State shall designate, in accordance with Article 4, sites as special areas of conservation taking account of the objectives set out in paragraph 1.’

6

Article 6 of the Habitats Directive states:

‘1.   For special areas of conservation, Member States shall establish the necessary conservation measures involving, if need be, appropriate management plans specifically designed for the sites or integrated into other development plans, and appropriate statutory, administrative or contractual measures which correspond to the ecological requirements of the natural habitat types in Annex I and the species in Annex II present on the sites.

2.   Member States shall take appropriate steps to avoid, in the special areas of conservation, the deterioration of natural habitats and the habitats of species as well as disturbance of the species for which the areas have been designated, in so far as such disturbance could be significant in relation to the objectives of this Directive.

3.   Any plan or project not directly connected with or necessary to the management of the site but likely to have a significant effect thereon, either individually or in combination with other plans or projects, shall be subject to appropriate assessment of its implications for the site in view of the site’s conservation objectives. In the light of the conclusions of the assessment of the implications for the site and subject to the provisions of paragraph 4, the competent national authorities shall agree to the plan or project only after having ascertained that it will not adversely affect the integrity of the site concerned and, if appropriate, after having obtained the opinion of the general public.

4.   If, in spite of a negative assessment of the implications for the site and in the absence of alternative solutions, a plan or project must nevertheless be carried out for imperative reasons of overriding public interest, including those of a social or economic nature, the Member State shall take all compensatory measures necessary to ensure that the overall coherence of Natura 2000 is protected. It shall inform the Commission of the compensatory measures adopted.

Where the site concerned hosts a priority natural habitat type and/or a priority species, the only considerations which may be raised are those relating to human health or public safety, to beneficial consequences of primary importance for the environment or, further to an opinion from the Commission, to other imperative reasons of overriding public interest.’

7

Article 7 of that directive provides:

‘Obligations arising under Article 6(2), (3) and (4) of this Directive shall replace any obligations arising under the first sentence of Article 4(4) of Directive 79/409/EEC in respect of areas classified pursuant to Article 4(1) or similarly recognised under Article 4(2) thereof, as from the date of implementation of this Directive or the date of classification or recognition by a Member State under Directive 79/409/EEC, where the latter date is later.’

8

Under decreto legislativo n. 163 – Codice dei contratti pubblici relativi a lavori, servizi e forniture in attuazione delle direttive 2004/17/CE e 2004/18/CE (Legislative Decree No 163 – Code on public works contracts, public service contracts and public supply contracts implementing Directives 2004/17/EC and 2004/18/EC) of 12 April 2006 (GURI No 100 of 2 May 2006) (‘Legislative Decree No 163/2006’), the procedure for developing an infrastructure project comprises two phases, the preliminary project and the definitive project.

9

Article 165 of Legislative Decree No 163/2006, entitled ‘Preliminary project. Procedure for assessment of environmental implications and siting’, provides in paragraphs 3, 5 and 7:

‘3.   In addition to the provisions of the technical annex referred to in Annex XXI, the preliminary project for the infrastructure works must, using an appropriate map, show the areas concerned, any buffer strips for those areas and the necessary safeguards; it must also indicate and show the performance characteristics, functional specifications and cost ceilings of the proposed infrastructure, including the cost ceiling for any works and measures to compensate for territorial and social impacts strictly connected to the operation of the works, up to a limit of 2% of the total cost of the works. That percentage must also include the costs of mitigating the environmental impacts identified in the environmental impact assessment procedure, subject to any other measures to be taken in accordance with specific Community obligations. Where works are subject to an environmental impact assessment under domestic law, the preliminary project must also be accompanied by an environmental impact study and be published in accordance with the procedures laid down by the applicable national or regional legislation.

…

5.   The preliminary project, drawn up in accordance with this article, must be approved by the CIPE.

…

7.   Where required by the regulations in force, that approval shall give rise to an environmental compliance assessment of the structure and shall, for all relevant planning and construction purposes, embody the State-region agreement on its siting and shall entail automatic adaptation of the adopted planning instruments in force; …’

10

Article 166 of that legislative decree, entitled ‘Definitive project. Public benefit of the works’, states in paragraphs 1 and 5:

‘1.   The definitive infrastructure project must be supplemented by a report by the designer certifying that it accords with the preliminary project and any requirements imposed at the time of approval, in particular the environmental and siting requirements. It must be accompanied by a description of any structures and measures to mitigate and compensate for environmental, territorial and social impacts.

