ECJ Provides Guidance on Interpretation of 'Adverse Effect on Safe Integrity'


A recently published judgment of the European Court of Justice (ECJ) in the Sweetman case has provided some guidance on what is meant by an "adverse effect on site integrity" under Article 6(3) of the Habitats Directive (the Directive). The case was heard as a result of a reference for a preliminary ruling from the Supreme Court in Ireland.

Although not part of the judgement of the court, the Opinion of the Advocate General on the questions raised in the reference provide some interesting insight.


The case relates to a decision of An Bord Pleanála to grant development consent to build a road through part of a Special Area of Conservation which would result in the permanent loss of limestone pavement, a priority natural habitat under Annex I of the Habitats Directive.

Article 6 of the Habitats Directive sets out tests which authorities must follow when assessing plans or projects that are likely to have a significant effect on sites designated under the Habitats Directive and the Birds Directive.

The ECJ judgement noted that in applying Article 6, the provisions must be construed as a whole in light of the conservation objectives pursued by the Directive. This point was noted by Advocate General in her Opinion, who stated that it is "an essential objective of the Directive that natural habitats listed in Annex I are maintained at and, where appropriate, restored to a favourable conservation status".

When is a plan or project likely to have a significant effect on a European site?

It is recognised that an appropriate assessment is only required where a plan or project is not directly connected with or necessary to the management of the site but is likely to have a significant effect on it, alone or in-combination. However, what is not entirely clear is when a plan or project is likely to have a significant effect. This question was not answered by the ECJ but the Advocate General did address it in her Opinion.

It is suggested by the Advocate General that the term 'likely' does not refer to probability, rather it is that "the possibility of there being a significant effect on the site will generate the need for an appropriate assessment". In her Opinion, this is said to create a de minimis threshold so that plans or projects with no appreciable effect on the site are not subject to appropriate assessment.

Precautionary Principle

Article 6(3) incorporates the precautionary principle, meaning that the competent authority must refuse permission where uncertainty remains as to the absence of adverse effects. The ECJ asserted that the appropriate assessment must "contain complete, precise and definitive findings and conclusions capable of removing all reasonable scientific doubt as to the effects of the works proposed".

The ECJ were clear that, under Article 6(3), a plan or project can only be permitted once:

1. all aspects of the plan or project which can, alone or in-combination, affect the site's conservation objectives have been identified; and
the competent authority is certain, in light of the best scientific knowledge in the field, that the plan or project will not have lasting adverse effects on site integrity.

When is there an adverse effect on site integrity?

Prior to Sweetman, there was little definitive guidance on what an adverse effect on site integrity was. The ECJ has now stated that it should be inferred that a site needs to be preserved at favourable conservation status if its integrity as a natural habitat is not to be adversely affected.

In addition, they established that a competent authority cannot give approval for a plan or project where "there is a risk of lasting harm to the ecological characteristics of sites which host priority natural habitat types", particularly where there is a risk that it will bring about the disappearance or the partial and irreparable destruction of a priority natural habitat on the site.

In answering the reference question from the Supreme Court of Ireland, the ECJ ruled that:

"a plan or project not directly connected with or necessary to the management of a site will adversely affect the integrity of that site if it is liable to prevent the lasting preservation of the constitutive characteristics of the site that are connected to the presence of a priority natural habitat whose conservation was the objective justifying the designation of the site in the list of sites of Community importance".


There are a number of statements in the ECJ judgement and the Advocate General's Opinion which are helpful in understanding and interpreting some of the important concepts and principles under the Habitats Directive.

However, one key difference between the ECJ's judgement and the Advocate General's Opinion is the scope of the key conclusions, i.e those on the meaning of an adverse effect on site integrity. While the Advocate General was willing to state conclusions on how Article 6(3) should be applied generally, the ECJ seemed to be keen to restrict the application of its conclusions.

The wording of the key conclusions in the judgement effectively only enables them to be applied to situations involving priority natural habitat types (i.e. those in danger of disappearance), which were at issue in the case. It is therefore still uncertain how the provisions of Article 6(3) would be interpreted in relation to a European site without a priority natural habitat type although Sweetman is unlikely to be the last case on interpretation of Article 6(3) of the Habitats Directive.