The Stage 2 criteria contained in Annex III of the Directive are rather vaguely defined. The European Topic Centre for Nature Conservation (ETC/NC) (now the European Topic Centre on Biodiversity) prepared further guidance (Criteria for assessing national lists of pSCI at biogeographical level) to aid assessment of proposed national site lists at biogeographical seminars. A working draft of these guidelines was endorsed by the EC Habitats Committee in 1997.

 

To streamline the assessment process at the biogeographical seminars, a preliminary 'pre-selection' phase has been adopted. This involves an assessment of the proportion of the total regional resource of each Annex I habitat and Annex II species contained within the proposed SAC series, and aims to identify those features for which more detailed scrutiny is desirable. The broad approach adopted is generally known as the '20/60 guidelines'. Habitats and species for which 60% or more of the total resource is contained within the proposed sites are generally considered to be a low priority for further scrutiny; features for which representation is less than 20% are a high priority, and those for which representation is between 20% and 60% are treated on a case-by-case basis. The EC has made it clear that this is for guidance only, and that these threshold values are intended to inform debate at the biogeographical seminars, and are not intended to be applied as rigid rules.

The ETC/NC paper also emphasised the importance of ensuring adequate coverage of the geographical range of each feature, and provided detailed criteria for selecting SCIs for the national site lists, expanding on the Stage 2 criteria listed in Annex III of the Directive.