ISSN:
1573-5052
Keywords:
Hétérogénéité
;
Limite optimale
;
Heterogeneity
;
Optimal limit
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Description / Table of Contents:
Résumé La notion de ‘limite optimale’ a été proposée pour l'étude de la structure horizontale de la végétation à l'aide de transects divisés en segments. La valeur d'une limite est estimée à partir de la différence entre l'hétérogénéité de l'ensemble de la ligne et la somme des hétérogénéités de la partie de la ligne à droite et de la partie de ligne à gauche de la limite envisagée. Ces hétérogénéités sont mesurées par H(E)=log2 C N F (F = nombre de présences de l'espèce E envisagée, N = le nombre de segments du transect). Cette notion a été appliquée ici à deux problèmes: - l'un au niveau spatial pour tenter de préciser à l'échelle du 1/250 000, les limites de régions écologiques, - l'autre pour étudier l'évolution dans le temps d'une culture après abandon.
Notes:
Summary The optimal limit conceived permits the appraisal of the value of the limits that one has imposed on a series of ordered events, frequently of segments (observing the presence or absence of a species) distributed along a transect in order to study the horizontal structure of the vegetation. The value of a limit is defined by the difference between the heterogeneity of the whole line and the sum of heterogeneities of its parts to the right and to the left of the limit envisaged. The heterogeneities H are themselves defined for F presences of a species E over N segments of a line by:line fig This value is elsewhere corrected, taking into account the expectation of the value of a limit. In a collection of several species, it is possible to take as a limit the mean of the limits obtained for each species. This mean is a first approximation that does not take into account the possible relations between these species. This concept of a limit has been applied here in two cases: The first, at a spatial level to determine the limits of ecological regions at a scale 1/250 000. In this application the data consist of observations, made along a transect of 80 km long divided into 64 equal segments, of the classes of five variables (altitude, actual vegetation, successional status of the vegetation, precipitation, geology). The results obtained permit the confirmation of the limits that had been proposed previously, and also, recognition of new ones which had been overlooked. The second, at an abstract level, to search for clear differences between stages in the evolution of abandoned cultivated land. This is concerned with samples distributed in time, i.e. with relevés that have been recorded in different postcultural stages. Here the segments are post-cultural stages and the stages are ordered according to the period elapsed since abandonment. The example given shows the importance of the method in recognizing stages due to abandonment after cultivation (in this case viticulture).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00055293
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