After the Rio Convention in 1992 the term biodiversity entered our lives, more or less as a panacea which would solve all ecological problems. However the term had been used long before Rio to express the diversity of life forms to be found in a particular place. Despite the simplicity and clarity of the term its content is one of the most abstract and debatable in ecology. The reason is that there are not one but many biodiversities at different levels of biological organisation, and that there is no uniform method of expressing or rather assessing this. In practice, four different levels of biodiversity can be distinguished, each having its own special value while at the same time being an inseparable part of the whole.

The first level is that of genetic diversity . Genetic diversity refers to the range of genotypes in a particular species. The greater the range the more tolerent the species in the face of external stresses such as pests and diseases, adverse climatic changes, etc. It is clear that natural species have a far greater range of genotypes than artificial or genetically improved species and hence are more robust and adaptable than the latter. In Hellas, due to its geographical position, variety of climate zones, mountainous terrain and history, plant and especially tree species show a high degree of genetic diversity, which has so far been very little studied. During the Ice Age, many Central and Northern European species migrated southwards and reached Hellas, thus creating either heterogeneous populations of one species or hybrids with the pre-existing species, and in this way expanding the range of genotypes. Well-known examples are the King Boris fir which is hybrid of cephalonian and silver fir, and the moesiac beech, hybrid of oriental and common beech. In these hybrid populations one meets all the variations and intermediate stages between the one species and the other, depending on the latitude and local climate. Another example of heterogeneity and consequently great genetic diversity comes from the population analysis of the scots pine in Pieria and the spruce in Rhodope. These species reached Hellas during the Ice Ages from different regions, whose characteristics they bear even today. Thus within a small area the scots pine is to be found in all its forms from tall, narrow, thin-branched Alpine types to rounded, thick-branched types from the plains of Poland. The same goes for the Norway spruce: types dispersed in Central Europe are found in Hellas gathered together in a relatively small area. This large genetic diversity of the above species (fir, beech, scots pine and spruce) is to be found in almost all Hellenic forest species. The same is probably true for other Hellenic plant and animal species. This, together with the great advantage that the country s ecosystems have, despite considerable degradation, remained qualitatively in their natural composition, makes Hellas very important as a gene bank and in general a reserve of genetic material that needs to be studied and conserved.

The second level is that of species biodiversity. This biodiversity is expressed as the number of plant and animal species to be found in a particular area. For many researchers however this definition is insufficient. They believe that the number of species does not always give a true measure of biodiversity, as the species population, the size of individuals, their biomass and the dominance of certain species also enter into the equation. Others measure biodiversity by the number of functions performed by the species in a particular ecosystem, in other words the number of niches. Since, however, it is difficult to evaluate all these parameters, for the time being we must be content to define species biodiversity as the number of plant and animal species found in a particular area or ecosystem. Species biodiversity is of obvious importance to ecological balance, the stability and operation of the feedback mechanisms in an ecosystem. The more species there are in an ecosystem, the more stable the system, the denser the food web and the biosystems, the smoother the biomass and energy flows and nutrient recycling, and the more efficient the operation of the feedback mechanisms. Apart from this, many organisms have in the course of their ontogenetic development become closely associated with other organisms, so that the existence of the one depends on the existence of the other. This is why the extinction of a species can have unforseable consequences. Hellas, for the reasons mentioned above, presents high species diversity. Indeed, for its size it contains the greatest biodiversity of all Member States of the European Union. Although this level of biodiversity has been studied more than any other, there is still need for further work, particularly as regards the spatial distribution of species.

The third level is that of habitat diversity, expressed as the number of links between plant and animal species (habitats) found in a particular area. The number of habitats and their spatial distribution form a mosaic of habitat types which puts its stamp on the landscape of the area, so by protecting habitats not only one protects the species that compose them but also preserves the character of the landscape. Hellas, due to its large number of links between plant and animal species, presents great habitat diversity, which unfortunately has been insufficiently studied despite its obvious importance. The competent authorities should accept the pressing need to map the country s plant communities, as being of vital importance for the conservation of Hellas s natural environment.

The fourth level of biodiversity is that of landscape diversity, expressed as the number of landscape types in an area. Landscapes include not only natural habitats but also man-made ecosystems such as farmland and human habitations. The number of natural or man-made habitat types, their spatial distribution and relative frequency determine the character of the landscape. In addition to landscape architecture, which is taught in many educational institutions, recently the new science of landscape ecology has been developed, to study the interactions and interrelationships between the ecosystems that compose a landscape and especially between natural and man-made ecosystems.

Greece has great landscape biodiversity, for the same reasons that it has great genetic, species and habitat biodiversity. The landscapes range from the semi-desert of Eastern Crete to the Scandinavian (northern) of Rhodope and the Alpine of Mts. Olympus, Smolikas, Timfi, Voras and the other mountain ranges of Northern Hellas. Within the relatively short distance from town Amphipolis to Central Rhodope one meets all the landscape types from the Mediterranean, with olives, holm oak and Arbutus sp., to the northern landscapes of boreal conifer forests with Norway spruce, Scots pine and birch.

To sum up, one can say that Hellas possesses a high degree of biodiversity at all levels-genetic, species, habitat and landscape.

Regardless of the distinctions between the different levels, biodiversity must be conservedas a continuum, as one entity. The conservation of each level depends on the conservation of the levels above and below. Landscape protection and conservation depends on the conservation of the biodiversity of the component habitats. The stability of the habitats depends on protection and conservation of the species that contribute to their structure, that is the species biodiversity, and the protection and survival of the species depends on the conservation of their genetic biodiversity, the conservation of the full range of genotypes.

In closing we would like to stress that the conservation of biodiversity at all levels is not a romantic ideal but a precondition for the sustainable management of natural resources, and consequently for the survival of man himself.