L A PROTECCIÓN DE LAS MINORÍAS EN EL T RATADO DE N EUILLY DE 1919.

The necessary time for the restoration of an ecosystem after a disturbance i.e. land use, is of great importance in nature conservation and consists an important criterion in many ecological evaluations. The restoration of an ecosystem after its destruction or disturbance is a successional process and includes both the restoration of the initial site conditions and the re-appearance of the typical for the site plant and animal communities (REIF et al. 2001).

In nature there are ecosystems that are adapted to frequent disturbances e.g. pioneer grasslands, shrublands, or woodlands on alluvial riverine sites. Such ecosystems can be restored in relatively short time that can range from a few years for the grasslands to some decades for the woodlands. On the other side, there are ecosystems with very long succession, e.g. virgin or old growth forests, moors, natural ponds, associated with special site conditions that require hundreds of years to be developed. These ecosystems can not be practically restored in case of destruction and for this reason they should be excluded from any use (PLACHTER 1991,BASTIAN &SCHREIBER 1994,

MERTZ 2000, REIF et al. 2001).

The restoration time of an ecosystem is often associated with its sensitivity against disturbances and can direct its management. For instance, while very long restoration time indicates that the ecosystem should be protected from any use, there are

ecosystems, such as some managed forms of forests, shrublands and grasslands, which can be restored on a relatively short basis either through succession, or extensive management, or by replacing them with similar ecosystems, e.g. plantations (MERTZ 2000).

Due to the fact that the restorability of the various ecosystems is not exactly known, it is a common praxis to define it in approximation to their regeneration / succession time. For this reason also the scales applied for this criterion in nature conservation are subjectively determined on a rough basis and often vary among specialists. However, the longer the succession of an ecosystem is, the more time is required for its restoration after a destruction, the higher its value in nature conservation and the more protection it deserves (PLACHTER 1991, BASTIAN & SCHREIBER 1994,

DIMOPOULOS et al.2000,MERTZ 2000).

The plant communities of the study area were evaluated for the criterion of restorability with a scale taking into account their succession time based on the respective scheme presented inPLACHTER (1991) and adjusted to the study conditions.

Specifically, the plant communities were classified into three restorability classes, which corresponded to short (< 20 years), medium (20-50 years) and relatively long (>50 years) succession / restoration time. The three classes were assigned with low, medium and high value for the criterion of restorability respectively.

The evaluation scheme assessed the restorability value of the plant communities through a rough approximation of the time the communities need to attain the typical species composition and structure. The classification took into account the land use type (forest, pasture, mowing, abandonment), the frequency of the disturbance (daily, periodical, occasional) and the approximate age of the vegetation. In general, this evaluation process is qualitative and can be considered subjective since the exact restoration time of the plant communities remains unknown.

OVERALL NATURE CONSERVATION EVALUATION

The results of the separate evaluations of the plant communities for each of the four nature conservation criteria have been used in a synthesis to derive an overall ecological evaluation. The synthesis was achieved through a classification of the communities on the basis of their similarity with respect to their diversity, naturalness, rarity and restorability. Before the classification, the high, medium and low value of the four criteria was replaced with the numbers 3, 2 and 1 respectively. The Ward algorithm and squared Euclidean distance were the settings of the classification. The classification aimed at aggregating the communities in groups characterized by similar pattern for the four nature conservation criteria, which were further investigated means a Principal Components Analysis (PCA) that was applied to the community set. The ecological characteristics of the identified community groups were further illustrated through the respective ordination plot and set the necessary ecological basis for the conservation management of the cultural landscape.

To facilitate the explanation of the community groups, after the classification the rank scale (1, 2 & 3) of the four criteria was reverted to the initial nominal scale, i.e. of low, medium and high value respectively.

Finally, the same classification procedure was applied twice more, each time by giving weight to a specific criterion (naturalness or diversity), which was considered of special gravity in the cases of two alternative management scenarios about the study area. According to the first scenario the management aimed at enhancing the naturalness of the area, thus special weight was given to the criterion of naturalness, which was multiplied by three (3) for all communities, while the other criteria remained as they were. The second scenario aimed at supporting the plant species diversity of the area and thus special weight was given to this criterion, which was tripled, while the other criteria kept their initial value. The z-standardization of the variables was applied in both cases, in order to prevent the oversized influence of the weighted criteria (BÜHL 2001).