AN ECOLOGICAL CLASSIFICATION OF FLORISTICAL RELEVES BY COUPLING A REGIONAL SURVEY WITH A NATIONAL DATA BANK

Abstract

The proposed method is based only on tlotistical data and nevertheless classifies the relevés into ecological groupings, corresponding to as similar environments as possible. It begins by calibrating the behaviour of each plant along a large gradient, in a national data bank of floristical releves, on the scale of France, the bank Sophy. It calibrates the behaviour of a plant by its fidelities to the 5,626 other plants of the bank, which are considered as indices of the environment. It defines a statistical space having 5.626 dimensions in which: 1) an axis measures the fidelity to a plant, considered as an ecological index; 2) a dot corresponds to the behaviour of a plant towards the indices; 3) the distance between two dots expresses the ecological difference between two behaviours; 4) the centre of gravity for the plants of a releve indicates the probable position of the relev6; 5) the distance between two releves expresses their ecological difference. Compared with this method, the correspondence factor analysis CFA: 1) locates the releves in a space, according to the fidelities of plants to releves, showing their floristical differences; 2) gives a weight to a plant according to its rarity, not its ecological behaviour; 3) deals only with subsets of the releves and rehandle the subsets by successive approximations; 4) transfers onto the graphs the empirical and intuitive method of a naturalist during field-work, The method is applied to about 400 releves in a district in the Northern Vosges (France). It generates an automatic classification of the releves, at several levels of synthesis. including the upper levels above the phytosociological classes. It explains half of the peculiarity of a type of plant community with 10 to 30 discriminant plants, which are the quantitative and gradual homologues of characteristic species.