…

5.   Approval of the definitive project, adopted by a majority of members of the CIPE, shall replace any other authorisation, approval or opinion, howsoever designated, and shall permit the completion and, for strategic production facilities, operation, of all the structures, services and activities provided for in the approved project.’

11

Under Article 183(6) of that legislative decree:

‘The environmental compatibility decision shall be adopted by the CIPE at the same time as approval of the preliminary project. Where the Ministro dell’ambiente e della tutela del territorio (Minister for the Environment and Protection of Land) or the Ministro per i beni e le attività culturali (Minister for Culture) has issued a negative reasoned opinion, the environmental compatibility decision shall be issued by the Council of Ministers at its next relevant meeting. The definitive project shall be monitored under Article 185(4) to ensure that it complies with the requirements [laid down by that decision].’

12

Article 185(4) and (5) of Legislative Decree No 163/2006 provides as follows:

‘4.   The [Environmental Impact Assessment] Committee:

5.   If the definitive project is different from the preliminary project, the [Environmental Impact Assessment] Committee shall report thereon to the Minister for the Environment and Protection of Land who shall, after assessment by the Committee, if the minister finds that the difference between the preliminary project and the definitive project involves a significant change in the overall environmental impact of the project, require that the environmental impact study be updated and republished, within 30 days of the submission by the contracting entity, the concessionaire or the general contractor, for the purpose in particular of enabling the public and private stakeholders to make any observations.

The environmental impact study may only be updated in respect of the part of the project affected by the change. In the event of failure to comply with the provisions and requirements laid down by the environmental compatibility decision, the minister in question, after issuing a notice to remedy the situation, shall ensure that the non-compliance is disclosed at the time of the interdepartmental conference, in relation to any renewal of the investigation.’

13

The Habitats Directive was transposed into the Italian legal order by decreto del presidente della Repubblica n. 357 – Regolamento recante attuazione della direttiva 92/43 (Decree of the President of the Republic No 357 – Regulation implementing Directive 92/43) of 8 September 1997 (Ordinary Supplement to GURI No 248 of 23 October 1997).

14

Article 5 of that decree, entitled ‘Assessment of Implications’, provides:

‘1.   Territorial planning and programming must take into account the ecological and environmental value of proposed sites of Community importance, sites of Community importance and special areas of conservation.

2.   The proponents of territorial, planning and sectoral plans … shall prepare … a study to identify and assess the effects which the plan may have on the site, taking into account its conservation objectives. Territorial plans that are required to undergo an impact assessment shall be submitted to the Minister for Environment and Protection of Land, where they are of national significance, and to the competent regions and autonomous provinces, where they are of regional, interregional, provincial or municipal significance.

3.   The proponents of works not directly connected with or necessary to maintaining a favourable conservation status for the species and habitats present on the site, but which may have a significant effect on the site itself, either on their own or in conjunction with other works, shall submit, for the purposes of the assessment of implications, a study designed to identify and assess, in accordance with the guidelines defined in Annex G, the main effects which those works may have on the proposed site of Community importance, on the site of Community importance or on the special area of conservation, taking into account the conservation objectives of those sites.

4.   For projects subject to the environmental impact assessment procedure … which concern … proposed sites of Community importance, sites of Community importance or the special areas of conservation, as defined in the present regulation, the assessment of implications shall be included within the scope of the abovementioned procedure which, in such a case, shall also consider the projects’ direct and indirect effects on the habitats and species on account of which those sites and areas were designated. To that end, the environmental impact study prepared by the proponent must include the factors relating to whether the project is compatible with the conservation aims provided for by the present regulation …

…

8.   Before issuing the final approval of the plan or action, the authority shall include the impact assessment in the file and, where applicable, shall determine the arrangements for consulting the public concerned by implementation of that plan or action.

9.   If, in spite of a negative assessment of the implications for the site and in the absence of alternative solutions, a plan or project must nevertheless be carried out for imperative reasons of overriding public interest, including those of a social or economic nature, the competent authorities shall take all compensatory measures necessary to ensure that the overall coherence of the “Natura 2000” network is protected and it shall inform the Minister for the Environment and Protection of Land of those measures for the purposes described in Article 13.

