The Habitats Directive requires Member States to use the criteria set out in the Directive to propose a national list of sites that provides appropriate representation of the habitat types listed in Annex I and the species listed in Annex II. The UK has had long experience of this kind of site selection process. The first major exercise to select a national site series was carried out by the Society for the Promotion of Nature Reserves, which in 1915 produced a provisional list of 273 areas in Britain worthy of protection as nature reserves - one of the first ever attempts to produce a series of areas to be protected by conservation measures (SPNR 1915; Rothschild & Marren 1997). This work helped to prepare the ground for the first official national strategy for nature conservation, which was set out in 1947 (Cmd. 7122 and Cmd. 7235) and led to the selection of a national series of sites notified as Sites of Special Scientific Interest (SSSIs) (Areas of Special Scientific Interest (ASSIs) in Northern Ireland).

The expanding information on and growing experience in nature conservation led to the publication of A nature conservation review (Ratcliffe 1977), a major site selection process which produced a revised list of biological sites considered to be of national importance for nature conservation. A major contribution of this work was to set out a series of clear, largely qualitative site selection criteria to guide and structure judgements about the nature conservation value of sites. The rationale and criteria used for site selection in the Review have been widely accepted and used in the UK, and the systems for conservation evaluation in many parts of the world draw upon them (Nature Conservancy Council 1989; Joint Nature Conservation Committee 1994). The criteria in Annex III of the Directive show similarities to those in the Review, and the UK has a great deal of practical experience in the use of such criteria for site evaluation and selection.

Despite the UK's long track record and experience in identifying areas of particular importance for wildlife conservation, identifying a national list of SACs in terms of Article 4 and Annex III posed a number of practical difficulties.

1.5.2.1 Relationship of SACs to SSSI/ASSIs
It is not appropriate simply to assume that all the UK's biological SSSIs and ASSIs should be put forward as candidate SACs. The Annex I list of habitat types and the Annex II list of species are special sub-sets of the habitats and species occurring in the EU, and they stem from application of the Article 1 definitions. Many SSSIs/ASSIs either have no, or no significant, occurrence of this subset of habitat types and species, and so cannot be regarded as of Community importance within the meaning of the Directive. Even where sites do have habitat types and species listed in the Directive they may not qualify for selection when assessed against the criteria set out in Annex III of the Directive and the other principles established. Furthermore, UK legislation does not enable the notification of marine sites below low water mark ⁵ as SSSI/ASSI. The UK has thus based site assessment on the criteria and principles set out in the Directive and has not simply made a selection based on existing protected areas. This has resulted in the identification of a large number of sites not previously notified as SSSI/ASSIs.

1.5.2.2 The role of expert opinion in site selection
The Annex III criteria are similar to UK domestic site selection guidelines in that they are principles by which to judge the relative importance of sites. The problems of applying such principles in practice are therefore familiar. Although some Annex III criteria (e.g. habitat extent) can be quantified relatively easily, scaling or quantifying the assessments for many of the criteria would necessarily be arbitrary. Even if it were possible to produce objective numerical values for each attribute, there would be a need to transform the various ratings into a common range of values, a process which would inevitably introduce an element of subjective weighting. There is currently no widely agreed way of determining such weighting and of then integrating the data into a single overall index (Margules 1986). Further, in any attempt to produce a single indicator value from assessments of a number of criteria there is the problem that intercorrelations are likely to introduce bias (Usher 1980). For example, in the Annex III criteria, there will always be a degree of positive correlation between the area of any site and the number of Annex I habitat types and Annex II species present on the site. As yet there is no broad consensus on how these problems should be resolved.

For these reasons, quantitative rule-based systems have so far not been widely adopted for the purpose of selecting statutory sites, either in the UK or elsewhere. The conservation agencies, faced with having to complete a major site-selection exercise within a limited timescale, using available data, felt that the risks of using any new, untried, quantitative rule-based approach outweighed any potential benefits. Instead, the proven approach, which recognises that site selection is essentially a matter of judgement and relies on a group of experts, each of whom understands the aims and guiding principles of the exercise, to make informed judgements to select an agreed list of sites, was used. The use of 'best expert judgement' is acknowledged as an appropriate means of ranking sites in the EC's guidance on the Natura 2000 Standard Data Form (European Commission DGXI 1995).

1.5.2.3 Interpretation of Annex I categories
Annex I of the Directive uses a classification of habitat types that differs in several important respects from vegetation classification systems that have traditionally been used in the UK. During site selection it was necessary to interpret the habitat information available in the UK in terms of the Annex I habitat list. This is a complex task for those habitat types, such as 7150 Depressions on peat substrates of the Rhynchosporion and 9180 Tilio-Acerion forests of slopes, screes and ravines, that do not correspond clearly to types in classifications that have been used in habitat surveys in the UK, such as the National Vegetation Classification Rodwell 1991a,b, 1992, 1995, 2000).

1.5.2.4 Wide-ranging species
Article 4(1) states: "for aquatic species which range over wide areas, ...sites will be proposed only where there is a clearly identifiable area representing the physical and biological factors essential for their life and reproduction". In the case of 1351 Harbour porpoise Phocoena phocoena, available evidence is that the species is widespread in territorial waters of the UK and the rest of northern Europe and is relatively evenly distributed. The site selection rationale for harbour porpoise is still being discussed by the EC and Member States, and the UK is currently considering whether it can identify sites which fulfil the criteria outlined in Article 4(1), and which contribute significantly towards maintaining favourable conservation status for this species.

The selection of sites for other wide-ranging species, such as 1355 Otter Lutra lutra and 1365 Common seal Phoca vitulina, has also presented certain difficulties (see section 1.5.4.2.1).

