The Australian Empty Quarter: epitome of a nutrient-desert

Everyone knows that Australia is the driest continent. However, how many know that 'desert' in Australia refers less to a lack of water than to a lack of nutrients?

On most maps of land use in Australia, a large-scale pattern is obvious but does not seem to have been pointed out as such. This is a broad vertical band across the western half of the continent, centred just west of the border between Western Australia (https://en.wikipedia.org/wiki/Western_Australia#/media/File:Western_Australia_in_Australia.svg) and South Australia/Northern Territory. The climate varies from tropical in the north to temperate in the south.

In this broad band there is, to this day, negligible farming or other utilisation of the land (see https://www.agriculture.gov.au/abares/aclump and https://www.veganaustralia.org.au/impact_of_a_vegan_agricultural_system_on_land_use and https://www.researchgate.net/figure/A-2000-01-national-scale-land-use-map-illustrating-the-broad-distribution-of-pastures_fig1_230817486 and https://www.moffittsfarm.com.au/2014/01/04/land-use-australia-2005-2006-source-abares/ and https://ars.els-cdn.com/content/image/1-s2.0-S0959378016300231-gr1.jpg and https://www.researchgate.net/figure/Sample-locations-and-land-use-types-in-Australia-The-agricultural-areas-of-Australia-are_fig1_288059143 and https://www.researchgate.net/figure/a-Carnahan-classification-of-current-vegetation-for-Australia-AUSLIG-1990-and-b_fig1_236770005 and https://www.creativespirits.info/aboriginalculture/land/aboriginal-homelands-outstations).

This feature needs a name, and I suggest we call it the Australian Empty Quarter.

What is most surprising about the Australian Empty Quarter is how densely-vegetated it is with evergreen perennial plants (https://diamantina-tour.rezdy.com/95387/great-victoria-desert-nullarbor-expedition?lang=ja and https://www.worldatlas.com/articles/where-does-the-great-victoria-desert-lie.html and https://www.abc.net.au/science/photos/2012/11/21/3636626.htm?xml=3636626.mediarss.xml#bigpicturepos and https://www.istockphoto.com/photo/marble-gum-gm532574825-55893698 and https://upload.wikimedia.org/wikipedia/commons/8/81/Eucalyptus_gongylocarpa.jpg and https://www.exploroz.com/wildflowers/395+marble-gum and https://www.alamy.com/stock-photo-camel-crossing-the-great-victoria-desert-western-australia-97792062.html).

The driest part of Australia, which has sparse vegetation, occurs far to the east and is a different geographical feature (http://www.truganinaweather.com/weather-education/australian-climate-maps.htm and https://en.wikipedia.org/wiki/Lake_Eyre_basin).

The Australian Empty Quarter, despite looking far more luxuriant than the conventional image of desert, is even poorer in large animals than the rest of the continent. The emu (Dromaius novaehollandiae, https://upload.wikimedia.org/wikipedia/commons/f/ff/Emu_distribution.png and https://upload.wikimedia.org/wikipedia/commons/8/8b/Dromaius_novaehollandiae_map_distribution_2.svg) and kangaroos (mainly Osphranter rufus, http://www.ecoclimax.com/2017/05/kangaroo-distribution-in-australia-vs.html and https://www.echidnawalkabout.com.au/macropods-kangaroos-of-australia/ and https://bio1152.nicerweb.com/Locked/media/ch52/kangaroo.html) are largely absent.

Various other species of animals show a similar gap in their distributions (https://www.researchgate.net/figure/Magpie-plumage-variants-and-their-distribution-across-the-Australian-continent_fig1_232248336 and https://edition.cnn.com/2019/09/15/australia/australia-magpie-death-intl-hnk-scli/index.html).

The most significant plants in the Australian Empty Quarter are hummock grasses belonging to the genus Triodia (https://en.wikipedia.org/wiki/Triodia_(plant)). These are adapted to nutrient-poverty and fire to the degree that they have minimal value for herbivores (https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-185X.2007.00017.x). Their leaves are woody, resinous and unpalatable.

The ultimate environmental reason for the Australian Empty Quarter is a combination of extreme flatness and underlying bedrock of nutrient-poor sediments such as sandstone. This land has been geologically stable since the time of dinosaurs, so that the soils, sandy and poor to start with, have become profoundly depleted of phosphorus and zinc in particular.

This limits herbivory so much that vegetation is left to grow until wildfire returns, and combustion has replaced digestion as the most important recycler of nutrients.

The Australian Empty Quarter is best understood as a nutrient-desert rather than a rainfall-desert because, even if it were well-watered, it would remain largely devoid of large animals. Although this zone is semi-arid, it is ecologically aligned with the African Empty Quarter (see my Post of July 18, 2021) rather than the conventional concept of a desert.

As an example of a nutrient-desert, the Australian Empty Quarter is far more extreme than the Kalahari-derived sand-sheet, covered with miombo woodland (https://en.wikipedia.org/wiki/Miombo), in Angola - in which the incidence of large animals is minimal by African standards but categorically greater than in any part of Australia.

One of the principles illustrated is this:

There are some climates just too dry for the vegetation to maintain cover over the land, and this is the conventional concept of desert. However, no soils on this Earth are so nutrient-poor that woody plants cannot grow on them, albeit slowly. Thus arises the combination we see in the Australian Empty Quarter: a vegetated plain effectively useless to man and beast.

Except, that is, for a camel...

Posted by milewski milewski, October 09, 2021 06:08

Comments

The following shows the locations of the major 'deserts' in Australia. However, of these only the relatively small Sturt Stony Desert and Strzelecki Desert are arid enough to conform to the concept of desert on other continents. Even the Simpson Desert is no drier than parts of the Kalahari or Sahel in Africa, which are usually regarded as semi-deserts: https://www.backyardchickens.com/hredirect2.php?c=5495231.

Posted by milewski about 1 year ago (Flag)

The Great Victoria Desert is acknowledged as the most extensive 'desert' in Australia. However, what does not come out in the usual accounts is that it is also by far the most luxuriantly vegetated 'desert' on Earth, having far more vegetation than, say, the semi-arid zone of North Africa called the Sahel: https://en.wikipedia.org/wiki/Great_Victoria_Desert.

Posted by milewski about 1 year ago (Flag)

The following is misleading unless one understands that, in Australia, 'desert' is a function not of aridity alone but instead a combination of nutrient-poverty and semi-aridity: https://en.wikipedia.org/wiki/Deserts_of_Australia.

Posted by milewski about 1 year ago (Flag)

The following map of variation in rainfall from year to year (https://www.researchgate.net/figure/Rainfall-variability-map-for-Australia-based-on-data-between-1900-and-1996-Variability_fig2_319404345) shoes a significant anomaly, relevant to the topic of this Post. The Australian Empty Quarter, instead of having particularly variable rainfall (presumably equivalent to proneness to drought), has rainfall more reliable than that in areas to the west and to the east.

Posted by milewski 3 months ago (Flag)

Grallina cyanoleuca provides a particularly good example of a species-distribution reflecting the Australian Empty Quarter: please scroll in https://animalia.bio/magpie-lark.

Posted by milewski 3 months ago (Flag)

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