10.   Where the sites concerned host priority natural habitat types and priority species, the plan or action which has been assessed as having a negative impact on the site of Community importance, may be carried out only by reference to requirements relating to human health or public safety, beneficial consequences of primary importance for the environment or, further to an opinion from the European Commission, for other imperative reasons of overriding public interest.’

15

Article 6 of that decree, entitled ‘Special protection areas’, provides:

‘1.   The “Natura 2000” network shall include the special protection areas … pursuant to Directive 79/409 …

2.   The obligations under Articles 4 and 5 shall also apply to the special protection areas referred to in paragraph 1.’

16

The decreto del Ministro dell’ambiente e della tutela del territorio e del mare (Decree of the Minister for the Environment and Protection of Land and Sea) of 6 December 2016 (GURI No 301 of 27 December 2016) designating a special area of conservation in the Alpine biogeographical region, a special area of conservation in the Continental biogeographical region and 140 special areas of conservation in the territory of the Lazio Region in the Mediterranean biogeographical region, under Article 3(2) of the Decree of the President of the Republic No 357 of 8 September 1997, includes, in Article 1(3), designation of the area entitled ‘Fiume Mignone (basso corso)’ as a special area of conservation.

17

The dispute in the main proceedings concerns approval of the preliminary works project for construction of an approximately 18 km section of State road No 675 linking Monte Romano Est and Tarquinia Sud in the Lazio Region. Those works are intended to facilitate the link, in Italy, between, first, the port of Civitavecchia and the A1 Milan-Naples motorway and, secondly, the Orte intermodal node, the Terni industrial area and the Ancona-Perugia route.

18

In 2004, the Ministero dell’ambiente e della tutela del territorio e del mare (Ministry of the Environment and Protection of Land and Sea, Italy) (‘MATTM’) issued an opinion favourable to construction of that section using the ‘violet route’. The CIPE approved that initial project by Decision No 11/2011.

19

However, in 2015, ANAS, the company appointed to carry out those works, filed an alternative ‘green route’ project, on account of the high cost of the ‘violet route’.

20

The MATTM’s Environmental Impact Assessment Committee issued an unfavourable opinion on that new project, stating that the economic costs of the ‘violet route’ could be reduced by dividing the route into two sections. The grounds for that negative opinion were that the ‘green route’ project did not include an in-depth study of its environmental impact and would affect a site of Community importance forming part of the Natura 2000 network, namely the ‘Fiume Mignone (basso corso)’ area.

21

In view of that negative opinion, the Ministero delle Infrastrutture e Trasporti (Ministry of Infrastructure and Transport, Italy) requested the Presidency of the Council of Ministers to initiate the procedure under Article 183(6) of Legislative Decree No 163/2006. The Presidency of the Council of Ministers requested the MATTM to assess whether the environmental impact of the ‘green route’ could be limited by means of mitigating and compensatory measures. That ministry’s Environmental Impact Assessment Committee issued a further negative opinion on that route, stressed that the harmful effects could not be mitigated by requirements or other measures and found the ‘violet route’ to be preferable in all respects.

22

By decision of 1 December 2017, the Council of Ministers nevertheless declared the preliminary project corresponding to the ‘green route’ to be compatible with environmental requirements, basing its decision on an ‘overriding public interest’ ground, that is to say, the need to complete a strategic route forming part of the TEN-T trans-European network for transport. However, it required the proponent, when drawing up the definitive project, to supplement the environmental impact study for the section in question and to comply with the landscaping and environmental requirements, observations and recommendations indicated by the interdepartmental conference called by the Ministry of Infrastructure and Transport.

23

On 28 February 2018, the CIPE approved the preliminary project for the ‘green route’, subject to certain requirements being met. The CIPE required ANAS to draw up the definitive project and the environmental impact study and named the Lazio Region as the body responsible for verifying that study in order, inter alia, to identify any additional mitigating and compensatory measures that might be necessary.

24

A number of environmental associations and natural persons brought proceedings before the Tribunale amministrativo regionale per il Lazio (Regional Administrative Court, Lazio, Italy) against the Council of Ministers decision of 1 December 2017 and the CIPE’s decision of 28 February 2018.

