Fidelity is the most fundamental notion of the Braun-Blanquet school of phytocoenology. It can be applied to all non-phenotypic taxa and to all syntaxa irrespective of their rank. This holds both for faithful and for differential taxa. In the latter case the range of syntaxa within which the taxon is differential should also be indicated.
Not only taxa, but also their growth-form and microhabitat may be characteristic for a given syntaxon. A new concept: 'elementary coenological unit' (ECU) is therefore introduced for a taxon-growth-formmicrohabitat combination. Fidelity of ECU's is restricted both in space and in time. Various cases as well as the causes of this limitation are discussed.
The criteria for fidelity are discussed, including abundance, cover degree, vitality, fertility and constancy (presence degree). It is demonstrated that these parameters by no means show parallel variation. Their biological significance is discussed. It is proposed to ignore the occurrence of species with reduced vitality and to base fidelity degrees on the thus modified total cover value TC' (scale Barkman, Doing & Segal, transformation values by Van der Maarel) in a given syntaxon divided by its TC' in the syntaxon with the most similar TC' value (TC' ratio).
The well-known scale of fidelity degrees by Szafer & Pawtowski is criticized and a new scale is proposed, which is equally quinquepartite, but has only two classes of fidelity. It also has two classes of infidelity and one class of indifferent species. The threshold values between these classes are proposed to be fixed at the TC' ratios 5, 2, 0,5 and 0,2.
Abbreviation: ECU = Elementary coenological unit
Introduction. Faithful and differential species
Fidelity is the most fundamental notion of the Braun-Blanquet (SIGMA, Zt~rich-Montpellier, French-Swiss) approach to phytosociology. It is also the concept through which this school differs from all other schools of vegetation science. Fidelity is often defined as the degree of preference of a species for a given association. In practice fidelity is often determined for taxa of lower Comm. no. 367 of the Biological Station Wijster of the Agricultural University Wageningen, The Netherlands