A Study of the Variability of Some Successional and Climax Plant Assemblage-Types Using Multiple Discriminant Analysis

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Abstract
Vascular plant-species assemblage-types, resulting from a previous classification of 636 sites located on grounds of known age in front of the Storbreen glacier, Jotunheimen, Norway, were analyzed by multiple discriminant analysis. The technique, which aims to differentiate as clearly as possible between the groups in any classification, permits the characterization of within- and between-type variability, and hence a better understanding of the nature of assemblage-types. Between-type variability (the spacing and arrangement of groups in species-space) was represented by the position of the assemblage-types in relation to the first 2 discriminant axes. Within-type variability (group tightness) was similarly represented in graphical form, and by a probabilistic measure of the proportion of sites that are significant members and non-members of types in multiple-discriminant space. It is inferred that within- and between-type variability and, apparently, the discreteness of types, increase during succession and from high to low altitudes; at low altitudes succession proceeds via a relatively large number of stages and to a greater variety of alternative climax states than it does at higher altitudes. The unity of an early-successional assemblage-type owes much to a low within-type variability, whereas the unity of a climax-type tends to be more dependent on relatively great between-type variability. The results do not support the commonly-accepted hypothesis that successions tend to converge. Successional divergence was substantiated in the study area by analyses at 4 levels of resolution and at 4 quadrat sizes.