25

According to that court, the authorities privileged economic interests and completion of a road link forming part of the TEN-T trans-European network for transport over protection of the environment, and postponed until the definitive project stage any attempts to identify appropriate solutions to protect the site of Community importance concerned by means of compensatory and mitigating measures which the MATTM Environmental Impact Assessment Committee had nevertheless found to be impossible for the ‘green route’. That court notes that the authorities themselves concede that they took an integrated approach by evaluating the environmental, landscaping, cultural and socio-economic aspects together. Under those circumstances, the referring court is uncertain whether the adoption of the preliminary project at issue is consistent with EU law.

26

In those circumstances the Tribunale amministrativo regionale per il Lazio (Regional Administrative Court, Lazio) decided to stay the proceedings and to refer the following questions to the Court of Justice for a preliminary ruling:

27

By its first and second questions, which can appropriately be examined together, the referring court enquires, in essence, whether Article 6 of the Habitats Directive, in conjunction with Directive 2009/147 where applicable to the main proceedings, must be interpreted as precluding national legislation that allows the procedure for approval of a plan or project to continue for imperative reasons of overriding public interest, where the impact of that plan or project on a special area of conservation cannot be mitigated and in respect of which the competent public authority has already issued a negative opinion, when there is an alternative solution that has already been approved from an environmental perspective.

28

According to the definition in Article 1(l) of the Habitats Directive, a special area of conservation is a ‘site of Community importance designated by the Member States through a statutory, administrative and/or contractual act where the necessary conservation measures are applied for the maintenance or restoration, at a favourable conservation status, of the natural habitats and/or the populations of the species for which the site is designated’.

29

Article 6 of that directive lays down measures intended to protect special areas of conservation. Article 6(3) in particular defines the circumstances in which a plan or project may be authorised where it is not directly connected with or necessary to the management of the site in question but likely to have a significant effect on it.

30

The Decree of 6 December 2016 of the Minister for the Environment and Protection of Land and Sea designated the area known as ‘Fiume Mignone (basso corso)’ as a special area of conservation. Furthermore, it is clear from the information provided by the referring court that that area is likely to be significantly affected by the road construction project at issue in the main proceedings. That project therefore falls within the scope of Article 6 of the Habitats Directive.

31

By contrast, Directive 2009/147 does not apply to a dispute such as that in the main proceedings. Admittedly, the applicants in the main proceedings contend that the lesser kestrel, which is included in Annex I to that directive and is thereby subject to special protection measures, is present in the area that the project passes through. However, Article 7 of the Habitats Directive provides that the obligations under Article 6 of that directive replace any obligations arising from the fact that a species is included on the list of protected species by virtue of Directive 79/409, which was codified and supplemented by Directive 2009/147, as from the date of classification under Directive 79/409, where the latter date is later than the date of implementation of the Habitats Directive (see, to that effect, judgments of 13 June 2002, Commission v Ireland, C‑117/00, EU:C:2002:366, paragraph 25, and of 17 April 2018, Commission v Poland (Białowieża Forest), C‑441/17, EU:C:2018:255, paragraph 109). It is, therefore, appropriate to interpret only the provisions of the Habitats Directive.

32

According to Article 6(2) of the Habitats Directive, the Member States have a general obligation to take appropriate steps to avoid, in special areas of conservation, the deterioration of habitats and significant disturbance of the species for which the areas have been designated (judgments of 7 September 2004, Waddenvereniging and Vogelbeschermingsvereniging, C‑127/02, EU:C:2004:482, paragraph 32, and of 20 September 2007, Commission v Italy, C‑304/05, EU:C:2007:532, paragraph 92). That obligation contributes to the intended creation of a coherent European ecological network, described in the seventh recital of that directive (judgment of 20 September 2007, Commission v Italy, C‑304/05, EU:C:2007:532, paragraph 93).

33

Article 6(3) of the Habitats Directive establishes a procedure, applicable to special areas of conservation, intended to ensure, by means of a preliminary examination, that a plan or project which is not directly connected with or necessary to the management of the site concerned but likely to have a significant effect on it is authorised only to the extent that it will not adversely affect the integrity of that site (judgments of 7 September 2004, Waddenvereniging and Vogelbeschermingsvereniging, C‑127/02, EU:C:2004:482, paragraph 34; of 26 October 2006, Commission v Portugal, C‑239/04, EU:C:2006:665, paragraph 19, and of 21 July 2016, Orleans and Others, C‑387/15 and C‑388/15, EU:C:2016:583, paragraph 43).