1.5.2.5 Artificial habitats and non-native and reintroduced species
Article 4(1) requires Member States to propose sites only for natural habitat types and species that are native to each Member State's territory. Article 3(1) requires these habitats and species to be maintained or, where appropriate, restored at favourable conservation status in their natural range. Accordingly, habitats and species occurring outside their natural range are not a reason for SAC selection, and are not listed as qualifying features on SACs in the UK. This affects several Annex I habitats which are defined primarily by their dominant species, e.g. 1320 Spartina swards (Spartinion maritimae) and 2160 Dunes with Hippophae rhamnoides. Stands of the widely-introduced invasive common cord-grass Spartina anglica, and stands of the invasive sea-buckthorn Hippophae rhamnoides resulting from introductions outside its natural range, are not considered eligible for site selection in the UK.

Artificial or anthropogenic examples of several other Annex I habitat types are also specifically excluded from selection, either by Annex I itself or by the descriptions in the Interpretation manual (e.g. 3150 Natural eutrophic lakes with Magnopotamion or Hydrocharition-type vegetation and 3160 Natural dystrophic lakes and ponds). However, the Manual makes it clear that artificial examples of certain habitats are eligible for selection as SACs, e.g. 3140 Hard oligo-mesotrophic waters with benthic vegetation of Chara spp., 6130 Calaminarian grasslands of the Violetalia calaminariae, and 7150 Depressions on peat substrates of the Rhynchosporion. For these habitats the selection of artificial examples has been considered on a case by case basis. In general, preference has been given to more natural habitat examples, but artificial stands have been selected where they are of outstanding conservation interest.
Similarly, in selecting sites for Annex II species, artificial habitats within the species' natural range are eligible for selection. Most sites selected for Annex II bat species are artificial mines, tunnels or buildings, while the majority of the most important breeding sites selected for 1166 Great crested newt Triturus cristatus are artificial ponds. For certain other species, e.g. 1092 White-clawed crayfish Austropotamobius pallipes and 1831 Floating water-plantain Luronium natans, preference has been given to natural sites, but some artificial examples supporting large populations have also been selected.

Article 22(a) provides for Member States to "study the desirability of re-introducing species in Annex IV that are native to their territory where this might contribute to their conservation, provided that an investigation, also taking into account experience in other Member States or elsewhere, has established that such re-introduction contributes effectively to re-establishing these species at a favourable conservation status and that it takes place only after proper consultation of the public concerned." Annex IV lists animal and plant species of Community interest in need of strict protection, a list which includes all species listed in Table 1.3 above which are native to, but now extinct in, the UK, together with 1337 European beaver Castor fiber. Although a number of these species are subject to species recovery programmes in the UK, none can yet be considered sufficiently re-established in the wild to justify consideration as qualifying features on SACs.

1.5.2.6 Data collation
The process of identifying SACs has been underpinned by the collation of information on the distribution and abundance of Annex I habitats and Annex II species, both on individual sites and across the UK. UK data on the distribution and extent of Annex I habitats and the range and population size of Annex II species were published in JNCC Report, No. 312 'Handbook on the UK status of EC Habitats Directive interest features' (Jackson & McLeod 2000, revised 2002).

At a national scale, data on the distribution and extent of Annex I habitats have been summarised from a variety of sources, in particular information collected during the development of the National Vegetation Classification (NVC) (Rodwell 1991 et seq.), the National Marine Habitat Classification for Britain and Ireland (Connor et al. 2004), and a range of habitat databases and inventories, mostly held by JNCC or the country agencies. At the site level, information sources range from detailed habitat surveys to local expert knowledge. Data have been difficult to obtain for some habitats, either because they have been poorly studied in the UK or because of problems in relating Annex I categories to standard UK vegetation classifications.

Good distribution data are available for the majority of Annex II species in the UK, as this country has a long history of biological recording. National data were obtained from the Biological Records Centre (BRC) at the Centre for Ecology and Hydrology (CEH). Information on population size is generally much harder to obtain, especially at a national scale, but reliable population counts are available for some species on some sites.

Considerable care was taken to ensure that site selection was based on the best available information, but (as in other Member States), the distribution and abundance within the UK of some Annex I habitat types and Annex II species are imperfectly known. This is particularly the case for inconspicuous plant and animal species (e.g. bryophytes and molluscs), and habitats which have been poorly studied in the UK (e.g. chasmophytic types). The timetable originally set out in the Directive precluded the commissioning of significant amounts of additional survey work to complement existing knowledge. However, for certain habitat types and species, critical appraisal led to the conclusion that current knowledge was inadequate to evaluate sites, and site selection was then necessarily delayed to await the results of additional information collection and analysis. Additional survey has since been undertaken both to improve knowledge of certain sites within the SAC series, and to provide an overview of the wider resource, for example a coastal lagoon survey of Scotland (Covey et al. 1998; Thorpe 1998; Thorpe et al. 1998). This process is still ongoing in a small number of cases in the terrestrial environment, and is likely to be required for offshore features.

The distribution and relative abundance of many habitat types and species are even less well understood within the EU as a whole. In the UK a best assessment has been made of the contribution that will be necessary to fulfil the Article 3.2 requirement for each Member State to "contribute to the creation of Natura 2000 in proportion to the representation within its territory of...[ Annex I]...habitat types and the habitats of [Annex II] species".

 

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⁵ Generally, Mean Low Water in England and Northern Ireland; Mean Low Water of Spring tides in Scotland. In Wales, the limit is Mean Low Water for SSSIs notified before 2002, and, for more recent notifications, the limit of Lowest Astronomical Tides, where the intertidal features extend down to LAT. There is no provision for marine SSSIs/ASSIs beyond low water mark, although boundaries sometimes extend more widely within estuaries and other enclosed waters.