In many regions fire has been a major ecological factor and should be regarded as part of the normal “climate”. It is the frequency of fire which has the most marked effect on vegetation. For a particular area, topography and the direction of the main fire winds have been the same for centuries. Given defined sources of fire, the frequency with which a particular area is burnt then depends on the nature of the agency starting the fires, the location of the area in relation to the source of fire, and the type of vegetation.