34

That provision accordingly identifies two separate stages. The first requires the Member States to carry out an appropriate assessment of the implications for a protected site of a plan or project when it is possible that the plan or project will have a significant effect on that site. The second stage, which occurs following the aforesaid appropriate assessment, allows such a plan or project to be authorised only if it will not adversely affect the integrity of the site concerned (judgments of 11 April 2013, Sweetman and Others, C‑258/11, EU:C:2013:220, paragraphs 29 and 31, and of 7 November 2018, Holohan and Others, C‑461/17, EU:C:2018:883, paragraph 31).

35

Article 6(4) of the Habitats Directive provides that if, in spite of a negative assessment carried out in accordance with the first sentence of Article 6(3) of the directive, a plan or project must nevertheless be carried out for imperative reasons of overriding public interest, including those of a social or economic nature, and there are no alternative solutions, the Member State is to take all compensatory measures necessary to ensure that the overall coherence of Natura 2000 is protected (judgment of 20 September 2007, Commission v Italy, C‑304/05, EU:C:2007:532, paragraph 81).

36

Article 6(4) of the Habitats Directive must, as an exception to the criterion for authorisation laid down in the second sentence of Article 6(3), be interpreted strictly (judgments of 20 September 2007, Commission v Italy, C‑304/05, EU:C:2007:532, paragraph 82, and of 17 April 2018, Commission v Poland (Białowieża Forest), C‑441/17, EU:C:2018:255, paragraph 189).

37

It is therefore clear from Article 6(3) of the Habitats Directive that the competent national authorities must in principle refuse to agree to a plan or project that risks adversely affecting the integrity of the site concerned. Notwithstanding its negative implications for that site, the plan or project in question may nevertheless be carried out, by way of derogation, in the circumstances laid down in Article 6(4) of that directive, if it is necessary to do so for imperative reasons of overriding public interest.

38

Where that occurs, it follows from the objective of conserving special areas that underpins Article 6 of the Habitats Directive that the adverse effects on the integrity of the site concerned must be reduced to a minimum. Nevertheless, in the light of its wording, Article 6(4) of that directive does not make the ability to prioritise imperative reasons of overriding public interest over the protection of a special area of conservation contingent upon it being possible to mitigate sufficiently the adverse effects on the integrity of that area. That provision intended to provide that, in exceptional circumstances, the objective of conserving natural habitats and wild fauna and flora in special areas of conservation can give way to other particularly pressing public interest considerations, provided nevertheless that the Member State concerned takes the necessary compensatory measures to preserve the overall coherence of the Natura 2000 European ecological network.

39

The referring court states that the imperative reasons of overriding public interest relied upon in relation to the ‘green route’ concern the lower cost of the works, the fact that it satisfies landscaping, historical, cultural and socio-economic protection considerations and the need to complete a trans-European road network.

40

It should be noted in that respect that Article 6(4) of the Habitats Directive requires that even justified adverse effects on the integrity of a special area of conservation may only be agreed if they are genuinely unavoidable, that is to say, where there are no alternative solutions.

41

Account being taken of the strict interpretation of Article 6(4) of the Habitats Directive, as noted in paragraph 34 above, it cannot be accepted that the economic cost alone of the measures capable of being considered in the review of alternatives may be a determining factor in the choice of alternative solutions under that provision (judgment of 14 January 2016, Grüne Liga Sachsen and Others, C‑399/14, EU:C:2016:10, paragraph 77).

42

In the case under analysis, it can be seen from the information provided to the Court that there is a variant of the project at issue in the main proceedings, referred to as the ‘violet route’, which received a favourable opinion from the MATTM in 2004.

43

It is for the referring court to determine whether the ‘violet route’ should be regarded as an alternative solution, within the meaning of Article 6(4) of the Habitats Directive, which is less disadvantageous for the integrity of the ‘Fiume Mignone (basso corso)’ special area of conservation than the ‘green route’.

