INVADE: Towards the simulation of plant spread

Abstract The development of a model of plant spread, INVADE, is described. It is a FORTRAN 77 program that will run on any IBM-compatible computer. Output is in the form of a matrix of 23 × 23 cells or a limited output version which is only total population for the matrix. The model was used to simulate spreading populations of Avena fatua over 3 years and its output compared with populations arising from deliberate introductions in the field. The population growth rate of A. fatua was markedly affected by the contrasting rainfall which occurred during the tests and the estimate of growth rate at a focus (or cell) based on Year 1 data for subsequent years was a large overestimate. However, with a given population growth rate per cell for each year, the model accurately predicted total population, area occupied and gross distribution of A. fatua . Possible uses of the model are described.