The development of computer simulation models is an important growth area in both pure and applied ecology. The opportunity that mathematical models provide to integrate the components of an ecosystem, results in the ability to make quantitative predictions about the future behaviour of that system, or of elements within it. This means that they are powerful tools with wide applications and enormous potential for increasing our understanding of natural systems and our ability to use them in a sustainable way. This book is, almost uniquely, a complete account of one such model, the Hurley Pasture Model, a dynamic, deterministic, mechanistic simulation model for grassland, which has been developed by the author over some twenty years, in collaboration with scientists at several centres. Firstly, the rationale and theoretical elements of this type of model are described. An overview of the Hurley grassland simulator and the derivation and construction of its plant, animal, soil and litter, water, and environment and management components is then given. Next, the model is evaluated by a series of long and short-term dynamic simulations and steady state responses, which demonstrate how predictions can be made about the effects of, for example, climate change or particular regimes of fertilizer application, grazing or cutting. This book will be of great value to grassland agronomists and modellers, crop physiologists and plant ecologists, and to students of ecology as a case study of a plant ecosystem model. It will also be of interest to other ecologists and environmentalists and those in the field of computer modelling and its applications.