Eucalypts – from wet to dry
Nothing evokes the Australian bush in quite the same way as the sight and smell of eucalypts. Not surprising, when about 95% of the forest trees of Australia belong to the genus Eucalyptus - with 100 or so species from the closely related Angophoras and Corymbias. Angophoras are restricted to the east of Australia but there are many Corymbias in Western Australia, mostly in the north, but including the widespread Marri C. calophylla and the beautiful Red-flowering Gum C. ficifolia) in the south west.
It is believed that eucalypts evolved in Australia after it broke free of Antarctica and began to drift north, becoming drier, more nutrient deficient, and more prone to fire. Since then, they have spread to most parts of Australia except the rainforests, the highest peaks and the most arid parts of the interior, and have evolved into around 800 species and more than 1000 taxa. They grow in many forms and associations – as tall forest, as open forests and woodlands, as mallees and shrublands. And they can grow in a surprising range of habitats, from high rainfall and high nutrient soils, through to wetland edges and salt lakes.
The form or habit of the individual species also varies: there are tall straight trunked trees like the karri, species like wandoo that are single stemmed but branching at low heights and with wide canopies, tall or short multi-stemmed mallees, medium sized steep-branching mallets, pure stands of straight but thin stemmed moorts and gimlets - even some species that are prostrate.
Western Australia boasts the majority of the Eucalypt species, and most of these are in the southwest. Estimates of numbers vary because of the regular revisions of taxonomy, the propensity for many eucalypts to hybridise with related species and subspecies, and the fact that new species are being regularly discovered and described. We know that the Great Western Woodlands for example is a centre for eucalypt diversity with over 20% of the total of Australia’s eucalypts occurring there.
While the value of forests, woodlands and mallee heathlands come from the complexity of their composition, structure and the functioning of all the associated organisms, there are some key roles that the eucalypts play. For many parts of the Gondwana Link area for example, they are the only species that can provide the nesting hollows needed by birds like Carnaby’s Cockatoo and other animals like possums and bats. Many have their own suites of invertebrates and complex micro-ecosystems operating within the canopies, bark or litter of the eucalypts.
Other important ecosystem services the eucalypts provide are those related to hydrology (the deep rooted eucalypts maintain the groundwater levels and prevent saline groundwater from rising to the surface) and carbon storage. Studies in both the Fitz-Stirling area and the Great Western Woodlands have demonstrated the capacity for the eucalypts to sequester large volumes of carbon in both their above and below ground growth. This is a major contributor to controlling rising carbon emissions and could be greatly increased by large scale restoration and careful fire management.
Read more and see some of the eucalypts that occur within the Gondwana Link area: