HABITAT TYPOLOGIES AND CONSERVATION OF BIODIVERSITY

Pierre Devillers, Jean Devillers-Terschuren and Roseline C. Beudels-Jamar

Royal Belgian Institute of Natural Sciences, Conservation Biology

The principal mechanism that drives the biodiversity crisis, threatening species, populations and biocoenoses, is habitat destruction, fragmentation and degradation. The establishment of coherent networks of areas under diverse levels of protection is the most adequate corrective measure and at the core of conservation strategies. Adapted to the conservation of the biological values targeted, these networks are usually capable of preserving most species and the communities they constitute. Overall conservation measures applied in the rest of the environment bring a complement of protection to less sensitive species and less fragile communities.

The individual sites that compose the networks are chosen for their contribution to the overall diversity of the system, to the complex requirements of a species or a community, or to the representation of the spectrum of their geographical and ecological variation. Some sites are established for the preservation of threatened or patrimonial species, with requirements that exceed those of most members of the communities to which they belong. For these sites, data about the target species are, and will remain, the best source of criteria for site selection. Other sites, perhaps a majority, should be dedicated to the conservation of the entire regional diversity. The definition of criteria for their selection is a central preoccupation of conservation biology. The total diversity of species, populations and interactions cannot be accurately inventoried, even less included in legislation. Resorting to surrogate variables is thus inescapable.

Traditionally, surrogates have been indicator species or groups of species. Although this approach, illustrated, in particular, by the hotspot methodology, has had undeniable successes. It has, however, shown its limitations. At the small scales of spatial resolution characteristic of conservation areas world-wide, networks established for distinct taxonomic groups are not congruent. It appears that a methodology based on the recognition of a sufficiently detailed array of habitat units offers an operational alternative. The holistic approach that it constitutes insures a less uncertain link between the units taken into consideration and their constituting elements than that which might exist between two unrelated taxonomic groups. At the same time, the integration effect of these units permits the consideration of a much smaller list of entities than the full array of species that contribute to their construction.

The Physis typology, derived from the methodology developed for the CORINE-Biotopes project, provides a framework to organise in an ordered sequence the habitats of the world. Within its scheme a habitat is a three-dimensional spatial entity that comprises at least one interface between air, water and ground spaces and includes both the physical environment and the communities of plants and animals that occupy it. Habitat definitions depends on the scale at which they are considered. The level of resolution of the Physis typology is that of the ecological requirements of small vertebrates, large invertebrates and vascular plants.

A unit in the Physis habitat typology is a habitat type, thus a characterisation of a collection of spatial entities sufficiently alike in abiotic conditions, physiognomy, composition of plant and animal communities to play similar roles from the point of view of nature conservation. There is an unavoidable degree of arbitrariness in deciding whether two communities are sufficiently similar to be referred to the same unit, or conversely, sufficiently different to warrant distinctive treatment. For plant communities, phytosociological criteria were used to assess degree of divergence and its relevance to sensitive species. For animal communities, data are often lacking precisely for the groups most in need of habitat conservation rather than species-specific programmes.

All habitat classifications use, alone or in combination, similarities in physiognomy, abiotic conditions, plant community composition, plant dominance, plant community succession and, sometimes, animal community composition to combine elementary units into collective entities of successively higher rank. The priority given to the various criteria and the ensuing classifications are necessarily a matter of choice. The guideline of the Physis habitat classification has been to use large-feature physiognomy, plant-community composition and biogeographical or ecological factors underpinning animal-community composition, in that order. The scheme allows for evolution of the hierarchy as understanding of the habitats of a geographical area improves, as new needs of identification arise, as an increasing portion of the total geographical area concerned is examined in detail without affecting previous applications of the list.

The method has, so far, been applied to three biogeographical realms. It has resulted in the constitution of three databases, accompanied by a number of satellites and excerpts :

A classification of Palaearctic habitats Habitats of South America Habitats of Africa

The CORINE-Biotopes inventory of sites of European Community significance for nature conservation was based on species-oriented and habitat-oriented criteria. The

latter resulted in a larger number of identified sites, in particular, in regions of

diffuse distribution of species.

Species lists

Species-orientedconservation areas

Hotspot conservation

Flagship species

Habitat lists

Habitat-orientedconservation areas

Indicator species

Habitat typologies

Surrogate indicators

Silent diversity

Target communities

Target species

Council Directive 92/43/EEC of the European Union on the conservation of

natural habitats and of wild fauna and flora. Appendix 1, listing habitats to be

included in the Natura 2000 Network was constructed on the basis of the CORINE-

Biotopes typology.

Keys to habitat identification at the regional level have been

derived from the Physis typology, in particular, in the Walloon

Region of Belgium.

Developments envisaged:

Extension of the continental frameworks to other parts of the world.Improvement of detailed regional coverage of existing continental typologies.Mapping of typology units.Investigation of scale factors.Validation of adequacy in coverage of silent biodiversity.

www.naturalsciences.be/cb/

The Physis habitat typology, and its predecessor, the CORINE-Biotopes habitat typology, have had a number of applications, at continental, regional and local scales. Among them:

The Physis typology was directly instrumental in establishing a list of priority habitats for the

Bern Convention. It is one of the tools of construction of the Emerald Network of sites

being identified throughout Europe at the initiative of the Council of Europe.

Clé d'identification provisoire des habitats de la Région wallonne

La clé est formée d'une série de tableaux. Chaque tableau offre un choix multiple dont les options correspondent à des cases. Dans chaque case se trouve un texte d'aide au choix, une borne d'information et une borne de sortie.

Annex I. Natural habitat types of community interest whose conservation requires the designation of special areas of conservation Interpretation Code: The hierarchical classification of habitats produced through the Corine programme (Corine biotopes project) is the reference work for this Annex. Most types of natural habitat quoted are accompanied by the corresponding Corine code.