44

In the light of the foregoing considerations, the answer to the first and second questions is that Article 6 of the Habitats Directive must be interpreted as not precluding national legislation that allows the procedure for approval of a plan or project to continue for imperative reasons of overriding public interest, where the impact of that plan or project on a special area of conservation cannot be mitigated and in respect of which the competent public authority has already issued a negative opinion, unless there is an existing solution that is less disadvantageous for the integrity of the area concerned, which it is for the referring court to determine.

45

By its third and fourth questions, which it is appropriate to consider together, the referring court asks, in essence, whether, where a plan or project has received an unfavourable assessment of its implications for a special area of conservation, under Article 6(3) of the Habitats Directive, and the Member State concerned has nevertheless decided, on the basis of Article 6(4), to implement that project or plan for imperative reasons of overriding public interest, Article 6 of that directive must be interpreted as precluding national legislation according to which further and more in-depth examinations and studies of the effects of the plan or project on the area and the identification of adequate compensatory and mitigating measures may be postponed to the stage of the definitive plan or project.

46

The third and fourth questions in fact contain three separate questions.

47

First, the referring court asks, by those questions, whether Article 6 of the Habitats Directive must be interpreted as precluding national legislation according to which further and more in-depth examinations and studies of the effects of the plan or project at issue on a special area of conservation may be postponed to the stage of the definitive plan or project, where the preliminary plan or project was not approved as part of assessment of the impact on that area.

48

Under Article 6(3) of the Habitats Directive, the competent national authority must refuse to approve the plan or project under consideration wherever any doubt remains that there are no harmful effects on the integrity of the site concerned. By integrating the precautionary principle that provision makes it possible to prevent in an effective manner adverse effects on the integrity of protected sites as a result of the plans or projects envisaged. A less stringent authorisation criterion could not ensure as effectively the fulfilment of the objective of site protection intended under that provision (judgments of 7 September 2004, Waddenvereniging and Vogelbeschermingsvereniging, C‑127/02, EU:C:2004:482, paragraphs 57 and 58; of 11 April 2013, Sweetman and Others, C‑258/11, EU:C:2013:220, paragraph 41; and of 21 July 2016, Orleans and Others, C‑387/15 and C‑388/15, EU:C:2016:583, paragraph 53).

49

The assessment carried out under Article 6(3) of the Habitats Directive cannot have lacunae and must contain complete, precise and definitive findings and conclusions capable of removing all reasonable scientific doubt as to the effects of the works proposed on the protected site concerned (see, to that effect, judgments of 11 April 2013, Sweetman and Others, C‑258/11, EU:C:2013:220, paragraph 44, and of 15 May 2014, Briels and Others, C‑521/12, EU:C:2014:330, paragraph 27).

50

It follows that the assessment under Article 6(3) of the Habitats Directive cannot properly be carried out on the basis of examinations and studies carried out subsequently. In consequence, wherever it is found necessary to supplement an assessment of the implications of a plan or project on an area of special conservation or to conduct more in-depth assessment, that assessment cannot be regarded as the assessment under Article 6(3).

51

In the present case, it is apparent from the documents before the Court that the competent authority expressly stated that it intended to apply Article 6(4) of the Habitats Directive. However, as a provision derogating from the criterion for authorisation laid down in Article 6(3) of that directive, Article 6(4) thereof can be applied only after the implications of a plan or project have been analysed in accordance with Article 6(3) (judgment of 21 July 2016, Orleans and Others, C‑387/15 and C‑388/15, EU:C:2016:583, paragraph 60).

52

Indeed, knowledge of those implications in the light of the conservation objectives relating to the site in question is a necessary prerequisite for the application of Article 6(4) of the Habitats Directive, since, in the absence of those elements, it is not possible to assess the conditions for the application of that derogating provision. The assessment of any imperative reasons of overriding public interest and that of the existence of alternatives that are less harmful to the environment require a weighing up against the damage caused to the site by the plan or project under consideration (judgment of 21 July 2016, Orleans and Others, C‑387/15 and C‑388/15, EU:C:2016:583, paragraph 61 and the case-law cited).

53

It follows that, when it applied Article 6(4) of the Habitats Directive, the competent authority in the dispute in the main proceedings must have taken the view that the already-carried-out unfavourable assessment of the implications of the project at issue in the main proceedings for the special area of conservation concerned was the assessment referred to in Article 6(3) of that directive. That assessment therefore could not be supplemented, as indicated in paragraph 48 above.

