The story is best told by beginning with the driving force of climate.

The landcover of the Earth is constantly changing. This change was and is driven by climate alone, and it has characteristic scales in space and in time.

The spatial patterns of distribution and the functioning of landcover types are predominantly determined by climate; principally the factors of precipitation and temperature, whose effects are modified by soil factors.

This key statement holds true whether it is applied at local or at global scales. Climate is the fundamental determinant of the nature, distribution and functioning of landcover on the Earth's surface over all time scales.

At one extreme, at global scales and over geological time scales, the evolution and patterns of distribution of landcover types have followed the changing climate and the movement of the continents. The terms we use today to describe the major biomes of the planet, ie the vegetation plus climate, such as 'equatorial rainforest', 'temperate forest', and 'boreal forest', reflect the close coupling of climate and landcover type. At the other extreme - local scales over seasons - landcover functioning is influenced only by weather events such as droughts and severe storms.

Consequently, the influence of climate on landcover can be described across all scales. For the questions in this chapter we can set aside the influence of climate on landcover over geological and evolutionary time scales, ie, over time scales of greater than 1000 years- and concentrate just on the time scales that are meaningful in terms of a human life span- ie a year to a decade.

Also, we can assume that the spatial patterns of vegetation we can map for the Australian continent or for the globe are, excluding the influence of man, determined by climate. However, if the climate changes - and climate is never stationary, then we can expect that the landcover of the Earth will (slowly) track the changing climate.