A computer method for the arrangement of phytosociological tables

Abstract

A phytosociological table is a matrix, each of whose rows corresponds to the occurrence of a particular plant species and each of whose columns corresponds to a sample plot in which the several species occur. Each plot list is called a releve. The elements of this matrix are binary, corresponding to the presence or absence of each species in each plot. Thus if the ith species is present in the jth releve, then the ijth element of the phytosociological table is equal to one; if the ith species is not present in the jth releve, then the ijth element is equal to zero. For over half a century, botanists have used tables of this kind to indicate patterns of association among species of plants by showing which combinations of species are either mutually present or mutually absent in groups of releves.1 One of the major problems in communicating the information in one of these tables is the problem of arranging the order of the rows and columns of the table so as best to display the relationships of mutual presence and mutual absence among the species. This problem has been solved in the past by selecting the best of a series of trial arrangements, based on the botanist's experience of putative associations among the several plant species and similarities among the releves in the table. While this method is adequate for most displays, it suffers from at least two serious drawbacks. First, the number of trial arrangements which the botanist may test in a reasonable amount of time is quite small; second, the arrangements which are most likely to be attempted are highly dependent on the training and experience of the individual botanist. In other words, it is quite possible that the “best” arrangement of species and releves for the display of a particular phytosociological table may vary substantially from botanist to botanist. In the interest of speeding up this procedure and making it more objective, we present a computer program for the arrangement of phytosociological tables.