Biodiversity evaluation in agricultural landscapes: An approach at two different scales

Evaluating biodiversity in agricultural areas requires two steps: (i) adequate measurement and (ii) pertinent interpretation. Since the whole spectrum of biodiversity in the sense of the Rio Convention cannot possibly be measured as such, adequate measurable correlates or surrogates have to be found. One possibility are standardized inventories to assess species diversity in specious groups of arthropods. They can provide reproducible and comparable values for estimates of site-specific biodiversity in the form of averaged rarefaction functions for the relationship between numbers of individuals and numbers of species in different habitats. Examples of 'rapid biodiversity assessment' are presented and their possibilities and limitations are discussed. At a higher integrative level, biodiversity evaluation can be based on landscape parameters. According to a proposed conceptual model, the 'mosaic concept', regional biodiversity mainly depends on structural parameters such as habitat diversity and landscape heterogeneity, and functionally on metacommunity dynamics. Approaches with a combination of both site-specific biodiversity measures and assessments of habitat diversity and heterogeneity are not yet established, but in the near future may lead to a scientifically based evaluation of the potential for increasing biodiversity by appropriate landscape management. In the light of scenarios for global change, maintaining high levels of overall biodiversity in agroecosystems may become as important for ecological sustainabilty as keeping up high abundances of presently well-adapted beneficial organisms. (C) 1997 Elsevier Science B.V.