The Use of Plant-to-Neighbour Distances for the Detection of Competition

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Abstract
In an aggregated plant population, the pattern within high density patches may be regular owing to competition. But tests for pattern applied to the whole population will usually indicate only the overall aggregation and will not reveal the localized regularity. Evidence as to whether or not a population exhibits such "within-clump" regularity may be obtained by collecting a sample of plant-to-neighbor distances that are less than some chosen value. The use of a sample thus truncated permits detailed study of the spatial pattern within the high density patches. Denoting the square of plant-to-neighbor distance by w, the frequency function of w in a non-competing population is monotonically decreasing from a finite value at w=O. If competition among the plants is causing them to be regularly spaced where their density is high, the distribution of w will have a mode at some w>O. The modal value of w is proportional to the area pre-empted by each plant. A test for within-clump regularity is described. Also, a method is proposed for estimating the modal value of w in populations exhibiting such regularity. Results from five natural populations of forest trees serve as examples.