54

Secondly, by its third and fourth questions, the referring court also asks whether Article 6 of the Habitats Directive must be interpreted as precluding national legislation according to which the identification of mitigating measures may be postponed to the stage of the definitive plan or project, where the plan or project at issue was not approved as part of assessment of the implications for a special area of conservation.

55

It should be noted at the outset that the wording of Article 6 of the Habitats Directive contains no reference to any concept of ‘mitigating measure’ (judgment of 21 July 2016, Orleans and Others, C‑387/15 and C‑388/15, EU:C:2016:583, paragraph 57).

56

If that expression denotes the protective measures aimed at avoiding or reducing any adverse effects of a plan or project on the site concerned, the requirement, noted in paragraph 49 above, that the assessment of a plan or project referred to in Article 6(3) of the Habitats Directive must contain complete, precise and definitive findings and conclusions means that those measures must be assessed at the same time as that plan or project itself and accordingly that those measures must form part of that plan or project (see, to that effect, judgment of 21 July 2016, Orleans and Others, C‑387/15 and C‑388/15, EU:C:2016:583, paragraph 54). They therefore cannot change the plan or project concerned once that assessment has taken place. To allow the plan or project to be modified by mitigation measures after its implications for the site concerned have been assessed would be tantamount to declining to assess not only the impact of the definitive plan or project but also the impact of those measures themselves on that site, thereby disregarding the objectives of Article 6 of that directive.

57

That article therefore precludes legislation under which identification of measures to mitigate the implications of a plan or project on a special area of conservation may be postponed to a stage subsequent to appropriate assessment of the implications within the meaning of Article 6(3).

58

Thirdly, by its third and fourth questions, the referring court asks whether Article 6 of the Habitats Directive must be interpreted as precluding national legislation according to which the identification of compensatory measures may be postponed to the stage of the definitive plan or project, where the plan or project at issue was not approved as part of assessment of the implications for a special area of conservation.

59

Under Article 6(4) of the Habitats Directive, the Member State concerned is to take the compensatory measures necessary to ensure the overall coherence of Natura 2000 if, in spite of a negative assessment of the implications for the site concerned and in the absence of alternative solutions, a plan or project must nevertheless be carried out for imperative reasons of overriding public interest.

60

The compensatory measures, if any are needed, are therefore identified after the appropriate assessment of the implications under Article 6(3) of the Habitats Directive.

61

Indeed, as indicated in paragraphs 51 and 52 above, Article 6(4) of that directive can apply only once the implications of a plan or project have been analysed in accordance with Article 6(3).

62

Furthermore, the very nature of compensatory measures is reason for their being identified once the negative implications of a plan or project for the site concerned have been assessed. Those measures are intended to produce effects of a different order, including after the plan or project at issue has been completed, in order to ensure or restore the coherence of the Natura 2000 European ecological network as a whole, taking into consideration the harm that the plan or project will inevitably cause to the integrity of the special area of conservation concerned.

63

The necessary compensatory measures should, therefore, be identified after the assessment established in Article 6(3) of the Habitats Directive, where it is proposed that the plan or project at issue should be implemented in spite of its negative impact on the special area of conservation concerned and if the other conditions for Article 6(4) of that directive to apply are met.

64

In the light of the foregoing considerations, the answer to the third and fourth questions is that where a plan or project has received an unfavourable assessment of its implications for a special area of conservation, under Article 6(3) of the Habitats Directive, and the Member State concerned has nevertheless decided, on the basis of Article 6(4), to carry out that project or plan for imperative reasons of overriding public interest, Article 6 of that directive must be interpreted as precluding national legislation according to which, after it has received an unfavourable assessment under Article 6(3) and before it has been definitively adopted under Article 6(4), that plan or project may be supplemented by measures to mitigate its implications for that area and those implications may continue to be assessed. By contrast, in the same situation, Article 6 of the Habitats Directive does not preclude legislation according to which compensatory measures may be identified in the context of the same decision, provided that the other conditions for applying Article 6(4) of that directive are also met.

