Threshold values for nature protection areas as indicators for bio-diversity - a regional evaluation of economic and ecological consequences

Threshold values for nature protection areas are used as indicators for their nature protection value. Several values related to a minimum share of the area in a region or a country have been proposed as basic conditions for a sound development of natural areas. Although the height of these thresholds is still a matter of extended scientific discussion (they range from 5 to 30% of the agricultural area), they have been embraced by political parties and legislation concerning nature protection. This paper highlights the consequences of the practical application of such thresholds. The example of an intensively used agricultural region, the Kraichgau in Baden-Wuerttemberg, is chosen. To improve the actual situation concerning bio-diversity, a selection of sites with a good potential for the development of oligothropic dry grassland was proposed. To evaluate the consequences of this proposal a GIS based modelling tool was used. By the connection of biological, economic and a-biotic models it was possible to describe the reactions of all these factors simultaneously in form of a scenario. The scenario describes an increase of dry grassland area of approximately 10%. Economically, the reduction of acreage leads to a change of crop ratio and a decrease of gross margin. Due to their profitability, row crops remain with their original amount within the rotation of crops and lead, therefore, to intensification within the region. The accompanied increase of erosion rates results in a higher nutrient impact to adjacent bio-topes (hedges, ridges), thus leading to their further deterioration. Consequently, the gain of bio-diversity in some parts of the region is coupled with a loss of bio-diversity in others. Analysing these results, the usefulness of using an integrated economic-ecological modelling system for the evaluation is shown. Later, discussion of the consequences for the economic as well as for the biotic situation provides an idea of the limitations of the thresholds as indicators with respect to their practical performance. Recommendations for the necessary differentiations pertaining to regional context are given to improve the validity of this indicator type. (C) 2003 Elsevier Science B.V. All rights reserved.