Australia: The Land Where Time Began

A biography of the Australian continent 

Simpson Desert Flora - the Dunefields

Sandhill canegrass (Zygochloa paradoxa) and lobed spinifex (Triodia basedowii) dominate the egetation of the dunefields of the Simpson Desert.

Sandhill canegrass

This species is a highly drought resistant, wiry perennial grass growing universally on the crests of mobile dunes. Its growth habit is as tangled clumps that are distributed sparsely, stabilising the sand of the open dune crests. A number of desert animals live in the clumps, such as the Eyrean grasswren (Amytarnis goyderi).

On the stable dune flanks and the interdune swales it is the lobed spinifex that dominates, growing in rounded clumps, or hummocks, that are dense and spiky. The sclerophyllous leaves of this plant are tightly rolled, forming stiff, sharply pointed spines. The leaf form serves a double function, reducing water loss and as a defence against most grazers. The high oil content of the leaves also reduces the water loss. The clumps eventually form rings as the central portions die, the outer portions continuing to grow leading to rings that gradually increase in diameter, as does the central bare patch that can get to several metres in diameter. Among the animals finding shelter in the lobed spinifex are lizards, termites, ants, birds, and small mammals.

These 2 plant species have been called the Zygochloa/Triodia complex by Robert Crocker, the first to document the association between the 2 species, describing the complex as "typical vegetation of the desert  and present throughout with remarkable homogeneity." It has since been found that the lobed spinifex is actually not universally present, particularly in area of the southern central dunefields. This is thought to result from the higher salinity and increased clay continent in this part of the desert.

Dune Crests

Very few plants can survive on the crests of the dunes. Canegrass (Zygochloa paradoxa) is one of these hardy plants.

Stable Dune Slopes

Lobed spinifex

The 2 genera, Triodia and Plectrachne, are among the 30 species that are found in associations known as hummock grasslands, or commonly as spinifex grasslands. These are found in all the major deserts of Australia. covering a total area of about 1/4 of the continent, making them the most widely spread vegetation type in Australia. Of these species that only one that is really spinifex Spinifex is restricted to sand dunes in coastal habitats. Hummock grassland is so widely known as spinifex grasslands, and for so long, that it is unlikely it will ever be anything but spinifex grasslands among most people.

Spinifex (Triodia basedowii) grows both on the stable slopes and in sandy interdune corridors. Some perennial shrubs of the genera Acacia, Eremophila and Grevillia, also grow in both locations, as do some seasonal herbs.

Interdune Corridors

The interdune corridors are on  a wide range of soil types. They can be relict alluvial flood-outs, salt pans and gibber surfaces. This variety is also shown in the varieties of vegetation associated with the various soil types. Examples of the vegetation found in these corridors are low open woodlands, tall open open schrublands made up of species such as Eucalyptus microtheca, Acacia georginae, A. aneura, A. kempiana, Hakea, Low open shrublands of the Atriplex vesicularia, A rummularia, Marieana aphylla, Holosarcia  spp. Muehkenbeckia cunninghamii. Sparse grasslands with a scattering of low trees and shrubs.

More than 800 species of plants have been documented from the Simpson Desert, mostly from the dunefields, a reflection of the varied habitats found there. Many are also found in refuge areas like flood plains where the infrequent floods from the erratic outback rivers occasionally bring water.

Unexpectedly to most, the Simpson Desert supports large populations of  flora and fauna. There are mammals and birds and lizards typically found in spinifex grasslands. . The Eyrean Grasswren is endemic to the Simpson area.

1. The Simpson Desert, Natural History and human Endeavour, Mark Shephard, Reed, 1994
2. Mary E White, Running Down, Water in a Changing Land, Kangaroo Press, 2000

Links

New South Wales Flora Online