Competition and skewness in plantations

Data published recently on the stem diameters in experimental Pinus Radiata plantations, show a skewness which is initially zero, first becomes negative and later reverses direction, becomes positive and increases indefinitely. This and other behaviour are explained using a zone-of-influence model based entirely upon competition between neighbouring trees. Negative skewness can be identified with the early stages of competition when only the largest trees compete. The model also generates bimodal distributions when competition is intense, as observed experimentally in annual plants. Further modes are generated as competition is increased further.