Growing plants modify the microclimate within which they grow by altering their physical structure. Thus individuals affect the subsequent growth of both themselves and competing neighbours. It is important that this feedback be represented in a model of dynamic vegetation change. A flexible generalised model "Ecospace" is presented, which was designed to be applicable to all terrestrial vegetation. The model uses a three-dimensional grid of hexagonal tiles to represent space above and below ground. Each individual plant may occupy one or more tiles within the grid. Any number of individuals may occupy each tile until all space is filled. Microclimate, comprising solar radiation, wind and temperature, is calculated for each tile. Plant growth depends on the microclimate of occupied tiles. Three different plant functional groups are represented. The current model can represent an area of up to 50 m2 for low shrub vegetation. However, at present, computer run time and restricted memory limits the volume which can practically be simulated. There is no fundamental reason why these limits could not be overcome. Some model runs are presented for heather plants growing under different structural and climatic regimes. Since the model represents the feedback of vegetation structure on microclimate, it is suitable for studies of the impact of changing weather patterns on ecosystems.