Spinifex; the prickly heart of Australia

Huddled along the moister parts of Australia's shores, most Australians have, inevitably, a limited concept of what most of our country is really like. For instance at least 20% of the entire country is dominated by Mulga acacia woodlands, which is remarkable in that this represents more than 1.5 million square kilometres. People do encounter some of the mulga lands while driving some of the inland highways, but they are less likely to be aware that perhaps another 30% of Australia is dominated by just one genus of grass, the formidable spinifex, or porcupine grasses. (Various authoritative sources vary in the percentage cover, which is fair enough, as 'dominate' is a difficult concept to define accurately.)

Spinifex clumps, Triodia sp., to the horizon and beyond, Great Sandy Desert, Western Australia.

In fact Triodia occurs in every mainland state of Australia, as shown by the records in the admirable Atlas of Living Australia below.

It would seem from this that even 30% is a serious understatement, but the key word is 'dominate'; between 22-33%
of the country has a spinifex cover similar to the Great Sandy Desert scene above,
but vast areas beyond this have some spinifex.

I've mentioned Triodia, but you may recall Plectrachne as another spinifex genus - I do, from my long-ago youth. I always struggled to tell the difference, and fortunately it turns out that in this case it wasn't just me, as Plectrachne has quietly been pushed into a bottom drawer, and all 65 spinifex species (all Australian) are now Triodia. (The 65 comes from the Australian National Botanic Gardens, which is always good enough for me; they also cite the upper figure of 33% of the land dominated by the sharp grasses.)

And just one more confusion to dispose of before we get properly into the prickly, itchy, wonderful world of spinifex. You may also be aware of a genus of grasses which bind coastal sand dunes around Australia, Asia, Africa and the Pacific - indeed they are more familiar to most than Triodia is - confusingly called Spinifex. These are not spinifex as we're discussing it here... Yes, I know, and I'm sorry, but you'll just have to accept it I'm afraid. 

Spinifex hirsutus (probably, but I'm totally quite sure of the species), Jurien Bay, north of Perth.

There's thus a good argument for using the name 'porcupine grass' for Triodia, but 'spinifex' is probably too ingrained for change now I suspect, and that's what I'm going to continue using today. 

Spinifex can dominate on sand plains and dunes, stony plains and rocky hillsides, as the following photos illustrate. The first three are in different parts of the Great Sandy Desert.

Flowering spinifex on deep sandy plains with Melaleuca glomerata.

On gibber plains, comprised of smooth wind-rounded pebbles broken down from the crusts of adjacent low ridges.
Note how pale these spinifex hummocks are; this area was in heavy drought, even by its own arid standards.
Spinifex is extraordinarily adapted to drought, one response being in the unusual nature of the numerous
densely tangled leaves. The fresh blades are green and flat (as in the previous and next pictures),
but after a dry period they become permanently folded; this means that the inner face of the leaf
is protected from desiccation while the outer face becomes dry and brown.

On long red sand dunes, with some tree and shrub cover as well.

On iron-red rocky hillside at Yandinga Gorge, Gawler Ranges, South Australia.

On rocky slopes below mulga on the ridges, Lark Quarry Conservation Park, central Queensland.

Grand views of countless spinifex clumps from the mighty Ormiston Pound walk,
western MacDonnell Ranges, central Australia.

While all spinifex is prickly, it is the desert species which provide a truly ferocious impenetrable barrier. The more northern species, which presumably get some annual rain from the monsoons, tend to be (relatively) softer.

'Soft' Spinifex, probably Triodia microstachya, on the dry plateau above Edith Falls
in Nitmiluk (formerly Katherine Gorge) National Park, near Katherine, Northern Territory.

As the mounds get bigger they expand outwards - in areas where fire hasn't occurred for some time hummocks can be up to two metres high and three metres across. If there's been no fire for over twenty years they start to form rings, as the inner material dies off completely. I assume that part of this process is due to a depletion of nutrients in the soil under the centre of the mound.

Mature Spinifex rings, Calpatanna Waterhole Conservation Park, Eyre Peninsula, South Australia (above)
and Great Sandy Desert (below).

