Local ranges of phytosociological associations: are they reflected in numerical classification?

Abstract

In the tradition of European phytosociology, delimitations of vegetation units such as associations are mostly based on data from small areas where more detailed vegetation sampling has been carried out. Such locally delimited vegetation units are often accepted in large-scale synthetic classifications, e.g. national vegetation monographs, and tentatively assigned to a small geographical range, forming groups of similar (vicarious) vegetation units in different small areas. These vicarious units, however, often overlap in species composition and are difficult to recognize from each other. We demonstrate this issue using an example of the classification of dry grasslands (Festuco-Brometea) in the Czech Republic. The standard vegetation classification of the Czech Republic supposes that the majority of accepted associations (66 out of 68) have a restricted distribution in one of the two major regions, Bohemia or Moravia. We compared the classification into traditional associations with the numerical classification of 1440 phytosociological relevés from the Czech Republic, in order to test whether the traditionally recognized associations with small geographical ranges are reflected in numerical classification. In various comparisons, the groups of relevés identified by numerical analysis occupied larger areas than the traditional associations. This suggests that with consistent use of total species composition as the vegetation classification criterion, the resulting classification will usually include more vegetation units with larger geographical ranges, while many of the traditional local associations will disappear.

Classification of mesic grasslands and their transitions of South Transdanubia (Hungary)

“…It seems time to revise these two association names and descriptions (Festuco commutatae-Cynosuretum and Anthyllido-Festucetum rubrae) based on statistical analyses, limit their application to narrower geographic areas and find appropriate names for the others. Moreover, if uniqueness and distinctness of narrow-range associations are not supported enough, it is advisable to adopt names from the syntaxonomic systems of neighbouring countries in order to standardise the nomenclature of syntaxa over the countries (KNOLLOVÁ et al 2006). Based on archive data and available literature of Central European countries (HÁJKOVÁ et al 2007, JANISOVÁ et al 2007, Festuco-Cynosuretum, Anthoxantho-Agrostietum and Festuco-Agrostietum seem equally applicable names for southern Hungarian extensive pastures.…”

Acer-Fraxinus dominated woods of the Italian peninsula: a floristic and phytogeographical analysis

“…1). This was predictable since, as recorded by Knollová et al [48], analyses based on large datasets identify groups of relevés that occupy larger areas than those identified by local datasets. In particular, it is clear that the more highly characterized sociological groups (e.g.…”

“…S1). They were classified numerically using TWINSPAN as divisive polythetic method [47] in order to characterize homogeneous floristic groups defined in a large-scale classification [48] and to avoid the problem of existing syntaxa based on a single/few relevés, without suitable synoptic tables. Five pseudo-species cut levels were selected, corresponding to 0, 2, 3, 5 and 7.…”

Scope and data set of the phytosociological database ‘Grasslands in the Polish Carpathians’

“…Some of them certainly reflect the arbitrary views of the authors who tended to put associations into very narrow categories; another may illustrate the actual temporal and spatial variability of the vegetation. To clear up the relationships among these syntaxa, a comparison of traditional classification system with results of numerical or supervised classification is needed [9][10][11].…”