Biodiversity, the ultimate agri-environmental indicator?: Potential and limits for the application of faunistic elements as gradual indicators in agroecosystems

Most political statements (e.g. convention on biodiversity), referring to existing approaches regarding the development of biotic agrienvironmental indicators focus mainly and nearly exclusively on "biodiversity", the enhancement of which is almost the overall target for the development of agricultural landscapes towards sustainability. In this regard the understanding of the term "biodiversity" is rather different: mostly it is interpreted as species richness, only occasionally as richness of varieties, cultivars or genetical expressions (e.g. micro-organisms). In this contribution the approach of evaluating the quality of species communities in agroecosystems mainly on the basis of "biodiversity" (in the sense of species richness), will be analysed critically. General difficulties of an exact sampling or establishment of biodiversity especially of invertebrate communities in agricultural landscapes will be highlighted. Arising from this synthesis, it is demonstrated that biotic agrienvironmental indicators should not only address a maximising of species numbers in agricultural habitats, but also a sustainable and long-term stability, and the reproductive potential of populations of species typical of agroecosystems. In this regard alternative biotic indicators for the assessment of the effects of husbandry practices are required that are based on existing knowledge of the reactions of populations and species communities to environmental stress, and which give information about the physiological fitness of populations of species that are relevant members of the agrobiocoenosis from both the qualitative (rarity, endangerment status) and functional point of view (natural enemies, parasitoids, decomposers). Regarding the sensitivity of those indicators it will be indicated that in contrast to many recent scientific experiments it is usually necessary to evaluate and compare cultivation intensities, that are quite similar (e.g. gradual differences in conventional managed farms and landscapes) as well as those displaying much larger differences (e.g. organic farming vs. conventional farming), because conventional farms currently cover nearly 90% of the area under plough in Europe. Finally an assessment of the practicality, the power of indication statements and the remaining work required to validate indicators will be provided for discussion, as well as suggestions for a simplification of indicator systems in order to minimise the input needed for data recording.