The Use of Point-to-Plant Distances in the Study of the Pattern of Plant Populations

Abstract

To determine whether or not the individuals of a plant population are distributed at random it is suggested that a sample of distances from randomly placed points to the plants nearest them be measured. An index of non-randomness denoted by [alpha] = [PI] L[SIGMA] r2/n may then be calculated, where [SIGMA]r2 is the sum of the squares of the point-to-plant distances, D is the mean number of plants per unit area and n is the number of distances measured. Then a is equal to, less than or greater than (n-l)/n according as the population is random, regular or aggregated. The significance of a departure of a from this value may be found from the fact that 2n a is distributed as X2 with 2n degrees of freedom. Further, [alpha] may be used as a measure of non-randomness and values of a from 2 different populations may be compared by a t-test. The use of random plants rather than random points as centers of measurement is shown to be theoretically less acceptable and to offer greater practical difficulties.