The Australian National Botanic Gardens has developed an impressive
and beautiful 'Red Centre Garden' complete with spinifex rings! However they didn't wait for the clumps
to mature, they simply planted the seedlings in circles! Very neat.
November 2013 above, and 12 months later, below.

 

The spinifex lands have been fire-managed by people for tens of thousands of years; the grass is rich in resins and it burns fiercely and regrows both from seeds in the soil and shoots from the plant base.

Burning spinifex, Uluru National Park.
I have read suggestions that the 'natural' fire regime may be only five years, but we also know
that mature spinifex (ie more than twenty years old) is essential habitat.

A study published in 2014 suggests that mass flowering is preceded by an unusually wet 12 months, and is followed by mass seeding which may help swamp seed predators (including ants and birds) and prevent them carrying away the whole crop. Flower heads tower over the spinifex hummocks.

Flowering spinifex, Lasseter Highway, central Australia...

... and near Ewaninga, north of Alice Springs, above and below.

The viciously-spined spinifex hummocks form an impregnable fortress for small animals which can dive into them, thwarting larger predators including us. Within the mound the leaves die (no point in maintaining leaves which can't photosynthesise, because they aren't receiving sunlight) and there is a tangle of stems. An idea of the richness of the spinifex world, an often apparently lifeless landscape, can be gained by examining the labyrinth of tracks around the spinifex in the morning.

While we were warm in our swags, the frosty night was well and truly awake!

Here are a few more spinifex dwellers.

Central Military Dragon Ctenophorus isolepis, Great Sandy Desert; it is rarely found away from spinifex.

Panther (or Leopard) Skink Ctenotus pantherinus, Ormiston Pound, Western MacDonnell Ranges.

The dense spinifex around the Ochre Pits, Western MacDonnells, is a noted site for the
widespread but elusive Rufous-crowned Emuwren, Australia's smallest bird, weighing just six grams!
I first saw them there, but it was many years before I managed my only photo of them.
They are only ever found where there is mature, unburnt spinifex.

Male Rufous-crowned Emuwren, Great Sandy Desert.
He emerged briefly from his spinifex castle to inspect us.

A lovely Spinifex Pigeon Geophaps plumifera, another species very closely associated with spinifex.
Bladensburg NP, central Queensland.

Spinifex takes up silicon from the soil to reinforce its spiny tips and harden of the leaves; the silicon particles can break off in a wound and become infected. As a result, uniquely among major world grasslands, spinifex is not grazed by large mammals. The only one which can do so is the Euro Macropus robustus. This diet is very low in nitrogen, essential for the necessary gut bacteria; the Euro compensates by recycling nitrogen from urea.

Euro; above (with Spinifex Pigeons) Bladensburg NP, central Queensland;
below, near Broken Hill.

 

The real spinifex grazers however are termites; the triangle of spinifex, termites and lizards in the Australian deserts has been likened to the great African grasslands, antelopes and lions (etc). The mass of termites per hectare in the central deserts is greater than that of all other animals. Each spinifex clump has a tunnel opening beneath its centre. In one small area near Alice Springs there are 50 termite species. In turn this supports the world’s greatest concentration and diversity of lizards.

The great termite mounds of the tropical Australian savannahs are famed, but those of the spinifex country can be equally impressive. Here are some examples.

Plenty Highway, north-east of Alice Springs.

Barkley Highway, north-eastern Northern Territory.

Great Sandy Desert, above and below.

 

Covered termite runway between spinifex clumps, Great Sandy Desert.
Termites don't like to be exposed to hot and dry air.

Finally, before we return to our lives which are probably mostly very distant from the wonderful spinifex country (and writing this has given me a great longing to get back out there as soon as we can travel freely again), let us just enjoy some of the beauty of spinifex.

Late afternoon, Palm Valley, central Australia.

Sand patterns from spinifex flowers blowing in the wind, Great Sandy Desert.

Kata Tjuta sunset through the spinifex flowers, above and below.

Sunset through spinifex flowers, Great Sandy Desert.

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