A Rapid Classification and Ordination Method and Its Application to Vegetation Mapping

Crawford, RM; Wishart, D

This paper describes firstly a rapid agglomerative method that can be used after the initial divisive process to check for any misclassification, and secondly a means of representing the variance both within and between the terminal groups by an ordination procedure. The need in ecological surveys for such a representation of the results of classification is demonstrated by the present dichotomy in the use of ordination and classification methods. A review of the problems involved in this divergence is given. The recently devised polythetic agglomerative methods of Jancy certainly give a solution to these problems, in that the ordination of the group centroids displays the relative distances between the resulting groups. However, as developed at present these methods are difficult to use with large surveys owing to the quadratic relationship between computation time and sampling number. In an attempt to overcome this difficulty the methods described in this paper achieve the economy in core storage which enables them to be used with large surveys by applying the same stategy as that used in previous communication. The basis of this approach was to look for the occurrence of groups produced by dividing the set of quadrats on the presence or absence of each species in turn. Thus each divisionof the data involved only N tests, where N sq. would have been necessary using existing methods. Thirdly a method is presented for mapping vegetation that has been sampled on a grid.

A Rapid Classification and Ordination Method and Its Application to Vegetation Mapping

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