ABSTRACT
Aikman and Watkinson (1980) proposed a theoretical model for the dynamic effect of competition on the time-courses of growth and survival of plants within an even-aged population. This early example of an individual based model achieved a link between effects at the level of the individual plant and those observable at the population level: e.g., computer simulations could generate the minus 3/2 power law limitation between the logarithms of mean mass of surviving plants and their number per unit area observed in some communities of plants. The specific relations in the original model to not give good fits to some sets of data and, inappropriately, give a positive stimulus to the simulated growth of larger plants from an addition of extra small plants. The structure of the model, however, is shown to provide an effective basis for a more empirical application to a multi-aged set of data. Data from even-aged carrot plants, grown at low density, are used to compare the fit from 7 plant growth relations, a Richards model giving the best fit. The data set is then expanded to include higher densities, and 8 options for describing competition between evenly sized plants were compared: a competition function related to the efficiency of use of Leaf Area Index proved effective. Expanding the data set to include multi-aged populations, fits are obtained for uneven competition relations.
