On being faced with the task of predicting the performance of lesserknown
crops in Papa New Guinea (PNG) for a land evaluation project, I
reviewed the ways in which plant/environment relationships have been
described. It became apparent that there was an hierarchical set of methods
within which one could identify four distinct levels labelled A to D in order
of increasing detail (Fig. 1). Each of these levels contained a distinct type of
environmentally-related information (Table 1).