7 - Point patterns

Summary

Introduction

In Chapter 1, one of the first topics introduced was the distinction between treating the information on the spatial arrangement of plants as dimensionless points in a plane or as a mosaic of patches filling the plane. In this chapter, we will examine a number of methods that evaluate certain properties related to spatial pattern using the positions of individual plants in a plane. Several reviews of the analysis of spatial point patterns are available (Diggle 1983; Upton & Fingleton 1985; Cressie 1991), and it is not the intention to repeat a great deal of the material covered in those books. Instead, those methods that parallel the approaches described elsewhere in this book, but using points rather than density or presence, will be emphasized. In general, the kind of data that will be used here is mapped plant positions within a defined study area or plot. Considerations of the shape of the study plot to be used are discussed in Chapter 2.

There are several considerations to be included in our examination and evaluation of methods based on the positions of individual plants. The first is that for an investigation of spatial pattern, techniques that merely distinguish among the three possibilities of clumped, more-or-less random, and overdispersed are not really of interest for the purposes of this book. We want to get more out the analysis; for example, if the plants are overdispersed, what is their spacing, how uniform is the spacing, is the spacing the same between plants of different kinds?