65

By its fifth and sixth questions, which it is appropriate to examine together, the referring court enquires, in essence, whether the Habitats Directive must be interpreted as precluding national legislation according to which the proponent of the works is to carry out a study of the implications of the plan or project at issue for the special area of conservation concerned and to include landscaping and environmental requirements, observations and recommendations in the definitive plan or project, after that plan or project has received a negative assessment by the competent authority.

66

First, it should be noted that neither the Habitats Directive nor the Court’s case-law precludes the proponent of the works from being requested to produce a study of the implications of its plan or project for the special area of conservation concerned, in support of the application for authorisation of that plan or project, on the basis of which the competent authority then carries out an assessment of the implications of that plan or project for that area, within the meaning of Article 6(3) of that directive.

67

Secondly, it is apparent from the wording of Article 6(3) of the Habitats Directive that the proponent of the works is not the person responsible for that assessment, but rather the competent authority, namely the public authority that the Member States designate as responsible for performing the duties arising from that directive (judgment of 7 November 2018, Holohan and Others, C‑461/17, EU:C:2018:883, paragraph 44).

68

Thirdly, as set out in paragraph 56 above, a plan or project cannot be changed after its implications for the special area of conservation concerned have been assessed, without calling into question the fact that that assessment is a full and definitive one and jeopardising the guarantee it represents for conservation of that area. The proponent of the works cannot, therefore, be requested to include requirements, observations and recommendations in the plan or project at issue where that plan or project has already received an unfavourable assessment by the competent authority, unless that authority reassesses the plan or project thus modified.

69

Fourthly, it is only modifications likely to have a significant impact on a special area of conservation that may not be made to a plan or project after the implications of that plan or project on that area have been assessed. By contrast, the parameters as to the effects of which there is no scientific doubt that they will not affect the site can be entirely left to be decided later by the proponent of the works (judgment of 7 November 2018, Holohan and Others, C‑461/17, EU:C:2018:883, paragraph 46).

70

In the light of the foregoing, the answer to the fifth and sixth questions is that the Habitats Directive must be interpreted as not precluding national legislation according to which the proponent of the works is to carry out a study of the implications of the plan or project at issue for the special area of conservation concerned, on the basis of which the competent authority then carries out an assessment of those implications. That directive does, by contrast, preclude national legislation that allows the proponent of the works to be requested to include landscaping and environmental requirements, observations and recommendations in the definitive plan or project, after that plan or project has received a negative assessment by the competent authority, without the plan or project thus modified having to be reassessed by that authority.

71

By its seventh question, the referring court asks, in essence, whether the Habitats Directive must be interpreted as precluding national legislation that allows an authority other than that responsible for assessing the implications of a plan or project on a special area of conservation to be appointed to verify the study of the implications for the area that must be annexed to the definitive plan or project.

72

First, since it contains no indication as to the authority that is competent to assess the implications for special areas of conservation of plans or projects that are likely to have significant effects on those areas, the Habitats Directive must be construed as leaving the task of designating that authority to the Member States.

73

Secondly, as noted in paragraph 49 above, the assessment of the implications of a plan or project for the special area of conservation concerned, referred to in Article 6(3) of the Habitats Directive, must contain complete, precise and definitive findings and conclusions capable of removing all reasonable scientific doubt as to the effects of the works proposed on the protected site concerned (see, to that effect, judgments of 11 April 2013, Sweetman and Others, C‑258/11, EU:C:2013:220, paragraph 44, and of 15 May 2014, Briels and Others, C‑521/12, EU:C:2014:330, paragraph 27). That is why, once it has been carried out, as it has in the present case (see paragraphs 51 to 53 above), that assessment cannot be continued or supplemented either by the authority that conducted it or by any other authority.

74

The answer to the seventh question is, therefore, that the Habitats Directive must be interpreted as meaning that, although it leaves to the Member States the task of designating the authority competent to assess the implications of a plan or project on a special area of conservation in accordance with the criteria laid down by the Court’s case-law, it does, by contrast, preclude any authority from continuing or supplementing that assessment once it has been carried out.

75

Since these proceedings are, for the parties to the main proceedings, a step in the action pending before the national court, the decision on costs is a matter for that court. Costs incurred in submitting observations to the Court, other than the costs of those parties, are not recoverable.

On those grounds, the Court (Sixth Chamber) hereby rules: