Different Types of Heterogeneity and Plant Competition in Monospecific Stands

The influence of four types of heterogeneity (heterogeneity in spatial arrangement, initial size heterogeneity, environmental heterogeneity in space and in time) on the development of a plant population was studied using a simple model of plant growth and competition. Parameters were estimated for Scots pine (Pinus sylvestris). The model showed that without heterogeneity the population became very unstable, so that even a small decrease in environmental favourability caused population collapse, because there was not any differentiation and competition was extremely severe. The presence of any type of heterogeneity created a basis for social differentiation of individuals. As a consequence, self-thinning occured and lowered the competition. The population became smaller, but more tolerant against decreases in environmental favourability. However, a glut of heterogeneity is rather deleterious, because it further diminished the population while adding nothing to its tolerance.