[article]
| Titre : |
The Vegetation of Exposed Sea Cliffs at South Stack, Anglessey, I. The multivariate Approach |
| Auteurs : |
F. B. Goldsmith, Auteur |
| Année de publication : |
1973 |
| Article en page(s) : |
pp. 787-818 |
| Langues : |
Anglais (eng) |
| Catégories : |
[ZG] Royaume-Uni
[habitats/milieux] 18 - Côtes rocheuses et falaises maritimes
[Thèmes] Végétation
|
| Mots-clés : |
communauté végétale |
| Résumé : |
"The vegetation of sea cliffs near South Stack, Anglesey, has been analysed using association-analysis and ordination. The data collected from sixty-five stands and seventy-seven species were exceptionally diverse and show wide ranges of stand richness and species abundance. They proved exacting for the techniques and provided an opportunity to comment on methodological weaknesses. Some simple coefficients and methods of axis construction failed to produce an ordination but Orloci's similarity coefficient and principal components analysis produced satisfactory results. This method was applied to three types of raw data matrices, i.e. using stands, species and environmental factors as individuals. Each yielded information not available from the others although the stand ordinations are considered the most useful. Different measures of species abundance and the effects of standardization have been compared and discussed. Ordination diagrams derived from frequency data were preferred to those from cover or presence/absence data. Standardization of the raw data by stands is recommended for data showing a range of richness when preparing stand ordinations and by species prior to constructing species ordinations. These standardizations reduce the effect of richness and abundance respectively. Association-analysis of these diverse data indicated several failings of the method. These include chaining which results from the exaggeration of χ2 values with rare species and species-poor stands, reversals of the hierarchy which result from the fact that χ2 max. is an unsuitable measure of class heterogeneity, and the arrangement of the final groups in order of richness (normal analysis) or abundance (inverse analysis). The results of the normal analysis were satisfactory but those of the inverse analysis were of little use. Association-analysis, due to its monothetic nature, often produces misclassifications so that some of the final classes need combining. The deletion of all rare species and species-poor stands is recommended prior to analysis. The over-riding importance of salinity as the major environmental factor was clearly demonstrated. However, stand richness and total plant cover may be used as indicators of competitive intensity. Their distribution on the ordination diagrams indicates that salinity acts indirectly on the maritime species through interspecific competition. The competitive ability of inland species is reduced by salt-spray and a saline soil so providing an environment suitable for the growth of sea-cliff halophytes. The importance of grazing and the influence of birds has also been discussed." (source : auteur) |
| Type de publication : |
périodique |
| Référence biblio : |
Goldsmith F.-B., 1973 - The Vegetation of Exposed Sea Cliffs at South Stack, Anglessey, I. The multivariate Approach. Journal of Ecology, 61 (3) : 787-818. |
| ID PMB : |
72234 |
| Permalink : |
http://www.cbnbrest.fr/catalogue_en_ligne/index.php?lvl=notice_display&id=72234 |
in Journal of Ecology > vol. 61, n°3 (Année 1973) . - pp. 787-818
[article]
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