With the advances in rendering hardware, it is possible to render very complex scenes in real-time. In general, computers do not have enough memory to store all the necessary information for sufficiently large areas. This paper discusses a way in which well-known techniques for modeling ecosystems can be applied to generate the placement of plants on a terrain automatically at run-time. Care was taken to pick algorithms that would be sufficiently fast to allow real-time computation, but also varied enough to allow for natural looking placement of plants and ecosystems while remaining deterministic. The techniques are discussed within a specific rendering framework, but can easily be adapted to other rendering engines.