An account is given of the development of a data-analysis system incorporating digitized information about ecological and biological traits of species, for use in environmental evaluation procedures. Fuzzy-coding of ecological traits is highlighted as being a valuable tool in this system: (i) it allows a quick and standardized transcription of the experts' knowledge about groups of species, (ii) it encapsulates the flexibility of some of the species traits or the varying degrees of precision with which they are known, (iii) it builds up numerical sets which can be processed with standard ordination methods and can therefore be incorporated into inter-battery analyses (e.g. co-inertia analysis) of field observation data and knowledge data bases. As an example, use of fuzzy-coded information for species of hoverflies (Syrphidae) in assessment of riverine wetland ecosystems is demonstrated, based on sites on the rivers Allier and Loire in central France.