The structure, function and stability of ecosystems vary considerably in both time and space. Ecological changes through time occur, and are of fundamental significance, on a wide range of time scales from the level of seconds and minutes to the many millions of years of evolutionary change documented in the fossil record. Much attention has been given by palaeontologists to establishing the sequence of evolutionary changes in plants and animals throughout the fossil record. Natural environmental changes which can trigger off secondary successions of formerly natural ecosystems include the impact of climatic extremes such as storm and tidal action, and the impact of natural lightning. The significance of ecological changes on the successional time scale is equally real, and there are a number of situations in which the principles of succession are of central importance in environmental management and in conservation in general. Ecological changes through time are inherent and vital in all ecosystems, whether natural or man-made.