Arranging phytosociological tables by species-relevé groups

Abstract. A newmethod of arranging phytosociological tables by species-relevé groups (blocks) on the basis of the density of rows and columns (relative species frequency and relative species number) is presented. Each block fulfils a given minimum criterion regarding its density. With a density threshold of e.g. 50 %, blocks are formed with only those species that are present in at least 50 % of the block's relevés, while at the same time the block's relevés comprise at least 50 % of the block's species. The procedure starts with the complete table and iteratively masks species and relevés with the smallest densities. This is performed step by step with species and relevés and continues until the given density threshold for all species and relevés is exceeded. Without any further parameters other than the minimum density, species-relevé groups of gradually decreasing size are formed. Data processing is performed with a computer program (ESPRESSO). The main application of the method is found in an effective pre-sorting of relevé data. The blocks formed can be arranged in the final table as desired.     

Elements for a system of data processing in phytosociology and ecology

Summary An organization for data-processing in phyto-sociology and plant ccology is deseribed. A good preparation by means of standard sheets for collecting and codifying information from the field is emphasized (Fig. 1). Fig. 2–5 present the arrangement and the logical sequence of the different methods of data analysis (ecological profiles, factor analysis,...) which allows the study of the relations between environmental and floristical variables, in a quick and efficient way. Cooperation with the Ecothèque méditerranéene at Montpellier is both necessary and fruitful. One example is presented using the selection e of 58 relevés of salt marsh vegetation retained by the Working Group for Data-Processing of the International Society for Vegetation Science.

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Résumé Les auteurs proposent ici une organisation du traitement des données en phytosociologie et phyto-écologie. L'organisation repose sur un système bien développé pour rassembler et codifier l'information des reléves. (fig.1). Un ordinogramme (Fig. 2–5) présente l'agencement et l'enchaînement des différentes méthodes d'analyse des données (profils écologiques, analyse factorielle, ...) qui permettent d'étudier les relations entre variables du milieu et variables floristiques. La conception de l'enchaînement des fichiers et des programmes de traitement permet d'aboutir assez rapidement aux résultats, facilitant ainsi la tâche du phytosociologue et du phyto-écologue. Ce travail a été réalisé en commun entre le C.E.P.E. Louis Emberger et l'Ecothèque méditerranéenne conduisant à une coopération nécessaire et utile. Une exemple est traité utilissant la sélection e de 58 relevés de milieux salés, sélection retenue par le groupe de travail traitement des données en phytosociologie de l'Association internationale de phytosociologie.

     

Clusla: A computer program for the clustering of large phytosociological data sets

Summary CLUSLA, a computer program for the clustering of very large phytosociological data sets is described. It is an elaboration of Janssen's (1975) simple procedure. The essence of the program is the creation of clusters, each starting with one relevé, as the relevés are entered in the program. Each new relevé that is sufficiently distinct from already existing clusters is considered a new cluster. The fusion criterion is the attainment of a certain level of (dis-) similarity between relevé and cluster. Bray and Curtis' dissimilarity measure with presence-absence data was used.The program, written in FORTRAN for an IBM 370–158 system, can deal with practically unlimited numbers of relevés, provided the product of the number of primary clusters and the number of species does not exceed 140.000. We adopted maxima of 100 and 1400 respectively.After the primary clustering round a reallocation is performed. Then a simple table is printed with information on the significance of occurrence of species in clusters according to a chi-square approach. The primary clusters can be treated again with a higher fusion threshold; or approached with more elaborate methods, in our case particularly the TABORD program.The program is demonstrated with a collection of 6072 relevés with 889 species of salt marsh vegetation from the Working-Group for Data-Processing.Contribution from the Working Group for Data-Processing in Phytosociology, International Society for Vegetation Science. Nomenclature follows the Trieste system, which will be published later.The authors are very grateful to Drs. Jan Janssen, Mike Dale, László Orlóci and Mike Austin for their comments on drafts of the program, and to Wil Kortekaas for her help in the interpretation of the tables.     

Phytopak

PHYTOPAK, a series of computer programs that facilitates the handling and analysis of large sets of phytosociological data is described. The programs are written in FORTRAN IV, and have been implemented on both IBM and CDC computers. The programs have been developed for use in the National Vegetation Classification, currently being undertaken in Britain, where a requirement for handling very large data-sets (up to 35 000 relevés with a total of over 3000 species represented) was the major requirement.The work described here forms part of the National Vegetation Classification supported by the Nature Conservancy Council. The financial support of J. P. H. by this project is gratefully acknowledged. We are particularly grateful to the University of Cambridge Computing Service for providing computing facilities and friendly advice. The conversion of the IBM version of PHYTOPAK into a CDC version was implemented by B.H. at the University of Manchester Regional Computer Centre, with the assistance of Mr. Cliff Stone. Dr. A. J. C. Malloch kindly provided us with his program for renumbering species code numbers which formed the basis of RENUM. We are grateful to Dr. P. Adam, Dr. M. P. Austin, Dr. M. B. Dale, and Mr. M. O. Hill for helpful comments and suggestions.     

Theoretical vegetation science on the way

Some historical notes are presented on the start and early development of the Working-Group for Data-Processing, now Working-Group for Theoretical Vegetation Science, of the International Association for Vegetation Science. One of the major outcomes of the first period of activities in the Working-Group has been the creation of a phytosociological coding and retrieval system to be used in combination with multivariate methods. One branch of classical phytosociology which could have profited much from the Working-Group's achievements, i.e. syntaxonomy, never developed fully into a numerical syntaxonomy and, in fact, it did not develop much at all over the last 20 yr.The next phase in the development of the Working Group is characterized by a strong emphasis on vegetation dynamics. First, these dynamical studies concentrated on real sequences of data from permanent plots, which were treated with the numerical methods available. Later, dynamical models started to be developed in order to predict succession and other forms of long-term vegetation dynamics, for which real data are not available.The third phase, which has been entered only recently, is characterized by an overall emphasis on vegetation theory, from which both the most appropriate choice of numerical methods in any particular case, and dynamical phenomena can be approached. Moreover, vegetation theory is of fundamental importance for the development of the plant community concept and of vegetation typology.In addition, some remarks are made on the growing need for vegetation ecology to cooperate with experimental ecophysiology and population ecology.