"Not all that Glistens is Gold" - Eucalypts of the Great Western Woodlands

Eucalypt diversity GWW. Photo: Barbara Madden

Article written by Nathan McQuoid and Sean Stankowksi

There are approximately 1095 taxa of eucalypt (comprising the genera Angophora, Corymbia and Eucalyptus) in Australia with 25% of all species found in the Great Western Woodlands.

Analysis using bioregions and subregions show there is a major centre of high species richness and endemicity in Australia’s semi-arid south-west 7 (Fig. 2.5 below). The Great Western Woodlands is the heart of this eucalypt diversity.

With data provided by the Western Australian Herbarium, the Wilderness Society conducted its own biogeographic analysis, and found that 351 taxa occur in the Great Western Woodlands—almost one-third of Australia’s taxa.

This profound diversity is represented in the mosaic of canopies visible from the granite domes rising above the subdued landscape. As you drive through the Great Western Woodlands, a rich pattern of woodland and mallee eucalypt varieties emerge, from salmon gums, black morels and bronze mallets, to silver gimlets, frosted gums and copper mallees. The area is a marvel of not only form and colour diversity, but also enormous species number.

Within Australia’s south-west, eucalypt richness and endemism are largely determined by rainfall. High rainfall areas are typically associated with low diversity, whilst areas that receive lower rainfall, particularly those associated with the transitional rainfall zone, exhibit high diversity.

The high number of species in the Great Western Woodlands is attributed to fluctuation in climatic regimes across the region over a very long period of time, resulting in vigorous adaptive responses and consequent speciation.

As the Great Western Woodlands is the last intact remnant of temperate woodland that falls on the transitional rainfall zone, this area would be expected to, and does, exhibit eucalypt species diversity and endemism which is second to none.

Figure 2.5

Map of Australia divided into IBRA subregions showing (a) the species richness of Eucalypt species within each subregion and (b) the number of endemic species to each subregion (e.g., species that are only found within one each subregion).