The Great Western Woodlands has a mosaic of different habitats throughout the region. The major habitats can be broadly summarised into five vegetation types: Woodland, mallee, grassland, shrubland and un-vegetated. The woodlands are the most common type of habitat covering more about 60%. Scientists cannot tell us how in these woodlands such big trees grow in such a dry climate.
Mallee ecosystems tend to be more dominant in the southern and north-eastern areas of the region, while shrublands on the sandplains are more common in the north and west and grasslands in the north-east.
It was the shrublands that scientists first recognised as being extremely diverse. Early European botanists were amazed by the subtle but significant differences within the vegetation.
More recently, the woodlands have also been recognised as containing extraordinarily diverse plant communities by global standards. This exists both in the understorey and among the tree species.
The composition and distribution of the broad vegetation types in the Great Western Woodlands appear to be driven by multiple factors.
For example, the woodlands are unique in their capacity to form relatively tall, productive vegetation under arid conditions with many endemic species and with a high degree of habitat adaptation.
Fires are rare in unlogged woodlands, but when they occur they can be devastating and are able to change a woodland into a mixture of mallee and shrubland. The shrublands also have an unusually large proportion of endemics but are different to both the woodlands and mallees in having a high number of species within very small spatial scales. Another difference is that few species in shrubland exhibit high fidelity for any one soil type.
In other semi-arid regions, mallee and woodland vegetation is correlated with edaphic parameters, such as soil moisture and nutrients, where as the floristic variation in shrublands have little reported correlation with soil parameters.
Much of the diversity of vegetation across the region is impossible to display on large-scale maps.
For example, there are unique plant communities on the immediate fringes of the salt lakes as well as on the small dunes that exist in the middle of these lake systems. The many granite hills, the banded ironstone formation outcrops, and the greenstone belt mosaics throughout the Great Western Woodlands are each home to unique wildlife.
The skeletal soil sheets of the inner aprons of granite exposures and hills and the heavy red sands of banded ironstone hills also represent their own vegetation systems. On these landforms, low woodlands and tall shrublands develop, dominated by sheoaks, wattles and broombush, with the occasional mallee species.
The biological and structural diversity of plant communities across the Great Western Woodlands is known to provide different foraging, nesting or roosting habitat for an array of animals.
